JP3429178B2 - Steel wire having excellent twisting characteristics, steel material for wire drawing, and method of manufacturing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a carbon steel wire (C content: 0.7 to 1.3%) which is a product without being subjected to heat treatment such as bluing while being subjected to cold working. The present invention relates to a steel wire having excellent twisting properties suitable for steel cord wires, wire saws, PC wire rope steel wires, and the like, a steel material for wire drawing suitable for manufacturing the steel wire, and a manufacturing method thereof.

[0002]

2. Description of the Related Art In manufacturing hard steel wires used for steel cords and various steel ropes, it is common to perform cold-drawing after subjecting a steel material for wire drawing to patenting. Is. In particular, in this cold drawing process, the strength of the steel wire will be enhanced. However, if the strength becomes too high by wire drawing, vertical cracks may occur, and ductility and toughness deteriorate, so it is difficult to achieve high strength only by wire drawing. Regarding this cause, models of texture, anisotropy of yield stress, etc. have been proposed, but there were also phenomena that could not be sorted out only by these.

It is known that proeutectoid cementite is harmful to the plastic deformation / fracture mechanism of pearlite (for example, JP-A-4-272134 and JP-A-5-9834).
9, JP-A-5-78754, JP-A-5-295436,
JP-A-5-295448, etc.), so that the pro-eutectoid cementite does not coexist with the main structure such as fine pearlite or pseudo-pearlite, it is subjected to a constant temperature transformation near the nose (around 550 ° C.) of the TTT (constant temperature transformation curve). The general idea of patenting treatment is to control a uniform and fine pearlite structure without causing the precipitation.

By the way, a life cycle assessment (LCA) has been introduced into the international environmental standards, and a growing need for reducing the environmental load has brought about a high value-added steel without using alloying elements that consume a large amount of energy for refining. It is desired to develop materials, and it is also desired to consider the recyclability of steel materials and the omission of heat sources due to improvement in patenting processability. The alloying elements such as Cr are added to the conventional high-strength steel wire for the purpose of increasing the strength of the steel wire and improving the drawability.
Considering the energy required for refining alloying elements such as r and the recyclability of steel materials, it is very effective to reduce the environmental load by not using alloying elements such as Cr as much as possible. . In a Fe-C-based steel wire, it is possible to increase the strength by increasing the C content, but since vertical cracking occurs when twisted, high strength is achieved without adding an alloying element such as Cr. It was considered difficult to achieve this.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is possible to obtain high strength without causing vertical cracking without adding an alloying element such as Cr. The present invention aims to provide a carbon steel wire and a method for manufacturing the same.

[0006]

The steel for wire drawing of the present invention, which has solved the above-mentioned problems, is a steel for wire drawing made of eutectoid steel or hyper-eutectoid steel, and has an average ferrite grain size of 4 ．
The gist is that it is 0 μm or less.

The term "eutectoid steel" or "hypereutectoid steel" as used in the present invention means a steel containing 0.7 to 1.3% of C.

Further, in producing the steel for wire drawing, the austenitizing temperature during the patenting treatment performed after hot working is set to 900 to 1000 ° C., and then forced cooling is performed to maintain the wire rod temperature at 530 to 610 ° C. It is recommended to adopt the method of performing pearlite transformation.
Alternatively, in the forced cooling step from the austenitizing temperature, a method of once cooling to 500 to 560 ° C. at the wire temperature and then performing pearlite transformation by maintaining the wire temperature at 530 to 610 ° C. by transformation recuperation is adopted. May be.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In order to increase the strength of an Fe-C steel wire, conventional simple structure control such as generating a uniform pearlite structure by patenting does not require high strength without alloying elements. Based on the recognition that it is impossible to achieve this, we focused on controlling the ultrafine structure.
As a result, the inventors of the present invention have controlled the ultrafine structure of the pearlite internal structure, specifically, by forming the lamellar cementite into a nanocrystal structure or amorphization, to obtain a high strength of the Fe-C steel wire. Has been realized (Japanese Patent Laid-Open No. 8-
120407, Japanese Patent Application No. 9-81324). However, the above-mentioned strengthening technology relates to ultrafine structure control, and lamellar cementite is also controlled to an amorphous state, and it is considered that there is little room for strengthening from the viewpoint of structure control.

Therefore, by paying attention to the phenomenon of vertical cracks that dominates the limit of strengthening of hard steel wire, the cause is clarified, and in particular, the generation and propagation mechanism of vertical cracks is fundamentally clarified.
Research was repeated to establish a method for further strengthening.

