Mastering the production of high-carbon wire rod – especially cord-grade wire rod – on a mini-complex

originally built at the Moldavian Metallurgical Plant to make ordinary wire rod was a daunting problem

that has been solved by a collaboration with the Ukrainian Academy of Science’s Institute of Metallurgy.

Researchers developed an integrated technology for making the steel, continuous-cast semifinished

products, and wire rod needed to make metal cord of ordinary, high, and ultrahigh strength. The wire rod

is characterized by a good-quality surface (defect depth no greater than 0.15 mm, with 95% being no

deeper than 0.10 mm), good deformability, and the ease with which it can be converted into wire, strands,

and cord structures.

The Moldavian Metallurgical Plant (MMZ) recently faced a complicated problem in attempting to master the pro-

duction of high-carbon cord-grade wire rod on the complex it uses to make ordinary grades of this product. The plant

resolved the problem in collaboration with the Institute of Ferrous Metallurgy (under the National Academy of Sciences

of Ukraine) [1]. The MMZ was designed without facilities for the vacuum degassing of steel or its electromagnetic mixing

during steelmaking and continuous casting. The problem was further complicated by the fact that ordinary grades of scrap

were used in the steelmaking charge and semifinished products of small cross (125 × 125 mm) were produced by the caster.

This provided for less deformation of the cast structure during the production of the wire rod.

The following are the main requirements in effect in regard to the quality indices of the steel, semifinished product

(SFP), and wire rod used to make metal cord:

• attainment of the prescribed contents of the main chemical elements – C, Mn, and Si, with optimization of the

steel’s contents of nonferrous-metal impurities – Cr, Ni, and Cu;

• the formation of a uniform chemical composition in the steel with minimal concentrations of harmful impurities

(P, S, As, Zn, Pb, Sn, etc.);

• the production of steel characterized by a high degree of cleanliness with respect to nonmetallic inclusions (NI), espe-

cially nondeformable inclusions; the absence of NI of complex chemical composition with a high percentage of Al2O3;

• the formation of a continuous-cast semifinished product (CCS) with a high surface finish, minimal segregation and

porosity, and the absence of exogeneous inclusions;

• the formation of a uniform structure and uniform mechanical properties in the wire rod over the length of the coil,

formation of the largest possible amount of sorbitic pearlite with minimal amounts of structurally free ferrite (SFF)

or cementite (SFC), and the absence of quenching structures.

The metallurgical complex used at the MMZ includes modern equipment: a 120-ton arc steelmaking furnace equip-

ped with alternative energy sources (gas-oxygen burners about the perimeter and bottom injection lances, similar to the

Metallurgist, Vol. 49, Nos. 11–12, 2005

ENSURING HIGH QUALITY INDICES FOR THE

WIRE ROD USED TO MAKE METAL CORD

V. V. Parusov, I. V. Derevyanchenko,A. B. Sychkov, A. M. Nesterenko,É. V. Parusov, and M. A. Zhigarev

UDC 621.778

Institute of Ferrous Metallurgy (National Academy of Sciences of Ukraine) and the Moldavian Metallurgical Plant.

Translated from Metallurg, No. 11, pp. 45–51, November, 2005.

0026-0894/05/1112-0439 ©2005 Springer Science+Business Media, Inc. 439

Danark system); a ladle-furnace unit (LFU); a VD/VOD-type vacuum degassing unit; a six-strand continuous caster which

provides for complete protection of the stream and electromagnetic mixing (EMM) of the steel being cast (Fig. 1). All this

guarantees that the chemical composition of cord-steel grades 70KRD, 80KRD, and 85KRD will be within the prescribed range

with respect to the concentrations (by mass) of the elements in the heats: ∆C = 0–0.01%; ∆Mn = 0–0.03%; ∆Si = 0–0.03%;

the scatter of values between the heats is ∆C = 0–0.04%; ∆Mn = 0–0.05%; ∆Si = 0–0.05%. The contents of phosphorus

and sulfur are no greater than 0.015% and 0.006%. The residual content of nonferrous-metal impurities is fairly high when

the steel is made on the basis of sorted scrap with the addition of up to 30% conversion pig iron or another raw material

