A wire rod, its production method and use

Abstract

The present application relates to the technical field of steel material, in particular to a wire rod and a preparation method and application thereof, the wire rod provided by the present application comprises, in percentage by mass, C 0.80-0.84%, Si 0.40-0.55%, Mn 0.65-0.75%, Cr 0.15-0.25%, V 0.03-0.05%, Al 0.01-0.03%, and the balance of iron and inevitable impurities, and the total mass of Si and Cr accounts for 0.65-0.70% of the total mass of the wire rod. Through the limitation of the composition and the amount of the wire rod, the initial strength of the wire rod is improved, the area reduction (≤90%) during wire drawing is reduced, the tensile strength loss and the stress loss at 1% elongation of the steel wire during galvanizing are reduced, and the torsional performance is improved.

Description

Technical Field

[0001] This invention relates to the field of steel materials technology, specifically to a wire rod, its preparation method, and its application. Background Technology

[0002] Galvanized steel strand, made from wire rod through pickling, drawing, galvanizing, and twisting, serves as the skeleton and load-bearing material of power transmission cables. Its strength grade restricts the span and transmission capacity of transmission lines. Currently, power grid construction is gradually developing towards energy conservation and environmental protection, mainly including ultra-high voltage and long-span, high-capacity power transmission. The strength grade of its load-bearing steel core, i.e., galvanized steel strand, is also required to be extremely high, needing to meet the G6A standard of the relevant enterprise standard Q / GDW 11275-2014.

[0003] The tensile strength of steel wire depends on the initial strength and reduction ratio of the wire rod, and can be estimated using the Thurlinkov empirical formula. Galvanizing steel wire is equivalent to a short-term annealing heat treatment at approximately 450℃, resulting in some recovery of work hardening, thus reducing tensile strength and stress. The degree of reduction in tensile strength and stress increases with increasing strength and reduction ratio. For high-strength steel wire, the tensile strength loss is approximately 5-7%, and for G6A steel wire, the strength loss during galvanizing is approximately 130 MPa. The greater the tensile strength loss during galvanizing, the higher the initial strength and the greater the reduction ratio of the wire rod required.

[0004] However, the high-strength steel cores currently used for overhead cables are generally hot-rolled wire rods containing 0.80-0.85% C, with an initial strength of less than 1200 MPa. This requires lead bath treatment of the wire rods or coarsely drawn steel wires. At the same time, numerous research results show that when the area reduction rate of the wire rods or coarsely drawn steel wires exceeds 90%, the torsional properties of the galvanized steel wires will decrease sharply and the fluctuations will intensify.

[0005] The raw material for manufacturing high-strength steel core galvanized steel wire for overhead cables using existing technology is generally H82B hot-rolled wire rod, whose main components are approximately C 0.82%, Si 0.20%, Mn 0.75%, and Cr 0.20%. The initial strength of the wire rod is <1200MPa. When producing galvanized steel wire of G6A strength grade, in order to meet the technical requirements for tensile strength, the area reduction rate must be higher than 90%. On the one hand, there is a phenomenon of tensile strength loss during the galvanizing process and excessive stress loss at 1% elongation. On the other hand, it leads to a reduction in the toughness of the steel wire, and the torsion and other technical indicators cannot meet the standard requirements, which is not conducive to the safe use of overhead cables. Summary of the Invention

[0006] Therefore, the technical problem to be solved by the present invention is to overcome the defects of the prior art where the initial strength of the wire rod is too low, and the tensile strength loss of the steel wire and the stress loss at 1% elongation are large during the galvanizing process, which easily leads to the failure of the tensile strength, stress at 1% elongation, torsion and other technical indicators of the overhead cable steel core to meet the standard requirements at the same time. Thus, the present invention provides a wire rod, its preparation method and application.

[0007] This invention provides a wire rod comprising, by weight percentage: 0.80-0.84% ​​C, 0.40-0.55% Si, 0.65-0.75% Mn, 0.15-0.25% Cr, 0.03-0.05% V, 0.01-0.03% Al, and the balance being iron and unavoidable impurities, wherein the total mass of Si and Cr accounts for 0.65-0.70% of the total mass of the wire rod.

