KR20190074661A - High strength wire rod having excellent drawability and method for manufacturing thereof - Google Patents

Abstract

The present invention relates to a high-strength steel wire rod used for a cable for a bridge, such as a cable-stayed bridge, a suspension bridge, and the like, and an anchor rope for a marine rescue, and the like, and, more preferably, to a high strength wire rod with excellent drawability and a method for manufacturing the same. The high-strength wire rod with excellent drawability comprises: 0.8-1.2% by weight of carbon (C); 0.5-1.5% by weight of silicon (Si); 0.2-0.6% by weight of manganese (Mn); 0.2-0.8% by weight of chromium (Cr); 0.3-1.5% by weight of cobalt (Co); and the balance being Fe and inevitable impurities, the high-strength wire rod comprising a ferrite phase at 3% or less of the area in a surface layer portion.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high strength wire rod,

TECHNICAL FIELD The present invention relates to a high-strength steel wire rod used for a cable for a bridge such as a cable-stayed bridge or a suspension bridge, an anchor rope for a marine structure, and more preferably a high-strength wire rod having excellent wire drawing workability and a method for manufacturing the wire rod.

The strength of steel wire for bridges and anchor lines for marine structures are mostly determined by the strength and demand of raw wire, patenting heat treatment (also called constant temperature heat treatment), drawing, plating and so on. The strength of the wire depends on the microstructure determined by the alloy components and the cooling conditions of the wire manufacturing process. The most effective way to increase the strength of the wire is the addition of alloying elements such as carbon (C), manganese (Mn), silicon (Si) and chromium (Cr). Of these, carbon is the most effective element for increasing the strength of pearlite structure, which is the base structure of wire rods.

By continuously increasing the content of carbon (C), the cementite fraction in the pearlite can be increased and the lamellar spacing can be made finer. However, the continuous increase of the C content causes the cementite phase So that it can not withstand deformation during the drawing process, and it can cause bonding of voids and the like, which may cause problems in the ductility of the final product. As a result, the limiting drafting amount is reduced, and the amount of work hardening is reduced, thereby failing to contribute to ultimate strength increase.

On the other hand, other alloying elements delay the transformation from austenite to pearlite during the heat treatment at constant temperature transformation, and the pearlite is composed of two phases of cementite and ferrite, and the alloying elements added are on one of cementite or ferrite The partitioning phenomenon occurs selectively so that the rate-determining step of the transformation is determined by redistribution of the alloying element, not phase separation due to diffusion of C (Non-Patent Document 1).

 Partitioning and pearlite growth kinetics in an Ni-Cr eutectoid steel, Materials Characterization 25, pp. 125-141 (1990) N. Ridley, M. A. Malik and G. W. Lorimer

One aspect of the present invention is to provide a steel wire having excellent high-quality drawing and excellent strength and a method of manufacturing the steel wire so as to produce high-strength drawing.

The problems to be solved by the present invention are not limited to the above-mentioned problems, and other problems not mentioned can be clearly understood by those skilled in the art from the following description.

In one aspect of the present invention, there is provided a steel sheet comprising, by weight%, 0.8 to 1.2% of C, 0.5 to 1.5% of Si, 0.2 to 0.6% of Mn, 0.2 to 0.8% of Cr, 0.3 to 1.5% of Co, Containing impurities,

The content of Co, Cr and Si satisfies the following relational expression 1,

And a ferrite phase in the surface layer portion in an area fraction of 3% or less.

[Relation 1]

0.4 * Si + 0.25 * Cr? Co? 0.5 * Si + 0.3 * Cr (each component symbol means addition amount)

Another embodiment of the present invention is a ferritic stainless steel comprising, by weight%, 0.8 to 1.2% of C, 0.5 to 1.5% of Si, 0.2 to 0.6% of Mn, 0.2 to 0.8% of Cr, 0.3 to 1.5% of Co, And an inevitable impurity, wherein the content of Co, Cr and Si satisfies the following relational expression 1:

Heating the prepared steel material to 1000 ° C or higher;

Subjecting the heated steel material to wire rolling and finishing rolling at 700 to 850 占 폚;

Rolling at 700 캜 or lower after the rolling; And

And cooling the steel sheet at a cooling rate of 1 to 5 ° C / sec up to 500 ° C after the winding.