(Sintikom®, Superkom, hot-briquetted iron). The use of a a pure raw material (metallized pellets) to make wire rod for metal

cord is very expensive. It was shown in [2] that contents of Cr ≤ 0.15%, Ni ≤ 0.15%, and Cu ≤ 0.25% do not adversely affect

the properties of the wire rod, its suitability for drawing and winding of the cord structures, or the characteristics of the fin-

ished product (metal cord, high-pressure hoses, and other products used in critical applications).

The behavior of boron and copper in steel is usually explained on the basis of the assumption [3] that boron occu-

pies an interstitial position in the lattice of iron in octahedral and tetrahedral cavities (pores). However, the validity of this

assumption is placed in doubt when one compares the dimensions of octa- and tetrahedral cavities in the lattices of α- and

γ-Fe and the size of the boron atom γB = 0.091 nm. In fact, the boron atom – which is 1.26 times larger than the nitrogen

atom and 1.18 times larger than the carbon atom (see Table 1) – is barely capable of occupying interstitial positions in cavi-

ties in the lattices of either modification of iron. The following formula [3] was used to calculate the distortion ε of the crys-

talline lattice of the solid solution at the sites where iron atoms are in direct contact with interstitial atoms:

ε = [(di – dc) /dc]·100, (1)

where di is the diameter of the interstitial atom, nm; dc is the maximum diameter of a cavity before the introduction of a dis-

solved atom into it, nm.

It has been determined [6] that for atoms of nitrogen, carbon, and boron introduced into the lattice of austenite

(γ-Fe-octapore), the distortion ε calculated from Eq. (1) is 35.8, 45.3, and 71.7%, respectively, i.e., ε is quite substantial for

boron. The following values of ε were obtained for the bcc lattice – the lattice of α-Fe-octapore: 278.95, 305.3, and 378.95%

440

ASF 120/95 MVA

VD-VOD vacuumdegassing unit

Mold with electromagneticmixing unit

Tundish

Steel-pouring ladle

ceramicNo. 1

ceramicNo. 2

Thermostat

10-s

tand

roug

hing

trai

n(h

oriz

onta

l sta

nds)

6-st

and

inte

rmed

iate

trai

n (h

oriz

onta

lst

ands

)5-

stan

d ro

ughi

ng tr

ain

(3 h

oriz

onta

l and

2 ve

rtic

al s

tand

s)

Hea

t-st

reng

then

ing

line

Inte

rmed

iate

rod-

mill

trai

n

Mid

dle

cool

ing

sect

ion

10-s

tand

rod

-mill

bloc

k

Wat

er-c

oolin

g lin

e

Las

er r

od-d

iam

eter

gag

e

Coi

ler

Stel

mor

line

Wire rod

Rolledsections

CCS

Ladle-furnace

Fig. 1. Diagram of the production of steel, CCS, and rolled products at the MMZ.

for interstitial atoms of nitrogen, carbon, and boron, respectively. It follows from this that the introduction of boron atoms

into the lattice of iron at interstitial positions is highly problematic – particularly for iron’s bcc modification.

At the same time, the equilibrium phase diagrams (Fig. 2) [3] show that boron has a certain degree of solubility in

α- and γ-Fe iron. According to Nicholson (Fig. 2a), the limiting solubility of boron is roughly 0.148 mass % in α-iron at

915°C and 0.150% in γ-Fe at 1176°C. According to MacBride (Fig. 2b), at 906°C boron content is 0.0025% in α-Fe and

0.00071% in γ-Fe, while it is 0.00189% at 1168°C. The difference between these findings can probably be attributed to a

difference in the purity of the materials used to perform the respective experiments.

