JP2001181789A - Small-diameter hot rolled high carbon steel wire rod excellent in wire drawability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small-diameter high carbon steel wire rod capable of wire drawing while securing high ductility at >=2.2 true strain in an as-hot-rolled state without intermediate heat treatment even if the precipitation of pro- eutectoid ferrite or pro-eutectoid cementite precipitating in a perfect pearlitic structure or pearlitic structure is not completely prevented. SOLUTION: This small-diameter hot rolled high carbon steel wire rod of <=4.5 mm diameter has a composition consisting of, by mass, 0.60-1.50% C, 0.05-0.50% Si, 0.05-1.20% Mn and the balance iron with inevitable impurities and also has >=8.5 austenite grain size after hot rolling. The structure of this wire rod is all composed of a pearlitic structure or is composed of a pearlitic structure containing pro-eutectoid ferrite or pro-eutectoid cementite of <=10 μm maximum length in <=5% area ratio. Further, the aspect ratio (maximum length/minimum width) of pro-eutectoid ferrite or pro-eutectoid cementite is >=3 on average, and pearlite colony size is <=30 μm on average.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a steel code,
A thin-diameter high-carbon hot-rolled wire excellent in drawability suitable for producing high-strength ultra-fine steel wires such as hose wires and cut-saw wires, and particularly, true strain of 2.2 or more as hot rolled The present invention relates to a small-diameter high-carbon hot-rolled wire rod capable of wire drawing.

[0002]

2. Description of the Related Art Conventionally, steel cords, hose wires,
In the production of high-strength ultra-fine steel wire such as cut-saw wire, high-carbon steel hot-rolled wire having a wire diameter of 5.5 to 5.0 mm is drawn to a final heat-treated wire diameter of 1.0 to 2.0 mm. At an intermediate stage, intermediate annealing such as AP is performed with a wire diameter of about 1.8 to 2.2 mm.

[0003] In order to reduce the manufacturing cost of high-strength extra-fine steel wire, there is an increasing demand for a wire rod having excellent drawability, which enables omission of intermediate heat treatment.

[0004] The drawability of a wire is greatly affected by the microstructure. High-carbon steel wire has the best wire drawability when its microstructure is adjusted to a perfect pearlite structure. However, after hot rolling, continuous cooling by air cooling, which is referred to as a Stellmore method, is generally performed, so that pro-eutectoid ferrite or pro-eutectoid cementite precipitates, thereby deteriorating drawability.

[0005] Proeutectoid ferrite or proeutectoid cementite can be prevented by increasing the cooling rate, but in this case, bainite or martensite is generated,
Further, it is not practical because the drawability may be deteriorated.

[0006] The drawability is also affected by the uniformity of the structure in the cross section of the wire. JISG 3502, 350
The minimum diameter of the high carbon steel wire specified in No. 6 is 5.5 mm, and the difference in the microstructure between the surface layer and the central portion is caused by air cooling. The sex worsens.

As a method of preventing the precipitation of pro-eutectoid ferrite or pro-eutectoid cementite and increasing the uniformity of the structure in the cross section, for example, as disclosed in JP-A-61-67723, A direct patenting method in which a medium to high carbon steel wire is wound in a non-concentric ring shape and introduced into a heat treatment tank to perform controlled cooling has been proposed.

Further, as described in Japanese Patent Application Laid-Open No. Hei 9-165650, when a wire of 5.5 mm or less of 0.6 to 0.85% C is rolled for finishing a bead wire, the finish is reduced. Rolling is performed at 950 to 1050 ° C.
After cooling to 00 ° C. in 3 to 10 seconds, it is transformed into pearlite by blast, mist, boiling water, lead bath, salt or the like. By this step, the structure is controlled such that the lamellar spacing is 0.11 to 0.17 μm, the ferrite mass is 1 to 5%, the distribution of the pearlite block size is 30 μm ² or more, the area ratio is 60% or more, and the structure is 20 μm ² or more, 80% or more. It is stated that high direct drawability can be secured by this.