[0008] Preferably, when the wire rod is used to prepare galvanized steel wire, the tensile strength loss rate of the steel wire during the galvanizing process is ≤4%.

[0009] The following details the function of each element in the wire rod of this invention:

[0010] Carbon (C) is the most basic strengthening element in steel. For every 0.01% increase in C content, the strength of the wire rod increases by approximately 10 MPa. However, excessive C can accumulate in the center of the wire rod, even forming a network of cementite, reducing the wire rod's plasticity and causing wire breakage during drawing. In this invention, the C content is selected to be in the range of 0.80-0.84%.

[0011] Si is an important deoxidizer, helping to reduce the oxygen content in steel and decrease inclusions. Simultaneously, Si is a ferrite strengthening element, capable of improving the strength of ferrite through solid solution strengthening and increasing the yield strength ratio. Furthermore, Si enrichment at the ferrite / cementite interface helps prevent cementite dissolution during hot-dip galvanizing, improving the thermal stability of the microstructure and reducing the decrease in tensile strength of the steel wire. However, excessive Si can cause decarburization, promoting cementite graphitization, reducing the surface quality and plasticity of the wire rod, and deteriorating its drawing performance. In this invention, the Si content is selected in the range of 0.40-0.55%.

[0012] In steel, manganese (Mn) is mainly used to increase the strength of the steel, while also increasing the stability of austenite and lowering the phase transformation temperature. Mn can also alter the composition of sulfides and reduce the harmful effects of sulfur (S). However, excessively high Mn content can increase the hardenability of wire rods, making them prone to developing abnormal structures such as martensite. In this invention, the Mn content is controlled at 0.65-0.75%.

[0013] Cr is a carbide-forming element, mainly present in cementite lamellars in steel. Through substitution, it forms alloyed cementite, which helps inhibit the dissolution of cementite during galvanizing of steel wire, reducing the loss of tensile strength. Simultaneously, Cr can improve the stability of austenite, preventing grain growth during hot rolling, and refining the pearlite lamellar spacing at the same cooling rate. Excessive Cr content easily leads to quenched structures, which is detrimental to microstructure control. In this invention, the Cr content is controlled at 0.15-0.25%.

[0014] V is a strong carbide-forming element, which can inhibit the growth of austenite grains during hot rolling. In the early stage of phase transformation, V forms VC particles on the austenite grain boundaries, reducing the C content at the grain boundaries and effectively inhibiting the formation of network cementite. During the phase transformation, V precipitates interspersed with the soft ferrite phase in pearlite, playing a precipitation strengthening role in the wire rod and helping to improve the tensile strength of the wire rod. However, excessive V content can easily lead to quenched structures, which is not conducive to microstructure control. In this invention, the V content is controlled at 0.03-0.05%.

[0015] The addition of Al is primarily for deoxidation, reducing the free oxygen content in the steel. However, excessive Al can easily cause nozzle clogging during the continuous casting of billets, affecting smooth production and deteriorating the surface quality of the cast billets. In this invention, the Al content is controlled within the range of 0.01-0.03%.

[0016] The target application of the wire rod of this invention is galvanized steel wire for G6A strength grade steel core of overhead power cables, with tensile strength ≥1960MPa, stress at 1% elongation ≥1670MPa, and torsion ≥12 times.

[0017] Compared to H82B hot-rolled wire rod, this invention increases the Si content and adds V, based on the following two considerations: First, by increasing the Si content and adding V in the alloy, the initial strength of the wire rod is improved, which can reduce the reduction rate of the wire rod during drawing and improve the plasticity index of the drawn steel wire; Second, by utilizing specific contents of Si and Cr, the dissolution of cementite can be prevented or inhibited during the galvanizing process, thereby improving the thermal stability of the microstructure and reducing the tensile strength and stress loss of the galvanized steel wire.

[0018] The present invention limits the content of Si, Cr, and V, as well as the total content of Si+Cr, based on two considerations: First, excessive Si can cause decarburization, reducing the surface quality and plasticity of the wire rod, worsening drawing performance, reducing drawing efficiency, and increasing energy consumption. Second, excessive Cr and V can easily lead to quenched structures, which is not conducive to the control of wire rod structure and affects the plasticity index of the steel wire.