Experiments involving the rolling of steel 20G2R (0.20–0.25% Cu) showed that for the technology used at the MMZ

to introduce boron into steel on the ladle-furnace unit in the form of cored wire, the ratio of the total boron content of the

steel (0.006–0.012%) to the boron content of the solid solution (0.002–0.004%) is roughly 3:1, i.e., a significant amount of

boron is dissolved in the steel’s ferrite.

The graphs in Fig. 3 [7] showing the change in the lattice period of γ-Fe (pure and with the addition of 0.005%

boron) in the temperature range 925–1200°C illustrate that the period is smaller throughout this range in γ-Fe. In steel

alloyed with boron, this can take place only when a substitutional solid solution is formed in γ-Fe. The octahedral cavities

are much smaller in the bcc lattice of α-Fe than they are in γ-Fe. Despite the small size of the tetrahedral cavities, atoms

of other elements enter the lattice of α-Fe mainly at octapores. This is connected with the fact [6] that the introduction of

atoms into α-Fe tetrapores leads to displacement of the equilibrium positions of four iron atoms, while the introduction of

atoms into octopores along the <100> direction displaces only two iron atoms. This explains (at least from a dimensional-

geometric standpoint) the increase in the limiting solubility of Cu in α-Fe. The introduction of Cu atoms into the lattice

of α-Fe – with Cu atoms being larger than iron atoms (see Table 1) – increases the lattice period of this iron and the level

441

TABLE 1. Parameters of Fe, Cu, N, C, and B atoms and Octa- and Tetrahedral Cavities in the

Lattices of Iron of the α- and γ-Modifications [4, 5]

Atomic radius, nm Cavity radius, nm

Fe Cu N C Bγ-Fe α-Fe

octa- tetra- octa- tetra-

0.127 0.128 0.072 0.077 0.091 0.053 0.029 0.019 0.036

0 0.1 0.2

1600

1400

1200

1000

800

1400

1200

1000

800

B, mass %0 10 20 30

B·10–3, mass %

0 50 100 150B·10–3, at. %

Temperature, °C

αδ

δ δ + liq

γ + liqγ + liq

γ + Fe2Bγ + Fe2B

α + Fe2B α + Fe2B

δ + γδ + γ

γγ

γ + αα + γ

α α

1381

1174

915

1165

911

a b

Fig. 2. Fe–B equilibrium phase diagrams according to Nicholson (a) and MacBride (b).

of the microstresses in it. Those stresses are compensated for by the presence of the smaller boron atoms occupying sub-

stitutional positions in α-Fe. This fact can in turn explain the high limiting solubility of Cu seen in the α-Fe of boron-bear-

ing steels in test specimens and rolled products at the MMZ, in addition to their reduced strength and high process ductility.

Nevertheless, it should be noted that at some additional cost the MMZ could ensure that the concentrations of

chromium, nickel, and copper in its steel are no greater than 0.06, 0.10, 0.15 mass %.

Mathematical modeling (with the optimum of the response function being found by the methods of nonparametric

statistics) for high-carbon (C ≥ 0.67%) wire rod showed that an increase in the combined content of chromium, nickel, and

copper within the range 0.15–0.45% is accompanied by a deterioration in its ductility properties (elongation ψ ≈ 30–36% in

the initial tests).

It has traditionally been thought that the presence of nitrogen – especially free nitrogen – adversely affects the duc-

tility and service properties of metal because it accelerates strain-aging. However, in a number of cases such aging can also

improve the properties of wire rod and wire products. For example, dynamic aging increases the endurance of high-carbon

wire. The static strain-aging seen on drawbenches on which the drawn wire is accumulated in magazine-type storage devices

with drums increases the wire’s low-cycle fatigue strength. The dynamic strain-aging characteristic of single-pass draw-

benches increases wire’s high-cycle fatigue strength. At the same time, micro-additions of boron bond with nitrogen in

nitrides and carbonitrides to inhibit aging and quenching. Boron also has a positive effect on the properties of steel: it refines

columnar crystals during crystallization, resulting in less axial segregation and improving the process ductility of wire rod

and wire without heat treatment (patenting) and increasing its deformability to 95–97% (this applies to the direct drawing of

5.5–mm-diam. wire rod into 1.2–1.0-mm wire without an intermediate heat treatment). Micro-additions of boron lengthen

the incubation period for the formation of ferrite and slow the formation of nucleation centers, which in high-carbon steel

leads to a decrease in the amount of SFF. It has been determined that cord steel should contain no more than 0.007% free

nitrogen and no more than 0.0025% boron. Such a ratio of nitrogen to boron maximizes the plasticizing effect of boron.