However, the method described in Japanese Patent Application Laid-Open No. 61-67723 is impractical because the rolling temperature and the cooling rate must be controlled, so that the equipment is greatly restricted and the cost is very high. . Furthermore, since it is intended for medium to high carbon steel wires, there is a limit to the amount of C contained that can ensure a uniform pearlite structure.

In Japanese Patent Application Laid-Open No. 9-165650, a bead wire is used.
0.85 for manufacturing high strength steel cord with MPa
It is important to ensure high direct drawability with a wire containing more than% C. At that time, the problem is proeutectoid cementite, but its microstructural specification and its control method are described. Absent.

Further, in order to secure high direct drawability in a wire rod of 0.6 to 0.85% C, there is a limit in controlling only the area ratio, the existing position and the existing ratio of the proeutectoid ferrite, and the shape is also controlled. There is a need to.

[0012]

SUMMARY OF THE INVENTION The present invention relates to a heat treatment in the middle of hot rolling without complete prevention of precipitation of pro-eutectoid ferrite or pro-eutectoid cementite in a complete pearlite structure or a pearlite structure. No true distortion
An object of the present invention is to provide a small-diameter high-carbon steel wire rod that can be drawn while ensuring high ductility at 2 or more.

[0013]

Means for Solving the Problems In order to solve the above problems,
As a result of studying the structure of small diameter high carbon steel wire rod, the following knowledge was obtained.

That is, if the austenite crystal grain size in the complete pearlite structure is 8.5 or more and the pearlite colony size is 30 μm or less on average, it is finely divided into:
It is possible to obtain better wire drawability than before in hot rolling. In the pearlite structure containing pro-eutectoid ferrite or pro-eutectoid cementite, coarse precipitation of pro-eutectoid ferrite or pro-eutectoid cementite is prevented, the area ratio is 5% or less, the maximum length is 10 μm or less, and the aspect ratio (maximum length / maximum length). Small width)
Is fine enough to satisfy 3 or more, it is possible to obtain excellent drawability while hot rolling without completely preventing precipitation. In addition, the precipitation of the pro-eutectoid ferrite and the pro-eutectoid cementite by dispersing the austenite particle size is dispersed, and coarse precipitation can be prevented. Further, the austenite grain size can be refined by increasing the rolling reduction during hot rolling, and by finishing the wire diameter to 4.5 mm or less, the uniformity in the cross section of the wire can be increased even with continuous cooling by air cooling. I found that.

The present invention has been completed based on the above findings, and the gist of the invention is as follows.

(1) In mass%, C: 0.60 to 1.5
0%, Si: 0.05 to 0.50%, Mn: 0.05 to
1.20%, the balance consists of iron and unavoidable impurities, the austenite grain size after hot rolling is 8.5 or more,
All tissues are pearlite structure or 5% or less in area ratio,
It has a pearlite structure containing pro-eutectoid ferrite or pro-eutectoid cementite having a maximum length of 10 μm or less. The aspect ratio (maximum length / minimum width) of pro-eutectoid ferrite or pro-eutectoid cementite is 3 or more on average, and the pearlite colony size is 30 μm on average. 3. The diameter is:
A small-diameter high-carbon hot-rolled wire excellent in wire-drawing workability that can be drawn as hot-rolled with a true strain of 2.2 or more and a true strain of 5 or less.

(2) Further, in mass%, Al: 0.00
The small-diameter high-carbon hot-rolled wire according to the above (1), containing less than 5%, and a total of 10 to 300 ppm of one or more of Ca, Mg, La, Ce and Hf.

(3) Further, in mass%, Cr: 0.05
-0.5%, V: 0.01-0.2%, Nb: 0.00
1 to 0.2%, Mo: 0.05 to 0.5%, B: 0.0
The small-diameter high-carbon hot-rolled wire according to the above (1) or (2), comprising one or more of 02 to 0.04%.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

First, the reasons for limiting the components of the small-diameter high-carbon wire of the present invention will be described.

