Wire rods, steel wires, cords for precision steel cords, and methods for manufacturing the same

Abstract

The present invention belongs to the technical field of a method for manufacturing wire rods, and specifically relates to a wire rod for a precision steel cord, a steel wire, a cord, and a method for manufacturing the same. The chemical components of the wire rod are in mass %, C: 0.79 to 0.84%, Si: 0.15 to 0.30%, Mn: 0.45 to 0.55%, P ≤ 0.015%, S: 0.0030 to 0.010%, total oxygen: 0.0008 to 0.0022%, Als: 0.0002 to 0.0012%, Mg: 0.0002 to 0.0012%, Nb: 0.0003 to 0.0009%, Mo: 0.0003 to 0.0012%, and the balance is Fe and inevitable impurities. The present invention makes the cross-sectional hardness distribution of the wire rod and the steel wire uniform by designing the chemical components and the manufacturing process, and meets the requirements for the twisting performance in the process of processing the wire rod into a precision steel cord by the user.

Description

Technical Field

[0001] The present invention relates to the technical field of a method for manufacturing a wire rod, and specifically relates to a wire rod for a precision steel cord, a steel wire, a cord, and a method for manufacturing the same.

Background Art

[0002] Coded steel wire rods are used in the production and manufacturing of tire steel cords. During the use process of the wire rod by users, processing such as tension and twisting of the wire rod is required, so the requirements for the processing performance of the wire rod by users are strict. The tissue hardness distribution of the wire rod is an important index that affects the processing performance of the wire rod. The tissue hardness of the wire rod is a comprehensive reflection of the chemical composition and tissue state, and the change in the tissue hardness across the cross-section of the wire rod directly reflects the uniform deformation ability across the cross-section of the wire rod. Since the hardness distribution across the cross-section of the wire rod is uniform, it is beneficial to improve the uniformity of the tissue hardness across the cross-section of the steel wire, and further, to improve the twisting performance of the steel wire and provide conditions for manufacturing precision steel cords with complex configurations.

[0003] In the invention of Patent Document 1 (Chinese Patent Application No. 201910638740.0), an ultra-fine ultra-high strength steel wire, a wire rod for the ultra-fine ultra-high strength steel wire, and a method for manufacturing the same are disclosed. The wire rod for the ultra-fine ultra-high strength steel wire has a chemical composition in mass%, C: 0.90% - 0.96%, Si: 0.12% - 0.30%, Mn: 0.30% - 0.65%, Cr: 0.10% - 0.30%, Al: ≤0.004%, Ti: ≤0.001%, Cu: ≤0.01%, Ni: ≤0.01%, S: ≤0.01%, P: ≤0.01%, O: ≤0.0006%, N: ≤0.0006%, and the balance consists of Fe and inevitable impurity elements. Among them, the inclusion size is ≤4 μm, and the average density of brittle inclusions is ≤2 pieces / mm 2It is so. The wire rod for the ultra-fine high-strength steel wire is used as a base material for manufacturing an ultra-fine high-strength steel wire with a diameter of 50 μm to 60 μm and a tensile strength of ≧ 4500 MPa. During the tensile manufacturing process of the ultra-fine high-strength steel wire, a length of ≧ 300 km of the non-damaged steel wire can be achieved. Its manufacturing method includes vacuum induction melting, remelting, forging, and rolling. The above wire rod is suitable for the manufacture of ultra-fine steel wires, but does not mention the twisting performance of the steel wires, the hardness distribution of the cross-section of the wire rod and the steel wire.

[0004] In order to meet the user's requirements for the processing performance of the wire rod for precision steel cords, especially the requirements for the twisting performance of the steel wires manufactured from the wire rod, it is necessary to develop a high-quality wire rod for precision steel cords with a uniform hardness distribution across the cross-section of the wire rod and a uniform hardness distribution across the cross-section of the steel wires manufactured from the wire rod, which is helpful for improving the twisting performance of the steel wires.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The present invention is made in view of the above technical problems, and provides a wire rod for precision steel cords, steel wires, cords and their manufacturing methods. The present invention makes the hardness distribution across the cross-section of the wire rod and the steel wire uniform through the design of chemical components and manufacturing processes, and meets the user's requirements for the twisting performance during the processing from the wire rod to the precision steel cord.