[Relation 1]

0.4 * Si + 0.25 * Cr? Co? 0.5 * Si + 0.3 * Cr (each component symbol means addition amount)

INDUSTRIAL APPLICABILITY The present invention can provide a wire having high strength without causing disconnection even during high-speed drawing by providing a wire having excellent excellent workability.

The various and advantageous advantages and effects of the present invention are not limited to the above description, and can be easily understood in the course of describing a specific embodiment of the present invention.

Fig. 1 is a photograph of the surface portion of Comparative Example 1 among the examples of the present invention. Fig.
2 is a photograph of a surface portion of Inventive Example 1 of an embodiment of the present invention.

In order to improve the strength of the high-carbon wire rod, an alloying element capable of strengthening solubility and reducing the lamellar spacing should be used. Typically, Si and Cr are used. However, these elements inevitably delay the growth of the cementite during the course of the phase transformation, and the cementite fragments become severe, thereby reducing the amount of marginal drawing in the subsequent drawing process. As a result, the tensile strength of the final steel wire There is also a limit.

The inventors of the present invention have found that cobalt (Co) accelerates transformation by increasing the activity of C, promotes pearlite transformation and smoothes the growth of cementite , Resulting in the present invention.

Hereinafter, the present invention will be described in detail. First, the wire alloy composition of the present invention will be described in detail. Hereinafter, the content of the alloy composition is expressed in weight%.

Carbon (C): 0.8 to 1.2%

C is an element that can most effectively increase the strength of a material, and it is known that when C is increased by 0.1% in pearlite steel, the strength can be improved by about 100 MPa. However, as the C content increases, the effect of this increase in strength decreases as the C content increases in the over-calcined form, and the thermodynamic stability of the austenite becomes unstable, so that a faster cooling rate is required to transform it into pearlite This is because the effect of increasing the strength is reduced because a certain level of cooling rate is determined for the commercial cooling method. When the C content is less than 0.8%, it is difficult to secure a tensile strength of 2400 MPa or more after drawing, since the basic fraction of cementite is small. When the C content exceeds 1.2%, Si, V, The generation of a cornerstone cementite of a certain level or more can not be prevented unless the cooling rate is secured to a certain level or more.

Silicon (Si): 0.5 to 1.5%

Si is mostly employed in ferrite in the austenite to pearlite transformation, and the diffusion rate is slower than that of C without being distributed to the cementite, and if the Si is employed in a large amount, the pearlite transformation is totally slowed. Therefore, it has an effect of refining the spacing of pearlite layers, and is basically an element effective in increasing strength because it exhibits solid solution strengthening effect while being dissolved in ferrite. Also, Si is mainly present in the ferrite and cementite interface portion, and it is preferable to set the Si content to be high because it helps stability of the cementite during drawing and heat treatment. If the content of Si is less than 0.5%, the effect of stabilizing the cementite is hardly observed. If the content of Si exceeds 1.5%, it is preferable that the content of Si is excessively less than the content of Fe ₂ SiO ₄ scale.

Manganese (Mn): 0.2 to 0.6%

Mn is not added to the full pearlite steels in a strength increasing effect, but is added in order to maintain the granularity at an appropriate level according to the cooling performance of the linear heat treatment and the LP heat treatment. If the content of Mn is less than 0.2%, the effect of incombustibility is hardly observed. If the content of Mn exceeds 0.6%, it is a high carbon steel and therefore it is possible to form a martensite structure together with C in the segregation portion.

Cr (Cr): 0.2 to 0.8%

Cr is a very useful element for increasing the strength of heat-treated wire rods by increasing the spacing between pearlite layers during constant-temperature transformation, enhancing work hardening during wire drawing, and widening the limits of wire drawing. If the Cr content is less than 0.2%, it is difficult to sufficiently effect the layer spacing. When the Cr content exceeds 0.8%, the cementite formation is not smooth and is present in a segmented form.

Cobalt (Co): 0.3 to 1.5%

Co increases the activity of C in high carbon steel to accelerate pearlite transformation and help to grow straight without being segregated during cementite plate growth. In addition, it inhibits cementite cementite growth and is therefore effective for controlling the phase transformation of high-carbon pearlite steels. When the content of Co is less than 0.3%, the effect of improving the cementitious plate phase is hardly expected. When the content of Co exceeds 1.5%, instability of C is increased and spheroidized cementite is formed. .

