CN107208208B - The carbon steel wire rod with high of excellent in wire-drawing workability - Google Patents

Abstract

The present invention relates to a hot-rolled high-carbon steel wire rod, wherein the steel composition contains C: 0.60-1.10%, Si: 0.02-2.0%, Mn: 0.1-2.0%, Cr: 0.3-1.6%, Al : 0.001～0.05%, N is limited to 0.008%, P is limited to 0.020%, S is limited to 0.020%, and the balance is Fe and unavoidable impurities. 95% or more of the area ratio in the section perpendicular to the longitudinal direction of the wire is pearlite, the average lamellar spacing of the pearlite is 50 to 100 nm, and the diameter from the center of the section perpendicular to the longitudinal direction of the wire is relative to the diameter D of the wire. The average value of the pearlite block diameters in the central portion within the circle of D/2 is 5 μm<pearlite block diameter<15 μm.

Description

High-carbon steel wire rod with excellent drawing processability

technical field

The present invention relates to a high-carbon steel wire used in various steel cables such as cables for power transmission lines and cables for suspension bridges after drawing.

Background technique

For high-carbon steel wire rods used in cables for power transmission lines, cables for suspension bridges, and various steel cables, etc., after drawing, they have high strength and high ductility, and pursue good wire drawing from the viewpoint of productivity. sex. Based on such requirements, various high-quality high-carbon wire rods have been developed so far.

For example, Patent Document 1 proposes a technique for obtaining good wire drawability by reducing the amount of solid solution N by addition of Ti and reducing the strain aging by solid solution Ti. In addition, Patent Document 2 proposes a technique for obtaining low strength and good wire drawability by controlling the morphology of cementite to be spheroidized. In Patent Document 3, it is proposed that by determining the contents of C, Si, Mn, P, S, N, Al, and O in the steel and controlling the area ratio of the second phase ferrite and the interlamellar spacing of pearlite, the fracture A wire rod technology with excellent wire drawing processability that is less likely to occur and can suppress die wear and prolong die life. In Patent Document 4, a high-carbon steel wire rod with C: 0.6 to 1.1% is proposed, which is a high-ductility high-carbon steel wire rod in which 95% or more is formed of a pearlite structure, and the central portion of the hot-rolled wire rod passes through an EBSP device. The pearlite block size of the measured pearlite has a maximum value of 45 μm or less and an average value of 10 to 25 μm.

prior art literature

patent documents

Patent Document 1: Japanese Patent Laid-Open No. 2012-097300

Patent Document 2: JP-A-2004-300497

Patent Document 3: JP-A-2007-327084

Patent Document 4: JP-A-2008-007856

Contents of the invention

The problem to be solved by the invention

However, according to the experiments of the inventors of the present invention, even if the above-mentioned techniques are used, in the case of a high-strength material exceeding 1300 MPa, it is not necessarily possible to improve the wire drawability by adding Ti and reducing solid-solution N. clear effect. In addition, the spheroidizing heat treatment has low strength after wire drawing and is not suitable for use as a high carbon steel wire.

The present invention is made in view of such actual conditions, and it is a subject of the present invention to provide a steel wire rod as a raw material for obtaining a steel wire having high strength and good wire-drawability.

solutions to problems

The present invention is a high-carbon steel wire rod to be a raw material of a high-strength steel wire, and its gist is as follows.

(1) A high-carbon steel wire rod, which is a high-carbon steel wire rod after hot rolling, and the steel components are C: 0.60-1.10%, Si: 0.02-2.0%, Mn: 0.1-2.0%, Cr : 0.3-1.6%, Al: 0.001-0.05%, Mo: 0.20% or less, Nb: 0.05% or less, V: 0.20% or less, Ti: 0.05% or less, B: 0.003% or less, N: 0.008% or less, P : 0.020% or less, and S: 0.020% or less, and the balance: Fe and unavoidable impurities,

The microstructure of the high-carbon steel wire rod is pearlite at least 95% of the area ratio in a section perpendicular to the wire rod length direction,

The average lamellar spacing of the aforementioned pearlite is 50-100 nm,

The diameter of the section perpendicular to the length direction of the wire rod from the center is D/2 relative to the diameter D of the wire rod, that is, the average value of the pearlite block diameter in the central part is greater than 5 μm and less than 15 μm,

In the area within 500 μm from the surface layer of the section perpendicular to the longitudinal direction of the wire rod, that is, the outer peripheral part, the crystal orientation <110> of ferrite in the pearlite structure has a concentration degree of 1.3 or more,

The tensile strength of the high carbon steel wire rod is above 1300MPa.

