High-strength, economical high-carbon steel wire rod and method for manufacturing the same

Abstract

This invention discloses a high-strength, economical high-carbon steel wire rod containing Fe and unavoidable impurities, and further contains the following chemical elements in mass percentage content: C: 0.84-0.89%, Si: 0.60-1.00%, Mn: 0.30-0.80%, Cr: 0.25-0.50%, V: 0.02-0.06%, Al: 0.02-0.05%, O: 0.0015-0.0035%, and N: 0.004-0.008%. Accordingly, this invention also discloses a method for manufacturing the above wire rod. Through a rational chemical composition design, this invention can meet the processing requirements for 2000 MPa high-strength, high-torsion-resistance galvanized steel wire at low processing costs.

Description

Technical Field

[0001] The present invention relates to a wire rod and a manufacturing method thereof, and particularly relates to a wire rod for cables and a manufacturing method thereof.

Background Art

[0002] Wire rods are raw materials for high-strength steel wires and steel stranded wires used in bridge cables. Large-diameter wire rods can be manufactured into high-strength steel wires through processes such as drawing, zinc plating, and stabilization. In order to complete the steel wire drawing process with a large reduction ratio, the wire rod must first have good drawing performance.

[0003] Furthermore, the continuous improvement of the steel wire strength grade also requires the continuous improvement of the wire rod strength. Alloy strengthening and grain refinement are the two most effective means to improve the wire rod strength. For example, in the Chinese patent document with the publication number CN101565797A and the publication date of October 28, 2009, titled "High-strength Zinc-plated Steel Wire and Its Application to Bridge Cable Manufacturing", the Si element content of the material is increased, and trace alloying elements such as V and Nb are added in combination to further improve the material strength.

[0004] Obtaining a high-sorbite structure in high-carbon wire rods is another important means to achieve strength improvement. For example, the wire rod with the publication number CN107299280 and the publication date of October 27, 2017, titled "Heat-treated Wire Rod for 2000MPa-class Cable Steel Wire" requires tissue control by offline isothermal treatment after hot rolling. After the hot-rolled wire rod is unwound, it undergoes austenitizing heating, isothermal salt bath, washing, and winding to obtain a heat-treated wire rod. The austenitizing heating temperature is 880 - 980°C, and the isothermal salt bath is 520 - 600°C.

[0005] However, current direct hot-rolled high-carbon wire rods cannot simultaneously meet the requirements for strength and high plasticity / toughness once the wire strength reaches 1960 MPa or higher. This necessitates offline isothermal treatment, the addition of large amounts of alloying elements, and double rolling of the bloom, making quality control difficult and production costs high.

[0006] Based on this, there is a need to provide a high-carbon wire rod and a method for manufacturing the same that can be produced at low cost, with high strength and high plasticity and toughness. [Overview of the project] [Problems that the invention aims to solve]

[0007] One of the objectives of the present invention is to provide a high-strength, economical high-carbon steel wire rod that can meet the processing requirements for high-strength, high-torsion performance galvanized steel wire with a strength of 2000 MPa at a low processing cost through a rational chemical composition design. [Means for solving the problem]

[0008] To achieve the above objective, the present invention proposes a high-strength and economical high-carbon steel wire rod, the steel wire rod containing Fe and unavoidable impurities, further C: 0.84~0.89%, Si: 0.60~1.00%, Mn: 0.30~0.80%, Cr: 0.25~0.50%, V: 0.02~0.06%, Al: 0.02~0.05%, O: 0.0015~0.0035%, N: 0.004~0.008% It contains each chemical element as indicated by its mass percentage content.

[0009] Furthermore, the present invention provides a high-strength and economical high-carbon steel wire rod, the mass percentage content of each chemical element in the steel wire rod is as follows: C: 0.84~0.89%, Si: 0.60~1.00%, Mn: 0.30~0.80%, Cr: 0.25~0.50%, V: 0.02~0.06%, Al: 0.02~0.05%, O: 0.0015~0.0035%, N: 0.004~0.008%, The remainder consists of Fe and other unavoidable impurities.

