Wire material, steel wire, cord, and method for manufacturing the same for precision steel cords.

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 methods for manufacturing wires, and more specifically to wires for precision steel cords, steel wires, cords, and methods for manufacturing the same. [Background technology]

[0002] Cord steel wire is used in the production and manufacture of tire steel cords. Since users require processing such as tensile strength and twisting during the wire's use, their requirements for wire processing performance are stringent. The microstructure hardness distribution of the wire is an important indicator affecting its processing performance. Wire microstructure hardness is a comprehensive reflection of its chemical composition and microstructure, and the change in microstructure hardness across the wire's cross-section directly reflects the uniform deformation capacity of that cross-section. A uniform hardness distribution across the wire's cross-section is advantageous for improving the uniformity of microstructure hardness across the steel wire's cross-section, and furthermore, it improves the twisting performance of the steel wire, providing conditions for manufacturing complex, precision steel cords.

[0003] Patent Document 1 (Chinese Patent Application No. 201910638740.0) discloses 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. The wire rod for the ultra-fine ultra-high-strength steel wire has a chemical composition of mass% of C: 0.90%~0.96%, Si: 0.12%~0.30%, Mn: 0.30%~0.65%, Cr: 0.10%. It contains approximately 0.30% of the following elements: Al: ≤0.004%, Ti: ≤0.001%, Cu: ≤0.01%, Ni: ≤0.01%, S: ≤0.01%, P: ≤0.01%, O: ≤0.0006%, and N: ≤0.0006%, with the remainder being Fe and unavoidable impurity elements. Among these, the inclusion size is ≤4 μm, and the average density of brittle inclusions is ≤2 particles / mm³. 2This wire rod for ultra-fine, ultra-high-strength steel wire is used as a base material for manufacturing ultra-fine, ultra-high-strength steel wire with a diameter of 50 μm to 60 μm and a tensile strength of ≥ 4500 MPa. In the tensile manufacturing process of ultra-fine, ultra-high-strength steel wire, an unbroken steel wire length of ≥ 300 km can be achieved. The manufacturing method includes vacuum induction melting, remelting, forging, and rolling. The above wire rod is suitable for the manufacture of ultra-fine steel wire, but the twisting performance of the steel wire and the hardness distribution of the wire rod and the cross-section of the steel wire are not mentioned.

[0004] To meet user requirements for the processing performance of precision steel cord wire, particularly for the twisting performance of steel wires manufactured from this wire, it is necessary to develop high-quality precision steel cord wire with a uniform hardness distribution across its cross-section, ensuring a uniform hardness distribution across the cross-section of the resulting steel wire, thereby improving the twisting performance of the steel wires. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Chinese Patent Application Publication No. 110230008 Specification [Overview of the project] [Problems that the invention aims to solve]

[0006] This invention has been made in view of the above technical problems and provides wire rods, steel wires, cords, and methods for manufacturing the same for precision steel cords. By designing the chemical composition and manufacturing process, this invention makes the hardness distribution of the cross-sections of the wire rods and steel wires uniform and satisfies the user's requirements for twisting performance during the processing from wire rods to precision steel cords. [Means for solving the problem]

[0007] To achieve the above objectives, the present invention employs the following technical means.

[0008] One embodiment of the present invention, a wire material for precision steel cord, has a chemical composition in mass percent of 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%, with the remainder being Fe and unavoidable impurities.

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

[0010] The reasons for selecting each chemical component of this invention and designing their content are as follows.

[0011] C: Carbon is the main element for controlling the strength of steel wire. If the carbon content is too low, it will not meet the user's requirements for the strength of the steel wire. If the carbon content is too high, the strength of the steel wire will exceed the user's requirements. Furthermore, a high carbon content increases the rate of breakage and defects in the steel wire during the tensile process. Therefore, in this invention, the carbon content is kept to 0.79% to 0.84%.

[0012] Silicon (Si) is a major deoxygenating element in high-carbon steel. If the silicon content is too low, deoxygenation of the molten steel will be insufficient. If the silicon content is too high, coarse silicate inclusions will form in the steel, reducing the tensile performance of the steel wire. Silicon is dissolved in ferrite, increasing its hardness, reducing the difference in hardness between ferrite and cementite, and improving the uniformity of the hardness of the steel wire structure. Therefore, in this invention, the silicon content is kept to 0.15% to 0.30%.