(2) The high carbon steel wire rod as described in (1) containing Mo: 0.02-0.20% by mass %.

(3) The high carbon steel wire rod according to (1) or (2), which contains 1 of Nb: 0.002 to 0.05%, V: 0.02 to 0.20%, and Ti: 0.002 to 0.05% by mass %. species or 2 species.

(4) The high carbon steel wire rod according to any one of (1) to (3), which contains B: 0.0003% to 0.003% by mass %.

(5) The high-carbon steel wire rod according to any one of (1) to (4), which contains Si: 0.02 to 1.0% by mass%.

(6) The high carbon steel wire rod according to any one of (1) to (5), wherein the average value of the pearlite block diameter is larger than 5 μm and smaller than 12 μm.

The effect of the invention

According to the present invention, it is possible to provide a high-carbon steel wire rod having a tensile strength of 1300 MPa or more and high ductility, and the industrial contribution is extremely significant.

Description of drawings

FIG. 1 is a diagram showing a central portion A and an outer peripheral portion B in a cross section perpendicular to the wire length direction.

Fig. 2 is a graph showing the relationship between wire drawing logarithmic strain (true distortion) and cumulative fracture rate.

Detailed ways

In order to solve the above-mentioned problems, the inventors of the present invention have repeatedly conducted various investigations and studies on the structure and heat treatment method of the steel wire rod. As a result, the findings (a) to (c) below were obtained.

(a) The addition of Cr promotes the miniaturization of the original γ particle size and miniaturizes the pearlite block size after phase transformation.

(b) The smaller the average value of the pearlite block diameters observed in the center portion A (specified) of the wire rod, the better the wire drawability.

(c) In the case of the <110> orientation set of ferrite crystal orientation observed in the outer peripheral portion B (regulation) of the section perpendicular to the wire length direction, the crystal rotation in the wire drawing becomes less, so it can be Suppresses the occurrence of voids caused by shear stress.

The ferrite crystal orientation in the wire length direction of the steel wire rod and the block diameter of pearlite have different distributions from the center to the surface layer. FIG. 1 shows a central portion A and an outer peripheral portion B in a cross section perpendicular to the longitudinal direction of the wire rod. In this specification, as shown in FIG. 1, the area within a circle with a diameter of 1/2D from the center of the wire rod with a diameter of Dmm is defined as the central part A, and the area within 500 μm from the surface layer is defined as Peripheral part B.

The pearlite block diameter can be measured by an electron backscattering (Electron Back Scatter Diffraction, referred to as EBSD) method by setting the central portion A in FIG. 1 as a measurement position. For example, a cross section perpendicular to the longitudinal direction of the wire rod is mirror-polished with colloidal silica particles, and the measurement by the EBSD method is performed near the center in the radial direction to create a ferrite crystal orientation map. For example, the mapping area is a rectangular area with a side of 500 μm or more, the pixel shape is arranged as regular hexagonal elements, and the measurement interval is 0.5 μm.

The degree of concentration of the ferrite crystal orientation <110> in the longitudinal direction of the wire rod can be measured by marking the crystal orientation of each pixel on the {110} pole figure by setting the outer peripheral portion B in FIG. 1 as the measurement position. More specifically, the concentration degree of the ferrite crystal orientation <110> can be measured by generating a {110} pole figure from the measurement result of the EBSD method, and performing texture analysis on the obtained pole figure. The degree of clustering is expressed as an intensity ratio with the case where the crystal orientation is random being set to 1.

In addition, when ferrite crystal orientation is identified by the EBSD method, information on the crystal orientation of ferrite is given to each hexagonal pixel, and as a result, the boundary between adjacent pixels defines the information on the angular difference in crystal orientation. If the boundary between two pixels has a ferrite crystal orientation inclination difference of 9° or more and the pixel boundary adjacent to it is also 9° or more, if the pixel boundaries with a tilt angle difference of 9° or more are continuous, they are Connections are defined as pearlite block grain boundaries.