[0010] In the high-strength, economical high-carbon steel wire rod of the present invention, the design principles for each chemical element are specifically as follows.

[0011] Carbon (C) is a necessary chemical component to guarantee the high strength of wire rods and galvanized steel wires. The carbon content determines the volume fraction of cementite in the sorbite structure of high-carbon wire rods. Increasing the carbon content in the wire rod is advantageous for the formation of more cementite lamellae, and a refined sorbite lamellar structure has better deformation and work hardening properties, which is advantageous for improving the strength of the steel wire in subsequent processing steps. Therefore, in this invention, it is necessary to control the carbon content to 0.84% ​​or higher. However, as the carbon content in the material increases, the difficulty of controlling segregation in the smelting and continuous casting processes increases, and in particular, when network cementite precipitates along the grain boundaries, the plasticity and toughness of the material decrease sharply. At the same time, as the carbon content increases, the spheroidization phenomenon of cementite is more likely to occur in the cooling process after rolling. Based on this, this invention controls the upper limit of the carbon content to 0.89%.

[0012] Si: In the smelting process, Si is often added to steel as a deoxidizer, and at the same time, Si dissolved in the ferrite phase of the wire rod significantly improves the material strength. Furthermore, in this invention, in the cooling phase transformation process of the wire rod, Si is concentrated at the interface between the ferrite phase and the cementite phase, and in the lead bath degreasing and hot galvanizing processes of steel wire drawn with a large reduction in surface area, the concentration of Si at the phase interface slows down the decomposition of the large-deformed cementite lamellae, reducing the loss of steel wire strength. Based on this, in order to ensure high strength of the wire rod and even higher strength of the steel wire after drawing, this invention controls the Si content to be more than 0.6%. However, if Si is excessive, it significantly reduces the plasticity of the steel, causing material embrittlement and cracking during torsion, so this invention controls the Si content to be between 0.60 and 1.0%.

[0013] Mn: The element Mn is often added as a deoxidizing agent in the steelmaking process. At the same time, Mn readily combines with harmful elements S in steel to form MnS, thereby reducing its harmfulness. Mn is also a commonly used strengthening element in steel, mainly playing a role in solid solution strengthening. The resulting alloy cementite has higher strength, so the Mn content in the alloy needs to be controlled to more than 0.30%. However, in this invention, if the Mn content is excessive, the tendency for grain coarsening during the material heating process increases, making it difficult to control the controlled cooling structure. This tendency is particularly strong when both the C and Si content in the steel is high. Based on this, this invention controls the amount of Mn added to less than 0.80%.

[0014] Cr: In this invention, the addition of Cr element refines the lamellar structure of the sorbite structure in the wire rod, simultaneously improving cementite strength and thus improving both material strength and plasticity. Therefore, this material contains more than 0.25% Cr. On the other hand, in order to prevent the appearance of abnormal martensite structures and reduce the difficulty of controlling the structure, and because the tendency for cementite to become spheroidal increases further as the Cr content increases, this invention controls the upper limit of the Cr content to 0.50%.

[0015] V, Al, O, N: V and Al readily combine with C and N to form nano-sized carbonitride precipitates. Simultaneously, Al combines with O to form aluminum oxide, which is advantageous for refining the austenite structure in the hot rolling process of wire rods, increasing the grain boundary area, providing more nucleation sites for sorbite structure transformation, facilitating the formation of a good layered sorbite lamellar structure, reducing the proportion of spherical and short rod-shaped degenerated cementite, and resulting in improved wire strength and torsional performance in the subsequent direct drawing process of hot-rolled wire rods. Based on this, the present invention controls the Al content range to 0.02-0.05% and the O content to over 0.0015% in order to exert the grain refinement effect of Al. On the other hand, to prevent the formation of excess aluminum oxide which leads to performance degradation, the present invention controls the O content to less than 0.0035%. Furthermore, to ensure that V and Al nitrogen carbides precipitate sufficiently in the temperature range of 800-900°C, and at the same time prevent excess V from promoting nucleation and growth of large-particle spheroidal carbides, the present invention controls the V addition range to 0.02-0.06% and the N element content to 0.004-0.008%.