Means for Solving the Problems

[0007] In order to achieve the above object, the present invention adopts the following technical means.

[0008] The wire rod for precision steel cord according to one embodiment of the present invention has chemical components by mass percentage: C: 0.79% to 0.84%, Si: 0.15% to 0.30%, Mn: 0.45% to 0.55%, P ≤ 0.015%, S: 0.0030% to 0.010%, total oxygen: 0.0008% to 0.0022%, Als: 0.0002% to 0.0012%, Mg: 0.0002% to 0.0012%, Nb: 0.0003% to 0.0009%, Mo: 0.0003% to 0.0012%, and the balance is Fe and inevitable impurities.

[0009] Furthermore, in the above technical means, the content of ferrite Si in the pearlite structure of the wire rod is 0.15% to 0.45%.

[0010] The reasons for the selection and design of the content of each chemical component of the present invention are as follows.

[0011] C: Carbon, as the main element for controlling the strength of the steel wire, if the carbon content is too low, the user's requirements for the strength of the steel wire cannot be met, and if the carbon content is too high, the strength of the steel wire will exceed the user's requirements. Also, a high carbon content increases the breakage rate and defective rate of the steel wire during the drawing process. Therefore, in the present invention, the carbon content is suppressed to 0.79% to 0.84%.

[0012] Si: Silicon element, as the main deoxidizing element of high-carbon steel, if the content of silicon element is too low, the deoxidation of molten steel will be insufficient, and if the content of silicon element is too high, coarse silicate inclusions will occur in the steel, reducing the tensile performance of the steel wire. The silicon element is dissolved in ferrite to increase the hardness of ferrite, reduce the hardness difference between ferrite and cementite, and improve the hardness uniformity of the steel wire structure. Therefore, in the present invention, the content of silicon element is suppressed to 0.15% to 0.30%.

[0013] Mn: As an element for increasing the strength of the wire rod, the manganese element can meet the user's requirements for the tensile strength of the steel wire. The manganese element lowers the eutectic transformation temperature of the steel, refines the pearlite structure of the steel wire, and plays a role in enhancing the deep processing ability of the steel wire. Therefore, in the present invention, the content of the manganese element is suppressed to 0.45% - 0.55%.

[0014] P: Phosphorus is likely to cause banded segregation in the wire rod and reduces the machining ability of the steel wire. Therefore, in the present invention, the content of the phosphorus element is suppressed to ≤0.015%.

[0015] S: If the sulfur element content in the steel is too high, it reduces the cold working performance of the steel wire. Since MnS inclusions have good deformation ability, an appropriate amount of sulfur element in the steel plays a role in reducing the risk of non-deformable inclusions in the steel and can prevent the occurrence of fine cracks caused by the inclusions. Therefore, in the present invention, the sulfur element content is suppressed to 0.0030% - 0.010%.

[0016] Total oxygen: If the oxygen content is too high, the size of the inclusions in the steel is large and the quantity is large, so fine cracks are likely to occur during the machining process of the steel wire, causing cracking of the steel wire. If the oxygen content is too low, the deformation ability of the inclusions in the steel wire is poor, and fine cracks are likely to occur between the inclusions and the steel wire matrix, which is disadvantageous for improving the machining performance of the steel wire. Therefore, in the present invention, the total oxygen content of the steel wire is suppressed to 0.0008% - 0.0022%.

[0017] Als: If the acid-soluble aluminum content is too high, the size of the Al2O3 inclusions in the steel becomes large, and it is easy to cause cracking of the steel wire during the processing. If the acid-soluble aluminum content of the wire rod is too low, the melting point of the inclusions in the steel is high, the deformation ability of the inclusions decreases, the local stress of the steel wire during the processing increases, and fine cracks are likely to occur in the steel wire, causing cracking and fracture of the steel wire. Therefore, in the present invention, the acid-soluble aluminum content is suppressed to 0.0002% - 0.0012%.