In the case where the pixel boundaries extending from the triple points of the pixels are all 9° or more, the pearlite block grain boundaries branch. When the condition that the crystal orientation difference of the pixel boundary is 9° or more is interrupted, the pixel boundary is not regarded as a pearlite block grain boundary and ignored. According to the above way of thinking, define a pixel boundary with a ferrite azimuth difference of more than 9° in the entire rectangular area, and when the pixel boundary surrounds a closed area, define the area as a pearlite block, and define the pixel boundary For pearlite block grain boundaries. In this way, pearlite block grain boundaries are shown on the diagram of ferrite crystal orientation, and the block diameter of pearlite is measured. However, when one grain of the defined pearlite block consists of 25 or less pixels, it is treated as noise and ignored. Among them, pearlite block and pearlite tumor have the same meaning. In addition, pearlite is lamellar pearlite.

The interlamellar spacing can be obtained as follows: corrode the cross-section perpendicular to the length direction of the wire with nitric acid etching solution, use SEM, and draw vertically at the position where the interlamellar spacing is the smallest in the field of view photographed at a magnification of 10,000 times The line is 5 interlamellar intervals, divide the length of 5 interlamellar intervals by 5. In addition, the imaging by SEM was performed at 10 or more fields of view, and the interlamellar spacing obtained in each field of view was divided by the number of fields of view to obtain an average value.

With regard to wire drawing workability, a test material having a length of 10 m was dipped in hydrochloric acid to remove scale, washed with water, and then subjected to a phosphate coating treatment, followed by dry wire drawing and evaluated. Wire drawing can be performed using a die made of WC-Co cemented carbide having a drawing die entrance (overall) angle of 20° and a borering length of about 0.3 times the hole diameter. The wire drawing speed is set at 50 m/min, and a dry wire drawing lubricant mainly composed of sodium stearate and calcium stearate can be used.

When wire breakage did not occur, the diameter of the die hole was reduced so that the area reduction ratio was 20%, and wire drawing was performed until wire breakage occurred. The evaluation was terminated when the total number of wire breakages reached 20, and the wire drawing workability was obtained from the wire diameter (wire diameter before wire drawing start) D0 of the test material and the die hole diameter D where wire breakage occurred according to the following formula.

Wire drawing degree (ε)=2×ln(D0/D)

At each degree of wire drawing, the number of breaks occurred was divided by 20 (total number of tests) to obtain the rate of breakage, and the accumulated rate of breakage so far was added to this to obtain the cumulative rate of breakage at each degree of wire drawing. Fig. 2 is a test result of a wire coil as a reference for judging that the wire drawability is good. When the degree of wire drawing is 1.7, the number of fractures is 1, and the cumulative fracture rate on the vertical axis is 0.05 (1/20). When the degree of wire drawing was 1.9, the number of times of breakage was 5 and the rate of breakage was 0.25. When the cumulative rate of breakage of 0.05 before that (degree of wire drawing 1.7) was added, the cumulative rate of breakage was 0.3. In addition, when the wire drawing degree becomes the maximum in 20 tests, the cumulative fracture rate becomes 1.0.

In the present invention, the degree of wire drawing at which the cumulative fracture rate becomes 0.5 was obtained from the graph and defined as wire drawability. As shown in FIG. 2 , the wire drawability of the wire coil as a reference for judging that the wire drawability is good was 2.23. Furthermore, the wire drawing rate of 0.9 with a cumulative breakage rate was 3.0, and the wire drawing rate of 1.0 with a cumulative breakage rate was 3.12. Therefore, in the present invention, the wire drawability is evaluated as good at 2.23 or more, more preferably at least 2.53, and even more preferably at 2.95 or more.

(for steel wire)

Next, the components of the steel wire rod of the present invention will be described. In addition, the % concerning a component is mass %.

