5500mpa grade diamond wire busbar steel wire and production method

Abstract

The application discloses a 5500MPa-grade diamond wire busbar steel wire and a production method thereof. The production method comprises the following steps: making a blank into a rod, and the spinning temperature is 910-930 DEG C; three-section salt bath cooling, the temperature of the first section is 600-620 DEG C, the roller speed is 0.30-0.40 m / s, the temperature of the second section is 580-600 DEG C, the roller speed is 0.25-0.30 m / s, the temperature of the third section is 570-580 DEG C, and the roller speed is 0.40-0.45 m / s; rough drawing, intermediate drawing, fine drawing, electroplated brass, and final drawing are sequentially performed, the soaking temperature after the rough drawing is heated to 940-950 DEG C, and the salt bath temperature is 600-620 DEG C; the soaking temperature after the intermediate drawing is 940-950 DEG C, and the salt bath temperature is 580-590 DEG C; and the soaking temperature after the fine drawing is 950-970 DEG C, and the salt bath temperature is 550-560 DEG C.

Description

Technical Field

[0001] This application belongs to the field of materials preparation technology, and relates to a method for producing 5500MPa grade diamond wire busbar steel wire, and a 5500MPa grade diamond wire busbar steel wire. Background Technology

[0002] Cutting wire, also known as cutting steel wire, is a special type of steel wire used for slicing and is widely used in aerospace, energy, and equipment industries. Diamond wire is a type of cutting wire with high-carbon steel wire as the base material and micron-sized diamond abrasive grains attached to the surface. It is widely used for efficient and precise cutting of solar silicon wafers, sapphire, monocrystalline silicon, and other hard and brittle materials.

[0003] To reduce material loss during the cutting process, diamond wire is continuously being developed towards higher strength and smaller diameter. Reducing the wire diameter helps improve the yield rate and lower processing costs, but this also places more stringent demands on the manufacturing process. Summary of the Invention

[0004] To address the aforementioned technical problems, the purpose of this application is to provide a 5500MPa grade diamond wire busbar steel wire and its production method, which can meet the market's high requirements for the diameter and strength of diamond wire.

[0005] To achieve the above-mentioned objectives, one embodiment of this application provides a method for producing 5500MPa grade diamond wire busbar steel wire, characterized in that the method for producing the steel wire includes:

[0006] The billet is formed into wire rods, and the wire rods are wound at a temperature of 910~930℃. The chemical composition of the billet, by mass percentage, includes: C 0.97~0.99%, Si 0.38~0.42%, Mn 0.65~0.75%, Cr 0.30~0.35%, Ni 0.16~0.25%, and any one of La 0.010~0.030% and Ce 0.005~0.02%; the remainder is Fe and unavoidable impurities, wherein the impurities include Al≤0.001%, Ti≤0.0005%, S≤0.002%, P≤0.003%, O≤0.0010%, and N≤0.0010%.

[0007] The wire rod is subjected to a three-stage salt bath cooling process. The salt bath temperature in the first stage is 600~620℃, and the roller speed of the wire rod is 0.30~0.40m / s. The salt bath temperature in the second stage is 580~600℃, and the roller speed of the wire rod is 0.25~0.30m / s. The salt bath temperature in the third stage is 570~580℃, and the roller speed of the wire rod is 0.40~0.45m / s.

[0008] The wire rod is sequentially subjected to rough drawing, intermediate drawing, fine drawing, brass plating, and final drawing to obtain the steel wire. Each of the rough drawing, intermediate drawing, and fine drawing processes involves heating and a salt bath. The uniform heating temperature after rough drawing is 940-950℃, and the salt bath temperature is 600-620℃. The uniform heating temperature after intermediate drawing is 940-950℃, and the salt bath temperature is 580-590℃. The uniform heating temperature after fine drawing is 950-970℃, and the salt bath temperature is 550-560℃.

[0009] In one embodiment, during the three-stage salt bath cooling process of the wire rod, the wire rod is air-cooled after the first and second salt baths, with the air-cooling temperature being 60~100℃ and the cooling time being 8~12s.

[0010] In one embodiment, the salt bath time after rough drawing is 8-10 seconds, the salt bath time after intermediate drawing is 6-9 seconds, and the salt bath time after fine drawing is 4-8 seconds.

[0011] In one embodiment, the heating after rough drawing includes a preheating section, a heating section, and a homogenizing section performed sequentially, with the temperature of the preheating section being 950~960°C and the temperature of the heating section being 980~990°C; the heating after intermediate drawing includes a heating section and a homogenizing section performed sequentially, with the temperature of the heating section being 930~940°C; and the heating after fine drawing includes a heating section and a homogenizing section performed sequentially, with the temperature of the heating section being 940~950°C.

[0012] In one embodiment, the diameter of the wire rod is 4.5~5.0 mm and the tensile strength is 1280~1350 MPa; the diameter of the intermediate wire obtained after rough drawing is 2.2~2.3 mm and the tensile strength is 2000~2100 MPa; the diameter of the intermediate wire obtained after intermediate drawing is 1.1~1.3 mm and the tensile strength is 1800~1850 MPa; and the diameter of the intermediate wire obtained after fine drawing is 0.4~0.5 mm and the tensile strength is 2420~2480 MPa.

[0013] In one embodiment, the rough drawing pass has a reduction rate of 9-11% and a drawing speed of 6-8 m / s; the intermediate drawing pass has a reduction rate of 10-12%; and the finish drawing pass has a reduction rate of 8-9%.

[0014] In one embodiment, during the electroplating of brass, the current density ratio of copper plating to zinc plating is (3.8~4.2):1, and the total thickness of the coating formed by electroplating brass is 75~80μm.

[0015] In one embodiment, the process of forming the billet into wire rod includes:

[0016] The billet is used as an electrode rod for electroslag remelting to obtain a remelted ingot;

[0017] The remelted ingot is slabred or forged into a steel billet, and the steel billet is then ground.

[0018] The steel billet is rolled into wire rod.