[0019] This invention provides a method for preparing the above-mentioned wire rod, including pre-desulfurization of raw hot metal, converter smelting, LF refining, continuous casting of large square billets, billet preparation, high-speed wire rod rolling, and Steyrmo controlled cooling process.

[0020] This process is designed specifically for the target product, ensuring product performance and metallurgical quality at a lower cost.

[0021] Preferably, the temperature of the pre-desulfurized molten iron at the station is 1300-1350℃, the sulfur content in the molten iron is controlled to be <0.008% at the end point, and the slag removal rate of the molten iron ladle is greater than 95%.

[0022] And / or, the endpoint control of the converter smelting is C 0.05-0.30%, P≤0.014%, S≤0.010%, and the tapping temperature is 1620-1660℃.

[0023] Preferably, the LF refining includes strong stirring before refining begins, refining, and soft stirring before refining ends;

[0024] And / or, the LF refining process is carried out with bottom blowing argon gas throughout, with a strong stirring bottom blowing argon gas pressure of 4-5 MPa and a strong stirring time of 2-3 min, a refining bottom blowing argon gas pressure of 0.5-5.0 MPa, a refining tapping temperature of 1510-1530℃, and a refining time of 35-50 min, and a soft stirring bottom blowing argon gas pressure of 0.5-0.6 MPa and a soft stirring time of 30-35 min.

[0025] The present invention uses soft stirring and bottom blowing argon to ensure that inclusions float to the surface.

[0026] Preferably, the large billet continuous casting adopts a low superheat casting temperature of 15-25℃ and a continuous casting speed of 0.6-0.7m / min;

[0027] And / or, the billet heating temperature is 1190-1230℃, the heating time is 240-300min, and the tapping temperature is 1040-1170℃.

[0028] Optionally, the dimensions of the large billet for continuous casting are 300mm × 390mm. Low superheat casting is used to prevent inclusions from accumulating and growing larger.

[0029] The billet rolling process involves rolling a large square billet into a small square billet. After the billet rolling process, a grinding wheel is used to grind the surface of the small square billet. The purpose of grinding is to remove defects on the surface of the billet, including cracks, folds, decarburization, etc., so that the surface of the billet is smooth and flat and less prone to surface defects such as folds.

[0030] The two-stage heating rolling process of large billet opening and small billet rolling can ensure the uniformity of composition under large deformation conditions, reduce the degree of center segregation, alleviate solidification segregation, improve material uniformity, and appropriately extend the allowable upper limit of C content.

[0031] Preferably, the heating temperature of the high-speed wire rod rolling is 1140-1180℃, the heating time is 60-90min, the tapping temperature is 1040-1070℃, the inlet temperature of the twistless finishing mill (NTM) is 940-970℃, the wire exiting temperature is 880-900℃, the rolling speed is 60-110m / s, and the rolling diameter is 6.5-9.0mm.

[0032] Preferably, the roller conveyor speed of the Stellmore controlled cooling system is 0.87-1.33 m / s, the fan opening degree is 10-90%, and there are 6-8 fans.

[0033] The roller speed and fan opening can ensure that abnormal structures such as network carbides and martensite do not appear on the wire rod.

[0034] Preferably, the microstructure of the prepared wire rod is as follows: grain size ≥ 7.5, sorbite percentage ≥ 85%, network carbides ≤ 1, and martensite ≤ 1.

[0035] Optionally, the microstructure of the prepared wire rod is required to be: grain size ≥ 8.5, sorbite percentage ≥ 90%, network carbides ≤ 0.5, and martensite ≤ 0.5.

[0036] The present invention also provides an application of the above-described wire rod or the wire rod prepared by the above-described preparation method in the high-strength steel core of overhead cables.

