WO2001046485A1

WO2001046485A1 - Direct patenting high strength wire rod and method for producing the same

Info

Publication number: WO2001046485A1
Application number: PCT/JP2000/009167
Authority: WO
Inventors: Seiki Nishida; Atsuhiko Yoshie; Naoshi Hikita; Susumu Sahara; Hitoshi Saito; Koji Yoshimura
Original assignee: Nippon Steel Corporation
Priority date: 1999-12-22
Filing date: 2000-12-22
Publication date: 2001-06-28
Also published as: MY128660A; KR100430068B1; KR20010102307A; CN1117171C; CN1341155A

Abstract

A direct patenting wire rod with a diameter of 4. 0 mm to 16 mm comprising a high carbon steel having a carbon content of 0. 7 % or more, wherein the layer in the range of at least 300 µm from the surface of the wire rod has an average carbon content of 0. 97 or less times that of the whole cross section of the wire rod, has a Vickers hardness of Hv 390 or less, and has an average separation between lamellas of 95 nm or more; and a method for producing the wire rod. The wire rod is a direct patenting high strength wire rod having a surface layer which is less prone to the occurrence of fretting martensite and thus is less susceptible to the occurrence of the cut due to a flaw formed by the handling during transportation or the like.

Description

Description High-strength direct patenting wire and its manufacturing method

The present invention is applicable to high-strength PC steel wire, PWS steel wire, Piano wire, steel cord, hose wire, bead wire, contact opening cable, fishing line, cut wire, saw wire, etc. The present invention relates to a wire capable of producing a high-strength steel wire to be used and a method for producing the same. Background art

In general, wires made of high carbon steel containing 0.6% or more carbon and used for steel cord, etc. are processed to a diameter of 5 to 16 mm by hot rolling, and then the structure is adjusted by adjusting cooling. It is used as wire. Generally, a wire is wound up and transported in a coil shape.

For example, Japanese Patent Application Laid-Open No. Sho 60-204865 discloses that the content of Mn is regulated to less than 0.3% to suppress the generation of a supercooled structure after lead patenting. By regulating the amounts of elements such as manganese, Mn, etc., ultra-fine wires with high strength and high toughness and ductility and high carbon steel wires for steel cords are disclosed. Japanese Patent Publication No. 63-24046 discloses that by increasing the Si content to 1.0% or more, the tensile strength of the lead-patented material is increased and the wire drawing rate is reduced. The disclosed high toughness and high ductility ultrafine wire II wire is disclosed.

Wires used for such high strength are broken due to scratches on the surface during the wire drawing process. For this reason, conventional wire rods have been devised so as not to damage as much as possible during transportation or handling of the coil. However, there is a limit to such efforts, and cuts due to flaws There is a need for wires that do not cause wire. Disclosure of the invention

The present invention has been made in order to solve the above-mentioned problems, and provides a wire rod that has reduced susceptibility to flaws generated in the process of transporting or secondary working of a hot-rolled wire rod and is resistant to flaws.

The gist of the present invention is as follows.

(1) High carbon steel containing 0.7% by mass or more of carbon in mass%, and the Vickers hardness of the layer from the surface layer to at least 300m shall be HV: 390 or less. Thus, the high-strength direct patenting wire is characterized in that the layer is a layer in which a scratched martensite structure is hardly generated.

(2) High carbon steel with a carbon content of 0.7% or more by mass%, and the average carbon content of the layer from the surface layer to at least 300m is the average carbon content in the entire cross section A high-strength direct patenting wire rod characterized in that the above-mentioned layer is a layer in which the abrasion martensite structure is hardly generated by setting the thickness to 0.997 times or less.

(3) High carbon steel containing 0.7% by mass or more of carbon by mass, and the Vickers hardness of the layer from the surface layer to at least 300 is set to HV: 390 or less, and By setting the average carbon content of the layer to 0.97 times or less of the average carbon content in the entire cross section, the layer is a layer in which a scratched martensite structure is hardly generated. A high-strength direct-patterning wire characterized by:

(4) The high-strength direct patenting wire according to any one of (1) to (3), wherein the average lamellar spacing in the layer is 95 nm or more.

(5) The steel component of the high carbon steel is expressed as C: 0.7-1.2%,

S i: 0.1 to 5%,

M n: 0.1 to 0%,

The high-strength direct patenting wire according to any one of the above (1) to (3), comprising a balance of Fe and unavoidable impurities.