[0016] Furthermore, in the high-strength and economical high-carbon steel wire rod of the present invention, the mass percentage content of the chemical elements in the steel wire rod further satisfies (V+Al) / (C+100N)≧1 / 35, where each chemical element in the formula is replaced with the numerical value before the percentage sign of the mass percentage content of the corresponding chemical element.

[0017] The present invention further ensures that nitrogen carbides of V and Al precipitate sufficiently in the temperature range of 800-900°C, while simultaneously preventing excess V from promoting nucleation and growth of large-particle spheroidal carbides by controlling (V+Al) / (C+100N) to ≥ 1 / 35. In some embodiments, (V+Al) / (C+100N) is controlled to ≥ 0.030. In some embodiments, (V+Al) / (C+100N) is controlled in the range of 0.030-0.065.

[0018] Furthermore, for other inevitable impurities in the high-strength and economical high-carbon steel wire rod of the present invention, Ti≤0.003%, Ca≤0.001%, P≤0.010%, and S≤0.010%.

[0019] The inevitable impurities in the present invention are mainly P, S, Ti, and Ca. When the contents of P and S elements are excessive, the brittleness of the material increases, especially显著 when segregation occurs. Therefore, in some embodiments of the present invention, the P content is controlled to be less than 0.010% and the S content is controlled to be less than 0.010%.

[0020] When the Ti element is excessive, a large amount of carbonitrides are formed in the steel, which is disadvantageous to the torsion performance and fatigue life of the steel wire. Therefore, in some embodiments of the present invention, the Ti content is controlled to be 0.003% or less.

[0021] Ca can lower the melting point of brittle inclusions in the wire rod and improve the torsion performance of the steel wire. However, when it is excessive, a large amount of spherical inclusions are generated, which is disadvantageous to the formation of the sorbite lamellar structure. Therefore, it is necessary to control its content to be less than 0.001%.

[0022] Furthermore, in the high-strength and economical high-carbon steel wire rod of the present invention, the microstructure of the steel wire rod includes a sorbite colony, and the size range of the sorbite colony is 2-30 μm.

[0023] Furthermore, in the high-strength and economical high-carbon steel wire rod of the present invention, the area ratio of spherical and short rod-shaped degenerated cementite in the microstructure of the steel wire rod is 0.6% or less.

[0024] Furthermore, in the high-strength and economical high-carbon steel wire rod of the present invention, the tensile strength of the steel wire rod is 1320 MPa or more, and the reduction ratio is 30% or more. In some embodiments, the tensile strength of the steel wire rod is 1350 MPa or more. In some embodiments, the tensile strength of the steel wire rod is 1320 to 1410 MPa. In some embodiments, the reduction ratio of the steel wire rod is 30 to 40%.

[0025] Another object of the present invention is to provide a high-strength and economical method for manufacturing high-carbon steel wire rods that can be produced using a relatively simple processing process to meet the processing requirements of high-strength, high-torsion performance galvanized steel wires with a strength of 2000 MPa.

[0026] Based on the above objectives, the present invention further provides a method for manufacturing high-strength and economical high-carbon steel wire rods, comprising the following steps: (1) Smelting, (2) Billet casting, (3) Heating: Heat to 950-1150°C and keep warm for 1.5-2.5 hours. (4) Wire rod rolling: The rolling speed is controlled to 20-60 m / s. (5) Cool by air cooling.

[0027] Furthermore, in step (1) of the present invention, vacuum degassing is performed for 15 to 26 minutes during the smelting process, preferably controlling the final O content to 0.0015 to 0.0035% and the N content to 0.004 to 0.008%.

