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Effect of alloy addition on inclusion evolution

in stainless steels

X Yin Y Sun Y Yang X Deng M Barati amp A McLean

Version Post-printAccepted Manuscript

Citation (published version)

Yin X Sun Y Yang Y Deng X Barati M and McLean A 2017 Effect of alloy addition on inclusion evolution in stainless steels Ironmaking amp Steelmaking 44(2) pp152-158

Publisherrsquos statement This is an Accepted Manuscript of an article published by Taylor amp Francis in Ironmaking and Steelmaking on May 26 2016 available online httpwwwtandfonlinecom1010800301923320161185285

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Effect of Alloy Addition on Inclusion Evolution in Stainless Steels

based on Three-Dimensional Investigation of Inclusions

Xue Yin Yanhui Sun Yindong Yang Mansoor Barati Alex McLean

Abstract

The number morphology size and composition of inclusions after deoxidation and alloying in Ti-

stabalized stainless steel were investigated This was carried out by electrolytic extraction of

complete inclusions from steel matrix followed by microscopic examination It was found that after

the addition of ferrosilicon and manganese and later aluminum the composition of inclusions

changed from manganese silicate-rich inclusions to alumina-rich inclusions After tapping and

titanium wire feeding three types of TiN inclusion morphologies were observed single twinned

and clusters Both the turbulence and Stokersquos collisions mechanisms play a considerable role in the

formation of cluster TiN

Key word Deoxidizer inclusion evolution electrolytic extraction three-dimensional

investigations

1 Introduction

Non-metallic inclusions in steel can cause deterioration of mechanical properties surface defects

initiation sites for corrosion-fatigue cracks and hydrogen embrittlement as wells as operational

complications such as clogging of the submerged entry nozzle (SEN) [1-4] However complete

removal of harmful inclusions from molten steel during the refining process is difficult An

alternative approach is to minimize the harmful effects of residual inclusions or to beneficially

utilize these inclusions through proper control and modification

Aluminum is one of the strongest deoxidizers [1415] for steel However due to the harmful effects of

Al2O3-rich inclusions on steel quality and process Si and Mn are often used as steel deoxidizers[56]

After deoxidation by SiMn the main constituents of inclusions are MnO and SiO2 Al2O3 and CaO

may also enter the steel through entrainment of the top slag Titanium is another deoxidizer with

beneficial effects in austenitic stainless steel as it suppresses chromium carbide precipitation in the

grain boundaries and reduces susceptibility to intergranular corrosion through the formation of very

stable titanium carbide [16] However the excessive Ti and N can form coarse TiN inclusions that grow

to large particles [17 18] As one type of inherently brittle nonmetallic inclusion they have often been

reported to act as fracture initiation sites [19-21] thus adversely affecting the fatigue life and toughness

of the steel [22-29] Moreover in titanium stabilized steels TiN is found in the submerged entry nozzle

(SEN) blockage materials Hasegawa [30] reported that the major deposited materials were made up

of A12O3 and TiN inclusions Maddalena [31] indicated that two distinct types of titanium nitride-

based deposits were found after analysis of clogged nozzles from titanium treated stainless steel

(types 321 and 409) pure TiN and TiN associated with a spinel phase Gao[32] reported that stainless

steel with Ti content exceeding 015 increases the risk of clogging significantly

The previous studies on TiN inclusions have concentrated on two dimensional (2D) investigation of

inclusions by sectioning steel samples limiting accurate chemical analysis of the inclusion surface

and obtaining a full understanding of their 3D features [33] In the present study electrolytic

extraction (EE) was employed to extract intact inclusions from steel matrix allowing three

dimensional investigations of inclusion characteristics (such as composition size number and

morphology) in steel samples taken after different deoxidizers additions After separating the

particles on the surface of film filter the particle size distribution was determined for most of the

major nonmetallic inclusion types found in the samples The evolution of different inclusions and

formation and growth mechanisms of TiN clusters were investigated and discussed

2 Experimental Procedure

21 Sample preparation

In this study inclusions formed in 17Cr austenitic stainless steel were investigated after

deoxidation and Ti-stabilization Steel scrap and alloys were initially melted in an intermediate

frequency induction furnace and the molten steel was subsequently decarburized deoxidized and

desulfurized in an AOD furnace After transfer to a ladle furnace the composition and temperature

of the steel were adjusted and argon injection was applied to enhance the removal of inclusions at

the ladle treatment station Table 1 presents the final composition of the steel before ingot casting

Table I Chemical composition of Ti-stabilized stainless steel (mass pct)

C Si Mn P S Cr Ni Ti Al N O

0032 037 113 0039 00017 1714 906 0307 0026 0025 00029

Steel samples for investigation of inclusions were obtained at various stages during the production

process according to the scheme shown in Figure 1 The samples were taken after the addition of

deoxidizing agents SiMn followed by Al after feeding titanium alloy wire and at the start of casting

Fig 1 Schematic illustration of sampling locations

22 Inclusion Characterization

Electrolytic extraction (EE) method was applied for extraction of inclusion particles The method

involves dissolution of steel matrix under an applied potential leaving intact particles behind Steel

sample (15 times 15 times 4mm) were subjected to EE in a 10 AA (10 vv acetylacetone-1wtv

tetramethylammonium chloride-methanol) electrolyte The current density was set at 40-50 mAcm-

2 during the extraction The weight of dissolved metal during electrolytic extraction was 012-02 g

with the EE time at about 25-3 hours After extraction the solution containing inclusions was

filtrated through a polytetrafluoroethylene (PTFE) membrane with an open pore size of 02 microm

After coating the membrane filter with gold under vacuum conditions the characteristics

(morphology size and composition) of extracted inclusions were investigated using the SEM

equipped with EDS The number of inclusions per unit volume (NV) was calculated as follows

filter metal

observed dissolved

vA

N nA W

[1]

where n is the number of inclusions in the appropriate size interval Afilter is the area of the film

filter Aobserved is the total observed area ρmetal is the density of the steel matrix and Wdissolved is the

dissolved weight of the steel during extraction

3 Result and Discussion

31 Morphology and size Changes of inclusions

Inclusions typically found after SiMn deoxidation are shown in Figure 2 The non-metallic

inclusions were classified into two different categories based on their composition and morphology

manganese silicates (Figure 2 (a) ~ (c)) and inclusions containing both oxide and manganese sulfide

(Figure 2 (d) ~ (f)) Most of the manganese silicate inclusions are spherical in shape (a) due to the

fact that these inclusions are liquid at steelmaking temperature It can be seen from (d) ~ (f) that

MnS patches are present at the surface of oxide inclusions Kim et al [34] and Wakoh et al [35]

reported that MnS phase could precipitate by S diffusion from the matrix to the oxide due to

segregation during cooling Such kind of MnS has often been found in the inclusions after SiMn

deoxidation [35-37] As the temperature is reduced an appreciable amount of sulfur has to diffuse into

the liquid (Si Mn)-rich oxide as the solubility of sulfur in solid steel is very low As a result the

(SiMn)-rich oxide is enriched in sulfur especially at the outer layer of inclusions and will be

supersaturated with sulfur on further cooling This sulfur is eventually precipitated as MnS phase

on the inclusion surface

Fig 2 Three-dimensional morphologies of inclusions extracted from steel samples after SiMn

After Al addition the silicate based inclusions are generally transformed into alumina-rich

inclusions according to Reactions [2] and [3] due to the higher affinity between Al and O The total

oxygen was about 110 ppm after SiMn deoxidation and decreased to 39 ppm after Al addition

Inclusions typically observed after Al additions are shown in Figure 3 These inclusions are irregular

in shape with a rough surface pointing to their presence in steel as solid phases due to their high

melting temperature

4[Al] + 3(SiO2)inclusion = 2(Al2O3)inclusion + 3[Si] [2]

2[Al] + 3(MnO)inclusion = (Al2O3)inclusion + 3[Mn] [3]

Fig 3 Three-dimensional morphologies of inclusions extracted from steel samples after Al addition

The particle size distributions of inclusions are shown in Figure 4 Most of the inclusions were

observed to be lt 4 microm in size with majority being around 15microm and 10microm after SiMn and Al

additions respectively Further the number density of inclusions is much higher after SiMn addition

than that of Al addition Noting that no obvious coarsening is happening during Al addition based

on the size distributions it is concluded that some inclusion have been removed during the refining

process

Fig 4 Particle size distributions of inclusions (a) After SiMn addition (b) After Al addition

32 Composition Change of inclusions

The inclusion compositions determined from the SEM-EDS analysis of steel samples after SiMn

and Al additions were plotted on the polythermal projection of the SiO2ndashMnOndashAl2O3 and SiO2ndash

Al2O3ndashMnO ternary diagram respectively as shown in Figure 5 calculated by FactSage 70 It should

be mentioned that CaO was also detected in the inclusions due to the interaction between slag and

steel its effect on the phase diagram and inclusion composition was however ignored due to the low

content (lt 5) and for simplification As can be seen from Figure 5 (a) after SiMn addition the

inclusion compositions are concentrated close to the MnO-SiO2 binary region which is almost in

liquid region due to its lower melting point than that of steel [38] This explains the spherical shape

of the inclusions in Figure 2 After Al addition the composition shifts towards high-alumina

phases near the Al2O3 corner with a higher melting point

Fig5 Calculated polythermal projection (a) After SiMn addition (b) After Al addition

Solid circles represent the composition of oxide inclusions

The effect of alumina content on the liquidus temperature and the primary crystalline phase of the

inclusions were calculated by FactSage 70 with the FToxid database as shown in Figure 6

Increasing the concentration of alumina in the inclusions changed the primary phase in the following

order SiO2 MnSiO3 (rhodonite) Mn3Al2Si3O12 (spessartite) MnAl2O4 (galaxite) and Al2O3 The

liquidus temperature of the inclusion first decreased with increasing alumina concentration up to

about 75 mol followed by a rebound after this composition In this study the alumina

concentration of the inclusions after Al addition was found to be over 60 explaining their solid

state in steelmaking temperatures and irregular morphologies as seen in Figure 3

Fig 6 Calculated liquidus temperatures in the MnO-SiO2-Al2O3 systems as a function of the concentration of

Al2O3 when the ratio of mol pct MnO to mol pct SiO2 is 075

33 Inclusion Characteristics after Ti addition

The TiN inclusion belongs to the cubic or triangular-shaped crystal phase system with a high melting

temperature and hardness making them difficult to deform during steel processing[24] Zhou et al

[39] reported that nitrides with the average size of 6 microm are equivalent to oxides with an average size

of 25 microm in terms of the deterioration of fatigue life

After Ti-core wire feeding inclusions with three distinct morphologies were identified single

particles of titanium nitride (Figure 7 (a) - (d)) twinned particles of titanium nitride (Figure 7 (e) -

(h) and clusters (Figure 7 (i) - (l)) Single TiN has a regular cubic structure while the twinned TiN

particles resembled two more cubic crystals colliding with with each other Maddalena et al

reported that this kind of TiN was caused only by growth of two nucleates [31] TiN clusters usually

have a larger size which may be broken up into smaller TiN particles as a stringer shape during

rolling process [4016] The microvoids in such stringers when exposed to an aqueous solution will

act as sites for pitting corrosion or the initiation of stress corrosion cracking negatively impacting

the to the steel quality

It should be pointed out that oxide particles were still observed in the steel samples after Ti addition

However due to their very low content less than 1 only TiN was discussed The oxide inclusions

can in fact act as the effective heterogeneous nuclei for TiN formation which was confirmed by two

dimensional analysis on the cross-sections[4041-44]

Fig 7 Three-dimensional morphologies of inclusions extracted from steel samples after Ti addition

Figure 8 gives the size distributions of the three types of TiN inclusions In sample L1 the number

densities of single and twinned TiN are dominant In sample C1 the density of large clusters has

increased due to agglomeration of single twinned or small clusters of TiN into bigger clusters Clusters

with the size more than 10 microm were also observed in sample C1 as shown in the upper right corner of

Figure 8 (b) These larger clusters can easily adhere to the nozzle wall and cause nozzle clogging

Moreover they can severely impact the steel quality if they appear in the final product

Fig 8 Size distributions of inclusions after Ti addition (a) Sample L1 (b) Sample C1

34 Formation and Growth Mechanism of TiN Clusters

The formation and growth of TiN clusters in the liquid steel appears to take place in two steps 1)

formation of small clusters by collision of single or twinned inclusions 2) growth of clusters by

collision with singletwinned inclusion or with other clusters There are three types of collision

which can happen between inclusions 1) Brownian collision due to the random movement of very

small inclusions in molten steel 2) Turbulence collision because of the turbulent flow of liquid steel

which can cause the inclusion collision 3) Stokersquos collision due to the density difference between

steel and inclusions so that larger inclusions ascend faster than smaller ones and collide with them

as they travel up Each of the collision mechanisms makes a contribution to the total number of

inclusion collisions

The collision number of inclusions in the liquid steel per unit time (ldquocollision raterdquo) can be

calculated by the following Equation [45]

i j

ij i j

dnw n n

dt [4]

where wij is the collision volume (m3s) of a certain collision phenomenon ni and nj are the number

of inclusions within certain size ranges and t is time (s) The collision volume for Brownian collision

( B

ijw[46]) Turbulence collision ( T

ijw[46]) and Stokersquos collision ( S

ijw[47]) can be expressed as following

respectively

Β

ij i j

i j

2kΤ 1 1w = + r +r

3μ r r

[5]

3

T

ij Fe i jw =13α περ μ r +r [6]

3

S Fe iij i j i j

2πg(ρ ρ )w = r +r r r

9μ

[7]

In these equations k is the Boltzmann constant (JK) T is the absolute temperature (K) micro is the

dynamic viscosity of steel (kgms) α is the collision efficiency ε is the turbulent energy dissipation

(m2s3) ρFe and ρi are the densities of the steel and inclusion respectively (kgm3) g is the

gravitational acceleration (ms2) and ri and rj are the radii of the two colliding inclusions (m)

Each of the different collision mechanism can make a contribution to the total number of collisions

Therefore collision volume wij was calculated using the parameters given in Table 2 in order to

determine the significance of the separate collision mechanisms It should be pointed out that the

calculation of collision volume was based on considering spherical inclusions in steel Therefore in

this study it was assumed that an irregular shape inclusion can rotate around its center due to the

liquid steel flow and can collide with other inclusions within the rotational region whose maximum

length equals to the inclusion diameter

Figure 9 presents the calculated values of the collision volumes for an inclusion of 148microm (size

with a highest content according to Figure 8 ) that collides with other inclusions of different sizes

It can be seen from Figure 9 that Brownian collision volume B

ijw is drastically smaller than that of

Stokersquos and Turbulent collision volume in all studied ranges of rj whose impact on inclusion growth

can be neglected Both Turbulence and Stokersquos collision mechanism have a much higher effect on

the collision volume compared to the Brownian collision They keep an increasing trend as a

function of increased size (more than 148microm) Moreover the effect of Turbulence collision is

higher than Stokes and the difference between these two collisions is decreasing as the inclusion

size increases within the the range studied here Therefore both Turbulence and Stokersquos mechanism

are believed to play a considerable role in inclusion coarsening

TableⅡ Data used in calculation of collision volumes

k

(JK)

T

(K)

micro

(kgms)

α

(m2s3)

ε

(m2s3)

ρFe

(kgm3)

ρi

(kgm3)

g

(ms2)

138times10-

23 1873 0005 03 00018 8000 5220 981

Fig 9 Collision volumes for an inclusion with a 148microm (ri=074microm) in diameter as a function of collision with

different sized inclusions

4 Conclusions

Inclusions characteristics (such as morphology composition and size distribution) were analyzed in steel

samples taken after different alloy additions using electrolytic extraction methods followed by SEM-

EDS characterization The following conclusions were drawn

(1) After the addition of ferrosilicon alloy and electrolytic manganese followed by aluminum the

composition of inclusions changed from manganese silicate-rich inclusions with spherical shapes to

alumina-rich inclusions with irregular shapes

(2) After Ti-stabilization three TiN inclusion morphologies were found single particle swinned

particles and clusters

(3) Both the Turbulence and Stokersquoss collision mechanism are the effective in formation and coarsening

of TiN clusters the Brownian collision mechanism appeared to play a minor role

5 Acknowledgments

The first author would like to thank China Scholarship Council (CSC) for support of her study abroad

Qingshan steel provided the stainless steel samples of this study The financial support by Natural

Sciences and Engineering Research Council of Canada is greatly acknowledged

6 Reference

[1] L Zhang BG Thomas State of the Art in Evaluation and Control of Steel Cleanliness ISIJ Int 2003

43(3) 271-291

[2] P Kaushik J Lehmann M Nadif State of the Art in Control of Inclusions Their Characterization and Future

Requirements Metall Materi Trans B 2012 43(4) 710-725

[3] P Kaushik H Pielet H Yin Inclusion CharacterizationndashTool for Measurement of Steel Cleanliness and

Process Control Part 1 Ironmaking amp Steelmaking 2009 36(8) 561-571

[4] ME Fine Fatigue Resistance of Metals Metall Trans A 1980 11(3)365ndash379

[5] S Chen M Jiang X He and X Wang Top Slag Refining for Inclusion Composition Transform Control in

Tire Cord Steel Int J Miner Metall Mater 2012 19(6) 490ndash98

[6] X Cai Y Bao L Lin C Gu Effect of Al Content on the Evolution of Non-Metallic Inclusions in SindashMn

Deoxidized Steel Steel Research International online version

[7] DH Woo YB Kang H G Lee Thermodynamic Study of Mno-SiO2-Al2O3 Slag System Liquidus Lines

and Activities of MnO at 1823 K Metall Mater Trans B 2002 33(6) 915-920

[8] K Ogawa T Onoe H Matsumoto K Narita On the behavior of inclusions in the flux treatment of high

carbon steels Tetsu-to-Haganeacute 1985 71(2) 29-32

[9] Y B Kang HG Lee Inclusions Chemistry for MnSi Deoxidized Steels Thermodynamic Predictions and

Experimental Confirmations ISIJ Int 2004 44(6)1006-1015

[10] T Fujisawa H Sakao Equilibrium between MnO-SiO2-Al2O3-FeO Slags and Liquid Steel Tetsu-to-

Haganeacute 1977 63(9) 1504-1511

[11] H Suito R Inoue Thermodynamics on Control of Inclusions Composition in Ultraclean Steels ISIJ Int

1996 36(5) 528-536

[12] IH Jung YB Kang S Decterov AD Pelton Thermodynamic Evaluation and Optimization of the MnO-

Al2O3 and MnO-Al2O3-SiO2 Systems and Applications to Inclusion Engineering Metall Materi Trans B

2004 35(2) 259-268

[13] JS Park JH Park Effect of Slag Composition on the Concentration of Al2O3 in the Inclusions in Si-Mn-

Killed Steel Metall Materi Trans B 2014 45(3)953-960

[14] SB Lee JH Choi HG Lee PH Rhee and SM Jung Aluminum Deoxidation Equilibrium in Liquid Fe-

16 Pct Cr Alloy Metall Mater Trans B 2005 36 (3) 414-16

[15] M Vanende M Guo J Proost B Blanpain P Wollants Formation and Morphology of Al2O3 Inclusions at

the Onset of Liquid Fe Deoxidation by Al Addition ISIJ Int 2011 51(1) 27-34

[16] M B Leban R Tisu The Effect of Tin Inclusions and Deformation-Induced Martensite on the Corrosion

Properties of AISI 321 Stainless Steel Eng Fail Anal 2013 33 430-38

[17] M Prikryl A Kroupa GC Weatherly SV Subramanian Precipitation Behavior in a Medium Carbon Ti-

V-N Microalloyed Steel Metall Mater Trans B 1996 27(5) 1149-1165

[18] Z Chen MH Loretto RC Cochrane Nature of Large Precipitates in Titanium-Containing HSLA Steels

Mater Sci Technol 1987 3(10) 836-844

[19] J Du M Strangwood and CL Davis Effect of Tin Particles and Grain Size on the Charpy Impact

Transition Temperature in Steels J Mater Sci Technol 2012 28 (10) 878-888

[20] W Yan YY Shan K Yang Effect of TiN Inclusions on the Impact Toughness of Low-Carbon Microalloyed

Steels Metall Mater Trans A 2006 37(7) 2147-2158

[21] MA Linaza JL Romero JM Rodriacuteguez-Ibabe JJ Urcola Influence of the Microstructure on the

Fracture Toughness and Fracture Mechanisms of Forging Steels Microalloyed with Titanium with Ferrite-

Pearlite Structures Scripta Metallurgica et Materialia 1993 29(4) 451-456

[22] T Uesugi Production of High-Carbon Chromium Bearing Steel in Vertical Type Continuous Caster Trans

ISIJ 1986 26(7) 614-620

[23] K Kunishige N Nagao Strengthening and Toughening of Hot-Direct-Rolled Steels by Addition of a Small

Amount of Titanium ISIJ Int 1989 29(11) 940-946

[24] MW Zhou H Yu Effects of Precipitates and Inclusions on the Fracture Toughness of Hot Rolling X70

Pipeline Steel Plates Int J Miner Metall Mater 2012 19(9) 805-11

[25] Y Cogne B Heritier J Monnot Relationship of Melting Practice Inclusion Type and Size with Fatigue

Resistance of Bearing Steels Proceedings of the Third International Conference on Clean Steel The Institute

of Metals Balatonfuumlred Hungary 1987 26-31

[26] A Echeverrıa JM Rodriguez-Ibabe Brittle Fracture Micromechanisms in Bainitic and Martensitic

Microstructures in a C-Mn-B Steel Scripta Materialia 1999 41 (2)131-136

[27] LP Zhang CL Davis M Strangwood Effect of TiN Particles and Microstructure on Fracture Toughness in

Simulated Heat-Affected Zones of a Structural Steel Metall Mater Trans A 1999 30 (8)2089-2096

[28] DP Fairchild DG Howden WAT Clark The Mechanism of Brittle Fracture in a Microalloyed Steel Part