[0019] In one embodiment, during electroslag remelting, the billet is remelted, refined, and resolidified under a protective atmosphere to form a remelted ingot. The melting rate of the electrode rod is 55~58 kg / h. After remelting, the remelted ingot is cooled, and the cooling rate is controlled to be ≤50℃ / h.

[0020] To achieve the above-mentioned application objectives, one embodiment of this application provides a 5500MPa grade diamond wire busbar steel wire, which is prepared using the production method of the 5500MPa grade diamond wire busbar steel wire described above.

[0021] In one embodiment, the steel wire has a diameter of 28~34μm, a tensile strength of ≥5500MPa, an elongation of ≥3.8%, a torsion count of ≥130 times, and a length of ≥450km for a single steel wire.

[0022] Compared with the prior art, the beneficial effects of this application include:

[0023] (1) Chemical composition design scheme: Through the synergistic effect of high carbon content and multi-element alloying elements, on the one hand, a full sorbite structure can be obtained and the strength advantage of the sorbite structure can be fully utilized. On the other hand, through the synergistic solid solution strengthening of the ferrite phase by Si and Ni, and the synergistic stabilizing strengthening of the cementite phase by Mn and Cr, the strength of the steel wire can be significantly improved without damaging the plasticity. The addition of trace rare earth elements can effectively purify the molten steel and further improve the processing performance of the steel. Finally, a beneficial match between high strength and high plasticity of the finished steel wire can be achieved, so that the strength of the steel wire can reach 5500MPa and above, and thus it can be used as the main wire of 5500MPa grade diamond wire.

[0024] (2) By designing the chemical composition scheme and combining the three-stage salt bath cooling and salt bath temperature control of the wire rod, the phase transformation process and salt bath temperature were precisely matched, thereby realizing the phase transformation path of high-density nucleation, full diffusion transformation and rapid phase transformation. This resulted in the wire rod having a uniform sorbitic structure and smaller lamellar spacing, which effectively suppressed the generation of abnormal structures such as grain boundary cementite and greatly reduced the wire breakage rate. This laid the foundation for the preparation of high-strength steel wire. Furthermore, by controlling the heating and salt bath treatment during the wire drawing process, the brittleness caused by work hardening caused by drawing was eliminated, and the steel wire was endowed with better structure and plasticity. This achieved a balance between ultra-high strength and excellent plasticity and toughness, thus enabling the preparation of ultra-high strength steel wire with a diameter of 28~34μm and a tensile strength ≥5500MPa. The number of twists of the steel wire is ≥130 times and the length of a single steel wire is ≥450km. It not only has excellent comprehensive performance, but also enables stable industrial production. Detailed Implementation

[0025] The technical solution of the present invention will be further described below with reference to specific embodiments, but the scope of protection is not limited to the description.

[0026] This application provides a 5500MPa grade diamond wire busbar steel wire and its production method.

[0027] One embodiment of this application provides a 5500MPa grade diamond wire busbar steel wire.

[0028] The chemical composition of the 5500MPa grade diamond wire busbar steel wire, by mass percentage, includes: C 0.97~0.99%, Si 0.38~0.42%, Mn 0.65~0.75%, Cr 0.30~0.35%, Ni 0.16~0.25%, and any one of La 0.010~0.030% and Ce 0.005~0.02%; the remainder is Fe and unavoidable impurities, including Al≤0.001%, Ti≤0.0005%, S≤0.002%, P≤0.003%, O≤0.0010%, and N≤0.0010%.

[0029] Specifically, the role of each element and its content in the chemical composition of steel wire is explained below.

[0030] Carbon (C): As a core strengthening element, it significantly improves the strength of steel wire through work hardening. This application controls the C content to 0.97%~0.99%, which can fully utilize the strengthening effect of carbon and effectively avoid the formation of proeutectoid cementite at grain boundaries when the carbon content exceeds 1.0%, thereby eliminating the risk of crack initiation and wire breakage caused by it.

[0031] Si, as a ferrite strengthening element, is dissolved in pearlite and ferrite lamellars, providing additional strengthening on the basis of carbon strengthening. In this application, the Si content is controlled at 0.38~0.42%, which can obtain sufficient solid solution strengthening effect while avoiding the problem that excessive silicon content promotes carbon atom diffusion and weakens the strength growth.

[0032] Mn, as a cementite strengthening element, can not only improve the strength of cementite but also refine the pearlite lamellars and grains, while delaying the dissolution of cementite during high-strain drawing, thus enhancing the final strengthening effect. In this application, the Mn content is controlled at 0.65%~0.75%, achieving a better balance between refining the microstructure, improving strength, and ensuring the controllability of the microstructure.

[0033] Cr: Improves wire rod strength by refining the pearlite structure and reducing the interlamellar spacing. In this application, the Cr content is controlled at 0.30~0.35%, which not only achieves a significant pearlite refinement and strengthening effect, but also avoids the formation of non-target structures such as bainite or martensite, thus reducing adverse effects on processing performance.

[0034] Ni (Ni): In steel, it is dissolved atomically in the ferrite lattice, causing lattice distortion and thus increasing the strength and hardness of the ferrite phase. This strengthening effect is further transferred to the pearlite clusters in high-carbon steel, enhancing its overall strength. Although the strengthening effect of nickel is not as significant as that of carbon, its advantage lies in its ability to improve strength without significantly compromising the plasticity and toughness of high-carbon steel. If the nickel content is too low, the strengthening effect is not obvious; while an excessively high nickel content can lead to overly stable supercooled austenite, making microstructure control difficult. This application controls the nickel content within the range of 0.16~0.25%, which is beneficial for achieving a synergistic improvement in strength and plasticity while maintaining stable microstructure properties.

[0035] Rare earth elements La and Ce can modify inclusions, refine microstructure, and strengthen interfaces. Rare earth elements preferentially combine with oxygen and sulfur in molten steel, thereby improving the morphology and type of inclusions and enhancing their ability to deform in tandem with the matrix. Rare earth elements segregate at grain boundaries and phase boundaries, reducing interfacial energy and strengthening grain boundary bonding, thus inhibiting crack propagation along grain boundaries. In this application, adding 0.010~0.030% La or 0.005~0.02% Ce can fully utilize the beneficial effects of La and Ce. However, if the La content exceeds 0.03% or the Ce content exceeds 0.02%, oxide aggregates are easily formed in high-carbon steel, resulting in irregular morphologies and reducing their beneficial effects.