(6) The steel component of the high carbon steel is expressed as

C: 0 7 1 2%,

S i 01-1.5%,

M n 0 1 to 1.0%

Cr 01 to 0.5%

V: 0.001 to 0.2%

Ν i 0 05 〜 1.0%

% Ο o 1 丄 o. 5%

C u 0 0 5 0 .8%

W: 00.50.8%

L a 0 0 0 0 5 to 0 .01%

C e 0 0 0 0 5 to 0 .01%

A 1 0 0 0 1 to 0 .06%

B: 0 0 0 0 5 to 0 .06%

T i 0 0 0 1 to 0 .06%

N b 0 0 0 1 to 0 .06%

The high-strength direct patenting wire according to any one of the above (1) to (3), comprising one or more of the following.

(7) A high-carbon steel having a carbon content of 0.7% or more by mass% is heated at 100 to 1200 ° C in a wire heating furnace, and then has a diameter of 4 to 16 mm. Hot rolling is performed, and the hot rolling is completed at a temperature of 850 ° C or more, cooled to 750 to 830 ° C within 15 seconds, and immediately thereafter, 400 ° C A method for producing a high-strength direct patenting wire, characterized by immersing it in a molten salt bath at up to 570 ° C to terminate perlite transformation.

(8) After heating a high-carbon steel containing 0.7% or more by mass in a wire rod heating furnace at 100 to 1200 ° C, the diameter of the steel is 4 to 16 mm. Hot rolling is performed at a temperature of 750 to 83 (TC temperature, and then immediately immersed in a molten salt bath of 400 to 570 t to complete the pearlite transformation. A method for producing a high-strength direct patenting wire rod, characterized in that:

(9) Perform the hot rolling described above, then wind up at a temperature of 750-830 ° C within 15 seconds, and immediately immerse it in a molten salt bath at 400-570 ° C. (8) The method for producing a high-strength direct patenting wire according to the above (8).

(10) The above (8), which is characterized in that, instead of being immersed in a molten salt bath at a temperature of 400 to 570 ° C., blast cooling is performed to terminate the pearlite transformation. The method for producing the high-strength direct patenting wire described.

(11) The carbon content in mass% is 0.7% or more, and the average carbon content of the layer from its surface to at least 300m is the average carbon content of all cross sections. 0.97 times or less of high carbon steel in a wire heating furnace

After heating at 100 to 1200 ° C, hot rolling to a diameter of 4 to 16 mm is performed, and the hot rolling is completed at a temperature of 75 0 ° C or more, and immediately thereafter.

A method for producing a high-strength direct patenting wire, characterized by immersing it in a molten salt bath at 400 to 570 ° C to terminate perlite transformation.

(1) The above-mentioned hot rolling is performed, and thereafter, it is wound at a temperature of 750 to 900 t, and is immediately immersed in a molten salt bath at 400 to 570 ° C. High strength direct patenting as described in (11) above Manufacturing method of wire rod.

(13) Instead of immersion in a molten salt bath at 400 to 570 ° C, the above-mentioned (1 The method for producing a high-strength direct patenting wire according to 1) or 1). BEST MODE FOR CARRYING OUT THE INVENTION

First, the reasons for limiting the steel composition will be described. All components are% by mass, which is synonymous with% by weight.

C is an element effective for strengthening, and it is necessary to set the amount of C to 0.7% or more in order to obtain a high-strength steel wire.However, if it is too high, proeutectoid cementite precipitates. Since the ductility tends to decrease, the ductility decreases and the drawability deteriorates. Therefore, the upper limit is set to 1.2%.

Si is an element necessary for the deoxidation of steel. Therefore, when the content is too small, the deoxidizing effect becomes insufficient, so 0.1% or more is added. Further, Si forms a solid solution with the graphite phase in the pearlite formed after the heat treatment and increases the strength after the patenting, but on the other hand, it impairs the heat treatment property, so the content is 1.5% or less.

For Mn, it is necessary to add 0.1% or more of Mn to secure the hardenability of steel. However, the addition of a large amount of Mn also delays the recovery of ductility during hot-dip galvanizing, so it is set to 1.0% or less.

Cr is added to improve the strength after patenting and the strength after wire drawing. Therefore, the amount of Cr added is set to 0.1% or more, at which the effect can be expected, and to 0.5% or less, at which the heat treatment property is not deteriorated due to the transformation delay at the time of patenting.

V is also added to improve the strength after patenting and the strength after wire drawing. If it is added, the effect appears. %. If added too much, the transformation is significantly delayed and the productivity is affected, so the content is set to 0.1% or less.