I Inclusion-Induced Cleavage Metall Mater Trans A 2000 31(3) 641-652

[29] MJ Balart CL Davis M Strangwood Cleavage Initiation in TindashVndashN and VndashN Microalloyed Ferriticndash

Pearlitic Forging Steels Mater Sci Eng A 2000 284 (1ndash2) 1-13

[30] M Hasegawa S Maruhashi Y Kamidate Y Muranaka F Hoshi Tundish Nozzle Constriction in

Continuous Casting of Titanium Bearing Stainless Steel Slabs Tetsu-to-Haganeacute 1984 70 (14) 1704-11

[31] R Maddalena R Rastogi S Bassem AW Cramb Nozzle Deposits in Titanium Treated Stainless Steels

Iron and Steelmaker 2000 27 (12) 71-79

[32] Y Gao K Sorimachi Formation of Clogging Materials in an Immersed Nozzle During Continuous Casting

of Titanium Stabilized Stainless Steel ISIJ Int 1993 33 (2) 291-297

[33] Y Bi AV Karasev PG Joumlnsson Evolution of Different Inclusions during Ladle Treatment and Continuous

Casting of Stainless Steel ISIJ Int 2013 53(12)2099ndash2109

[34] HS Kim HG Lee KS OH Precipitation Behavior of Mns on Oxide Inclusions in SiMn Deoxidized

Steel Metall Mater Int 2000 6(4) 305ndash10

[35] M Wakoh T Sawai S Mizoguchi Effect of oxide particles on MnS precipitation in low S steels Tetsu-to-

Haganeacute 1992 78(11)1697ndash1704

[36] M Wakoh T Sawai S Mizoguchi Effect of S Content on the MnS Precipitation in Steel with Oxide

Nuclei ISIJ Int 1996 36(8)1014ndash1021

[37] HS Kim HG Lee KS OH MnS Precipitation in Association with Manganese Silicate Inclusions in

SiMn Deoxidized Steel Metall Mater Trans A 2001 32A (6)1519ndash1525

[38] S S Babu S A David J M Vitek K Mundra T DebRoy Development of Macro- and Microstructures of

Carbon-manganese Low Alloy Steel Welds Inclusion Formation Mater Sci Technol 1995 11(2)186ndash199

[39] DG Zhou J Fu XC Chen J Li Precipitation Behavior of TiN in Bearing Steel J Mater Sci Technol

2003 19(2) 184ndash186

[40] F Meng J Wang EH KW Han The Role of TiN Inclusions in Stress Corrosion Crack Initiation for Alloy

690TT in High-Temperature and High Pressure Water Corros Sci 2010 52(3) 927ndash932

[41] Y Xu Z Chen M Gong D Shu Y Tian X Yuan Effects of Mg Addition on Inclusions Formation and

Resultant Solidification Structure Changes of Ti-Stabilized Ultra-Pure Ferritic Stainless Steel Journal of

Iron and Steel Research International 2014 21(6) 583-588

[42] A S Nick H Fredriksson On the Relationship between Inclusions and Pores Part I Precipitation Trans

Indian Inst Met 2012 65(6) 791-794

[43] JH Park Effect of Inclusions on the Solidification Structures of Ferritic Stainless Steel Computational and

Experimental Study of Inclusion Evolution Calphad 201135(4) 455-462

[44] W Yan YY Shan K Yang Influence of Tin Inclusions on the Cleavage Fracture Behavior of Low-Carbon

Microalloyed Steels Metallurgical and Materials Transactions A 2007 38(6) 1211-1222

[45] M Soumlder PG Joumlnsson L Jonsson Inclusion Growth and Removal in Gas-stirred Ladles Steel Res Int

2004 75(2) 128-138

[46] S Taniguchi A Kikuchi Mechanisms of Collision and Coagulation between Fine Particles in Fluid Tetsu-

to-Haganeacute 1992 78(4) 527-535

[47] U Lindborg KTorssell A Collision Model for the Growth and Separation of Deoxidation Products Trans

Met Soc AIME 1968 242 94-102

1 Introduction

Non-metallic inclusions in steel can cause deterioration of mechanical properties surface defects

initiation sites for corrosion-fatigue cracks and hydrogen embrittlement as wells as operational

complications such as clogging of the submerged entry nozzle (SEN) [1-4] However complete

removal of harmful inclusions from molten steel during the refining process is difficult An

alternative approach is to minimize the harmful effects of residual inclusions or to beneficially

utilize these inclusions through proper control and modification

Aluminum is one of the strongest deoxidizers [1415] for steel However due to the harmful effects of

Al2O3-rich inclusions on steel quality and process Si and Mn are often used as steel deoxidizers[56]

After deoxidation by SiMn the main constituents of inclusions are MnO and SiO2 Al2O3 and CaO

may also enter the steel through entrainment of the top slag Titanium is another deoxidizer with

beneficial effects in austenitic stainless steel as it suppresses chromium carbide precipitation in the

grain boundaries and reduces susceptibility to intergranular corrosion through the formation of very

stable titanium carbide [16] However the excessive Ti and N can form coarse TiN inclusions that grow

to large particles [17 18] As one type of inherently brittle nonmetallic inclusion they have often been

reported to act as fracture initiation sites [19-21] thus adversely affecting the fatigue life and toughness

of the steel [22-29] Moreover in titanium stabilized steels TiN is found in the submerged entry nozzle

(SEN) blockage materials Hasegawa [30] reported that the major deposited materials were made up

of A12O3 and TiN inclusions Maddalena [31] indicated that two distinct types of titanium nitride-

based deposits were found after analysis of clogged nozzles from titanium treated stainless steel

(types 321 and 409) pure TiN and TiN associated with a spinel phase Gao[32] reported that stainless

steel with Ti content exceeding 015 increases the risk of clogging significantly

The previous studies on TiN inclusions have concentrated on two dimensional (2D) investigation of

inclusions by sectioning steel samples limiting accurate chemical analysis of the inclusion surface

and obtaining a full understanding of their 3D features [33] In the present study electrolytic

extraction (EE) was employed to extract intact inclusions from steel matrix allowing three

dimensional investigations of inclusion characteristics (such as composition size number and

morphology) in steel samples taken after different deoxidizers additions After separating the

particles on the surface of film filter the particle size distribution was determined for most of the

major nonmetallic inclusion types found in the samples The evolution of different inclusions and

formation and growth mechanisms of TiN clusters were investigated and discussed

2 Experimental Procedure

21 Sample preparation

In this study inclusions formed in 17Cr austenitic stainless steel were investigated after

deoxidation and Ti-stabilization Steel scrap and alloys were initially melted in an intermediate

frequency induction furnace and the molten steel was subsequently decarburized deoxidized and

desulfurized in an AOD furnace After transfer to a ladle furnace the composition and temperature

of the steel were adjusted and argon injection was applied to enhance the removal of inclusions at

the ladle treatment station Table 1 presents the final composition of the steel before ingot casting

Table I Chemical composition of Ti-stabilized stainless steel (mass pct)

C Si Mn P S Cr Ni Ti Al N O

0032 037 113 0039 00017 1714 906 0307 0026 0025 00029

Steel samples for investigation of inclusions were obtained at various stages during the production

process according to the scheme shown in Figure 1 The samples were taken after the addition of

deoxidizing agents SiMn followed by Al after feeding titanium alloy wire and at the start of casting

Fig 1 Schematic illustration of sampling locations

22 Inclusion Characterization

Electrolytic extraction (EE) method was applied for extraction of inclusion particles The method

involves dissolution of steel matrix under an applied potential leaving intact particles behind Steel

sample (15 times 15 times 4mm) were subjected to EE in a 10 AA (10 vv acetylacetone-1wtv

tetramethylammonium chloride-methanol) electrolyte The current density was set at 40-50 mAcm-

2 during the extraction The weight of dissolved metal during electrolytic extraction was 012-02 g

with the EE time at about 25-3 hours After extraction the solution containing inclusions was

filtrated through a polytetrafluoroethylene (PTFE) membrane with an open pore size of 02 microm

After coating the membrane filter with gold under vacuum conditions the characteristics

(morphology size and composition) of extracted inclusions were investigated using the SEM

equipped with EDS The number of inclusions per unit volume (NV) was calculated as follows

filter metal

observed dissolved

vA

N nA W

[1]

where n is the number of inclusions in the appropriate size interval Afilter is the area of the film

filter Aobserved is the total observed area ρmetal is the density of the steel matrix and Wdissolved is the

dissolved weight of the steel during extraction

3 Result and Discussion

31 Morphology and size Changes of inclusions

Inclusions typically found after SiMn deoxidation are shown in Figure 2 The non-metallic

inclusions were classified into two different categories based on their composition and morphology

manganese silicates (Figure 2 (a) ~ (c)) and inclusions containing both oxide and manganese sulfide

(Figure 2 (d) ~ (f)) Most of the manganese silicate inclusions are spherical in shape (a) due to the

fact that these inclusions are liquid at steelmaking temperature It can be seen from (d) ~ (f) that

MnS patches are present at the surface of oxide inclusions Kim et al [34] and Wakoh et al [35]

reported that MnS phase could precipitate by S diffusion from the matrix to the oxide due to

segregation during cooling Such kind of MnS has often been found in the inclusions after SiMn

deoxidation [35-37] As the temperature is reduced an appreciable amount of sulfur has to diffuse into

the liquid (Si Mn)-rich oxide as the solubility of sulfur in solid steel is very low As a result the

(SiMn)-rich oxide is enriched in sulfur especially at the outer layer of inclusions and will be

supersaturated with sulfur on further cooling This sulfur is eventually precipitated as MnS phase

on the inclusion surface

Fig 2 Three-dimensional morphologies of inclusions extracted from steel samples after SiMn

After Al addition the silicate based inclusions are generally transformed into alumina-rich

inclusions according to Reactions [2] and [3] due to the higher affinity between Al and O The total

oxygen was about 110 ppm after SiMn deoxidation and decreased to 39 ppm after Al addition

Inclusions typically observed after Al additions are shown in Figure 3 These inclusions are irregular

in shape with a rough surface pointing to their presence in steel as solid phases due to their high

melting temperature

4[Al] + 3(SiO2)inclusion = 2(Al2O3)inclusion + 3[Si] [2]

2[Al] + 3(MnO)inclusion = (Al2O3)inclusion + 3[Mn] [3]

Fig 3 Three-dimensional morphologies of inclusions extracted from steel samples after Al addition

The particle size distributions of inclusions are shown in Figure 4 Most of the inclusions were

observed to be lt 4 microm in size with majority being around 15microm and 10microm after SiMn and Al

additions respectively Further the number density of inclusions is much higher after SiMn addition

than that of Al addition Noting that no obvious coarsening is happening during Al addition based

on the size distributions it is concluded that some inclusion have been removed during the refining

process

Fig 4 Particle size distributions of inclusions (a) After SiMn addition (b) After Al addition

32 Composition Change of inclusions

The inclusion compositions determined from the SEM-EDS analysis of steel samples after SiMn

and Al additions were plotted on the polythermal projection of the SiO2ndashMnOndashAl2O3 and SiO2ndash

Al2O3ndashMnO ternary diagram respectively as shown in Figure 5 calculated by FactSage 70 It should

be mentioned that CaO was also detected in the inclusions due to the interaction between slag and

steel its effect on the phase diagram and inclusion composition was however ignored due to the low

content (lt 5) and for simplification As can be seen from Figure 5 (a) after SiMn addition the

inclusion compositions are concentrated close to the MnO-SiO2 binary region which is almost in

liquid region due to its lower melting point than that of steel [38] This explains the spherical shape

of the inclusions in Figure 2 After Al addition the composition shifts towards high-alumina

phases near the Al2O3 corner with a higher melting point

Fig5 Calculated polythermal projection (a) After SiMn addition (b) After Al addition

Solid circles represent the composition of oxide inclusions

The effect of alumina content on the liquidus temperature and the primary crystalline phase of the

inclusions were calculated by FactSage 70 with the FToxid database as shown in Figure 6

Increasing the concentration of alumina in the inclusions changed the primary phase in the following

order SiO2 MnSiO3 (rhodonite) Mn3Al2Si3O12 (spessartite) MnAl2O4 (galaxite) and Al2O3 The

liquidus temperature of the inclusion first decreased with increasing alumina concentration up to

about 75 mol followed by a rebound after this composition In this study the alumina

concentration of the inclusions after Al addition was found to be over 60 explaining their solid

state in steelmaking temperatures and irregular morphologies as seen in Figure 3

Fig 6 Calculated liquidus temperatures in the MnO-SiO2-Al2O3 systems as a function of the concentration of

Al2O3 when the ratio of mol pct MnO to mol pct SiO2 is 075

33 Inclusion Characteristics after Ti addition

The TiN inclusion belongs to the cubic or triangular-shaped crystal phase system with a high melting

temperature and hardness making them difficult to deform during steel processing[24] Zhou et al

[39] reported that nitrides with the average size of 6 microm are equivalent to oxides with an average size

of 25 microm in terms of the deterioration of fatigue life

After Ti-core wire feeding inclusions with three distinct morphologies were identified single

particles of titanium nitride (Figure 7 (a) - (d)) twinned particles of titanium nitride (Figure 7 (e) -

(h) and clusters (Figure 7 (i) - (l)) Single TiN has a regular cubic structure while the twinned TiN

particles resembled two more cubic crystals colliding with with each other Maddalena et al

reported that this kind of TiN was caused only by growth of two nucleates [31] TiN clusters usually

have a larger size which may be broken up into smaller TiN particles as a stringer shape during

rolling process [4016] The microvoids in such stringers when exposed to an aqueous solution will

act as sites for pitting corrosion or the initiation of stress corrosion cracking negatively impacting

the to the steel quality

It should be pointed out that oxide particles were still observed in the steel samples after Ti addition

However due to their very low content less than 1 only TiN was discussed The oxide inclusions

can in fact act as the effective heterogeneous nuclei for TiN formation which was confirmed by two

dimensional analysis on the cross-sections[4041-44]

Fig 7 Three-dimensional morphologies of inclusions extracted from steel samples after Ti addition

Figure 8 gives the size distributions of the three types of TiN inclusions In sample L1 the number

densities of single and twinned TiN are dominant In sample C1 the density of large clusters has

increased due to agglomeration of single twinned or small clusters of TiN into bigger clusters Clusters

with the size more than 10 microm were also observed in sample C1 as shown in the upper right corner of

Figure 8 (b) These larger clusters can easily adhere to the nozzle wall and cause nozzle clogging

Moreover they can severely impact the steel quality if they appear in the final product

Fig 8 Size distributions of inclusions after Ti addition (a) Sample L1 (b) Sample C1

34 Formation and Growth Mechanism of TiN Clusters

The formation and growth of TiN clusters in the liquid steel appears to take place in two steps 1)

formation of small clusters by collision of single or twinned inclusions 2) growth of clusters by

collision with singletwinned inclusion or with other clusters There are three types of collision

which can happen between inclusions 1) Brownian collision due to the random movement of very

small inclusions in molten steel 2) Turbulence collision because of the turbulent flow of liquid steel

which can cause the inclusion collision 3) Stokersquos collision due to the density difference between

steel and inclusions so that larger inclusions ascend faster than smaller ones and collide with them

as they travel up Each of the collision mechanisms makes a contribution to the total number of

inclusion collisions

The collision number of inclusions in the liquid steel per unit time (ldquocollision raterdquo) can be

calculated by the following Equation [45]

i j

ij i j

dnw n n

dt [4]

where wij is the collision volume (m3s) of a certain collision phenomenon ni and nj are the number

of inclusions within certain size ranges and t is time (s) The collision volume for Brownian collision

( B

ijw[46]) Turbulence collision ( T

ijw[46]) and Stokersquos collision ( S

ijw[47]) can be expressed as following

respectively

Β

ij i j

i j

2kΤ 1 1w = + r +r

3μ r r

[5]

3

T

ij Fe i jw =13α περ μ r +r [6]

3

S Fe iij i j i j

2πg(ρ ρ )w = r +r r r

9μ

[7]

In these equations k is the Boltzmann constant (JK) T is the absolute temperature (K) micro is the

dynamic viscosity of steel (kgms) α is the collision efficiency ε is the turbulent energy dissipation

(m2s3) ρFe and ρi are the densities of the steel and inclusion respectively (kgm3) g is the

gravitational acceleration (ms2) and ri and rj are the radii of the two colliding inclusions (m)

Each of the different collision mechanism can make a contribution to the total number of collisions

Therefore collision volume wij was calculated using the parameters given in Table 2 in order to

determine the significance of the separate collision mechanisms It should be pointed out that the

calculation of collision volume was based on considering spherical inclusions in steel Therefore in

this study it was assumed that an irregular shape inclusion can rotate around its center due to the

liquid steel flow and can collide with other inclusions within the rotational region whose maximum

length equals to the inclusion diameter

Figure 9 presents the calculated values of the collision volumes for an inclusion of 148microm (size

with a highest content according to Figure 8 ) that collides with other inclusions of different sizes

It can be seen from Figure 9 that Brownian collision volume B

ijw is drastically smaller than that of

Stokersquos and Turbulent collision volume in all studied ranges of rj whose impact on inclusion growth

can be neglected Both Turbulence and Stokersquos collision mechanism have a much higher effect on

the collision volume compared to the Brownian collision They keep an increasing trend as a

function of increased size (more than 148microm) Moreover the effect of Turbulence collision is

higher than Stokes and the difference between these two collisions is decreasing as the inclusion

size increases within the the range studied here Therefore both Turbulence and Stokersquos mechanism

are believed to play a considerable role in inclusion coarsening

TableⅡ Data used in calculation of collision volumes

k

(JK)

T

(K)

micro

(kgms)

α

(m2s3)

ε

(m2s3)

ρFe

(kgm3)

ρi

(kgm3)

g

(ms2)

138times10-

23 1873 0005 03 00018 8000 5220 981

Fig 9 Collision volumes for an inclusion with a 148microm (ri=074microm) in diameter as a function of collision with

different sized inclusions

4 Conclusions

Inclusions characteristics (such as morphology composition and size distribution) were analyzed in steel

samples taken after different alloy additions using electrolytic extraction methods followed by SEM-

EDS characterization The following conclusions were drawn

(1) After the addition of ferrosilicon alloy and electrolytic manganese followed by aluminum the

composition of inclusions changed from manganese silicate-rich inclusions with spherical shapes to

alumina-rich inclusions with irregular shapes

(2) After Ti-stabilization three TiN inclusion morphologies were found single particle swinned

particles and clusters

(3) Both the Turbulence and Stokersquoss collision mechanism are the effective in formation and coarsening

of TiN clusters the Brownian collision mechanism appeared to play a minor role

5 Acknowledgments

The first author would like to thank China Scholarship Council (CSC) for support of her study abroad

Qingshan steel provided the stainless steel samples of this study The financial support by Natural

Sciences and Engineering Research Council of Canada is greatly acknowledged

6 Reference

[1] L Zhang BG Thomas State of the Art in Evaluation and Control of Steel Cleanliness ISIJ Int 2003

43(3) 271-291

[2] P Kaushik J Lehmann M Nadif State of the Art in Control of Inclusions Their Characterization and Future

Requirements Metall Materi Trans B 2012 43(4) 710-725

[3] P Kaushik H Pielet H Yin Inclusion CharacterizationndashTool for Measurement of Steel Cleanliness and

Process Control Part 1 Ironmaking amp Steelmaking 2009 36(8) 561-571

[4] ME Fine Fatigue Resistance of Metals Metall Trans A 1980 11(3)365ndash379

[5] S Chen M Jiang X He and X Wang Top Slag Refining for Inclusion Composition Transform Control in

Tire Cord Steel Int J Miner Metall Mater 2012 19(6) 490ndash98

[6] X Cai Y Bao L Lin C Gu Effect of Al Content on the Evolution of Non-Metallic Inclusions in SindashMn

Deoxidized Steel Steel Research International online version

[7] DH Woo YB Kang H G Lee Thermodynamic Study of Mno-SiO2-Al2O3 Slag System Liquidus Lines

and Activities of MnO at 1823 K Metall Mater Trans B 2002 33(6) 915-920

[8] K Ogawa T Onoe H Matsumoto K Narita On the behavior of inclusions in the flux treatment of high

carbon steels Tetsu-to-Haganeacute 1985 71(2) 29-32

[9] Y B Kang HG Lee Inclusions Chemistry for MnSi Deoxidized Steels Thermodynamic Predictions and

Experimental Confirmations ISIJ Int 2004 44(6)1006-1015

[10] T Fujisawa H Sakao Equilibrium between MnO-SiO2-Al2O3-FeO Slags and Liquid Steel Tetsu-to-

Haganeacute 1977 63(9) 1504-1511

[11] H Suito R Inoue Thermodynamics on Control of Inclusions Composition in Ultraclean Steels ISIJ Int

1996 36(5) 528-536

[12] IH Jung YB Kang S Decterov AD Pelton Thermodynamic Evaluation and Optimization of the MnO-

Al2O3 and MnO-Al2O3-SiO2 Systems and Applications to Inclusion Engineering Metall Materi Trans B

2004 35(2) 259-268

[13] JS Park JH Park Effect of Slag Composition on the Concentration of Al2O3 in the Inclusions in Si-Mn-

Killed Steel Metall Materi Trans B 2014 45(3)953-960

[14] SB Lee JH Choi HG Lee PH Rhee and SM Jung Aluminum Deoxidation Equilibrium in Liquid Fe-

16 Pct Cr Alloy Metall Mater Trans B 2005 36 (3) 414-16

[15] M Vanende M Guo J Proost B Blanpain P Wollants Formation and Morphology of Al2O3 Inclusions at

the Onset of Liquid Fe Deoxidation by Al Addition ISIJ Int 2011 51(1) 27-34

[16] M B Leban R Tisu The Effect of Tin Inclusions and Deformation-Induced Martensite on the Corrosion

Properties of AISI 321 Stainless Steel Eng Fail Anal 2013 33 430-38

[17] M Prikryl A Kroupa GC Weatherly SV Subramanian Precipitation Behavior in a Medium Carbon Ti-