[0036] Impurity elements: By limiting the upper limit of Al and Ti content, the formation of hard inclusions such as Al2O3 and titanium carbonitride can be avoided; S, P, O and N are controlled at extremely low levels to minimize their adverse effects on the toughness and processing performance of steel wire.

[0037] Thus, the chemical composition design of this embodiment, through the synergistic effect of high carbon content and multiple alloying elements, on the one hand, can obtain a full sorbitic structure and give full play to the strength advantages of the sorbitic structure; on the other hand, through the synergistic solid solution strengthening of the ferrite phase by Si and Ni, and the synergistic stabilizing strengthening of the cementite phase by Mn and Cr, the strength of the steel wire is significantly improved without compromising plasticity. The addition of trace rare earth elements can effectively purify the molten steel and further improve the processing performance of the steel. Ultimately, a beneficial match between high strength and high plasticity is achieved in the finished steel wire, so that the strength of the steel wire can reach 5500MPa and above, and thus it can be used as the main wire of 5500MPa grade diamond wire.

[0038] In one embodiment, the diameter of the 5500MPa grade diamond wire busbar steel wire is 28~34μm. The mechanical properties of the steel wire are tested according to GB / T228.1 "Metallic materials, tensile testing—Part 1: Test methods at room temperature," and the number of torsion cycles is tested according to YB / T 6105 "Diamond wire busbar steel wire." The results show that the 5500MPa grade diamond wire busbar steel wire has a tensile strength ≥5500MPa, elongation ≥3.8%, and a number of torsion cycles ≥130. The length of a single wire is ≥450km, meaning that without welding, the length of a single wire can reach 450km or more, far exceeding market demands for good drawing performance, low wire breakage rate, and high-strength steel wire.

[0039] One embodiment of this application provides a method for producing 5500MPa grade diamond wire busbar steel wire as described above. In this embodiment, the method for producing the steel wire includes:

[0040] The billet is processed into wire rod. The wire rod is wound at a temperature of 910~930℃. The chemical composition of the billet is consistent with that of the final 5500MPa grade diamond wire, specifically, the chemical composition of the billet, by mass percentage, includes: C 0.97~0.99%, Si 0.38~0.42%, Mn 0.65~0.75%, Cr 0.30~0.35%, Ni 0.16~0.25%, and either La 0.010~0.030% or Ce 0.005~0.02%; the remainder is Fe and unavoidable impurities, including Al≤0.001%, Ti≤0.0005%, S≤0.002%, P≤0.003%, O≤0.0010%, and N≤0.0010%.

[0041] The wire rod is subjected to a three-stage salt bath cooling process. In the first stage, the salt bath temperature is 600-620℃, and the wire rod roller speed is 0.30-0.40 m / s. In the second stage, the salt bath temperature is 580-600℃, and the wire rod roller speed is 0.25-0.30 m / s. In the third stage, the salt bath temperature is 570-580℃, and the wire rod roller speed is 0.40-0.45 m / s. During the first salt bath, the wire rod is at a high temperature after being spun out. The high cooling capacity of the molten salt allows the wire rod to quickly pass through the high-temperature austenite region, preventing the formation of coarse pearlite. At the same time, it forms a large number of uniform nucleation sites within the austenite, providing a microstructure basis for subsequent phase transformation. The temperature control of the second salt bath provides a relatively stable temperature environment for the supercooled austenite phase transformation, allowing it to fully and uniformly transform into sorbite. The diffusion phase transformation occurs fully within the "nose tip temperature" range of sorbite transformation, resulting in a sorbite microstructure with small lamellar spacing. The temperature of the third salt bath is even lower, allowing for further phase transformation and ensuring that no untransformed austenite remains, thus improving the microstructure uniformity of the wire rod.

[0042] The wire rod is sequentially subjected to rough drawing, intermediate drawing, finish drawing, brass plating, and final drawing to obtain the steel wire. Each stage of rough drawing, intermediate drawing, and finish drawing is followed by heating and salt bath treatment. The homogenization temperature after rough drawing is 940-950℃, and the salt bath temperature is 600-620℃; the homogenization temperature after intermediate drawing is 940-950℃, and the salt bath temperature is 580-590℃; the homogenization temperature after finish drawing is 950-970℃, and the salt bath temperature is 550-560℃. As the wire rod is drawn, its diameter gradually decreases, and its internal deformation energy gradually increases. By intermittently heating and salt bath treatment during the wire rod drawing process, the work hardening caused by drawing is restored to a sorbite structure suitable for drawing, thereby eliminating the brittleness caused by work hardening.

[0043] Therefore, by designing a chemical composition scheme and combining it with three-stage salt bath cooling and temperature control of the wire rod, a precise match between the phase transformation process and the salt bath temperature was achieved. This enabled a phase transformation path that achieves high-density nucleation, full diffusion transformation, and rapid phase transformation, resulting in a uniform sorbitic structure in the wire rod with smaller lamellar spacing. This effectively suppressed the formation of abnormal structures such as grain boundary cementite, significantly reducing the wire breakage rate and laying the foundation for the preparation of high-strength steel wire. Furthermore, by controlling the heating and salt bath treatment during the wire drawing process, the brittleness caused by work hardening during drawing was eliminated, and the steel wire was endowed with better structure and plasticity. A balance between ultra-high strength and excellent ductility and toughness was achieved, enabling the preparation of ultra-high strength steel wire with a diameter of 28~34μm and a tensile strength ≥5500MPa. The wire can withstand ≥130 twists and the length of a single wire can reach ≥450km. This not only demonstrates excellent comprehensive performance but also enables stable industrial production.