[0018] Mg: The magnesium element controls the oxygen content in the steel and also controls the type of inclusions in the steel. If the magnesium content is too high, inclusions of Mg-Al spinels will form in the steel, reducing the processing performance of the steel wire. An appropriate amount of magnesium content in the steel can improve the deformation performance of the inclusions, expand the region with high deformability of the inclusions, and contribute to the improvement of the deformation ability of the steel wire. Therefore, in the present invention, the magnesium content is suppressed to 0.0002% - 0.0012%.

[0019] Nb: The niobium element suppresses the growth of the steel billet crystal grains during the heating of the steel billet and improves the uniformity of the hardness distribution of the steel wire structure. However, if the niobium content in the steel is too high, work hardening during the deformation process of the wire rod becomes prominent, reducing the deep processing ability of the wire rod. Therefore, in the present invention, the Nb content is suppressed to 0.0003% - 0.0009%.

[0020] Mo: Molybdenum is a strong carbide-forming element. Due to the dispersed distribution of molybdenum carbides, the crystal grains of the steel wire are refined, and the uniformity of the hardness distribution across the cross-section of the steel wire is improved. However, if the molybdenum content in the steel is too high, the machining performance of the wire rod will be reduced. Therefore, in the present invention, the Mo content is suppressed to 0.0003% - 0.0012%.

[0021] The present invention further provides a method for manufacturing a wire rod for precision steel cord. The method includes the following steps.

[0022] (1) Continuous casting process: The molten steel that has been smelted is continuously cast. The cross-sectional size of the continuous casting billet is (250 - 300) mm * (350 - 400) mm, the crystal grain size on the surface of the continuous casting billet is 260 - 520 μm, the crystal grain size at the core of the continuous casting billet is 800 - 1100 μm, the carbon segregation index at the position of 1 / 2 thickness on the center line in the length direction of the cross-section of the continuous casting billet is suppressed to 0.95 - 1.07, the carbon segregation index at the position of 1 / 4 thickness on the center line in the length direction of the cross-section of the continuous casting billet is suppressed to 0.96 - 1.06, and the carbon segregation index at the surface position of the center line in the length direction of the cross-section of the continuous casting billet is suppressed to 0.94 - 1.0.

[0023] (2) Heating and rolling process: The continuously cast billet is charged into a heating furnace in a hot state and heated. The total heating time in the furnace is 3.8 - 4.5 h, the temperature in the soaking section is 1230 - 1280 °C, the soaking time in the soaking section is 40 - 60 min. After heating the continuously cast billet, it is continuously rolled into a square billet. The final rolling temperature is 940 - 1050 °C, and the cross-sectional size of the square billet is (140 - 180) mm * (140 - 180) mm.

[0024] (3) Wire rod rolling process: The total heating time of the square billet in the furnace is 150 - 170 min, the temperature in the soaking section is 1130 - 1170 °C, the soaking time in the soaking section is 30 - 50 min. Due to the high-temperature diffusion of the steel billet, the segregation of elements such as carbon and manganese is reduced, and the grain size of the steel billet is suppressed. After heating the square billet, it undergoes rough rolling, medium rolling, pre-finishing rolling, finishing rolling, and twin module block rolling, and then wire making is carried out to form a wire rod. The rolling specification of the wire rod is 5.0 - 6.0 mm.

[0025] (4) Wire rod cooling process: The wire rod after wire making is cooled on an air-cooling roller table. The precipitation start temperature of the cementite of the wire rod is suppressed to 740 - 770 °C, the sub-cooling degree of the pearlite phase transformation of the wire rod is suppressed to 100 - 150 °C. When the phase transformation time on the air-cooling line is 4 - 6 s, the pearlite content of the wire rod is ≥ 50%. When the phase transformation time is 14 - 16 s, the pearlite content is ≥ 95%. The finally cooled wire rod mainly has a sorbite structure, which contributes to the tensile strength of the steel wire by the user.