Ni is also added to improve the strength after patenting and the strength after wire drawing. When added, the content is set to 0.05% or more at which the effect is exhibited, and when added too much, the transformation is significantly delayed and productivity is affected, so the content is set to 1.0% or less.

M 0 is also added to improve the strength after patenting and the strength after wire drawing. When added, the content is set to 0.1% or more, at which the effect is exhibited, and when added excessively, the pearlite transformation is remarkably delayed, and productivity is lowered.

Cu is added to improve corrosion fatigue properties. When added, the content is set to 0.05% or more at which the effect is exhibited, and when added excessively, the content is set to 0.8% or less, which significantly delays the transformation of the pellets and has no effect of lowering the productivity.

W is added to improve corrosion fatigue properties. When added, the content is set to 0.05% or more, at which the effect is exhibited, and when added excessively, the content is set to 0.8% or less, which significantly delays the pearlite transformation and has no effect of lowering productivity. These elements are more effective when added in combination.

In addition, by adding a small amount of La and Ce (0.00.05% to 0.01%), corrosion fatigue characteristics can be improved.

A 1 is added to reduce the size of the perlite block. When it is added, it is added in an amount of 0.001% or more that exhibits the effect. Since added pressure amounts to zero. 0 6 percent reduces the wire drawability increased inclusions hard, such as eight 1 ₂ 03

B is added to reduce the particle block size. If it is added, add 0.005% or more to show the effect. If too much element is added, the isothermal transformation is delayed and hard 0.06% or less, because it is easy to generate birds.

Ti is added to reduce the size of the perlite block. If it is added, it should be added in an amount of 0.001% or more that shows the effect. If the amount of the added element is too large, the isothermal transformation is delayed and hard micro-martensite is generated, so that the content is set to 0.06% or less.

Nb is added to make the pearlite block size fine. If it is added, it should be added in an amount of 0.001% or more that shows the effect. If the amount of the added element is too large, the isothermal transformation is delayed and hard micro-martensite is easily generated, so the content is set to 0.06% or less.

P easily forms an embrittlement structure due to segregation, and S is an element that easily forms inclusions, so that it is desirable to set each of them to not more than 0.02% at which adverse effects are reduced.

Next, the production method of the present invention will be described.

After being melted, the steel adjusted to the above-described steel composition is continuously formed into blooms or billets. The bloomed steel is hot rolled into billets by slab rolling. The billet is heated in a wire heating furnace from 100 ° C to 100 t to make the steel structure austenitic. The temperature for austenitization must be at least 900 ° C or higher in order to keep the temperature during austenite rolling below the austenitizing temperature. On the other hand, if the temperature is excessively increased, the finishing temperature of the rolling becomes high, and the grain growth of austenite is promoted. Thereafter, the heated billet is formed into a shape having a diameter of 4 to 16 by hot rolling, and hot rolling is completed at a temperature of 800 t or more.

When the finishing temperature at this time is set to 850 ° C or more, the wire is immediately cooled in order to reduce the austenite grain size near the surface layer of the wire, and the winding temperature is reduced to 75 ° C within 15 seconds. It must be adjusted between 0 ° C and 830 t. If the time is more than 15 seconds, grain growth tends to occur. Adjust within at least 15 seconds.

If the temperature after cooling is lower than 750 t, the transformation starts, and the non-uniformity becomes too large. Also, when the temperature exceeds 830 ° C, the austenite in the surface layer becomes large, and the lamellar spacing is 95 nm, which hardly generates martensite by scraping the structure within at least 300 ULm from the surface layer. It is difficult to establish the above organization.

Immediately thereafter, immediately immersed in a molten salt at 530 ° C: ~ 570 ° C to terminate the pearlite transformation, whereby the pearlite or Vickers hardness with a lamella spacing of 95 nm or more is obtained. Adjust the organization to HV 390 or less. When the temperature of the melting solution is lower than 530 ° C, it is difficult to make the lamellar spacing to 95 nm or more. In addition, if it is more than 570 t, the strength is too low, so it is desirable to make it less than 570 t. When the finish rolling temperature is set at 750 to 830 ° C, the pearlite transformation is completed by immersion in a molten salt bath at 400 to 570 ° C immediately after the finish rolling. A product with similar characteristics can also be obtained by adopting a process that allows the same. The same effect can be obtained even if the cooling after winding is performed by blast cooling or mist cooling.