The inventors of the present invention used a field emission scanning electron microscope (hereinafter referred to as FE-SEM) capable of observing a fracture surface and a structure in a high-decomposition state and confirmed a phenomenon of vertical cracking of a fine structure. I investigated the relationship. Maximum magnification is 5 for general-purpose SEM
The maximum magnification of FE-SEM is 500,000 times, while it is about 1,000 times. By using this FE-SEM, observation of an ultrafine structure in a region that could not be observed until now. Can be evaluated. Therefore, when the cross-sectional structure of the steel wire with vertical cracks was investigated by FE-SEM, ferrite was observed in the drawn wire after patenting even with hyper-eutectoid steel, and ferrite had a large effect on vertical cracks. I found out.

FIG. 5 is a FE-S of a portion (a) in which a vertical crack has occurred in the drawn wire material after patenting in which a vertical crack has occurred in the twist test and a portion (b) in which no vertical crack has occurred.
It is an EM cross section observation photograph. Vertical crack occurrence site [Fig. 5
The ferrite seen in (a)] has a coarse grain size on average, and many voids were observed along the ferrite. On the other hand, the ferrite in the part of the same wire where vertical cracking did not occur [Fig. 5 (b)] was relatively fine, and the probability that voids could be seen along the ferrite was also low.

Next, using the same rolled material, a steel material subjected to normal patenting treatment (corresponding to steel material No. 2 in the embodiment described later) and austenitizing and quenching before the patenting treatment are performed. Prepare two types of steel materials (corresponding to No. 4 in the examples described later) with homogenization and refinement of the structure (nodule and pro-eutectoid ferrite), and wire drawing them for twisting test. went. The former had vertical cracks at a tensile strength of 3950 MPa, but the latter had no vertical cracks with the same tensile strength. The FE-SEM observation photograph of the cross section of the former drawn wire is shown in FIG.
It is (a) and the latter FE-SEM photograph is FIG.6 (b). It can be seen that the latter has smaller volume fraction of ferrite and smaller average grain size.

From the above knowledge, vertical cracking means that when external stress is applied to coarse one of ferrites distributed unevenly in the wire rod, stress concentration occurs, resulting in local stress exceeding crack generation / propagation resistance. It can be said that the phenomenon of destruction occurs unevenly as a result of generating a field. Moreover, in the manufacturing method of patenting + wire drawing that has been performed so far, coarse ferrite exists even in the wire drawing material of hyper-eutectoid steel,
It can be seen that this was the cause of vertical cracking. Therefore, it is considered that by controlling the non-uniformity of the ferrite grain size distribution before and after drawing, the vertical cracking limit strength can be further improved by controlling the structure.

Therefore, using FE-SEM, the relationship between the grain size of ferrite in the steel material before wire drawing and the occurrence of vertical cracks was examined under the following observation conditions.

Observation position: 1 / 4D Observation magnification: 10,000 times Field of view: 8 locations (cross section, counterclockwise, 0, 45, 9
0,135,180,225,270,315 °) 8) Etching: Method for determining average particle size of nital: Do = Σ (Da × Db × π /
4) ^0.5 / n (ferrite grain major axis is Da, minor axis is Db
Assuming that it is an ellipse, it is divided by the measurement number n from the total area to obtain Do. ) As a result, the average grain size Do of the ferrite is 4.0 μm.
It has been found that vertical cracking may occur when the value exceeds. When vertical cracks occur, the mechanical properties of the wire deteriorate, so the Do value should be 4.0 μm or less,
The smaller the ferrite grain size Do before wire drawing, the better.

In order to suppress the fracture phenomenon of vertical cracking, it is desirable to control the maximum grain size, not the average grain size. The maximum grain size (major axis length) is preferably 12 μm or less. Since it is difficult to measure the maximum grain size, in the present invention, the structural state of the steel material is defined by an average value that is easily evaluated by the number of fields of view that is statistically reliable.

In the production of the steel material and steel wire of the present invention, in order to achieve fine dispersion of proeutectoid ferrite, it is austenitized prior to patenting, the components are homogenized, and then a uniform dispersion state is maintained by quenching. You can do the final patenting as it is. This is a treatment performed in order to eliminate the non-uniformity more than that of a steel material having a considerably fine and uniform pearlite structure by the patenting treatment. During this treatment, if the holding time at the austenitizing temperature is too long, or if the austenitizing temperature is excessively high, the austenitizing grain size becomes coarse and, on the contrary, the structure becomes nonuniform. If the austenitizing time is too short or the austenitizing temperature is too low, homogenization becomes insufficient and this effect cannot be obtained. Therefore, at 850-950 ° C, 1-
It is desirable to perform austenitization for about 10 minutes.