[0026] In the above invention, further, in step (1), the molten steel is molten iron scrap and steel scrap, among which the steel scrap accounts for 5% - 10% of the molten steel by mass%.

[0027] In the above invention, further, in step (1), after melting the molten steel in a converter, it is refined in an LF furnace. The refining time in the LF furnace is 30 to 50 minutes, the refining temperature is 1450 to 1550 °C, argon gas stirring is performed in the molten steel refining process, and the argon gas flow rate is 200 to 500 NL / min.

[0028] In the above invention, further, in step (3), the temperature of the rolled material when carried out from the pre-finishing rolling mill is 950 to 1000 °C, and the temperature compensation deformation rate coefficient of the last pass of the pre-finishing rolling of the rolled material is (1.1 to 2.6) * 10 13 s -1 and the temperature of the rolled material when entering the finishing rolling mill is 880 to 960 °C, and the temperature compensation deformation rate coefficient of the last pass of the finishing rolling of the rolled material is (1.6 to 3.2) * 10 14 s -1 and the temperature when entering the twin module block is 890 to 940 °C, and the temperature compensation deformation rate coefficient of the last pass of the twin module block of the rolled material is (4.5 to 9.9) * 10 14 s -1 is.

[0029] In the above invention, further, in step (3), the wire rod production wire temperature is 910 to 940 °C. By controlling the wire rod production wire temperature high, the cooling rate of the wire rod on the air-cooling roller table is increased, and a basis for controlling the final structure of the wire rod is built.

[0030] The present invention further provides a precision steel wire, and the steel wire is manufactured from the above wire rod.

[0031] The present invention further provides a method for manufacturing a precision steel wire, and the method includes the following steps. a. Mechanical descaling process: Perform a mechanical descaling treatment on the wire rod, and the residual rate of the iron oxide film on the wire rod surface is ≦ 0.07%. b. Wire rod drawing process: Draw the wire rod through a plurality of passes to make an intermediate wire with a diameter of 0.8 to 1.2 mm. c. Heat treatment process of intermediate wire: Heat the intermediate wire to 880 - 915 °C, then cool it to cause a phase change at 555 - 575 °C. d. Steel wire drawing process: Draw the heat-treated intermediate wire to produce a steel wire with a diameter of 0.15 - 0.20 mm.

[0032] The present invention further provides a precision cord, and the cord is manufactured using a steel wire.

Advantages of the Invention

[0033] According to the present invention, there are the following advantages. According to the present invention, through chemical composition and manufacturing process design, the hardness distribution of the cross-section of the wire rod and the steel wire is made uniform, meeting the user's requirements for the twisting performance in the process of processing the wire rod into a precision steel cord. The difference value of the hardness at different parts along the cross-section of the wire rod with a diameter of 5.5 mm is suppressed within 35 HV, and the difference value of the hardness at different parts along the cross-section of the steel wire with a diameter of 0.175 mm is suppressed within 10 HV. Thereby, the quality requirements of users for the production of steel wires and steel cords can be met.

Brief Description of the Drawings

[0034]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0035] To more clearly illustrate the objectives, technical solutions, and advantages of the embodiments of the present invention, the following will more clearly and completely describe the technical solutions in the embodiments of the present invention. It goes without saying that the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art without creative labor based on the embodiments in the present invention shall all be included in the protection scope of the present invention.

[0036] The chemical compositions of the wire rods according to Embodiments 1 - 6 of the present invention are shown in Table 1.

[0037] [Table 1]

[0038] The manufacturing method of the wire rod for the above-mentioned precision steel cord includes the following processes. (1) Smelting process: The molten steel is scrap steel and waste steel. Among them, the waste steel accounts for 5% - 10% of the molten steel by mass%. After smelting the molten steel in a converter, it is refined in an LF furnace. The refining time in the LF furnace is 30 - 50 min, the refining temperature is 1450 - 1550 °C, argon gas stirring is carried out in the refining process of the molten steel, and the argon gas flow rate is 200 - 500 NL / min.

