Research ArticlePickling Behaviour of 2205 Duplex Stainless Steel Hot-RolledStrips in Sulfuric Acid Electrolytes

Jianguo Peng 12 and Moucheng Li 1

1Institute of Materials Shanghai University Shanghai 200072 China2Research Institute Baoshan Iron amp Steel Co Ltd Shanghai 200431 China

Correspondence should be addressed to Jianguo Peng peng_jianguobaosteelcom and Moucheng Li mouchenglishueducn

Received 9 August 2019 Accepted 17 March 2020 Published 9 April 2020

Academic Editor Stefano Bellucci

Copyright copy 2020 Jianguo Peng and Moucheng Li +is is an open access article distributed under the Creative CommonsAttribution License which permits unrestricted use distribution and reproduction in anymedium provided the original work isproperly cited

Pickling behaviour of the oxide layer on hot-rolled 2205 duplex stainless steel (DSS) was studied in H2SO4 solutions withelectrolytic workstation +e pickling rate at 75degC increases slightly with the H2SO4 concentration from 100 to 250 g Lminus1 butincreases markedly as the concentration is higher than 250 g Lminus1 +e solution temperature greatly accelerates the pickling rateFe3+ ion is an effective oxidant which shows stronger inhibitive effect+e rotating disk electrode was used to simulate the movingstate of steel strips in practice +e movement with the speed from 0 to 20mminminus1 results in weak acceleration effect on thepickling process Under dynamic conditions the pickling rate increases noticeably with changing the pulse current density from 0to 02A cmminus2 +e industrial pickling efficiency of 2205 DSS hot-rolled strips increases from 5ndash8mmin to 15ndash18mmin +esurface quality is improved

1 Introduction

Type 2205 duplex stainless steel (DSS) has been used widelyin many industries for its excellent mechanical propertiesand corrosion resistance [1ndash6] However the oxide scalesformed on the surface of 2205 DSS during rolling and heattreatment are stable and dense due to the high chromiummolybdenum and nitrogen contents [7] Moreover oxidenodules may often grow on the surface of 2205 DSS for thedifferent oxidation rates of ferritic and austenitic phases athigh temperature [8 9] +erefore the pickling of 2205 DSShot-rolled strips is more difficult than that of standardaustenitic grades [10]

+e pickling process of stainless steels is used to removethe oxide scales and chromium depleted layer in order torestore the corrosion resistance and ensure the surface finish[11 12] +e industrial pickling process includes mechanicaldescaling prepickling and mixed acid pickling A me-chanical descaling is achieved through breaking grindingroto blasting and sand blasting processes Prepickling isperformed either anodically or cathodically in acid or

neutral electrolytes with certain current densities [13ndash15]+e general electrolytes are Na2SO4 H2SO4 H3PO4 HClHF and H2O2 Mixed acid pickling is the final step todissolve the oxide scales in H2SO4-HF [16] H3PO4-H2SO4[17] HCl-HF [18] or HNO3-HF [19]

Prepickling plays a critical role in the industrial pro-duction process of 2205 DSS hot-rolled strips Na2SO4electrolytes can conduct electricity but they cannot dissolvethe oxides and matrix [20] H2SO4 solutions can dissolve theoxide scales and matrix [16 21] H3PO4 solutions have goodproperties of dissolving oxide scales but their costs areexpensive [22] HCl solutions can dissolve ferrous oxidesbut chloride corrosion is the big problem [18 23ndash25] HFsolutions can dissolve oxide scales and SiO2 but there is aserious intergranular corrosion problem [16 18] +e dis-solving effect of H2O2 is remarkable on the Cr-depleted layerof stainless steel but unsatisfactory on the oxide scale[26 27] After comparison H2SO4 solutions are extensivelyused in practice for their low cost and chemical stability

Pickling process can be simulated with static and dy-namic conditions at the laboratories +ere are many studies

HindawiAdvances in Materials Science and EngineeringVolume 2020 Article ID 4562418 10 pageshttpsdoiorg10115520204562418

on static pickling [16ndash26] but very few on dynamic pickling[22] +e stainless steel strips in the industrial picklingprocess are moving +erefore the studies focused on dy-namic pickling are of practical significance

+e pickling technology and mechanism are well knownfor the austenitic and ferritic stainless steels in the literaturebut there are few systematical reports focused on the picklingfor duplex stainless steel especially for DSS 2205 hot-rolledstrips With the rapid development of economy and livingstandard the demand for 2205 DSS is increasing quicklyHowever the production of 2205 DSS is restricted greatly byits pickling process It is necessary to study the pickling lawsand improve the pickling efficiency for 2205 DSS hot-rolledstrips In this work the pickling behaviour of the 2205 DSShot-rolled strip in H2SO4 electrolytes under both static anddynamic conditions was investigated +e pickling mecha-nism was discussed on the basis of mass loss and surfaceanalysis

2 Experimental

21 Materials A hot-rolled 2205 duplex stainless steel stripwith a thickness of 40mm was used as the test materials Itschemical composition is given in Table 1

22 Sample Preparation A plate of 300times 300mm was cutfrom the strip and annealed at 1140degC for 4min Afterannealing the plate was taken out from the furnace andcooled down in air +e annealed plate was subjected to sandblasting to remove its main oxides on the surface and thenwas cut into the test specimen of 5times 5mm +e specimenswere covered with epoxy resin leaving a working area of5times 5mm and cleaned with alcohol before pickling

23PicklingMeasurement Pickling tests were carried out onthe workstation as shown in Figure 1 A specimen fixed onthe rotating disk with a diameter of 15 cm was used as theworking electrode a platinum sheet as the counterelectrodeand HgHg2SO4 as the reference electrode +e analyticallypure H2SO4 ferrous sulfate iron sulfate and deionizedwater were used to prepare the electrolytes +e picklingprocesses were performed with a Princeton potentiostat(PAR 273A)

24 Electrochemical Measurement +e corrosion potentialand electrochemical impedance spectroscopy (EIS) of thetest specimens were measured during the pickling processwith a Princeton potentiostat (VMP3) Each specimen wasfixed on the cell sidewall with a 1 cm2 round hole +e testspecimen was used as the working electrode the platinumsheet was used as the counterelectrode and the HgHg2SO4was used as the reference electrode (MSE)

All test samples were immersed in the electrolytes for2min During electrolysis the electrolytic time was 81seconds with three periods For each period the specimenwas polarized anodically for 18 seconds and cathodically for9 seconds at various current densities +e pickling rate was

calculated from the mass loss of the specimen with a pre-cision of 001mg +e specimens were characterized withscanning electron microscopy (FEI Quanta 600) and Ramanspectroscopy (Renishaw inVia)

3 Results

31 Characterization of Oxide Scales In general the oxidescale of the hot-rolled 2205 DSS strip after annealing can bedivided into an inner layer and an outer layer [7] Chro-mium is rich in the inner layer while iron is rich in the outerlayer +e outer layer is consisted of Fe2O3 Fe3O4 andFeCr2O4 and the inner layer is composed mainly ofFeCr2O4 [28] +e outer layer may be partially removed bymechanical descaling +e FeCr2O4 is the oxide with aspinel structure which is insoluble in most industrial acids[7 29]

As shown in Figure 2 a few oxide scales remain on thesurface of the test specimen after shot blasting Ramanspectrum in Figure 3 indicates that the residual oxides on thesurface of 2205 DSS hot-rolled strip are composed of Fe2O3Fe3O4 and FeCr2O4 Among them the content of FeCr2O4 isthe highest as seen from its peak intensity +is implies thatthe pickling of the 2205 DSS hot-rolled strip is difficult

32 Chemical Pickling Properties under Static Conditions+e static chemical pickling of stainless steel in H2SO4solutions is mainly related with acid concentration picklingtemperature and concentration of metal ions For moststeels higher pickling temperature higher concentration ofH2SO4 solutions and lower concentration of metal ions canimprove its pickling efficiency in the initial pickling stage forits strong dissolving capacity After pickling for a certaintime the strong dissolving capacity may deteriorate picklingresult for the corrosion of matrix

Table 1 Chemical composition of 2205 DSS specimens (wt )

C Si Mn S P Cr Ni Mo N0024 062 142 0001 0024 2113 546 311 015

RDEWE

WE4

2

3

1

RECE

Electrochemicalworkstation

Figure 1 Electrolytic workstation used for dynamic pickling tests1 thermostat water bath 2 electrolyte 3 rotating disk 4specimen

2 Advances in Materials Science and Engineering

+e effect of H2SO4 concentration on static pickling rateand typical surface images of specimens at 75degC are shown inFigures 4 and 5 +e pickling efficiency has a positive cor-relation with H2SO4 concentration It can be seen that thepickling rate has a transition at about 250 g Lminus1 When theconcentration increases from 100 g Lminus1 to 250 g Lminus1 thepickling rate is accelerated slightly and many oxide scalesremain on the surface When the concentration increasesfrom 250 g Lminus1 to 450 g Lminus1 the pickling rate is acceleratedmarkedly to remove most of the oxide scales

Figure 6 gives the static pickling rates of specimens in300 g Lminus1 H2SO4 solutions at different temperatures +epickling efficiency has a positive correlation with the solu-tion temperature With the increasing temperature from50degC to 90degC the pickling rate increases gradually fromabout 174 to 128 gmminus2 minminus1 and the retained oxide scalesreduced noticeably as shown in Figure 7

+e metal ions in the H2SO4 solutions include ironchromium molybdenum nickel manganese titanium andniobium ions +e conventional metal elements in industrialH2SO4 electrolytes are shown in Table 2 Among them ironis the main element +erefore the iron ions play the mainimpact on the pickling process

+e effect of iron ions on the static pickling of thespecimen was studied in 300 g Lminus1H2SO4 solutions at 75degCand the results are given in Figure 8 +e pickling efficiencyhas a negative correlation with the concentration of ironions With increasing concentration of ferric ions from05 g Lminus1 to 60 g Lminus1 the pickling rate declines sharply at firstto less than 1 gmminus2 minminus1 and then decreases insignificantlyWith increasing concentration of ferrous ions the picklingrate decreases slowly but shows higher values in comparisonwith ferric ions+e ferric ions are an effective oxidant whichcan enhance the corrosion potential of test specimens [16]and then reduce their dissolution rate remarkably In orderto improve the pickling rate of 2205 DSS hot-rolled stripsnew sulfuric acid solutions without iron ions are necessary

33 Chemical Pickling Properties under Dynamic ConditionsIn order to see the difference between dynamic and staticpickling of hot-rolled 2205 DSS strips the rotating disk wasapplied to create the movement between specimens and acidsolutions +e variation of pickling rate of the specimen in300 g Lminus1H2SO4 solutions at 75degC with rotary speed is givenin Figure 9 +e pickling efficiency has a positive correlationwith moving speed of the specimen +e pickling rate ishigher in the dynamic cases than in the static case Howeverwith the increase of rotary speed from 5 to 20mminminus1 thepickling rate only enlarges slightly from about 75 to78 gmminus2 minminus1 It is evident that the acceleration effect ofdynamic speed is very weak

34 Electrolytic Pickling Properties under DynamicConditions +e applied polarization plays a role in picklingprocess Figure 10 gives the variation of the dynamic picklingrate at 10mminminus1 for specimens in 300 g Lminus1 H2SO4 solu-tions at 75degC with pulse current density +e pickling ratebecomes higher with increasing the pulse current densityfrom 0 to 02degA cmminus2 +e rate is about 21 times larger at

200 400 600 800 1000 1200

FeCr

2O4

Fe2O

3

Fe3O

4 F

e 2O

3

Fe2O

3

Fe3O

4

Inte

nsity

(au

)

Raman shi (cmndash1)

Figure 3 Raman spectrum for the test specimen

100 150 200 250 300 350 400 450

4

6

8

10

12

14

16

H2SO4 concentration (g Lndash1)

Wei

ght l

oss r

ate (

gmndash2

min

ndash1)

Figure 4 Variation of the static pickling rate in H2SO4 at 75degC withdifferent concentrations

Figure 2 Surface image for the test specimen

Advances in Materials Science and Engineering 3

(a) (b)

Figure 5 SEM surface images after static pickling in H2SO4 solutions at 75degC with different concentrations (a) 300 g Lminus1 and (b) 450 g Lminus1

50 55 60 65 70 75 80 85 900

2

4

6

8

10

12

14

Temperature (degC)

Wei

ght l

oss r

ate (

gmndash2

min

ndash1)

Figure 6 +e static pickling rate of the specimen in 300 g Lminus1 H2SO4 solutions at different temperatures

(a) (b)

Figure 7 SEM surface images after static pickling in 300 g Lminus1 H2SO4 solutions at temperatures 60degC (a) and 90degC (b)

4 Advances in Materials Science and Engineering

02 A cmminus2 than at 0A cmminus2 (ie the chemical pickling) +eelectrolytic pickling efficiency has a positive correlation withthe pulse current density After dynamic electrolytic pick-ling there is almost no oxide scales on the specimen surfacescompared with static electrolytic pickling With the increaseof current density from 004A cmminus2 to 02 A cmminus2 the Cr-depleted layer may dissolve obviously and the surfaces be-come smooth as shown in Figure 11

4 Discussion

+e residual oxides on the surface of the test specimen arecomposed of Fe2O3 Fe3O4 and FeCr2O4 as shown inFigure 3 While pickling of 2205 DSS hot-rolled strips inH2SO4 electrolytes it involves two processes chemicalpickling process and electrolytic pickling process

When chemical pickling is carried on for 2205 DSS FeOFe2O3 Fe3O4 and alloying elements can be dissolved inH2SO4 solutions +e chemical pickling process involves thefollowing chemical reactions [30]

FeO + H2SO4⟶ FeSO4 + H2O (1)

Fe3O4 + 4H2SO4⟶ FeSO4 + Fe2 SO4( 11138573 + 4H2O (2)

Fe2O3 + 3H2SO4⟶ Fe2 SO4( 11138573 + 3H2O (3)

Fe + H2SO4⟶ FeSO4 + H2uarr (4)

Ni + H2SO4⟶ NiSO4 + H2uarr (5)

Cr + H2SO4⟶ CrSO4 + H2uarr (6)

+e oxide scales on the test specimen are mainlycomprised of FeCr2O4 as shown in Figure 3 +e FeCr2O4 isinsoluble in sulfuric acid solution [7] +e matrix of 2205DSS is dissolved slowly in sulfuric acid solution for its ex-cellent corrosion resistance +e oxide scales on the testspecimen are dissolved very slowly in sulfuric acid solutionsby means of peeling mechanically +erefore the chemicalpickling of the 2205 DSS hot-rolled strip is very slow Formost stainless steels higher pickling temperature and sul-furic acid concentration do not increase their pickling ef-ficiency after a certain level [30] But for 2205 DSS the oxidescales still exist after chemical pickling in 450 g Lminus1 H2SO4 at90degC

Table 2 Concentration of metal ions in industrial H2SO4 solutions

Ions Fe Cr Mn Ni Cu Nb Ti MoConcentration(gL) 206 280 006 055 lt001 lt001 lt001 004

0 10 20 30 40 50 60

0

2

4

6

8

10

Concentration of metal ions (g Lndash1)

Wei

ght l

oss r

ate (

gmndash2

min

ndash1)

Fe2+Fe3+

Figure 8 +e static pickling rate in 300 g Lminus1H2SO4 solutions at75degC with different iron ions

0 5 10 15 202

3

4

5

6

7

8

9

10

Rotary speed (m minndash1)

Wei

ght l

oss r

ate (

gmndash2

min

ndash1)

Figure 9 Dynamic pickling rate in 300 g Lminus1H2SO4 solutions at75degC under different rotary speed conditions

000 004 008 012 016 020

6

8

10

12

14

16

18

20

Current density (A cmndash2)

Wei

ght l

oss r

ate (

gmndash2

min

ndash1)

Figure 10 Variation of the dynamic pickling rate with currentdensity in 300 g Lminus1H2SO4 solutions at 75degC

Advances in Materials Science and Engineering 5

At the beginning of the static chemical pickling processsmall gas bubbles nucleate and grow on the specimensurface During the pickling process more and more gasbubbles will form and adsorb on the specimen surfacewhich must reduce the contact areas of effective picklingAs for the dynamic pickling of specimens on the rotatingdisk the movement may decrease the adsorption andgrowth of gas bubbles on the specimen surface to a certainextent [31] +erefore the chemical pickling rate of theannealed 2205 DSS specimens under dynamic condition ishigher than under static condition Nevertheless the ac-celeration effect of dynamic speed is very weak with about5sim10 increase in the pickling rates as observed inFigure 8

When sulfuric acid is used as an electrolyte it canconduct electricity +e test specimen serves as the anodeand cathode with the alternative change When the testspecimen serves as the relative anode the insoluble FeCr2O4is oxidized into soluble HCrO4

minus and Cr2O72minus +e anodic

electrolytic reactions are as follows [10 30 32]

2H2O⟶ O2uarr + 4H++ 4e (7)

FeCr2O4 + 4H2O⟶ FeO + HCrO4minus

+ 7H++ 6e (8)

FeCr2O4 + 4H2O⟶ FeO + Cr2O72minus

+ 8H++ 6e (9)

2FeO3⟶ 4Fe3++ 3O2uarr + 12e (10)

When the test specimen serves as the relative cathodeCr(OH)3 and Fe(OH)3 are deposited on the surface of thetest specimen H2 is precipitated between the oxide layerswhich is beneficial to the separation of the deposited sedi-ment from the matrix+e cathodic electrolytic reactions areas follows [10 30 32]

2H2O + 2e⟶ 2OHminus+ H2uarr (11)

Fe3++ 3OHminus ⟶ Fe(OH)3darr (12)

CrO42minus

+ 4H2O + 6e⟶ Cr(OH)3darr (13)

Cr2O72minus

+ 4H2O + 6e⟶ 2Cr(OH)3darr + 8OHminus (14)

Electrolytic pickling is faster than normal chemicalpickling for most stainless steels [20] +e electrolyticpickling process in H2SO4 electrolytes is the combined effectof electrolysis and chemical pickling When the electrolyticpickling is performed under static conditions a maximum ofabout 20 of the current goes to dissolution reactionswhereas about 80 of the current is consumed in oxygen gasproduction [10] For the dense and compact oxide scales ofthe test specimens spallation or peeling of the oxide scalesinduced by gas evolution does not play a decisive role Asshown in Figure 11 the oxide scales are remained on the testspecimens after static electrolytic pickling When the

Oxide scale

(a)

Oxide scale

(b)

Oxide scale

(c)

(d) (e) (f )