The range of the C content is 0.70 to 1.30%. However, by setting the wire diameter to 4.5 mm or less and obtaining an austenite grain size of 8.5 or more, the range in which proeutectoid ferrite and proeutectoid cementite can be suppressed is expanded, and
It becomes possible to set it to 0 to 1.50%. Further, since the austenite grains are fine, the austenite grains at the time of patenting after wire drawing become fine, so that coarsening of proeutectoid ferrite or proeutectoid cementite can be prevented. For this reason, C was limited to 0.60 to 1.50%.

Si has the effect of suppressing the precipitation of proeutectoid cementite even with the same amount of carbon. Further, Si not only has the effect of increasing the strength of ferrite in pearlite, but also has the effect of concentrating at the ferrite / cementite interface in pearlite, preventing the decomposition of cementite due to an increase in temperature, and reducing the decrease in strength. If it is less than 05%, the above effects cannot be exhibited. When the amount of Si is large, when the wire diameter is large, the cooling rate is slow, so that the thickness of the ferrite layer in the pearlite increases, and since Si concentrates at the interface with cementite, the deformability inside the ferrite layer is not sufficient. Uniformity occurs and the wire drawing workability deteriorates. 3. The diameter of the wire
When the thickness is 5 mm or less, the width of the ferrite layer in the pearlite structure is reduced, and the non-uniformity of the deformability is reduced. On the other hand, if it exceeds 0.50%, S which is harmful to wire drawing workability
Since it is easy to generate iO ₂ -based inclusions, 0.05%
The range was limited to 0.50%.

Mn is an element effective for improving hardenability and increasing strength, and has an effect of preventing precipitation of proeutectoid ferrite and proeutectoid cementite. Further, Mn converts solid solution S in steel to M
It is fixed as nS and has the effect of preventing the deterioration of ductility due to solid solution S. If it is less than 0.05%, the above effect cannot be obtained. On the other hand, Mn is an element that easily segregates, and when the amount of Mn increases, a supercooled structure such as martensite, which is harmful to wire drawing workability, is generated in the segregated portion. 4.5mm diameter wire
By setting the content to be below, the amount of processing at the time of rolling is increased, and the segregated portion can be reduced. When the content is 1.20% or less, generation of a supercooled structure harmful to wire drawing workability can be prevented. . For this reason, it limited to the range of 0.05 to 1.20%.

If the content of Al is 0.005% by mass or more, hard nonmetallic inclusions such as alumina increase, and steel
Al: 0.005% was set as the upper limit in order to increase the number of breaks in the ultrafine wire drawing step and the twisting step such as welding.

The oxides of Ca, Mg, La, Ce, and Hf are compounded with a hard oxide such as SiO ₂ to lower the melting point of the inclusions to form inclusions having a high deformability, thereby obtaining steel. This has the effect of reducing wire breakage in the ultra-fine wire drawing step and the twisting step such as wire. Ca, Mg, La, C
No effect is observed when the sum of one or more of e and Hf is less than 10 ppm, so that Ca, Mg, La, Ce, Hf
Or a total of two or more of the above: 10 ppm as a lower limit.

On the other hand, one of Ca, Mg, La, Ce and Hf
When the total of the species or two or more species is> 300 ppm, the effect is saturated, and inclusions that are not complexed such as CaO, LaO, and CeO increase, and the disconnection in the ultrafine drawing process and the twisting process increases. , Mg, La, Ce, Hf, or a total of one or more thereof: 300 ppm as an upper limit.

Note that La, Ce and Hf can be added as misch metal.

Further, one or more of Cr, V, Nb, Mo and B are contained, all of which work to improve the strength.