Although the Co itself affects the pearlite transformation, it does not exhibit a strengthening effect such as solid solution strengthening or precipitation strengthening, so that it is effective to use it together with the strengthening effect element in order to produce high strength fresh pearlite. In the case of adding Co, the pearlite phase transformation speed is accelerated. Therefore, transformation is started during the cooling process of the material to the transformation temperature during the heat treatment at constant temperature transformation, and coarse pearlite is mixed therein. can do. Therefore, in order to solve this problem, the content of Co, Si and Cr in the present invention preferably satisfies the following relational expression (1).

[Relation 1]

0.4 * Si + 0.25 * Cr? Co? 0.5 * Si + 0.3 * Cr

Here, the symbol of each element means the content (weight%) of each component.

(Al), 0.015% or less of phosphorus (P), 0.015% or less of sulfur (S), 0.002 to 0.01% of nitrogen (N), or 0.002% or less of oxygen (O) . ≪ / RTI > The above Al, P, S, N and O are components ordinarily included in the technical field of the present invention.

The above-mentioned Al is a useful component as a deoxidizer, and it is preferably contained in an amount of 0.02% or more, but if it exceeds 0.05%, cold workability may be deteriorated.

P is inevitably contained as an impurity, which is segregated in the grain boundaries to lower the toughness of the steel and reduce the delayed fracture resistance. Therefore, it is preferable to control P as low as possible. The S is inevitably contained as an impurity and emulsified in the steel to reduce delayed fracture resistance, so that it is preferable to control the S as low as possible.

N is usually contained in an amount of 0.002% or more, but when it is excessive, the amount of solid solution nitrogen is increased to increase the deformation resistance of the steel, thereby deteriorating the cold workability.

The O exists in the form of a nonmetallic inclusion, and since the nonmetallic inclusions become a starting point of fracture, the fatigue strength and cold workability of the steel may be lowered. Therefore, it is preferable that the O is kept as low as possible.

The rest of the composition is Fe. However, it is not possible to exclude inevitable impurities that are not intended from the raw material or the surrounding environment in a conventional manufacturing process, since they may be inevitably incorporated. These impurities are not specifically referred to in this specification, as they are known to one of ordinary skill in the art.

Next, the wire microstructure of the present invention will be described in detail.

The wire rod of the present invention contains pearlite (at least 95% in area fraction) as the main structure, and preferably is a perfect pearlite (at least 99% in area fraction).

The wire material of the present invention preferably has an area fraction of pure ferrite present in the surface layer portion (preferably in a region from the surface to a depth of 30 mu m) of 3% or less. Here, pure ferrite means ferrite which is distinguished from pearlite consisting of ferrite and cementite.

So far, in the process of manufacturing wire rods, wire rods were hot rolled to produce wire rods. However, in the process, the surface layer of the wire rod is maintained at a high temperature, thereby causing decarburization. By the decarburization, the surface layer portion is not transformed from austenite to pearlite, and a large amount of ferrite structure is formed. The ferrite formed on the surface layer in this way may cause delamination during drawing, which may cause a problem of deterioration of workability. However, in the wire of the present invention, ferrite is formed in an area fraction of not more than 3% from the surface to 30 占 퐉, thereby solving the problem that may occur in the drawing process.

Hereinafter, a method for manufacturing a wire rod, which is another aspect of the present invention, will be described in detail.

First, a steel material satisfying the alloy composition described above is prepared, and the prepared steel material is heated to 1000 캜 or higher. The kind of the steel material is not particularly limited, but it is preferably a billet or a bloom for producing a wire rod. If the heating temperature is less than 1000 캜, sufficient homogenization of the steel material can be achieved. The upper limit of the heating temperature is not particularly limited, but it is preferred that the heating temperature does not exceed 1300 占 폚 in consideration of economical efficiency.

The heated steel is subjected to co-hot-rolling to produce a wire rod. At this time, in order to suppress the surface decarburization of the wire rod to suppress the formation of pure ferrite in the surface layer portion, the finish rolling temperature in the hot rolling is preferably 700 to 850 ° C, and it is preferable that the hot rolling is performed at 700 ° C or less after the hot rolling .