V-N Microalloyed Steel Metall Mater Trans B 1996 27(5) 1149-1165

[18] Z Chen MH Loretto RC Cochrane Nature of Large Precipitates in Titanium-Containing HSLA Steels

Mater Sci Technol 1987 3(10) 836-844

[19] J Du M Strangwood and CL Davis Effect of Tin Particles and Grain Size on the Charpy Impact

Transition Temperature in Steels J Mater Sci Technol 2012 28 (10) 878-888

[20] W Yan YY Shan K Yang Effect of TiN Inclusions on the Impact Toughness of Low-Carbon Microalloyed

Steels Metall Mater Trans A 2006 37(7) 2147-2158

[21] MA Linaza JL Romero JM Rodriacuteguez-Ibabe JJ Urcola Influence of the Microstructure on the

Fracture Toughness and Fracture Mechanisms of Forging Steels Microalloyed with Titanium with Ferrite-

Pearlite Structures Scripta Metallurgica et Materialia 1993 29(4) 451-456

[22] T Uesugi Production of High-Carbon Chromium Bearing Steel in Vertical Type Continuous Caster Trans

ISIJ 1986 26(7) 614-620

[23] K Kunishige N Nagao Strengthening and Toughening of Hot-Direct-Rolled Steels by Addition of a Small

Amount of Titanium ISIJ Int 1989 29(11) 940-946

[24] MW Zhou H Yu Effects of Precipitates and Inclusions on the Fracture Toughness of Hot Rolling X70

Pipeline Steel Plates Int J Miner Metall Mater 2012 19(9) 805-11

[25] Y Cogne B Heritier J Monnot Relationship of Melting Practice Inclusion Type and Size with Fatigue

Resistance of Bearing Steels Proceedings of the Third International Conference on Clean Steel The Institute

of Metals Balatonfuumlred Hungary 1987 26-31

[26] A Echeverrıa JM Rodriguez-Ibabe Brittle Fracture Micromechanisms in Bainitic and Martensitic

Microstructures in a C-Mn-B Steel Scripta Materialia 1999 41 (2)131-136

[27] LP Zhang CL Davis M Strangwood Effect of TiN Particles and Microstructure on Fracture Toughness in

Simulated Heat-Affected Zones of a Structural Steel Metall Mater Trans A 1999 30 (8)2089-2096

[28] DP Fairchild DG Howden WAT Clark The Mechanism of Brittle Fracture in a Microalloyed Steel Part

I Inclusion-Induced Cleavage Metall Mater Trans A 2000 31(3) 641-652

[29] MJ Balart CL Davis M Strangwood Cleavage Initiation in TindashVndashN and VndashN Microalloyed Ferriticndash

Pearlitic Forging Steels Mater Sci Eng A 2000 284 (1ndash2) 1-13

[30] M Hasegawa S Maruhashi Y Kamidate Y Muranaka F Hoshi Tundish Nozzle Constriction in

Continuous Casting of Titanium Bearing Stainless Steel Slabs Tetsu-to-Haganeacute 1984 70 (14) 1704-11

[31] R Maddalena R Rastogi S Bassem AW Cramb Nozzle Deposits in Titanium Treated Stainless Steels

Iron and Steelmaker 2000 27 (12) 71-79

[32] Y Gao K Sorimachi Formation of Clogging Materials in an Immersed Nozzle During Continuous Casting

of Titanium Stabilized Stainless Steel ISIJ Int 1993 33 (2) 291-297

[33] Y Bi AV Karasev PG Joumlnsson Evolution of Different Inclusions during Ladle Treatment and Continuous

Casting of Stainless Steel ISIJ Int 2013 53(12)2099ndash2109

[34] HS Kim HG Lee KS OH Precipitation Behavior of Mns on Oxide Inclusions in SiMn Deoxidized

Steel Metall Mater Int 2000 6(4) 305ndash10

[35] M Wakoh T Sawai S Mizoguchi Effect of oxide particles on MnS precipitation in low S steels Tetsu-to-

Haganeacute 1992 78(11)1697ndash1704

[36] M Wakoh T Sawai S Mizoguchi Effect of S Content on the MnS Precipitation in Steel with Oxide

Nuclei ISIJ Int 1996 36(8)1014ndash1021

[37] HS Kim HG Lee KS OH MnS Precipitation in Association with Manganese Silicate Inclusions in

SiMn Deoxidized Steel Metall Mater Trans A 2001 32A (6)1519ndash1525

[38] S S Babu S A David J M Vitek K Mundra T DebRoy Development of Macro- and Microstructures of

Carbon-manganese Low Alloy Steel Welds Inclusion Formation Mater Sci Technol 1995 11(2)186ndash199

[39] DG Zhou J Fu XC Chen J Li Precipitation Behavior of TiN in Bearing Steel J Mater Sci Technol

2003 19(2) 184ndash186

[40] F Meng J Wang EH KW Han The Role of TiN Inclusions in Stress Corrosion Crack Initiation for Alloy

690TT in High-Temperature and High Pressure Water Corros Sci 2010 52(3) 927ndash932

[41] Y Xu Z Chen M Gong D Shu Y Tian X Yuan Effects of Mg Addition on Inclusions Formation and

Resultant Solidification Structure Changes of Ti-Stabilized Ultra-Pure Ferritic Stainless Steel Journal of

Iron and Steel Research International 2014 21(6) 583-588

[42] A S Nick H Fredriksson On the Relationship between Inclusions and Pores Part I Precipitation Trans

Indian Inst Met 2012 65(6) 791-794

[43] JH Park Effect of Inclusions on the Solidification Structures of Ferritic Stainless Steel Computational and

Experimental Study of Inclusion Evolution Calphad 201135(4) 455-462

[44] W Yan YY Shan K Yang Influence of Tin Inclusions on the Cleavage Fracture Behavior of Low-Carbon

Microalloyed Steels Metallurgical and Materials Transactions A 2007 38(6) 1211-1222

[45] M Soumlder PG Joumlnsson L Jonsson Inclusion Growth and Removal in Gas-stirred Ladles Steel Res Int

2004 75(2) 128-138

[46] S Taniguchi A Kikuchi Mechanisms of Collision and Coagulation between Fine Particles in Fluid Tetsu-

to-Haganeacute 1992 78(4) 527-535

[47] U Lindborg KTorssell A Collision Model for the Growth and Separation of Deoxidation Products Trans

Met Soc AIME 1968 242 94-102

Table I Chemical composition of Ti-stabilized stainless steel (mass pct)

C Si Mn P S Cr Ni Ti Al N O

0032 037 113 0039 00017 1714 906 0307 0026 0025 00029

Steel samples for investigation of inclusions were obtained at various stages during the production

process according to the scheme shown in Figure 1 The samples were taken after the addition of

deoxidizing agents SiMn followed by Al after feeding titanium alloy wire and at the start of casting

Fig 1 Schematic illustration of sampling locations

22 Inclusion Characterization

Electrolytic extraction (EE) method was applied for extraction of inclusion particles The method

involves dissolution of steel matrix under an applied potential leaving intact particles behind Steel

sample (15 times 15 times 4mm) were subjected to EE in a 10 AA (10 vv acetylacetone-1wtv

tetramethylammonium chloride-methanol) electrolyte The current density was set at 40-50 mAcm-

2 during the extraction The weight of dissolved metal during electrolytic extraction was 012-02 g

with the EE time at about 25-3 hours After extraction the solution containing inclusions was

filtrated through a polytetrafluoroethylene (PTFE) membrane with an open pore size of 02 microm

After coating the membrane filter with gold under vacuum conditions the characteristics

(morphology size and composition) of extracted inclusions were investigated using the SEM

equipped with EDS The number of inclusions per unit volume (NV) was calculated as follows

filter metal

observed dissolved

vA

N nA W

[1]

where n is the number of inclusions in the appropriate size interval Afilter is the area of the film

filter Aobserved is the total observed area ρmetal is the density of the steel matrix and Wdissolved is the

dissolved weight of the steel during extraction

3 Result and Discussion

31 Morphology and size Changes of inclusions

Inclusions typically found after SiMn deoxidation are shown in Figure 2 The non-metallic

inclusions were classified into two different categories based on their composition and morphology

manganese silicates (Figure 2 (a) ~ (c)) and inclusions containing both oxide and manganese sulfide

(Figure 2 (d) ~ (f)) Most of the manganese silicate inclusions are spherical in shape (a) due to the

fact that these inclusions are liquid at steelmaking temperature It can be seen from (d) ~ (f) that

MnS patches are present at the surface of oxide inclusions Kim et al [34] and Wakoh et al [35]

reported that MnS phase could precipitate by S diffusion from the matrix to the oxide due to

segregation during cooling Such kind of MnS has often been found in the inclusions after SiMn

deoxidation [35-37] As the temperature is reduced an appreciable amount of sulfur has to diffuse into

the liquid (Si Mn)-rich oxide as the solubility of sulfur in solid steel is very low As a result the

(SiMn)-rich oxide is enriched in sulfur especially at the outer layer of inclusions and will be

supersaturated with sulfur on further cooling This sulfur is eventually precipitated as MnS phase

on the inclusion surface

Fig 2 Three-dimensional morphologies of inclusions extracted from steel samples after SiMn

After Al addition the silicate based inclusions are generally transformed into alumina-rich

inclusions according to Reactions [2] and [3] due to the higher affinity between Al and O The total

oxygen was about 110 ppm after SiMn deoxidation and decreased to 39 ppm after Al addition

Inclusions typically observed after Al additions are shown in Figure 3 These inclusions are irregular

in shape with a rough surface pointing to their presence in steel as solid phases due to their high

melting temperature

4[Al] + 3(SiO2)inclusion = 2(Al2O3)inclusion + 3[Si] [2]

2[Al] + 3(MnO)inclusion = (Al2O3)inclusion + 3[Mn] [3]

Fig 3 Three-dimensional morphologies of inclusions extracted from steel samples after Al addition

The particle size distributions of inclusions are shown in Figure 4 Most of the inclusions were

observed to be lt 4 microm in size with majority being around 15microm and 10microm after SiMn and Al

additions respectively Further the number density of inclusions is much higher after SiMn addition

than that of Al addition Noting that no obvious coarsening is happening during Al addition based

on the size distributions it is concluded that some inclusion have been removed during the refining

process

Fig 4 Particle size distributions of inclusions (a) After SiMn addition (b) After Al addition

32 Composition Change of inclusions

The inclusion compositions determined from the SEM-EDS analysis of steel samples after SiMn

and Al additions were plotted on the polythermal projection of the SiO2ndashMnOndashAl2O3 and SiO2ndash

Al2O3ndashMnO ternary diagram respectively as shown in Figure 5 calculated by FactSage 70 It should

be mentioned that CaO was also detected in the inclusions due to the interaction between slag and

steel its effect on the phase diagram and inclusion composition was however ignored due to the low

content (lt 5) and for simplification As can be seen from Figure 5 (a) after SiMn addition the

inclusion compositions are concentrated close to the MnO-SiO2 binary region which is almost in

liquid region due to its lower melting point than that of steel [38] This explains the spherical shape

of the inclusions in Figure 2 After Al addition the composition shifts towards high-alumina

phases near the Al2O3 corner with a higher melting point

Fig5 Calculated polythermal projection (a) After SiMn addition (b) After Al addition

Solid circles represent the composition of oxide inclusions

The effect of alumina content on the liquidus temperature and the primary crystalline phase of the

inclusions were calculated by FactSage 70 with the FToxid database as shown in Figure 6

Increasing the concentration of alumina in the inclusions changed the primary phase in the following

order SiO2 MnSiO3 (rhodonite) Mn3Al2Si3O12 (spessartite) MnAl2O4 (galaxite) and Al2O3 The

liquidus temperature of the inclusion first decreased with increasing alumina concentration up to

about 75 mol followed by a rebound after this composition In this study the alumina

concentration of the inclusions after Al addition was found to be over 60 explaining their solid

state in steelmaking temperatures and irregular morphologies as seen in Figure 3

Fig 6 Calculated liquidus temperatures in the MnO-SiO2-Al2O3 systems as a function of the concentration of

Al2O3 when the ratio of mol pct MnO to mol pct SiO2 is 075

33 Inclusion Characteristics after Ti addition

The TiN inclusion belongs to the cubic or triangular-shaped crystal phase system with a high melting

temperature and hardness making them difficult to deform during steel processing[24] Zhou et al

[39] reported that nitrides with the average size of 6 microm are equivalent to oxides with an average size

of 25 microm in terms of the deterioration of fatigue life

After Ti-core wire feeding inclusions with three distinct morphologies were identified single

particles of titanium nitride (Figure 7 (a) - (d)) twinned particles of titanium nitride (Figure 7 (e) -

(h) and clusters (Figure 7 (i) - (l)) Single TiN has a regular cubic structure while the twinned TiN

particles resembled two more cubic crystals colliding with with each other Maddalena et al

reported that this kind of TiN was caused only by growth of two nucleates [31] TiN clusters usually

have a larger size which may be broken up into smaller TiN particles as a stringer shape during

rolling process [4016] The microvoids in such stringers when exposed to an aqueous solution will

act as sites for pitting corrosion or the initiation of stress corrosion cracking negatively impacting

the to the steel quality

It should be pointed out that oxide particles were still observed in the steel samples after Ti addition

However due to their very low content less than 1 only TiN was discussed The oxide inclusions

can in fact act as the effective heterogeneous nuclei for TiN formation which was confirmed by two

dimensional analysis on the cross-sections[4041-44]

Fig 7 Three-dimensional morphologies of inclusions extracted from steel samples after Ti addition

Figure 8 gives the size distributions of the three types of TiN inclusions In sample L1 the number

densities of single and twinned TiN are dominant In sample C1 the density of large clusters has

increased due to agglomeration of single twinned or small clusters of TiN into bigger clusters Clusters

with the size more than 10 microm were also observed in sample C1 as shown in the upper right corner of

Figure 8 (b) These larger clusters can easily adhere to the nozzle wall and cause nozzle clogging

Moreover they can severely impact the steel quality if they appear in the final product

Fig 8 Size distributions of inclusions after Ti addition (a) Sample L1 (b) Sample C1

34 Formation and Growth Mechanism of TiN Clusters

The formation and growth of TiN clusters in the liquid steel appears to take place in two steps 1)

formation of small clusters by collision of single or twinned inclusions 2) growth of clusters by

collision with singletwinned inclusion or with other clusters There are three types of collision

which can happen between inclusions 1) Brownian collision due to the random movement of very

small inclusions in molten steel 2) Turbulence collision because of the turbulent flow of liquid steel

which can cause the inclusion collision 3) Stokersquos collision due to the density difference between

steel and inclusions so that larger inclusions ascend faster than smaller ones and collide with them

as they travel up Each of the collision mechanisms makes a contribution to the total number of

inclusion collisions

The collision number of inclusions in the liquid steel per unit time (ldquocollision raterdquo) can be

calculated by the following Equation [45]

i j

ij i j

dnw n n

dt [4]

where wij is the collision volume (m3s) of a certain collision phenomenon ni and nj are the number

of inclusions within certain size ranges and t is time (s) The collision volume for Brownian collision

( B

ijw[46]) Turbulence collision ( T

ijw[46]) and Stokersquos collision ( S

ijw[47]) can be expressed as following

respectively

Β

ij i j

i j

2kΤ 1 1w = + r +r

3μ r r

[5]

3

T

ij Fe i jw =13α περ μ r +r [6]

3

S Fe iij i j i j

2πg(ρ ρ )w = r +r r r

9μ

[7]

In these equations k is the Boltzmann constant (JK) T is the absolute temperature (K) micro is the

dynamic viscosity of steel (kgms) α is the collision efficiency ε is the turbulent energy dissipation

(m2s3) ρFe and ρi are the densities of the steel and inclusion respectively (kgm3) g is the

gravitational acceleration (ms2) and ri and rj are the radii of the two colliding inclusions (m)

Each of the different collision mechanism can make a contribution to the total number of collisions

Therefore collision volume wij was calculated using the parameters given in Table 2 in order to

determine the significance of the separate collision mechanisms It should be pointed out that the

calculation of collision volume was based on considering spherical inclusions in steel Therefore in

this study it was assumed that an irregular shape inclusion can rotate around its center due to the

liquid steel flow and can collide with other inclusions within the rotational region whose maximum

length equals to the inclusion diameter

Figure 9 presents the calculated values of the collision volumes for an inclusion of 148microm (size

with a highest content according to Figure 8 ) that collides with other inclusions of different sizes

It can be seen from Figure 9 that Brownian collision volume B

ijw is drastically smaller than that of

Stokersquos and Turbulent collision volume in all studied ranges of rj whose impact on inclusion growth

can be neglected Both Turbulence and Stokersquos collision mechanism have a much higher effect on

the collision volume compared to the Brownian collision They keep an increasing trend as a

function of increased size (more than 148microm) Moreover the effect of Turbulence collision is

higher than Stokes and the difference between these two collisions is decreasing as the inclusion

size increases within the the range studied here Therefore both Turbulence and Stokersquos mechanism

are believed to play a considerable role in inclusion coarsening

TableⅡ Data used in calculation of collision volumes

k

(JK)

T

(K)

micro

(kgms)

α

(m2s3)

ε

(m2s3)

ρFe

(kgm3)

ρi

(kgm3)

g

(ms2)

138times10-

23 1873 0005 03 00018 8000 5220 981

Fig 9 Collision volumes for an inclusion with a 148microm (ri=074microm) in diameter as a function of collision with

different sized inclusions

4 Conclusions

Inclusions characteristics (such as morphology composition and size distribution) were analyzed in steel

samples taken after different alloy additions using electrolytic extraction methods followed by SEM-

EDS characterization The following conclusions were drawn

(1) After the addition of ferrosilicon alloy and electrolytic manganese followed by aluminum the

composition of inclusions changed from manganese silicate-rich inclusions with spherical shapes to

alumina-rich inclusions with irregular shapes

(2) After Ti-stabilization three TiN inclusion morphologies were found single particle swinned

particles and clusters

(3) Both the Turbulence and Stokersquoss collision mechanism are the effective in formation and coarsening

of TiN clusters the Brownian collision mechanism appeared to play a minor role

5 Acknowledgments

The first author would like to thank China Scholarship Council (CSC) for support of her study abroad

Qingshan steel provided the stainless steel samples of this study The financial support by Natural

Sciences and Engineering Research Council of Canada is greatly acknowledged

6 Reference

[1] L Zhang BG Thomas State of the Art in Evaluation and Control of Steel Cleanliness ISIJ Int 2003

43(3) 271-291

[2] P Kaushik J Lehmann M Nadif State of the Art in Control of Inclusions Their Characterization and Future

Requirements Metall Materi Trans B 2012 43(4) 710-725

[3] P Kaushik H Pielet H Yin Inclusion CharacterizationndashTool for Measurement of Steel Cleanliness and

Process Control Part 1 Ironmaking amp Steelmaking 2009 36(8) 561-571

[4] ME Fine Fatigue Resistance of Metals Metall Trans A 1980 11(3)365ndash379

[5] S Chen M Jiang X He and X Wang Top Slag Refining for Inclusion Composition Transform Control in

Tire Cord Steel Int J Miner Metall Mater 2012 19(6) 490ndash98

[6] X Cai Y Bao L Lin C Gu Effect of Al Content on the Evolution of Non-Metallic Inclusions in SindashMn

Deoxidized Steel Steel Research International online version

[7] DH Woo YB Kang H G Lee Thermodynamic Study of Mno-SiO2-Al2O3 Slag System Liquidus Lines

and Activities of MnO at 1823 K Metall Mater Trans B 2002 33(6) 915-920

[8] K Ogawa T Onoe H Matsumoto K Narita On the behavior of inclusions in the flux treatment of high

carbon steels Tetsu-to-Haganeacute 1985 71(2) 29-32

[9] Y B Kang HG Lee Inclusions Chemistry for MnSi Deoxidized Steels Thermodynamic Predictions and

Experimental Confirmations ISIJ Int 2004 44(6)1006-1015

[10] T Fujisawa H Sakao Equilibrium between MnO-SiO2-Al2O3-FeO Slags and Liquid Steel Tetsu-to-

Haganeacute 1977 63(9) 1504-1511

[11] H Suito R Inoue Thermodynamics on Control of Inclusions Composition in Ultraclean Steels ISIJ Int

1996 36(5) 528-536

[12] IH Jung YB Kang S Decterov AD Pelton Thermodynamic Evaluation and Optimization of the MnO-

Al2O3 and MnO-Al2O3-SiO2 Systems and Applications to Inclusion Engineering Metall Materi Trans B

2004 35(2) 259-268

[13] JS Park JH Park Effect of Slag Composition on the Concentration of Al2O3 in the Inclusions in Si-Mn-

Killed Steel Metall Materi Trans B 2014 45(3)953-960

[14] SB Lee JH Choi HG Lee PH Rhee and SM Jung Aluminum Deoxidation Equilibrium in Liquid Fe-

16 Pct Cr Alloy Metall Mater Trans B 2005 36 (3) 414-16

[15] M Vanende M Guo J Proost B Blanpain P Wollants Formation and Morphology of Al2O3 Inclusions at

the Onset of Liquid Fe Deoxidation by Al Addition ISIJ Int 2011 51(1) 27-34

[16] M B Leban R Tisu The Effect of Tin Inclusions and Deformation-Induced Martensite on the Corrosion

Properties of AISI 321 Stainless Steel Eng Fail Anal 2013 33 430-38

[17] M Prikryl A Kroupa GC Weatherly SV Subramanian Precipitation Behavior in a Medium Carbon Ti-

V-N Microalloyed Steel Metall Mater Trans B 1996 27(5) 1149-1165

[18] Z Chen MH Loretto RC Cochrane Nature of Large Precipitates in Titanium-Containing HSLA Steels

Mater Sci Technol 1987 3(10) 836-844

[19] J Du M Strangwood and CL Davis Effect of Tin Particles and Grain Size on the Charpy Impact

Transition Temperature in Steels J Mater Sci Technol 2012 28 (10) 878-888

[20] W Yan YY Shan K Yang Effect of TiN Inclusions on the Impact Toughness of Low-Carbon Microalloyed