Further, if care is inadvertently performed, quenching cracks may occur and wire drawing may not be possible. Therefore, it is desirable to exercise extreme caution in quenching.

Regarding the deterioration of toughness and ductility due to the second phase structure other than the pro-eutectoid cementite, it has been reported that ferrite and pseudo-pearlite at the former austenite grain boundary deteriorates the wire drawability. -ISI
J (vol.3, 1990, p1811) ", the formation of ferrite and pseudo-pearlite at the grain boundaries is suppressed by the addition of Cr, and it has been shown that the addition of Cr is effective in improving the ductility of the steel wire. ing. However, there is no description about the morphology (for example, grain size) of the ferrite and the ductility of the steel wire, and as in the manufacturing method of the present invention, the alloying element is intentionally added in consideration of the reduction of environmental load. Without saying, it does not mean to suppress the growth of ferrite in the manufacturing process.

In addition, "Iron and Steel (vol.79, 1993, No. 9, P89,
(Fig. 4) ”indicates that in the hyper-eutectoid steel, the carbon negative segregation zone (Carb
An example in which an on-depleted zone) is formed and a structure like ferrite is formed is reported. In this case, it is reported that the pro-eutectoid cementite is too thin to be observed even when observed by an optical microscope after picral etching. Strictly observing the ferrite according to the present invention by TEM observation, no pro-eutectoid cementite was observed in the vicinity of the ferrite according to the present invention, so that the properties different from those reported in the above "iron and steel" were observed. It is considered to be ferrite. In addition, the organization reported in "Iron and Steel" above
Although it is said that it does not adversely affect the ductility of steel wire,
The ferrite pointed out in the present invention deteriorates the vertical crack resistance, and the two are also different in this respect.

As described above, the above-mentioned literature has reported to some extent that ferrite has been observed in patenting + wire drawn materials, and the relationship with the occurrence / propagation behavior of vertical cracks has not been investigated. That is, the present inventors have clarified the causal relationship between the ferrite and the vertical cracks for the first time, and completed the present invention.

The steel material for wire drawing according to the present invention and the steel wire having excellent twisting characteristics have been described above. Next, the method for producing the steel material for wire drawing according to the present invention will be described in detail.

Ferrite and pearlite are produced in hypoeutectoid steel, and pearlite and cementite are produced in hypereutectoid steel.
Hypereutectoid steel is preferred. However, in the hyper-eutectoid steel, ferrite is generated due to the presence of the negative segregation portion of carbon, which causes vertical cracking. In order to prevent the formation of ferrite, it is effective to perform homogenization treatment (specifically, austenitization) before patenting, and then perform patenting, as described above. However, in this manufacturing method, the heat treatment is repeated twice, which consumes a large amount of fuel and is not desirable from the viewpoint of reducing the environmental load. Moreover, it cannot be said to be an optimal manufacturing method in terms of practical use, because it involves capital investment at the industrialization stage.

Therefore, the present inventors have further earnestly studied a method for making ferrite fine and harmless without performing homogenizing treatment before patenting. As a result, it was found that it is very effective to control the cooling rate from the heating in the austenite region during patenting to the end of the isothermal transformation. Specifically, a method of performing the pearlite transformation by setting the austenitizing heating temperature during the patenting treatment performed after hot working to 900 to 1000 ° C., then performing forced cooling, and maintaining the wire rod temperature at 560 to 610 ° C. Or, in the cooling step from the austenitizing temperature to the isothermal transformation temperature, the wire temperature is once supercooled to 500 to 560 ° C, and then the temperature is raised again by reheat to obtain a constant temperature of 530 to 610 ° C at the wire temperature. If a method of maintaining the transformation temperature is adopted, the ferrite grains can be made fine.

At least 9 is required for austenite conversion.
If not heated to above 00 ° C., undissolved cementite remains and deteriorates the properties of the steel wire. However, the heating temperature is 100
If it exceeds 0 ° C., the austenite grain size tends to be coarsened, the ferrite is also coarsened, and the delamination generation limit strength is lowered. Therefore, the austenitizing temperature should be 900-1000 ° C.