[0039] [Table 2]

[0040] (2) Continuous casting process: The smelted molten steel is continuously cast. The size of the cross-section of the continuous casting billet is (250 - 300) mm * (350 - 400) mm. The grain size of the surface of the continuous casting billet is 260 - 520 μm, the grain size of the core of the continuous casting billet is 800 - 1100 μm. The carbon segregation index at the position of 1 / 2 thickness on the center line in the longitudinal direction of the cross-section of the continuous casting billet is suppressed to 0.95 - 1.07, the carbon segregation index at the position of 1 / 4 thickness on the center line in the longitudinal direction of the cross-section of the continuous casting billet is suppressed to 0.96 - 1.06, and the carbon segregation index on the surface of the center line in the longitudinal direction of the cross-section of the continuous casting billet is suppressed to 0.94 - 1.0.

[0041] [Table 3]

[0042] (3) Heating and Rolling Process: The continuously cast billet is charged into a heating furnace in a hot state for heating. The total heating time in the furnace is 3.8 - 4.5 h, the temperature in the soaking section is 1230 - 1280 °C, and the soaking time in the soaking section is 40 - 60 min. After heating the continuously cast billet, it is continuously rolled into a square billet. The finishing rolling temperature is 940 - 1050 °C, and the cross-sectional size of the square billet is (140 - 180) mm * (140 - 180) mm.

[0043]

Table 4

[0044] (4) Wire Rod Rolling Process: The total heating time of the square billet in the furnace is 150 - 170 min, the temperature in the soaking section is 1130 - 1170 °C, and the soaking time in the soaking section is 30 - 50 min. Due to the high-temperature diffusion of the steel billet, the segregation of elements such as carbon and manganese is reduced, and the grain size of the steel billet is suppressed. After heating the square billet, rough rolling, medium rolling, pre-finishing rolling, finishing rolling, and twin-module block rolling are carried out. The temperature of the rolled material when it is discharged from the pre-finishing rolling mill is 950 - 1000 °C, and the temperature compensation deformation rate coefficient of the last pass of the pre-finishing rolling of the rolled material is (1.1 - 2.6) * 10 13 s -1 . When the rolled material enters the finishing rolling mill, the temperature is 880 - 960 °C, and the temperature compensation deformation rate coefficient of the last pass of the finishing rolling of the rolled material is (1.6 - 3.2) * 10 14 s -1 . When the rolled material enters the twin-module block, the temperature is 890 - 940 °C, and the temperature compensation deformation rate coefficient of the last pass of the twin-module block of the rolled material is (4.5 - 9.9) * 10 14 s -1 . Then, wire drawing is carried out to form wire rods. The wire drawing temperature of the wire rods is 910 - 940 °C. Due to the high wire drawing temperature of the wire rods, the cooling rate of the wire rods on the air-cooling roller table is increased, laying a foundation for controlling the final structure of the wire rods. The rolling specification of the wire rods is 5.0 - 6.0 mm.

[0045]

Table 5

[0046]

Table 6

[0047] (5) Wire cooling process: After wire manufacturing, the wire is placed on an air-cooling roller table for cooling to suppress the austenite precipitation start temperature of the wire to 740 - 770 °C, suppress the phase change supercooling degree of the pearlite in the wire to 100 - 150 °C. When the phase change time on the air-cooling line is 4 - 6 s, the pearlite content of the wire is ≥ 50%, and when the phase change time is 14 - 16 s, the pearlite content is ≥ 95%. Finally, the cooled wire mainly has a sorbite structure, which is beneficial for the tension of the steel wire by the user.

[0048]

Table 7

[0049] The method for manufacturing a steel wire using the above wire includes the following steps. a. Mechanical descaling process: The wire is subjected to a mechanical descaling treatment, and the residual rate of the iron oxide film on the wire surface is ≤ 0.07%. b. Wire drawing process: The wire is drawn through multiple passes to produce an intermediate wire with a diameter of 0.8 - 1.2 mm. c. Heat treatment process of the intermediate wire: After heating the intermediate wire to 880 - 915 °C, it is cooled to cause a phase change at 555 - 575 °C. d. Steel wire drawing process: The heat-treated intermediate wire is drawn to produce a steel wire with a diameter of 0.15 - 0.20 mm.