[0013] Manganese (Mn) is an element that enhances the strength of wire, meeting user requirements for the tensile strength of steel wire. It also lowers the eutectic transition temperature of steel, refines the pearlite structure of steel wire, and improves the deep processing capability of steel wire. Therefore, in this invention, the manganese content is limited to 0.45% to 0.55%.

[0014] P: Phosphorus is prone to causing zonal segregation in wire, which reduces the machinability of steel wire. Therefore, in this invention, the phosphorus element content is limited to ≤0.015%.

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

[0016] Total oxygen: If the oxygen content is too high, the size and number of inclusions in the steel are large, making it easy for fine cracks to form during the machining process of the steel wire, which can cause the steel wire to crack. If the oxygen content is too low, the deformation ability of the inclusions in the steel wire is poor, making it easy for fine cracks to form between the inclusions and the steel wire substrate, which is detrimental to improving the machining performance of the steel wire. Therefore, in this invention, the total oxygen content of the steel wire is kept to 0.0008% to 0.0022%.

[0017] Als: If the acid-soluble aluminum content is too high, the size of Al2O3 inclusions in the steel increases, making the steel wire more prone to cracking during processing. If the acid-soluble aluminum content of the wire is too low, the melting point of the inclusions in the steel increases, reducing their deformability. This increases local stress on the steel wire during processing, making it prone to the formation of fine cracks, which can lead to cracking and fracture of the steel wire. Therefore, in this invention, the acid-soluble aluminum content is kept to 0.0002% to 0.0012%.

[0018] Mg: The magnesium element controls the oxygen content in steel and also controls the type of inclusions in 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 improves the deformation performance of the inclusions, expands the region with high deformability of the inclusions, and contributes to the improvement of the deformation ability of the steel wire. Therefore, in this invention, the magnesium content is suppressed to 0.0002% - 0.0012%.

[0019] Nb: The niobium element suppresses the growth of the crystal grains of the steel billet during heating and improves the uniformity of the hardness 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 significant, reducing the deep processing ability of the wire rod. Therefore, in this 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 is reduced. Therefore, in this invention, the Mo content is suppressed to 0.0003% - 0.0012%.

[0021] This invention further provides a method for manufacturing wire rods for precision steel cords. The method includes the following steps.

[0022] (1) Continuous casting process: The molten steel after smelting 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 in 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 placed in a heating furnace in a heated state and heated. The total heating time in the furnace is 3.8 to 4.5 hours, the temperature of the soaking area is 1230 to 1280°C, and the heat retention time of the soaking area is 40 to 60 minutes. After heating the continuously cast billet, it is continuously rolled into a square billet. The temperature at the end of the continuous rolling is 940 to 1050°C, and the cross-sectional size of the square billet is (140 to 180) mm * (140 to 180) mm.

[0024] (3) Wire Rolling Process: The total heating time for the square billet in the furnace is 150-170 min, the temperature of the soaking section is 1130-1170°C, and the heat retention time of the soaking section is 30-50 min. High-temperature diffusion of the steel billet reduces segregation of elements such as carbon and manganese, and suppresses the crystal grain size of the steel billet. After heating the square billet, it undergoes rough rolling, intermediate rolling, pre-finishing rolling, finish rolling, and twin module block rolling before being made into wire rod, with a rolling specification of 5.0-6.0 mm for the wire rod.

[0025] (4) Wire Cooling Process: After wire production, the wire is cooled on an air-cooled roller table to suppress the cementite precipitation start temperature of the wire to 740-770°C, and the subcooling degree of the pearlite phase change of the wire to 100-150°C. If the phase change time on the air-cooling line is 4-6 s, the pearlite content of the wire is ≥50%, and if the phase change time is 14-16 s, the pearlite content is ≥95%. The final cooled wire mainly has a sorbite structure and contributes to the tensile strength of the steel wire by the user.