Steels Metall Mater Trans A 2006 37(7) 2147-2158

[21] MA Linaza JL Romero JM Rodriacuteguez-Ibabe JJ Urcola Influence of the Microstructure on the

Fracture Toughness and Fracture Mechanisms of Forging Steels Microalloyed with Titanium with Ferrite-

Pearlite Structures Scripta Metallurgica et Materialia 1993 29(4) 451-456

[22] T Uesugi Production of High-Carbon Chromium Bearing Steel in Vertical Type Continuous Caster Trans

ISIJ 1986 26(7) 614-620

[23] K Kunishige N Nagao Strengthening and Toughening of Hot-Direct-Rolled Steels by Addition of a Small

Amount of Titanium ISIJ Int 1989 29(11) 940-946

[24] MW Zhou H Yu Effects of Precipitates and Inclusions on the Fracture Toughness of Hot Rolling X70

Pipeline Steel Plates Int J Miner Metall Mater 2012 19(9) 805-11

[25] Y Cogne B Heritier J Monnot Relationship of Melting Practice Inclusion Type and Size with Fatigue

Resistance of Bearing Steels Proceedings of the Third International Conference on Clean Steel The Institute

of Metals Balatonfuumlred Hungary 1987 26-31

[26] A Echeverrıa JM Rodriguez-Ibabe Brittle Fracture Micromechanisms in Bainitic and Martensitic

Microstructures in a C-Mn-B Steel Scripta Materialia 1999 41 (2)131-136

[27] LP Zhang CL Davis M Strangwood Effect of TiN Particles and Microstructure on Fracture Toughness in

Simulated Heat-Affected Zones of a Structural Steel Metall Mater Trans A 1999 30 (8)2089-2096

[28] DP Fairchild DG Howden WAT Clark The Mechanism of Brittle Fracture in a Microalloyed Steel Part

I Inclusion-Induced Cleavage Metall Mater Trans A 2000 31(3) 641-652

[29] MJ Balart CL Davis M Strangwood Cleavage Initiation in TindashVndashN and VndashN Microalloyed Ferriticndash

Pearlitic Forging Steels Mater Sci Eng A 2000 284 (1ndash2) 1-13

[30] M Hasegawa S Maruhashi Y Kamidate Y Muranaka F Hoshi Tundish Nozzle Constriction in

Continuous Casting of Titanium Bearing Stainless Steel Slabs Tetsu-to-Haganeacute 1984 70 (14) 1704-11

[31] R Maddalena R Rastogi S Bassem AW Cramb Nozzle Deposits in Titanium Treated Stainless Steels

Iron and Steelmaker 2000 27 (12) 71-79

[32] Y Gao K Sorimachi Formation of Clogging Materials in an Immersed Nozzle During Continuous Casting

of Titanium Stabilized Stainless Steel ISIJ Int 1993 33 (2) 291-297

[33] Y Bi AV Karasev PG Joumlnsson Evolution of Different Inclusions during Ladle Treatment and Continuous

Casting of Stainless Steel ISIJ Int 2013 53(12)2099ndash2109

[34] HS Kim HG Lee KS OH Precipitation Behavior of Mns on Oxide Inclusions in SiMn Deoxidized

Steel Metall Mater Int 2000 6(4) 305ndash10

[35] M Wakoh T Sawai S Mizoguchi Effect of oxide particles on MnS precipitation in low S steels Tetsu-to-

Haganeacute 1992 78(11)1697ndash1704

[36] M Wakoh T Sawai S Mizoguchi Effect of S Content on the MnS Precipitation in Steel with Oxide

Nuclei ISIJ Int 1996 36(8)1014ndash1021

[37] HS Kim HG Lee KS OH MnS Precipitation in Association with Manganese Silicate Inclusions in

SiMn Deoxidized Steel Metall Mater Trans A 2001 32A (6)1519ndash1525

[38] S S Babu S A David J M Vitek K Mundra T DebRoy Development of Macro- and Microstructures of

Carbon-manganese Low Alloy Steel Welds Inclusion Formation Mater Sci Technol 1995 11(2)186ndash199

[39] DG Zhou J Fu XC Chen J Li Precipitation Behavior of TiN in Bearing Steel J Mater Sci Technol

2003 19(2) 184ndash186

[40] F Meng J Wang EH KW Han The Role of TiN Inclusions in Stress Corrosion Crack Initiation for Alloy

690TT in High-Temperature and High Pressure Water Corros Sci 2010 52(3) 927ndash932

[41] Y Xu Z Chen M Gong D Shu Y Tian X Yuan Effects of Mg Addition on Inclusions Formation and

Resultant Solidification Structure Changes of Ti-Stabilized Ultra-Pure Ferritic Stainless Steel Journal of

Iron and Steel Research International 2014 21(6) 583-588

[42] A S Nick H Fredriksson On the Relationship between Inclusions and Pores Part I Precipitation Trans

Indian Inst Met 2012 65(6) 791-794

[43] JH Park Effect of Inclusions on the Solidification Structures of Ferritic Stainless Steel Computational and

Experimental Study of Inclusion Evolution Calphad 201135(4) 455-462

[44] W Yan YY Shan K Yang Influence of Tin Inclusions on the Cleavage Fracture Behavior of Low-Carbon

Microalloyed Steels Metallurgical and Materials Transactions A 2007 38(6) 1211-1222

[45] M Soumlder PG Joumlnsson L Jonsson Inclusion Growth and Removal in Gas-stirred Ladles Steel Res Int

2004 75(2) 128-138

[46] S Taniguchi A Kikuchi Mechanisms of Collision and Coagulation between Fine Particles in Fluid Tetsu-

to-Haganeacute 1992 78(4) 527-535

[47] U Lindborg KTorssell A Collision Model for the Growth and Separation of Deoxidation Products Trans

Met Soc AIME 1968 242 94-102

reported that MnS phase could precipitate by S diffusion from the matrix to the oxide due to

segregation during cooling Such kind of MnS has often been found in the inclusions after SiMn

deoxidation [35-37] As the temperature is reduced an appreciable amount of sulfur has to diffuse into

the liquid (Si Mn)-rich oxide as the solubility of sulfur in solid steel is very low As a result the

(SiMn)-rich oxide is enriched in sulfur especially at the outer layer of inclusions and will be

supersaturated with sulfur on further cooling This sulfur is eventually precipitated as MnS phase

on the inclusion surface

Fig 2 Three-dimensional morphologies of inclusions extracted from steel samples after SiMn

After Al addition the silicate based inclusions are generally transformed into alumina-rich

inclusions according to Reactions [2] and [3] due to the higher affinity between Al and O The total

oxygen was about 110 ppm after SiMn deoxidation and decreased to 39 ppm after Al addition

Inclusions typically observed after Al additions are shown in Figure 3 These inclusions are irregular

in shape with a rough surface pointing to their presence in steel as solid phases due to their high

melting temperature

4[Al] + 3(SiO2)inclusion = 2(Al2O3)inclusion + 3[Si] [2]

2[Al] + 3(MnO)inclusion = (Al2O3)inclusion + 3[Mn] [3]

Fig 3 Three-dimensional morphologies of inclusions extracted from steel samples after Al addition

The particle size distributions of inclusions are shown in Figure 4 Most of the inclusions were

observed to be lt 4 microm in size with majority being around 15microm and 10microm after SiMn and Al

additions respectively Further the number density of inclusions is much higher after SiMn addition

than that of Al addition Noting that no obvious coarsening is happening during Al addition based

on the size distributions it is concluded that some inclusion have been removed during the refining

process

Fig 4 Particle size distributions of inclusions (a) After SiMn addition (b) After Al addition

32 Composition Change of inclusions

The inclusion compositions determined from the SEM-EDS analysis of steel samples after SiMn

and Al additions were plotted on the polythermal projection of the SiO2ndashMnOndashAl2O3 and SiO2ndash

Al2O3ndashMnO ternary diagram respectively as shown in Figure 5 calculated by FactSage 70 It should

be mentioned that CaO was also detected in the inclusions due to the interaction between slag and

steel its effect on the phase diagram and inclusion composition was however ignored due to the low

content (lt 5) and for simplification As can be seen from Figure 5 (a) after SiMn addition the

inclusion compositions are concentrated close to the MnO-SiO2 binary region which is almost in

liquid region due to its lower melting point than that of steel [38] This explains the spherical shape

of the inclusions in Figure 2 After Al addition the composition shifts towards high-alumina

phases near the Al2O3 corner with a higher melting point

Fig5 Calculated polythermal projection (a) After SiMn addition (b) After Al addition

Solid circles represent the composition of oxide inclusions

The effect of alumina content on the liquidus temperature and the primary crystalline phase of the

inclusions were calculated by FactSage 70 with the FToxid database as shown in Figure 6

Increasing the concentration of alumina in the inclusions changed the primary phase in the following

order SiO2 MnSiO3 (rhodonite) Mn3Al2Si3O12 (spessartite) MnAl2O4 (galaxite) and Al2O3 The

liquidus temperature of the inclusion first decreased with increasing alumina concentration up to

about 75 mol followed by a rebound after this composition In this study the alumina

concentration of the inclusions after Al addition was found to be over 60 explaining their solid

state in steelmaking temperatures and irregular morphologies as seen in Figure 3

Fig 6 Calculated liquidus temperatures in the MnO-SiO2-Al2O3 systems as a function of the concentration of

Al2O3 when the ratio of mol pct MnO to mol pct SiO2 is 075

33 Inclusion Characteristics after Ti addition

The TiN inclusion belongs to the cubic or triangular-shaped crystal phase system with a high melting

temperature and hardness making them difficult to deform during steel processing[24] Zhou et al

[39] reported that nitrides with the average size of 6 microm are equivalent to oxides with an average size

of 25 microm in terms of the deterioration of fatigue life

After Ti-core wire feeding inclusions with three distinct morphologies were identified single

particles of titanium nitride (Figure 7 (a) - (d)) twinned particles of titanium nitride (Figure 7 (e) -

(h) and clusters (Figure 7 (i) - (l)) Single TiN has a regular cubic structure while the twinned TiN

particles resembled two more cubic crystals colliding with with each other Maddalena et al

reported that this kind of TiN was caused only by growth of two nucleates [31] TiN clusters usually

have a larger size which may be broken up into smaller TiN particles as a stringer shape during

rolling process [4016] The microvoids in such stringers when exposed to an aqueous solution will

act as sites for pitting corrosion or the initiation of stress corrosion cracking negatively impacting

the to the steel quality

It should be pointed out that oxide particles were still observed in the steel samples after Ti addition

However due to their very low content less than 1 only TiN was discussed The oxide inclusions

can in fact act as the effective heterogeneous nuclei for TiN formation which was confirmed by two

dimensional analysis on the cross-sections[4041-44]

Fig 7 Three-dimensional morphologies of inclusions extracted from steel samples after Ti addition

Figure 8 gives the size distributions of the three types of TiN inclusions In sample L1 the number

densities of single and twinned TiN are dominant In sample C1 the density of large clusters has

increased due to agglomeration of single twinned or small clusters of TiN into bigger clusters Clusters

with the size more than 10 microm were also observed in sample C1 as shown in the upper right corner of

Figure 8 (b) These larger clusters can easily adhere to the nozzle wall and cause nozzle clogging

Moreover they can severely impact the steel quality if they appear in the final product

Fig 8 Size distributions of inclusions after Ti addition (a) Sample L1 (b) Sample C1

34 Formation and Growth Mechanism of TiN Clusters

The formation and growth of TiN clusters in the liquid steel appears to take place in two steps 1)

formation of small clusters by collision of single or twinned inclusions 2) growth of clusters by

collision with singletwinned inclusion or with other clusters There are three types of collision

which can happen between inclusions 1) Brownian collision due to the random movement of very

small inclusions in molten steel 2) Turbulence collision because of the turbulent flow of liquid steel

which can cause the inclusion collision 3) Stokersquos collision due to the density difference between

steel and inclusions so that larger inclusions ascend faster than smaller ones and collide with them

as they travel up Each of the collision mechanisms makes a contribution to the total number of

inclusion collisions

The collision number of inclusions in the liquid steel per unit time (ldquocollision raterdquo) can be

calculated by the following Equation [45]

i j

ij i j

dnw n n

dt [4]

where wij is the collision volume (m3s) of a certain collision phenomenon ni and nj are the number

of inclusions within certain size ranges and t is time (s) The collision volume for Brownian collision

( B

ijw[46]) Turbulence collision ( T

ijw[46]) and Stokersquos collision ( S

ijw[47]) can be expressed as following

respectively

Β

ij i j

i j

2kΤ 1 1w = + r +r

3μ r r

[5]

3

T

ij Fe i jw =13α περ μ r +r [6]

3

S Fe iij i j i j

2πg(ρ ρ )w = r +r r r

9μ

[7]

In these equations k is the Boltzmann constant (JK) T is the absolute temperature (K) micro is the

dynamic viscosity of steel (kgms) α is the collision efficiency ε is the turbulent energy dissipation

(m2s3) ρFe and ρi are the densities of the steel and inclusion respectively (kgm3) g is the

gravitational acceleration (ms2) and ri and rj are the radii of the two colliding inclusions (m)

Each of the different collision mechanism can make a contribution to the total number of collisions

Therefore collision volume wij was calculated using the parameters given in Table 2 in order to

determine the significance of the separate collision mechanisms It should be pointed out that the

calculation of collision volume was based on considering spherical inclusions in steel Therefore in

this study it was assumed that an irregular shape inclusion can rotate around its center due to the

liquid steel flow and can collide with other inclusions within the rotational region whose maximum

length equals to the inclusion diameter

Figure 9 presents the calculated values of the collision volumes for an inclusion of 148microm (size

with a highest content according to Figure 8 ) that collides with other inclusions of different sizes

It can be seen from Figure 9 that Brownian collision volume B

ijw is drastically smaller than that of

Stokersquos and Turbulent collision volume in all studied ranges of rj whose impact on inclusion growth

can be neglected Both Turbulence and Stokersquos collision mechanism have a much higher effect on

the collision volume compared to the Brownian collision They keep an increasing trend as a

function of increased size (more than 148microm) Moreover the effect of Turbulence collision is

higher than Stokes and the difference between these two collisions is decreasing as the inclusion

size increases within the the range studied here Therefore both Turbulence and Stokersquos mechanism

are believed to play a considerable role in inclusion coarsening

TableⅡ Data used in calculation of collision volumes

k

(JK)

T

(K)

micro

(kgms)

α

(m2s3)

ε

(m2s3)

ρFe

(kgm3)

ρi

(kgm3)

g

(ms2)

138times10-

23 1873 0005 03 00018 8000 5220 981

Fig 9 Collision volumes for an inclusion with a 148microm (ri=074microm) in diameter as a function of collision with

different sized inclusions

4 Conclusions

Inclusions characteristics (such as morphology composition and size distribution) were analyzed in steel

samples taken after different alloy additions using electrolytic extraction methods followed by SEM-

EDS characterization The following conclusions were drawn

(1) After the addition of ferrosilicon alloy and electrolytic manganese followed by aluminum the

composition of inclusions changed from manganese silicate-rich inclusions with spherical shapes to

alumina-rich inclusions with irregular shapes

(2) After Ti-stabilization three TiN inclusion morphologies were found single particle swinned

particles and clusters

(3) Both the Turbulence and Stokersquoss collision mechanism are the effective in formation and coarsening

of TiN clusters the Brownian collision mechanism appeared to play a minor role

5 Acknowledgments

The first author would like to thank China Scholarship Council (CSC) for support of her study abroad

Qingshan steel provided the stainless steel samples of this study The financial support by Natural

Sciences and Engineering Research Council of Canada is greatly acknowledged

6 Reference

[1] L Zhang BG Thomas State of the Art in Evaluation and Control of Steel Cleanliness ISIJ Int 2003

43(3) 271-291

[2] P Kaushik J Lehmann M Nadif State of the Art in Control of Inclusions Their Characterization and Future

Requirements Metall Materi Trans B 2012 43(4) 710-725

[3] P Kaushik H Pielet H Yin Inclusion CharacterizationndashTool for Measurement of Steel Cleanliness and

Process Control Part 1 Ironmaking amp Steelmaking 2009 36(8) 561-571

[4] ME Fine Fatigue Resistance of Metals Metall Trans A 1980 11(3)365ndash379

[5] S Chen M Jiang X He and X Wang Top Slag Refining for Inclusion Composition Transform Control in

Tire Cord Steel Int J Miner Metall Mater 2012 19(6) 490ndash98

[6] X Cai Y Bao L Lin C Gu Effect of Al Content on the Evolution of Non-Metallic Inclusions in SindashMn

Deoxidized Steel Steel Research International online version

[7] DH Woo YB Kang H G Lee Thermodynamic Study of Mno-SiO2-Al2O3 Slag System Liquidus Lines

and Activities of MnO at 1823 K Metall Mater Trans B 2002 33(6) 915-920

[8] K Ogawa T Onoe H Matsumoto K Narita On the behavior of inclusions in the flux treatment of high

carbon steels Tetsu-to-Haganeacute 1985 71(2) 29-32

[9] Y B Kang HG Lee Inclusions Chemistry for MnSi Deoxidized Steels Thermodynamic Predictions and

Experimental Confirmations ISIJ Int 2004 44(6)1006-1015

[10] T Fujisawa H Sakao Equilibrium between MnO-SiO2-Al2O3-FeO Slags and Liquid Steel Tetsu-to-

Haganeacute 1977 63(9) 1504-1511

[11] H Suito R Inoue Thermodynamics on Control of Inclusions Composition in Ultraclean Steels ISIJ Int

1996 36(5) 528-536

[12] IH Jung YB Kang S Decterov AD Pelton Thermodynamic Evaluation and Optimization of the MnO-

Al2O3 and MnO-Al2O3-SiO2 Systems and Applications to Inclusion Engineering Metall Materi Trans B

2004 35(2) 259-268

[13] JS Park JH Park Effect of Slag Composition on the Concentration of Al2O3 in the Inclusions in Si-Mn-

Killed Steel Metall Materi Trans B 2014 45(3)953-960

[14] SB Lee JH Choi HG Lee PH Rhee and SM Jung Aluminum Deoxidation Equilibrium in Liquid Fe-

16 Pct Cr Alloy Metall Mater Trans B 2005 36 (3) 414-16

[15] M Vanende M Guo J Proost B Blanpain P Wollants Formation and Morphology of Al2O3 Inclusions at

the Onset of Liquid Fe Deoxidation by Al Addition ISIJ Int 2011 51(1) 27-34

[16] M B Leban R Tisu The Effect of Tin Inclusions and Deformation-Induced Martensite on the Corrosion

Properties of AISI 321 Stainless Steel Eng Fail Anal 2013 33 430-38

[17] M Prikryl A Kroupa GC Weatherly SV Subramanian Precipitation Behavior in a Medium Carbon Ti-

V-N Microalloyed Steel Metall Mater Trans B 1996 27(5) 1149-1165

[18] Z Chen MH Loretto RC Cochrane Nature of Large Precipitates in Titanium-Containing HSLA Steels

Mater Sci Technol 1987 3(10) 836-844

[19] J Du M Strangwood and CL Davis Effect of Tin Particles and Grain Size on the Charpy Impact

Transition Temperature in Steels J Mater Sci Technol 2012 28 (10) 878-888

[20] W Yan YY Shan K Yang Effect of TiN Inclusions on the Impact Toughness of Low-Carbon Microalloyed

Steels Metall Mater Trans A 2006 37(7) 2147-2158

[21] MA Linaza JL Romero JM Rodriacuteguez-Ibabe JJ Urcola Influence of the Microstructure on the

Fracture Toughness and Fracture Mechanisms of Forging Steels Microalloyed with Titanium with Ferrite-

Pearlite Structures Scripta Metallurgica et Materialia 1993 29(4) 451-456

[22] T Uesugi Production of High-Carbon Chromium Bearing Steel in Vertical Type Continuous Caster Trans

ISIJ 1986 26(7) 614-620

[23] K Kunishige N Nagao Strengthening and Toughening of Hot-Direct-Rolled Steels by Addition of a Small

Amount of Titanium ISIJ Int 1989 29(11) 940-946

[24] MW Zhou H Yu Effects of Precipitates and Inclusions on the Fracture Toughness of Hot Rolling X70

Pipeline Steel Plates Int J Miner Metall Mater 2012 19(9) 805-11

[25] Y Cogne B Heritier J Monnot Relationship of Melting Practice Inclusion Type and Size with Fatigue

Resistance of Bearing Steels Proceedings of the Third International Conference on Clean Steel The Institute

of Metals Balatonfuumlred Hungary 1987 26-31

[26] A Echeverrıa JM Rodriguez-Ibabe Brittle Fracture Micromechanisms in Bainitic and Martensitic

Microstructures in a C-Mn-B Steel Scripta Materialia 1999 41 (2)131-136

[27] LP Zhang CL Davis M Strangwood Effect of TiN Particles and Microstructure on Fracture Toughness in

Simulated Heat-Affected Zones of a Structural Steel Metall Mater Trans A 1999 30 (8)2089-2096

[28] DP Fairchild DG Howden WAT Clark The Mechanism of Brittle Fracture in a Microalloyed Steel Part

I Inclusion-Induced Cleavage Metall Mater Trans A 2000 31(3) 641-652

[29] MJ Balart CL Davis M Strangwood Cleavage Initiation in TindashVndashN and VndashN Microalloyed Ferriticndash

Pearlitic Forging Steels Mater Sci Eng A 2000 284 (1ndash2) 1-13

[30] M Hasegawa S Maruhashi Y Kamidate Y Muranaka F Hoshi Tundish Nozzle Constriction in

Continuous Casting of Titanium Bearing Stainless Steel Slabs Tetsu-to-Haganeacute 1984 70 (14) 1704-11

[31] R Maddalena R Rastogi S Bassem AW Cramb Nozzle Deposits in Titanium Treated Stainless Steels