The water-cooling may be performed as one method for controlling the finish rolling temperature to 700 to 850 ° C. On the other hand, when cooling by water cooling or the like, only the material surface is cooled, and since the temperature inside the material is high, the temperature difference between the inside and the outside can be increased. In order to solve this problem, it is possible to maintain the inner and outer portions uniformly for 2 to 5 seconds by using a loop facility and then to take up the winding.

On the other hand, cooling is performed after the winding. The cooling is preferably performed at a temperature of 500 ° C at a rate of 1 to 5 ° C / sec. The wire rod of the present invention preferably contains pearlite as the main structure. If the cooling rate is too slow, cornerstone cementite is likely to occur. If the cooling rate is too high, bainite is generated. Therefore, it is preferable to perform the cooling at the cooling rate.

Cooling after pearlite transformation is after finishing the transformation, so there is no special care, but if the cooling finish is too slow, the temperature of the material may be too high even when the cooling zone is removed, which may hinder the coil transportation etc. May be needed.

On the other hand, a micro pearlite structure suitable for drawing processing can be made again by subjecting the wire rod produced as described above to heat treatment at constant temperature transformation. The heat treatment is for optimizing the drawing process. The heat treatment is performed by heating at 950 to 1050 占 폚 and then immersing in a lead or salt bath at 550 to 650 占 폚 for 3 to 5 minutes. The heat treatment again austenitizes the pearlite structure and recreates the fine pearlite structure suitable for drawing.

The heat-treated wire rod has a tensile strength of 1350 MPa or more and a reduction ratio of area (RA) of 20% or more.

After the constant-temperature transformation heat treatment is performed, the steel wire can be manufactured by drawing. At this time, the wire can be fresh at a reduction rate of 15 to 20% per pass. The wire of the present invention has an increased drawing limit, can secure a high strength of 2200 MPa or more after drawing, .

Hereinafter, embodiments of the present invention will be described in detail. It should be noted that the following examples are intended to illustrate and assist in understanding the present invention and not to limit the scope of the present invention. The scope of the present invention is defined by the matters set forth in the claims and the matters reasonably deduced therefrom.

(Example 1)

A billet (160x160) having the composition shown in the following Table 1 (the unit is weight% and the remainder is Fe and unavoidable impurities) was prepared, and then heated at 1010 to 1050 ° C for about 90 minutes, and then subjected to hot rolling. The temperature of the material was controlled at 750 to 850 ° C immediately after finish rolling through water cooling during rolling, and winding was performed at a temperature of 630 to 680 ° C. A loop was applied to all the materials to reduce the internal and external temperature variations of the material after the water-cooling. On the other hand, pearlite transformation was induced at a cooling rate of 1 to 5 DEG C / sec to 500 DEG C by controlling the blowing air according to the coiling temperature.

After the wire rod having a diameter of 12 mm (? 12 mm) was produced as described above, the properties thereof were evaluated, and the results are shown in Table 2. Both the inventive material and the comparative material had a complete pearlite structure with a pearlite fraction of 99% or more, but it was confirmed that the RA of the inventive material was improved by about 5% or more.

On the other hand, the wire rod was austenitized in a 1000 ° C heating furnace for 10 minutes, immersed in a 580 ° C bath for 3 minutes, and then washed with water to prepare a heat treatment material. The mechanical properties after the heat treatment at constant temperature transformation were evaluated and are shown together in Table 2. Both homogeneous and fine pearlite structure is ensured for both the inventive material and the comparative material, and the tensile strength and RA can be increased compared to the wire rod state. However, in the case of the inventive material, the RA was estimated to be about 5% higher than the comparative material.

division C (% by weight) Si (% by weight) Mn (% by weight) Cr (wt%) Co (% by weight) Inventory 1 0.80 1.5 0.6 0.6 0.9 Inventory 2 0.90 1.3 0.6 0.6 0.8 Inventory 3 0.90 1.1 0.4 0.4 0.6 Invention 4 1.00 0.9 0.4 0.4 0.5 Invention Article 5 1.10 0.7 0.2 0.2 0.4 Inventions 6 1.20 0.5 0.2 0.2 0.3 Comparison 1 0.80 1.5 0.6 0.6 - Comparative material 2 0.90 1.3 0.6 0.6 - Comparative material 3 0.90 1.1 0.4 0.4 - Comparison 4 1.00 0.9 0.4 0.4 - Comparative material 5 1.10 0.7 0.2 0.2 - Comparative material 6 1.20 0.5 0.2 0.2 -