The vacuum degassing of steel to remove most of its gases – especially hydrogen (hydrogen content 2–6 ppm before

degassing and 0.3–1.5 ppm afterwards) and, to a lesser extent, nitrogen (0.010–0.012 and 0.005–0.007%, respectively) leads to

an additional increase in the ductility of wire rod. For example, whereas initial tests show that the reduction of area ψ = 30–35%

for steel 70KRD wire rod not subjected to vacuum degassing, the corresponding figure for the vacuum-degassed steel is 38–45%.

Low contents of harmful impurities in steel – P ≤ 0.010; S ≤ 0.005; As ≤ 0.01; Zn ≤ 0.001; Pb ≤ 0.01; Sn ≤ 0.01%

– additionally improves the ductility characteristics of wire rod and its ability to undergo intensive deformation in the cold state.

Nonmetallic inclusions (NI) – mainly oxides, silicates, sulfides, and nitrides of metals and nonmetals – are formed

as a result of reactions connected with alloying, desulfurization, dephosphorization, and deoxidation of the steel (endogenous

inclusions). They are also products of wear of the lining materials (exogenous inclusions).

442

900

Fe

Fe–0.005% B

1000 1100 1200

0.367

0.366

0.365

a, nm

T, °C

Fig. 3. Dependence of the lattice period of pure γ-Fe and γ-Fe–0.005% B

on temperature.

The presence of nondeformable NI in a metallic matrix results in the formation of microscopic cavities – disconti-

nuities in the metal that can subsequently lead to the fracture of wire rod and wire. The deformability of NI can be evaluat-

ed by means of the deformability index ν, which is determined by the degrees of deformation of NI in the matrix. The greater

the value of this index, the more ductile the NI, and at ν = 1 the NI and the metal have the same deformability. The most

dangerous NI (ν = 0) are aluminates and alumocalcinates with a high melting point, while the most ductile NI are manganese

sulfides (ν = 1). The melting point of these sulfides is no higher than 1400°C. Manganese sulfides are easily deformed and

break up into fragments during the hot rolling of wire rod, forming fine ductile stringer-type NI that readily undergo defor-

mation during subsequent cold drawing. Aluminates exert the most harmful effect on steel [8].

Globular inclusions are usually formed during the production and casting of steel (as was confirmed by the studies

being reported here). Depending on their ductility, during subsequent hot deformation and, sometimes, during cold defor-

mation as well these inclusions either remain in globular form or are broken up and drawn out into stringers extending in the

rolling direction. Steel is inoculated with rare-earth metals and calcium [9] to refine the coarse NI, convert some unde-

formable NI to the ductile state, and transfer the remaining undeformable NI to the slag. The MMZ makes effective use of

inoculation (including for high-carbon cord steel) with calcium on a ladle-furnace unit through the introduction of several

quantities of calcium-bearing cored wire (SiCa, FeCa). This can convert undeformable aluminates MgO·Al2O3 and

CaO·Al2O3 with the ratio Ca/ao = 0.60–1.20 (where ao is active oxygen) to a ductile compound with a low melting point –

12CaO·7Al2O3 – that is easily transferred to the slag. Hard high-melting aluminates are formed at other values of Ca/ao and

can lead to encrustation of nozzles and the formation of NI in the steel.

The use of steel-pouring ladles with a magnesian lining reduces the contamination of steel by exogenous NI.