Iron and Steelmaker 2000 27 (12) 71-79

[32] Y Gao K Sorimachi Formation of Clogging Materials in an Immersed Nozzle During Continuous Casting

of Titanium Stabilized Stainless Steel ISIJ Int 1993 33 (2) 291-297

[33] Y Bi AV Karasev PG Joumlnsson Evolution of Different Inclusions during Ladle Treatment and Continuous

Casting of Stainless Steel ISIJ Int 2013 53(12)2099ndash2109

[34] HS Kim HG Lee KS OH Precipitation Behavior of Mns on Oxide Inclusions in SiMn Deoxidized

Steel Metall Mater Int 2000 6(4) 305ndash10

[35] M Wakoh T Sawai S Mizoguchi Effect of oxide particles on MnS precipitation in low S steels Tetsu-to-

Haganeacute 1992 78(11)1697ndash1704

[36] M Wakoh T Sawai S Mizoguchi Effect of S Content on the MnS Precipitation in Steel with Oxide

Nuclei ISIJ Int 1996 36(8)1014ndash1021

[37] HS Kim HG Lee KS OH MnS Precipitation in Association with Manganese Silicate Inclusions in

SiMn Deoxidized Steel Metall Mater Trans A 2001 32A (6)1519ndash1525

[38] S S Babu S A David J M Vitek K Mundra T DebRoy Development of Macro- and Microstructures of

Carbon-manganese Low Alloy Steel Welds Inclusion Formation Mater Sci Technol 1995 11(2)186ndash199

[39] DG Zhou J Fu XC Chen J Li Precipitation Behavior of TiN in Bearing Steel J Mater Sci Technol

2003 19(2) 184ndash186

[40] F Meng J Wang EH KW Han The Role of TiN Inclusions in Stress Corrosion Crack Initiation for Alloy

690TT in High-Temperature and High Pressure Water Corros Sci 2010 52(3) 927ndash932

[41] Y Xu Z Chen M Gong D Shu Y Tian X Yuan Effects of Mg Addition on Inclusions Formation and

Resultant Solidification Structure Changes of Ti-Stabilized Ultra-Pure Ferritic Stainless Steel Journal of

Iron and Steel Research International 2014 21(6) 583-588

[42] A S Nick H Fredriksson On the Relationship between Inclusions and Pores Part I Precipitation Trans

Indian Inst Met 2012 65(6) 791-794

[43] JH Park Effect of Inclusions on the Solidification Structures of Ferritic Stainless Steel Computational and

Experimental Study of Inclusion Evolution Calphad 201135(4) 455-462

[44] W Yan YY Shan K Yang Influence of Tin Inclusions on the Cleavage Fracture Behavior of Low-Carbon

Microalloyed Steels Metallurgical and Materials Transactions A 2007 38(6) 1211-1222

[45] M Soumlder PG Joumlnsson L Jonsson Inclusion Growth and Removal in Gas-stirred Ladles Steel Res Int

2004 75(2) 128-138

[46] S Taniguchi A Kikuchi Mechanisms of Collision and Coagulation between Fine Particles in Fluid Tetsu-

to-Haganeacute 1992 78(4) 527-535

[47] U Lindborg KTorssell A Collision Model for the Growth and Separation of Deoxidation Products Trans

Met Soc AIME 1968 242 94-102

additions respectively Further the number density of inclusions is much higher after SiMn addition

than that of Al addition Noting that no obvious coarsening is happening during Al addition based

on the size distributions it is concluded that some inclusion have been removed during the refining

process

Fig 4 Particle size distributions of inclusions (a) After SiMn addition (b) After Al addition

32 Composition Change of inclusions

The inclusion compositions determined from the SEM-EDS analysis of steel samples after SiMn

and Al additions were plotted on the polythermal projection of the SiO2ndashMnOndashAl2O3 and SiO2ndash

Al2O3ndashMnO ternary diagram respectively as shown in Figure 5 calculated by FactSage 70 It should

be mentioned that CaO was also detected in the inclusions due to the interaction between slag and

steel its effect on the phase diagram and inclusion composition was however ignored due to the low

content (lt 5) and for simplification As can be seen from Figure 5 (a) after SiMn addition the

inclusion compositions are concentrated close to the MnO-SiO2 binary region which is almost in

liquid region due to its lower melting point than that of steel [38] This explains the spherical shape

of the inclusions in Figure 2 After Al addition the composition shifts towards high-alumina

phases near the Al2O3 corner with a higher melting point

Fig5 Calculated polythermal projection (a) After SiMn addition (b) After Al addition

Solid circles represent the composition of oxide inclusions

The effect of alumina content on the liquidus temperature and the primary crystalline phase of the

inclusions were calculated by FactSage 70 with the FToxid database as shown in Figure 6

Increasing the concentration of alumina in the inclusions changed the primary phase in the following

order SiO2 MnSiO3 (rhodonite) Mn3Al2Si3O12 (spessartite) MnAl2O4 (galaxite) and Al2O3 The

liquidus temperature of the inclusion first decreased with increasing alumina concentration up to

about 75 mol followed by a rebound after this composition In this study the alumina

concentration of the inclusions after Al addition was found to be over 60 explaining their solid

state in steelmaking temperatures and irregular morphologies as seen in Figure 3

Fig 6 Calculated liquidus temperatures in the MnO-SiO2-Al2O3 systems as a function of the concentration of

Al2O3 when the ratio of mol pct MnO to mol pct SiO2 is 075

33 Inclusion Characteristics after Ti addition

The TiN inclusion belongs to the cubic or triangular-shaped crystal phase system with a high melting

temperature and hardness making them difficult to deform during steel processing[24] Zhou et al

[39] reported that nitrides with the average size of 6 microm are equivalent to oxides with an average size

of 25 microm in terms of the deterioration of fatigue life

After Ti-core wire feeding inclusions with three distinct morphologies were identified single

particles of titanium nitride (Figure 7 (a) - (d)) twinned particles of titanium nitride (Figure 7 (e) -

(h) and clusters (Figure 7 (i) - (l)) Single TiN has a regular cubic structure while the twinned TiN

particles resembled two more cubic crystals colliding with with each other Maddalena et al

reported that this kind of TiN was caused only by growth of two nucleates [31] TiN clusters usually

have a larger size which may be broken up into smaller TiN particles as a stringer shape during

rolling process [4016] The microvoids in such stringers when exposed to an aqueous solution will

act as sites for pitting corrosion or the initiation of stress corrosion cracking negatively impacting

the to the steel quality

It should be pointed out that oxide particles were still observed in the steel samples after Ti addition

However due to their very low content less than 1 only TiN was discussed The oxide inclusions

can in fact act as the effective heterogeneous nuclei for TiN formation which was confirmed by two

dimensional analysis on the cross-sections[4041-44]

Fig 7 Three-dimensional morphologies of inclusions extracted from steel samples after Ti addition

Figure 8 gives the size distributions of the three types of TiN inclusions In sample L1 the number

densities of single and twinned TiN are dominant In sample C1 the density of large clusters has

increased due to agglomeration of single twinned or small clusters of TiN into bigger clusters Clusters

with the size more than 10 microm were also observed in sample C1 as shown in the upper right corner of

Figure 8 (b) These larger clusters can easily adhere to the nozzle wall and cause nozzle clogging

Moreover they can severely impact the steel quality if they appear in the final product

Fig 8 Size distributions of inclusions after Ti addition (a) Sample L1 (b) Sample C1

34 Formation and Growth Mechanism of TiN Clusters

The formation and growth of TiN clusters in the liquid steel appears to take place in two steps 1)

formation of small clusters by collision of single or twinned inclusions 2) growth of clusters by

collision with singletwinned inclusion or with other clusters There are three types of collision

which can happen between inclusions 1) Brownian collision due to the random movement of very

small inclusions in molten steel 2) Turbulence collision because of the turbulent flow of liquid steel

which can cause the inclusion collision 3) Stokersquos collision due to the density difference between

steel and inclusions so that larger inclusions ascend faster than smaller ones and collide with them

as they travel up Each of the collision mechanisms makes a contribution to the total number of

inclusion collisions

The collision number of inclusions in the liquid steel per unit time (ldquocollision raterdquo) can be

calculated by the following Equation [45]

i j

ij i j

dnw n n

dt [4]

where wij is the collision volume (m3s) of a certain collision phenomenon ni and nj are the number

of inclusions within certain size ranges and t is time (s) The collision volume for Brownian collision

( B

ijw[46]) Turbulence collision ( T

ijw[46]) and Stokersquos collision ( S

ijw[47]) can be expressed as following

respectively

Β

ij i j

i j

2kΤ 1 1w = + r +r

3μ r r

[5]

3

T

ij Fe i jw =13α περ μ r +r [6]

3

S Fe iij i j i j

2πg(ρ ρ )w = r +r r r

9μ

[7]

In these equations k is the Boltzmann constant (JK) T is the absolute temperature (K) micro is the

dynamic viscosity of steel (kgms) α is the collision efficiency ε is the turbulent energy dissipation

(m2s3) ρFe and ρi are the densities of the steel and inclusion respectively (kgm3) g is the

gravitational acceleration (ms2) and ri and rj are the radii of the two colliding inclusions (m)

Each of the different collision mechanism can make a contribution to the total number of collisions

Therefore collision volume wij was calculated using the parameters given in Table 2 in order to

determine the significance of the separate collision mechanisms It should be pointed out that the

calculation of collision volume was based on considering spherical inclusions in steel Therefore in

this study it was assumed that an irregular shape inclusion can rotate around its center due to the

liquid steel flow and can collide with other inclusions within the rotational region whose maximum

length equals to the inclusion diameter

Figure 9 presents the calculated values of the collision volumes for an inclusion of 148microm (size

with a highest content according to Figure 8 ) that collides with other inclusions of different sizes

It can be seen from Figure 9 that Brownian collision volume B

ijw is drastically smaller than that of

Stokersquos and Turbulent collision volume in all studied ranges of rj whose impact on inclusion growth

can be neglected Both Turbulence and Stokersquos collision mechanism have a much higher effect on

the collision volume compared to the Brownian collision They keep an increasing trend as a

function of increased size (more than 148microm) Moreover the effect of Turbulence collision is

higher than Stokes and the difference between these two collisions is decreasing as the inclusion

size increases within the the range studied here Therefore both Turbulence and Stokersquos mechanism

are believed to play a considerable role in inclusion coarsening

TableⅡ Data used in calculation of collision volumes

k

(JK)

T

(K)

micro

(kgms)

α

(m2s3)

ε

(m2s3)

ρFe

(kgm3)

ρi

(kgm3)

g

(ms2)

138times10-

23 1873 0005 03 00018 8000 5220 981

Fig 9 Collision volumes for an inclusion with a 148microm (ri=074microm) in diameter as a function of collision with

different sized inclusions

4 Conclusions

Inclusions characteristics (such as morphology composition and size distribution) were analyzed in steel

samples taken after different alloy additions using electrolytic extraction methods followed by SEM-

EDS characterization The following conclusions were drawn

(1) After the addition of ferrosilicon alloy and electrolytic manganese followed by aluminum the

composition of inclusions changed from manganese silicate-rich inclusions with spherical shapes to

alumina-rich inclusions with irregular shapes

(2) After Ti-stabilization three TiN inclusion morphologies were found single particle swinned

particles and clusters

(3) Both the Turbulence and Stokersquoss collision mechanism are the effective in formation and coarsening

of TiN clusters the Brownian collision mechanism appeared to play a minor role

5 Acknowledgments

The first author would like to thank China Scholarship Council (CSC) for support of her study abroad

Qingshan steel provided the stainless steel samples of this study The financial support by Natural

Sciences and Engineering Research Council of Canada is greatly acknowledged

6 Reference

[1] L Zhang BG Thomas State of the Art in Evaluation and Control of Steel Cleanliness ISIJ Int 2003

43(3) 271-291

[2] P Kaushik J Lehmann M Nadif State of the Art in Control of Inclusions Their Characterization and Future

Requirements Metall Materi Trans B 2012 43(4) 710-725

[3] P Kaushik H Pielet H Yin Inclusion CharacterizationndashTool for Measurement of Steel Cleanliness and

Process Control Part 1 Ironmaking amp Steelmaking 2009 36(8) 561-571

[4] ME Fine Fatigue Resistance of Metals Metall Trans A 1980 11(3)365ndash379

[5] S Chen M Jiang X He and X Wang Top Slag Refining for Inclusion Composition Transform Control in

Tire Cord Steel Int J Miner Metall Mater 2012 19(6) 490ndash98

[6] X Cai Y Bao L Lin C Gu Effect of Al Content on the Evolution of Non-Metallic Inclusions in SindashMn

Deoxidized Steel Steel Research International online version

[7] DH Woo YB Kang H G Lee Thermodynamic Study of Mno-SiO2-Al2O3 Slag System Liquidus Lines

and Activities of MnO at 1823 K Metall Mater Trans B 2002 33(6) 915-920

[8] K Ogawa T Onoe H Matsumoto K Narita On the behavior of inclusions in the flux treatment of high

carbon steels Tetsu-to-Haganeacute 1985 71(2) 29-32

[9] Y B Kang HG Lee Inclusions Chemistry for MnSi Deoxidized Steels Thermodynamic Predictions and

Experimental Confirmations ISIJ Int 2004 44(6)1006-1015

[10] T Fujisawa H Sakao Equilibrium between MnO-SiO2-Al2O3-FeO Slags and Liquid Steel Tetsu-to-

Haganeacute 1977 63(9) 1504-1511

[11] H Suito R Inoue Thermodynamics on Control of Inclusions Composition in Ultraclean Steels ISIJ Int

1996 36(5) 528-536

[12] IH Jung YB Kang S Decterov AD Pelton Thermodynamic Evaluation and Optimization of the MnO-

Al2O3 and MnO-Al2O3-SiO2 Systems and Applications to Inclusion Engineering Metall Materi Trans B

2004 35(2) 259-268

[13] JS Park JH Park Effect of Slag Composition on the Concentration of Al2O3 in the Inclusions in Si-Mn-

Killed Steel Metall Materi Trans B 2014 45(3)953-960

[14] SB Lee JH Choi HG Lee PH Rhee and SM Jung Aluminum Deoxidation Equilibrium in Liquid Fe-

16 Pct Cr Alloy Metall Mater Trans B 2005 36 (3) 414-16

[15] M Vanende M Guo J Proost B Blanpain P Wollants Formation and Morphology of Al2O3 Inclusions at

the Onset of Liquid Fe Deoxidation by Al Addition ISIJ Int 2011 51(1) 27-34

[16] M B Leban R Tisu The Effect of Tin Inclusions and Deformation-Induced Martensite on the Corrosion

Properties of AISI 321 Stainless Steel Eng Fail Anal 2013 33 430-38

[17] M Prikryl A Kroupa GC Weatherly SV Subramanian Precipitation Behavior in a Medium Carbon Ti-

V-N Microalloyed Steel Metall Mater Trans B 1996 27(5) 1149-1165

[18] Z Chen MH Loretto RC Cochrane Nature of Large Precipitates in Titanium-Containing HSLA Steels

Mater Sci Technol 1987 3(10) 836-844

[19] J Du M Strangwood and CL Davis Effect of Tin Particles and Grain Size on the Charpy Impact

Transition Temperature in Steels J Mater Sci Technol 2012 28 (10) 878-888

[20] W Yan YY Shan K Yang Effect of TiN Inclusions on the Impact Toughness of Low-Carbon Microalloyed

Steels Metall Mater Trans A 2006 37(7) 2147-2158

[21] MA Linaza JL Romero JM Rodriacuteguez-Ibabe JJ Urcola Influence of the Microstructure on the

Fracture Toughness and Fracture Mechanisms of Forging Steels Microalloyed with Titanium with Ferrite-

Pearlite Structures Scripta Metallurgica et Materialia 1993 29(4) 451-456

[22] T Uesugi Production of High-Carbon Chromium Bearing Steel in Vertical Type Continuous Caster Trans

ISIJ 1986 26(7) 614-620

[23] K Kunishige N Nagao Strengthening and Toughening of Hot-Direct-Rolled Steels by Addition of a Small

Amount of Titanium ISIJ Int 1989 29(11) 940-946

[24] MW Zhou H Yu Effects of Precipitates and Inclusions on the Fracture Toughness of Hot Rolling X70

Pipeline Steel Plates Int J Miner Metall Mater 2012 19(9) 805-11

[25] Y Cogne B Heritier J Monnot Relationship of Melting Practice Inclusion Type and Size with Fatigue

Resistance of Bearing Steels Proceedings of the Third International Conference on Clean Steel The Institute

of Metals Balatonfuumlred Hungary 1987 26-31

[26] A Echeverrıa JM Rodriguez-Ibabe Brittle Fracture Micromechanisms in Bainitic and Martensitic

Microstructures in a C-Mn-B Steel Scripta Materialia 1999 41 (2)131-136

[27] LP Zhang CL Davis M Strangwood Effect of TiN Particles and Microstructure on Fracture Toughness in

Simulated Heat-Affected Zones of a Structural Steel Metall Mater Trans A 1999 30 (8)2089-2096

[28] DP Fairchild DG Howden WAT Clark The Mechanism of Brittle Fracture in a Microalloyed Steel Part

I Inclusion-Induced Cleavage Metall Mater Trans A 2000 31(3) 641-652

[29] MJ Balart CL Davis M Strangwood Cleavage Initiation in TindashVndashN and VndashN Microalloyed Ferriticndash

Pearlitic Forging Steels Mater Sci Eng A 2000 284 (1ndash2) 1-13

[30] M Hasegawa S Maruhashi Y Kamidate Y Muranaka F Hoshi Tundish Nozzle Constriction in

Continuous Casting of Titanium Bearing Stainless Steel Slabs Tetsu-to-Haganeacute 1984 70 (14) 1704-11

[31] R Maddalena R Rastogi S Bassem AW Cramb Nozzle Deposits in Titanium Treated Stainless Steels

Iron and Steelmaker 2000 27 (12) 71-79

[32] Y Gao K Sorimachi Formation of Clogging Materials in an Immersed Nozzle During Continuous Casting

of Titanium Stabilized Stainless Steel ISIJ Int 1993 33 (2) 291-297

[33] Y Bi AV Karasev PG Joumlnsson Evolution of Different Inclusions during Ladle Treatment and Continuous

Casting of Stainless Steel ISIJ Int 2013 53(12)2099ndash2109

[34] HS Kim HG Lee KS OH Precipitation Behavior of Mns on Oxide Inclusions in SiMn Deoxidized

Steel Metall Mater Int 2000 6(4) 305ndash10

[35] M Wakoh T Sawai S Mizoguchi Effect of oxide particles on MnS precipitation in low S steels Tetsu-to-

Haganeacute 1992 78(11)1697ndash1704

[36] M Wakoh T Sawai S Mizoguchi Effect of S Content on the MnS Precipitation in Steel with Oxide

Nuclei ISIJ Int 1996 36(8)1014ndash1021

[37] HS Kim HG Lee KS OH MnS Precipitation in Association with Manganese Silicate Inclusions in

SiMn Deoxidized Steel Metall Mater Trans A 2001 32A (6)1519ndash1525

[38] S S Babu S A David J M Vitek K Mundra T DebRoy Development of Macro- and Microstructures of

Carbon-manganese Low Alloy Steel Welds Inclusion Formation Mater Sci Technol 1995 11(2)186ndash199

[39] DG Zhou J Fu XC Chen J Li Precipitation Behavior of TiN in Bearing Steel J Mater Sci Technol

2003 19(2) 184ndash186

[40] F Meng J Wang EH KW Han The Role of TiN Inclusions in Stress Corrosion Crack Initiation for Alloy

690TT in High-Temperature and High Pressure Water Corros Sci 2010 52(3) 927ndash932

[41] Y Xu Z Chen M Gong D Shu Y Tian X Yuan Effects of Mg Addition on Inclusions Formation and

Resultant Solidification Structure Changes of Ti-Stabilized Ultra-Pure Ferritic Stainless Steel Journal of

Iron and Steel Research International 2014 21(6) 583-588

[42] A S Nick H Fredriksson On the Relationship between Inclusions and Pores Part I Precipitation Trans

Indian Inst Met 2012 65(6) 791-794

[43] JH Park Effect of Inclusions on the Solidification Structures of Ferritic Stainless Steel Computational and

Experimental Study of Inclusion Evolution Calphad 201135(4) 455-462

[44] W Yan YY Shan K Yang Influence of Tin Inclusions on the Cleavage Fracture Behavior of Low-Carbon

Microalloyed Steels Metallurgical and Materials Transactions A 2007 38(6) 1211-1222

[45] M Soumlder PG Joumlnsson L Jonsson Inclusion Growth and Removal in Gas-stirred Ladles Steel Res Int

2004 75(2) 128-138

[46] S Taniguchi A Kikuchi Mechanisms of Collision and Coagulation between Fine Particles in Fluid Tetsu-

to-Haganeacute 1992 78(4) 527-535

[47] U Lindborg KTorssell A Collision Model for the Growth and Separation of Deoxidation Products Trans

Met Soc AIME 1968 242 94-102

liquidus temperature of the inclusion first decreased with increasing alumina concentration up to

about 75 mol followed by a rebound after this composition In this study the alumina

concentration of the inclusions after Al addition was found to be over 60 explaining their solid

state in steelmaking temperatures and irregular morphologies as seen in Figure 3

Fig 6 Calculated liquidus temperatures in the MnO-SiO2-Al2O3 systems as a function of the concentration of

Al2O3 when the ratio of mol pct MnO to mol pct SiO2 is 075

33 Inclusion Characteristics after Ti addition

The TiN inclusion belongs to the cubic or triangular-shaped crystal phase system with a high melting

temperature and hardness making them difficult to deform during steel processing[24] Zhou et al

[39] reported that nitrides with the average size of 6 microm are equivalent to oxides with an average size

of 25 microm in terms of the deterioration of fatigue life

After Ti-core wire feeding inclusions with three distinct morphologies were identified single

particles of titanium nitride (Figure 7 (a) - (d)) twinned particles of titanium nitride (Figure 7 (e) -