[0044] For example, by heating and salt bath treatment after rough drawing, the tensile strength of the intermediate wire after rough drawing can be controlled to be 1400~1450MPa, the area reduction rate ≥40%, and the grain size to be 7~7.5μm; by heating and salt bath treatment after intermediate drawing, the tensile strength of the intermediate wire after intermediate drawing can be controlled to be 1460~1480MPa, and the area reduction rate ≥45%; by heating and salt bath treatment after fine drawing, the tensile strength of the intermediate wire after fine drawing can be further increased to 1520~1540MPa, with an area reduction rate ≥43% and a grain size to be 8.2~8.8μm.

[0045] In one embodiment, during the three-stage salt bath cooling process for the wire rod, the wire rod is air-cooled after the first and second salt baths, with the air-cooling temperature at 60~100°C and the cooling time at 8~12 seconds. This not only removes the molten salt adhering to the surface of the wire rod but also prevents the temperature from dropping too rapidly.

[0046] The salt bath time after rough drawing is 8-10 s, after intermediate drawing it is 6-9 s, and after finish drawing it is 4-8 s. The intermediate wire after rough drawing has a larger diameter and a larger heat capacity. Controlling the salt bath time to 8-10 s ensures that the intermediate wire undergoes sufficient phase transformation to sorbite, avoiding uneven microstructure caused by differences in cooling rates between the core and surface. After intermediate and finish drawing, the wire diameter becomes smaller and the heat capacity decreases. Especially after finish drawing, controlling the salt bath time allows for precise control of the sorbite lamellar spacing, adapting to subsequent large strain drawing and meeting the initial microstructure conditions for drawing 5500 MPa steel wire.

[0047] The heating process after rough drawing includes a preheating section, a heating section, and a homogenizing section, performed sequentially. The temperature of the preheating section is 950~960℃, and the temperature of the heating section is 980~990℃. The heating process after intermediate drawing includes a heating section and a homogenizing section, performed sequentially. The temperature of the heating section is 930~940℃. The heating process after fine drawing includes a heating section and a homogenizing section, performed sequentially. The temperature of the heating section is 940~950℃.

[0048] The diameter of the intermediate wire after rough drawing is still relatively large. By employing a three-stage heating process—preheating, heating, and soaking—the temperature difference between the core and surface of the intermediate wire can be significantly reduced. A gradual heating process avoids thermal stress cracking, while the soaking stage ensures homogenization of the microstructure and composition, safely and thoroughly eliminating work hardening caused by rough drawing. After intermediate drawing, the diameter of the intermediate wire decreases further. A two-stage heating process is sufficient to achieve stable temperatures for both the surface and core. Using a slightly lower temperature allows the microstructure of the intermediate wire to recover austenitization, which is then used in subsequent salt bath treatment to form a sorbite microstructure, restoring plasticity for subsequent drawing. After finish drawing, the diameter of the intermediate wire is even smaller, requiring only a two-stage heating process. Heating to a slightly higher austenitization temperature creates a grain size and lamellar spacing suitable for the next stage of large deformation. Thus, by scientifically setting the heating process and temperature after rough drawing, intermediate drawing, and finish drawing, the microstructure of the intermediate wire after each stage can be controlled, laying a good microstructure foundation for subsequent processing.

[0049] The aforementioned heat equalization temperature is the temperature of the heat equalization zone.

[0050] In one embodiment, the wire rod has a diameter of 4.5~5.0 mm and a tensile strength of 1280~1350 MPa. This allows it to be used to draw ultra-high strength steel wires with a diameter of 28~34 μm and a tensile strength ≥5500 MPa, for use as the main wire of diamond wire.

[0051] In one embodiment, the diameter of the intermediate wire obtained after rough drawing is controlled to be 2.2~2.3 mm and the tensile strength is controlled to be 2000~2100 MPa; the diameter of the intermediate wire obtained after intermediate drawing is controlled to be 1.1~1.3 mm and the tensile strength is controlled to be 1800~1850 MPa; and the diameter of the intermediate wire obtained after fine drawing is controlled to be 0.4~0.5 mm and the tensile strength is controlled to be 2420~2480 MPa. By controlling the diameter of the intermediate wire obtained after rough drawing, intermediate drawing, and fine drawing, it is beneficial to further draw and prepare steel wires with finer diameters. By controlling the tensile strength of the intermediate wire obtained after rough drawing, intermediate drawing, and fine drawing, on the one hand, it can prevent the tensile strength of the intermediate wire from being too high during the drawing process, which would lead to defects in the core, and on the other hand, it can prevent the tensile strength of the intermediate wire from being too low during the drawing process, which would lead to the internal deformation of the intermediate wire not reaching a uniform deformation structure, which would be detrimental to subsequent heating and salt bath heat treatment. On the other hand, by monitoring the diameter and tensile strength of the intermediate wire at these key nodes after rough drawing, intermediate drawing, and fine drawing, the specifications and tensile strength of the final finished steel wire can be ensured to meet the requirements.

[0052] Specifically, by controlling the reduction rate of the rough drawing pass to be 9-11% and the drawing speed to be 6-8 m / s, the diameter of the intermediate wire after rough drawing can be 2.2-2.3 mm and the tensile strength can be 2000-2100 MPa, based on the tensile strength of the aforementioned wire rod; the reduction rate of the intermediate drawing pass to be 10-12% can be used to obtain an intermediate wire diameter of 1.1-1.3 mm and a tensile strength of 1800-1850 MPa; and the reduction rate of the finish drawing pass to be 8-9% can be used to obtain an intermediate wire diameter of 0.4-0.5 mm and a tensile strength of 2420-2480 MPa.

[0053] During the drawing process of high carbon steel wire rod, internal damage increases and accumulates as the deformation increases. By controlling the reduction rate of each pass in the roughing, intermediate drawing and finishing processes, that is, controlling the deformation of each pass, damage during the drawing process can be reduced, ensuring uniform and refined microstructure and reducing wire breakage rate.