Next, the cause of wire breakage when a wire is damaged will be described.

The depth of the flaw entering the wire is as large as about 100 m. In this case, the most influential on the break is the presence of hard martensite formed on the surface layer by the heat generated when the flaw is formed. In order to detoxify the occurrence of martensite, which causes wire breakage, a Pickers hardness of at least 300 m from the surface layer should be HV 390 or less, or at least 300 m from the surface layer. It is necessary to adjust the average lamella spacing of the layers above 95 nm. As a result, the martensite formed when a flaw is formed will not be generated or will be harmlessly thin. Further, in the present invention, the steel adjusted to the above-mentioned steel composition is continuously rusted into blooms or pellets after being melted. By adding pure iron to the vicinity of the mold in the mold at the time of this construction, the carbon concentration of at least 30 from the surface layer is set to 0.9 times or less of the average carbon concentration. In the case of over 0.97 times, after winding at a winding temperature of 850 ° C or more, which is a general manufacturing process, the molten salt is heated at a temperature of 400 ° C to 530 ° C. When immersed in a pearlite structure, the Pickers hardness in the range of at least 300 m from the surface layer is Hv 390 or less, or the average lamella spacing is 95 nm or more. I can't do that. Therefore, the carbon content of at least 300 m from the surface layer needs to be 0.97 times or less of the average concentration of the entire cross section.

Example 1

Table 1 shows the chemical composition of the steel of the present invention used in the trial production. Table 1 shows the chemical composition of the comparative steel. The steel of the present invention and the comparative steel were melted in a converter, and then formed into a bloom of 500 mm × 300 mm by continuous forming. Then, it was hot rolled into a 112 mm square billet. Thereafter, the wire was heated at 110 to 1200 ° C., and hot-rolled into a wire having a diameter of 5.5 to 13 mm.

Table 2 shows the manufacturing conditions including the temperature after the completion of hot rolling of the wire, and Table 2 shows the hardness of the surface layer and the lamellar spacing of the surface of the obtained wire.

In the present invention steels 1 to 15, the chemical composition and microstructure of the steel are adjusted according to the present invention.

Comparative steel 16 had the same steel composition as the steel of the present invention, with a finishing temperature of 900 t in hot rolling, and a temperature of 850 ° C higher than that of the present invention due to subsequent cooling. is there. Comparative steel 17 has the same steel composition as the steel of the present invention, and has a finishing temperature in hot rolling and a subsequent winding temperature within the range of the present invention, but it is required to cool down to the winding temperature. This is the case where the execution time is longer than that of the present invention.

Comparative steel 18 had the same steel composition as the steel of the present invention, and had a winding temperature of 800 ° C. higher than that of the present invention without cooling after finishing in hot rolling without cooling.

Comparative steel 19 has the same steel composition as the steel of the present invention, but has a lower heating temperature and a lower winding temperature than the present invention.

Comparative steel 20 has the same steel composition as the steel of the present invention, but has a higher heating temperature but more intense finish cooling and a lower winding temperature than the present invention.

These wires were artificially flawed, and the thickness of the martensite formed under the flaws was measured. In addition, the two-ton coils of these wires were transported 30 times repeatedly with the hook of the fork lift rubbing against the wires, and the number of breaks in the elongation process was examined. Table 2 shows the results.

Nos. 1 to 15 manufactured according to the present invention have good martensite thickness and show good results with a small number of disconnections.

On the other hand, the comparative steels 11 to 13 have a larger martensite thickness and the number of disconnections is higher than that of the steel of the present invention. Further, the comparative steels 14 to 15 have a small martensite thickness, but have a low drawing shown in Table 1, and the number of disconnections shown in Table 2 is higher than that of the steel of the present invention. Table 1 Chemical composition of the steel of the present invention (mass%)