(h) and clusters (Figure 7 (i) - (l)) Single TiN has a regular cubic structure while the twinned TiN

particles resembled two more cubic crystals colliding with with each other Maddalena et al

reported that this kind of TiN was caused only by growth of two nucleates [31] TiN clusters usually

have a larger size which may be broken up into smaller TiN particles as a stringer shape during

rolling process [4016] The microvoids in such stringers when exposed to an aqueous solution will

act as sites for pitting corrosion or the initiation of stress corrosion cracking negatively impacting

the to the steel quality

It should be pointed out that oxide particles were still observed in the steel samples after Ti addition

However due to their very low content less than 1 only TiN was discussed The oxide inclusions

can in fact act as the effective heterogeneous nuclei for TiN formation which was confirmed by two

dimensional analysis on the cross-sections[4041-44]

Fig 7 Three-dimensional morphologies of inclusions extracted from steel samples after Ti addition

Figure 8 gives the size distributions of the three types of TiN inclusions In sample L1 the number

densities of single and twinned TiN are dominant In sample C1 the density of large clusters has

increased due to agglomeration of single twinned or small clusters of TiN into bigger clusters Clusters

with the size more than 10 microm were also observed in sample C1 as shown in the upper right corner of

Figure 8 (b) These larger clusters can easily adhere to the nozzle wall and cause nozzle clogging

Moreover they can severely impact the steel quality if they appear in the final product

Fig 8 Size distributions of inclusions after Ti addition (a) Sample L1 (b) Sample C1

34 Formation and Growth Mechanism of TiN Clusters

The formation and growth of TiN clusters in the liquid steel appears to take place in two steps 1)

formation of small clusters by collision of single or twinned inclusions 2) growth of clusters by

collision with singletwinned inclusion or with other clusters There are three types of collision

which can happen between inclusions 1) Brownian collision due to the random movement of very

small inclusions in molten steel 2) Turbulence collision because of the turbulent flow of liquid steel

which can cause the inclusion collision 3) Stokersquos collision due to the density difference between

steel and inclusions so that larger inclusions ascend faster than smaller ones and collide with them

as they travel up Each of the collision mechanisms makes a contribution to the total number of

inclusion collisions

The collision number of inclusions in the liquid steel per unit time (ldquocollision raterdquo) can be

calculated by the following Equation [45]

i j

ij i j

dnw n n

dt [4]

where wij is the collision volume (m3s) of a certain collision phenomenon ni and nj are the number

of inclusions within certain size ranges and t is time (s) The collision volume for Brownian collision

( B

ijw[46]) Turbulence collision ( T

ijw[46]) and Stokersquos collision ( S

ijw[47]) can be expressed as following

respectively

Β

ij i j

i j

2kΤ 1 1w = + r +r

3μ r r

[5]

3

T

ij Fe i jw =13α περ μ r +r [6]

3

S Fe iij i j i j

2πg(ρ ρ )w = r +r r r

9μ

[7]

In these equations k is the Boltzmann constant (JK) T is the absolute temperature (K) micro is the

dynamic viscosity of steel (kgms) α is the collision efficiency ε is the turbulent energy dissipation

(m2s3) ρFe and ρi are the densities of the steel and inclusion respectively (kgm3) g is the

gravitational acceleration (ms2) and ri and rj are the radii of the two colliding inclusions (m)

Each of the different collision mechanism can make a contribution to the total number of collisions

Therefore collision volume wij was calculated using the parameters given in Table 2 in order to

determine the significance of the separate collision mechanisms It should be pointed out that the

calculation of collision volume was based on considering spherical inclusions in steel Therefore in

this study it was assumed that an irregular shape inclusion can rotate around its center due to the

liquid steel flow and can collide with other inclusions within the rotational region whose maximum

length equals to the inclusion diameter

Figure 9 presents the calculated values of the collision volumes for an inclusion of 148microm (size

with a highest content according to Figure 8 ) that collides with other inclusions of different sizes

It can be seen from Figure 9 that Brownian collision volume B

ijw is drastically smaller than that of

Stokersquos and Turbulent collision volume in all studied ranges of rj whose impact on inclusion growth

can be neglected Both Turbulence and Stokersquos collision mechanism have a much higher effect on

the collision volume compared to the Brownian collision They keep an increasing trend as a

function of increased size (more than 148microm) Moreover the effect of Turbulence collision is

higher than Stokes and the difference between these two collisions is decreasing as the inclusion

size increases within the the range studied here Therefore both Turbulence and Stokersquos mechanism

are believed to play a considerable role in inclusion coarsening

TableⅡ Data used in calculation of collision volumes

k

(JK)

T

(K)

micro

(kgms)

α

(m2s3)

ε

(m2s3)

ρFe

(kgm3)

ρi

(kgm3)

g

(ms2)

138times10-

23 1873 0005 03 00018 8000 5220 981

Fig 9 Collision volumes for an inclusion with a 148microm (ri=074microm) in diameter as a function of collision with

different sized inclusions

4 Conclusions

Inclusions characteristics (such as morphology composition and size distribution) were analyzed in steel

samples taken after different alloy additions using electrolytic extraction methods followed by SEM-

EDS characterization The following conclusions were drawn

(1) After the addition of ferrosilicon alloy and electrolytic manganese followed by aluminum the

composition of inclusions changed from manganese silicate-rich inclusions with spherical shapes to

alumina-rich inclusions with irregular shapes

(2) After Ti-stabilization three TiN inclusion morphologies were found single particle swinned

particles and clusters

(3) Both the Turbulence and Stokersquoss collision mechanism are the effective in formation and coarsening

of TiN clusters the Brownian collision mechanism appeared to play a minor role

5 Acknowledgments

The first author would like to thank China Scholarship Council (CSC) for support of her study abroad

Qingshan steel provided the stainless steel samples of this study The financial support by Natural

Sciences and Engineering Research Council of Canada is greatly acknowledged

6 Reference

[1] L Zhang BG Thomas State of the Art in Evaluation and Control of Steel Cleanliness ISIJ Int 2003

43(3) 271-291

[2] P Kaushik J Lehmann M Nadif State of the Art in Control of Inclusions Their Characterization and Future

Requirements Metall Materi Trans B 2012 43(4) 710-725

[3] P Kaushik H Pielet H Yin Inclusion CharacterizationndashTool for Measurement of Steel Cleanliness and

Process Control Part 1 Ironmaking amp Steelmaking 2009 36(8) 561-571

[4] ME Fine Fatigue Resistance of Metals Metall Trans A 1980 11(3)365ndash379

[5] S Chen M Jiang X He and X Wang Top Slag Refining for Inclusion Composition Transform Control in

Tire Cord Steel Int J Miner Metall Mater 2012 19(6) 490ndash98

[6] X Cai Y Bao L Lin C Gu Effect of Al Content on the Evolution of Non-Metallic Inclusions in SindashMn

Deoxidized Steel Steel Research International online version

[7] DH Woo YB Kang H G Lee Thermodynamic Study of Mno-SiO2-Al2O3 Slag System Liquidus Lines

and Activities of MnO at 1823 K Metall Mater Trans B 2002 33(6) 915-920

[8] K Ogawa T Onoe H Matsumoto K Narita On the behavior of inclusions in the flux treatment of high

carbon steels Tetsu-to-Haganeacute 1985 71(2) 29-32

[9] Y B Kang HG Lee Inclusions Chemistry for MnSi Deoxidized Steels Thermodynamic Predictions and

Experimental Confirmations ISIJ Int 2004 44(6)1006-1015

[10] T Fujisawa H Sakao Equilibrium between MnO-SiO2-Al2O3-FeO Slags and Liquid Steel Tetsu-to-

Haganeacute 1977 63(9) 1504-1511

[11] H Suito R Inoue Thermodynamics on Control of Inclusions Composition in Ultraclean Steels ISIJ Int

1996 36(5) 528-536

[12] IH Jung YB Kang S Decterov AD Pelton Thermodynamic Evaluation and Optimization of the MnO-

Al2O3 and MnO-Al2O3-SiO2 Systems and Applications to Inclusion Engineering Metall Materi Trans B

2004 35(2) 259-268

[13] JS Park JH Park Effect of Slag Composition on the Concentration of Al2O3 in the Inclusions in Si-Mn-

Killed Steel Metall Materi Trans B 2014 45(3)953-960

[14] SB Lee JH Choi HG Lee PH Rhee and SM Jung Aluminum Deoxidation Equilibrium in Liquid Fe-

16 Pct Cr Alloy Metall Mater Trans B 2005 36 (3) 414-16

[15] M Vanende M Guo J Proost B Blanpain P Wollants Formation and Morphology of Al2O3 Inclusions at

the Onset of Liquid Fe Deoxidation by Al Addition ISIJ Int 2011 51(1) 27-34

[16] M B Leban R Tisu The Effect of Tin Inclusions and Deformation-Induced Martensite on the Corrosion

Properties of AISI 321 Stainless Steel Eng Fail Anal 2013 33 430-38

[17] M Prikryl A Kroupa GC Weatherly SV Subramanian Precipitation Behavior in a Medium Carbon Ti-

V-N Microalloyed Steel Metall Mater Trans B 1996 27(5) 1149-1165

[18] Z Chen MH Loretto RC Cochrane Nature of Large Precipitates in Titanium-Containing HSLA Steels

Mater Sci Technol 1987 3(10) 836-844

[19] J Du M Strangwood and CL Davis Effect of Tin Particles and Grain Size on the Charpy Impact

Transition Temperature in Steels J Mater Sci Technol 2012 28 (10) 878-888

[20] W Yan YY Shan K Yang Effect of TiN Inclusions on the Impact Toughness of Low-Carbon Microalloyed

Steels Metall Mater Trans A 2006 37(7) 2147-2158

[21] MA Linaza JL Romero JM Rodriacuteguez-Ibabe JJ Urcola Influence of the Microstructure on the

Fracture Toughness and Fracture Mechanisms of Forging Steels Microalloyed with Titanium with Ferrite-

Pearlite Structures Scripta Metallurgica et Materialia 1993 29(4) 451-456

[22] T Uesugi Production of High-Carbon Chromium Bearing Steel in Vertical Type Continuous Caster Trans

ISIJ 1986 26(7) 614-620

[23] K Kunishige N Nagao Strengthening and Toughening of Hot-Direct-Rolled Steels by Addition of a Small

Amount of Titanium ISIJ Int 1989 29(11) 940-946

[24] MW Zhou H Yu Effects of Precipitates and Inclusions on the Fracture Toughness of Hot Rolling X70

Pipeline Steel Plates Int J Miner Metall Mater 2012 19(9) 805-11

[25] Y Cogne B Heritier J Monnot Relationship of Melting Practice Inclusion Type and Size with Fatigue

Resistance of Bearing Steels Proceedings of the Third International Conference on Clean Steel The Institute

of Metals Balatonfuumlred Hungary 1987 26-31

[26] A Echeverrıa JM Rodriguez-Ibabe Brittle Fracture Micromechanisms in Bainitic and Martensitic

Microstructures in a C-Mn-B Steel Scripta Materialia 1999 41 (2)131-136

[27] LP Zhang CL Davis M Strangwood Effect of TiN Particles and Microstructure on Fracture Toughness in

Simulated Heat-Affected Zones of a Structural Steel Metall Mater Trans A 1999 30 (8)2089-2096

[28] DP Fairchild DG Howden WAT Clark The Mechanism of Brittle Fracture in a Microalloyed Steel Part

I Inclusion-Induced Cleavage Metall Mater Trans A 2000 31(3) 641-652

[29] MJ Balart CL Davis M Strangwood Cleavage Initiation in TindashVndashN and VndashN Microalloyed Ferriticndash

Pearlitic Forging Steels Mater Sci Eng A 2000 284 (1ndash2) 1-13

[30] M Hasegawa S Maruhashi Y Kamidate Y Muranaka F Hoshi Tundish Nozzle Constriction in

Continuous Casting of Titanium Bearing Stainless Steel Slabs Tetsu-to-Haganeacute 1984 70 (14) 1704-11

[31] R Maddalena R Rastogi S Bassem AW Cramb Nozzle Deposits in Titanium Treated Stainless Steels

Iron and Steelmaker 2000 27 (12) 71-79

[32] Y Gao K Sorimachi Formation of Clogging Materials in an Immersed Nozzle During Continuous Casting

of Titanium Stabilized Stainless Steel ISIJ Int 1993 33 (2) 291-297

[33] Y Bi AV Karasev PG Joumlnsson Evolution of Different Inclusions during Ladle Treatment and Continuous

Casting of Stainless Steel ISIJ Int 2013 53(12)2099ndash2109

[34] HS Kim HG Lee KS OH Precipitation Behavior of Mns on Oxide Inclusions in SiMn Deoxidized

Steel Metall Mater Int 2000 6(4) 305ndash10

[35] M Wakoh T Sawai S Mizoguchi Effect of oxide particles on MnS precipitation in low S steels Tetsu-to-

Haganeacute 1992 78(11)1697ndash1704

[36] M Wakoh T Sawai S Mizoguchi Effect of S Content on the MnS Precipitation in Steel with Oxide

Nuclei ISIJ Int 1996 36(8)1014ndash1021

[37] HS Kim HG Lee KS OH MnS Precipitation in Association with Manganese Silicate Inclusions in

SiMn Deoxidized Steel Metall Mater Trans A 2001 32A (6)1519ndash1525

[38] S S Babu S A David J M Vitek K Mundra T DebRoy Development of Macro- and Microstructures of

Carbon-manganese Low Alloy Steel Welds Inclusion Formation Mater Sci Technol 1995 11(2)186ndash199

[39] DG Zhou J Fu XC Chen J Li Precipitation Behavior of TiN in Bearing Steel J Mater Sci Technol

2003 19(2) 184ndash186

[40] F Meng J Wang EH KW Han The Role of TiN Inclusions in Stress Corrosion Crack Initiation for Alloy

690TT in High-Temperature and High Pressure Water Corros Sci 2010 52(3) 927ndash932

[41] Y Xu Z Chen M Gong D Shu Y Tian X Yuan Effects of Mg Addition on Inclusions Formation and

Resultant Solidification Structure Changes of Ti-Stabilized Ultra-Pure Ferritic Stainless Steel Journal of

Iron and Steel Research International 2014 21(6) 583-588

[42] A S Nick H Fredriksson On the Relationship between Inclusions and Pores Part I Precipitation Trans

Indian Inst Met 2012 65(6) 791-794

[43] JH Park Effect of Inclusions on the Solidification Structures of Ferritic Stainless Steel Computational and

Experimental Study of Inclusion Evolution Calphad 201135(4) 455-462

[44] W Yan YY Shan K Yang Influence of Tin Inclusions on the Cleavage Fracture Behavior of Low-Carbon

Microalloyed Steels Metallurgical and Materials Transactions A 2007 38(6) 1211-1222

[45] M Soumlder PG Joumlnsson L Jonsson Inclusion Growth and Removal in Gas-stirred Ladles Steel Res Int

2004 75(2) 128-138

[46] S Taniguchi A Kikuchi Mechanisms of Collision and Coagulation between Fine Particles in Fluid Tetsu-

to-Haganeacute 1992 78(4) 527-535

[47] U Lindborg KTorssell A Collision Model for the Growth and Separation of Deoxidation Products Trans

Met Soc AIME 1968 242 94-102

Fig 7 Three-dimensional morphologies of inclusions extracted from steel samples after Ti addition

Figure 8 gives the size distributions of the three types of TiN inclusions In sample L1 the number

densities of single and twinned TiN are dominant In sample C1 the density of large clusters has

increased due to agglomeration of single twinned or small clusters of TiN into bigger clusters Clusters

with the size more than 10 microm were also observed in sample C1 as shown in the upper right corner of

Figure 8 (b) These larger clusters can easily adhere to the nozzle wall and cause nozzle clogging

Moreover they can severely impact the steel quality if they appear in the final product

Fig 8 Size distributions of inclusions after Ti addition (a) Sample L1 (b) Sample C1

34 Formation and Growth Mechanism of TiN Clusters

The formation and growth of TiN clusters in the liquid steel appears to take place in two steps 1)

formation of small clusters by collision of single or twinned inclusions 2) growth of clusters by

collision with singletwinned inclusion or with other clusters There are three types of collision

which can happen between inclusions 1) Brownian collision due to the random movement of very

small inclusions in molten steel 2) Turbulence collision because of the turbulent flow of liquid steel

which can cause the inclusion collision 3) Stokersquos collision due to the density difference between

steel and inclusions so that larger inclusions ascend faster than smaller ones and collide with them

as they travel up Each of the collision mechanisms makes a contribution to the total number of

inclusion collisions

The collision number of inclusions in the liquid steel per unit time (ldquocollision raterdquo) can be

calculated by the following Equation [45]

i j

ij i j

dnw n n

dt [4]

where wij is the collision volume (m3s) of a certain collision phenomenon ni and nj are the number

of inclusions within certain size ranges and t is time (s) The collision volume for Brownian collision

( B

ijw[46]) Turbulence collision ( T

ijw[46]) and Stokersquos collision ( S

ijw[47]) can be expressed as following

respectively

Β

ij i j

i j

2kΤ 1 1w = + r +r

3μ r r

[5]

3

T

ij Fe i jw =13α περ μ r +r [6]

3

S Fe iij i j i j

2πg(ρ ρ )w = r +r r r

9μ

[7]

In these equations k is the Boltzmann constant (JK) T is the absolute temperature (K) micro is the

dynamic viscosity of steel (kgms) α is the collision efficiency ε is the turbulent energy dissipation

(m2s3) ρFe and ρi are the densities of the steel and inclusion respectively (kgm3) g is the

gravitational acceleration (ms2) and ri and rj are the radii of the two colliding inclusions (m)

Each of the different collision mechanism can make a contribution to the total number of collisions

Therefore collision volume wij was calculated using the parameters given in Table 2 in order to

determine the significance of the separate collision mechanisms It should be pointed out that the

calculation of collision volume was based on considering spherical inclusions in steel Therefore in

this study it was assumed that an irregular shape inclusion can rotate around its center due to the

liquid steel flow and can collide with other inclusions within the rotational region whose maximum

length equals to the inclusion diameter

Figure 9 presents the calculated values of the collision volumes for an inclusion of 148microm (size

with a highest content according to Figure 8 ) that collides with other inclusions of different sizes

It can be seen from Figure 9 that Brownian collision volume B

ijw is drastically smaller than that of

Stokersquos and Turbulent collision volume in all studied ranges of rj whose impact on inclusion growth

can be neglected Both Turbulence and Stokersquos collision mechanism have a much higher effect on

the collision volume compared to the Brownian collision They keep an increasing trend as a

function of increased size (more than 148microm) Moreover the effect of Turbulence collision is

higher than Stokes and the difference between these two collisions is decreasing as the inclusion

size increases within the the range studied here Therefore both Turbulence and Stokersquos mechanism

are believed to play a considerable role in inclusion coarsening

TableⅡ Data used in calculation of collision volumes

k

(JK)

T

(K)

micro

(kgms)

α

(m2s3)

ε

(m2s3)

ρFe

(kgm3)

ρi

(kgm3)

g

(ms2)

138times10-

23 1873 0005 03 00018 8000 5220 981

Fig 9 Collision volumes for an inclusion with a 148microm (ri=074microm) in diameter as a function of collision with

different sized inclusions

4 Conclusions

Inclusions characteristics (such as morphology composition and size distribution) were analyzed in steel

samples taken after different alloy additions using electrolytic extraction methods followed by SEM-

EDS characterization The following conclusions were drawn

(1) After the addition of ferrosilicon alloy and electrolytic manganese followed by aluminum the

composition of inclusions changed from manganese silicate-rich inclusions with spherical shapes to

alumina-rich inclusions with irregular shapes

(2) After Ti-stabilization three TiN inclusion morphologies were found single particle swinned

particles and clusters

(3) Both the Turbulence and Stokersquoss collision mechanism are the effective in formation and coarsening

of TiN clusters the Brownian collision mechanism appeared to play a minor role

5 Acknowledgments

The first author would like to thank China Scholarship Council (CSC) for support of her study abroad

Qingshan steel provided the stainless steel samples of this study The financial support by Natural

Sciences and Engineering Research Council of Canada is greatly acknowledged

6 Reference

[1] L Zhang BG Thomas State of the Art in Evaluation and Control of Steel Cleanliness ISIJ Int 2003

43(3) 271-291

[2] P Kaushik J Lehmann M Nadif State of the Art in Control of Inclusions Their Characterization and Future

Requirements Metall Materi Trans B 2012 43(4) 710-725

[3] P Kaushik H Pielet H Yin Inclusion CharacterizationndashTool for Measurement of Steel Cleanliness and

Process Control Part 1 Ironmaking amp Steelmaking 2009 36(8) 561-571

[4] ME Fine Fatigue Resistance of Metals Metall Trans A 1980 11(3)365ndash379

[5] S Chen M Jiang X He and X Wang Top Slag Refining for Inclusion Composition Transform Control in

Tire Cord Steel Int J Miner Metall Mater 2012 19(6) 490ndash98

[6] X Cai Y Bao L Lin C Gu Effect of Al Content on the Evolution of Non-Metallic Inclusions in SindashMn

Deoxidized Steel Steel Research International online version

[7] DH Woo YB Kang H G Lee Thermodynamic Study of Mno-SiO2-Al2O3 Slag System Liquidus Lines

and Activities of MnO at 1823 K Metall Mater Trans B 2002 33(6) 915-920

[8] K Ogawa T Onoe H Matsumoto K Narita On the behavior of inclusions in the flux treatment of high

carbon steels Tetsu-to-Haganeacute 1985 71(2) 29-32

[9] Y B Kang HG Lee Inclusions Chemistry for MnSi Deoxidized Steels Thermodynamic Predictions and

Experimental Confirmations ISIJ Int 2004 44(6)1006-1015

[10] T Fujisawa H Sakao Equilibrium between MnO-SiO2-Al2O3-FeO Slags and Liquid Steel Tetsu-to-

Haganeacute 1977 63(9) 1504-1511

[11] H Suito R Inoue Thermodynamics on Control of Inclusions Composition in Ultraclean Steels ISIJ Int