<for ingredients>

C

C is an element that makes the structure into pearlite and improves the strength. When the amount of C is less than 0.60%, non-pearlite structures such as grain boundary ferrite are formed to impair wire drawability, and the tensile strength of the ultra-thin steel wire also decreases. On the other hand, when the amount of C exceeds 1.10%, non-pearlite structures such as pro-eutectoid cementite are formed, and wire drawability deteriorates. Therefore, the amount of C is limited to the range of 0.60 to 1.10%. The amount of C is preferably set to 0.65% or more.

Si

Si is an element used for deoxidation of steel and also contributes to solid solution strengthening. In order to obtain the effect, 0.02% or more of Si is added. The amount of Si is preferably set to 0.05% or more. On the other hand, when the amount of Si exceeds 2.0%, surface decarburization tends to occur in the hot rolling process, so the upper limit is made 2.0%. The amount of Si is preferably 1.0% or less, more preferably 0.5% or less.

mn

Mn is an element used for deoxidation and desulfurization, and is added in an amount of 0.1% or more. On the other hand, when the amount of Mn exceeds 2.0%, the pearlite transformation is significantly delayed, and the time for the lead bath quenching treatment becomes longer, so the amount of Mn is made 2.0% or less. The amount of Mn is preferably 1.0% or less.

Cr

Cr is an element that refines the original γ particle size and refines the pearlite structure, and also contributes to high strength. In order to obtain the effect, 0.3% or more of Cr is added. On the other hand, when the amount of Cr exceeds 1.6%, pro-eutectoid cementite is precipitated and wire drawability is reduced, so the upper limit is made 1.6%. Preferably, it is 1.3% or less. More preferably, it is 1.0% or less.

al

Al is an element having a deoxidizing effect, and is necessary to reduce the amount of oxygen in steel. However, when the Al content is less than 0.001%, it is difficult to obtain this effect. On the other hand, Al tends to form hard oxide-based inclusions. In particular, when the Al content exceeds 0.05%, the formation of coarse oxide-based inclusions becomes significant, resulting in a significant decrease in wire drawability. Therefore, the content of Al is set to 0.001 to 0.05%. The lower limit is more preferably 0.01% or more, and the upper limit is more preferably 0.04% or less.

N

N is an element that fixes to dislocations during cold wire drawing to increase the strength of the steel wire and conversely lowers the wire drawability. In particular, when the N content exceeds 0.008%, the reduction in wire drawability becomes remarkable. Therefore, the N content is limited to 0.008% or less. More preferably, it is 0.005% or less.

P

P is easy to segregate in steel, and during segregation, the eutectoid transformation is significantly delayed, so the eutectoid transformation is not completed, and hard martensite is easily formed. In order to prevent this problem, the P content is limited to 0.02% or less.

S

When a large amount of S exists, a large amount of MnS is formed to lower the ductility of the steel, so it is limited to 0.020% or less. More preferably, it is 0.01% or less.

Mo

Addition of Mo is optional. If added, it has the effect of improving the tensile strength of a steel wire rod. In order to obtain this effect, it is desirable to add 0.02% or more of Mo. However, when the content of Mo exceeds 0.20%, a martensitic structure is likely to be formed, and the wire drawability decreases. Therefore, the content of Mo is preferably 0.02 to 0.20%. More preferably, it is 0.08% or less.

V

The addition of V is arbitrary. If added, carbonitrides are formed in the steel wire rod, the pearlite block diameter is reduced, and wire drawing workability is improved. In order to obtain this effect, it is desirable to add 0.02% or more of V. However, when the V content exceeds 0.20%, coarse carbonitrides are likely to be formed, and the wire drawability may decrease. Therefore, the content of V is preferably 0.02 to 0.20%. More preferably, it is 0.08% or less.

Nb

Addition of Nb is optional. If added, carbonitrides are formed in the steel wire rod, the pearlite block diameter is reduced, and wire drawing workability is improved. In order to obtain this effect, it is desirable to add 0.002% or more of Nb. However, when the Nb content exceeds 0.05%, coarse carbonitrides are likely to be formed, and the wire drawability may decrease. Therefore, the content of Nb is preferably 0.002 to 0.05%. More preferably, it is 0.02% or less.