c Si Mn P S Cr V Ni Mo w Al R Ti

1 0.72 0.20 0.51 0.016 0.008 0.21 0.01 0.10 0.10 0005

2 0.82 0.21 0.71 0.014 0.010 one 0.028 0005

3 0.82 0.20 0.48 0.012 0.006 One--One--0: 034--

4 0.83 0.21 0.62 0.013 0.008 0.10 0.80 0.10

Books 5 0.86 0.71 II

0.72 0.012 0.006 0.21

6 1.02 0.21 0.30 0.008 0.008 0.10 0.30 0.50 0.05

Departure 7 0.98 1.20 0.29 0.013 0.006 0.21 0.01 006

8 0.82 0.20 0.92 0.013 0.003 0.001 0.80 0.01

Light 9 0.92 0.21 0.29 0.40 ― ― ― ― ― ―

10 0.84 0.21 0.72 0.01 Steel 11 0.84 0.15 0.33 0.016 0.012 0.10 0.05 0.10

12 0.82 0.20 0.50 0.013 0.013 0.041

13 0.86 0.20 0.39 0.008 0.011 0.10 0.10 0.80

14 0.92 0.80 0.99 0.012 0.011 0.12

15 1.15 0.20 0.32 0.004 0.012

16 0.82 0.20 0.71 0.016 0.008 0.032

Ratio 17 0.82 0.21 0.76 0.014 0.010 0.028

Comparison 18 0.82 0.21 0.77 0.013 0.008 0.031

Steel 19 0.82 0.21 0.82 0.012 0.008 0.034

20 0.82 0.21 0.71 0.012 0.009 0.033

Table 2 Processing of hot-rolled wire

DLP: Molten salt salt knotting

DP: Blast cooling

Example .

Table 3 shows the chemical compositions of the steel of the present invention and the comparative steel used in the trial production. The steel of the present invention and the comparative steel were melted in a converter, and then made into a bloom of 500 mra x 300 mm by continuous forming. Then, it was hot rolled to form a 112 mm square billet. Then, after heating at 110 to 1200 ° C, a wire rod having a diameter of 5.5 mm to 13 mm was formed by hot rolling.

Table 4 shows the manufacturing conditions including the carbon content ratio obtained by dividing the carbon concentration of 300 m from the surface layer of the wire by the average carbon content of the entire cross-sectional area of the wire, and the temperature after completion of hot rolling.

Table 4 shows the hardness of the surface layer and the lamellar spacing of the surface layer of the obtained wire.

In the present invention steels 1 to 15, the chemical composition and the microstructure of the steel are adjusted according to the present invention. On the other hand, comparative steels 16 and 17 have the same steel composition and rolling method as the steel of the present invention, but have a higher carbon content ratio than the steel of the present invention.

These wires were artificially flawed, and the thickness of the martensite formed under the flaws was measured. In addition, a 2t coil of these wires was transported 30 times with the forklift hook rubbing against the wires, and the number of breaks during the elongation process was examined. Table 4 shows the results.

The steels 1 to 15 of the present invention produced according to the present invention have a small martensite thickness and show good results with a small number of disconnections. On the other hand, the comparative steels 16 to 17 have a larger martensite thickness and the number of disconnections is higher than that of the present invention steel. ,one

Table 3 Conversion of the present invention} (mass ° / ₀ )

C Si Mn P S Cr V Ni Mo Cu W A1 B Ti Nb La Ce

1 0.72 0.21 0.51 0.012 0.009 0.21 0.01 0.20 0.10 0.10 ― ― 0.007 ― ― 0.001 ―

2 0.82 0.21 0.72 0.011 0.010 ― ― ― ― 1 ― 0.029 ― ― 0.006 ― 1

3 0.84 0.19 0.48 0.014 0.008 ― 1 ― 1 ― 0.032 ― ― 1 ― ―

4 0.83 0.29 0.63 0.012 0.009 ― 0.10 0.80 0.10 One-one--one---Book 5 0.87 0.72 0.72 0.014 0.008 0.20---one---0.006---one

6 1.00 0.18 0.32 0.010 0.008 0.10-0.30 0.50 0.13 0.05 One----0.001

7 0.97

Departure 1.17 0.29 0.013 0.006 0.21 0.01---One---0.06--

8 0.83 0.21 0.81 0.013 0.003-0.002--0.75--0.02----Clear 9 0.92 0.19 0.31 0.012 0.009 0.40----------

10 0.94 0.21 0.72 0.011 0.006 0.02

Steel 11 0.83 0.16 0.32 0.016 0.012 0.10 0.08 0.15

12 0.82 0.18 0.48 0.013 0.013 0.039

13 0.86 0.19 0.32 0.008 0.011 0.10 0.12 0.77

14 0.92 0.79 0.86 0.012 0.011 0.16

15 1.15 0.18 0.31 0.005 0.012

16 0.81 0.20 0.71 0.016 0.008 0.032

17 0.81 0.21 0.76 0.014 0.010 0.028

Table 4 f E / "L ^ force DXI

DLP: Molten salt salt patenting

DP: blast cooling patenting

Industrial applicability

By using the present invention, it is possible to easily obtain a high-strength wire with less disconnection due to flaws.