Although not shown in Table 1, the manufactured wire rod has a composition of 0.02 to 0.05 wt% of Al, 0.015 wt% or less of P, 0.015 wt% or less of S, 0.002 to 0.01 wt% of N, and 0.002 wt% or less of O And the remainder includes Fe and other unavoidable impurities.

division Φ12㎜ wire rod After constant temperature transformation heat treatment Tensile Strength (MPa) RA (%) Tensile Strength (MPa) RA (%) Inventory 1 1236 16 1357 21 Inventory 2 1323 24 1402 29 Inventory 3 1327 31 1420 35 Invention 4 1360 33 1501 36 Invention Article 5 1359 33 1492 36 Inventions 6 1397 26 1482 31 Comparison 1 1227 9 1348 15 Comparative material 2 1285 13 1289 18 Comparative material 3 1302 23 1401 26 Comparison 4 1342 25 1446 30 Comparative material 5 1355 26 1438 30 Comparative material 6 1401 18 1456 24

The heat-treated wire rod was drawn at a reduction rate of 10 to 15% per pass, and the tensile strength (unit: MPa) according to the wire diameter per pass was evaluated. The results are shown in Table 3.

division Tensile strength (MPa) according to the diameter (mm) 12 mm 10.19 mm 8.66 mm 7.36 mm 6.26 mm 5.32 mm 4.52 mm 4.17 mm Inventory 1 1357 1429 1521 1624 1745 1888 2024 2252 Inventory 2 1402 1481 1583 1690 1815 1960 2105 2281 Inventory 3 1420 1493 1589 1701 1840 1975 2150 2306 Invention 4 1501 1573 1682 1811 1950 2098 2264 2405 Invention Article 5 1492 1563 1662 1808 1935 2089 2249 2395 Inventions 6 1482 1550 1642 1800 1915 2079 2222 2391 Comparison 1 1348 1414 1513 1621 1738 1884 2020 2196 (del.) Comparative material 2 1289 1483 1549 1688 1821 1955 2107 2290 (del.) Comparative material 3 1401 1489 1588 1691 1841 1973 2130 2256 (del.) Comparison 4 1446 1534 1649 1800 1930 2089 2235 (del.) 2299 (del.) Comparative material 5 1438 1533 1632 1801 1915 2055 2221 (del.) 2310 (del.) Comparative material 6 1456 1545 1687 1821 1933 2089 2200 (del.) 2298 (del.)

(Del. In Table 3 means the occurrence of delamination during drawing processing)

As shown in the results of Table 3, it can be seen that the inventive materials satisfying the conditions of the present invention are superior to the comparative material in the limiting cut-off rate at which delamination does not occur. As for the total reduction ratio, the comparative materials showed a reduction rate as low as 80.3% and 85.8%, respectively, as compared with the minimum reduction of 87.9% of invented materials.

In addition, as the work hardening amount increases according to the increase in the critical tensile strength, it is possible to manufacture a steel wire having a strength of 2200 MPa or more in the case of the present invention material, but this is not the case in the case of the comparative material.

(Example 2)

On the other hand, a steel material having the composition of inventive materials 1 to 6 of Table 1 was prepared, and the prepared steel material was hot-rolled in the following two ways to produce a wire material.

The method 1 is the same as the process in the first embodiment.

Unlike the method of Embodiment 1, the method 2 is a method in which the finishing rolling temperature is 900 占 폚 to 25 占 폚, the coiling temperature is 850 占 폚 to 25 占 폚, and the cooling and cooling is performed at a cooling rate of about 10 占 폚 / s .