[0028] Furthermore, in step (2) of the manufacturing method of the present invention, the billet is cast by a small billet continuous casting machine, preferably argon gas protection can be employed in the casting process, the size of the small billet can be 260 mm or less, the width-to-thickness ratio can be 4:3 or less, and more preferably the step of grinding the billet is also included, and the defect depth on the billet surface after grinding is 0.5 mm or less.

[0029] Furthermore, in step (2) of the manufacturing method of the present invention, the carbon segregation in the center of the billet is controlled to less than 1.06 by adjusting the drawing speed, cooling, and end reduction parameters in the continuous casting process.

[0030] Furthermore, in step (4) of the manufacturing method of the present invention, the finish rolling mill group inlet temperature is controlled to 930-990°C, the diameter reduction constant diameter rolling mill group inlet temperature is controlled to 930-990°C, and the discharge temperature is controlled to 920-980°C, preferably the size of the steel wire rod obtained by rolling is Φ11-16 mm.

[0031] Furthermore, in step (5) of the manufacturing method of the present invention, the air cooling step is performed on a Stermore line.

[0032] Air cooling can be performed using a well-known Stermore fan in this field. In some embodiments, in step (5) of the manufacturing method of the present invention, the airflow adjustment range of the Stermore line is controlled to 80-100% for F1-F8 fans and 0-45% for F9-F14 fans.

[0033] In the manufacturing method of the present invention, after wire rod rolling, the microstructure transformation of the wire rod is controlled by adjusting the fan airflow of the Stermore line to optimize the wire rod structure. After Stermore cooling, the wire rod forms a good layered sorbite lamellar structure, free from martensite abnormalities, with sorbite colony sizes of 2-30 μm, and the ratio of spherical and short rod-shaped degenerated cementite in the wire rod is 0.6% or less, which is advantageous for subsequent steel wire drawing.

[0034] The present invention further provides a galvanized steel wire, which is obtained by drawing the high-strength, economical high-carbon steel wire rod described above, galvanizing it, and stabilizing it, wherein the tensile strength of the galvanized steel wire is 2000 MPa or more, and the torsion value is 11 turns or more.

[0035] The galvanized steel wire can be manufactured using conventional drawing, galvanizing, and stabilization processes. In some embodiments, the high-carbon wire rod is drawn in 6 to 9 passes, with a drawing speed of 1.0 to 4.0 m / s. In some embodiments, the galvanizing temperature is 430 to 480°C. In some embodiments, the stabilization temperature is 300 to 400°C, and the stabilization speed is 150 to 200 m / min.

[0036] Preferably, the tensile strength of the galvanized steel wire is 2020 MPa or higher, and the torsion value is 15 turns or higher. In some embodiments, the tensile strength of the galvanized steel wire is 2000 to 2075 MPa, and the torsion value is 11 to 30 turns.

[0037] The high-strength and economical high-carbon steel wire rod of the present invention has the following advantages and beneficial effects.

[0038] The high-strength, economical high-carbon steel wire rod of the present invention has the advantage of low cost because, during the composition design, it uses a small number of alloying elements and their content is relatively low.

[0039] The present invention provides a method for manufacturing high-strength, economical high-carbon steel wire rods that is simple in process, does not require steps such as isothermal treatment, and can produce wire rods with a good balance of strength and plasticity, meeting the requirements for drawing and galvanizing high-strength steel wires.

[0040] The microstructure of the high-strength, economical high-carbon steel wire rod of the present invention is mainly sorbite, with sorbite colonies refined to a size of 2-30 μm, the area ratio of spherical and short rod-shaped degenerate cementite in the wire rod being less than 0.6%, central carbon segregation being less than 1.06%, and no abnormal structures in the microstructure.