Cr is an element effective for reducing the cementite interval in pearlite, increasing the strength, and improving the rate of wire drawing work hardening. In addition, the thickness of the ferrite layer also decreases due to the narrow spacing of cementite,
This has the effect of reducing the non-uniformity of the deformability of the ferrite layer due to the non-uniform distribution of Si. Further, hardenability is improved, and there is an effect of reducing precipitation of pro-eutectoid ferrite and pro-eutectoid cementite. If the content is less than 0.05%, the desired hardenability cannot be obtained. On the other hand, if the content of Cr exceeds 1.60%, the hardenability becomes too high, and a supercooled structure harmful to the drawability is formed. appear. For this reason, it limited to the range of 0.05% to 1.60%.

Mo is an important element for improving the hardenability of steel to increase the tensile strength of the wire rod and increasing the amount of carbide and the hardness of carbide. Mo: 0.05% or more is required. However, when Mo: more than 0.5%, work cracking occurs, so Mo: 0.05-0.5%.

V and Nb increase the strength and precipitate as NbCN or VN during hot rolling and subsequent cooling to reduce solid solution N in steel, thereby reducing strain hardening during wire drawing. . For this reason, wire drawing workability can be improved. However, V: less than 0.01%, N
b: If less than 0.001%, the effect cannot be obtained.
When V: more than 0.2% and Nb: more than 0.2%, the effect is saturated and the steel is hardened, thereby deteriorating the drawability. Therefore, V: 0.01 to 0.2%, Nb:
It was limited to 0.001 to 0.2%.

B is added with an expectation of an effect of fixing N and S and promoting pearlite transformation using BN or the like as a transformation nucleus. However, when B <0.002%, the effect is not recognized. The lower limit was 0.002%. On the other hand, B> 0.0
At 4%, the effect is saturated and the harmful effect of lowering the ductility is remarkable, so B: 0.04% was made the upper limit.

The unavoidable impurities are permissible as long as they are within the range that is usually present in this type of steel. For example, each of P and S is preferably set to 0.03% or less.

Next, the reason for limiting the average austenite grain size and structure will be described.

The austenite grains (γ grains) can be refined by increasing the rolling reduction during hot rolling of the steel slab having the steel component of the present invention to make the wire diameter 4.5 mm or less. By making the austenite grains finer, the pearlite transformation is promoted, and the grain-size precipitation of proeutectoid ferrite or proeutectoid cementite can be prevented.

The high carbon steel wire has the best drawability when the microstructure is completely pearlite.
When proeutectoid ferrite is contained in the pearlite structure, strain concentrates on proeutectoid ferrite which is easily deformed during wire drawing, and voids are generated at the interface between pearlite and proeutectoid ferrite. If wire drawing is further continued, voids grow to form cracks, and these cracks are connected to each other to cause disconnection, so that wire drawing is inferior to perfect pearlite structure.

When proeutectoid cementite is contained in the pearlite structure, the pearlite structure has a better deformability than the proeutectoid cementite, so that the pearlite structure is deformed preferentially, and the proeutectoid cementite is hardly deformed. do not do. For this reason, voids and cracks occur at the interface between proeutectoid cementite and pearlite. When wire drawing is further performed, these voids and cracks grow and connect to break. Voids and cracks generated during wire drawing not only cause disconnection, but also deteriorate the ductility of the steel wire after wire drawing.

The adverse effect of other structures contained in the pearlite structure is due to a difference in deformability from the pearlite structure during wire drawing, and reducing the content of these structures reduces the number of voids and cracks. The number of voids and cracks can be reduced by further reducing the size.

In order to obtain a drawability close to a perfect pearlite structure with a pearlite structure containing pro-eutectoid ferrite or pro-eutectoid cementite, the content of pro-eutectoid ferrite or pro-eutectoid cementite is determined by measuring the average area ratio in the structure observation by 5 % Or less. When proeutectoid ferrite or proeutectoid cementite having an area ratio exceeding 5% is contained, even if these structures are refined, voids and cracks occur more frequently, which causes ductility deterioration and disconnection.