The ferrite area from the surface to the depth of 30 mu m was observed for the wire rod prepared as described above, and the results are shown in Table 4. [

division Steel Manufacturing method Ferrite area fraction (%) from surface to 30 탆 Inventory 1 Inventory 1 Method 1 0.7 Comparative Example 1 Inventory 1 Method 2 7.8 Inventory 2 Inventory 2 Method 1 0.6 Comparative Example 2 Inventory 2 Method 2 9.2 Inventory 3 Inventory 3 Method 1 0.8 Comparative Example 3 Inventory 3 Method 2 10.4 Honorable 4 Invention 4 Method 1 0.7 Comparative Example 4 Invention 4 Method 2 8.5 Inventory 5 Invention Article 5 Method 1 0.6 Comparative Example 5 Invention Article 5 Method 2 6.3 Inventory 6 Inventions 6 Method 1 0.6 Comparative Example 6 Inventions 6 Method 2 5.8

The wire materials of Examples 1, 3 and 6 and Comparative Examples 1, 3 and 6 having the results of Table 4 were subjected to the same constant temperature transformation heat treatment as in Example 1 and then subjected to drawing processing at a reduction ratio of 10 to 15% , And delamination due to the change in the wire diameter was observed. The results are shown in Table 5 below.

division Whether dilation occurs according to the diameter 5.32 mm 4.52 mm 4.17 mm Inventory 1 Not occurring Not occurring Not occurring Inventory 3 Not occurring Not occurring Not occurring Inventory 6 Not occurring Not occurring Not occurring Comparative Example 1 Not occurring Occur Occur Comparative Example 3 Not occurring Occur Occur Comparative Example 6 Occur Occur Occur

Fig. 1 is a photograph of a surface portion of Comparative Example 1 among the wire rods shown in Table 4, and Fig. 2 is a photograph of a surface portion of Inventive Example 1. Fig. 1 and 2, it can be confirmed that a large amount of ferrite structure is formed on the surface portion of the wire rod (specifically, the portion from the surface to the depth of 30 mu m) in the conventional method. However, in FIG. 2, It can be confirmed that pearlite is uniformly formed.

As can be seen from the results in Table 5, in the case of the inventions in which the fraction of the ferrite existing up to the depth of 30 탆 from the surface of the wire does not exceed 3%, machining is possible without drawing delamination during drawing, , Delamination occurs, which limits the amount of drawing processing.

Claims (9)

And the balance contains Fe and unavoidable impurities, wherein the content of C is from 0.8 to 1.2%, Si is from 0.5 to 1.5%, Mn is from 0.2 to 0.6%, Cr is from 0.2 to 0.8%, Co is from 0.3 to 1.5%
The content of Co, Cr and Si satisfies the following relational expression 1,
High strength wire with excellent workability with 3% or less ferrite phase in the surface layer as an area fraction.
[Relation 1]
0.4 * Si + 0.25 * Cr? Co? 0.5 * Si + 0.3 * Cr (each component symbol means addition amount)
The method according to claim 1,
Wherein the wire rod comprises pearlite as a main structure and has excellent drawability.
The method according to claim 1,
The surface layer is a high strength wire having excellent drawability from the surface of the wire to 30 mu m.
4. The method according to any one of claims 1 to 3,
A high strength wire excellent in drawability with a tensile strength of 1350 MPa or more and a reduction ratio of area (RA) of 20% or more after heat treatment of the wire rod.
And the balance contains Fe and unavoidable impurities, wherein the content of C is from 0.8 to 1.2%, Si is from 0.5 to 1.5%, Mn is from 0.2 to 0.6%, Cr is from 0.2 to 0.8%, Co is from 0.3 to 1.5% Preparing a steel material having a content of Co, Cr and Si satisfying the following relational expression 1;
Heating the prepared steel material to 1000 ° C or higher;
Subjecting the heated steel material to wire rolling and finishing rolling at 700 to 850 占 폚;
Rolling at 700 캜 or lower after the rolling; And
After the winding, cooling is performed at a cooling rate of 1 to 5 ° C / sec up to 500 ° C
Wherein the high-strength wire rod has excellent drawability.
[Relation 1]
0.4 * Si + 0.25 * Cr? Co? 0.5 * Si + 0.3 * Cr (each component symbol means addition amount)
The method of claim 5,
And a step of cooling the wire rod during water cooling to obtain a high strength wire rod excellent in drawability.
The method of claim 5,
Further comprising the step of holding the wire for 2 to 5 seconds before the winding.
A method for manufacturing a high strength wire having excellent drawability, wherein the wire material produced by any one of claims 5 to 7 is heated to 950 to 1050 캜 and immersed in a lead or salt bath at 550 to 650 캜 for heat treatment at a constant temperature.
The method of claim 8,
Wherein the heat-treated wire rod is drawn to a reduction ratio of 10 to 15% per pass to produce a steel wire.

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