[0050]

Table 8

[0051] Hardness tests are performed on the wires and steel wires of the above Examples 1 - 6. Hardness test method for wire rod: Divide the radius of the cross-section of the wire rod into five equal parts, measure the hardness values at six points from the surface to the core, and analyze the hardness difference value of the cross-section. Refer to the schematic diagram in Figure 1. Hardness test method for steel wire: Divide the radius of the cross-section of the steel wire into two equal parts, measure the hardness values at three points from the surface to the core, and analyze the hardness difference value of the cross-section. Refer to the schematic diagram in Figure 2. The test results are shown in Table 9.

[0052]

Table 9

[0053] The above embodiments are only preferred embodiments of the present invention and do not limit the embodiments. The protection scope of the present invention should be based on the scope defined by the claims. In addition to the above description, other different forms of changes or modifications are possible. The obvious changes or modifications brought about thereby are also within the scope of the present invention.

[0054] (Supplementary Note) (Supplementary Note 1) The chemical composition is, by mass%, C: 0.79% - 0.84%, Si: 0.15% - 0.30%, Mn: 0.45% - 0.55%, P ≤ 0.015%, S: 0.0030% - 0.010%, total oxygen: 0.0008% - 0.0022%, Als: 0.0002% - 0.0012%, Mg: 0.0002% - 0.0012%, Nb: 0.0003% - 0.0009%, Mo: 0.0003% - 0.0012%, and the balance is Fe and inevitable impurities. Wire rod for precision steel cord, characterized in that it is such.

[0055] (Supplementary Note 2) The ferrite Si content in the pearlite structure of the wire rod is 0.15% - 0.45%. Wire rod for precision steel cord according to Supplementary Note 1, characterized in that it is such.

[0056] (Supplementary Note 3) The molten steel is continuously cast. The cross-sectional size of the continuously cast billet is (250 - 300) mm * (350 - 400) mm. The surface grain size of the continuously cast billet is 260 - 520 μm, and the core grain size of the continuously cast billet is 800 - 1100 μm. The carbon segregation index at the 1 / 2 thickness position on the longitudinal center line of the cross-section of the continuously cast billet is suppressed to 0.95 - 1.07. The carbon segregation index at the 1 / 4 thickness position on the longitudinal center line of the cross-section of the continuously cast billet is suppressed to 0.96 - 1.06. The carbon segregation index on the surface of the longitudinal center line of the cross-section of the continuously cast billet is suppressed to 0.94 - 1.0. This is the continuous casting process, The continuously cast billet is charged into a heating furnace in a hot state and heated. The total heating time in the furnace is 3.8 - 4.5 h, the temperature of the soaking section is 1230 - 1280 °C, and the temperature holding time of the soaking section is 40 - 60 min. After heating the continuously cast billet, it is continuously rolled into a square billet. The final rolling temperature is 940 - 1050 °C, and the cross-sectional size of the square billet is (140 - 180) mm * (140 - 180) mm. This is the heating and rolling process, The total heating time of the square billet in the furnace is 150 - 170 min, the temperature of the soaking section is 1130 - 1170 °C, and the temperature holding time of the soaking section is 30 - 50 min. After heating the square billet, it undergoes rough rolling, medium rolling, pre-finishing rolling, finishing rolling, and twin module block rolling, and then wire drawing is carried out to form a wire rod. The rolling specification of the wire rod is 5.0 - 6.0 mm. This is the wire rod rolling process, The wire rod after wire drawing is cooled on an air-cooling roller table. The precipitation start temperature of the cementite in the wire rod is suppressed to 740 - 770 °C, and the subcooling degree of the pearlite phase transformation of the wire rod is suppressed to 100 - 150 °C. When the phase transformation time on the air-cooling line is 4 - 6 s, the pearlite content of the wire rod is ≥ 50%. When the phase transformation time is 14 - 16 s, the pearlite content is ≥ 95%. This is the wire rod cooling process, including A method for manufacturing a wire rod for precision steel cord according to claim 1 or 2, characterized in that.