[0041] The high-strength, economical high-carbon steel wire rod of the present invention can achieve a tensile strength of 1320 MPa or more, while simultaneously possessing good plasticity and a reduction ratio exceeding 30%. Therefore, by directly drawing, galvanizing, and stabilizing this wire rod, it is possible to produce galvanized steel wire for bridge cables and high-strength steel strands with a strength exceeding 2000 MPa and a torsional strength exceeding 11 turns. This results in low processing costs, meets the requirements for use in large-span bridges and construction projects, reduces project investment, and saves costs. [Modes for carrying out the invention]

[0042] The following interpretation and explanation will be made in conjunction with specific embodiments to further describe the high-strength, economical high-carbon steel wire rod and its manufacturing method according to the present invention, but this interpretation and explanation will not unduly limit the technical solutions of the present invention.

[0043] Examples 1-10 and Comparative Examples 1-3 The high-strength, economical high-carbon steel wire rods of Examples 1 to 10 were all manufactured using the following steps.

[0044] (1) After electric furnace or converter smelting, off-furnace refining was performed. Off-furnace refining employed an LF furnace + VD or RH degassing process, adjusting the composition and amount of synthetic slag added during the smelting process to control the P and S element content in the steel to less than 0.010% and less than 0.010%, respectively. The vacuum degassing time was 15-26 mins, and the final O content was controlled to 0.0015-0.0035% and the N content to 0.004-0.008%.

[0045] (2) Billets were cast using a small billet continuous casting machine, with argon gas protection during the casting process. The size of the small billets was set to 260 mm or less, the width-to-thickness ratio to 4:3 or less, and the carbon segregation in the center of the billets was controlled to less than 1.06 by adjusting the drawing speed, cooling, and end reduction parameters during the continuous casting process. The chemical composition of the obtained billets is shown in Table 1. The billets underwent eddy current testing, magnetic particle testing, grinding with a grinder, and additional magnetic particle testing and grinding to remove defects such as cracks and dents from the ingot surface. The defect depth was 0.5 mm or less.

[0046] (3) The small billets were heated to 950-1150°C and kept warm for 1.5-2.5 hours.

[0047] (4) The wire rods were rolled, with the rolling speed controlled to 20-60 m / s, the finish rolling mill inlet temperature controlled to 930-990°C, the diameter reduction / constant diameter rolling mill inlet temperature controlled to 930-990°C, and the discharge temperature controlled to 920-980°C. The size specifications of the rolled wire rods were Φ11-16 mm.

[0048] (5) Cooling by Stermore fan: The fan airflow for F1 to F8 was 80 to 100%, and the fan airflow for F9 to F14 was 0 to 45%.

[0049] The control wire rods of Comparative Examples 1 to 3 were also manufactured using the same process as described above, but their chemical composition and specific process parameters at each step did not meet the design requirements of the present invention.

[0050] Table 1 shows the mass percentages of each chemical element in the high-strength, economical high-carbon steel wire rods of Examples 1-10 and Comparative Examples 1-3.

[0051] [Table 1]

[0052] Table 2 shows the specific process parameters for the wire rods of Examples 1 to 10 and the control wire rods of Comparative Examples 1 to 3 in the steps described above.

[0053] [Table 2]

[0054] The wire rods from Examples 1-10 and the control wire rods from Comparative Examples 1-3 were sampled, and the microstructure of each example sample was observed and analyzed. The relevant observation and analysis results are shown in Table 3 below. The samples were examined using a scanning electron microscope, and the obtained tissue images were statistically analyzed for area ratio by type.

[0055] Table 3 shows the microstructural characteristics of the wire rods from Examples 1-10 and the control wire rods from Comparative Examples 1-3.

[0056] [Table 3]

[0057] As shown in Table 3, the size range (average size) of sorbite colonies in the wire rods of Examples 1 to 10 was 2 to 30 μm, while the size of the sorbite colonies in the comparative examples was larger than that of the present invention. Furthermore, the area ratio of spherical and short rod-shaped degenerated cementite in the microstructure of the wire rods of Examples 1 to 10 of the present invention was less than 0.6% in all cases, while it was greater than 0.6% in all of the comparative examples 1 to 3.