The following experiments were conducted to find the cooling conditions. That is, using a general-purpose heating furnace and a fluidized bed furnace, the Fe-0.90% C steel having a wire diameter of 1.3 mmφ
It was heated to 10 ° C., the temperature of the fluidized bed furnace was set to 540 ° C., and the cooling temperature pattern of the conventional method from the austenitizing temperature to the isothermal transformation was measured. The result is shown by the solid line in FIG.
A region where the temperature increased was observed in the cooling pattern 5 seconds after the start of cooling. This is a temperature rise due to transformation recuperation during pearlite transformation, and it can be seen that the actual cooling rate is delayed. And, the effect of offsetting the cooling effect due to this recuperation is a factor that reduces the degree of supercooling as an average value in continuous cooling, inhibits the refinement of the lamella spacing, and causes the ferrite to grow coarsely. Conceivable.

Therefore, if either of the following patenting methods [A] and [B] is adopted, the lamellar spacing of the pearlite structure can be made finer and the coarsening of ferrite can be prevented.

[A] The austenitizing heating temperature during the patenting treatment performed after hot working is 900 to 1000 ° C.
Then, forced cooling is performed, and the wire temperature is 530 to 61.
It is a method of maintaining the temperature at 0 ° C to carry out pearlite transformation,
A typical temperature pattern is shown in FIG. Specifically, Ps (pearlite transformation start temperature), Pf (pearlite transformation end temperature), and the maximum temperature during pearlite transformation all need to be in the range of 530 to 610 ° C. By performing the pearlite transformation in the above temperature range, the average lamella spacing becomes fine and the ferrite grain size can be made fine.

In the transformation recuperation, since the transformation rate of the hyper-eutectoid steel is too fast, the amount of heat generated per unit time increases, and even if the furnace temperature is controlled to be high or low, the heat removal rate cannot keep up. It occurs in. Therefore, it is necessary to positively lower the temperature inside the furnace, and for heat generation due to recuperation, if a cooling gas (for example, inert nitrogen gas) is used to locally increase the heat removal rate, transformation Sometimes a constant temperature transformation can be achieved without excessive heating.

[B] In the cooling step from the austenitizing temperature to the pearlite transformation temperature, the wire rod temperature is 50.
This is a method in which pearlite transformation is performed by supercooling to a temperature in the range of 0 to 560 ° C., then raising the temperature by recuperation and maintaining the wire rod temperature at 530 to 610 ° C., and is indicated by a broken line in FIG.

As shown in FIG. 4, in the 0.90% C steel, the transformation nose temperature determined by TTT (in this steel type,
It can be seen that there is a region where bainite transformation does not occur even at a temperature of 600 to 540 ° C. or lower). That is, FIG.
As shown in, it is understood that bainite is not formed in the region up to 6 seconds at 500 ° C. That is, it is stored at 500 ° C. within 6 seconds by supercooling patenting, and by utilizing the transformation recuperation heat, the maximum temperature of the Bs point or higher near 560 ° C. is set so as not to cross the Bs point (bainite transformation start point) (see FIG. 4). ), The average degree of supercooling is increased, the generation and growth of ferrite is suppressed, and the delamination resistance is also improved.

In addition to the above patenting methods [A] and [B], austening, repeated rapid heating, etc. can be used to refine the austenite grains (grain size number 10 or more), as shown in FIG. It has been reported that Bs (bainite transformation start temperature) and Pf (pearlite transformation end temperature) are reversed, and bainite is not formed even at a nose temperature or lower. By using this method, the degree of supercooling can be increased, so that the lamella spacing can be made fine, and the ferrite grain size can be made fine by making the austenite fine, and the vertical cracking resistance can be improved.

The present invention aims to attain high strength and ductility without adding alloying elements, taking environmental load characteristics, recyclability, etc. into consideration. It is not the one to dare to positively use it only as a means. However, when alloying elements are added from the viewpoint of corrosion resistance and the like, there is no problem unless coarse proeutectoid ferrite or proeutectoid cementite is formed.

Further, in the conventional method, since the transformation speed is too fast, the temperature rise due to the transformation heat generation becomes a problem. Therefore, it is possible to add an alloying element that delays the transformation speed to suppress the amount of heat generated by transformation per unit time. From this point of view alone, Cr is a preferable additive element because it can delay the transformation rate and is effective for refining lamella.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following Examples are not intended to limit the present invention, and any modification of the design of the present invention can be made in view of the gist of the preceding and the following. Are included in the technical scope of.