[0057] (Appendix 4) In the continuous casting process, the molten steel is scrap steel and steel scraps. The steel scraps account for 5% - 10% of the molten steel by mass. The manufacturing method according to Supplementary Note 3, characterized in that...

[0058] (Supplementary Note 5) In the continuous casting process, after melting the molten steel in a converter, it is refined in an LF furnace. The refining time in the LF furnace is 30 - 50 min, and the refining temperature is 1450 - 1550 °C. Argon gas stirring is carried out during the refining process of the molten steel, and the argon gas flow rate is 200 - 500 NL / min. The manufacturing method according to Supplementary Note 3, characterized in that...

[0059] (Supplementary Note 6) In the wire rod rolling process, the temperature of the rolled material when carried out from the finishing rolling mill is 950 - 1000 °C, and the temperature compensation deformation rate coefficient of the last pass of the pre-finishing rolling of the rolled material is (1.1 - 2.6)×10 13 s -1 . When entering the finishing rolling mill, the temperature of the rolled material is 880 - 960 °C, and the temperature compensation deformation rate coefficient of the last pass of the finishing rolling of the rolled material is (1.6 - 3.2)×10 14 s -1 . When entering the twin module block, the temperature is 890 - 940 °C, and the temperature compensation deformation rate coefficient of the last pass of the twin module block of the rolled material is (4.5 - 9.9)×10 14 s -1 . The manufacturing method according to Supplementary Note 3, characterized in that...

[0060] (Supplementary Note 7) In the wire rod rolling process, the wire manufacturing temperature of the wire rod is 910 - 940 °C. The manufacturing method according to Supplementary Note 3, characterized in that...

[0061] (Supplementary Note 8) Precision steel wire, manufactured from the wire rod according to Supplementary Note 1 or 2. The precision steel wire, characterized in that...

[0062] (Supplementary Note 9) A mechanical scale removal process is performed on the wire rod, and the mechanical scale removal step in which the residual rate of the iron oxide film on the wire rod surface is ≦ 0.07%, a wire rod drawing step of drawing the wire rod through a plurality of passes to form an intermediate wire having a diameter of 0.8 to 1.2 mm, a heat treatment step of heating the intermediate wire to 880 to 915 °C and then cooling it to cause a phase change at 555 to 575 °C, a steel wire drawing step of drawing the heat-treated intermediate wire to form a steel wire having a diameter of 0.15 to 0.20 mm, and including a method for manufacturing a precision steel wire according to Supplementary Note 8, characterized by the above.

[0063] (Supplementary Note 10) a precision cord, manufactured from the steel wire according to Supplementary Note 8, a precision cord characterized by the above.

Claims

1. The chemical components are, by mass%, C: 0.79% to 0.84%, Si: 0.15% to 0.30%, Mn: 0.45% to 0.55%, P ≤ 0.015%, S: 0.0030% to 0.010%, total oxygen: 0.0008% to 0.0022%, Als: 0.0002% to 0.0012%, Mg: 0.0002% to 0.0012%, Nb: 0.0003% to 0.0009%, Mo: 0.0003% to 0.0012%, with the balance being Fe and inevitable impurities. A wire rod for precision steel cord, characterized by the above.

2. The ferrite Si content in the pearlite structure of the wire rod is 0.15% to 0.45%. The wire rod for precision steel cord according to Claim 1, characterized by the above.

3. A continuous casting process in which the molten steel after melting is continuously cast. The cross-sectional size of the continuous casting billet is (250 - 300) mm * (350 - 400) mm, the surface crystal grain size of the continuous casting billet is 260 - 520 μm, the core crystal grain size of the continuous casting billet is 800 - 1100 μm. The carbon segregation index at the position of 1 / 2 thickness on the center line in the length direction of the cross-section of the continuous casting billet is suppressed to 0.95 - 1.07, the carbon segregation index at the position of 1 / 4 thickness on the center line in the length direction of the cross-section of the continuous casting billet is suppressed to 0.96 - 1.06, and the carbon segregation index on the surface of the center line in the length direction of the cross-section of the continuous casting billet is suppressed to 0.94 - 1.