As shown in FIGS. 1 and 2, proeutectoid ferrite or proeutectoid cementite can be drawn to a shape with an average aspect ratio of 3 or more to a true strain of 2.2 or more, and a maximum length of 10 μm or less. By making the particles finer, it is possible to obtain drawability close to a perfect pearlite structure. If the maximum length exceeds 10 μm, the interface will be cracked due to the growth of voids generated, which may cause deterioration of ductility and disconnection of the steel wire. If the aspect ratio is less than 3, even if the maximum length is less than 10 μm, voids are likely to be generated, which causes deterioration of ductility and breakage of the steel wire. For this reason,
In order to secure the ductility of the steel wire and prevent the wire from breaking, it is necessary that the aspect ratio is 3 or more and the maximum length is 10 μm or less.

Further, during the drawing process, the fiber structure of the pearlite colony is developed while rotating the crystal. However, it is necessary to refine the colony and to ensure the high rotation of the colony. It is effective to secure the processing limit. Colony
In order to ensure high rotational properties, it is necessary to control the pearlite colony size to 30 μm or less in addition to controlling proeutectoid sentite and proeutectoid ferrite within the range of the present invention.

For the above reasons, in order to obtain drawability close to a perfect pearlite structure in a pearlite structure containing proeutectoid ferrite or proeutectoid cementite, the area ratio of proeutectoid ferrite or proeutectoid cementite is 5% or less and the maximum length is 1
0 μm or less, aspect ratio of 3 or more, perlite colony
The size was limited to 30 μm or less.

The proeutectoid ferrite (proeutec)
“Toid ferrite” refers to ferrite (α) precipitated from austenite by Ar ₃ transformation. Proeutectoid ferrite precipitates along the austenite grain boundaries. In addition, proeutectoid cementite (proeut)
"Ectoid cementite" refers to cementite precipitated from the Acm line. This cementite (F
e ₃ C) precipitates along the austenite grain boundaries,
Its shape is reticulated.

Proeutectoid ferrite can be observed with a microscope by corrosion with nital and proeutectoid cementite with sodium picrate solution.

In the middle of the wire (a half of the radius), x3 of the site where pro-eutectoid ferrite and cementite are deposited
SEM photographs of 000 to 5000 are taken, the maximum length and maximum width of proeutectoid ferrite and cementite are measured, and the ratio (maximum length / maximum width) is calculated. It is within the scope of the present invention that the measurement is performed at 10 points and the average is 3 or more.

In order to make the structure of the hot-rolled wire rod into the above-mentioned structure, it is necessary to refine austenite crystal grains. By refining the austenite grains, the area of the austenite grain boundary which becomes the precipitation site of pro-eutectoid ferrite or pro-eutectoid cementite increases, and the precipitation of pro-eutectoid ferrite or pro-eutectoid cementite is not coarsened because the precipitation is dispersed. Further, it becomes possible to make the pearlite colony fine. If the austenite grain size is less than 8.5, the grain boundary area becomes insufficient and the above-mentioned structure cannot be obtained. Therefore, the austenite grain size was limited to 8.5 or more.
The austenite crystal grain size was obtained by directly quenching the wire rod immediately after winding at the time of wire rod rolling on a stelmova, and measuring the austenite crystal grain diameter in accordance with the average particle size measuring method of JIS G 0551. is there.

In hot rolling, it is impossible to increase the austenite grain size of a normal 5.5 mm diameter wire to 8.5 or more by increasing the strain rate by increasing the rolling rate, and special rolling such as low-temperature rolling is not possible. is necessary. In order to increase the austenite grain size to 8.5 or more by increasing the rolling speed, the diameter of the wire needs to be 4.5 mm or less.