[0054] In one embodiment, during brass electroplating, the current density ratio of copper plating to zinc plating is controlled at (3.8~4.2):1, and the total thickness of the brass plating layer is 75~80μm. The formation of a brass structure through copper and zinc plating can alleviate internal stress in the plating layer to a certain extent, improving its toughness and uniformity. By controlling the structure and thickness of the plating layer, excellent conductivity can be ensured, providing a strong bond between the diamond particles and the steel substrate during subsequent diamond wire fabrication. Furthermore, this thickness range of plating provides lubrication for subsequent final drawing, leaving a 3~6μm plating layer on the surface of the finished steel wire. After final drawing, the plating layer ensures that the diamond particles are firmly and uniformly bonded to the surface of the steel wire.

[0055] Specifically, the final drawing process uses a water tank to further draw the intermediate wire after electroplating brass into finished steel wires with a diameter of 0.028~0.034mm.

[0056] This application also provides a wire rod and a method for producing the same. This wire rod can be used to draw the 5500MPa grade diamond wire rod.

[0057] One embodiment of this application provides a wire rod. This wire rod can be used to draw and prepare the 5500MPa grade diamond wire main conductor steel wire, and further prepare 5500MPa grade diamond wire. Of course, it is not limited to this; for example, it can also be used to draw other steel wire products according to the actual production needs of the enterprise.

[0058] The chemical composition of the wire rod, by mass percentage, includes: C 0.97~0.99%, Si 0.38~0.42%, Mn 0.65~0.75%, Cr 0.30~0.35%, Ni 0.16~0.25%, and any one of La 0.010~0.030% and Ce 0.005~0.02%; the remainder is Fe and unavoidable impurities, wherein the impurities include Al≤0.001%, Ti≤0.0005%, S≤0.002%, P≤0.003%, O≤0.0010%, and N≤0.0010%.

[0059] The chemical composition of the wire rod is consistent with that of the steel wire obtained by further drawing. The role of each element and its content is as described above and will not be repeated here.

[0060] Through this chemical composition design scheme, the advantages of pearlitic structure can be fully utilized by the synergistic effect of high carbon content and multiple alloying elements, laying the foundation for the high strength of wire rod, and thus enabling the preparation of 5500MPa grade diamond wire rod.

[0061] In one embodiment, the diameter of the wire rod is 4.5~5.0mm, which can meet the requirements for drawing and preparing steel wire.

[0062] Referring to GB / T 228.1 "Metallic materials, tensile testing—Part 1: Test at room temperature," the mechanical properties of the wire rod were tested, and the tensile strength was found to be 1280~1350 MPa, with a reduction of area of ​​36~45%. This allows it to be used as a base material for further drawing into steel wire, laying the foundation for producing steel wire with a tensile strength of 5500 MPa and above. Furthermore, the wire rod exhibits excellent drawing performance, which can reduce the wire breakage rate during the drawing process.

[0063] The inclusion composition was analyzed by scanning electron microscopy (SEM) using energy dispersive spectroscopy (EDS), and the number of inclusions per unit area was statistically analyzed. The inclusions in the wire rod were determined to be SiO2-MnO-Al2O3 composite inclusions, with the Al2O3 content <10%. Microhardness (HV) testing was performed according to ISO 6507-1 "Metallic materials - Vickers hardness test", and the microhardness of the inclusions in the wire rod was found to be <1200 HV. The number density of inclusions per unit area was determined to be ≤5 inclusions / mm². 2 The size of the inclusions within 1 mm of the wire rod surface is ≤3 μm.

[0064] Based on the composition, hardness, quantity, and size of inclusions in this wire rod, the internal quality and cleanliness of the wire rod can be significantly improved. The lower inclusion density and smaller inclusion size directly improve the material uniformity of the wire rod, laying a solid foundation for subsequent drawing to ultra-fine diameters and withstanding extremely high strengths. The type and hardness of these inclusions ensure that, while maintaining the inclusions as ductile inclusions, the hot rolling process can deform in coordination with the steel matrix, further improving the deep processing performance of the wire rod.

[0065] The wire rod was tested in accordance with ISO 16120-1 "Non-alloy steel wire rod for wire making - Part 1: General requirements", and the grain boundary carbide level was found to be ≤ B.

[0066] The wire rod was tested according to YB / T 4411 "Evaluation Method of Network Cementite in High Carbon Steel Wire Rod", and the martensite level in the wire rod was found to be 0.

[0067] In summary, the wire rod of this embodiment has high purity, uniform structure, high mechanical properties, and good drawing performance, which can meet the requirements for the preparation of diamond wire. Moreover, the wire rod of this application can be used to produce diamond wire rods with a diameter of 28~34μm, tensile strength ≥5500MPa, torsion cycles ≥130 times, and elongation ≥3.8%. Furthermore, the length of a single wire can be ≥450km without welding, which far meets the market demand for good drawing performance, low wire breakage rate, and high-strength steel wire.

[0068] This application provides a method for producing the aforementioned wire rod according to one embodiment. In this embodiment, a billet is formed into wire rod. Specifically, it includes:

[0069] The billet is used as an electrode rod for electroslag remelting to obtain a remelted ingot;

[0070] The remelted ingot is slabred or forged into a steel billet, and the steel billet is then ground.

[0071] The steel billet is rolled into wire rod.

[0072] Therefore, by electroslag remelting the billet into molten steel and then solidifying it again to form a remelted ingot, further refining and sequential crystallization of the metal can be achieved, inclusions can be deeply removed and secondary modified, and segregation during solidification can be significantly improved. This allows control over the morphology and quantity of inclusions, as well as regulation of the wire rod structure, thereby achieving a high degree of homogenization of the wire rod structure and properties.

[0073] In one embodiment, during electroslag remelting, the billet is remelted, refined, and resolidified under a protective atmosphere to form a remelted ingot. The melting rate of the electrode rod is 55~58 kg / h. After remelting, the remelted ingot is cooled, and the cooling rate is controlled to be ≤50℃ / h.

[0074] In one embodiment, the billet is a small square billet. The small square billet is sequentially subjected to electroslag remelting, billet forming and grinding, and high-speed wire rolling to prepare the wire rod.