Figure 11 SEM surface images after static (andashc)) and dynamic (dndashf)) pickling in 300 g Lminus1 H2SO4 solutions at 75degC with current density004A cmminus2 (a and d) 012A cmminus2 (b and e) and 02A cmminus2 (c and f)

6 Advances in Materials Science and Engineering

0 50 100 150 200 250 300 350ndash10

ndash08

ndash06

ndash04

ndash02

00

02

E we (

V)

Time (s)

No iron ions10gLndash1Fe2+

10gLndash1Fe3+

Figure 12 Corrosion potential in 300 g Lminus1H2SO4 solutions at 75degC containing different Fe ions

1 2 3 4 5 6ndash1

0

0

1

2

3

4

5

ndashZPrime

(Ω cm

2 )

Zprime(Ω cm2)

(a)

0

ndashZPrime

(Ω cm

2 )

Zprime(Ω cm2)2 4 6 8 10 12

ndash1

0

1

2

3

4

5

(b)

ndashZPrime

(Ω cm

2 )

Zprime(Ω cm2)0 100 200 300 400 500 600 700

0

100

200

300

400

500

(c)

RfRt

Cdl

Cf

Rs

(d)

Figure 13 Nyquist plots in 300 g Lminus1H2SO4 solutions at 75degC containing no ions (a) 10 g Lminus1 Fe2+ (b) and 10 g Lminus1 Fe3+ (c) and thecorresponding circuit of the impedance spectrum (d)

Advances in Materials Science and Engineering 7

electrolytic pickling is performed under dynamic conditionsthe rotary disk develops a rational way for producing activeedges efficiently where catalytic activity of the test speci-mens is improved and its pickling rate is accelerated [33 34]+e dynamic electrolytic pickling rate at 02 A cmminus2 is about21 times higher than the chemical pickling which may giverise to a smooth specimen surface without oxide scales

+e Fe3+ ions are an effective oxidant which enhancedthe corrosion potential as shown in Figure 12 When no Feions were added in the H2SO4 solutions the corrosionpotential quickly declined at the beginning of the immersiontime after about 50 s it remained constant (approximatelyminus075 VMSE) subsequently as the immersion time increasedWhen 10 g Lminus1 Fe2+ was added in the H2SO4 solutions thecorrosion potential quickly declined at the beginning of theimmersion time after about 100 s it remained unchangedWhen 10 g Lminus1 Fe3+ was added in the H2SO4 solutions thecorrosion potential increased slowly from 0062 VMSE to0137 VMSE as the immersion time increased +e EISNyquist plots recorded on the test specimens immersed in300 g Lminus1 H2SO4 solutions containing no ions 10 g Lminus1 Fe2+and 10 g Lminus1 Fe3+ under the Ecorr conditions (ie the freecorrosion states) is presented in Figure 13 +e semicirclesize enlarged slightly with the addition of 10 g Lminus1 Fe 2+ butincreased noticeably with the addition of the 10 g Lminus1 Fe 3+

for its high impedanceIn order to show the dissolution process for the speci-

mens in 300 g Lminus1H2SO4 solutions at 75degC containing dif-ferent Fe ions the equivalent circuit model is proposed inFigure 13(d) according to the EIS features in Figure 13 Rs isthe electrolyte resistance Rf is the resistance of oxide layerremained on the specimens Rt is the charge transfer re-sistance Cf and Cdl can be replaced with constant phaseelement (CPE) [35] +e impedance of CPE is written inequation (15) where Y0 is the admittance magnitude of CPEand α is the exponential term Table 3 gives the fitted resultsof EIS spectra +e calculated spectra are shown as a solidcurve in Figure 13 which fit the experimental data very wellIt can be concluded that the model provided a reliabledescription for the corrosion systems

ZCPE 1

Y0(jω)α (15)

5 Application and Performance

According to the abovementioned results the picklingprocess of hot-rolled 2205 DSS is optimized through thehigh H2SO4 concentration high solution temperature andproper electrolysis current density in the industrial pre-pickling of 2205 DSS hot-rolled strips +e pickling effi-ciency is improved remarkably which increases the

production rate from 5ndash8mminminus1 to 15ndash18mminminus1 Be-sides the surface finish after pickling is notably enhanced asshown in Figure 14

6 Conclusion

+e pickling behaviour of hot-rolled 2205 DSS withannealing and mechanical descaling treatments in H2SO4solutions under both static and dynamic conditions has ledto the following conclusions

(1) In the static chemical pickling process the picklingrate may be accelerated noticeably by increasing thesolution temperature and H2SO4 concentration butbe decelerated greatly by Fe3+ ions

(2) +e chemical pickling process can be enhancedweakly by the moving speed of the specimen from 0to 20mminminus1 because the movement decreases theadsorption and growth of gas bubbles on the spec-imen surface to a certain extent

(3) Under dynamic conditions the electrolytic picklingrate increases markedly with changing the pulsecurrent density from 004 to 02Acmminus2 +e electro-lytic pickling rate at 02A cmminus2 is about 21 times largerthan the chemical pickling rate in 300 g Lminus1H2SO4 at75degC resulting in the smooth and clean specimensurfaces

Data Availability

+e tables and figures data used to support the findings ofthis study are available from the corresponding author uponreasonable request

Conflicts of Interest

+e authors declare that there are no conflicts of interestregarding the publication of this paper

Table 3 Fitted results for EIS spectra in 300 g Lminus1H2SO4 solutions at 75degC containing different ions

Ions Rs Ω cm2 Y0-f Sα Ωminus1 cmminus2 αf Rf Ω cm2 Y0-dl Sα Ωminus1 cmminus2 αdl Rt Ω cm2

No ions 082 000218 087 280 00658 092 1610 g Lminus1 Fe2+ 094 000185 096 314 0093 084 1010 g Lminus1 Fe3+ 104 0000133 095 5499 0000281 068 706

Figure 14 Optical surface of the 2205 DSS hot-rolled strip afterindustrial pickling with optimized pickling process

8 Advances in Materials Science and Engineering

Acknowledgments

+e authors gratefully acknowledge the financial supportfrom the National Natural Science Foundation of China(Grant nos U1660205 and U1960103)

References

[1] Y-Y Wu and F Presuel-Moreno ldquoChloride levels that ini-tiated corrosion of duplex stainless steel embedded in mor-tarrdquo Advances in Materials Science and Engineering vol 2019Article ID 6949176 6 pages 2019

[2] T Li Y Zhang L Gao and Y Zhang ldquoOptimization ofFCAWparameters for ferrite content in 2205 DSS welds basedon the taguchi design methodrdquo Advances in Materials Scienceand Engineering vol 2018 Article ID 7950607 7 pages 2018

[3] Q Meng P La L Yao P Zhang Y Wei and X Guo ldquoEffectof Al onmicrostructure and properties of hot-rolled 2205 dualstainless steelrdquo Advances in Materials Science and Engineer-ing vol 2016 Article ID 7518067 8 pages 2016

[4] Z-g Song H Feng and S-m Hu ldquoDevelopment of Chineseduplex stainless steel in recent yearsrdquo Journal of Iron and SteelResearch International vol 24 no 2 pp 121ndash130 2017

[5] Z Y Liu C F Dong X G Li Q Zhi and Y F Cheng ldquoStresscorrosion cracking of 2205 duplex stainless steel in H2S-CO2environmentrdquo Journal of Materials Science vol 44 no 16pp 4228ndash4234 2009

[6] R N Gun Duplex Stainless Steels Vol 1 Abington Pub-lishing Cambridge UK 1994

[7] L-F Li Z-H Jiang and Y Riquier ldquoHigh-temperatureoxidation of duplex stainless steels in air and mixed gas of airand CH4rdquo Corrosion Science vol 47 no 1 pp 57ndash68 2005

[8] J G Peng M C Li S Z Luo et al ldquoOxidation characteristicsof duplex stainless steel 2205 in simulated combustion at-mosphererdquo Materials Research Innovation vol 19 no suppl5 pp 245ndash249 2015

[9] J G Peng and M C Li ldquoHigh temperature oxidation be-haviour of DSS 2205 in humid airrdquo Advanced MaterialsResearch vol 900 pp 673ndash676 2014

[10] N Ipek B Holm R Pettersson G Runnsjo and M KarlssonldquoElectrolytic pickling of duplex stainless steelrdquo Materials andCorrosion vol 56 no 8 pp 521ndash532 2005

[11] J G Peng S Z Luo andW B Dong ldquoStudy on the simulatedpickling of 443NT medium chrome ferritic stainless steelrdquoBaosteel Technical Research vol 4 no 1 pp pp50ndash52 2010

[12] L-F Li M Daerden P Caenen and J-P Celis ldquoElectro-chemical behavior of hot-rolled 304 stainless steel duringchemical pickling in HCl-based electrolytesrdquo Journal of 3eElectrochemical Society vol 153 no 5 pp B145ndashB150 2006

[13] J Hilden J Virtanen O Forsen and J Aromaa ldquoElectrolyticpickling of stainless steel studied by electrochemical polar-isation and DC resistance measurements combined withsurface analysisrdquo Electrochimica Acta vol 46 no 24-25pp 3859ndash3866 2001

[14] L-F Li P Caenen and M-F Jiang ldquoElectrolytic pickling ofthe oxide layer on hot-rolled 304 stainless steel in sodiumsulphaterdquo Corrosion Science vol 50 no 10 pp 2824ndash28302008

[15] W G Chen Y Q Chen and H L Pang ldquoStudy of Na2SO4electrolytic pickling process on 304 stainless steelrdquo ChinaMetallurgy vol 19 no 1 pp 16ndash23 2009

[16] L-F Li P Caenen and J-P Celis ldquoChemical pickling of 304stainless steel in fluoride- and sulfate-containing acidic

electrolytesrdquo Journal of 3e Electrochemical Society vol 152no 9 pp B352ndashB357 2005

[17] C A Huang and C C Hsu ldquo+e electrochemical polishingbehaviour of duplex stainless steel (SAF 2205) in phos-phoric-sulfuric mixed acidsrdquo International Journal of Ad-vance Manufacture Technology vol 34 no 9-10pp 904ndash910 2007

[18] L-F Li P Caenen M Daerden et al ldquoMechanism of singleand multiple step pickling of 304 stainless steel in acidelectrolytesrdquo Corrosion Science vol 47 no 5 pp 1307ndash13242005

[19] B S Covino J V Scalera T J Driscoll and J P CarterldquoDissolution behavior of 304 stainless steel in HNO3HFmixturesrdquo Metallurgical Transactions A vol 17 no 1pp 137ndash149 1986

[20] N Ipek N Lior M Vynnycky and F H Bark ldquoNumericaland experimental study of the effect of gas evolution inelectrolytic picklingrdquo Journal of Applied Electrochemistryvol 36 no 12 pp 1367ndash1379 2006

[21] M Abdallah ldquoGuar gum as corrosion inhibitor for carbonsteel in sulfuric acid solutionsrdquo Portugaliae ElectrochimicaActa vol 22 no 2 pp 161ndash175 2004

[22] C A Huang J H Chang W J Zhao et al ldquoExamination ofthe electropolishing behaviour of 73 brass in a 70 H3PO4solution using a rotating disc electroderdquo Materials Chemistryand Physics vol 146 no 3 pp 230ndash239 2014

[23] Q Xie P-y Shi C-j Liu M-f Jiang et al ldquoEffects of differentoxidants on HCl-based pickling process of 430 stainless steelrdquoJournal of Iron and Steel Research International vol 23 no 8pp 778ndash783 2016

[24] W H Hao L Y Qin and D L Liu ldquo+e effect of hydro-chloric acid concentration on pickling of duplex stainlesssteelrdquo Corrosion Protection vol 33 no suppl 2 pp 69ndash712012

[25] H Y Li and A C Zhao ldquoPickling behaviour of duplexstainless steel 2205 in hydrochloric acid solutionrdquoAdvances inMaterials Science and Engineering vol 2018 Article ID9754528 6 pages 2018

[26] C J Brown ldquoProcess and apparatus for recovery of peroxidecontaining pickling solutionsrdquo International Patent PCTCA0201598 2002

[27] R Jiang G Zou W Shi Y Liang and S Xiang ldquoCorrosionbehavior of plasma-nitrided 904L austenitic stainless steel inhydrofluoric acidrdquo Journal of Materials Engineering andPerformance vol 28 no 3 pp 1863ndash1872 2019

[28] C Donik A Kocijan J T Grant M Jenko A Drenik andB Pihlar ldquoXPS study of duplex stainless steel oxidized byoxygen atomsrdquo Corrosion Science vol 51 no 4 pp 827ndash8322009

[29] Y Xu Q Jin J Li X Xiao X Zhang and L Jiang ldquoOxidationinduced phase transformation of duplex stainless steel 25Cr-10Mn-2Ni-3Mo-08W-08Cu-05Nrdquo Corrosion Sciencevol 55 pp 233ndash237 2012

[30] ASM Handbook Committee ASM Handbook Volume 5Surface Engineering ASM International Cleveland OH USA2007

[31] J Eigeldinger and H Vogt ldquo+e bubble coverage of gas-evolving electrodes in a flowing electrolyterdquo ElectrochimicaActa vol 45 no 27 pp 4449ndash4456 2000

[32] M Pourbaix Atlas of Electrochemical Equilibria in AqueousSolutions Pergamon Press Oxford UK 2nd edition 1966

[33] Z G Wang H-H H Wu Q Li et al ldquoReversing interfacialcatalysis of ambipolar WSe2 single crystalrdquo Advanced Sciencevol 7 Article ID 1901382 pp 1ndash9 2019

Advances in Materials Science and Engineering 9

[34] Z Wang Q Li H Xu et al ldquoControllable etching of MoS2basal planes for enhanced hydrogen evolution through theformation of active edge sitesrdquo Nano Energy vol 49pp 634ndash643 2018

[35] M C Li C L Zeng S Z Luo J N Shen H C Lin andC N Cao ldquoElectrochemical corrosion characteristics of type316 stainless steel in simulated anode environment forPEMFCrdquo Electrochimica Acta vol 48 no 12 pp 1735ndash17412003

10 Advances in Materials Science and Engineering

+e effect of H2SO4 concentration on static pickling rateand typical surface images of specimens at 75degC are shown inFigures 4 and 5 +e pickling efficiency has a positive cor-relation with H2SO4 concentration It can be seen that thepickling rate has a transition at about 250 g Lminus1 When theconcentration increases from 100 g Lminus1 to 250 g Lminus1 thepickling rate is accelerated slightly and many oxide scalesremain on the surface When the concentration increasesfrom 250 g Lminus1 to 450 g Lminus1 the pickling rate is acceleratedmarkedly to remove most of the oxide scales

Figure 6 gives the static pickling rates of specimens in300 g Lminus1 H2SO4 solutions at different temperatures +epickling efficiency has a positive correlation with the solu-tion temperature With the increasing temperature from50degC to 90degC the pickling rate increases gradually fromabout 174 to 128 gmminus2 minminus1 and the retained oxide scalesreduced noticeably as shown in Figure 7

+e metal ions in the H2SO4 solutions include ironchromium molybdenum nickel manganese titanium andniobium ions +e conventional metal elements in industrialH2SO4 electrolytes are shown in Table 2 Among them ironis the main element +erefore the iron ions play the mainimpact on the pickling process

+e effect of iron ions on the static pickling of thespecimen was studied in 300 g Lminus1H2SO4 solutions at 75degCand the results are given in Figure 8 +e pickling efficiencyhas a negative correlation with the concentration of ironions With increasing concentration of ferric ions from05 g Lminus1 to 60 g Lminus1 the pickling rate declines sharply at firstto less than 1 gmminus2 minminus1 and then decreases insignificantlyWith increasing concentration of ferrous ions the picklingrate decreases slowly but shows higher values in comparisonwith ferric ions+e ferric ions are an effective oxidant whichcan enhance the corrosion potential of test specimens [16]and then reduce their dissolution rate remarkably In orderto improve the pickling rate of 2205 DSS hot-rolled stripsnew sulfuric acid solutions without iron ions are necessary

33 Chemical Pickling Properties under Dynamic ConditionsIn order to see the difference between dynamic and staticpickling of hot-rolled 2205 DSS strips the rotating disk wasapplied to create the movement between specimens and acidsolutions +e variation of pickling rate of the specimen in300 g Lminus1H2SO4 solutions at 75degC with rotary speed is givenin Figure 9 +e pickling efficiency has a positive correlationwith moving speed of the specimen +e pickling rate ishigher in the dynamic cases than in the static case Howeverwith the increase of rotary speed from 5 to 20mminminus1 thepickling rate only enlarges slightly from about 75 to78 gmminus2 minminus1 It is evident that the acceleration effect ofdynamic speed is very weak

34 Electrolytic Pickling Properties under DynamicConditions +e applied polarization plays a role in picklingprocess Figure 10 gives the variation of the dynamic picklingrate at 10mminminus1 for specimens in 300 g Lminus1 H2SO4 solu-tions at 75degC with pulse current density +e pickling ratebecomes higher with increasing the pulse current densityfrom 0 to 02degA cmminus2 +e rate is about 21 times larger at

200 400 600 800 1000 1200

FeCr

2O4

Fe2O

3

Fe3O

4 F

e 2O

3

Fe2O

3

Fe3O

4

Inte

nsity

(au

)

Raman shi (cmndash1)

Figure 3 Raman spectrum for the test specimen

100 150 200 250 300 350 400 450

4

6

8

10

12

14

16

H2SO4 concentration (g Lndash1)

Wei

ght l

oss r

ate (

gmndash2

min

ndash1)

Figure 4 Variation of the static pickling rate in H2SO4 at 75degC withdifferent concentrations

Figure 2 Surface image for the test specimen

Advances in Materials Science and Engineering 3

(a) (b)

Figure 5 SEM surface images after static pickling in H2SO4 solutions at 75degC with different concentrations (a) 300 g Lminus1 and (b) 450 g Lminus1

50 55 60 65 70 75 80 85 900

2

4

6

8

10

12

14

Temperature (degC)

Wei

ght l

oss r

ate (

gmndash2

min

ndash1)

Figure 6 +e static pickling rate of the specimen in 300 g Lminus1 H2SO4 solutions at different temperatures

(a) (b)

Figure 7 SEM surface images after static pickling in 300 g Lminus1 H2SO4 solutions at temperatures 60degC (a) and 90degC (b)

4 Advances in Materials Science and Engineering

02 A cmminus2 than at 0A cmminus2 (ie the chemical pickling) +eelectrolytic pickling efficiency has a positive correlation withthe pulse current density After dynamic electrolytic pick-ling there is almost no oxide scales on the specimen surfacescompared with static electrolytic pickling With the increaseof current density from 004A cmminus2 to 02 A cmminus2 the Cr-depleted layer may dissolve obviously and the surfaces be-come smooth as shown in Figure 11