[0037] The technical solution of this invention has the following advantages:

[0038] 1. The wire rod provided by the present invention, by mass percentage, comprises: C 0.80-0.84%, Si 0.40-0.55%, Mn 0.65-0.75%, Cr 0.15-0.25%, V 0.03-0.05%, Al 0.01-0.03%, and the balance being iron and unavoidable impurities, wherein the total mass of Si and Cr accounts for 0.65-0.70% of the total mass of the wire rod. The Si content of 0.40-0.55% and the V content of 0.03-0.05% can, on the one hand, improve the initial tensile strength of the wire rod, reduce the reduction rate during wire rod drawing, and improve the plasticity index of the drawn steel wire; on the other hand, the specific content of Si and Cr can prevent or inhibit the dissolution of cementite during galvanizing, improve the thermal stability of the microstructure, and reduce the degree of strength loss of the galvanized steel wire. Limiting the content of Si, Cr, and V, as well as the total Si+Cr content, is based on two aspects: First, excessive Si can cause decarburization, reducing the surface quality and plasticity of the wire rod, worsening drawing performance, reducing drawing efficiency, and increasing energy consumption. Second, excessive Cr and V can easily lead to quenched structures, which is detrimental to the control of the wire rod's microstructure and affects the plasticity index of the steel wire. This invention, by limiting the composition and dosage of the wire rod, works in synergy to improve the initial strength of the wire rod, reduce the reduction rate during wire rod drawing (≤90%), reduce the tensile strength loss of the steel wire during the galvanizing process and the stress loss at 1% elongation, and improve torsional performance. This invention relates to wire rods used in the manufacture of galvanized steel wire for high-strength steel cores in overhead cables for power systems. During the galvanizing process, the stress loss and strength loss of the steel wire are ≤4% when the elongation is 1%. Its performance fully meets the requirements of G6A galvanized steel wire in the relevant power grid company enterprise standard Q / GDW 11275-2014. Furthermore, the galvanized steel wire has excellent torsional performance, with a torsion of ≥12 times, ensuring the safety of overhead cables. It is suitable for galvanized steel wire for G6A strength grade steel cores in overhead cables for power systems.

[0039] 2. This invention provides a method for preparing wire rod, including pre-desulfurization of raw hot metal, converter smelting, LF refining, continuous casting of large billets, billet preparation, high-speed wire rod rolling, and Stellmore controlled cooling process. This process flow is designed for the target product, does not employ RH vacuum treatment or salt bath treatment, and can reduce production costs. The preparation method provided by this invention ensures product performance and metallurgical quality at a lower cost. Detailed Implementation

[0040] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0041] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0042] Examples and Comparative Examples

[0043] A method for preparing wire rod includes the following steps;

[0044] 1. Wire rod composition design

[0045] By mass percentage, the wire rod comprises: C 0.80-0.84%, Si 0.40-0.55%, Mn 0.65-0.75%, Cr 0.15-0.25%, V 0.03-0.05%, Al 0.01-0.03%, and the balance being iron and unavoidable impurities, with the total mass of Si and Cr accounting for 0.65-0.70% of the total mass of the wire rod.

[0046] 2. Steelmaking process

[0047] Pre-desulfurization of raw molten iron: The temperature of molten iron leaving the station is 1300-1350℃, the sulfur content in the molten iron is controlled at the end point to be <0.008%, and the slag removal rate of the molten iron ladle is greater than 95%;

[0048] Converter smelting: final control C 0.05-0.30%, P≤0.014%, S≤0.010%, tapping temperature 1620-1660℃;

[0049] LF refining: The LF refining includes strong stirring before refining begins, refining, and soft stirring before refining ends;

[0050] The LF refining process uses bottom-blowing argon gas throughout. The strong stirring bottom-blowing argon gas pressure is 4-5 MPa, the strong stirring time is 2-3 min, the refining bottom-blowing argon gas pressure is 0.5-5.0 MPa, the refining tapping temperature is 1510-1530℃, and the refining time is 35-50 min. The soft stirring bottom-blowing argon gas pressure is 0.5-0.6 MPa, and the soft stirring time is 30-35 min.

[0051] Large billet continuous casting: Casting is performed at a low superheat of 15-25℃, with a continuous casting size of 300×390mm. 2 For large square billets, the continuous casting speed is 0.6-0.7 m / min.

[0052] 3. Rolling process

[0053] Billet preparation: heating temperature 1190-1230℃, heating time 240-300min, tapping temperature 1040-1170℃, the cross-sectional dimensions of the billet are 140mm×140mm.