By setting the wire diameter to 4.5 mm or less, it is possible to increase the initial cooling rate during cooling after hot rolling, and to reduce the amount of proeutectoid ferrite or proeutectoid cementite. Therefore, the wire drawing workability is improved. Further, since the difference in cooling rate between the surface layer portion and the central portion becomes small, the structure can be made uniform. Therefore, even with a perfect pearlite structure, drawability is improved as compared with a wire having a large diameter. For this reason, the diameter of the wire is 4.5 mm.
Limited to the following.

FIG. 3 is a graph showing the relationship between austenite grain size and pearlite colony size (μm).

As shown in FIG. 3, the smaller the austenite grain size, the smaller the pearlite colony size. In the present invention, when the austenite grain size is 8.5 or more, the pearlite colony size becomes 30 μm or less on average, and the true strain of 2.2 or more can be drawn (drawing as hot rolled).

Further, proeutectoid ferrite and proeutectoid cementite are precipitated by the pearlite transformation, and the area ratio is 5% or less, the maximum length is 10 μm or less, and the aspect ratio (maximum length / maximum width) is 3 or less. In this case, raw drawing can be performed as it is during hot rolling.

The true strain of the wire drawing is determined by a wire diameter d (m) at which an abnormal break occurs in a wire having a diameter D (mm) in a twist test.
m), the true strain ε can be expressed by the following equation.

Ε = 2 × ln (D / d) The higher the true strain, the better the drawability.

The area ratio, length, and width of proeutectoid ferrite and proeutectoid cementite can be measured from photographs taken and observed with a scanning electron microscope.

Further, the reason why the wire diameter after hot rolling is limited to 4.5 mm or less will be described.

By performing hot rolling to a wire diameter of 4.5 mm or less, it is possible to reduce non-uniform cooling in the cross section of the wire and to obtain a uniform structure up to the center. Furthermore, when the same billet is used for the material of the wire material, even if the wire material is rolled with the same component and the same cooling pattern, the reduction of the austenite grains is promoted by the increase in the reduction amount, and the proeutectoid cementite is refined. The wire drawing workability is further improved. For this reason, the wire diameter of the wire was limited to 4.5 mm or less.

[0057]

EXAMPLES Specific examples of the present invention will be described in comparison with comparative examples.

Tables 1 to 3 show the chemical compositions of the test materials and the drawability of the wires finished to a wire diameter of 3.0, 4.0, 4.5, 5.0, 5.5 mm by hot rolling. Show. Using these wires, proeutectoid ferrite, proeutectoid cementite, pearlite,
The structures of bainite and martensite were observed to evaluate the drawability. The wire drawing was performed without subjecting the hot-rolled wire to heat treatment. The limit drawing true strain ε is the drawing true strain [ε = 2 × ln (D / d) up to the wire diameter (d mm) at which abnormal breakage occurs in the torsion test, D = diameter of wire (mm). ]
And The drawability was determined to be good if the wire was significantly improved compared to the 5.5 mm wire having the same chemical composition. The area ratio, the maximum length, and the aspect ratio of proeutectoid ferrite and proeutectoid cementite were measured from photographs observed and taken with a scanning electron microscope. These test results are also shown in Tables 1 to 3.

[0059]

[Table 1]

[0060]

[Table 2]

[0061]

[Table 3]

As shown in Table 1, in each of the examples of the present invention, the austenite crystal grain size was 8.5 or more, and bainite and martensite harmful to wire drawing were not generated.
The area ratio, maximum length, aspect ratio, and pearlite colony size of proeutectoid ferrite or proeutectoid cementite are 5% or less, 10 μm or less, 3 or more, and 30 μm or less, respectively. Is good. In particular, the addition of Ca + Mg + REM promotes further refinement of the γ-grain, improves the drawing limit, and also softens hard non-metallic inclusions, thereby reducing the non-metal in the steel code manufacturing process. The number of disconnections caused by inclusions can be greatly reduced.