4 Discussion

+e residual oxides on the surface of the test specimen arecomposed of Fe2O3 Fe3O4 and FeCr2O4 as shown inFigure 3 While pickling of 2205 DSS hot-rolled strips inH2SO4 electrolytes it involves two processes chemicalpickling process and electrolytic pickling process

When chemical pickling is carried on for 2205 DSS FeOFe2O3 Fe3O4 and alloying elements can be dissolved inH2SO4 solutions +e chemical pickling process involves thefollowing chemical reactions [30]

FeO + H2SO4⟶ FeSO4 + H2O (1)

Fe3O4 + 4H2SO4⟶ FeSO4 + Fe2 SO4( 11138573 + 4H2O (2)

Fe2O3 + 3H2SO4⟶ Fe2 SO4( 11138573 + 3H2O (3)

Fe + H2SO4⟶ FeSO4 + H2uarr (4)

Ni + H2SO4⟶ NiSO4 + H2uarr (5)

Cr + H2SO4⟶ CrSO4 + H2uarr (6)

+e oxide scales on the test specimen are mainlycomprised of FeCr2O4 as shown in Figure 3 +e FeCr2O4 isinsoluble in sulfuric acid solution [7] +e matrix of 2205DSS is dissolved slowly in sulfuric acid solution for its ex-cellent corrosion resistance +e oxide scales on the testspecimen are dissolved very slowly in sulfuric acid solutionsby means of peeling mechanically +erefore the chemicalpickling of the 2205 DSS hot-rolled strip is very slow Formost stainless steels higher pickling temperature and sul-furic acid concentration do not increase their pickling ef-ficiency after a certain level [30] But for 2205 DSS the oxidescales still exist after chemical pickling in 450 g Lminus1 H2SO4 at90degC

Table 2 Concentration of metal ions in industrial H2SO4 solutions

Ions Fe Cr Mn Ni Cu Nb Ti MoConcentration(gL) 206 280 006 055 lt001 lt001 lt001 004

0 10 20 30 40 50 60

0

2

4

6

8

10

Concentration of metal ions (g Lndash1)

Wei

ght l

oss r

ate (

gmndash2

min

ndash1)

Fe2+Fe3+

Figure 8 +e static pickling rate in 300 g Lminus1H2SO4 solutions at75degC with different iron ions

0 5 10 15 202

3

4

5

6

7

8

9

10

Rotary speed (m minndash1)

Wei

ght l

oss r

ate (

gmndash2

min

ndash1)

Figure 9 Dynamic pickling rate in 300 g Lminus1H2SO4 solutions at75degC under different rotary speed conditions

000 004 008 012 016 020

6

8

10

12

14

16

18

20

Current density (A cmndash2)

Wei

ght l

oss r

ate (

gmndash2

min

ndash1)

Figure 10 Variation of the dynamic pickling rate with currentdensity in 300 g Lminus1H2SO4 solutions at 75degC

Advances in Materials Science and Engineering 5

At the beginning of the static chemical pickling processsmall gas bubbles nucleate and grow on the specimensurface During the pickling process more and more gasbubbles will form and adsorb on the specimen surfacewhich must reduce the contact areas of effective picklingAs for the dynamic pickling of specimens on the rotatingdisk the movement may decrease the adsorption andgrowth of gas bubbles on the specimen surface to a certainextent [31] +erefore the chemical pickling rate of theannealed 2205 DSS specimens under dynamic condition ishigher than under static condition Nevertheless the ac-celeration effect of dynamic speed is very weak with about5sim10 increase in the pickling rates as observed inFigure 8

When sulfuric acid is used as an electrolyte it canconduct electricity +e test specimen serves as the anodeand cathode with the alternative change When the testspecimen serves as the relative anode the insoluble FeCr2O4is oxidized into soluble HCrO4

minus and Cr2O72minus +e anodic

electrolytic reactions are as follows [10 30 32]

2H2O⟶ O2uarr + 4H++ 4e (7)

FeCr2O4 + 4H2O⟶ FeO + HCrO4minus

+ 7H++ 6e (8)

FeCr2O4 + 4H2O⟶ FeO + Cr2O72minus

+ 8H++ 6e (9)

2FeO3⟶ 4Fe3++ 3O2uarr + 12e (10)

When the test specimen serves as the relative cathodeCr(OH)3 and Fe(OH)3 are deposited on the surface of thetest specimen H2 is precipitated between the oxide layerswhich is beneficial to the separation of the deposited sedi-ment from the matrix+e cathodic electrolytic reactions areas follows [10 30 32]

2H2O + 2e⟶ 2OHminus+ H2uarr (11)

Fe3++ 3OHminus ⟶ Fe(OH)3darr (12)

CrO42minus

+ 4H2O + 6e⟶ Cr(OH)3darr (13)

Cr2O72minus

+ 4H2O + 6e⟶ 2Cr(OH)3darr + 8OHminus (14)

Electrolytic pickling is faster than normal chemicalpickling for most stainless steels [20] +e electrolyticpickling process in H2SO4 electrolytes is the combined effectof electrolysis and chemical pickling When the electrolyticpickling is performed under static conditions a maximum ofabout 20 of the current goes to dissolution reactionswhereas about 80 of the current is consumed in oxygen gasproduction [10] For the dense and compact oxide scales ofthe test specimens spallation or peeling of the oxide scalesinduced by gas evolution does not play a decisive role Asshown in Figure 11 the oxide scales are remained on the testspecimens after static electrolytic pickling When the

Oxide scale

(a)

Oxide scale

(b)

Oxide scale

(c)

(d) (e) (f )

Figure 11 SEM surface images after static (andashc)) and dynamic (dndashf)) pickling in 300 g Lminus1 H2SO4 solutions at 75degC with current density004A cmminus2 (a and d) 012A cmminus2 (b and e) and 02A cmminus2 (c and f)

6 Advances in Materials Science and Engineering

0 50 100 150 200 250 300 350ndash10

ndash08

ndash06

ndash04

ndash02

00

02

E we (

V)

Time (s)

No iron ions10gLndash1Fe2+

10gLndash1Fe3+

Figure 12 Corrosion potential in 300 g Lminus1H2SO4 solutions at 75degC containing different Fe ions

1 2 3 4 5 6ndash1

0

0

1

2

3

4

5

ndashZPrime

(Ω cm

2 )

Zprime(Ω cm2)

(a)

0

ndashZPrime

(Ω cm

2 )

Zprime(Ω cm2)2 4 6 8 10 12

ndash1

0

1

2

3

4

5

(b)

ndashZPrime

(Ω cm

2 )

Zprime(Ω cm2)0 100 200 300 400 500 600 700

0

100

200

300

400

500

(c)

RfRt

Cdl

Cf

Rs

(d)

Figure 13 Nyquist plots in 300 g Lminus1H2SO4 solutions at 75degC containing no ions (a) 10 g Lminus1 Fe2+ (b) and 10 g Lminus1 Fe3+ (c) and thecorresponding circuit of the impedance spectrum (d)

Advances in Materials Science and Engineering 7

electrolytic pickling is performed under dynamic conditionsthe rotary disk develops a rational way for producing activeedges efficiently where catalytic activity of the test speci-mens is improved and its pickling rate is accelerated [33 34]+e dynamic electrolytic pickling rate at 02 A cmminus2 is about21 times higher than the chemical pickling which may giverise to a smooth specimen surface without oxide scales

+e Fe3+ ions are an effective oxidant which enhancedthe corrosion potential as shown in Figure 12 When no Feions were added in the H2SO4 solutions the corrosionpotential quickly declined at the beginning of the immersiontime after about 50 s it remained constant (approximatelyminus075 VMSE) subsequently as the immersion time increasedWhen 10 g Lminus1 Fe2+ was added in the H2SO4 solutions thecorrosion potential quickly declined at the beginning of theimmersion time after about 100 s it remained unchangedWhen 10 g Lminus1 Fe3+ was added in the H2SO4 solutions thecorrosion potential increased slowly from 0062 VMSE to0137 VMSE as the immersion time increased +e EISNyquist plots recorded on the test specimens immersed in300 g Lminus1 H2SO4 solutions containing no ions 10 g Lminus1 Fe2+and 10 g Lminus1 Fe3+ under the Ecorr conditions (ie the freecorrosion states) is presented in Figure 13 +e semicirclesize enlarged slightly with the addition of 10 g Lminus1 Fe 2+ butincreased noticeably with the addition of the 10 g Lminus1 Fe 3+

for its high impedanceIn order to show the dissolution process for the speci-

mens in 300 g Lminus1H2SO4 solutions at 75degC containing dif-ferent Fe ions the equivalent circuit model is proposed inFigure 13(d) according to the EIS features in Figure 13 Rs isthe electrolyte resistance Rf is the resistance of oxide layerremained on the specimens Rt is the charge transfer re-sistance Cf and Cdl can be replaced with constant phaseelement (CPE) [35] +e impedance of CPE is written inequation (15) where Y0 is the admittance magnitude of CPEand α is the exponential term Table 3 gives the fitted resultsof EIS spectra +e calculated spectra are shown as a solidcurve in Figure 13 which fit the experimental data very wellIt can be concluded that the model provided a reliabledescription for the corrosion systems

ZCPE 1

Y0(jω)α (15)

5 Application and Performance

According to the abovementioned results the picklingprocess of hot-rolled 2205 DSS is optimized through thehigh H2SO4 concentration high solution temperature andproper electrolysis current density in the industrial pre-pickling of 2205 DSS hot-rolled strips +e pickling effi-ciency is improved remarkably which increases the

production rate from 5ndash8mminminus1 to 15ndash18mminminus1 Be-sides the surface finish after pickling is notably enhanced asshown in Figure 14

6 Conclusion

+e pickling behaviour of hot-rolled 2205 DSS withannealing and mechanical descaling treatments in H2SO4solutions under both static and dynamic conditions has ledto the following conclusions

(1) In the static chemical pickling process the picklingrate may be accelerated noticeably by increasing thesolution temperature and H2SO4 concentration butbe decelerated greatly by Fe3+ ions

(2) +e chemical pickling process can be enhancedweakly by the moving speed of the specimen from 0to 20mminminus1 because the movement decreases theadsorption and growth of gas bubbles on the spec-imen surface to a certain extent

(3) Under dynamic conditions the electrolytic picklingrate increases markedly with changing the pulsecurrent density from 004 to 02Acmminus2 +e electro-lytic pickling rate at 02A cmminus2 is about 21 times largerthan the chemical pickling rate in 300 g Lminus1H2SO4 at75degC resulting in the smooth and clean specimensurfaces

Data Availability

+e tables and figures data used to support the findings ofthis study are available from the corresponding author uponreasonable request

Conflicts of Interest

+e authors declare that there are no conflicts of interestregarding the publication of this paper

Table 3 Fitted results for EIS spectra in 300 g Lminus1H2SO4 solutions at 75degC containing different ions

Ions Rs Ω cm2 Y0-f Sα Ωminus1 cmminus2 αf Rf Ω cm2 Y0-dl Sα Ωminus1 cmminus2 αdl Rt Ω cm2

No ions 082 000218 087 280 00658 092 1610 g Lminus1 Fe2+ 094 000185 096 314 0093 084 1010 g Lminus1 Fe3+ 104 0000133 095 5499 0000281 068 706

Figure 14 Optical surface of the 2205 DSS hot-rolled strip afterindustrial pickling with optimized pickling process

8 Advances in Materials Science and Engineering

Acknowledgments

+e authors gratefully acknowledge the financial supportfrom the National Natural Science Foundation of China(Grant nos U1660205 and U1960103)

References

[1] Y-Y Wu and F Presuel-Moreno ldquoChloride levels that ini-tiated corrosion of duplex stainless steel embedded in mor-tarrdquo Advances in Materials Science and Engineering vol 2019Article ID 6949176 6 pages 2019

[2] T Li Y Zhang L Gao and Y Zhang ldquoOptimization ofFCAWparameters for ferrite content in 2205 DSS welds basedon the taguchi design methodrdquo Advances in Materials Scienceand Engineering vol 2018 Article ID 7950607 7 pages 2018

[3] Q Meng P La L Yao P Zhang Y Wei and X Guo ldquoEffectof Al onmicrostructure and properties of hot-rolled 2205 dualstainless steelrdquo Advances in Materials Science and Engineer-ing vol 2016 Article ID 7518067 8 pages 2016

[4] Z-g Song H Feng and S-m Hu ldquoDevelopment of Chineseduplex stainless steel in recent yearsrdquo Journal of Iron and SteelResearch International vol 24 no 2 pp 121ndash130 2017

[5] Z Y Liu C F Dong X G Li Q Zhi and Y F Cheng ldquoStresscorrosion cracking of 2205 duplex stainless steel in H2S-CO2environmentrdquo Journal of Materials Science vol 44 no 16pp 4228ndash4234 2009

[6] R N Gun Duplex Stainless Steels Vol 1 Abington Pub-lishing Cambridge UK 1994

[7] L-F Li Z-H Jiang and Y Riquier ldquoHigh-temperatureoxidation of duplex stainless steels in air and mixed gas of airand CH4rdquo Corrosion Science vol 47 no 1 pp 57ndash68 2005

[8] J G Peng M C Li S Z Luo et al ldquoOxidation characteristicsof duplex stainless steel 2205 in simulated combustion at-mosphererdquo Materials Research Innovation vol 19 no suppl5 pp 245ndash249 2015

[9] J G Peng and M C Li ldquoHigh temperature oxidation be-haviour of DSS 2205 in humid airrdquo Advanced MaterialsResearch vol 900 pp 673ndash676 2014

[10] N Ipek B Holm R Pettersson G Runnsjo and M KarlssonldquoElectrolytic pickling of duplex stainless steelrdquo Materials andCorrosion vol 56 no 8 pp 521ndash532 2005

[11] J G Peng S Z Luo andW B Dong ldquoStudy on the simulatedpickling of 443NT medium chrome ferritic stainless steelrdquoBaosteel Technical Research vol 4 no 1 pp pp50ndash52 2010

[12] L-F Li M Daerden P Caenen and J-P Celis ldquoElectro-chemical behavior of hot-rolled 304 stainless steel duringchemical pickling in HCl-based electrolytesrdquo Journal of 3eElectrochemical Society vol 153 no 5 pp B145ndashB150 2006

[13] J Hilden J Virtanen O Forsen and J Aromaa ldquoElectrolyticpickling of stainless steel studied by electrochemical polar-isation and DC resistance measurements combined withsurface analysisrdquo Electrochimica Acta vol 46 no 24-25pp 3859ndash3866 2001

[14] L-F Li P Caenen and M-F Jiang ldquoElectrolytic pickling ofthe oxide layer on hot-rolled 304 stainless steel in sodiumsulphaterdquo Corrosion Science vol 50 no 10 pp 2824ndash28302008

[15] W G Chen Y Q Chen and H L Pang ldquoStudy of Na2SO4electrolytic pickling process on 304 stainless steelrdquo ChinaMetallurgy vol 19 no 1 pp 16ndash23 2009

[16] L-F Li P Caenen and J-P Celis ldquoChemical pickling of 304stainless steel in fluoride- and sulfate-containing acidic

electrolytesrdquo Journal of 3e Electrochemical Society vol 152no 9 pp B352ndashB357 2005

[17] C A Huang and C C Hsu ldquo+e electrochemical polishingbehaviour of duplex stainless steel (SAF 2205) in phos-phoric-sulfuric mixed acidsrdquo International Journal of Ad-vance Manufacture Technology vol 34 no 9-10pp 904ndash910 2007

[18] L-F Li P Caenen M Daerden et al ldquoMechanism of singleand multiple step pickling of 304 stainless steel in acidelectrolytesrdquo Corrosion Science vol 47 no 5 pp 1307ndash13242005

[19] B S Covino J V Scalera T J Driscoll and J P CarterldquoDissolution behavior of 304 stainless steel in HNO3HFmixturesrdquo Metallurgical Transactions A vol 17 no 1pp 137ndash149 1986

[20] N Ipek N Lior M Vynnycky and F H Bark ldquoNumericaland experimental study of the effect of gas evolution inelectrolytic picklingrdquo Journal of Applied Electrochemistryvol 36 no 12 pp 1367ndash1379 2006

[21] M Abdallah ldquoGuar gum as corrosion inhibitor for carbonsteel in sulfuric acid solutionsrdquo Portugaliae ElectrochimicaActa vol 22 no 2 pp 161ndash175 2004

[22] C A Huang J H Chang W J Zhao et al ldquoExamination ofthe electropolishing behaviour of 73 brass in a 70 H3PO4solution using a rotating disc electroderdquo Materials Chemistryand Physics vol 146 no 3 pp 230ndash239 2014

[23] Q Xie P-y Shi C-j Liu M-f Jiang et al ldquoEffects of differentoxidants on HCl-based pickling process of 430 stainless steelrdquoJournal of Iron and Steel Research International vol 23 no 8pp 778ndash783 2016

[24] W H Hao L Y Qin and D L Liu ldquo+e effect of hydro-chloric acid concentration on pickling of duplex stainlesssteelrdquo Corrosion Protection vol 33 no suppl 2 pp 69ndash712012

[25] H Y Li and A C Zhao ldquoPickling behaviour of duplexstainless steel 2205 in hydrochloric acid solutionrdquoAdvances inMaterials Science and Engineering vol 2018 Article ID9754528 6 pages 2018

[26] C J Brown ldquoProcess and apparatus for recovery of peroxidecontaining pickling solutionsrdquo International Patent PCTCA0201598 2002

[27] R Jiang G Zou W Shi Y Liang and S Xiang ldquoCorrosionbehavior of plasma-nitrided 904L austenitic stainless steel inhydrofluoric acidrdquo Journal of Materials Engineering andPerformance vol 28 no 3 pp 1863ndash1872 2019

[28] C Donik A Kocijan J T Grant M Jenko A Drenik andB Pihlar ldquoXPS study of duplex stainless steel oxidized byoxygen atomsrdquo Corrosion Science vol 51 no 4 pp 827ndash8322009

[29] Y Xu Q Jin J Li X Xiao X Zhang and L Jiang ldquoOxidationinduced phase transformation of duplex stainless steel 25Cr-10Mn-2Ni-3Mo-08W-08Cu-05Nrdquo Corrosion Sciencevol 55 pp 233ndash237 2012

[30] ASM Handbook Committee ASM Handbook Volume 5Surface Engineering ASM International Cleveland OH USA2007

[31] J Eigeldinger and H Vogt ldquo+e bubble coverage of gas-evolving electrodes in a flowing electrolyterdquo ElectrochimicaActa vol 45 no 27 pp 4449ndash4456 2000