[0054] High-speed wire rod rolling: heating temperature 1140-1180℃, heating time 60-90min, tapping temperature 1040-1070℃, NTM inlet temperature 940-970℃, wire drawing temperature 880-900℃, rolling speed 60-110m / s, rolling diameter 6.5-9.0mm.

[0055] 4. Cooling process

[0056] Stellmore controlled cooling: roller conveyor speed is controlled at 0.87-1.33m / s, fan opening degree is 10-90%, and 6-8 fans are running.

[0057] The specific control of components and parameters in each embodiment and comparative example is as follows:

[0058] Table 1. Main chemical components and preparation diameter of wire rod

[0059]

[0060] Table 2-1 Steelmaking Process

[0061]

[0062] Table 2-2 Steelmaking Process

[0063]

[0064] Table 3 Rolling Process

[0065]

[0066] Table 4 Cooling Process

[0067]

[0068]

[0069] Test Example 1

[0070] The metallographic microstructure and mechanical properties of the wire rods obtained in Examples 1-3 and Comparative Example 1 were determined according to GB / T6394-2017, YB / T169-2014, YB / T4412-2014, YB / T 4411-2014 and GB / T 228.1-2010. The results are shown in Table 5.

[0071] Table 5

[0072]

[0073] Test Example 2

[0074] The wire rods obtained in Examples 1-3 and Comparative Example 1 were subjected to conventional pickling, 9-10 draw passes, zinc plating at 445-460℃, and twisting to obtain galvanized steel strands. The zinc layer quality of the galvanized steel wires all met the Class A requirements of GB / T 3428-2012. The test object in this example is a single-wire galvanized steel wire. Comparative Example 1 of this example obtained G6A-3.12mm galvanized steel wire (i.e., Comparative Example 1-1) and G6A-2.79mm galvanized steel wire (i.e., Comparative Example 1-2) through the same conventional pickling, drawing, and galvanizing processes. The reduction ratio (area reduction rate) was calculated to represent the percentage decrease in cross-sectional area of ​​the wire rod after drawing into steel wire, compared to the original wire rod cross-section. The diameter, number of twists, winding, and mechanical properties (stress and tensile strength at 1% elongation) of the G6A galvanized steel wire corresponding to the examples and comparative examples were measured before and after galvanizing, according to Q / GDW 11275-2014. The test results are shown in Table 6.

[0075] The galvanized steel wire is comprehensively judged based on the test data. The requirements are: tensile strength ≥1960MPa, stress at 1% elongation ≥1670MPa, torsion ≥12 times, and no breakage when wound with a mandrel of 4 times the diameter for 8 turns. If all of these conditions are met, the wire is considered qualified.

[0076] Table 6

[0077]

[0078] Example 1, the present invention Specialized wire rod, Si = 0.48%, Si+Cr = 0.70%, initial strength 1240MPa. Using this wire rod to produce G6A-3.12mm galvanized steel wire, the reduction ratio is 88.6%, strength and stress loss during galvanizing are ≤4.0%, tensile strength after galvanizing is 2030MPa, stress at 1% elongation after galvanizing is 1700MPa, and torsion is tested 16-19 times. All technical indicators meet the standard requirements, and the overall performance is deemed qualified.

[0079] Comparative Example 1-1, Ordinary H82B wire rod, Si = 0.20% < 0.40%, Si + Cr = 0.37% < 0.65%, initial strength 1190 MPa. Using this wire rod to produce G6A-3.12mm galvanized steel wire, the area reduction rate is 88.6%, the tensile strength loss during galvanizing is 6.4%, the tensile strength after galvanizing is 1910 MPa, and the stress at 1% elongation after galvanizing is 1650 MPa, a loss of 4.6%. Both the tensile strength and the stress at 1% elongation do not meet the G6A technical requirements, and the wire rod can withstand 17-22 torsion cycles. Overall performance is deemed unqualified.

[0080] Given that the strength and stress of the finished steel wire in Comparative Example 1-1 do not meet the performance requirements of G6A, the same ordinary steel wire was used... When H82B wire rod is used to produce G6A-2.79mm galvanized steel wire (Comparative Examples 1-2 in Table 6) with an increased reduction rate (i.e., a reduction rate of 90.9% > 90%), the strength loss during the galvanizing process is 6.6%, the tensile strength after galvanizing is 1990MPa, and the stress at 1% elongation after galvanizing is 1670MPa. Both strength and stress meet the G6A technical requirements. However, it can withstand 5-13 torsion cycles, with most cycles falling short of 12. Therefore, its overall performance is deemed unqualified.