Replacing ferrosilicon FS-75 (which has an aluminum content above 1.5%) with calcium carbide SiC (without metal-

lic aluminum) and optimizing the casting temperature (tc ≈ tliq + 30°C) made it possible to improve the castability of steel.

It was determined that the following set of measures can alleviate the contamination of metal by NI:

• increasing the consumption of calcium-bearing cored wire;

• replacing the acidic lining of the tundish with a basic lining;

• optimizing the composition of the heat-insulating and refining materials used in the tundish that do not contain

oxides of iron or oxides of manganese;

• blowing the steel in the tundish with argon through special injection devices;

• providing protection from oxidation for the stream of steel flowing from the ladle to the tundish and from the

tundish to the mold.

In practice, NI are evaluated by several methods. They can be classified as follows:

Standard methods, in which NI are evaluated on the basis of comparative schematic standard specimen-images creat-

ed for individual types of NI: point and stringer oxides, brittle, ductile, and nondeformable silicates, and sulfides (GOST 1778,

method Sh4); sulfides – A; aluminates – B; silicates – C; globular oxides – D (ASTM E 45), etc. These standards evalu-

ate the frequency of appearance of the inclusions, their thickness, and their length. They are highly subjective.

Analytical methods, which determine either the ratio of the surface area of NI to a unit volume of the specimen

(GOST 1778, method P) or a coefficient which characterizes physical nonuniformity (this method was developed by the

All-Russia Scientific Research Institute of Hardware, or VNIIMETIZ). This coefficient is determined from the formula

Kpn = [SNI/Swr]·100, %, where SNI and Swr are the total surface area of the NI in the cross section of wire and the cross-sec-

tional area of the wire itself. For example, Kpn ≤ 3–5% is recommended for metal cord. In a number of cases, testers assess

“penalty” points (such as in the methods devised by the Belgium company Bekaert and the French firm Michelin).

The method developed by the company Pirelli (Italy) provides for determination of the number, density, dimensions,

and chemical composition of each inclusion and subsequent graphical representation of these NI on a special diagram.

Experience with use of the triangular oxide diagram developed by Pirelli to evaluate NI showed that the use of NI density as

one of the criteria is not an effective means of accurately evaluating the degree of contamination undergone by steel due to

NI (Fig. 4). Pirelli revised the method in 2004 as a result of this, the method now giving results in the form of the number

of inclusions no smaller than 1 µm found in each specimen and the distribution of the inclusions with respect to size (as a

percentage of the total number of inclusions) for each size classification.

443

In our view, a combination of the Pirelli and VNIIMETIZ methods would be the best to evaluate the NI contamina-

tion of steel.

Hardware production conditions at the MMZ could be improved significantly (with the incidence of wire rupture

during being reduced to no more than 1.5–2 ton–1 during micro-drawing and no more than 2–2.5 ton–1 in the twisting of

strands and the formation of cord structures) by alleviating the NI contamination of wire rod of high-carbon steels 70KRD,

80KRD, and 85KRD for standard, high-strength, and superhigh-strength cord and implementing other measures to elevate

quality indices. Figure 5 shows the dynamics of the decrease in the NI contamination of high-carbon steel for metal cord dur-

ing different production periods at the MMZ:

1998 – production of cord without complete protection of the steel from oxidation, its inoculation with up to 150 m

of Ca-bearing cored wire, and with the use of all-alumina-lined ladles;

1999 – cord production with complete protection of the steel from oxidation and optimum inoculation with up to

300–350 m of Ca-bearing cored wire;

2000–2001 – same as above, but with the use of ladles having magnesia-lined walls and an alumina-lined bottom;

2001 – same as above, in addition to the use of EMM on all strands of the continuous caster;

2002 – same as above, in addition to the use of EMM in the VD unit;

2003 – same as above, in addition to experimental testing of all-magnesia-lined ladles.