[0075] The electroslag remelting process involves using the small billet as an electrode rod for electroslag remelting to obtain a remelted ingot.

[0076] The billet preparation and grinding process involves either cutting or forging the remelted ingot into a billet and grinding the billet.

[0077] The high-speed wire rolling process refers to rolling steel billets into wire rods using high-speed wire rolling.

[0078] In one embodiment, the small billet is prepared through converter smelting, LF refining, and continuous casting processes.

[0079] The specific implementation methods for each process are described below.

[0080] (1) Converter smelting process

[0081] Raw materials are added to the converter, and oxygen is blown throughout the process to smelt steel. Oxygen blowing refers to injecting oxygen onto the surface of the molten steel. Specifically, oxygen blowing is performed using an oxygen lance positioned above the molten steel surface.

[0082] In one embodiment, the smelting raw materials include scrap steel and pre-desulfurized molten iron. The scrap steel accounts for 10-18% of the smelting raw materials by mass. Preferably, the scrap steel is clean scrap steel with low impurity element content. The chemical composition of the clean scrap steel, by mass percentage, includes: Cr < 0.05%, Ni < 0.05%, Cu < 0.02%, Mo < 0.01%, Ti < 0.05%, Nb < 0.005%, V < 0.05%, and S ≤ 0.010%. The pre-desulfurized molten iron has an S content ≤ 0.002%, and the charging temperature of the pre-desulfurized molten iron when added to the converter is 1350-1400℃.

[0083] In one embodiment, the chemical composition of the molten iron before pre-desulfurization, by mass percentage, includes: Si 0.5~0.7%, P≤0.1%, S≤0.035%, Ti≤0.04%, and the slag removal rate of the molten iron before pre-desulfurization is ≥99%. This ensures that the molten steel has fewer harmful elements and higher purity from the beginning of steelmaking, which is beneficial for the precise control of inclusions in the subsequent process.

[0084] In one embodiment, after adding smelting raw materials to the converter, oxygen is blown to raise the temperature, and 15-25 kg / t of lime and 6-8 kg / t of dolomite are added to form slag, controlling the slag basicity to 1.5-1.6. This can accelerate silicon removal and reduce splashing during the blowing process.

[0085] It is understandable that the "t" in "kg / t" here refers to the mass of molten steel. For example, 15~25 kg / t of lime and 6~8 kg / t of dolomite means that 15~25 kg of lime and 6~8 kg of dolomite are added per ton of molten steel. The total amount of lime and dolomite added is calculated by multiplying this corresponding value by the tonnage of molten steel. The same applies below, and will not be elaborated further.

[0086] When the molten pool temperature rises to 1350~1420℃ and the FeO content in the slag is 13~14%, 80~85% of the slag is poured out. By controlling the molten pool temperature, the situation where it is too low to easily pour out the slag can be avoided, and the situation where the temperature is too high can be avoided as it is not conducive to the reaction between lime and phosphorus, thus the P content can be controlled to ≤0.01%. The slag is poured out by tilting the converter.

[0087] Afterwards, a slag adjustment is performed, adding 16-20 kg / t of lime and 2-3 kg / t of Fe oxides to control the slag basicity at 2.6-3.0, the molten pool temperature at 1650-1670℃, and the FeO content in the slag at 17-19%. This can control the P content to ≤0.002%.

[0088] The Fe oxides include at least one of FeO, Fe2O3, and Fe3O4. Specifically, the oxide scale removed during steel production can be used, such as the oxide scale removed from the surface of the small billet after casting in the continuous casting process of this application. Since the oxide scale is entirely composed of Fe oxides, including but not limited to FeO, Fe2O3, and Fe3O4, the oxide scale can be recycled, saving costs.

[0089] A second slag adjustment is then performed, adding 10-20 kg / t of lime and 5-6 kg / t of dolomite to control the slag basicity at 4.0-5.0, magnesium oxide content at 9-12%, and FeO content at 23-28%. Steel is then tapped at 1640-1660℃, with 10% of the steel remaining at the tapping point. This avoids slag spillage during tapping, preventing phosphorus reversion.

[0090] In one embodiment, during the oxygen blowing and heating stage, the height of the oxygen lance above the liquid surface is controlled to be 1.12~1.30m, and the oxygen flow rate is 17500~18500m³ / h. 3 The oxygen flow rate is maintained at 15800-16800 m³ / h to ensure thorough mixing of the molten pool. During the initial slag conditioning stage, the oxygen lance is positioned 1.8-1.9 m above the liquid surface, and the oxygen flow rate is 15800-16800 m³ / h. 3 / h. During the secondary slag conditioning stage, the oxygen lance is controlled to be 1.6~1.8m above the liquid surface, and the oxygen flow rate is 15800~16800m³ / h. 3 / h. By coordinating the control of oxygen lance position and oxygen flow rate, the system optimizes the thermodynamic and kinetic conditions of the metallurgical reaction, laying the initial metallurgical foundation for achieving ultra-high clean smelting. The oxygen blowing heating stage uses a lower oxygen lance position and a high flow rate to form a high-intensity impact jet, ensuring rapid and complete decarburization and dephosphorization reactions, reducing the burden on subsequent refining processes. The primary slag conditioning stage uses a higher oxygen lance position and a slightly lower flow rate to avoid localized over-oxidation and temperature unevenness caused by high-intensity oxygen blowing, resulting in a stable and uniform temperature rise in the molten pool, facilitating subsequent precise operations. The oxygen lance position and flow rate in the secondary slag conditioning stage allow for final fine-tuning of the slag's foaming degree, oxidizing properties, and fluidity, ensuring the slag has a better ability to adsorb inclusions, reducing metal splashing, and improving yield.