[32] M Pourbaix Atlas of Electrochemical Equilibria in AqueousSolutions Pergamon Press Oxford UK 2nd edition 1966

[33] Z G Wang H-H H Wu Q Li et al ldquoReversing interfacialcatalysis of ambipolar WSe2 single crystalrdquo Advanced Sciencevol 7 Article ID 1901382 pp 1ndash9 2019

Advances in Materials Science and Engineering 9

[34] Z Wang Q Li H Xu et al ldquoControllable etching of MoS2basal planes for enhanced hydrogen evolution through theformation of active edge sitesrdquo Nano Energy vol 49pp 634ndash643 2018

[35] M C Li C L Zeng S Z Luo J N Shen H C Lin andC N Cao ldquoElectrochemical corrosion characteristics of type316 stainless steel in simulated anode environment forPEMFCrdquo Electrochimica Acta vol 48 no 12 pp 1735ndash17412003

10 Advances in Materials Science and Engineering

(a) (b)

Figure 5 SEM surface images after static pickling in H2SO4 solutions at 75degC with different concentrations (a) 300 g Lminus1 and (b) 450 g Lminus1

50 55 60 65 70 75 80 85 900

2

4

6

8

10

12

14

Temperature (degC)

Wei

ght l

oss r

ate (

gmndash2

min

ndash1)

Figure 6 +e static pickling rate of the specimen in 300 g Lminus1 H2SO4 solutions at different temperatures

(a) (b)

Figure 7 SEM surface images after static pickling in 300 g Lminus1 H2SO4 solutions at temperatures 60degC (a) and 90degC (b)

4 Advances in Materials Science and Engineering

02 A cmminus2 than at 0A cmminus2 (ie the chemical pickling) +eelectrolytic pickling efficiency has a positive correlation withthe pulse current density After dynamic electrolytic pick-ling there is almost no oxide scales on the specimen surfacescompared with static electrolytic pickling With the increaseof current density from 004A cmminus2 to 02 A cmminus2 the Cr-depleted layer may dissolve obviously and the surfaces be-come smooth as shown in Figure 11

4 Discussion

+e residual oxides on the surface of the test specimen arecomposed of Fe2O3 Fe3O4 and FeCr2O4 as shown inFigure 3 While pickling of 2205 DSS hot-rolled strips inH2SO4 electrolytes it involves two processes chemicalpickling process and electrolytic pickling process

When chemical pickling is carried on for 2205 DSS FeOFe2O3 Fe3O4 and alloying elements can be dissolved inH2SO4 solutions +e chemical pickling process involves thefollowing chemical reactions [30]

FeO + H2SO4⟶ FeSO4 + H2O (1)

Fe3O4 + 4H2SO4⟶ FeSO4 + Fe2 SO4( 11138573 + 4H2O (2)

Fe2O3 + 3H2SO4⟶ Fe2 SO4( 11138573 + 3H2O (3)

Fe + H2SO4⟶ FeSO4 + H2uarr (4)

Ni + H2SO4⟶ NiSO4 + H2uarr (5)

Cr + H2SO4⟶ CrSO4 + H2uarr (6)

+e oxide scales on the test specimen are mainlycomprised of FeCr2O4 as shown in Figure 3 +e FeCr2O4 isinsoluble in sulfuric acid solution [7] +e matrix of 2205DSS is dissolved slowly in sulfuric acid solution for its ex-cellent corrosion resistance +e oxide scales on the testspecimen are dissolved very slowly in sulfuric acid solutionsby means of peeling mechanically +erefore the chemicalpickling of the 2205 DSS hot-rolled strip is very slow Formost stainless steels higher pickling temperature and sul-furic acid concentration do not increase their pickling ef-ficiency after a certain level [30] But for 2205 DSS the oxidescales still exist after chemical pickling in 450 g Lminus1 H2SO4 at90degC

Table 2 Concentration of metal ions in industrial H2SO4 solutions

Ions Fe Cr Mn Ni Cu Nb Ti MoConcentration(gL) 206 280 006 055 lt001 lt001 lt001 004

0 10 20 30 40 50 60

0

2

4

6

8

10

Concentration of metal ions (g Lndash1)

Wei

ght l

oss r

ate (

gmndash2

min

ndash1)

Fe2+Fe3+

Figure 8 +e static pickling rate in 300 g Lminus1H2SO4 solutions at75degC with different iron ions

0 5 10 15 202

3

4

5

6

7

8

9

10

Rotary speed (m minndash1)

Wei

ght l

oss r

ate (

gmndash2

min

ndash1)

Figure 9 Dynamic pickling rate in 300 g Lminus1H2SO4 solutions at75degC under different rotary speed conditions

000 004 008 012 016 020

6

8

10

12

14

16

18

20

Current density (A cmndash2)

Wei

ght l

oss r

ate (

gmndash2

min

ndash1)

Figure 10 Variation of the dynamic pickling rate with currentdensity in 300 g Lminus1H2SO4 solutions at 75degC

Advances in Materials Science and Engineering 5

At the beginning of the static chemical pickling processsmall gas bubbles nucleate and grow on the specimensurface During the pickling process more and more gasbubbles will form and adsorb on the specimen surfacewhich must reduce the contact areas of effective picklingAs for the dynamic pickling of specimens on the rotatingdisk the movement may decrease the adsorption andgrowth of gas bubbles on the specimen surface to a certainextent [31] +erefore the chemical pickling rate of theannealed 2205 DSS specimens under dynamic condition ishigher than under static condition Nevertheless the ac-celeration effect of dynamic speed is very weak with about5sim10 increase in the pickling rates as observed inFigure 8

When sulfuric acid is used as an electrolyte it canconduct electricity +e test specimen serves as the anodeand cathode with the alternative change When the testspecimen serves as the relative anode the insoluble FeCr2O4is oxidized into soluble HCrO4

minus and Cr2O72minus +e anodic

electrolytic reactions are as follows [10 30 32]

2H2O⟶ O2uarr + 4H++ 4e (7)

FeCr2O4 + 4H2O⟶ FeO + HCrO4minus

+ 7H++ 6e (8)

FeCr2O4 + 4H2O⟶ FeO + Cr2O72minus

+ 8H++ 6e (9)

2FeO3⟶ 4Fe3++ 3O2uarr + 12e (10)

When the test specimen serves as the relative cathodeCr(OH)3 and Fe(OH)3 are deposited on the surface of thetest specimen H2 is precipitated between the oxide layerswhich is beneficial to the separation of the deposited sedi-ment from the matrix+e cathodic electrolytic reactions areas follows [10 30 32]

2H2O + 2e⟶ 2OHminus+ H2uarr (11)

Fe3++ 3OHminus ⟶ Fe(OH)3darr (12)

CrO42minus

+ 4H2O + 6e⟶ Cr(OH)3darr (13)

Cr2O72minus

+ 4H2O + 6e⟶ 2Cr(OH)3darr + 8OHminus (14)

Electrolytic pickling is faster than normal chemicalpickling for most stainless steels [20] +e electrolyticpickling process in H2SO4 electrolytes is the combined effectof electrolysis and chemical pickling When the electrolyticpickling is performed under static conditions a maximum ofabout 20 of the current goes to dissolution reactionswhereas about 80 of the current is consumed in oxygen gasproduction [10] For the dense and compact oxide scales ofthe test specimens spallation or peeling of the oxide scalesinduced by gas evolution does not play a decisive role Asshown in Figure 11 the oxide scales are remained on the testspecimens after static electrolytic pickling When the

Oxide scale

(a)

Oxide scale

(b)

Oxide scale

(c)

(d) (e) (f )

Figure 11 SEM surface images after static (andashc)) and dynamic (dndashf)) pickling in 300 g Lminus1 H2SO4 solutions at 75degC with current density004A cmminus2 (a and d) 012A cmminus2 (b and e) and 02A cmminus2 (c and f)

6 Advances in Materials Science and Engineering

0 50 100 150 200 250 300 350ndash10

ndash08

ndash06

ndash04

ndash02

00

02

E we (

V)

Time (s)

No iron ions10gLndash1Fe2+

10gLndash1Fe3+

Figure 12 Corrosion potential in 300 g Lminus1H2SO4 solutions at 75degC containing different Fe ions

1 2 3 4 5 6ndash1

0

0

1

2

3

4

5

ndashZPrime

(Ω cm

2 )

Zprime(Ω cm2)

(a)

0

ndashZPrime

(Ω cm

2 )

Zprime(Ω cm2)2 4 6 8 10 12

ndash1

0

1

2

3

4

5

(b)

ndashZPrime

(Ω cm

2 )

Zprime(Ω cm2)0 100 200 300 400 500 600 700

0

100

200

300

400

500

(c)

RfRt

Cdl

Cf

Rs

(d)

Figure 13 Nyquist plots in 300 g Lminus1H2SO4 solutions at 75degC containing no ions (a) 10 g Lminus1 Fe2+ (b) and 10 g Lminus1 Fe3+ (c) and thecorresponding circuit of the impedance spectrum (d)

Advances in Materials Science and Engineering 7

electrolytic pickling is performed under dynamic conditionsthe rotary disk develops a rational way for producing activeedges efficiently where catalytic activity of the test speci-mens is improved and its pickling rate is accelerated [33 34]+e dynamic electrolytic pickling rate at 02 A cmminus2 is about21 times higher than the chemical pickling which may giverise to a smooth specimen surface without oxide scales

+e Fe3+ ions are an effective oxidant which enhancedthe corrosion potential as shown in Figure 12 When no Feions were added in the H2SO4 solutions the corrosionpotential quickly declined at the beginning of the immersiontime after about 50 s it remained constant (approximatelyminus075 VMSE) subsequently as the immersion time increasedWhen 10 g Lminus1 Fe2+ was added in the H2SO4 solutions thecorrosion potential quickly declined at the beginning of theimmersion time after about 100 s it remained unchangedWhen 10 g Lminus1 Fe3+ was added in the H2SO4 solutions thecorrosion potential increased slowly from 0062 VMSE to0137 VMSE as the immersion time increased +e EISNyquist plots recorded on the test specimens immersed in300 g Lminus1 H2SO4 solutions containing no ions 10 g Lminus1 Fe2+and 10 g Lminus1 Fe3+ under the Ecorr conditions (ie the freecorrosion states) is presented in Figure 13 +e semicirclesize enlarged slightly with the addition of 10 g Lminus1 Fe 2+ butincreased noticeably with the addition of the 10 g Lminus1 Fe 3+

for its high impedanceIn order to show the dissolution process for the speci-

mens in 300 g Lminus1H2SO4 solutions at 75degC containing dif-ferent Fe ions the equivalent circuit model is proposed inFigure 13(d) according to the EIS features in Figure 13 Rs isthe electrolyte resistance Rf is the resistance of oxide layerremained on the specimens Rt is the charge transfer re-sistance Cf and Cdl can be replaced with constant phaseelement (CPE) [35] +e impedance of CPE is written inequation (15) where Y0 is the admittance magnitude of CPEand α is the exponential term Table 3 gives the fitted resultsof EIS spectra +e calculated spectra are shown as a solidcurve in Figure 13 which fit the experimental data very wellIt can be concluded that the model provided a reliabledescription for the corrosion systems

ZCPE 1

Y0(jω)α (15)

5 Application and Performance

According to the abovementioned results the picklingprocess of hot-rolled 2205 DSS is optimized through thehigh H2SO4 concentration high solution temperature andproper electrolysis current density in the industrial pre-pickling of 2205 DSS hot-rolled strips +e pickling effi-ciency is improved remarkably which increases the

production rate from 5ndash8mminminus1 to 15ndash18mminminus1 Be-sides the surface finish after pickling is notably enhanced asshown in Figure 14

6 Conclusion

+e pickling behaviour of hot-rolled 2205 DSS withannealing and mechanical descaling treatments in H2SO4solutions under both static and dynamic conditions has ledto the following conclusions

(1) In the static chemical pickling process the picklingrate may be accelerated noticeably by increasing thesolution temperature and H2SO4 concentration butbe decelerated greatly by Fe3+ ions

(2) +e chemical pickling process can be enhancedweakly by the moving speed of the specimen from 0to 20mminminus1 because the movement decreases theadsorption and growth of gas bubbles on the spec-imen surface to a certain extent

(3) Under dynamic conditions the electrolytic picklingrate increases markedly with changing the pulsecurrent density from 004 to 02Acmminus2 +e electro-lytic pickling rate at 02A cmminus2 is about 21 times largerthan the chemical pickling rate in 300 g Lminus1H2SO4 at75degC resulting in the smooth and clean specimensurfaces

Data Availability

+e tables and figures data used to support the findings ofthis study are available from the corresponding author uponreasonable request

Conflicts of Interest

+e authors declare that there are no conflicts of interestregarding the publication of this paper

Table 3 Fitted results for EIS spectra in 300 g Lminus1H2SO4 solutions at 75degC containing different ions

Ions Rs Ω cm2 Y0-f Sα Ωminus1 cmminus2 αf Rf Ω cm2 Y0-dl Sα Ωminus1 cmminus2 αdl Rt Ω cm2

No ions 082 000218 087 280 00658 092 1610 g Lminus1 Fe2+ 094 000185 096 314 0093 084 1010 g Lminus1 Fe3+ 104 0000133 095 5499 0000281 068 706

Figure 14 Optical surface of the 2205 DSS hot-rolled strip afterindustrial pickling with optimized pickling process

8 Advances in Materials Science and Engineering

Acknowledgments

+e authors gratefully acknowledge the financial supportfrom the National Natural Science Foundation of China(Grant nos U1660205 and U1960103)

References

[1] Y-Y Wu and F Presuel-Moreno ldquoChloride levels that ini-tiated corrosion of duplex stainless steel embedded in mor-tarrdquo Advances in Materials Science and Engineering vol 2019Article ID 6949176 6 pages 2019

[2] T Li Y Zhang L Gao and Y Zhang ldquoOptimization ofFCAWparameters for ferrite content in 2205 DSS welds basedon the taguchi design methodrdquo Advances in Materials Scienceand Engineering vol 2018 Article ID 7950607 7 pages 2018

[3] Q Meng P La L Yao P Zhang Y Wei and X Guo ldquoEffectof Al onmicrostructure and properties of hot-rolled 2205 dualstainless steelrdquo Advances in Materials Science and Engineer-ing vol 2016 Article ID 7518067 8 pages 2016

[4] Z-g Song H Feng and S-m Hu ldquoDevelopment of Chineseduplex stainless steel in recent yearsrdquo Journal of Iron and SteelResearch International vol 24 no 2 pp 121ndash130 2017

[5] Z Y Liu C F Dong X G Li Q Zhi and Y F Cheng ldquoStresscorrosion cracking of 2205 duplex stainless steel in H2S-CO2environmentrdquo Journal of Materials Science vol 44 no 16pp 4228ndash4234 2009

[6] R N Gun Duplex Stainless Steels Vol 1 Abington Pub-lishing Cambridge UK 1994

[7] L-F Li Z-H Jiang and Y Riquier ldquoHigh-temperatureoxidation of duplex stainless steels in air and mixed gas of airand CH4rdquo Corrosion Science vol 47 no 1 pp 57ndash68 2005

[8] J G Peng M C Li S Z Luo et al ldquoOxidation characteristicsof duplex stainless steel 2205 in simulated combustion at-mosphererdquo Materials Research Innovation vol 19 no suppl5 pp 245ndash249 2015

[9] J G Peng and M C Li ldquoHigh temperature oxidation be-haviour of DSS 2205 in humid airrdquo Advanced MaterialsResearch vol 900 pp 673ndash676 2014

[10] N Ipek B Holm R Pettersson G Runnsjo and M KarlssonldquoElectrolytic pickling of duplex stainless steelrdquo Materials andCorrosion vol 56 no 8 pp 521ndash532 2005

[11] J G Peng S Z Luo andW B Dong ldquoStudy on the simulatedpickling of 443NT medium chrome ferritic stainless steelrdquoBaosteel Technical Research vol 4 no 1 pp pp50ndash52 2010

[12] L-F Li M Daerden P Caenen and J-P Celis ldquoElectro-chemical behavior of hot-rolled 304 stainless steel duringchemical pickling in HCl-based electrolytesrdquo Journal of 3eElectrochemical Society vol 153 no 5 pp B145ndashB150 2006

[13] J Hilden J Virtanen O Forsen and J Aromaa ldquoElectrolyticpickling of stainless steel studied by electrochemical polar-isation and DC resistance measurements combined withsurface analysisrdquo Electrochimica Acta vol 46 no 24-25pp 3859ndash3866 2001

[14] L-F Li P Caenen and M-F Jiang ldquoElectrolytic pickling ofthe oxide layer on hot-rolled 304 stainless steel in sodiumsulphaterdquo Corrosion Science vol 50 no 10 pp 2824ndash28302008

[15] W G Chen Y Q Chen and H L Pang ldquoStudy of Na2SO4electrolytic pickling process on 304 stainless steelrdquo ChinaMetallurgy vol 19 no 1 pp 16ndash23 2009

[16] L-F Li P Caenen and J-P Celis ldquoChemical pickling of 304stainless steel in fluoride- and sulfate-containing acidic

electrolytesrdquo Journal of 3e Electrochemical Society vol 152no 9 pp B352ndashB357 2005

[17] C A Huang and C C Hsu ldquo+e electrochemical polishingbehaviour of duplex stainless steel (SAF 2205) in phos-phoric-sulfuric mixed acidsrdquo International Journal of Ad-vance Manufacture Technology vol 34 no 9-10pp 904ndash910 2007

[18] L-F Li P Caenen M Daerden et al ldquoMechanism of singleand multiple step pickling of 304 stainless steel in acidelectrolytesrdquo Corrosion Science vol 47 no 5 pp 1307ndash13242005

[19] B S Covino J V Scalera T J Driscoll and J P CarterldquoDissolution behavior of 304 stainless steel in HNO3HFmixturesrdquo Metallurgical Transactions A vol 17 no 1pp 137ndash149 1986

[20] N Ipek N Lior M Vynnycky and F H Bark ldquoNumericaland experimental study of the effect of gas evolution inelectrolytic picklingrdquo Journal of Applied Electrochemistryvol 36 no 12 pp 1367ndash1379 2006

[21] M Abdallah ldquoGuar gum as corrosion inhibitor for carbonsteel in sulfuric acid solutionsrdquo Portugaliae ElectrochimicaActa vol 22 no 2 pp 161ndash175 2004

[22] C A Huang J H Chang W J Zhao et al ldquoExamination ofthe electropolishing behaviour of 73 brass in a 70 H3PO4solution using a rotating disc electroderdquo Materials Chemistryand Physics vol 146 no 3 pp 230ndash239 2014