The unit points for NI were determined in accordance with GOST 1778:

• unit NI/spm – unit NI in one specimen (Σpts spm/n, where n is the number of tested specimens) and Σun = ΣΣ;

un. max = ΣXmax/6, where Xmax = XPOmax + XSO

max + XNSmax + XBS

max + XDSmax + XS

max; similarly, un. av = ΣXcomp/6 (PO stands for

444

No.Area,

Total Number of inclusions with the Inclusion distribution

of mm2

number of following dimensions, µm by zone

specimen inclusions1 2 3 A B C

1 1.67 27 20 6 1 26 1

2 1.67 42 35 5 2 41 1

3 1.67 41 36 5 41

4 1.25 32 27 5 32

5 1.25 41 30 11 38 3

Total 7.51 183 148 32 3 178 5

81% 17% 2% 97% 3%

Note. There were no inclusions of 4–10 µm or larger.

0

A B C

20 40 60 80 100

0

2

4

6

8

10

10

8

6

4

2

0

Al2O3

SiO2

MgO CaO MnO

Fig. 4. Example of determination of the NI contamination of metal from a ternary oxide diagram.

point oxides, SO for stringer oxides, NS for nondeformable silicates, BS for brittle silicates, DS for ductile silicates, and S

for sulfides).

To form a quality macrostructure and minimize segregation effects in the CCS and wire rod, it is best to cast

steel so as to maximize the size of the region occupied by equiaxed crystals and minimize the size of the region occupied by

columnar crystals.

The MMZ studied the segregation of chemical elements in CCS that were rolled into wire rod and evaluated the

effectiveness of installing an EMM unit designed by VNIIMETMASh (All-Russia Scientific Research, Planning, and Design

Institute of Metallurgical Machinery). The coils of the EMM unit were positioned as close as possible to the metal inside the

molds of the caster – one coil was positioned around the copper sleeves. This arrangement made the operation of the coils

more efficient.

The study results were as follows:

• the main segregating elements in the steel made at the MMZ are C, P, Mn, Cr, and Si; the use of EMM in the crys-

tallization of the steel helps realize an inoculating effect in which particles are separated from the dendrites and moved

toward the middle of the CCS. This speeds up crystallization by increasing the number of crystallization centers. In

addition, EMM markedly increases the size of the region occupied by equiaxed crystals (by an average of 1.7), so that

the axial segregation and porosity that develops in the casting tend to be dispersed over a wider region;

• dendritic segregation in the CCS results in the development of segregation bands, “strings,” and striation, and

residues of these structural features end up in the wire rod and wire;

• segregation at the macroscopic and microscopic levels also results in the formation of sections of martensite 5–200 µm

long in the central sections of high-carbon wire rod.

To eliminate the effects of quenching structures, a number of metallurgical plants (the Belarus Metallurgical Plant,

Oskol’skii Electrometallurgical Combine, etc.) slow the cooling of the cast ingot under hoods or in heated or unheated pits

to realize homogenizing annealing at high temperatures (on the order of 1200°C) over a long period of time (at least 6 h).

Plants have also developed optimum crystallization regimes with the use of casting speeds of 2.5–3 m/min and heating of the

metal about 30°C above the liquidus temperature.

However, many well-known companies allow the presence of quenching structures even in cord-grade wire rod.

For example, martensite up to 20 µm long is allowed in the central parts of the cross section of wire rod in one case (the

Bekaert company). Also, isolated sections of martensite with a maximum length of 20 µm are allowed in the production

of 0.15–0.20-mm-diam. wire at the MMZ.

445

1998

1

2

3

4

1999 2000 2001 2002 2003

5

4

3

2

1

0

Production periods

NI, points

Fig. 5. Diagram of the decrease in the NI contamination of wire rod made of high-carbon

steel: 1) unit NI/spm; 2) Σun; 3) un. max; 4) un. av.