Ti

Addition of Ti is optional. If added, carbides or nitrides are formed in the steel wire rod, the pearlite block diameter is reduced, and wire drawing workability is improved. In order to obtain this effect, it is desirable to add 0.002% or more of Ti. However, when the Ti content exceeds 0.05%, coarse carbides or nitrides are likely to be formed, and the wire drawability may start to decrease. Therefore, it is preferable to set the content of Ti to 0.02 to 0.05%. More preferably, it is 0.03% or less.

B

The addition of B is arbitrary. When added, the solid solution N in the steel wire rod is formed into BN, the solid solution N in the steel is reduced, and the wire drawability is improved. In order to obtain this effect, it is desirable to add 0.0003% or more of B. However, when the B content exceeds 0.003%, coarse nitrides are likely to be formed, and the wire drawability may decrease. Therefore, the content of B is preferably 0.0003 to 0.003%. More preferably, it is 0.002% or less.

<For metallographic structure>

Next, the metallographic structure of the steel wire rod of the present invention will be described.

Area ratio

Non-pearlite structures such as proeutectoid ferrite and proeutectoid cementite cause cracks in final wire drawing. In embodiment of this invention, in order to improve wire-drawability, the area ratio of pearlite is made into 95 % or more. The balance is non-pearlite structures such as proeutectoid ferrite and proeutectoid cementite. It should be noted that the above-mentioned metallographic structure can be determined as follows: a cross-section of the wire rod cut perpendicular to the length direction of the wire rod is cut as a sample, mirror-polished, and then observed with a scanning electron microscope. In addition, the area ratio of each metallographic structure can be calculated|required using the planimetry method or the spot counting method from the result of scanning electron microscope observation. Preferably, the observation magnification is, for example, 1000 times or more, and the observed area is, for example, 1000 μm ² or more. For example, when determining the area ratio by the point counting method, it is preferable to set the measurement points to 200 points or more.

block diameter of pearlite

As mentioned above, when the block size of pearlite (hereinafter, also referred to as pearlite block size) exceeds 15 μm, wire drawability decreases, so it is set to 15 μm or less. More preferably, it is 12 μm or less. In addition, when the pearlite block diameter is 5 μm or less, the non-pearlite structure increases, so 5 μm is made the lower limit.

Concentration degree of ferrite crystal orientation <110>

When the ferrite crystal orientation <110> is concentrated in the outer peripheral portion of the cross-section perpendicular to the longitudinal direction of the wire rod, it is possible to suppress orientation rotation during wire drawing and suppress void formation due to shear deformation. In the present invention, the concentration degree of the ferrite crystal orientation <110> is set to be 1.3 or more in order to achieve this effect. Preferably it is 1.5 or more, More preferably, it is 1.7 or more.

It should be noted that the pearlite block size and the concentration degree of the ferrite crystal orientation <110> can be determined by the EBSD method as described above.

Lamellar spacing

The metallographic structure in the present invention is mainly pearlite, and the steel wire rod is aimed to have a tensile strength of 1300 MPa or more, preferably 1350 MPa or more, more preferably 1400 MPa or more. In order to obtain this strength, the average interlamellar spacing of pearlite shown in Examples described later needs to be 100 nm or less. In addition, when the average lamellar spacing of pearlite is less than 50 nm, bainite structures other than pearlite are mixed, the target strength cannot be obtained, and the wire work hardening rate decreases, so the lower limit is made 50 nm.

<For the manufacturing method of the steel wire rod>

Next, the manufacturing method of the steel wire rod of this invention is demonstrated using a specific example. It should be noted that the following descriptions are merely examples for illustrating the present invention, and do not limit the scope of the present invention.

The steel wire rod of the present invention is manufactured by melting steel having the above-mentioned composition by a conventional method, casting it, and hot rolling the obtained steel slab. Hot rolling is performed by heating the billet to about 1150°C. The finishing temperature of hot rolling is 740-880°C. After finishing rolling, in order to produce pearlite phase transformation, it is cooled by means of forced air cooling, spray cooling, water cooling, etc. at 25°C/sec to 40°C/sec until it reaches 550°C to 650°C (primary cooling). After keeping the temperature for 30 seconds to 180 seconds, it is cooled to 300°C by means of air cooling or water cooling at a rate of 2°C/second or more (secondary cooling), and cooled to room temperature by means such as letting cool. In addition, the diameter of a wire rod will not be specifically limited as long as necessary work hardening can be ensured at the time of making a steel wire.