1996 36(5) 528-536

[12] IH Jung YB Kang S Decterov AD Pelton Thermodynamic Evaluation and Optimization of the MnO-

Al2O3 and MnO-Al2O3-SiO2 Systems and Applications to Inclusion Engineering Metall Materi Trans B

2004 35(2) 259-268

[13] JS Park JH Park Effect of Slag Composition on the Concentration of Al2O3 in the Inclusions in Si-Mn-

Killed Steel Metall Materi Trans B 2014 45(3)953-960

[14] SB Lee JH Choi HG Lee PH Rhee and SM Jung Aluminum Deoxidation Equilibrium in Liquid Fe-

16 Pct Cr Alloy Metall Mater Trans B 2005 36 (3) 414-16

[15] M Vanende M Guo J Proost B Blanpain P Wollants Formation and Morphology of Al2O3 Inclusions at

the Onset of Liquid Fe Deoxidation by Al Addition ISIJ Int 2011 51(1) 27-34

[16] M B Leban R Tisu The Effect of Tin Inclusions and Deformation-Induced Martensite on the Corrosion

Properties of AISI 321 Stainless Steel Eng Fail Anal 2013 33 430-38

[17] M Prikryl A Kroupa GC Weatherly SV Subramanian Precipitation Behavior in a Medium Carbon Ti-

V-N Microalloyed Steel Metall Mater Trans B 1996 27(5) 1149-1165

[18] Z Chen MH Loretto RC Cochrane Nature of Large Precipitates in Titanium-Containing HSLA Steels

Mater Sci Technol 1987 3(10) 836-844

[19] J Du M Strangwood and CL Davis Effect of Tin Particles and Grain Size on the Charpy Impact

Transition Temperature in Steels J Mater Sci Technol 2012 28 (10) 878-888

[20] W Yan YY Shan K Yang Effect of TiN Inclusions on the Impact Toughness of Low-Carbon Microalloyed

Steels Metall Mater Trans A 2006 37(7) 2147-2158

[21] MA Linaza JL Romero JM Rodriacuteguez-Ibabe JJ Urcola Influence of the Microstructure on the

Fracture Toughness and Fracture Mechanisms of Forging Steels Microalloyed with Titanium with Ferrite-

Pearlite Structures Scripta Metallurgica et Materialia 1993 29(4) 451-456

[22] T Uesugi Production of High-Carbon Chromium Bearing Steel in Vertical Type Continuous Caster Trans

ISIJ 1986 26(7) 614-620

[23] K Kunishige N Nagao Strengthening and Toughening of Hot-Direct-Rolled Steels by Addition of a Small

Amount of Titanium ISIJ Int 1989 29(11) 940-946

[24] MW Zhou H Yu Effects of Precipitates and Inclusions on the Fracture Toughness of Hot Rolling X70

Pipeline Steel Plates Int J Miner Metall Mater 2012 19(9) 805-11

[25] Y Cogne B Heritier J Monnot Relationship of Melting Practice Inclusion Type and Size with Fatigue

Resistance of Bearing Steels Proceedings of the Third International Conference on Clean Steel The Institute

of Metals Balatonfuumlred Hungary 1987 26-31

[26] A Echeverrıa JM Rodriguez-Ibabe Brittle Fracture Micromechanisms in Bainitic and Martensitic

Microstructures in a C-Mn-B Steel Scripta Materialia 1999 41 (2)131-136

[27] LP Zhang CL Davis M Strangwood Effect of TiN Particles and Microstructure on Fracture Toughness in

Simulated Heat-Affected Zones of a Structural Steel Metall Mater Trans A 1999 30 (8)2089-2096

[28] DP Fairchild DG Howden WAT Clark The Mechanism of Brittle Fracture in a Microalloyed Steel Part

I Inclusion-Induced Cleavage Metall Mater Trans A 2000 31(3) 641-652

[29] MJ Balart CL Davis M Strangwood Cleavage Initiation in TindashVndashN and VndashN Microalloyed Ferriticndash

Pearlitic Forging Steels Mater Sci Eng A 2000 284 (1ndash2) 1-13

[30] M Hasegawa S Maruhashi Y Kamidate Y Muranaka F Hoshi Tundish Nozzle Constriction in

Continuous Casting of Titanium Bearing Stainless Steel Slabs Tetsu-to-Haganeacute 1984 70 (14) 1704-11

[31] R Maddalena R Rastogi S Bassem AW Cramb Nozzle Deposits in Titanium Treated Stainless Steels

Iron and Steelmaker 2000 27 (12) 71-79

[32] Y Gao K Sorimachi Formation of Clogging Materials in an Immersed Nozzle During Continuous Casting

of Titanium Stabilized Stainless Steel ISIJ Int 1993 33 (2) 291-297

[33] Y Bi AV Karasev PG Joumlnsson Evolution of Different Inclusions during Ladle Treatment and Continuous

Casting of Stainless Steel ISIJ Int 2013 53(12)2099ndash2109

[34] HS Kim HG Lee KS OH Precipitation Behavior of Mns on Oxide Inclusions in SiMn Deoxidized

Steel Metall Mater Int 2000 6(4) 305ndash10

[35] M Wakoh T Sawai S Mizoguchi Effect of oxide particles on MnS precipitation in low S steels Tetsu-to-

Haganeacute 1992 78(11)1697ndash1704

[36] M Wakoh T Sawai S Mizoguchi Effect of S Content on the MnS Precipitation in Steel with Oxide

Nuclei ISIJ Int 1996 36(8)1014ndash1021

[37] HS Kim HG Lee KS OH MnS Precipitation in Association with Manganese Silicate Inclusions in

SiMn Deoxidized Steel Metall Mater Trans A 2001 32A (6)1519ndash1525

[38] S S Babu S A David J M Vitek K Mundra T DebRoy Development of Macro- and Microstructures of

Carbon-manganese Low Alloy Steel Welds Inclusion Formation Mater Sci Technol 1995 11(2)186ndash199

[39] DG Zhou J Fu XC Chen J Li Precipitation Behavior of TiN in Bearing Steel J Mater Sci Technol

2003 19(2) 184ndash186

[40] F Meng J Wang EH KW Han The Role of TiN Inclusions in Stress Corrosion Crack Initiation for Alloy

690TT in High-Temperature and High Pressure Water Corros Sci 2010 52(3) 927ndash932

[41] Y Xu Z Chen M Gong D Shu Y Tian X Yuan Effects of Mg Addition on Inclusions Formation and

Resultant Solidification Structure Changes of Ti-Stabilized Ultra-Pure Ferritic Stainless Steel Journal of

Iron and Steel Research International 2014 21(6) 583-588

[42] A S Nick H Fredriksson On the Relationship between Inclusions and Pores Part I Precipitation Trans

Indian Inst Met 2012 65(6) 791-794

[43] JH Park Effect of Inclusions on the Solidification Structures of Ferritic Stainless Steel Computational and

Experimental Study of Inclusion Evolution Calphad 201135(4) 455-462

[44] W Yan YY Shan K Yang Influence of Tin Inclusions on the Cleavage Fracture Behavior of Low-Carbon

Microalloyed Steels Metallurgical and Materials Transactions A 2007 38(6) 1211-1222

[45] M Soumlder PG Joumlnsson L Jonsson Inclusion Growth and Removal in Gas-stirred Ladles Steel Res Int

2004 75(2) 128-138

[46] S Taniguchi A Kikuchi Mechanisms of Collision and Coagulation between Fine Particles in Fluid Tetsu-

to-Haganeacute 1992 78(4) 527-535

[47] U Lindborg KTorssell A Collision Model for the Growth and Separation of Deoxidation Products Trans

Met Soc AIME 1968 242 94-102

calculated by the following Equation [45]

i j

ij i j

dnw n n

dt [4]

where wij is the collision volume (m3s) of a certain collision phenomenon ni and nj are the number

of inclusions within certain size ranges and t is time (s) The collision volume for Brownian collision

( B

ijw[46]) Turbulence collision ( T

ijw[46]) and Stokersquos collision ( S

ijw[47]) can be expressed as following

respectively

Β

ij i j

i j

2kΤ 1 1w = + r +r

3μ r r

[5]

3

T

ij Fe i jw =13α περ μ r +r [6]

3

S Fe iij i j i j

2πg(ρ ρ )w = r +r r r

9μ

[7]

In these equations k is the Boltzmann constant (JK) T is the absolute temperature (K) micro is the

dynamic viscosity of steel (kgms) α is the collision efficiency ε is the turbulent energy dissipation

(m2s3) ρFe and ρi are the densities of the steel and inclusion respectively (kgm3) g is the

gravitational acceleration (ms2) and ri and rj are the radii of the two colliding inclusions (m)

Each of the different collision mechanism can make a contribution to the total number of collisions

Therefore collision volume wij was calculated using the parameters given in Table 2 in order to

determine the significance of the separate collision mechanisms It should be pointed out that the

calculation of collision volume was based on considering spherical inclusions in steel Therefore in

this study it was assumed that an irregular shape inclusion can rotate around its center due to the

liquid steel flow and can collide with other inclusions within the rotational region whose maximum

length equals to the inclusion diameter

Figure 9 presents the calculated values of the collision volumes for an inclusion of 148microm (size

with a highest content according to Figure 8 ) that collides with other inclusions of different sizes

It can be seen from Figure 9 that Brownian collision volume B

ijw is drastically smaller than that of

Stokersquos and Turbulent collision volume in all studied ranges of rj whose impact on inclusion growth

can be neglected Both Turbulence and Stokersquos collision mechanism have a much higher effect on

the collision volume compared to the Brownian collision They keep an increasing trend as a

function of increased size (more than 148microm) Moreover the effect of Turbulence collision is

higher than Stokes and the difference between these two collisions is decreasing as the inclusion

size increases within the the range studied here Therefore both Turbulence and Stokersquos mechanism

are believed to play a considerable role in inclusion coarsening

TableⅡ Data used in calculation of collision volumes

k

(JK)

T

(K)

micro

(kgms)

α

(m2s3)

ε

(m2s3)

ρFe

(kgm3)

ρi

(kgm3)

g

(ms2)

138times10-

23 1873 0005 03 00018 8000 5220 981

Fig 9 Collision volumes for an inclusion with a 148microm (ri=074microm) in diameter as a function of collision with

different sized inclusions

4 Conclusions

Inclusions characteristics (such as morphology composition and size distribution) were analyzed in steel

samples taken after different alloy additions using electrolytic extraction methods followed by SEM-

EDS characterization The following conclusions were drawn

(1) After the addition of ferrosilicon alloy and electrolytic manganese followed by aluminum the

composition of inclusions changed from manganese silicate-rich inclusions with spherical shapes to

alumina-rich inclusions with irregular shapes

(2) After Ti-stabilization three TiN inclusion morphologies were found single particle swinned

particles and clusters

(3) Both the Turbulence and Stokersquoss collision mechanism are the effective in formation and coarsening

of TiN clusters the Brownian collision mechanism appeared to play a minor role

5 Acknowledgments

The first author would like to thank China Scholarship Council (CSC) for support of her study abroad

Qingshan steel provided the stainless steel samples of this study The financial support by Natural

Sciences and Engineering Research Council of Canada is greatly acknowledged

6 Reference

[1] L Zhang BG Thomas State of the Art in Evaluation and Control of Steel Cleanliness ISIJ Int 2003

43(3) 271-291

[2] P Kaushik J Lehmann M Nadif State of the Art in Control of Inclusions Their Characterization and Future

Requirements Metall Materi Trans B 2012 43(4) 710-725

[3] P Kaushik H Pielet H Yin Inclusion CharacterizationndashTool for Measurement of Steel Cleanliness and

Process Control Part 1 Ironmaking amp Steelmaking 2009 36(8) 561-571

[4] ME Fine Fatigue Resistance of Metals Metall Trans A 1980 11(3)365ndash379

[5] S Chen M Jiang X He and X Wang Top Slag Refining for Inclusion Composition Transform Control in

Tire Cord Steel Int J Miner Metall Mater 2012 19(6) 490ndash98

[6] X Cai Y Bao L Lin C Gu Effect of Al Content on the Evolution of Non-Metallic Inclusions in SindashMn

Deoxidized Steel Steel Research International online version

[7] DH Woo YB Kang H G Lee Thermodynamic Study of Mno-SiO2-Al2O3 Slag System Liquidus Lines

and Activities of MnO at 1823 K Metall Mater Trans B 2002 33(6) 915-920

[8] K Ogawa T Onoe H Matsumoto K Narita On the behavior of inclusions in the flux treatment of high

carbon steels Tetsu-to-Haganeacute 1985 71(2) 29-32

[9] Y B Kang HG Lee Inclusions Chemistry for MnSi Deoxidized Steels Thermodynamic Predictions and

Experimental Confirmations ISIJ Int 2004 44(6)1006-1015

[10] T Fujisawa H Sakao Equilibrium between MnO-SiO2-Al2O3-FeO Slags and Liquid Steel Tetsu-to-

Haganeacute 1977 63(9) 1504-1511

[11] H Suito R Inoue Thermodynamics on Control of Inclusions Composition in Ultraclean Steels ISIJ Int

1996 36(5) 528-536

[12] IH Jung YB Kang S Decterov AD Pelton Thermodynamic Evaluation and Optimization of the MnO-

Al2O3 and MnO-Al2O3-SiO2 Systems and Applications to Inclusion Engineering Metall Materi Trans B

2004 35(2) 259-268

[13] JS Park JH Park Effect of Slag Composition on the Concentration of Al2O3 in the Inclusions in Si-Mn-

Killed Steel Metall Materi Trans B 2014 45(3)953-960

[14] SB Lee JH Choi HG Lee PH Rhee and SM Jung Aluminum Deoxidation Equilibrium in Liquid Fe-

16 Pct Cr Alloy Metall Mater Trans B 2005 36 (3) 414-16

[15] M Vanende M Guo J Proost B Blanpain P Wollants Formation and Morphology of Al2O3 Inclusions at

the Onset of Liquid Fe Deoxidation by Al Addition ISIJ Int 2011 51(1) 27-34

[16] M B Leban R Tisu The Effect of Tin Inclusions and Deformation-Induced Martensite on the Corrosion

Properties of AISI 321 Stainless Steel Eng Fail Anal 2013 33 430-38

[17] M Prikryl A Kroupa GC Weatherly SV Subramanian Precipitation Behavior in a Medium Carbon Ti-

V-N Microalloyed Steel Metall Mater Trans B 1996 27(5) 1149-1165

[18] Z Chen MH Loretto RC Cochrane Nature of Large Precipitates in Titanium-Containing HSLA Steels

Mater Sci Technol 1987 3(10) 836-844

[19] J Du M Strangwood and CL Davis Effect of Tin Particles and Grain Size on the Charpy Impact

Transition Temperature in Steels J Mater Sci Technol 2012 28 (10) 878-888

[20] W Yan YY Shan K Yang Effect of TiN Inclusions on the Impact Toughness of Low-Carbon Microalloyed

Steels Metall Mater Trans A 2006 37(7) 2147-2158

[21] MA Linaza JL Romero JM Rodriacuteguez-Ibabe JJ Urcola Influence of the Microstructure on the

Fracture Toughness and Fracture Mechanisms of Forging Steels Microalloyed with Titanium with Ferrite-

Pearlite Structures Scripta Metallurgica et Materialia 1993 29(4) 451-456

[22] T Uesugi Production of High-Carbon Chromium Bearing Steel in Vertical Type Continuous Caster Trans

ISIJ 1986 26(7) 614-620

[23] K Kunishige N Nagao Strengthening and Toughening of Hot-Direct-Rolled Steels by Addition of a Small

Amount of Titanium ISIJ Int 1989 29(11) 940-946

[24] MW Zhou H Yu Effects of Precipitates and Inclusions on the Fracture Toughness of Hot Rolling X70

Pipeline Steel Plates Int J Miner Metall Mater 2012 19(9) 805-11

[25] Y Cogne B Heritier J Monnot Relationship of Melting Practice Inclusion Type and Size with Fatigue

Resistance of Bearing Steels Proceedings of the Third International Conference on Clean Steel The Institute

of Metals Balatonfuumlred Hungary 1987 26-31

[26] A Echeverrıa JM Rodriguez-Ibabe Brittle Fracture Micromechanisms in Bainitic and Martensitic

Microstructures in a C-Mn-B Steel Scripta Materialia 1999 41 (2)131-136

[27] LP Zhang CL Davis M Strangwood Effect of TiN Particles and Microstructure on Fracture Toughness in

Simulated Heat-Affected Zones of a Structural Steel Metall Mater Trans A 1999 30 (8)2089-2096

[28] DP Fairchild DG Howden WAT Clark The Mechanism of Brittle Fracture in a Microalloyed Steel Part

I Inclusion-Induced Cleavage Metall Mater Trans A 2000 31(3) 641-652

[29] MJ Balart CL Davis M Strangwood Cleavage Initiation in TindashVndashN and VndashN Microalloyed Ferriticndash

Pearlitic Forging Steels Mater Sci Eng A 2000 284 (1ndash2) 1-13

[30] M Hasegawa S Maruhashi Y Kamidate Y Muranaka F Hoshi Tundish Nozzle Constriction in

Continuous Casting of Titanium Bearing Stainless Steel Slabs Tetsu-to-Haganeacute 1984 70 (14) 1704-11

[31] R Maddalena R Rastogi S Bassem AW Cramb Nozzle Deposits in Titanium Treated Stainless Steels

Iron and Steelmaker 2000 27 (12) 71-79

[32] Y Gao K Sorimachi Formation of Clogging Materials in an Immersed Nozzle During Continuous Casting

of Titanium Stabilized Stainless Steel ISIJ Int 1993 33 (2) 291-297

[33] Y Bi AV Karasev PG Joumlnsson Evolution of Different Inclusions during Ladle Treatment and Continuous

Casting of Stainless Steel ISIJ Int 2013 53(12)2099ndash2109

[34] HS Kim HG Lee KS OH Precipitation Behavior of Mns on Oxide Inclusions in SiMn Deoxidized

Steel Metall Mater Int 2000 6(4) 305ndash10

[35] M Wakoh T Sawai S Mizoguchi Effect of oxide particles on MnS precipitation in low S steels Tetsu-to-

Haganeacute 1992 78(11)1697ndash1704

[36] M Wakoh T Sawai S Mizoguchi Effect of S Content on the MnS Precipitation in Steel with Oxide

Nuclei ISIJ Int 1996 36(8)1014ndash1021

[37] HS Kim HG Lee KS OH MnS Precipitation in Association with Manganese Silicate Inclusions in

SiMn Deoxidized Steel Metall Mater Trans A 2001 32A (6)1519ndash1525

[38] S S Babu S A David J M Vitek K Mundra T DebRoy Development of Macro- and Microstructures of

Carbon-manganese Low Alloy Steel Welds Inclusion Formation Mater Sci Technol 1995 11(2)186ndash199

[39] DG Zhou J Fu XC Chen J Li Precipitation Behavior of TiN in Bearing Steel J Mater Sci Technol

2003 19(2) 184ndash186

[40] F Meng J Wang EH KW Han The Role of TiN Inclusions in Stress Corrosion Crack Initiation for Alloy

690TT in High-Temperature and High Pressure Water Corros Sci 2010 52(3) 927ndash932

[41] Y Xu Z Chen M Gong D Shu Y Tian X Yuan Effects of Mg Addition on Inclusions Formation and

Resultant Solidification Structure Changes of Ti-Stabilized Ultra-Pure Ferritic Stainless Steel Journal of

Iron and Steel Research International 2014 21(6) 583-588

[42] A S Nick H Fredriksson On the Relationship between Inclusions and Pores Part I Precipitation Trans

Indian Inst Met 2012 65(6) 791-794

[43] JH Park Effect of Inclusions on the Solidification Structures of Ferritic Stainless Steel Computational and

Experimental Study of Inclusion Evolution Calphad 201135(4) 455-462

[44] W Yan YY Shan K Yang Influence of Tin Inclusions on the Cleavage Fracture Behavior of Low-Carbon

Microalloyed Steels Metallurgical and Materials Transactions A 2007 38(6) 1211-1222

[45] M Soumlder PG Joumlnsson L Jonsson Inclusion Growth and Removal in Gas-stirred Ladles Steel Res Int

2004 75(2) 128-138

[46] S Taniguchi A Kikuchi Mechanisms of Collision and Coagulation between Fine Particles in Fluid Tetsu-

to-Haganeacute 1992 78(4) 527-535

[47] U Lindborg KTorssell A Collision Model for the Growth and Separation of Deoxidation Products Trans

Met Soc AIME 1968 242 94-102

Fig 9 Collision volumes for an inclusion with a 148microm (ri=074microm) in diameter as a function of collision with

different sized inclusions

4 Conclusions

Inclusions characteristics (such as morphology composition and size distribution) were analyzed in steel

samples taken after different alloy additions using electrolytic extraction methods followed by SEM-

EDS characterization The following conclusions were drawn

(1) After the addition of ferrosilicon alloy and electrolytic manganese followed by aluminum the

composition of inclusions changed from manganese silicate-rich inclusions with spherical shapes to

alumina-rich inclusions with irregular shapes

(2) After Ti-stabilization three TiN inclusion morphologies were found single particle swinned

particles and clusters

(3) Both the Turbulence and Stokersquoss collision mechanism are the effective in formation and coarsening

of TiN clusters the Brownian collision mechanism appeared to play a minor role

5 Acknowledgments

The first author would like to thank China Scholarship Council (CSC) for support of her study abroad

Qingshan steel provided the stainless steel samples of this study The financial support by Natural

Sciences and Engineering Research Council of Canada is greatly acknowledged

6 Reference

[1] L Zhang BG Thomas State of the Art in Evaluation and Control of Steel Cleanliness ISIJ Int 2003

43(3) 271-291

[2] P Kaushik J Lehmann M Nadif State of the Art in Control of Inclusions Their Characterization and Future

Requirements Metall Materi Trans B 2012 43(4) 710-725

[3] P Kaushik H Pielet H Yin Inclusion CharacterizationndashTool for Measurement of Steel Cleanliness and