Claims

The scope of the claims

1. High carbon steel containing 0.7% by mass or more of carbon by mass. The Vickers hardness of the layer from its surface up to at least 300m is H.

V: a high strength direct patenting wire rod characterized in that the layer is not more than 390, whereby the layer is a layer in which abrasion martensite tissue is hardly generated.

2. High carbon steel with a carbon content of 0.7% or more by mass%. The average carbon content of the layer from the surface layer to at least 300m is the average carbon content of the entire cross section. A high-strength direct-patterning wire characterized in that by setting the ratio to 0.97 or less, the layer is a layer in which the abrasion martensite structure is hardly generated.

3. High carbon steel with a carbon content of 0.7% or more by mass%, and the Vickers hardness of the layer from its surface up to at least 300;

V: 390 or less and the average carbon content of the layer is 0.97 times or less the average carbon content of the entire cross section, so that the layer has a scratched martensite structure. A high-strength direct-patterning wire characterized by having a layer that is difficult to generate.

4. The high-strength direct patenting wire according to any one of claims 1 to 3, wherein the average lamellar spacing in the layer is 95 nm or more.

5. The steel component of the high carbon steel is expressed in mass%

C: 0.7 to 2%,

S i: 0.1 to 1.5%,

Mn: 0.1 to 1.0%,

The high-strength direct patenting wire according to any one of claims 1 to 3, comprising a balance of Fe and unavoidable impurities.

6. The steel composition of the high carbon steel is

C 0.72%,

C • 1 Ί

1 Π U, 1 丄. 0 70>

Mn: 0.1%, including 0.1%

C Γ: 0.10.5%

V 0 .0 0 1 0 .2%

Ni 0.05-1.0%

0.5%

Cu 0.05-0.8%

W: 0.05 to 0.8%

A 0 .0 0 0 5 to 0 .01%

C e 0 .0 0 0 5 to 0 .01%

A10.001-0.06%

B: 0.005 to 0.006%

T i: 0.001 to 0.06%

Nb: 0.001 to 0.06%

The high-strength direct patenting wire according to any one of claims 1 to 3, comprising one or more of the following.

7. High carbon steel with a carbon content of 0.7% or more by mass% is heated in a wire heating furnace at 100 to 1200 ° C to a diameter of 4 to 16 mm. Hot rolling is performed, and the hot rolling is completed at a temperature of 850 ° C or higher, cooled to 750 to 830t within 15 seconds, and immediately thereafter, 400 to 570 ° A method for producing a high-strength direct patenting wire, characterized by immersing it in a molten salt bath of C to complete the pearlite transformation.

8. High-carbon steel with a carbon content of 0.7% or more in mass% is heated at 100 to 1200 ° C. in a wire heating furnace, and then has a diameter of 4 to 16 mm. Hot rolling is performed, and the hot rolling is completed at a temperature of 750 to 830 t. And immediately thereafter, immersing it in a molten salt bath at 400 to 570 ° C. to complete the pearlite transformation, thereby producing a high-strength direct patenting wire.

9. Perform the hot rolling, and then finish within 50 seconds 50-830. The method for producing a high-strength direct patenting wire according to claim 8, wherein the wire is wound at a temperature of (:) and immediately immersed in a molten salt bath at 400 to 570 ° C.

10. The high-strength direct material according to claim 8, wherein, instead of being immersed in the molten salt bath of 400 to 570, blast cooling is performed to terminate the pearlite transformation. Manufacturing method of patented wire rod.

11. The carbon content is 0.7% by mass or more, and the average carbon content of the layer up to at least 300 m from the surface layer is 0.3% of the average carbon content of the entire cross section. 9-7 times or less high-carbon steel is heated in a wire heating furnace at 100 to 1200 ° C, and then hot-rolled to a diameter of 4 to 16 mm. A high-strength direct patenting wire characterized by ending at a temperature of 50 ° C or higher and immediately immersing it in a molten salt bath at 400 to 570 ° C to terminate the pearlite transformation. Production method

12. The above hot rolling is carried out, then wound up at a temperature of 750 to 900 ° C, and then immediately immersed in a molten salt bath at 400 to 570 ° C. 12. The method for producing a high-strength direct patenting wire according to claim 11, wherein:

13. The perlite transformation is completed by blast cooling instead of being immersed in a molten salt bath at 400 to 570 ° C. 2. The method for producing a high-strength direct patenting wire according to 2.