[23] Q Xie P-y Shi C-j Liu M-f Jiang et al ldquoEffects of differentoxidants on HCl-based pickling process of 430 stainless steelrdquoJournal of Iron and Steel Research International vol 23 no 8pp 778ndash783 2016

[24] W H Hao L Y Qin and D L Liu ldquo+e effect of hydro-chloric acid concentration on pickling of duplex stainlesssteelrdquo Corrosion Protection vol 33 no suppl 2 pp 69ndash712012

[25] H Y Li and A C Zhao ldquoPickling behaviour of duplexstainless steel 2205 in hydrochloric acid solutionrdquoAdvances inMaterials Science and Engineering vol 2018 Article ID9754528 6 pages 2018

[26] C J Brown ldquoProcess and apparatus for recovery of peroxidecontaining pickling solutionsrdquo International Patent PCTCA0201598 2002

[27] R Jiang G Zou W Shi Y Liang and S Xiang ldquoCorrosionbehavior of plasma-nitrided 904L austenitic stainless steel inhydrofluoric acidrdquo Journal of Materials Engineering andPerformance vol 28 no 3 pp 1863ndash1872 2019

[28] C Donik A Kocijan J T Grant M Jenko A Drenik andB Pihlar ldquoXPS study of duplex stainless steel oxidized byoxygen atomsrdquo Corrosion Science vol 51 no 4 pp 827ndash8322009

[29] Y Xu Q Jin J Li X Xiao X Zhang and L Jiang ldquoOxidationinduced phase transformation of duplex stainless steel 25Cr-10Mn-2Ni-3Mo-08W-08Cu-05Nrdquo Corrosion Sciencevol 55 pp 233ndash237 2012

[30] ASM Handbook Committee ASM Handbook Volume 5Surface Engineering ASM International Cleveland OH USA2007

[31] J Eigeldinger and H Vogt ldquo+e bubble coverage of gas-evolving electrodes in a flowing electrolyterdquo ElectrochimicaActa vol 45 no 27 pp 4449ndash4456 2000

[32] M Pourbaix Atlas of Electrochemical Equilibria in AqueousSolutions Pergamon Press Oxford UK 2nd edition 1966

[33] Z G Wang H-H H Wu Q Li et al ldquoReversing interfacialcatalysis of ambipolar WSe2 single crystalrdquo Advanced Sciencevol 7 Article ID 1901382 pp 1ndash9 2019

Advances in Materials Science and Engineering 9

[34] Z Wang Q Li H Xu et al ldquoControllable etching of MoS2basal planes for enhanced hydrogen evolution through theformation of active edge sitesrdquo Nano Energy vol 49pp 634ndash643 2018

[35] M C Li C L Zeng S Z Luo J N Shen H C Lin andC N Cao ldquoElectrochemical corrosion characteristics of type316 stainless steel in simulated anode environment forPEMFCrdquo Electrochimica Acta vol 48 no 12 pp 1735ndash17412003

10 Advances in Materials Science and Engineering

02 A cmminus2 than at 0A cmminus2 (ie the chemical pickling) +eelectrolytic pickling efficiency has a positive correlation withthe pulse current density After dynamic electrolytic pick-ling there is almost no oxide scales on the specimen surfacescompared with static electrolytic pickling With the increaseof current density from 004A cmminus2 to 02 A cmminus2 the Cr-depleted layer may dissolve obviously and the surfaces be-come smooth as shown in Figure 11

4 Discussion

+e residual oxides on the surface of the test specimen arecomposed of Fe2O3 Fe3O4 and FeCr2O4 as shown inFigure 3 While pickling of 2205 DSS hot-rolled strips inH2SO4 electrolytes it involves two processes chemicalpickling process and electrolytic pickling process

When chemical pickling is carried on for 2205 DSS FeOFe2O3 Fe3O4 and alloying elements can be dissolved inH2SO4 solutions +e chemical pickling process involves thefollowing chemical reactions [30]

FeO + H2SO4⟶ FeSO4 + H2O (1)

Fe3O4 + 4H2SO4⟶ FeSO4 + Fe2 SO4( 11138573 + 4H2O (2)

Fe2O3 + 3H2SO4⟶ Fe2 SO4( 11138573 + 3H2O (3)

Fe + H2SO4⟶ FeSO4 + H2uarr (4)

Ni + H2SO4⟶ NiSO4 + H2uarr (5)

Cr + H2SO4⟶ CrSO4 + H2uarr (6)

+e oxide scales on the test specimen are mainlycomprised of FeCr2O4 as shown in Figure 3 +e FeCr2O4 isinsoluble in sulfuric acid solution [7] +e matrix of 2205DSS is dissolved slowly in sulfuric acid solution for its ex-cellent corrosion resistance +e oxide scales on the testspecimen are dissolved very slowly in sulfuric acid solutionsby means of peeling mechanically +erefore the chemicalpickling of the 2205 DSS hot-rolled strip is very slow Formost stainless steels higher pickling temperature and sul-furic acid concentration do not increase their pickling ef-ficiency after a certain level [30] But for 2205 DSS the oxidescales still exist after chemical pickling in 450 g Lminus1 H2SO4 at90degC

Table 2 Concentration of metal ions in industrial H2SO4 solutions

Ions Fe Cr Mn Ni Cu Nb Ti MoConcentration(gL) 206 280 006 055 lt001 lt001 lt001 004

0 10 20 30 40 50 60

0

2

4

6

8

10

Concentration of metal ions (g Lndash1)

Wei

ght l

oss r

ate (

gmndash2

min

ndash1)

Fe2+Fe3+

Figure 8 +e static pickling rate in 300 g Lminus1H2SO4 solutions at75degC with different iron ions

0 5 10 15 202

3

4

5

6

7

8

9

10

Rotary speed (m minndash1)

Wei

ght l

oss r

ate (

gmndash2

min

ndash1)

Figure 9 Dynamic pickling rate in 300 g Lminus1H2SO4 solutions at75degC under different rotary speed conditions

000 004 008 012 016 020

6

8

10

12

14

16

18

20

Current density (A cmndash2)

Wei

ght l

oss r

ate (

gmndash2

min

ndash1)

Figure 10 Variation of the dynamic pickling rate with currentdensity in 300 g Lminus1H2SO4 solutions at 75degC

Advances in Materials Science and Engineering 5

At the beginning of the static chemical pickling processsmall gas bubbles nucleate and grow on the specimensurface During the pickling process more and more gasbubbles will form and adsorb on the specimen surfacewhich must reduce the contact areas of effective picklingAs for the dynamic pickling of specimens on the rotatingdisk the movement may decrease the adsorption andgrowth of gas bubbles on the specimen surface to a certainextent [31] +erefore the chemical pickling rate of theannealed 2205 DSS specimens under dynamic condition ishigher than under static condition Nevertheless the ac-celeration effect of dynamic speed is very weak with about5sim10 increase in the pickling rates as observed inFigure 8

When sulfuric acid is used as an electrolyte it canconduct electricity +e test specimen serves as the anodeand cathode with the alternative change When the testspecimen serves as the relative anode the insoluble FeCr2O4is oxidized into soluble HCrO4

minus and Cr2O72minus +e anodic

electrolytic reactions are as follows [10 30 32]

2H2O⟶ O2uarr + 4H++ 4e (7)

FeCr2O4 + 4H2O⟶ FeO + HCrO4minus

+ 7H++ 6e (8)

FeCr2O4 + 4H2O⟶ FeO + Cr2O72minus

+ 8H++ 6e (9)

2FeO3⟶ 4Fe3++ 3O2uarr + 12e (10)

When the test specimen serves as the relative cathodeCr(OH)3 and Fe(OH)3 are deposited on the surface of thetest specimen H2 is precipitated between the oxide layerswhich is beneficial to the separation of the deposited sedi-ment from the matrix+e cathodic electrolytic reactions areas follows [10 30 32]

2H2O + 2e⟶ 2OHminus+ H2uarr (11)

Fe3++ 3OHminus ⟶ Fe(OH)3darr (12)

CrO42minus

+ 4H2O + 6e⟶ Cr(OH)3darr (13)

Cr2O72minus

+ 4H2O + 6e⟶ 2Cr(OH)3darr + 8OHminus (14)

Electrolytic pickling is faster than normal chemicalpickling for most stainless steels [20] +e electrolyticpickling process in H2SO4 electrolytes is the combined effectof electrolysis and chemical pickling When the electrolyticpickling is performed under static conditions a maximum ofabout 20 of the current goes to dissolution reactionswhereas about 80 of the current is consumed in oxygen gasproduction [10] For the dense and compact oxide scales ofthe test specimens spallation or peeling of the oxide scalesinduced by gas evolution does not play a decisive role Asshown in Figure 11 the oxide scales are remained on the testspecimens after static electrolytic pickling When the

Oxide scale

(a)

Oxide scale

(b)

Oxide scale

(c)

(d) (e) (f )

Figure 11 SEM surface images after static (andashc)) and dynamic (dndashf)) pickling in 300 g Lminus1 H2SO4 solutions at 75degC with current density004A cmminus2 (a and d) 012A cmminus2 (b and e) and 02A cmminus2 (c and f)

6 Advances in Materials Science and Engineering

0 50 100 150 200 250 300 350ndash10

ndash08

ndash06

ndash04

ndash02

00

02

E we (

V)

Time (s)

No iron ions10gLndash1Fe2+

10gLndash1Fe3+

Figure 12 Corrosion potential in 300 g Lminus1H2SO4 solutions at 75degC containing different Fe ions

1 2 3 4 5 6ndash1

0

0

1

2

3

4

5

ndashZPrime

(Ω cm

2 )

Zprime(Ω cm2)

(a)

0

ndashZPrime

(Ω cm

2 )

Zprime(Ω cm2)2 4 6 8 10 12

ndash1

0

1

2

3

4

5

(b)

ndashZPrime

(Ω cm

2 )

Zprime(Ω cm2)0 100 200 300 400 500 600 700

0

100

200

300

400

500

(c)

RfRt

Cdl

Cf

Rs

(d)

Figure 13 Nyquist plots in 300 g Lminus1H2SO4 solutions at 75degC containing no ions (a) 10 g Lminus1 Fe2+ (b) and 10 g Lminus1 Fe3+ (c) and thecorresponding circuit of the impedance spectrum (d)

Advances in Materials Science and Engineering 7

electrolytic pickling is performed under dynamic conditionsthe rotary disk develops a rational way for producing activeedges efficiently where catalytic activity of the test speci-mens is improved and its pickling rate is accelerated [33 34]+e dynamic electrolytic pickling rate at 02 A cmminus2 is about21 times higher than the chemical pickling which may giverise to a smooth specimen surface without oxide scales

+e Fe3+ ions are an effective oxidant which enhancedthe corrosion potential as shown in Figure 12 When no Feions were added in the H2SO4 solutions the corrosionpotential quickly declined at the beginning of the immersiontime after about 50 s it remained constant (approximatelyminus075 VMSE) subsequently as the immersion time increasedWhen 10 g Lminus1 Fe2+ was added in the H2SO4 solutions thecorrosion potential quickly declined at the beginning of theimmersion time after about 100 s it remained unchangedWhen 10 g Lminus1 Fe3+ was added in the H2SO4 solutions thecorrosion potential increased slowly from 0062 VMSE to0137 VMSE as the immersion time increased +e EISNyquist plots recorded on the test specimens immersed in300 g Lminus1 H2SO4 solutions containing no ions 10 g Lminus1 Fe2+and 10 g Lminus1 Fe3+ under the Ecorr conditions (ie the freecorrosion states) is presented in Figure 13 +e semicirclesize enlarged slightly with the addition of 10 g Lminus1 Fe 2+ butincreased noticeably with the addition of the 10 g Lminus1 Fe 3+

for its high impedanceIn order to show the dissolution process for the speci-

mens in 300 g Lminus1H2SO4 solutions at 75degC containing dif-ferent Fe ions the equivalent circuit model is proposed inFigure 13(d) according to the EIS features in Figure 13 Rs isthe electrolyte resistance Rf is the resistance of oxide layerremained on the specimens Rt is the charge transfer re-sistance Cf and Cdl can be replaced with constant phaseelement (CPE) [35] +e impedance of CPE is written inequation (15) where Y0 is the admittance magnitude of CPEand α is the exponential term Table 3 gives the fitted resultsof EIS spectra +e calculated spectra are shown as a solidcurve in Figure 13 which fit the experimental data very wellIt can be concluded that the model provided a reliabledescription for the corrosion systems

ZCPE 1

Y0(jω)α (15)

5 Application and Performance

According to the abovementioned results the picklingprocess of hot-rolled 2205 DSS is optimized through thehigh H2SO4 concentration high solution temperature andproper electrolysis current density in the industrial pre-pickling of 2205 DSS hot-rolled strips +e pickling effi-ciency is improved remarkably which increases the

production rate from 5ndash8mminminus1 to 15ndash18mminminus1 Be-sides the surface finish after pickling is notably enhanced asshown in Figure 14

6 Conclusion

+e pickling behaviour of hot-rolled 2205 DSS withannealing and mechanical descaling treatments in H2SO4solutions under both static and dynamic conditions has ledto the following conclusions

(1) In the static chemical pickling process the picklingrate may be accelerated noticeably by increasing thesolution temperature and H2SO4 concentration butbe decelerated greatly by Fe3+ ions

(2) +e chemical pickling process can be enhancedweakly by the moving speed of the specimen from 0to 20mminminus1 because the movement decreases theadsorption and growth of gas bubbles on the spec-imen surface to a certain extent

(3) Under dynamic conditions the electrolytic picklingrate increases markedly with changing the pulsecurrent density from 004 to 02Acmminus2 +e electro-lytic pickling rate at 02A cmminus2 is about 21 times largerthan the chemical pickling rate in 300 g Lminus1H2SO4 at75degC resulting in the smooth and clean specimensurfaces

Data Availability

+e tables and figures data used to support the findings ofthis study are available from the corresponding author uponreasonable request

Conflicts of Interest

+e authors declare that there are no conflicts of interestregarding the publication of this paper

Table 3 Fitted results for EIS spectra in 300 g Lminus1H2SO4 solutions at 75degC containing different ions

Ions Rs Ω cm2 Y0-f Sα Ωminus1 cmminus2 αf Rf Ω cm2 Y0-dl Sα Ωminus1 cmminus2 αdl Rt Ω cm2

No ions 082 000218 087 280 00658 092 1610 g Lminus1 Fe2+ 094 000185 096 314 0093 084 1010 g Lminus1 Fe3+ 104 0000133 095 5499 0000281 068 706

Figure 14 Optical surface of the 2205 DSS hot-rolled strip afterindustrial pickling with optimized pickling process

8 Advances in Materials Science and Engineering

Acknowledgments

+e authors gratefully acknowledge the financial supportfrom the National Natural Science Foundation of China(Grant nos U1660205 and U1960103)

References

[1] Y-Y Wu and F Presuel-Moreno ldquoChloride levels that ini-tiated corrosion of duplex stainless steel embedded in mor-tarrdquo Advances in Materials Science and Engineering vol 2019Article ID 6949176 6 pages 2019

[2] T Li Y Zhang L Gao and Y Zhang ldquoOptimization ofFCAWparameters for ferrite content in 2205 DSS welds basedon the taguchi design methodrdquo Advances in Materials Scienceand Engineering vol 2018 Article ID 7950607 7 pages 2018

[3] Q Meng P La L Yao P Zhang Y Wei and X Guo ldquoEffectof Al onmicrostructure and properties of hot-rolled 2205 dualstainless steelrdquo Advances in Materials Science and Engineer-ing vol 2016 Article ID 7518067 8 pages 2016

[4] Z-g Song H Feng and S-m Hu ldquoDevelopment of Chineseduplex stainless steel in recent yearsrdquo Journal of Iron and SteelResearch International vol 24 no 2 pp 121ndash130 2017

[5] Z Y Liu C F Dong X G Li Q Zhi and Y F Cheng ldquoStresscorrosion cracking of 2205 duplex stainless steel in H2S-CO2environmentrdquo Journal of Materials Science vol 44 no 16pp 4228ndash4234 2009

[6] R N Gun Duplex Stainless Steels Vol 1 Abington Pub-lishing Cambridge UK 1994

[7] L-F Li Z-H Jiang and Y Riquier ldquoHigh-temperatureoxidation of duplex stainless steels in air and mixed gas of airand CH4rdquo Corrosion Science vol 47 no 1 pp 57ndash68 2005

[8] J G Peng M C Li S Z Luo et al ldquoOxidation characteristicsof duplex stainless steel 2205 in simulated combustion at-mosphererdquo Materials Research Innovation vol 19 no suppl5 pp 245ndash249 2015

[9] J G Peng and M C Li ldquoHigh temperature oxidation be-haviour of DSS 2205 in humid airrdquo Advanced MaterialsResearch vol 900 pp 673ndash676 2014

[10] N Ipek B Holm R Pettersson G Runnsjo and M KarlssonldquoElectrolytic pickling of duplex stainless steelrdquo Materials andCorrosion vol 56 no 8 pp 521ndash532 2005

[11] J G Peng S Z Luo andW B Dong ldquoStudy on the simulatedpickling of 443NT medium chrome ferritic stainless steelrdquoBaosteel Technical Research vol 4 no 1 pp pp50ndash52 2010

[12] L-F Li M Daerden P Caenen and J-P Celis ldquoElectro-chemical behavior of hot-rolled 304 stainless steel duringchemical pickling in HCl-based electrolytesrdquo Journal of 3eElectrochemical Society vol 153 no 5 pp B145ndashB150 2006

[13] J Hilden J Virtanen O Forsen and J Aromaa ldquoElectrolyticpickling of stainless steel studied by electrochemical polar-isation and DC resistance measurements combined withsurface analysisrdquo Electrochimica Acta vol 46 no 24-25pp 3859ndash3866 2001

[14] L-F Li P Caenen and M-F Jiang ldquoElectrolytic pickling ofthe oxide layer on hot-rolled 304 stainless steel in sodiumsulphaterdquo Corrosion Science vol 50 no 10 pp 2824ndash28302008

[15] W G Chen Y Q Chen and H L Pang ldquoStudy of Na2SO4electrolytic pickling process on 304 stainless steelrdquo ChinaMetallurgy vol 19 no 1 pp 16ndash23 2009

[16] L-F Li P Caenen and J-P Celis ldquoChemical pickling of 304stainless steel in fluoride- and sulfate-containing acidic

electrolytesrdquo Journal of 3e Electrochemical Society vol 152no 9 pp B352ndashB357 2005