[0091] In one embodiment, a low-phosphorus alloy is added to the molten steel when one-third of the steel has been tapped for alloying. This not only buffers the impact and temperature drop during alloy addition but also utilizes the strong impact of the subsequent steel flow to stir the steel, accelerating alloy melting and ensuring uniform composition, thus preventing alloy settling or agglomeration. The phosphorus content in the low-phosphorus alloy is ≤0.005%. When half the steel has been tapped, 2.8~3.2 kg / t of lime is added to the molten steel for slag formation. At this point, the temperature of the molten steel promotes rapid pre-melting of the lime, and the newly formed slag layer can adsorb early inclusions floating in the molten steel, adjusting the slag composition.

[0092] (2) LF refining process

[0093] The molten steel obtained from the converter smelting process is sent to the LF furnace for refining in order to fine-tune the chemical composition of the molten steel, deoxidize and desulfurize it, and control the modification of inclusions.

[0094] In one embodiment, after the ladle arrives at the station, it is heated by electricity, and then alloying is performed to fine-tune the chemical composition of the molten steel according to the target composition. Next, lime and calcium carbide are added for white slag treatment, controlling the chemical composition of the white slag by mass percentage as follows: CaO 70-85%, Al₂O₃ 10-20%, SiO₂ 5-8%, T·Fe+MnO ≤1%, and the basicity of the white slag is 13-15. The white slag is then removed. Next, synthetic slag and lime are added for slag formation, controlling the slag basicity to 0.8-0.9, the melting point of inclusions to 1160-1200°C, and the tapping temperature to 1547-1553°C.

[0095] When treating white slag, the amount of lime added is 5~8 kg / t, the amount of calcium carbide added is 1.3~1.4 kg / t, and the treatment time for white slag is 4~8 min.

[0096] The white slag is removed using a slag removal machine, with a slag removal rate controlled at ≥98%, thereby ensuring that the sulfur content in the molten steel is ≤0.0018%.

[0097] The LF refining process uses argon gas for bottom blowing throughout the ladle process. During the heating stage, the flow rate of bottom blowing argon gas is 300~350 NL / min, and during the alloying stage, the flow rate of bottom blowing argon gas is 380~450 NL / min.

[0098] When adding synthetic slag and lime for slag formation, the amount of synthetic slag added is 7.2~8.6 kg / t, and the amount of lime added is 0.2~0.3 kg / t. The chemical composition of the synthetic slag, by mass percentage, includes: CaO 28~33%, SiO2 35~40%, Al2O3 ≤2%, MgO 8~10%, CaF 27~12%, with the remainder being FeO. This allows for control over the slag basicity and the melting point of inclusions.

[0099] (3) Continuous casting process

[0100] The molten steel from the LF refining process is fed into a continuous casting machine and cast into small square billets. The cross-sectional dimensions of the small square billets are (120~140)mm × (120~140)mm.

[0101] The superheat during steel casting should be controlled at 17~23℃. By controlling the superheat during steel casting, the solute in the core of the small billet can diffuse fully, reducing center segregation of the small billet.

[0102] In one embodiment, after casting to form a small square billet, the oxide scale on the surface of the small square billet is removed, thereby reducing the impact of the oxide scale on subsequent electroslag remelting.

[0103] Specifically, shot blasting can be used to remove the oxide scale from the surface of the small billet. The shot blasting machine uses shot of different particle sizes for shot blasting. The shot speed during shot blasting is 9~10m / s, and the moving speed of the small billet in the shot blasting machine is 5~7m / min. This can improve the oxide scale removal effect.

[0104] In one embodiment, the shot blasting machine uses two different particle sizes for shot blasting: 1.5~2.5mm and 3.2~4mm, respectively. By using two particle sizes in combination, both the oxide scale removal effect and efficiency can be considered, overcoming the limitations of shot blasting with a single particle size. Using only large-particle shot may cause excessive impact on small billets and create new surface unevenness, while using only small-particle shot is inefficient and difficult to effectively remove thick oxide scale.

[0105] Optionally, in the two types of pellets, the mass percentage of pellets with a particle size of 1.5~2.5mm is 55~65%, and the remainder is pellets with a particle size of 3.2~4mm.

[0106] (4) Electroslag remelting process

[0107] The small square billets obtained from the continuous casting process are used as electrode rods. Under a protective atmosphere, they are electroslag remelted, refined, and resolidified to form remelted ingots. The melting rate of the electrode rods is 55~58 kg / h. After remelting, the remelted ingots are cooled, and the cooling rate is controlled to be ≤50℃ / h.

[0108] Thus, by performing electroslag remelting under a protective atmosphere, the molten steel can not only be prevented from being oxidized and the formation of inclusions can be reduced, but also the impurity elements (i.e., harmful elements) can be strictly controlled, thereby ensuring the high purity of the final wire rod, greatly reducing the formation of inclusions, and significantly reducing the size of inclusions, resulting in a uniform chemical composition.

[0109] It is understandable that the chemical composition of the remelted ingot is consistent with that of the final wire rod, which will not be elaborated here.

[0110] Therefore, by combining converter smelting, LF refining and electroslag remelting processes, not only can the morphology and quantity of inclusions be controlled and the purity improved, thus achieving regulation of the wire rod structure, but the process flow is also short, greatly shortening the production cycle and improving production efficiency.

[0111] The protective atmosphere can specifically be an atmosphere composed of an inert gas, such as argon.

[0112] In some embodiments, the remelted ingot is cylindrical and has a cross-sectional diameter of 280-320 mm.

[0113] In one specific embodiment, after the electrode rod is in place, an arc is ignited to form a slag pool. The current during the slag formation process is controlled to be 5.8~6.0kA and the voltage to be 55~60V, so that the electrode rod can be melted. The flow rate of the protective atmosphere is controlled to be 10~15L / min, so that the electrode rod is oxidized during the remelting process and oxide inclusions are generated.

[0114] The chemical composition of the slag used for slag formation, by mass percentage, includes: CaF2 52-55%, CaO 20-24%, Al2O3 17-19%, with the remainder being MgO. By using quaternary slag to form a slag pool, impurities in the remelted steel can be adsorbed, further improving the purity of the final wire rod.

[0115] The amount of slag material added for slag making is 45~55kg / t. The slag material is pre-baked and added in two batches. The amount of the first batch of slag material added is 15~20kg / t. After the first batch of slag material is completely melted, the remaining slag material is added, which is the second batch of slag material.