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

[0027] In the above invention, in step (1), the molten steel is smelted in a converter and then 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 during 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 it is discharged from the pre-finishing mill is 950~1000°C, and the temperature-compensated deformation rate coefficient of the final pass of the pre-finishing roll of the rolled material is (1.1~2.6)*10 13 s -1 Therefore, the temperature of the rolled material when it enters the finishing mill is 880~960°C, and the temperature-compensated deformation rate coefficient for the final pass of the finishing roll of the rolled material is (1.6~3.2)*10 14 s -1 The temperature when entering the twin module block is 890-940°C, and the temperature-compensated deformation rate coefficient for the final pass of the rolled material in the twin module block is (4.5-9.9)*10 14 s -1 That is the case.

[0029] In the above invention, in step (3), the wire making temperature is set to 910-940°C. By controlling the wire making temperature to a high level, the cooling rate of the wire on the air-cooled roller table is increased, laying the foundation for controlling the final structure of the wire.

[0030] The present invention further provides a precision steel wire, the steel wire being manufactured from the above-mentioned wire material.

[0031] The present invention further provides a method for manufacturing precision steel wire, the method comprising the following steps. a. Mechanical scale removal process: The wire is subjected to a mechanical scale removal treatment, and the residual iron oxide film on the wire surface is ≤0.07%. b. Wire tensioning process: The wire is pulled through multiple passes to create an intermediate wire with a diameter of 0.8 to 1.2 mm. c. Heat treatment process for the intermediate wire: The intermediate wire is heated to 880-915°C, then cooled and subjected to a phase change at 555-575°C. d. Steel wire tensioning process: The heat-treated intermediate wire is tensioned to create a steel wire with a diameter of 0.15 to 0.20 mm.

[0032] The present invention further provides a precision cord, which is manufactured using steel wire. [Effects of the Invention]

[0033] The present invention offers the following advantages. This invention, through chemical composition and manufacturing process design, achieves a uniform hardness distribution across the cross-sections of wire and steel wire, meeting user requirements for twisting performance during the processing of wire into precision steel cord. It suppresses the difference in hardness between different parts along the cross-section of a 5.5 mm diameter wire to within 35 HV, and the difference in hardness between different parts along the cross-section of a 0.175 mm diameter steel wire to within 10 HV, thereby meeting user requirements for the mass production of steel wire and steel cord. [Brief explanation of the drawing]

[0034] [Figure 1] This is a schematic diagram of a hardness test on the cross-section of a wire. [Figure 2] This is a schematic diagram of a hardness test on the cross-section of a steel wire. [Modes for carrying out the invention]

[0035] To further clarify the object, technical solution, and merits of the embodiments of the present invention, the technical solution in the embodiments of the present invention will be described below in more clarity and completeness, although it goes without saying that the embodiments described are not all embodiments but only a portion of the embodiments of the present invention. All other embodiments that a person skilled in the art could obtain without creative work based on the embodiments of the present invention shall be included within the scope of protection of the present invention.

[0036] Table 1 shows the chemical composition of the wires according to Examples 1 to 6 of the present invention.

[0037] [Table 1]

[0038] The manufacturing method for the above-mentioned precision steel cord wire includes the following steps. (1) Smelting process: Molten steel consists of molten iron and scrap steel, of which scrap steel accounts for 5% to 10% by mass of the molten steel. The molten steel is smelted in a converter and then refined in an LF furnace. The refining time in the LF furnace is 30 to 50 minutes, and the refining temperature is 1450 to 1550°C. Argon gas is stirred during the refining process of the molten steel, and the argon gas flow rate is 200 to 500 NL / min.