[17] C A Huang and C C Hsu ldquo+e electrochemical polishingbehaviour of duplex stainless steel (SAF 2205) in phos-phoric-sulfuric mixed acidsrdquo International Journal of Ad-vance Manufacture Technology vol 34 no 9-10pp 904ndash910 2007

[18] L-F Li P Caenen M Daerden et al ldquoMechanism of singleand multiple step pickling of 304 stainless steel in acidelectrolytesrdquo Corrosion Science vol 47 no 5 pp 1307ndash13242005

[19] B S Covino J V Scalera T J Driscoll and J P CarterldquoDissolution behavior of 304 stainless steel in HNO3HFmixturesrdquo Metallurgical Transactions A vol 17 no 1pp 137ndash149 1986

[20] N Ipek N Lior M Vynnycky and F H Bark ldquoNumericaland experimental study of the effect of gas evolution inelectrolytic picklingrdquo Journal of Applied Electrochemistryvol 36 no 12 pp 1367ndash1379 2006

[21] M Abdallah ldquoGuar gum as corrosion inhibitor for carbonsteel in sulfuric acid solutionsrdquo Portugaliae ElectrochimicaActa vol 22 no 2 pp 161ndash175 2004

[22] C A Huang J H Chang W J Zhao et al ldquoExamination ofthe electropolishing behaviour of 73 brass in a 70 H3PO4solution using a rotating disc electroderdquo Materials Chemistryand Physics vol 146 no 3 pp 230ndash239 2014

[23] Q Xie P-y Shi C-j Liu M-f Jiang et al ldquoEffects of differentoxidants on HCl-based pickling process of 430 stainless steelrdquoJournal of Iron and Steel Research International vol 23 no 8pp 778ndash783 2016

[24] W H Hao L Y Qin and D L Liu ldquo+e effect of hydro-chloric acid concentration on pickling of duplex stainlesssteelrdquo Corrosion Protection vol 33 no suppl 2 pp 69ndash712012

[25] H Y Li and A C Zhao ldquoPickling behaviour of duplexstainless steel 2205 in hydrochloric acid solutionrdquoAdvances inMaterials Science and Engineering vol 2018 Article ID9754528 6 pages 2018

[26] C J Brown ldquoProcess and apparatus for recovery of peroxidecontaining pickling solutionsrdquo International Patent PCTCA0201598 2002

[27] R Jiang G Zou W Shi Y Liang and S Xiang ldquoCorrosionbehavior of plasma-nitrided 904L austenitic stainless steel inhydrofluoric acidrdquo Journal of Materials Engineering andPerformance vol 28 no 3 pp 1863ndash1872 2019

[28] C Donik A Kocijan J T Grant M Jenko A Drenik andB Pihlar ldquoXPS study of duplex stainless steel oxidized byoxygen atomsrdquo Corrosion Science vol 51 no 4 pp 827ndash8322009

[29] Y Xu Q Jin J Li X Xiao X Zhang and L Jiang ldquoOxidationinduced phase transformation of duplex stainless steel 25Cr-10Mn-2Ni-3Mo-08W-08Cu-05Nrdquo Corrosion Sciencevol 55 pp 233ndash237 2012

[30] ASM Handbook Committee ASM Handbook Volume 5Surface Engineering ASM International Cleveland OH USA2007

[31] J Eigeldinger and H Vogt ldquo+e bubble coverage of gas-evolving electrodes in a flowing electrolyterdquo ElectrochimicaActa vol 45 no 27 pp 4449ndash4456 2000

[32] M Pourbaix Atlas of Electrochemical Equilibria in AqueousSolutions Pergamon Press Oxford UK 2nd edition 1966

[33] Z G Wang H-H H Wu Q Li et al ldquoReversing interfacialcatalysis of ambipolar WSe2 single crystalrdquo Advanced Sciencevol 7 Article ID 1901382 pp 1ndash9 2019

Advances in Materials Science and Engineering 9

[34] Z Wang Q Li H Xu et al ldquoControllable etching of MoS2basal planes for enhanced hydrogen evolution through theformation of active edge sitesrdquo Nano Energy vol 49pp 634ndash643 2018

[35] M C Li C L Zeng S Z Luo J N Shen H C Lin andC N Cao ldquoElectrochemical corrosion characteristics of type316 stainless steel in simulated anode environment forPEMFCrdquo Electrochimica Acta vol 48 no 12 pp 1735ndash17412003

10 Advances in Materials Science and Engineering

At the beginning of the static chemical pickling processsmall gas bubbles nucleate and grow on the specimensurface During the pickling process more and more gasbubbles will form and adsorb on the specimen surfacewhich must reduce the contact areas of effective picklingAs for the dynamic pickling of specimens on the rotatingdisk the movement may decrease the adsorption andgrowth of gas bubbles on the specimen surface to a certainextent [31] +erefore the chemical pickling rate of theannealed 2205 DSS specimens under dynamic condition ishigher than under static condition Nevertheless the ac-celeration effect of dynamic speed is very weak with about5sim10 increase in the pickling rates as observed inFigure 8

When sulfuric acid is used as an electrolyte it canconduct electricity +e test specimen serves as the anodeand cathode with the alternative change When the testspecimen serves as the relative anode the insoluble FeCr2O4is oxidized into soluble HCrO4

minus and Cr2O72minus +e anodic

electrolytic reactions are as follows [10 30 32]

2H2O⟶ O2uarr + 4H++ 4e (7)

FeCr2O4 + 4H2O⟶ FeO + HCrO4minus

+ 7H++ 6e (8)

FeCr2O4 + 4H2O⟶ FeO + Cr2O72minus

+ 8H++ 6e (9)

2FeO3⟶ 4Fe3++ 3O2uarr + 12e (10)

When the test specimen serves as the relative cathodeCr(OH)3 and Fe(OH)3 are deposited on the surface of thetest specimen H2 is precipitated between the oxide layerswhich is beneficial to the separation of the deposited sedi-ment from the matrix+e cathodic electrolytic reactions areas follows [10 30 32]

2H2O + 2e⟶ 2OHminus+ H2uarr (11)

Fe3++ 3OHminus ⟶ Fe(OH)3darr (12)

CrO42minus

+ 4H2O + 6e⟶ Cr(OH)3darr (13)

Cr2O72minus

+ 4H2O + 6e⟶ 2Cr(OH)3darr + 8OHminus (14)

Electrolytic pickling is faster than normal chemicalpickling for most stainless steels [20] +e electrolyticpickling process in H2SO4 electrolytes is the combined effectof electrolysis and chemical pickling When the electrolyticpickling is performed under static conditions a maximum ofabout 20 of the current goes to dissolution reactionswhereas about 80 of the current is consumed in oxygen gasproduction [10] For the dense and compact oxide scales ofthe test specimens spallation or peeling of the oxide scalesinduced by gas evolution does not play a decisive role Asshown in Figure 11 the oxide scales are remained on the testspecimens after static electrolytic pickling When the

Oxide scale

(a)

Oxide scale

(b)

Oxide scale

(c)

(d) (e) (f )

Figure 11 SEM surface images after static (andashc)) and dynamic (dndashf)) pickling in 300 g Lminus1 H2SO4 solutions at 75degC with current density004A cmminus2 (a and d) 012A cmminus2 (b and e) and 02A cmminus2 (c and f)

6 Advances in Materials Science and Engineering

0 50 100 150 200 250 300 350ndash10

ndash08

ndash06

ndash04

ndash02

00

02

E we (

V)

Time (s)

No iron ions10gLndash1Fe2+

10gLndash1Fe3+

Figure 12 Corrosion potential in 300 g Lminus1H2SO4 solutions at 75degC containing different Fe ions

1 2 3 4 5 6ndash1

0

0

1

2

3

4

5

ndashZPrime

(Ω cm

2 )

Zprime(Ω cm2)

(a)

0

ndashZPrime

(Ω cm

2 )

Zprime(Ω cm2)2 4 6 8 10 12

ndash1

0

1

2

3

4

5

(b)

ndashZPrime

(Ω cm

2 )

Zprime(Ω cm2)0 100 200 300 400 500 600 700

0

100

200

300

400

500

(c)

RfRt

Cdl

Cf

Rs

(d)

Figure 13 Nyquist plots in 300 g Lminus1H2SO4 solutions at 75degC containing no ions (a) 10 g Lminus1 Fe2+ (b) and 10 g Lminus1 Fe3+ (c) and thecorresponding circuit of the impedance spectrum (d)

Advances in Materials Science and Engineering 7

electrolytic pickling is performed under dynamic conditionsthe rotary disk develops a rational way for producing activeedges efficiently where catalytic activity of the test speci-mens is improved and its pickling rate is accelerated [33 34]+e dynamic electrolytic pickling rate at 02 A cmminus2 is about21 times higher than the chemical pickling which may giverise to a smooth specimen surface without oxide scales

+e Fe3+ ions are an effective oxidant which enhancedthe corrosion potential as shown in Figure 12 When no Feions were added in the H2SO4 solutions the corrosionpotential quickly declined at the beginning of the immersiontime after about 50 s it remained constant (approximatelyminus075 VMSE) subsequently as the immersion time increasedWhen 10 g Lminus1 Fe2+ was added in the H2SO4 solutions thecorrosion potential quickly declined at the beginning of theimmersion time after about 100 s it remained unchangedWhen 10 g Lminus1 Fe3+ was added in the H2SO4 solutions thecorrosion potential increased slowly from 0062 VMSE to0137 VMSE as the immersion time increased +e EISNyquist plots recorded on the test specimens immersed in300 g Lminus1 H2SO4 solutions containing no ions 10 g Lminus1 Fe2+and 10 g Lminus1 Fe3+ under the Ecorr conditions (ie the freecorrosion states) is presented in Figure 13 +e semicirclesize enlarged slightly with the addition of 10 g Lminus1 Fe 2+ butincreased noticeably with the addition of the 10 g Lminus1 Fe 3+

for its high impedanceIn order to show the dissolution process for the speci-

mens in 300 g Lminus1H2SO4 solutions at 75degC containing dif-ferent Fe ions the equivalent circuit model is proposed inFigure 13(d) according to the EIS features in Figure 13 Rs isthe electrolyte resistance Rf is the resistance of oxide layerremained on the specimens Rt is the charge transfer re-sistance Cf and Cdl can be replaced with constant phaseelement (CPE) [35] +e impedance of CPE is written inequation (15) where Y0 is the admittance magnitude of CPEand α is the exponential term Table 3 gives the fitted resultsof EIS spectra +e calculated spectra are shown as a solidcurve in Figure 13 which fit the experimental data very wellIt can be concluded that the model provided a reliabledescription for the corrosion systems

ZCPE 1

Y0(jω)α (15)

5 Application and Performance

According to the abovementioned results the picklingprocess of hot-rolled 2205 DSS is optimized through thehigh H2SO4 concentration high solution temperature andproper electrolysis current density in the industrial pre-pickling of 2205 DSS hot-rolled strips +e pickling effi-ciency is improved remarkably which increases the

production rate from 5ndash8mminminus1 to 15ndash18mminminus1 Be-sides the surface finish after pickling is notably enhanced asshown in Figure 14

6 Conclusion

+e pickling behaviour of hot-rolled 2205 DSS withannealing and mechanical descaling treatments in H2SO4solutions under both static and dynamic conditions has ledto the following conclusions

(1) In the static chemical pickling process the picklingrate may be accelerated noticeably by increasing thesolution temperature and H2SO4 concentration butbe decelerated greatly by Fe3+ ions

(2) +e chemical pickling process can be enhancedweakly by the moving speed of the specimen from 0to 20mminminus1 because the movement decreases theadsorption and growth of gas bubbles on the spec-imen surface to a certain extent

(3) Under dynamic conditions the electrolytic picklingrate increases markedly with changing the pulsecurrent density from 004 to 02Acmminus2 +e electro-lytic pickling rate at 02A cmminus2 is about 21 times largerthan the chemical pickling rate in 300 g Lminus1H2SO4 at75degC resulting in the smooth and clean specimensurfaces

Data Availability

+e tables and figures data used to support the findings ofthis study are available from the corresponding author uponreasonable request

Conflicts of Interest

+e authors declare that there are no conflicts of interestregarding the publication of this paper

Table 3 Fitted results for EIS spectra in 300 g Lminus1H2SO4 solutions at 75degC containing different ions

Ions Rs Ω cm2 Y0-f Sα Ωminus1 cmminus2 αf Rf Ω cm2 Y0-dl Sα Ωminus1 cmminus2 αdl Rt Ω cm2

No ions 082 000218 087 280 00658 092 1610 g Lminus1 Fe2+ 094 000185 096 314 0093 084 1010 g Lminus1 Fe3+ 104 0000133 095 5499 0000281 068 706

Figure 14 Optical surface of the 2205 DSS hot-rolled strip afterindustrial pickling with optimized pickling process

8 Advances in Materials Science and Engineering

Acknowledgments

+e authors gratefully acknowledge the financial supportfrom the National Natural Science Foundation of China(Grant nos U1660205 and U1960103)

References

[1] Y-Y Wu and F Presuel-Moreno ldquoChloride levels that ini-tiated corrosion of duplex stainless steel embedded in mor-tarrdquo Advances in Materials Science and Engineering vol 2019Article ID 6949176 6 pages 2019

[2] T Li Y Zhang L Gao and Y Zhang ldquoOptimization ofFCAWparameters for ferrite content in 2205 DSS welds basedon the taguchi design methodrdquo Advances in Materials Scienceand Engineering vol 2018 Article ID 7950607 7 pages 2018

[3] Q Meng P La L Yao P Zhang Y Wei and X Guo ldquoEffectof Al onmicrostructure and properties of hot-rolled 2205 dualstainless steelrdquo Advances in Materials Science and Engineer-ing vol 2016 Article ID 7518067 8 pages 2016

[4] Z-g Song H Feng and S-m Hu ldquoDevelopment of Chineseduplex stainless steel in recent yearsrdquo Journal of Iron and SteelResearch International vol 24 no 2 pp 121ndash130 2017

[5] Z Y Liu C F Dong X G Li Q Zhi and Y F Cheng ldquoStresscorrosion cracking of 2205 duplex stainless steel in H2S-CO2environmentrdquo Journal of Materials Science vol 44 no 16pp 4228ndash4234 2009

[6] R N Gun Duplex Stainless Steels Vol 1 Abington Pub-lishing Cambridge UK 1994

[7] L-F Li Z-H Jiang and Y Riquier ldquoHigh-temperatureoxidation of duplex stainless steels in air and mixed gas of airand CH4rdquo Corrosion Science vol 47 no 1 pp 57ndash68 2005

[8] J G Peng M C Li S Z Luo et al ldquoOxidation characteristicsof duplex stainless steel 2205 in simulated combustion at-mosphererdquo Materials Research Innovation vol 19 no suppl5 pp 245ndash249 2015

[9] J G Peng and M C Li ldquoHigh temperature oxidation be-haviour of DSS 2205 in humid airrdquo Advanced MaterialsResearch vol 900 pp 673ndash676 2014

[10] N Ipek B Holm R Pettersson G Runnsjo and M KarlssonldquoElectrolytic pickling of duplex stainless steelrdquo Materials andCorrosion vol 56 no 8 pp 521ndash532 2005

[11] J G Peng S Z Luo andW B Dong ldquoStudy on the simulatedpickling of 443NT medium chrome ferritic stainless steelrdquoBaosteel Technical Research vol 4 no 1 pp pp50ndash52 2010

[12] L-F Li M Daerden P Caenen and J-P Celis ldquoElectro-chemical behavior of hot-rolled 304 stainless steel duringchemical pickling in HCl-based electrolytesrdquo Journal of 3eElectrochemical Society vol 153 no 5 pp B145ndashB150 2006

[13] J Hilden J Virtanen O Forsen and J Aromaa ldquoElectrolyticpickling of stainless steel studied by electrochemical polar-isation and DC resistance measurements combined withsurface analysisrdquo Electrochimica Acta vol 46 no 24-25pp 3859ndash3866 2001

[14] L-F Li P Caenen and M-F Jiang ldquoElectrolytic pickling ofthe oxide layer on hot-rolled 304 stainless steel in sodiumsulphaterdquo Corrosion Science vol 50 no 10 pp 2824ndash28302008

[15] W G Chen Y Q Chen and H L Pang ldquoStudy of Na2SO4electrolytic pickling process on 304 stainless steelrdquo ChinaMetallurgy vol 19 no 1 pp 16ndash23 2009

[16] L-F Li P Caenen and J-P Celis ldquoChemical pickling of 304stainless steel in fluoride- and sulfate-containing acidic

electrolytesrdquo Journal of 3e Electrochemical Society vol 152no 9 pp B352ndashB357 2005

[17] C A Huang and C C Hsu ldquo+e electrochemical polishingbehaviour of duplex stainless steel (SAF 2205) in phos-phoric-sulfuric mixed acidsrdquo International Journal of Ad-vance Manufacture Technology vol 34 no 9-10pp 904ndash910 2007

[18] L-F Li P Caenen M Daerden et al ldquoMechanism of singleand multiple step pickling of 304 stainless steel in acidelectrolytesrdquo Corrosion Science vol 47 no 5 pp 1307ndash13242005

[19] B S Covino J V Scalera T J Driscoll and J P CarterldquoDissolution behavior of 304 stainless steel in HNO3HFmixturesrdquo Metallurgical Transactions A vol 17 no 1pp 137ndash149 1986

[20] N Ipek N Lior M Vynnycky and F H Bark ldquoNumericaland experimental study of the effect of gas evolution inelectrolytic picklingrdquo Journal of Applied Electrochemistryvol 36 no 12 pp 1367ndash1379 2006

[21] M Abdallah ldquoGuar gum as corrosion inhibitor for carbonsteel in sulfuric acid solutionsrdquo Portugaliae ElectrochimicaActa vol 22 no 2 pp 161ndash175 2004

[22] C A Huang J H Chang W J Zhao et al ldquoExamination ofthe electropolishing behaviour of 73 brass in a 70 H3PO4solution using a rotating disc electroderdquo Materials Chemistryand Physics vol 146 no 3 pp 230ndash239 2014

[23] Q Xie P-y Shi C-j Liu M-f Jiang et al ldquoEffects of differentoxidants on HCl-based pickling process of 430 stainless steelrdquoJournal of Iron and Steel Research International vol 23 no 8pp 778ndash783 2016

[24] W H Hao L Y Qin and D L Liu ldquo+e effect of hydro-chloric acid concentration on pickling of duplex stainlesssteelrdquo Corrosion Protection vol 33 no suppl 2 pp 69ndash712012

[25] H Y Li and A C Zhao ldquoPickling behaviour of duplexstainless steel 2205 in hydrochloric acid solutionrdquoAdvances inMaterials Science and Engineering vol 2018 Article ID9754528 6 pages 2018