[0058] To verify the mechanical performance of the wire rods in each example and comparative example, the inventors again sampled the wire rods of Examples 1 to 10 and the control wire rods of Comparative Examples 1 to 3 obtained in the above process steps, and performed mechanical performance tests according to GB / T 228.1 Metallic materials Tensile tests Part 1: Room temperature test methods. The results of the mechanical performance tests are shown in Table 4.

[0059] Table 4 shows the performance test results of the wire rods from Examples 1 to 10 and the control wire rods from Comparative Examples 1 to 3.

[0060] [Table 4]

[0061] As can be seen from Table 4, the tensile strength of the wire rods in Examples 1 to 10 of the present invention was 1320 MPa or higher, and the reduction ratio was 30% or higher. On the other hand, while Comparative Examples 1 and 2 satisfied the tensile strength requirements of the present invention, their reduction ratio was less than 30%, and while Comparative Example 3 satisfied the reduction ratio requirements of the present invention, its tensile strength was lower than that of the present invention. This indicates that Comparative Examples 1 to 3 could not achieve both strength and plasticity.

[0062] To demonstrate that high-strength galvanized steel wire can be obtained using the wire rods of the present invention, the wire rods of Examples 1 to 10 and the control wire rods of Comparative Examples 1 to 3 were drawn through 6 to 9 passes, galvanized, and stabilized (Table 5) to produce galvanized steel wire. The galvanized steel wires produced in Examples 1 to 10 and Comparative Examples 1 to 3 were subjected to relevant performance tests, and the results of the performance tests are shown in Table 6.

[0063] [Table 5]

[0064] The relevant performance testing methods were as follows:

[0065] Tensile Test: Using GB / T 228.1 Metallic Materials Tensile Test Part 1: Room Temperature Test Method, tensile tests were performed to measure the tensile strength of the steel wires of Examples 1 to 10 and the control steel wires of Comparative Examples 1 to 3.

[0066] Torsion Test: Using GB / T 239.1 Metallic Materials Wire Rods Part 1: Unidirectional Torsion Test Method, the torsion values ​​of 100D gauge length samples of steel wires from Examples 1 to 10 and control steel wires from Comparative Examples 1 to 3 were measured.

[0067] Table 6 shows the performance test results for the steel wires of Examples 1 to 10 and the control steel wires of Comparative Examples 1 to 3.

[0068] [Table 6]

[0069] As can be seen from Table 6, the steel wires of Examples 1 to 10, obtained by drawing out the above wire rods, galvanizing them, and stabilizing them, exhibit further improved tensile strength. Their tensile strengths all exceed 2000 MPa, and their torsional strengths are 11 turns or more, effectively meeting the production requirements for large-span, long-life bridge cables.

[0070] Furthermore, the combination methods of each technical feature in this application are not limited to the combination methods described in the claims of this application or the combination methods described in the specific embodiments, and all technical features described in this application can be freely combined or combined in any manner as long as they do not contradict each other.

[0071] Furthermore, the embodiments described above are merely specific examples of the present invention. The present invention is not limited to the embodiments described above, and similar changes or modifications can be obtained from or easily conceived by those skilled in the art from the content disclosed herein, and are within the scope of protection of the present invention.

Claims

1. A high-strength, economical high-carbon steel wire rod containing Fe and unavoidable impurities, wherein the steel wire rod further C：0.84～0.89%、 Si: 0.60–1.00%, Mn: 0.30–0.80%, Cr：0.25～0.50%、 V：0.02～0.06%、 Al：0.02～0.05%、 O：0.0015～0.0035%、 N：0.004～0.008% A high-strength, economical high-carbon steel wire rod characterized by containing each chemical element as indicated by its mass percentage content.