[0039] [Table 2]

[0040] (2) Continuous casting process: 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, 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 centerline in the longitudinal direction 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 centerline in the longitudinal direction of the cross-section of the continuously cast billet is suppressed to 0.96~1.06, and the carbon segregation index on the surface of the centerline in the longitudinal direction of the cross-section of the continuously cast 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 zone is 1230 - 1280 °C, the soaking time in the soaking zone 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 zone is 1130 - 1170 °C, the soaking time in the soaking zone 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, intermediate rolling, pre-finishing rolling, finishing rolling and twin-module block rolling are carried out. The temperature of the rolled material when carried out 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 and the temperature of the rolled material when entering the finishing rolling mill 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 and the temperature when entering the twin-module block 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 and then wire drawing is carried out to make 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 on the air-cooling roller table of the wire rods 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 production, the wire is cooled by placing it on an air-cooled roller table. The temperature at which cementite precipitation begins in the wire is kept to 740-770°C, and the subcooling temperature of the phase change of pearlite in the wire is kept to 100-150°C. When the phase change time on the air-cooling line is 4-6 seconds, the pearlite content of the wire is ≥50%. When the phase change time is 14-16 seconds, the pearlite content is ≥95%. The wire after final cooling mainly has a sorbite structure, which is advantageous for the user's steel wire tensile strength.

[0048] [Table 7]

[0049] The method for manufacturing steel wire using the above-mentioned wire material includes the following steps. a. Mechanical scale removal process: The wire is subjected to a mechanical scale removal treatment, and the residual iron oxide film on the wire surface is ≤0.07%. b. Wire tensioning process: The wire is pulled through multiple passes to produce intermediate wires with a diameter of 0.8 to 1.2 mm. c. Heat treatment process for the intermediate wire: The intermediate wire is heated to 880-915°C, then cooled to induce a phase change at 555-575°C. d. Steel wire tensioning process: After heat treatment, the intermediate wire is tensioned to produce steel wire with a diameter of 0.15 to 0.20 mm.

[0050] [Table 8]

[0051] Hardness tests are performed on the wires and steel wires of the above Examples 1 to 6. Wire hardness testing method: The radius of the wire's cross-section is divided into five equal parts, and the hardness values ​​are measured at six points from the surface to the core. The hardness difference across the cross-section is then analyzed. Refer to the schematic diagram in Figure 1. Steel wire hardness test method: The radius of the cross-section of the steel wire is divided into two equal parts, and the hardness values ​​are measured at three points from the surface to the core. The difference in hardness across the cross-section is then analyzed. Refer to the schematic diagram in Figure 2. The test results are shown in Table 9.

[0052] [Table 9]

[0053] The embodiments described above are merely preferred embodiments of the present invention and do not limit the embodiments. The scope of protection of the present invention should be limited to the scope defined by the claims. In addition to the above description, other different forms of modification or alteration are possible. Any obvious changes or alterations resulting therefrom are also within the scope of the present invention.

[0054] (Note) (Note 1) The chemical composition, in mass%, is as follows: 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%, with the remainder being Fe and unavoidable impurities. A wire material for precision steel cords characterized by the following features.

[0055] (Note 2) The ferrite Si content in the pearlite structure of the aforementioned wire is 0.15% to 0.45%. The precision steel cord wire material described in Appendix 1, characterized by the features described herein.

[0056] (Note 3) A continuous casting process is performed in which molten steel is continuously cast, the cross-sectional size of the continuously cast billet is (250~300) mm * (350~400) mm, the crystal grain size on the surface of the continuously cast billet is 260~520 μm, the crystal grain size of the core of the continuously cast billet is 800~1100 μm, the carbon segregation index at the 1 / 2 thickness position on the longitudinal centerline 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 centerline of the cross-section of the continuously cast billet is suppressed to 0.96~1.06, and the carbon segregation index on the surface of the longitudinal centerline of the cross-section of the continuously cast billet is suppressed to 0.94~1.0. The process involves heating a continuously cast billet in a heated furnace for a total heating time of 3.8 to 4.5 hours, with a uniform temperature of 1230 to 1280°C and a temperature holding time of 40 to 60 minutes. After heating, the billet is continuously rolled into a square billet, with a final rolling temperature of 940 to 1050°C and a cross-sectional size of (140 to 180) mm * (140 to 180) mm. The total heating time in the furnace for the square billet is 150-170 min, the temperature of the soaking section is 1130-1170°C, and the temperature holding time in the soaking section is 30-50 min. After heating the square billet, it undergoes rough rolling, intermediate rolling, pre-finish rolling, finish rolling, and twin module block rolling before being made into wire rod. The wire rod rolling specifications are 5.0-6.0 mm. A wire cooling process is included in which the wire is cooled on an air-cooled roller table after wire production, the cementite precipitation start temperature of the wire is suppressed to 740-770°C, the subcooling degree of the perlite phase change of the wire is suppressed to 100-150°C, and if the phase change time on the air-cooling line is 4-6 s, the perlite content of the wire is ≥50%, and if the phase change time is 14-16 s, the perlite content is ≥95%. A method for manufacturing precision steel cord wire as described in Appendix 1 or 2, characterized by the present invention.