Process Control Part 1 Ironmaking amp Steelmaking 2009 36(8) 561-571

[4] ME Fine Fatigue Resistance of Metals Metall Trans A 1980 11(3)365ndash379

[5] S Chen M Jiang X He and X Wang Top Slag Refining for Inclusion Composition Transform Control in

Tire Cord Steel Int J Miner Metall Mater 2012 19(6) 490ndash98

[6] X Cai Y Bao L Lin C Gu Effect of Al Content on the Evolution of Non-Metallic Inclusions in SindashMn

Deoxidized Steel Steel Research International online version

[7] DH Woo YB Kang H G Lee Thermodynamic Study of Mno-SiO2-Al2O3 Slag System Liquidus Lines

and Activities of MnO at 1823 K Metall Mater Trans B 2002 33(6) 915-920

[8] K Ogawa T Onoe H Matsumoto K Narita On the behavior of inclusions in the flux treatment of high

carbon steels Tetsu-to-Haganeacute 1985 71(2) 29-32

[9] Y B Kang HG Lee Inclusions Chemistry for MnSi Deoxidized Steels Thermodynamic Predictions and

Experimental Confirmations ISIJ Int 2004 44(6)1006-1015

[10] T Fujisawa H Sakao Equilibrium between MnO-SiO2-Al2O3-FeO Slags and Liquid Steel Tetsu-to-

Haganeacute 1977 63(9) 1504-1511

[11] H Suito R Inoue Thermodynamics on Control of Inclusions Composition in Ultraclean Steels ISIJ Int

1996 36(5) 528-536

[12] IH Jung YB Kang S Decterov AD Pelton Thermodynamic Evaluation and Optimization of the MnO-

Al2O3 and MnO-Al2O3-SiO2 Systems and Applications to Inclusion Engineering Metall Materi Trans B

2004 35(2) 259-268

[13] JS Park JH Park Effect of Slag Composition on the Concentration of Al2O3 in the Inclusions in Si-Mn-

Killed Steel Metall Materi Trans B 2014 45(3)953-960

[14] SB Lee JH Choi HG Lee PH Rhee and SM Jung Aluminum Deoxidation Equilibrium in Liquid Fe-

16 Pct Cr Alloy Metall Mater Trans B 2005 36 (3) 414-16

[15] M Vanende M Guo J Proost B Blanpain P Wollants Formation and Morphology of Al2O3 Inclusions at

the Onset of Liquid Fe Deoxidation by Al Addition ISIJ Int 2011 51(1) 27-34

[16] M B Leban R Tisu The Effect of Tin Inclusions and Deformation-Induced Martensite on the Corrosion

Properties of AISI 321 Stainless Steel Eng Fail Anal 2013 33 430-38

[17] M Prikryl A Kroupa GC Weatherly SV Subramanian Precipitation Behavior in a Medium Carbon Ti-

V-N Microalloyed Steel Metall Mater Trans B 1996 27(5) 1149-1165

[18] Z Chen MH Loretto RC Cochrane Nature of Large Precipitates in Titanium-Containing HSLA Steels

Mater Sci Technol 1987 3(10) 836-844

[19] J Du M Strangwood and CL Davis Effect of Tin Particles and Grain Size on the Charpy Impact

Transition Temperature in Steels J Mater Sci Technol 2012 28 (10) 878-888

[20] W Yan YY Shan K Yang Effect of TiN Inclusions on the Impact Toughness of Low-Carbon Microalloyed

Steels Metall Mater Trans A 2006 37(7) 2147-2158

[21] MA Linaza JL Romero JM Rodriacuteguez-Ibabe JJ Urcola Influence of the Microstructure on the

Fracture Toughness and Fracture Mechanisms of Forging Steels Microalloyed with Titanium with Ferrite-

Pearlite Structures Scripta Metallurgica et Materialia 1993 29(4) 451-456

[22] T Uesugi Production of High-Carbon Chromium Bearing Steel in Vertical Type Continuous Caster Trans

ISIJ 1986 26(7) 614-620

[23] K Kunishige N Nagao Strengthening and Toughening of Hot-Direct-Rolled Steels by Addition of a Small

Amount of Titanium ISIJ Int 1989 29(11) 940-946

[24] MW Zhou H Yu Effects of Precipitates and Inclusions on the Fracture Toughness of Hot Rolling X70

Pipeline Steel Plates Int J Miner Metall Mater 2012 19(9) 805-11

[25] Y Cogne B Heritier J Monnot Relationship of Melting Practice Inclusion Type and Size with Fatigue

Resistance of Bearing Steels Proceedings of the Third International Conference on Clean Steel The Institute

of Metals Balatonfuumlred Hungary 1987 26-31

[26] A Echeverrıa JM Rodriguez-Ibabe Brittle Fracture Micromechanisms in Bainitic and Martensitic

Microstructures in a C-Mn-B Steel Scripta Materialia 1999 41 (2)131-136

[27] LP Zhang CL Davis M Strangwood Effect of TiN Particles and Microstructure on Fracture Toughness in

Simulated Heat-Affected Zones of a Structural Steel Metall Mater Trans A 1999 30 (8)2089-2096

[28] DP Fairchild DG Howden WAT Clark The Mechanism of Brittle Fracture in a Microalloyed Steel Part

I Inclusion-Induced Cleavage Metall Mater Trans A 2000 31(3) 641-652

[29] MJ Balart CL Davis M Strangwood Cleavage Initiation in TindashVndashN and VndashN Microalloyed Ferriticndash

Pearlitic Forging Steels Mater Sci Eng A 2000 284 (1ndash2) 1-13

[30] M Hasegawa S Maruhashi Y Kamidate Y Muranaka F Hoshi Tundish Nozzle Constriction in

Continuous Casting of Titanium Bearing Stainless Steel Slabs Tetsu-to-Haganeacute 1984 70 (14) 1704-11

[31] R Maddalena R Rastogi S Bassem AW Cramb Nozzle Deposits in Titanium Treated Stainless Steels

Iron and Steelmaker 2000 27 (12) 71-79

[32] Y Gao K Sorimachi Formation of Clogging Materials in an Immersed Nozzle During Continuous Casting

of Titanium Stabilized Stainless Steel ISIJ Int 1993 33 (2) 291-297

[33] Y Bi AV Karasev PG Joumlnsson Evolution of Different Inclusions during Ladle Treatment and Continuous

Casting of Stainless Steel ISIJ Int 2013 53(12)2099ndash2109

[34] HS Kim HG Lee KS OH Precipitation Behavior of Mns on Oxide Inclusions in SiMn Deoxidized

Steel Metall Mater Int 2000 6(4) 305ndash10

[35] M Wakoh T Sawai S Mizoguchi Effect of oxide particles on MnS precipitation in low S steels Tetsu-to-

Haganeacute 1992 78(11)1697ndash1704

[36] M Wakoh T Sawai S Mizoguchi Effect of S Content on the MnS Precipitation in Steel with Oxide

Nuclei ISIJ Int 1996 36(8)1014ndash1021

[37] HS Kim HG Lee KS OH MnS Precipitation in Association with Manganese Silicate Inclusions in

SiMn Deoxidized Steel Metall Mater Trans A 2001 32A (6)1519ndash1525

[38] S S Babu S A David J M Vitek K Mundra T DebRoy Development of Macro- and Microstructures of

Carbon-manganese Low Alloy Steel Welds Inclusion Formation Mater Sci Technol 1995 11(2)186ndash199

[39] DG Zhou J Fu XC Chen J Li Precipitation Behavior of TiN in Bearing Steel J Mater Sci Technol

2003 19(2) 184ndash186

[40] F Meng J Wang EH KW Han The Role of TiN Inclusions in Stress Corrosion Crack Initiation for Alloy

690TT in High-Temperature and High Pressure Water Corros Sci 2010 52(3) 927ndash932

[41] Y Xu Z Chen M Gong D Shu Y Tian X Yuan Effects of Mg Addition on Inclusions Formation and

Resultant Solidification Structure Changes of Ti-Stabilized Ultra-Pure Ferritic Stainless Steel Journal of

Iron and Steel Research International 2014 21(6) 583-588

[42] A S Nick H Fredriksson On the Relationship between Inclusions and Pores Part I Precipitation Trans

Indian Inst Met 2012 65(6) 791-794

[43] JH Park Effect of Inclusions on the Solidification Structures of Ferritic Stainless Steel Computational and

Experimental Study of Inclusion Evolution Calphad 201135(4) 455-462

[44] W Yan YY Shan K Yang Influence of Tin Inclusions on the Cleavage Fracture Behavior of Low-Carbon

Microalloyed Steels Metallurgical and Materials Transactions A 2007 38(6) 1211-1222

[45] M Soumlder PG Joumlnsson L Jonsson Inclusion Growth and Removal in Gas-stirred Ladles Steel Res Int

2004 75(2) 128-138

[46] S Taniguchi A Kikuchi Mechanisms of Collision and Coagulation between Fine Particles in Fluid Tetsu-

to-Haganeacute 1992 78(4) 527-535

[47] U Lindborg KTorssell A Collision Model for the Growth and Separation of Deoxidation Products Trans

Met Soc AIME 1968 242 94-102

[6] X Cai Y Bao L Lin C Gu Effect of Al Content on the Evolution of Non-Metallic Inclusions in SindashMn

Deoxidized Steel Steel Research International online version

[7] DH Woo YB Kang H G Lee Thermodynamic Study of Mno-SiO2-Al2O3 Slag System Liquidus Lines

and Activities of MnO at 1823 K Metall Mater Trans B 2002 33(6) 915-920

[8] K Ogawa T Onoe H Matsumoto K Narita On the behavior of inclusions in the flux treatment of high

carbon steels Tetsu-to-Haganeacute 1985 71(2) 29-32

[9] Y B Kang HG Lee Inclusions Chemistry for MnSi Deoxidized Steels Thermodynamic Predictions and

Experimental Confirmations ISIJ Int 2004 44(6)1006-1015

[10] T Fujisawa H Sakao Equilibrium between MnO-SiO2-Al2O3-FeO Slags and Liquid Steel Tetsu-to-

Haganeacute 1977 63(9) 1504-1511

[11] H Suito R Inoue Thermodynamics on Control of Inclusions Composition in Ultraclean Steels ISIJ Int

1996 36(5) 528-536

[12] IH Jung YB Kang S Decterov AD Pelton Thermodynamic Evaluation and Optimization of the MnO-

Al2O3 and MnO-Al2O3-SiO2 Systems and Applications to Inclusion Engineering Metall Materi Trans B

2004 35(2) 259-268

[13] JS Park JH Park Effect of Slag Composition on the Concentration of Al2O3 in the Inclusions in Si-Mn-

Killed Steel Metall Materi Trans B 2014 45(3)953-960

[14] SB Lee JH Choi HG Lee PH Rhee and SM Jung Aluminum Deoxidation Equilibrium in Liquid Fe-

16 Pct Cr Alloy Metall Mater Trans B 2005 36 (3) 414-16

[15] M Vanende M Guo J Proost B Blanpain P Wollants Formation and Morphology of Al2O3 Inclusions at

the Onset of Liquid Fe Deoxidation by Al Addition ISIJ Int 2011 51(1) 27-34

[16] M B Leban R Tisu The Effect of Tin Inclusions and Deformation-Induced Martensite on the Corrosion

Properties of AISI 321 Stainless Steel Eng Fail Anal 2013 33 430-38

[17] M Prikryl A Kroupa GC Weatherly SV Subramanian Precipitation Behavior in a Medium Carbon Ti-

V-N Microalloyed Steel Metall Mater Trans B 1996 27(5) 1149-1165

[18] Z Chen MH Loretto RC Cochrane Nature of Large Precipitates in Titanium-Containing HSLA Steels

Mater Sci Technol 1987 3(10) 836-844

[19] J Du M Strangwood and CL Davis Effect of Tin Particles and Grain Size on the Charpy Impact

Transition Temperature in Steels J Mater Sci Technol 2012 28 (10) 878-888

[20] W Yan YY Shan K Yang Effect of TiN Inclusions on the Impact Toughness of Low-Carbon Microalloyed

Steels Metall Mater Trans A 2006 37(7) 2147-2158

[21] MA Linaza JL Romero JM Rodriacuteguez-Ibabe JJ Urcola Influence of the Microstructure on the

Fracture Toughness and Fracture Mechanisms of Forging Steels Microalloyed with Titanium with Ferrite-

Pearlite Structures Scripta Metallurgica et Materialia 1993 29(4) 451-456

[22] T Uesugi Production of High-Carbon Chromium Bearing Steel in Vertical Type Continuous Caster Trans

ISIJ 1986 26(7) 614-620

[23] K Kunishige N Nagao Strengthening and Toughening of Hot-Direct-Rolled Steels by Addition of a Small

Amount of Titanium ISIJ Int 1989 29(11) 940-946

[24] MW Zhou H Yu Effects of Precipitates and Inclusions on the Fracture Toughness of Hot Rolling X70

Pipeline Steel Plates Int J Miner Metall Mater 2012 19(9) 805-11

[25] Y Cogne B Heritier J Monnot Relationship of Melting Practice Inclusion Type and Size with Fatigue

Resistance of Bearing Steels Proceedings of the Third International Conference on Clean Steel The Institute

of Metals Balatonfuumlred Hungary 1987 26-31

[26] A Echeverrıa JM Rodriguez-Ibabe Brittle Fracture Micromechanisms in Bainitic and Martensitic

Microstructures in a C-Mn-B Steel Scripta Materialia 1999 41 (2)131-136

[27] LP Zhang CL Davis M Strangwood Effect of TiN Particles and Microstructure on Fracture Toughness in

Simulated Heat-Affected Zones of a Structural Steel Metall Mater Trans A 1999 30 (8)2089-2096

[28] DP Fairchild DG Howden WAT Clark The Mechanism of Brittle Fracture in a Microalloyed Steel Part

I Inclusion-Induced Cleavage Metall Mater Trans A 2000 31(3) 641-652

[29] MJ Balart CL Davis M Strangwood Cleavage Initiation in TindashVndashN and VndashN Microalloyed Ferriticndash

Pearlitic Forging Steels Mater Sci Eng A 2000 284 (1ndash2) 1-13

[30] M Hasegawa S Maruhashi Y Kamidate Y Muranaka F Hoshi Tundish Nozzle Constriction in

Continuous Casting of Titanium Bearing Stainless Steel Slabs Tetsu-to-Haganeacute 1984 70 (14) 1704-11

[31] R Maddalena R Rastogi S Bassem AW Cramb Nozzle Deposits in Titanium Treated Stainless Steels

Iron and Steelmaker 2000 27 (12) 71-79

[32] Y Gao K Sorimachi Formation of Clogging Materials in an Immersed Nozzle During Continuous Casting

of Titanium Stabilized Stainless Steel ISIJ Int 1993 33 (2) 291-297

[33] Y Bi AV Karasev PG Joumlnsson Evolution of Different Inclusions during Ladle Treatment and Continuous

Casting of Stainless Steel ISIJ Int 2013 53(12)2099ndash2109

[34] HS Kim HG Lee KS OH Precipitation Behavior of Mns on Oxide Inclusions in SiMn Deoxidized

Steel Metall Mater Int 2000 6(4) 305ndash10

[35] M Wakoh T Sawai S Mizoguchi Effect of oxide particles on MnS precipitation in low S steels Tetsu-to-

Haganeacute 1992 78(11)1697ndash1704

[36] M Wakoh T Sawai S Mizoguchi Effect of S Content on the MnS Precipitation in Steel with Oxide

Nuclei ISIJ Int 1996 36(8)1014ndash1021

[37] HS Kim HG Lee KS OH MnS Precipitation in Association with Manganese Silicate Inclusions in

SiMn Deoxidized Steel Metall Mater Trans A 2001 32A (6)1519ndash1525

[38] S S Babu S A David J M Vitek K Mundra T DebRoy Development of Macro- and Microstructures of

Carbon-manganese Low Alloy Steel Welds Inclusion Formation Mater Sci Technol 1995 11(2)186ndash199

[39] DG Zhou J Fu XC Chen J Li Precipitation Behavior of TiN in Bearing Steel J Mater Sci Technol

2003 19(2) 184ndash186

[40] F Meng J Wang EH KW Han The Role of TiN Inclusions in Stress Corrosion Crack Initiation for Alloy

690TT in High-Temperature and High Pressure Water Corros Sci 2010 52(3) 927ndash932

[41] Y Xu Z Chen M Gong D Shu Y Tian X Yuan Effects of Mg Addition on Inclusions Formation and

Resultant Solidification Structure Changes of Ti-Stabilized Ultra-Pure Ferritic Stainless Steel Journal of

Iron and Steel Research International 2014 21(6) 583-588

[42] A S Nick H Fredriksson On the Relationship between Inclusions and Pores Part I Precipitation Trans

Indian Inst Met 2012 65(6) 791-794

[43] JH Park Effect of Inclusions on the Solidification Structures of Ferritic Stainless Steel Computational and

Experimental Study of Inclusion Evolution Calphad 201135(4) 455-462

[44] W Yan YY Shan K Yang Influence of Tin Inclusions on the Cleavage Fracture Behavior of Low-Carbon

Microalloyed Steels Metallurgical and Materials Transactions A 2007 38(6) 1211-1222

[45] M Soumlder PG Joumlnsson L Jonsson Inclusion Growth and Removal in Gas-stirred Ladles Steel Res Int

2004 75(2) 128-138

[46] S Taniguchi A Kikuchi Mechanisms of Collision and Coagulation between Fine Particles in Fluid Tetsu-

to-Haganeacute 1992 78(4) 527-535

[47] U Lindborg KTorssell A Collision Model for the Growth and Separation of Deoxidation Products Trans

Met Soc AIME 1968 242 94-102

Microstructures in a C-Mn-B Steel Scripta Materialia 1999 41 (2)131-136

[27] LP Zhang CL Davis M Strangwood Effect of TiN Particles and Microstructure on Fracture Toughness in

Simulated Heat-Affected Zones of a Structural Steel Metall Mater Trans A 1999 30 (8)2089-2096

[28] DP Fairchild DG Howden WAT Clark The Mechanism of Brittle Fracture in a Microalloyed Steel Part

I Inclusion-Induced Cleavage Metall Mater Trans A 2000 31(3) 641-652

[29] MJ Balart CL Davis M Strangwood Cleavage Initiation in TindashVndashN and VndashN Microalloyed Ferriticndash

Pearlitic Forging Steels Mater Sci Eng A 2000 284 (1ndash2) 1-13

[30] M Hasegawa S Maruhashi Y Kamidate Y Muranaka F Hoshi Tundish Nozzle Constriction in

Continuous Casting of Titanium Bearing Stainless Steel Slabs Tetsu-to-Haganeacute 1984 70 (14) 1704-11

[31] R Maddalena R Rastogi S Bassem AW Cramb Nozzle Deposits in Titanium Treated Stainless Steels

Iron and Steelmaker 2000 27 (12) 71-79

[32] Y Gao K Sorimachi Formation of Clogging Materials in an Immersed Nozzle During Continuous Casting

of Titanium Stabilized Stainless Steel ISIJ Int 1993 33 (2) 291-297

[33] Y Bi AV Karasev PG Joumlnsson Evolution of Different Inclusions during Ladle Treatment and Continuous

Casting of Stainless Steel ISIJ Int 2013 53(12)2099ndash2109

[34] HS Kim HG Lee KS OH Precipitation Behavior of Mns on Oxide Inclusions in SiMn Deoxidized

Steel Metall Mater Int 2000 6(4) 305ndash10

[35] M Wakoh T Sawai S Mizoguchi Effect of oxide particles on MnS precipitation in low S steels Tetsu-to-

Haganeacute 1992 78(11)1697ndash1704

[36] M Wakoh T Sawai S Mizoguchi Effect of S Content on the MnS Precipitation in Steel with Oxide

Nuclei ISIJ Int 1996 36(8)1014ndash1021

[37] HS Kim HG Lee KS OH MnS Precipitation in Association with Manganese Silicate Inclusions in

SiMn Deoxidized Steel Metall Mater Trans A 2001 32A (6)1519ndash1525

[38] S S Babu S A David J M Vitek K Mundra T DebRoy Development of Macro- and Microstructures of

Carbon-manganese Low Alloy Steel Welds Inclusion Formation Mater Sci Technol 1995 11(2)186ndash199

[39] DG Zhou J Fu XC Chen J Li Precipitation Behavior of TiN in Bearing Steel J Mater Sci Technol

2003 19(2) 184ndash186

[40] F Meng J Wang EH KW Han The Role of TiN Inclusions in Stress Corrosion Crack Initiation for Alloy

690TT in High-Temperature and High Pressure Water Corros Sci 2010 52(3) 927ndash932

[41] Y Xu Z Chen M Gong D Shu Y Tian X Yuan Effects of Mg Addition on Inclusions Formation and

Resultant Solidification Structure Changes of Ti-Stabilized Ultra-Pure Ferritic Stainless Steel Journal of

Iron and Steel Research International 2014 21(6) 583-588

[42] A S Nick H Fredriksson On the Relationship between Inclusions and Pores Part I Precipitation Trans

Indian Inst Met 2012 65(6) 791-794

[43] JH Park Effect of Inclusions on the Solidification Structures of Ferritic Stainless Steel Computational and

Experimental Study of Inclusion Evolution Calphad 201135(4) 455-462

[44] W Yan YY Shan K Yang Influence of Tin Inclusions on the Cleavage Fracture Behavior of Low-Carbon

Microalloyed Steels Metallurgical and Materials Transactions A 2007 38(6) 1211-1222

[45] M Soumlder PG Joumlnsson L Jonsson Inclusion Growth and Removal in Gas-stirred Ladles Steel Res Int

2004 75(2) 128-138

[46] S Taniguchi A Kikuchi Mechanisms of Collision and Coagulation between Fine Particles in Fluid Tetsu-

to-Haganeacute 1992 78(4) 527-535

[47] U Lindborg KTorssell A Collision Model for the Growth and Separation of Deoxidation Products Trans

Met Soc AIME 1968 242 94-102