[0037]

Example 1 As shown in Table 1 and Table 2, 0.90% C steel (Example 1
.About.16), 0.97% C steel (Examples 17 to 32), 0.
Rough drawing was performed using 5.5 mmφ rolled material of three steel types of 97% C-0.2% Cr steel (Examples 33 to 40) to prepare several kinds of steel materials having different wire diameters. Among these, the steel materials of Comparative Examples were subjected to brass plating after ordinary patenting treatment, and then wet drawn to a finished wire diameter of 0.2 mmφ. Further, the steel material of the present invention example was first subjected to austenitizing treatment + quenching, followed by patenting + brass plating, and wet drawing to a finished wire diameter of 0.2 mmφ.

For each test material, wire diameter d before and after final drawing
₀ , d ₁ , the diameter of the pro-eutectoid ferrite before final wire drawing Do, and the calculated value of the diameter of the pro-eutectoid ferrite Do 'were obtained, and the tensile strength (TS) was measured to check whether longitudinal cracks occurred. It was The results are shown in Tables 1 and 2.

[0039]

[Table 1]

[0040]

[Table 2]

No. 1,5,9,13,17,21,2
Nos. 5, 29, 33, and 37 are 1.35 mmφ steel materials that are normally patented (950 ° C. austenite → 55
This is a comparative example in which the 0 ° C. transformation) was drawn to about 0.2 mmφ, and the pro-eutectoid ferrite grain size Do and the calculated value Do ′ before drawing exceeded 4.0 μm. A vertical crack occurred.

No. 2, 6, 10, 14, 18, 22,
Nos. 26, 30, 34, and 38 are 1.35 mmφ steel materials, and are subjected to ordinary patenting treatment (at 920 ° C. austenizing → 5
This is a comparative example in which the 50 ° C. transformation) was drawn to about 0.2 mmφ and the pro-eutectoid ferrite grain size Do and the calculated value Do ′ before drawing exceeded 4.0 μm. A vertical crack occurred.

No. 3,7,11,19,23,26,
Nos. 31, 35, and 39 are steels of 1.35 mmφ austenitized at 950 ° C., quenched and then patented (920 ° C. austenite → 550 ° C. transformation), and drawn to about 0.2 mmφ. This is an example of the present invention in which the pro-eutectoid ferrite grain size Do and the calculated value Do ′ before wire drawing are 4.0 μm or less, and no vertical cracking occurred.

No. No. 15 is a steel material of 1.35 mmφ austenitized at 950 ° C., air-cooled, and then patented (920 ° C. austenite → 550 ° C. transformation) and drawn to about 0.2 mmφ, before drawing. Eutectoid ferrite grain size Do and calculated value Do 'are 4.0
In the comparative example in which the thickness exceeds μm, vertical cracking occurred.

No. 4,8,12,16,20,24,
28, 32, 36, 40 are made of 1.35 mmφ steel material 95
After heat treatment for austenitizing and quenching at 0 ° C. was repeated twice, patenting (920 ° C. austenitization + 550 ° C. transformation) was drawn to about 0.2 mmφ. As shown in Table 2, this is an example of the present invention in which the pro-eutectoid ferrite grain diameter Do and the calculated value Do ′ before wire drawing are 4.0 μm or less, and no vertical cracking occurs.

Example 2 As shown in Tables 3 and 4, 0.90% C steel (Examples 41 to 7)
Rough wire drawing was performed using the rolled material of 5.5 mmφ of 6), and several kinds of steel materials having different wire diameters were prepared. Some of them were usually patented and brass-plated, and then wet drawn to a finished wire diameter of 0.2 mmφ. In addition, a part of the above patenting method [A] (gas cooling during constant temperature transformation to suppress transformation recuperation to achieve more complete constant temperature transformation) + wet plating to finish wire diameter 0.2 mmφ after brass plating I went. In addition, a part of the above patenting [B] [minimum temperature is 500 ° C. (actual line temperature measured value) by supercooling, and is reheated to 560 ° C. (actual line temperature measured value) by transformation reheat to realize constant temperature transformation] + brass After plating, wet drawing was performed to a finished wire diameter of 0.2 mmφ.

For each test material, wire diameter d before and after final drawing
₀ , d ₁ and the pro-eutectoid ferrite diameter Do before and after the final wire drawing, the calculated value Do ′ of the pro-eutectoid ferrite diameter was obtained, and the tensile strength (TS) was measured to determine longitudinal cracking. The presence or absence of occurrence was investigated. The results are shown in Tables 3 and 4.