[0057] (Note 4) In the aforementioned continuous casting process, the molten steel consists of molten iron and scrap steel, with the scrap steel accounting for 5% to 10% of the molten steel by mass. The manufacturing method described in Appendix 3, characterized by the features described herein.

[0058] (Note 5) In the continuous casting process described above, the molten steel is smelted in a converter and then refined in an LF furnace, with a refining time of 30-50 minutes and a refining temperature of 1450-1550°C. Argon gas stirring is performed during the molten steel refining process, and the argon gas flow rate is 200-500 NL / min. The manufacturing method described in Appendix 3, characterized by the features described herein.

[0059] (Note 6) In the wire rolling process described above, the temperature of the rolled material when it is discharged from the pre-finishing mill is 950-1000°C, and the temperature-compensated deformation rate coefficient of the final pass of the pre-finishing rolling of the rolled material is (1.1-2.6)*10 13 s -1 Therefore, the temperature of the rolled material when it enters the finishing mill is 880~960°C, and the temperature-compensated deformation rate coefficient of the final pass of the finishing roll of the rolled material is (1.6~3.2)*10 14 s -1 The temperature when entering the twin module block is 890-940°C, and the temperature-compensated deformation rate coefficient for the final pass of the rolled material's twin module block is (4.5-9.9)*10 14 s -1 That is, The manufacturing method described in Appendix 3, characterized by the features described herein.

[0060] (Note 7) In the wire rolling process, the wire manufacturing temperature is 910 to 940°C. The manufacturing method described in Appendix 3, characterized by the features described herein.

[0061] (Note 8) Precision steel wire, manufactured from the wire material described in Appendix 1 or 2, A precision steel wire characterized by the following features.

[0062] (Note 9) A mechanical scale removal process is performed on the wire, and the residual iron oxide film on the wire surface is ≤0.07%. The wire tensioning process involves pulling the wire through multiple passes to create an intermediate wire with a diameter of 0.8 to 1.2 mm, and The intermediate wire is heated to 880-915°C, then cooled and undergoes a phase change at 555-575°C in a heat treatment process for the intermediate wire. This process includes a steel wire tensile process in which the heat-treated intermediate wire is pulled to create a steel wire with a diameter of 0.15 to 0.20 mm. A method for manufacturing precision steel wire as described in Appendix 8, characterized by the features described above.

[0063] (Note 10) A precision cord, manufactured from the steel wire described in Appendix 8, A precision code characterized by the following features.

Claims

1. The chemical composition, in mass%, is as follows: 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%, with the remainder being Fe and unavoidable impurities. A wire material for precision steel cords characterized by the following features.

2. The ferrite Si content in the pearlite structure of the aforementioned wire is 0.15% to 0.45%. The wire material for precision steel cord according to feature 1.

3. A precision steel wire, manufactured from the wire material for precision steel cords described in claim 1 or 2, A precision steel wire characterized by the following features.

4. A mechanical scale removal process is performed on the wire, and the residual iron oxide film on the wire surface is ≤0.07%. The wire tensioning process involves pulling the wire through multiple passes to create an intermediate wire with a diameter of 0.8 to 1.2 mm, The intermediate wire is heated to 880-915°C, then cooled and undergoes a phase change at 555-575°C in a heat treatment process for the intermediate wire. This process includes a steel wire tensile process in which the heat-treated intermediate wire is pulled to form a steel wire with a diameter of 0.15 to 0.20 mm. The method for manufacturing precision steel wire according to feature 3.

5. A precision cord, manufactured from the precision steel wire described in claim 3, A precision code characterized by the following features.

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