[26] C J Brown ldquoProcess and apparatus for recovery of peroxidecontaining pickling solutionsrdquo International Patent PCTCA0201598 2002

[27] R Jiang G Zou W Shi Y Liang and S Xiang ldquoCorrosionbehavior of plasma-nitrided 904L austenitic stainless steel inhydrofluoric acidrdquo Journal of Materials Engineering andPerformance vol 28 no 3 pp 1863ndash1872 2019

[28] C Donik A Kocijan J T Grant M Jenko A Drenik andB Pihlar ldquoXPS study of duplex stainless steel oxidized byoxygen atomsrdquo Corrosion Science vol 51 no 4 pp 827ndash8322009

[29] Y Xu Q Jin J Li X Xiao X Zhang and L Jiang ldquoOxidationinduced phase transformation of duplex stainless steel 25Cr-10Mn-2Ni-3Mo-08W-08Cu-05Nrdquo Corrosion Sciencevol 55 pp 233ndash237 2012

[30] ASM Handbook Committee ASM Handbook Volume 5Surface Engineering ASM International Cleveland OH USA2007

[31] J Eigeldinger and H Vogt ldquo+e bubble coverage of gas-evolving electrodes in a flowing electrolyterdquo ElectrochimicaActa vol 45 no 27 pp 4449ndash4456 2000

[32] M Pourbaix Atlas of Electrochemical Equilibria in AqueousSolutions Pergamon Press Oxford UK 2nd edition 1966

[33] Z G Wang H-H H Wu Q Li et al ldquoReversing interfacialcatalysis of ambipolar WSe2 single crystalrdquo Advanced Sciencevol 7 Article ID 1901382 pp 1ndash9 2019

Advances in Materials Science and Engineering 9

[34] Z Wang Q Li H Xu et al ldquoControllable etching of MoS2basal planes for enhanced hydrogen evolution through theformation of active edge sitesrdquo Nano Energy vol 49pp 634ndash643 2018

[35] M C Li C L Zeng S Z Luo J N Shen H C Lin andC N Cao ldquoElectrochemical corrosion characteristics of type316 stainless steel in simulated anode environment forPEMFCrdquo Electrochimica Acta vol 48 no 12 pp 1735ndash17412003

10 Advances in Materials Science and Engineering

0 50 100 150 200 250 300 350ndash10

ndash08

ndash06

ndash04

ndash02

00

02

E we (

V)

Time (s)

No iron ions10gLndash1Fe2+

10gLndash1Fe3+

Figure 12 Corrosion potential in 300 g Lminus1H2SO4 solutions at 75degC containing different Fe ions

1 2 3 4 5 6ndash1

0

0

1

2

3

4

5

ndashZPrime

(Ω cm

2 )

Zprime(Ω cm2)

(a)

0

ndashZPrime

(Ω cm

2 )

Zprime(Ω cm2)2 4 6 8 10 12

ndash1

0

1

2

3

4

5

(b)

ndashZPrime

(Ω cm

2 )

Zprime(Ω cm2)0 100 200 300 400 500 600 700

0

100

200

300

400

500

(c)

RfRt

Cdl

Cf

Rs

(d)

Figure 13 Nyquist plots in 300 g Lminus1H2SO4 solutions at 75degC containing no ions (a) 10 g Lminus1 Fe2+ (b) and 10 g Lminus1 Fe3+ (c) and thecorresponding circuit of the impedance spectrum (d)

Advances in Materials Science and Engineering 7

electrolytic pickling is performed under dynamic conditionsthe rotary disk develops a rational way for producing activeedges efficiently where catalytic activity of the test speci-mens is improved and its pickling rate is accelerated [33 34]+e dynamic electrolytic pickling rate at 02 A cmminus2 is about21 times higher than the chemical pickling which may giverise to a smooth specimen surface without oxide scales

+e Fe3+ ions are an effective oxidant which enhancedthe corrosion potential as shown in Figure 12 When no Feions were added in the H2SO4 solutions the corrosionpotential quickly declined at the beginning of the immersiontime after about 50 s it remained constant (approximatelyminus075 VMSE) subsequently as the immersion time increasedWhen 10 g Lminus1 Fe2+ was added in the H2SO4 solutions thecorrosion potential quickly declined at the beginning of theimmersion time after about 100 s it remained unchangedWhen 10 g Lminus1 Fe3+ was added in the H2SO4 solutions thecorrosion potential increased slowly from 0062 VMSE to0137 VMSE as the immersion time increased +e EISNyquist plots recorded on the test specimens immersed in300 g Lminus1 H2SO4 solutions containing no ions 10 g Lminus1 Fe2+and 10 g Lminus1 Fe3+ under the Ecorr conditions (ie the freecorrosion states) is presented in Figure 13 +e semicirclesize enlarged slightly with the addition of 10 g Lminus1 Fe 2+ butincreased noticeably with the addition of the 10 g Lminus1 Fe 3+

for its high impedanceIn order to show the dissolution process for the speci-

mens in 300 g Lminus1H2SO4 solutions at 75degC containing dif-ferent Fe ions the equivalent circuit model is proposed inFigure 13(d) according to the EIS features in Figure 13 Rs isthe electrolyte resistance Rf is the resistance of oxide layerremained on the specimens Rt is the charge transfer re-sistance Cf and Cdl can be replaced with constant phaseelement (CPE) [35] +e impedance of CPE is written inequation (15) where Y0 is the admittance magnitude of CPEand α is the exponential term Table 3 gives the fitted resultsof EIS spectra +e calculated spectra are shown as a solidcurve in Figure 13 which fit the experimental data very wellIt can be concluded that the model provided a reliabledescription for the corrosion systems

ZCPE 1

Y0(jω)α (15)

5 Application and Performance

According to the abovementioned results the picklingprocess of hot-rolled 2205 DSS is optimized through thehigh H2SO4 concentration high solution temperature andproper electrolysis current density in the industrial pre-pickling of 2205 DSS hot-rolled strips +e pickling effi-ciency is improved remarkably which increases the

production rate from 5ndash8mminminus1 to 15ndash18mminminus1 Be-sides the surface finish after pickling is notably enhanced asshown in Figure 14

6 Conclusion

+e pickling behaviour of hot-rolled 2205 DSS withannealing and mechanical descaling treatments in H2SO4solutions under both static and dynamic conditions has ledto the following conclusions

(1) In the static chemical pickling process the picklingrate may be accelerated noticeably by increasing thesolution temperature and H2SO4 concentration butbe decelerated greatly by Fe3+ ions

(2) +e chemical pickling process can be enhancedweakly by the moving speed of the specimen from 0to 20mminminus1 because the movement decreases theadsorption and growth of gas bubbles on the spec-imen surface to a certain extent

(3) Under dynamic conditions the electrolytic picklingrate increases markedly with changing the pulsecurrent density from 004 to 02Acmminus2 +e electro-lytic pickling rate at 02A cmminus2 is about 21 times largerthan the chemical pickling rate in 300 g Lminus1H2SO4 at75degC resulting in the smooth and clean specimensurfaces

Data Availability

+e tables and figures data used to support the findings ofthis study are available from the corresponding author uponreasonable request

Conflicts of Interest

+e authors declare that there are no conflicts of interestregarding the publication of this paper

Table 3 Fitted results for EIS spectra in 300 g Lminus1H2SO4 solutions at 75degC containing different ions

Ions Rs Ω cm2 Y0-f Sα Ωminus1 cmminus2 αf Rf Ω cm2 Y0-dl Sα Ωminus1 cmminus2 αdl Rt Ω cm2

No ions 082 000218 087 280 00658 092 1610 g Lminus1 Fe2+ 094 000185 096 314 0093 084 1010 g Lminus1 Fe3+ 104 0000133 095 5499 0000281 068 706

Figure 14 Optical surface of the 2205 DSS hot-rolled strip afterindustrial pickling with optimized pickling process

8 Advances in Materials Science and Engineering

Acknowledgments

+e authors gratefully acknowledge the financial supportfrom the National Natural Science Foundation of China(Grant nos U1660205 and U1960103)

References

[1] Y-Y Wu and F Presuel-Moreno ldquoChloride levels that ini-tiated corrosion of duplex stainless steel embedded in mor-tarrdquo Advances in Materials Science and Engineering vol 2019Article ID 6949176 6 pages 2019

[2] T Li Y Zhang L Gao and Y Zhang ldquoOptimization ofFCAWparameters for ferrite content in 2205 DSS welds basedon the taguchi design methodrdquo Advances in Materials Scienceand Engineering vol 2018 Article ID 7950607 7 pages 2018

[3] Q Meng P La L Yao P Zhang Y Wei and X Guo ldquoEffectof Al onmicrostructure and properties of hot-rolled 2205 dualstainless steelrdquo Advances in Materials Science and Engineer-ing vol 2016 Article ID 7518067 8 pages 2016

[4] Z-g Song H Feng and S-m Hu ldquoDevelopment of Chineseduplex stainless steel in recent yearsrdquo Journal of Iron and SteelResearch International vol 24 no 2 pp 121ndash130 2017

[5] Z Y Liu C F Dong X G Li Q Zhi and Y F Cheng ldquoStresscorrosion cracking of 2205 duplex stainless steel in H2S-CO2environmentrdquo Journal of Materials Science vol 44 no 16pp 4228ndash4234 2009

[6] R N Gun Duplex Stainless Steels Vol 1 Abington Pub-lishing Cambridge UK 1994

[7] L-F Li Z-H Jiang and Y Riquier ldquoHigh-temperatureoxidation of duplex stainless steels in air and mixed gas of airand CH4rdquo Corrosion Science vol 47 no 1 pp 57ndash68 2005

[8] J G Peng M C Li S Z Luo et al ldquoOxidation characteristicsof duplex stainless steel 2205 in simulated combustion at-mosphererdquo Materials Research Innovation vol 19 no suppl5 pp 245ndash249 2015

[9] J G Peng and M C Li ldquoHigh temperature oxidation be-haviour of DSS 2205 in humid airrdquo Advanced MaterialsResearch vol 900 pp 673ndash676 2014

[10] N Ipek B Holm R Pettersson G Runnsjo and M KarlssonldquoElectrolytic pickling of duplex stainless steelrdquo Materials andCorrosion vol 56 no 8 pp 521ndash532 2005

[11] J G Peng S Z Luo andW B Dong ldquoStudy on the simulatedpickling of 443NT medium chrome ferritic stainless steelrdquoBaosteel Technical Research vol 4 no 1 pp pp50ndash52 2010

[12] L-F Li M Daerden P Caenen and J-P Celis ldquoElectro-chemical behavior of hot-rolled 304 stainless steel duringchemical pickling in HCl-based electrolytesrdquo Journal of 3eElectrochemical Society vol 153 no 5 pp B145ndashB150 2006

[13] J Hilden J Virtanen O Forsen and J Aromaa ldquoElectrolyticpickling of stainless steel studied by electrochemical polar-isation and DC resistance measurements combined withsurface analysisrdquo Electrochimica Acta vol 46 no 24-25pp 3859ndash3866 2001

[14] L-F Li P Caenen and M-F Jiang ldquoElectrolytic pickling ofthe oxide layer on hot-rolled 304 stainless steel in sodiumsulphaterdquo Corrosion Science vol 50 no 10 pp 2824ndash28302008

[15] W G Chen Y Q Chen and H L Pang ldquoStudy of Na2SO4electrolytic pickling process on 304 stainless steelrdquo ChinaMetallurgy vol 19 no 1 pp 16ndash23 2009

[16] L-F Li P Caenen and J-P Celis ldquoChemical pickling of 304stainless steel in fluoride- and sulfate-containing acidic

electrolytesrdquo Journal of 3e Electrochemical Society vol 152no 9 pp B352ndashB357 2005

[17] C A Huang and C C Hsu ldquo+e electrochemical polishingbehaviour of duplex stainless steel (SAF 2205) in phos-phoric-sulfuric mixed acidsrdquo International Journal of Ad-vance Manufacture Technology vol 34 no 9-10pp 904ndash910 2007

[18] L-F Li P Caenen M Daerden et al ldquoMechanism of singleand multiple step pickling of 304 stainless steel in acidelectrolytesrdquo Corrosion Science vol 47 no 5 pp 1307ndash13242005

[19] B S Covino J V Scalera T J Driscoll and J P CarterldquoDissolution behavior of 304 stainless steel in HNO3HFmixturesrdquo Metallurgical Transactions A vol 17 no 1pp 137ndash149 1986

[20] N Ipek N Lior M Vynnycky and F H Bark ldquoNumericaland experimental study of the effect of gas evolution inelectrolytic picklingrdquo Journal of Applied Electrochemistryvol 36 no 12 pp 1367ndash1379 2006

[21] M Abdallah ldquoGuar gum as corrosion inhibitor for carbonsteel in sulfuric acid solutionsrdquo Portugaliae ElectrochimicaActa vol 22 no 2 pp 161ndash175 2004

[22] C A Huang J H Chang W J Zhao et al ldquoExamination ofthe electropolishing behaviour of 73 brass in a 70 H3PO4solution using a rotating disc electroderdquo Materials Chemistryand Physics vol 146 no 3 pp 230ndash239 2014

[23] Q Xie P-y Shi C-j Liu M-f Jiang et al ldquoEffects of differentoxidants on HCl-based pickling process of 430 stainless steelrdquoJournal of Iron and Steel Research International vol 23 no 8pp 778ndash783 2016

[24] W H Hao L Y Qin and D L Liu ldquo+e effect of hydro-chloric acid concentration on pickling of duplex stainlesssteelrdquo Corrosion Protection vol 33 no suppl 2 pp 69ndash712012

[25] H Y Li and A C Zhao ldquoPickling behaviour of duplexstainless steel 2205 in hydrochloric acid solutionrdquoAdvances inMaterials Science and Engineering vol 2018 Article ID9754528 6 pages 2018

[26] C J Brown ldquoProcess and apparatus for recovery of peroxidecontaining pickling solutionsrdquo International Patent PCTCA0201598 2002

[27] R Jiang G Zou W Shi Y Liang and S Xiang ldquoCorrosionbehavior of plasma-nitrided 904L austenitic stainless steel inhydrofluoric acidrdquo Journal of Materials Engineering andPerformance vol 28 no 3 pp 1863ndash1872 2019

[28] C Donik A Kocijan J T Grant M Jenko A Drenik andB Pihlar ldquoXPS study of duplex stainless steel oxidized byoxygen atomsrdquo Corrosion Science vol 51 no 4 pp 827ndash8322009

[29] Y Xu Q Jin J Li X Xiao X Zhang and L Jiang ldquoOxidationinduced phase transformation of duplex stainless steel 25Cr-10Mn-2Ni-3Mo-08W-08Cu-05Nrdquo Corrosion Sciencevol 55 pp 233ndash237 2012

[30] ASM Handbook Committee ASM Handbook Volume 5Surface Engineering ASM International Cleveland OH USA2007

[31] J Eigeldinger and H Vogt ldquo+e bubble coverage of gas-evolving electrodes in a flowing electrolyterdquo ElectrochimicaActa vol 45 no 27 pp 4449ndash4456 2000

[32] M Pourbaix Atlas of Electrochemical Equilibria in AqueousSolutions Pergamon Press Oxford UK 2nd edition 1966

[33] Z G Wang H-H H Wu Q Li et al ldquoReversing interfacialcatalysis of ambipolar WSe2 single crystalrdquo Advanced Sciencevol 7 Article ID 1901382 pp 1ndash9 2019

Advances in Materials Science and Engineering 9

[34] Z Wang Q Li H Xu et al ldquoControllable etching of MoS2basal planes for enhanced hydrogen evolution through theformation of active edge sitesrdquo Nano Energy vol 49pp 634ndash643 2018

[35] M C Li C L Zeng S Z Luo J N Shen H C Lin andC N Cao ldquoElectrochemical corrosion characteristics of type316 stainless steel in simulated anode environment forPEMFCrdquo Electrochimica Acta vol 48 no 12 pp 1735ndash17412003

10 Advances in Materials Science and Engineering

electrolytic pickling is performed under dynamic conditionsthe rotary disk develops a rational way for producing activeedges efficiently where catalytic activity of the test speci-mens is improved and its pickling rate is accelerated [33 34]+e dynamic electrolytic pickling rate at 02 A cmminus2 is about21 times higher than the chemical pickling which may giverise to a smooth specimen surface without oxide scales

+e Fe3+ ions are an effective oxidant which enhancedthe corrosion potential as shown in Figure 12 When no Feions were added in the H2SO4 solutions the corrosionpotential quickly declined at the beginning of the immersiontime after about 50 s it remained constant (approximatelyminus075 VMSE) subsequently as the immersion time increasedWhen 10 g Lminus1 Fe2+ was added in the H2SO4 solutions thecorrosion potential quickly declined at the beginning of theimmersion time after about 100 s it remained unchangedWhen 10 g Lminus1 Fe3+ was added in the H2SO4 solutions thecorrosion potential increased slowly from 0062 VMSE to0137 VMSE as the immersion time increased +e EISNyquist plots recorded on the test specimens immersed in300 g Lminus1 H2SO4 solutions containing no ions 10 g Lminus1 Fe2+and 10 g Lminus1 Fe3+ under the Ecorr conditions (ie the freecorrosion states) is presented in Figure 13 +e semicirclesize enlarged slightly with the addition of 10 g Lminus1 Fe 2+ butincreased noticeably with the addition of the 10 g Lminus1 Fe 3+

for its high impedanceIn order to show the dissolution process for the speci-

mens in 300 g Lminus1H2SO4 solutions at 75degC containing dif-ferent Fe ions the equivalent circuit model is proposed inFigure 13(d) according to the EIS features in Figure 13 Rs isthe electrolyte resistance Rf is the resistance of oxide layerremained on the specimens Rt is the charge transfer re-sistance Cf and Cdl can be replaced with constant phaseelement (CPE) [35] +e impedance of CPE is written inequation (15) where Y0 is the admittance magnitude of CPEand α is the exponential term Table 3 gives the fitted resultsof EIS spectra +e calculated spectra are shown as a solidcurve in Figure 13 which fit the experimental data very wellIt can be concluded that the model provided a reliabledescription for the corrosion systems

ZCPE 1

Y0(jω)α (15)

5 Application and Performance

According to the abovementioned results the picklingprocess of hot-rolled 2205 DSS is optimized through thehigh H2SO4 concentration high solution temperature andproper electrolysis current density in the industrial pre-pickling of 2205 DSS hot-rolled strips +e pickling effi-ciency is improved remarkably which increases the

production rate from 5ndash8mminminus1 to 15ndash18mminminus1 Be-sides the surface finish after pickling is notably enhanced asshown in Figure 14