[0081] Example 2, the present invention Specialized wire rod, Si = 0.50%, Si+Cr = 0.69%, initial strength 1240MPa. Using this wire rod to produce G6A-2.79mm galvanized steel wire, the reduction in surface area is 88.5%, strength loss during galvanizing is 3.8%, tensile strength after galvanizing is 2020MPa, stress at 1% elongation after galvanizing is 1690MPa, and torsion is tested 16-22 times. All technical indicators meet the standard requirements, and the overall performance is deemed qualified.

[0082] Example 3, the present invention Specialized wire rod, Si = 0.48%, Si+Cr = 0.65%, initial strength 1250MPa. Using this wire rod to produce G6A-2.40mm galvanized steel wire, the area reduction rate is 88.2%, the strength loss during galvanizing is 3.8%, the tensile strength after galvanizing is 2000MPa, the stress at 1% elongation after galvanizing is 1680MPa, and it withstands 20-30 cycles of torsion. All technical indicators meet the standard requirements, and the overall performance is deemed qualified.

[0083] The wire rod of this invention has high initial strength and a reduction rate of ≤90%, which reduces the tensile strength loss and stress loss at 1% elongation of the drawn steel wire during the galvanizing process. This ensures that the tensile strength and stress at 1% elongation of the galvanized steel wire meet the standard requirements, and also has excellent torsional performance, thereby ensuring the safety of overhead cables.

[0084] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A type of wire rod, characterized in that, The wire rod comprises, by mass percentage: C 0.80-0.84%, Si 0.40-0.55%, Mn 0.65-0.75%, Cr 0.15-0.25%, V 0.03-0.05%, Al 0.01-0.03%, and the balance being iron and unavoidable impurities, wherein the total mass of Si and Cr accounts for 0.65-0.70% of the total mass of the wire rod; when the wire rod is used to prepare galvanized steel wire, the tensile strength loss rate of the steel wire during the galvanizing process is ≤4%; the microstructure requirements of the wire rod are: grain size ≥7.5, sorbite percentage ≥85%, network carbides ≤1, and martensite ≤1.

2. The method for preparing the wire rod according to claim 1, characterized in that, This includes the processes of pre-desulfurization of raw molten iron, converter smelting, LF refining, continuous casting of large billets, billet preparation, high-speed wire rod rolling, and Steyrmo controlled cooling.

3. The method for preparing wire rod according to claim 2, characterized in that, The temperature of the pre-desulfurized molten iron at the station is 1300-1350℃, the final control is that the sulfur content in the molten iron is <0.008%, and the slag removal rate of the molten iron ladle is greater than 95%. And / or, the endpoint control of the converter smelting is C 0.05-0.30%, P≤0.014%, S≤0.010%, and the tapping temperature is 1620-1660℃.

4. The method for preparing wire rod according to claim 2 or 3, characterized in that, The large billet continuous casting adopts a low superheat casting temperature of 15-25℃ and a continuous casting speed of 0.6-0.7m / min; And / or, the billet heating temperature is 1190-1230℃, the heating time is 240-300min, and the tapping temperature is 1040-1170℃.

5. The method for preparing wire rod according to claim 2 or 3, characterized in that, The heating temperature for the high-speed wire rod rolling is 1140-1180℃, the heating time is 60-90min, the tapping temperature is 1040-1070℃, the inlet temperature of the twistless finishing mill is 940-970℃, the wire exiting temperature is 880-900℃, the rolling speed is 60-110m / s, and the rolling diameter is 6.5-9.0mm.

6. The method for preparing wire rod according to claim 2 or 3, characterized in that, The Stellmore controlled cooling system has a roller conveyor speed of 0.87-1.33 m / s, a fan opening degree of 10-90%, and 6-8 fans.

7. The application of the wire rod of claim 1 or the wire rod prepared by any one of claims 2-6 in the high-strength steel core of overhead cables.

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