When the finish rolling temperature of hot rolling is higher than 880°C, the effect of refining the original γ grain size becomes small, so it is set to 880°C or lower. In addition, when rolling is performed at less than 740°C, pro-eutectoid ferrite is precipitated during rolling, so the lower limit is made 740°C.

When the cooling rate in primary cooling is less than 25° C./sec, the original γ particle size becomes coarse, so the lower limit is made 25° C./sec. Cooling exceeding 40°C/sec is difficult in actual production, so it is set to 40°C/sec or less.

When the holding temperature exceeds 650°C, the original γ particle size becomes coarse and the strength decreases, so the upper limit is made 650°C. In addition, when it is less than 550°C, the non-pearlite structure increases, so the lower limit is made 550°C.

If the retention time is less than 30 seconds, the pearlite transformation is not completed and the non-pearlite structure increases, so the lower limit is made 30 seconds. In addition, holding for more than 180 seconds leads to deterioration of productivity and reduction of wire rod strength due to shape collapse of lamellar pearlite, so the upper limit is made 180 seconds.

In the secondary cooling, the lower limit of the secondary cooling rate up to 300°C is set to 2°C/sec if the slow cooling such as furnace cooling is performed in the temperature range of 300°C or higher and less than 2°C/sec. . In addition, the cooling rate from 300 degreeC to room temperature need not be considered.

Example

Hereinafter, the steel wire rod and the manufacturing method of the steel wire rod according to the embodiment of the present invention will be specifically described while showing examples. It should be noted that the examples shown below are only examples of the steel wire rod and the manufacturing method of the steel wire rod described in the embodiments of the present invention, and the steel wire rod and the manufacturing method of the steel wire rod described in the present invention are not limited to Examples below.

For high-carbon steel hot-rolled wire rods with the composition shown in Table 1, by changing the hot-rolling conditions shown in Table 2, the same pearlite structure was produced, but the diameter of the pearlite block in the center and the diameter of the surface layer Wire rods with different ferrite crystal orientation <110> concentration and tensile strength. These wires were evaluated using wire drawing process critical strain. The results are shown in Table 3.

[Table 1]

steel type C Si mn Cr al Mo B Nb C Ti A 0.82 0.2 0.5 0.5 0.029 - - - - - invention steel B 1.07 0.05 0.1 1.2 0.028 - - - - - invention steel C 0.62 1.5 1.5 0.3 0.004 0.1 - - - - invention steel D. 0.92 0.2 0.5 0.5 0.045 - 0.002 - - - invention steel E. 1.08 0.05 0.5 0.8 0.030 - - 0.01 0.1 - invention steel f 0.83 0.15 0.2 0.7 0.035 - - - - 0.03 invention steel G 0.92 0.05 0.5 0.1 0.004 - - - - - compare steel h 0.82 0.2 2.5 0.5 0.018 - - - - - compare steel I 1.35 0.05 0.5 1 0.022 - - - - - compare steel

[Table 2]

[table 3]

Specific production methods of these high carbon steel wire rods are described below. As shown in Table 1, the chemical composition of the wire rod is smelted in a converter, and the steel ingot is initially rolled to produce a 155mm square small and medium-sized steel billet. After heating to about 1150°C, the rolling end temperature is 740°C to Hot rolling was performed in a range of 880° C. to obtain a wire rod with a diameter of 10 mm.

The wire rod after the above-mentioned hot rolling is immediately cooled to a range of 550° C. to 650° C. by spraying cooling water through a nozzle through a cooling zone provided on a rolling line. At this time, change the amount of water and water cooling time to control the reached temperature. In addition, the wire rod is subsequently cooled to a range of 650°C to 550°C by forced air cooling at a cooling rate of 5°C/sec to 25°C/sec. Thereafter, the temperature range is maintained for about 60 seconds to complete the pearlite phase transformation, and cooled to room temperature by air cooling.

The pearlite area ratio (%), pearlite block diameter, lamellar spacing, ferrite crystal orientation, and tensile strength of these steel wire rods were measured.

The pearlite area ratio was obtained by etching a mirror-polished sample with a mixed solution of nitric acid and ethanol on the cross section obtained by cutting the wire rod, and observing the center between the surface and the center of the wire rod at 2000 magnifications.