0. The continuous casting billet is charged into a heating furnace in a hot state and heated. The total heating time in the furnace is 3.8 - 4.5 h, the temperature of the soaking section is 1230 - 1280 °C, and the temperature holding time of the soaking section is 40 - 60 min. After heating the continuous casting billet, it is continuously rolled into a square billet. The final rolling temperature is 940 - 1050 °C, and the cross-sectional size of the square billet is (140 - 180) mm * (140 - 180) mm. A heating and rolling process. The total heating time of the square billet in the furnace is 150 - 170 min, the temperature of the soaking section is 1130 - 1170 °C, and the temperature holding time of the soaking section is 30 - 50 min. After heating the square billet, it undergoes rough rolling, medium rolling, pre-finishing rolling, finishing rolling, and twin module block rolling, and then wire drawing is carried out to form a wire rod. The rolling specification of the wire rod is 5.0 - 6.0 mm. A wire rod rolling process. Cool the wire after wire drawing with an air-cooling roller table, suppress the precipitation start temperature of cementite in the wire to 740 - 770 °C, suppress the subcooling degree of the pearlite phase transformation of the wire to 100 - 150 °C, and when the phase transformation time on the air-cooling line is 4 - 6 s, the pearlite content of the wire is ≥ 50%, and when the phase transformation time is 14 - 16 s, a wire cooling process in which the pearlite content is ≥ 95%, The method for manufacturing a wire for precision steel cord according to claim 1 or 2, characterized in that.

4. In the continuous casting process, the molten steel is molten iron and scrap steel, and the scrap steel accounts for 5% - 10% of the molten steel by mass. The manufacturing method according to claim 3, characterized in that.

5. In the continuous casting process, after melting the molten steel in a converter and then refining it in an LF furnace, the refining time in the LF furnace is 30 - 50 min, the refining temperature is 1450 - 1550 °C, argon gas stirring is performed in the refining process of the molten steel, and the argon gas flow rate is 200 - 500 NL / min. The manufacturing method according to claim 3, characterized in that.

6. In the wire rod rolling process, the temperature of the rolled material when carried out from the finishing rolling mill is 950 to 1000 °C, and the temperature compensation deformation rate coefficient of the last pass of the pre-finishing rolling of the rolled material is (1.1 to 2.6) * 10 １３ s －１ , the temperature of the rolled material when entering the finishing rolling mill is 880 to 960 °C, and the temperature compensation deformation rate coefficient of the last pass of the finishing rolling of the rolled material is (1.6 to 3.2) * 10 １４ s －１ , the temperature when entering the twin module block is 890 to 940 °C, and the temperature compensation deformation rate coefficient of the last pass of the twin module block of the rolled material is (4.5 to 9.9) * 10 １４ s －１ is as follows. The manufacturing method according to claim 3, characterized in that.

7. In the wire rolling process, the wire drawing temperature of the wire is 910 - 940 °C. The manufacturing method according to claim 3, characterized in that.

8. A precision steel wire, manufactured from the wire according to claim 1 or 2. The precision steel wire, characterized in that.

9. A mechanical scale removal process in which a mechanical scale removal treatment is performed on the wire and the residual rate of the iron oxide film on the wire surface is ≤ 0.07%, A wire drawing process in which the wire is drawn through a plurality of passes to form an intermediate wire with a diameter of 0.8 - 1.2 mm, A heat treatment process for the intermediate wire in which the intermediate wire is heated to 880 - 915 °C and then cooled to undergo a phase transformation at 555 - 575 °C, A wire drawing process for the steel wire in which the heat-treated intermediate wire is drawn to form a steel wire with a diameter of 0.15 - 0.20 mm, including. The method for manufacturing a precision steel wire according to claim 8, characterized in that.

10. A precision cord, manufactured from the steel wire according to claim 8. The precision cord, characterized in that.

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