[0048]

[Table 3]

[0049]

[Table 4]

No. 41, 47, 53, 59, 65, 7
No. 1 is a comparative example in which the heating temperature for austenitizing was too high at 1050 ° C., and the austenite grains were coarse and the ferrite grain size was more than 4.0 μm, and vertical cracking occurred.

No. 42, 48, 54, 60, 66, 7
No. 2 is a comparative example in which the heating temperature is appropriate at 910 ° C., but the conventional heat treatment pattern is adopted, and the maximum temperature during pearlite transformation exceeds 610 ° C. due to recuperation during pearlite transformation. , Ferrite grain size is 4.0μ
Vertical cracks occurred beyond m.

No. 43, 49, 55, 61, 67, 7
No. 3 is a comparative example when the pearlite transformation end temperature was 520 ° C., which was too low, and bainite, which was a supercooled structure, was formed. The ferrite grain size also exceeded 4.0 μm and vertical cracking occurred.

No. 44, 50, 56, 62, 68, 7
No. 4 is a comparative example in which the austenitizing temperature was 850 ° C., which was too low, and undissolved carbides remained. Further, the ferrite grain size also exceeded 4.0 μm, and vertical cracking occurred.

No. 45,51,57,63,69,7
No. 5 was supercooled from the austenitizing temperature to 500 ° C., and the pearlite transformation temperature was 530 to 530 due to the subsequent heat recovery.
It is an example of the present invention that is properly controlled in the range of 610 ° C., a substantial average supercooling degree is made high without forming bainite, fine lamella spacing and fine ferrite are achieved, and the ferrite grain size is also It was 4.0 μm or less, and no vertical cracking occurred.

No. 46, 52, 58, 64, 70, 7
No. 6 is an example of the present invention in which the temperature rise due to the transformation recuperation in the fluidized bed furnace is suppressed by the draft heat treatment for blowing the cooling gas,
The pearlite transformation temperature was properly controlled in the range of 530 to 610 ° C., the ferrite grain size was 4.0 μm or less, and no vertical cracking occurred.

[0056]

EFFECTS OF THE INVENTION Since the present invention is constituted as described above, a carbon steel wire and a carbon steel wire which can obtain high strength without causing vertical cracking without adding an alloying element such as Cr A manufacturing method can now be provided.

[Brief description of drawings]

FIG. 1 is a graph showing a relationship between an actually measured value and a predicted value of a ferrite grain size.

FIG. 2 is a graph showing the prediction accuracy of the ferrite grain size along the drawing direction.

FIG. 3 is a graph showing a cooling pattern during quenching after austenitization.

FIG. 4 is a graph showing a continuous cooling transformation curve of 0.90% C hyper-eutectoid steel.

FIG. 5 is an FE-SEM photograph showing a cross-sectional structure of a portion (a) where vertical cracks have occurred and a portion (b) where vertical cracks have not occurred after the twisting test of the drawn wire material.

FIG. 6 is an FE-SE showing a structure in a cross section of the drawn wire material.
It is an M photograph, (a) is a prior art example, (b) is this invention example.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Nobuhiko Ibaraki 2 Nadahamahigashi-cho, Nada-ku, Kobe Kamido Steel Works, Ltd. Inside the Kobe Steel Works (56) Reference JP-A-5-214443 (JP, A) JP HEI 7-90495 (JP, A) JP-A-3-240919 (JP, A) JP-A-10-183242 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C22C 38/00 -38/60 C21D 9/52

Claims (3)

(57) [Claims] 1. Carbon in an amount of 0.7 to 1.3% (“mass%”)
Means The same shall apply hereinafter) , which is a steel for wire drawing, which has an average grain size of ferrite of 4.0 μm or less, and has excellent twisting characteristics. 2. The method for producing a steel material for wire drawing according to claim 1, wherein the austenitizing temperature at the time of patenting treatment performed after hot working is set to 900 to 1000 ° C., and the wire temperature is then forced to cool. A method for producing a steel material for wire drawing, which comprises performing pearlite transformation while maintaining the temperature at 530 to 610 ° C. 3. In the forced cooling step from the austenitizing temperature, after the wire temperature is once cooled to 500 to 560 ° C., the wire temperature is maintained at 530 to 610 ° C. by recuperation to perform pearlite transformation. 2. The manufacturing method according to 2 .