Several quality indices must be satisfied in the production of wire rod, and the improvement of one index often low-

ers the value of another index. It is necessary to seek the optimum result, i.e., to determine the relative importance of each

index. For example, increasing the dispersity of the pearlite in high-carbon wire rod outweighs the significance of having the

amount of secondary scale that is formed increase or of increasing the degree of decarbonization of the steel. However, when

the product has coarse surface defects, obtaining fine pearlite loses its importance because of the greater danger of rupture of

the wire rod or wire due to the presence of the defects. Thus, we studied the quality characteristics of wire rod (microstruc-

ture, degree of decarbonization, scale formation, surface defects) and their combined effect on the properties of the rod and

the wire formed from it (Fig. 6) [10, 11].

Study of the dependence of the amount of pearlite corresponding to 1 point on the coiling temperature

(950–1000°C) showed that there are two temperature ranges in which the distance between the plates of pearlite decrease:

950–1000°C and below 700°C. Nearly 100% finely dispersed pearlite corresponding to 1 point (d < 0.2 µm) is formed in

these cases. However, an intolerable post-quench structure – temper sorbite – is formed in the surface layers of the wire

rod when the temperature of the metal is below 700°C. This structure makes it appreciably more difficult to convert the rod

into wire. A different problem develops at high coiling temperatures (950–1000°C) – the average amount of secondary scale

446

800 900 1000

q

hdc.l

hdc.l, %

P

P, pt.1, %

7

2

2.50

50

85

Coiling temperature, °C

q, kg/ton

1998

1

2

1999 2000 2001 2002 2003

160

120

80

40

0

Years

Incidence of wire-rod breakage, ton–1

Fig. 6. Change in the dispersity of the pearlite P, the depth of the decarbonized layer

hdc.l, and the amount of scale q on the surface of wire rod made of high-carbon

steel 70 in relation to the coiling temperature.

Fig. 7. Ease of processing (incidence of breakage, ton–1) of metal cord at the Silur plant:

1) twisting of strands and metal cord; 2) micro-drawing.

formed increases to 6–8 kg/ton from the 2–4 kg/ton seen at 800–850°C. The greater scale formation is accompanied by

a 20–30% decrease in the amount of fine pearlite that is obtained in the steel. However, the scale formed at 950–1000°C

consists mainly of wustite, and the latter is not converted into martensite if the coils are rapidly cooled with fans (this

includes fan cooling in the temperature range 570–400°C). Thus, this scale can then be easily removed either chemically

or mechanically before the drawing operation. The increase in the amount of metal consumed in the scale can be ignored,

since the increase in the fineness of the pearlite combined with the decrease in decarbonization depth improves the deforma-

bility of the wire rod and wire during drawing and the formation of cables, strands, and metal cord. Thus, the optimum tem-

perature range for coiling is 950–1000°C.

The increase in pearlite dispersity and decrease in decarbonization that are seen with an increase in the coiling tem-

perature to 950–1000°C can be explained as follows. After cooling with water, nonequilibrium (abnormal) structures such

as temper sorbite, granular pearlite, and structurally free cementite and ferrite are formed in the surface layers of the wire rod.

They are collectively evaluated as a visible decarbonized layer. The structures are dispersed at temperatures in the range

A1–820°C, but at higher temperatures they are film-like precipitates located along the boundaries of former austenite grains.

The structures are absent when wire rod is coiled at or above 950°C. In keeping with these features of formation of the abnor-

mal structures in carbon-steel wire rod, the depth of the decarbonized layer is minimal at a coiling temperature of

950–1000°C and increases with a decrease in coiling temperature to A1–820°C.

447

1997 1998 1999 2000 2001 2002 2003 2004

1999 2000 2001 2002 2003 2004

100

80

40

60

20

0

20

30

10

0

Years

Output, 103 tons

0.486.063

1.175

13

50

29.2

61.3

85.6

0.36

5.1

15.8

10.7

22

26.3

a

b

Fig. 8. Dynamics of the production of high-carbon steel at the MMZ: a) total volume;

b) cord-grade steel.

The deformability of wire rod and wire also has an effect on the actual grain size. For wire rod made of high-car-

bon steel, the optimum grain size corresponds to 7–11 points.