6 Conclusion

+e pickling behaviour of hot-rolled 2205 DSS withannealing and mechanical descaling treatments in H2SO4solutions under both static and dynamic conditions has ledto the following conclusions

(1) In the static chemical pickling process the picklingrate may be accelerated noticeably by increasing thesolution temperature and H2SO4 concentration butbe decelerated greatly by Fe3+ ions

(2) +e chemical pickling process can be enhancedweakly by the moving speed of the specimen from 0to 20mminminus1 because the movement decreases theadsorption and growth of gas bubbles on the spec-imen surface to a certain extent

(3) Under dynamic conditions the electrolytic picklingrate increases markedly with changing the pulsecurrent density from 004 to 02Acmminus2 +e electro-lytic pickling rate at 02A cmminus2 is about 21 times largerthan the chemical pickling rate in 300 g Lminus1H2SO4 at75degC resulting in the smooth and clean specimensurfaces

Data Availability

+e tables and figures data used to support the findings ofthis study are available from the corresponding author uponreasonable request

Conflicts of Interest

+e authors declare that there are no conflicts of interestregarding the publication of this paper

Table 3 Fitted results for EIS spectra in 300 g Lminus1H2SO4 solutions at 75degC containing different ions

Ions Rs Ω cm2 Y0-f Sα Ωminus1 cmminus2 αf Rf Ω cm2 Y0-dl Sα Ωminus1 cmminus2 αdl Rt Ω cm2

No ions 082 000218 087 280 00658 092 1610 g Lminus1 Fe2+ 094 000185 096 314 0093 084 1010 g Lminus1 Fe3+ 104 0000133 095 5499 0000281 068 706

Figure 14 Optical surface of the 2205 DSS hot-rolled strip afterindustrial pickling with optimized pickling process

8 Advances in Materials Science and Engineering

Acknowledgments

+e authors gratefully acknowledge the financial supportfrom the National Natural Science Foundation of China(Grant nos U1660205 and U1960103)

References

[1] Y-Y Wu and F Presuel-Moreno ldquoChloride levels that ini-tiated corrosion of duplex stainless steel embedded in mor-tarrdquo Advances in Materials Science and Engineering vol 2019Article ID 6949176 6 pages 2019

[2] T Li Y Zhang L Gao and Y Zhang ldquoOptimization ofFCAWparameters for ferrite content in 2205 DSS welds basedon the taguchi design methodrdquo Advances in Materials Scienceand Engineering vol 2018 Article ID 7950607 7 pages 2018

[3] Q Meng P La L Yao P Zhang Y Wei and X Guo ldquoEffectof Al onmicrostructure and properties of hot-rolled 2205 dualstainless steelrdquo Advances in Materials Science and Engineer-ing vol 2016 Article ID 7518067 8 pages 2016

[4] Z-g Song H Feng and S-m Hu ldquoDevelopment of Chineseduplex stainless steel in recent yearsrdquo Journal of Iron and SteelResearch International vol 24 no 2 pp 121ndash130 2017

[5] Z Y Liu C F Dong X G Li Q Zhi and Y F Cheng ldquoStresscorrosion cracking of 2205 duplex stainless steel in H2S-CO2environmentrdquo Journal of Materials Science vol 44 no 16pp 4228ndash4234 2009

[6] R N Gun Duplex Stainless Steels Vol 1 Abington Pub-lishing Cambridge UK 1994

[7] L-F Li Z-H Jiang and Y Riquier ldquoHigh-temperatureoxidation of duplex stainless steels in air and mixed gas of airand CH4rdquo Corrosion Science vol 47 no 1 pp 57ndash68 2005

[8] J G Peng M C Li S Z Luo et al ldquoOxidation characteristicsof duplex stainless steel 2205 in simulated combustion at-mosphererdquo Materials Research Innovation vol 19 no suppl5 pp 245ndash249 2015

[9] J G Peng and M C Li ldquoHigh temperature oxidation be-haviour of DSS 2205 in humid airrdquo Advanced MaterialsResearch vol 900 pp 673ndash676 2014

[10] N Ipek B Holm R Pettersson G Runnsjo and M KarlssonldquoElectrolytic pickling of duplex stainless steelrdquo Materials andCorrosion vol 56 no 8 pp 521ndash532 2005

[11] J G Peng S Z Luo andW B Dong ldquoStudy on the simulatedpickling of 443NT medium chrome ferritic stainless steelrdquoBaosteel Technical Research vol 4 no 1 pp pp50ndash52 2010

[12] L-F Li M Daerden P Caenen and J-P Celis ldquoElectro-chemical behavior of hot-rolled 304 stainless steel duringchemical pickling in HCl-based electrolytesrdquo Journal of 3eElectrochemical Society vol 153 no 5 pp B145ndashB150 2006

[13] J Hilden J Virtanen O Forsen and J Aromaa ldquoElectrolyticpickling of stainless steel studied by electrochemical polar-isation and DC resistance measurements combined withsurface analysisrdquo Electrochimica Acta vol 46 no 24-25pp 3859ndash3866 2001

[14] L-F Li P Caenen and M-F Jiang ldquoElectrolytic pickling ofthe oxide layer on hot-rolled 304 stainless steel in sodiumsulphaterdquo Corrosion Science vol 50 no 10 pp 2824ndash28302008

[15] W G Chen Y Q Chen and H L Pang ldquoStudy of Na2SO4electrolytic pickling process on 304 stainless steelrdquo ChinaMetallurgy vol 19 no 1 pp 16ndash23 2009

[16] L-F Li P Caenen and J-P Celis ldquoChemical pickling of 304stainless steel in fluoride- and sulfate-containing acidic

electrolytesrdquo Journal of 3e Electrochemical Society vol 152no 9 pp B352ndashB357 2005

[17] C A Huang and C C Hsu ldquo+e electrochemical polishingbehaviour of duplex stainless steel (SAF 2205) in phos-phoric-sulfuric mixed acidsrdquo International Journal of Ad-vance Manufacture Technology vol 34 no 9-10pp 904ndash910 2007

[18] L-F Li P Caenen M Daerden et al ldquoMechanism of singleand multiple step pickling of 304 stainless steel in acidelectrolytesrdquo Corrosion Science vol 47 no 5 pp 1307ndash13242005

[19] B S Covino J V Scalera T J Driscoll and J P CarterldquoDissolution behavior of 304 stainless steel in HNO3HFmixturesrdquo Metallurgical Transactions A vol 17 no 1pp 137ndash149 1986

[20] N Ipek N Lior M Vynnycky and F H Bark ldquoNumericaland experimental study of the effect of gas evolution inelectrolytic picklingrdquo Journal of Applied Electrochemistryvol 36 no 12 pp 1367ndash1379 2006

[21] M Abdallah ldquoGuar gum as corrosion inhibitor for carbonsteel in sulfuric acid solutionsrdquo Portugaliae ElectrochimicaActa vol 22 no 2 pp 161ndash175 2004

[22] C A Huang J H Chang W J Zhao et al ldquoExamination ofthe electropolishing behaviour of 73 brass in a 70 H3PO4solution using a rotating disc electroderdquo Materials Chemistryand Physics vol 146 no 3 pp 230ndash239 2014

[23] Q Xie P-y Shi C-j Liu M-f Jiang et al ldquoEffects of differentoxidants on HCl-based pickling process of 430 stainless steelrdquoJournal of Iron and Steel Research International vol 23 no 8pp 778ndash783 2016

[24] W H Hao L Y Qin and D L Liu ldquo+e effect of hydro-chloric acid concentration on pickling of duplex stainlesssteelrdquo Corrosion Protection vol 33 no suppl 2 pp 69ndash712012

[25] H Y Li and A C Zhao ldquoPickling behaviour of duplexstainless steel 2205 in hydrochloric acid solutionrdquoAdvances inMaterials Science and Engineering vol 2018 Article ID9754528 6 pages 2018

[26] C J Brown ldquoProcess and apparatus for recovery of peroxidecontaining pickling solutionsrdquo International Patent PCTCA0201598 2002

[27] R Jiang G Zou W Shi Y Liang and S Xiang ldquoCorrosionbehavior of plasma-nitrided 904L austenitic stainless steel inhydrofluoric acidrdquo Journal of Materials Engineering andPerformance vol 28 no 3 pp 1863ndash1872 2019

[28] C Donik A Kocijan J T Grant M Jenko A Drenik andB Pihlar ldquoXPS study of duplex stainless steel oxidized byoxygen atomsrdquo Corrosion Science vol 51 no 4 pp 827ndash8322009

[29] Y Xu Q Jin J Li X Xiao X Zhang and L Jiang ldquoOxidationinduced phase transformation of duplex stainless steel 25Cr-10Mn-2Ni-3Mo-08W-08Cu-05Nrdquo Corrosion Sciencevol 55 pp 233ndash237 2012

[30] ASM Handbook Committee ASM Handbook Volume 5Surface Engineering ASM International Cleveland OH USA2007

[31] J Eigeldinger and H Vogt ldquo+e bubble coverage of gas-evolving electrodes in a flowing electrolyterdquo ElectrochimicaActa vol 45 no 27 pp 4449ndash4456 2000

[32] M Pourbaix Atlas of Electrochemical Equilibria in AqueousSolutions Pergamon Press Oxford UK 2nd edition 1966

[33] Z G Wang H-H H Wu Q Li et al ldquoReversing interfacialcatalysis of ambipolar WSe2 single crystalrdquo Advanced Sciencevol 7 Article ID 1901382 pp 1ndash9 2019

Advances in Materials Science and Engineering 9

[34] Z Wang Q Li H Xu et al ldquoControllable etching of MoS2basal planes for enhanced hydrogen evolution through theformation of active edge sitesrdquo Nano Energy vol 49pp 634ndash643 2018

[35] M C Li C L Zeng S Z Luo J N Shen H C Lin andC N Cao ldquoElectrochemical corrosion characteristics of type316 stainless steel in simulated anode environment forPEMFCrdquo Electrochimica Acta vol 48 no 12 pp 1735ndash17412003

10 Advances in Materials Science and Engineering

Acknowledgments

+e authors gratefully acknowledge the financial supportfrom the National Natural Science Foundation of China(Grant nos U1660205 and U1960103)

References

[1] Y-Y Wu and F Presuel-Moreno ldquoChloride levels that ini-tiated corrosion of duplex stainless steel embedded in mor-tarrdquo Advances in Materials Science and Engineering vol 2019Article ID 6949176 6 pages 2019

[2] T Li Y Zhang L Gao and Y Zhang ldquoOptimization ofFCAWparameters for ferrite content in 2205 DSS welds basedon the taguchi design methodrdquo Advances in Materials Scienceand Engineering vol 2018 Article ID 7950607 7 pages 2018

[3] Q Meng P La L Yao P Zhang Y Wei and X Guo ldquoEffectof Al onmicrostructure and properties of hot-rolled 2205 dualstainless steelrdquo Advances in Materials Science and Engineer-ing vol 2016 Article ID 7518067 8 pages 2016

[4] Z-g Song H Feng and S-m Hu ldquoDevelopment of Chineseduplex stainless steel in recent yearsrdquo Journal of Iron and SteelResearch International vol 24 no 2 pp 121ndash130 2017

[5] Z Y Liu C F Dong X G Li Q Zhi and Y F Cheng ldquoStresscorrosion cracking of 2205 duplex stainless steel in H2S-CO2environmentrdquo Journal of Materials Science vol 44 no 16pp 4228ndash4234 2009

[6] R N Gun Duplex Stainless Steels Vol 1 Abington Pub-lishing Cambridge UK 1994

[7] L-F Li Z-H Jiang and Y Riquier ldquoHigh-temperatureoxidation of duplex stainless steels in air and mixed gas of airand CH4rdquo Corrosion Science vol 47 no 1 pp 57ndash68 2005

[8] J G Peng M C Li S Z Luo et al ldquoOxidation characteristicsof duplex stainless steel 2205 in simulated combustion at-mosphererdquo Materials Research Innovation vol 19 no suppl5 pp 245ndash249 2015

[9] J G Peng and M C Li ldquoHigh temperature oxidation be-haviour of DSS 2205 in humid airrdquo Advanced MaterialsResearch vol 900 pp 673ndash676 2014

[10] N Ipek B Holm R Pettersson G Runnsjo and M KarlssonldquoElectrolytic pickling of duplex stainless steelrdquo Materials andCorrosion vol 56 no 8 pp 521ndash532 2005

[11] J G Peng S Z Luo andW B Dong ldquoStudy on the simulatedpickling of 443NT medium chrome ferritic stainless steelrdquoBaosteel Technical Research vol 4 no 1 pp pp50ndash52 2010

[12] L-F Li M Daerden P Caenen and J-P Celis ldquoElectro-chemical behavior of hot-rolled 304 stainless steel duringchemical pickling in HCl-based electrolytesrdquo Journal of 3eElectrochemical Society vol 153 no 5 pp B145ndashB150 2006

[13] J Hilden J Virtanen O Forsen and J Aromaa ldquoElectrolyticpickling of stainless steel studied by electrochemical polar-isation and DC resistance measurements combined withsurface analysisrdquo Electrochimica Acta vol 46 no 24-25pp 3859ndash3866 2001

[14] L-F Li P Caenen and M-F Jiang ldquoElectrolytic pickling ofthe oxide layer on hot-rolled 304 stainless steel in sodiumsulphaterdquo Corrosion Science vol 50 no 10 pp 2824ndash28302008

[15] W G Chen Y Q Chen and H L Pang ldquoStudy of Na2SO4electrolytic pickling process on 304 stainless steelrdquo ChinaMetallurgy vol 19 no 1 pp 16ndash23 2009

[16] L-F Li P Caenen and J-P Celis ldquoChemical pickling of 304stainless steel in fluoride- and sulfate-containing acidic

electrolytesrdquo Journal of 3e Electrochemical Society vol 152no 9 pp B352ndashB357 2005

[17] C A Huang and C C Hsu ldquo+e electrochemical polishingbehaviour of duplex stainless steel (SAF 2205) in phos-phoric-sulfuric mixed acidsrdquo International Journal of Ad-vance Manufacture Technology vol 34 no 9-10pp 904ndash910 2007

[18] L-F Li P Caenen M Daerden et al ldquoMechanism of singleand multiple step pickling of 304 stainless steel in acidelectrolytesrdquo Corrosion Science vol 47 no 5 pp 1307ndash13242005

[19] B S Covino J V Scalera T J Driscoll and J P CarterldquoDissolution behavior of 304 stainless steel in HNO3HFmixturesrdquo Metallurgical Transactions A vol 17 no 1pp 137ndash149 1986

[20] N Ipek N Lior M Vynnycky and F H Bark ldquoNumericaland experimental study of the effect of gas evolution inelectrolytic picklingrdquo Journal of Applied Electrochemistryvol 36 no 12 pp 1367ndash1379 2006

[21] M Abdallah ldquoGuar gum as corrosion inhibitor for carbonsteel in sulfuric acid solutionsrdquo Portugaliae ElectrochimicaActa vol 22 no 2 pp 161ndash175 2004

[22] C A Huang J H Chang W J Zhao et al ldquoExamination ofthe electropolishing behaviour of 73 brass in a 70 H3PO4solution using a rotating disc electroderdquo Materials Chemistryand Physics vol 146 no 3 pp 230ndash239 2014

[23] Q Xie P-y Shi C-j Liu M-f Jiang et al ldquoEffects of differentoxidants on HCl-based pickling process of 430 stainless steelrdquoJournal of Iron and Steel Research International vol 23 no 8pp 778ndash783 2016

[24] W H Hao L Y Qin and D L Liu ldquo+e effect of hydro-chloric acid concentration on pickling of duplex stainlesssteelrdquo Corrosion Protection vol 33 no suppl 2 pp 69ndash712012

[25] H Y Li and A C Zhao ldquoPickling behaviour of duplexstainless steel 2205 in hydrochloric acid solutionrdquoAdvances inMaterials Science and Engineering vol 2018 Article ID9754528 6 pages 2018

[26] C J Brown ldquoProcess and apparatus for recovery of peroxidecontaining pickling solutionsrdquo International Patent PCTCA0201598 2002

[27] R Jiang G Zou W Shi Y Liang and S Xiang ldquoCorrosionbehavior of plasma-nitrided 904L austenitic stainless steel inhydrofluoric acidrdquo Journal of Materials Engineering andPerformance vol 28 no 3 pp 1863ndash1872 2019

[28] C Donik A Kocijan J T Grant M Jenko A Drenik andB Pihlar ldquoXPS study of duplex stainless steel oxidized byoxygen atomsrdquo Corrosion Science vol 51 no 4 pp 827ndash8322009

[29] Y Xu Q Jin J Li X Xiao X Zhang and L Jiang ldquoOxidationinduced phase transformation of duplex stainless steel 25Cr-10Mn-2Ni-3Mo-08W-08Cu-05Nrdquo Corrosion Sciencevol 55 pp 233ndash237 2012

[30] ASM Handbook Committee ASM Handbook Volume 5Surface Engineering ASM International Cleveland OH USA2007

[31] J Eigeldinger and H Vogt ldquo+e bubble coverage of gas-evolving electrodes in a flowing electrolyterdquo ElectrochimicaActa vol 45 no 27 pp 4449ndash4456 2000

[32] M Pourbaix Atlas of Electrochemical Equilibria in AqueousSolutions Pergamon Press Oxford UK 2nd edition 1966

[33] Z G Wang H-H H Wu Q Li et al ldquoReversing interfacialcatalysis of ambipolar WSe2 single crystalrdquo Advanced Sciencevol 7 Article ID 1901382 pp 1ndash9 2019

Advances in Materials Science and Engineering 9

[34] Z Wang Q Li H Xu et al ldquoControllable etching of MoS2basal planes for enhanced hydrogen evolution through theformation of active edge sitesrdquo Nano Energy vol 49pp 634ndash643 2018

[35] M C Li C L Zeng S Z Luo J N Shen H C Lin andC N Cao ldquoElectrochemical corrosion characteristics of type316 stainless steel in simulated anode environment forPEMFCrdquo Electrochimica Acta vol 48 no 12 pp 1735ndash17412003

10 Advances in Materials Science and Engineering

[34] Z Wang Q Li H Xu et al ldquoControllable etching of MoS2basal planes for enhanced hydrogen evolution through theformation of active edge sitesrdquo Nano Energy vol 49pp 634ndash643 2018

[35] M C Li C L Zeng S Z Luo J N Shen H C Lin andC N Cao ldquoElectrochemical corrosion characteristics of type316 stainless steel in simulated anode environment forPEMFCrdquo Electrochimica Acta vol 48 no 12 pp 1735ndash17412003

10 Advances in Materials Science and Engineering