The pearlite block diameter and interlamellar spacing were measured in a region of 62500 μm ² within a range of 5 mm from the center of the steel wire rod. The concentration degree of ferrite orientation <110> was measured in a region of 62500 μm ² within a range of 500 μm from the surface layer using an EBSD measuring device manufactured by TSL Corporation.

The tensile test was performed based on JIS Z 2241. Regarding wire drawing workability, as described above, dry wire drawing was performed, and the total number of wire breakages was set to 20, and a graph of the relationship between wire drawing logarithmic strain and cumulative fracture rate was made, and the wire drawing with a cumulative fracture rate of 50% was The number should be evaluated. The results are shown in Table 3. PBS is the average of pearlite block diameter.

Since No. 10 has a high retention temperature, the interlamellar distance is large and the tensile strength is insufficient.

In No. 11, the amount of Cr was low, and the micronization of the pearlite block diameter was not sufficient, so the critical strain in wire drawing was small.

In No. 12, the amount of Mn was large, the pearlite transformation was not completed, and the area ratio of pearlite was very small, so the critical strain for wire drawing became small.

The amount of C in No.13 is high, and pro-eutectoid cementite is formed, so the area ratio of pearlite is small, and the critical strain of wire drawing becomes small.

The holding time of No.14 is short, and secondary cooling is performed before the pearlite transformation is completed, so the area ratio of pearlite is small, and the critical strain of wire drawing becomes small.

The primary cooling rate of No.15 is small, and the original γ particle size is coarsened, so the pearlite block size is large, and the critical strain of wire drawing becomes small.

In No. 16, the retention time was long, the shape of lamellar pearlite collapsed, and the tensile strength was insufficient.

In No. 17, the finish rolling temperature is low, a large amount of proeutectoid ferrite is formed, the tensile strength is insufficient, and the critical strain of wire drawing becomes small.

No. 18 has a high finish rolling temperature and coarsened original γ particle size, so the pearlite block size is large, and the critical strain of wire drawing becomes small.

In No. 19, the secondary cooling rate was small, the shape of lamellar pearlite collapsed, and the tensile strength decreased.

Claims (6)

1. Be the carbon steel wire rod with high after hot rolling 1. a kind of carbon steel wire rod with high, composition of steel with quality % be calculated as C:0.60~1.10%, Si:0.02~2.0%, Mn:0.1~2.0%, Cr:0.3~1.6%, Al:0.001~0.05%, Mo:0.20% or less, Nb: 0.05% or less, V:0.20% or less, Ti:0.05% or less, B:0.003% or less, N:0.008% or less, P:0.020% with Under and S:0.020% hereinafter, and surplus: Fe and inevitable impurity,

   The above are pearly-lustres for the tissue of the carbon steel wire rod with high in terms of in the area ratio in the section vertical with length of wires direction 95% Body,

   The average platelet spacing of the pearlite is 50~100nm,

   Within the circle that the diameter since center in the section vertical with length of wires direction is D/2 relative to the diameter D of wire rod The average value of region, that is, central part pearlite block diameter be greater than 5 μm and less than 15 μm,

   Region, that is, peripheral part the section vertical with length of wires direction is since surface layer within 500 μm, pearlitic structrure In ferritic crystal orientation<110>aggregation degree be 1.3 or more,

   The tensile strength of the carbon steel wire rod with high is 1300MPa or more.
2. 2. carbon steel wire rod with high according to claim 1, wherein contain Mo:0.02~0.20% in terms of quality %.
3. 3. carbon steel wire rod with high according to claim 1, wherein contain Nb:0.002~0.05%, V in terms of quality %: 0.02~0.20%, one kind or two or more among Ti:0.002~0.05%.
4. 4. carbon steel wire rod with high according to claim 1, wherein contain B:0.0003~0.003% in terms of quality %.
5. 5. carbon steel wire rod with high according to claim 1, wherein contain Si:0.02~1.0% in terms of quality %.
6. 6. carbon steel wire rod with high according to any one of claims 1 to 5, wherein the average value of pearlite block diameter is greater than 5 μm And less than 12 μm.