The positive effect of decarbonization of the surface of wire rod on its commercial properties can be explained as

follows. Mild decarbonization of the surface increases the ductility of the steel in bending and torsion due to its low sensi-

tivity to stress concentrators and high resistance to crack propagation. The formation of compressive residual stresses in the

decarbonized surface layer of wire rod and wire increases the fatigue strength and endurance of the product when it is used

in cables. It also increases corrosion resistance and improves the galvanizing of the wire by preventing the Rebinder

effect [12]. Friction is less likely to result in the formation of martensite in the decarbonized layer, so that the associated sur-

face cracks and flakes are also less likely to form. Consequently, it is necessary to ensure that the depth of decarbonization

of the wire rod is uniform about its perimeter. An analysis of the quality of wire rod made by different manufacturers showed

that the rod made by the MMZ is characterized by a decarbonization layer that is uniform in this direction. This is another

indication of the quality of the factory’s product.

The following factors (Fig. 7) have impacted the processing of metal cord at the client plant during different periods:

1997–2001 – production of cord of standard strength with the grade designations 9L15/27, 28L18, and 22L15; 2002–2004 –

additional production of cord in the ultrahigh-strength classes 3L30NT and 9L20/35NT; 2001 – increase in the incidence of

wire rupture due to an increase in casting speed; 2002–2004 – production of wire rod made of vacuum-degassed steel.

Thus, the MMZ has developed an integrated technology that produces steel, CCS, and wire rod for making metal

cord of standard, high, and ultrahigh strength (Fig. 8). The wire rod is characterized by a low incidence of surface defects

(defect depth is no greater than 0.15 mm, and it is no more than 0.1 mm in 95% of the cases), good deformability, and the

ease with which it can be converted into wire, strands, and cord.

REFERENCES

1. V. V. Parusov, A. M. Nesterenko, A. B. Sychkov, and O. V. Parusov, “Development of the principles and successful

introduction of an integrated technology for making wire rod from carbon steel at the Moldavian Metallurgical

Plant,” Metallurg. Gornorud. Promst., No. 8–9, 302–306 (2002).

2. V. V. Parusov, A. I. Vilipp, and A. B. Sychkov, “Effect of impurity elements on the quality of carbon wire rod,” Stal’,

No. 12, 53–55 (2002).

3. H. J. Goldstadt, Interstitial Alloys [Russian translation], Mir, Mosow (1971).

4. G. V. Samsonov (ed.), Properties of the Elements [in Russian], Metallurgiya, Moscow (1976), Part 1.

5. R. Kahn (ed.), Physical Metallurgy. Vol 1. Atomic Structure of Metals and Alloys [Russian translation], Mir,

Moscow (1967).

6. A. M. Nesterenko and A. B. Sychkov, “Dimensional-geometric aspects of the alloying of steel with boron and cop-

per,” in: Fundamental and Applied Problems of Ferrous Metallurgy: Symposium, Vizion, Dnepropetrovsk (2004),

Vol. 7, pp. 181–183.

7. L. I. Mirkin, x-Ray Inspection of Materials Used in Machine Construction: Handbook [in Russian], Mashino-

stroenie, Moscow (1979).

8. S. I. Gubenko, Transformation of Nonmetallic Inclusions in Steel [in Russian], Metallurgiya, Moscow (1991).

9. D. A. Dyudkin, “Aspects of the overall effect of calcium on the properties of liquid and solid steel,” Stal’, No. 1,

20–28 (1999).

10. V. V. Parusov, A. N. Sav’yuk, A. B. Sychkov, et al., “Study of the feasibility of removing most of the scale from the

surface of wire rod before drawing,” Metallurg, No. 6, 69–72 (2004).

11. V. V. Parusov, A. B. Sychkov, M. A. Zhigaev, and A. V. Perchatkin, “Formation of the optimum microstructure in

high-carbon wire rod,” Stal’, No. 1, 82–85 (2005).

12. Kh. N. Belalov, “Formation of the properties of rope wire,” in: Steel Cables, Astroprint, Odessa (2001),

pp. 105–116.

448