2. The mass percentage content of each chemical element in the steel wire rod is C：0.84～0.89%、 Si: 0.60–1.00%, Mn: 0.30–0.80%, Cr：0.25～0.50%、 V：0.02～0.06%、 Al：0.02～0.05%、 O：0.0015～0.0035%、 N：0.004～0.008%、 The high-strength and economical high-carbon steel wire rod according to claim 1, characterized in that the remainder is Fe and other unavoidable impurities.

3. The high-strength, economical high-carbon steel wire rod according to claim 1 or 2, characterized in that the mass percentage content of the chemical elements in the steel wire rod further satisfies (V + Al) / (C + 100N) ≥ 1 / 35, and each chemical element in the formula is replaced with the numerical value before the percentage sign of the mass percentage content of the corresponding chemical element.

4. A high-strength, economical high-carbon steel wire rod according to claim 1 or 2, characterized in that, regarding other unavoidable impurities, Ti ≤ 0.003%, Ca ≤ 0.001%, P ≤ 0.010%, and S ≤ 0.010%.

5. The high-strength and economical high-carbon steel wire rod according to claim 1 or 2, characterized in that the microstructure of the steel wire rod contains sorbite colonies, and the size range of the sorbite colonies is 2 to 30 μm.

6. The high-strength and economical high-carbon steel wire rod according to claim 1 or 2, characterized in that the area ratio of spherical and short rod-shaped degenerated cementite in the microstructure of the steel wire rod is 0.6% or less.

7. The high-strength and economical high-carbon steel wire rod according to claim 1 or 2, characterized in that the tensile strength of the steel wire rod is 1320 MPa or more and the reduction ratio is 30% or more.

8. A method for manufacturing a high-strength and economical high-carbon steel wire rod according to any one of claims 1 to 7, (1) Smelting, (2) Billet casting, (3) Heating: Heat to 950-1150°C and keep warm for 1.5-2.5 hours. (4) Wire rod rolling: The rolling speed is controlled to 20-60 m / s. (5) Cool by air cooling A manufacturing method characterized by including the following step.

9. The manufacturing method according to claim 8, characterized in that in step (1), vacuum degassing is performed for 15 to 26 minutes during the smelting process, preferably controlling the endpoint O content to 0.0015 to 0.0035% and the N content to 0.004 to 0.008%.

10. The manufacturing method according to claim 8, characterized in that in step (2), the billet is cast by a small billet continuous casting machine, preferably with argon gas protection during the casting process, the size of the billet obtained by casting is such that the side length is 260 mm or less and the width-to-thickness ratio is 1.06 or less, and more preferably the step of grinding the billet is also included, and after grinding, the defect depth on the surface of the billet is 0.5 mm or less.

11. The manufacturing method according to claim 10, characterized in that the central carbon segregation of the billet is less than 1.

06.

12. The manufacturing method according to claim 8, characterized in that in step (4), the finish rolling mill group inlet temperature is controlled to 930 to 990°C, the diameter reduction constant rolling mill group inlet temperature is controlled to 930 to 990°C, and the discharge temperature is controlled to 920 to 980°C, and preferably the size of the steel wire rod obtained by rolling is Φ11 to 16 mm.

13. The manufacturing method according to claim 8, characterized in that in step (5), the air cooling step is performed on a Stelmore line.

14. The manufacturing method according to claim 13, characterized in that in step (5), the airflow of the F1 to F8 fans of the Stermore fan group is controlled to 80 to 100%, and the airflow of the F9 to F14 fans to 0 to 45%.

15. A galvanized steel wire obtained by drawing a high-strength, economical high-carbon steel wire rod according to any one of claims 1 to 7, galvanizing it, and stabilizing it, wherein the tensile strength of the galvanized steel wire is 2000 MPa or more, and the torsion value is 11 turns or more, preferably the tensile strength of the galvanized steel wire is 2020 MPa or more, and the torsion value is 15 turns or more.

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