On the other hand, the comparative example N shown in Table 2
o. In No. 20, proeutectoid cementite was coarsely precipitated because the C content was excessive, and the wire drawing workability was deteriorated.

No. No. 21 was insufficient in deoxidation due to too little Si. In addition, it is not practical as compared with No. 2 and the strength at the time of producing steel code is low due to the low content of Si. No. Sample No. 22 has poor drawability due to the high content of Si and the generation of SiO ₂ -based inclusions harmful to wiredrawing. No. 23 has a low Mn content,
Since the S detoxifying effect of MnS cannot be sufficiently exerted and the flaws occurred during wire rod rolling, The wire drawing workability is poor as compared with 2. No. In No. 24, martensite and bainite were generated due to the high Mn content. In comparison with No. 2, the wire drawing workability was deteriorated.

No. 24 to 27 are Cr, V, Nb, M
Since the contents of o and B are high, martensite and bainite are generated, and the drawability is deteriorated. No. Sample No. 28 has a small amount of Al added and does not deteriorate the intermediate wire drawing workability, but steel alloys are not used because the number of Al ₂ O ₃ -based intermediate materials increases.
However, there is a problem that the disconnection rate in the finishing wire drawing process when manufacturing the wire becomes high.

As shown in Table 3, no. 29 and 30 fall under the chemical composition range of the present invention, but because the wire diameter is large,
The rolling reduction during rolling is insufficient, austenite crystal grains are not refined, so that coarse precipitation of proeutectoid cementite cannot be prevented, and the pearlite colony size becomes coarse, and a wire diameter within the range of the present invention. The wire drawing workability is worse than that of the wire rod.

[0067]

According to the present invention, the austenite grains are refined by reducing the diameter of the wire by hot rolling, the pearlite transformation is promoted, and the shape of the proeutectoid ferrite and the proeutectoid cementite is prevented. By controlling the temperature, it is possible to obtain a small-diameter high-carbon steel wire having extremely excellent drawability while hot rolling.

For this reason, wire drawing can be performed while hot rolling is performed, and wire drawing can be performed only by performing final patenting as necessary, and the number of intermediate patentings required for wire drawing can be reduced. Since it can be largely omitted, it is possible to achieve energy saving and a significant reduction in manufacturing cost.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the aspect ratio of proeutectoid ferrite and the true strain in critical wire drawing.

FIG. 2 is a graph showing the relationship between the aspect ratio of proeutectoid cementite and the true strain of critical wire drawing.

FIG. 3 is a graph showing the relationship between austenite grain size and pearlite colony size (μm).

Claims (3)

[Claims] 1. A mass% of C: 0.60 to 1.50%,
Si: 0.05 to 0.50%, Mn: 0.05 to 1.2
0%, the balance consists of iron and unavoidable impurities, the austenite grain size after hot rolling is 8.5 or more, and the initial structure is all pearlite structure or 5% or less in area ratio and 10 μm or less in maximum length. A pearlite structure containing ferrite or proeutectoid cementite, wherein the aspect ratio (maximum length / minimum width) of the proeutectoid ferrite or proeutectoid cementite is 3 or more on average, and the pearlite colony size is 30 μm or less on average. Is 4.5mm
A small-diameter high-carbon hot-rolled wire excellent in wire-drawing workability that can be drawn while hot-rolled with a true strain of 2.2 or more. 2. The composition according to claim 1, further comprising, by mass%, less than 0.005% of Al and one or more of Ca, Mg, La, Ce and Hf in a total amount of 10 to 300 ppm. The small-diameter high-carbon hot-rolled wire according to claim 1. 3. The composition according to claim 1, wherein the content of Cr is 0.05 to 0.1% by mass.
5%, V: 0.01-0.2%, Nb: 0.001-
0.2%, Mo: 0.05-0.5%, B: 0.002
3. The small-diameter high-carbon hot-rolled wire according to claim 1 or 2, which contains one or more of 0.04% or less.