[0116] After slag formation is completed, the current density is controlled to be constant, and the current density is 0.13~0.15A / mm. 2During the remelting process, the slag pool depth is maintained at 92-95 mm to remelt the electrode rod, and the melting rate of the electrode rod is controlled at 55-58 kg / h. Specifically, the slag pool depth can be maintained by adding slag material.

[0117] When the electrode rod is remelted to 10% of its original mass, the control current is gradually reduced at preset time intervals until the electrode rod is completely melted and the molten pool solidifies. As the remelting of the electrode rod progresses, its length becomes shorter towards the end of the remelting process. By gradually reducing the control current at preset time intervals, the melting rate can be controlled.

[0118] The preset time interval is 8~12 minutes, and the current decreases in a stepwise manner to 5.0~5.5kA, 4.2~4.7kA, and 2.6~3.0kA respectively.

[0119] Optionally, after remelting, the remelted ingot is sent to a slow cooling pit for cooling, thereby ensuring a cooling rate of ≤50℃ / h.

[0120] (5) Blank preparation and grinding process

[0121] The remelted ingot is slabred or forged into a steel billet, which is then ground. The cross-sectional dimensions of the steel billet are (130~150)mm × (130~150)mm. The steel billet is preferably a square billet.

[0122] In one embodiment, the remelted ingot is heated and then rolled into a billet. The homogenization temperature during heating is 1200~1230℃. During the rolling process, in the first three passes, the reduction rate of each pass is ≤9%, and the surface temperature of the rolled piece is controlled to be ≥1100℃. In the last four passes, the reduction rate of each pass is 10~15%, and the surface temperature of the rolled piece is controlled to be ≥950℃. In this way, the smaller reduction rate in the first three passes can avoid excessive deformation impact on the core, prevent internal cracks in the core due to insufficient plasticity, and the high temperature and small deformation also help to reduce the temperature difference between the core and the surface. The slightly larger reduction rate in the last four passes can break up the coarse austenite grains through large deformation and introduce a large number of dislocations, providing a large number of nucleation sites for subsequent phase transformation, thereby achieving the refinement and homogenization of the microstructure.

[0123] In one embodiment, when heating the remelted ingot, the heating rate is controlled at 60~70℃ / h when the temperature is ≤700℃. This heating rate can effectively reduce the stress of the remelted ingot and prevent cracking, thus fundamentally eliminating the risk of cracking in the alloyed hypereutectoid steel remelted ingot during the initial heating stage. When the temperature is above 700℃, the heating rate is controlled at 120~160℃ / h, which improves heating efficiency and helps to obtain finer initial austenite grains.

[0124] In one embodiment, the billet is fully re-grinded to optimize its surface quality, eliminate defects such as surface pits and decarburization layers, thereby creating a good foundation for subsequent high-speed wire rolling; and shot blasting is performed after the full re-grinding to remove burrs remaining on the billet surface.

[0125] Preferably, the single-sided grinding depth during full grinding is ≥2mm, the decarburization layer removal rate on the billet surface is ≥90%, and the traveling speed of the grinding carriage is 30~35m / min; the shot size used in shot blasting is 3.5~5.0mm, the shot velocity is 9.5~12m / s, and the billet's moving speed in the shot blasting machine is 4~6m / min. This ensures that the final billet surface is smooth and burr-free.

[0126] Specifically, a 24-mesh grinding wheel can be used to fully grind the steel billet.

[0127] Magnetic particle inspection is performed, specifically by controlling the concentration of fluorescent magnetic powder to 0.8~0.9 g / L. An aqueous solution of the mixed fluorescent magnetic powder is sprayed onto the surface of the steel billet through a nozzle, using an intensity of 980~1200 μW / cm². 2 Ultraviolet light was used for observation, and the defect density of the steel billet was measured to be ≤0.02 defects / m.

[0128] (6) High-speed wire rolling process

[0129] The steel billet is rolled into wire rod. The initial rolling temperature is 1150~1180℃, and the wire drawing temperature is 910~930℃, in order to further refine the wire rod structure and facilitate the temperature control of subsequent salt bath cooling.

[0130] The rolling process involves roughing, intermediate rolling, pre-finishing rolling, finishing rolling, and sizing rolling. The entry temperature for finishing rolling is 1000–1050℃, and the exit temperature is 1000–1020℃. The temperature difference between the core and surface of the workpiece is controlled to be ≤6℃ during finishing rolling. High-temperature finishing rolling causes dynamic recrystallization of austenite grains, thoroughly refining and homogenizing the non-uniform grains. The minimal core-surface temperature difference ensures highly coordinated and synchronized metal flow between the core and surface during rolling deformation, preventing uneven deformation caused by temperature differences.

[0131] Preferably, in the high-speed wire rolling process, the steel billet is rolled into a wire rod with a diameter of 4.5~5.0mm. That is, the wire rod produced by the production method based on this embodiment has a final diameter of 4.5~5.0mm, which can meet the requirements of subsequent drawing to prepare steel wire.

[0132] In one embodiment, the high-speed wire rod rolling is carried out using a 26-stand mill, which includes 6 stands for roughing, 6 stands for intermediate rolling, 4 stands for pre-finishing, 8 stands for finishing, and 2 sizing mills for reducing and sizing.

[0133] (7) Salt bath cooling process

[0134] The wire rod is cooled using a three-stage salt bath. In the first stage, the salt bath temperature is 600~620℃ and the wire rod roller speed is 0.30~0.40m / s. In the second stage, the salt bath temperature is 580~600℃ and the wire rod roller speed is 0.25~0.30m / s. In the third stage, the salt bath temperature is 570~580℃ and the wire rod roller speed is 0.40~0.45m / s.

[0135] After exiting the salt bath, the residual molten salt on the surface of the wire rod is washed off before winding and packaging.

[0136] In one embodiment, during the three-stage salt bath cooling process for the wire rod, the wire rod is air-cooled after the first and second salt baths, with the air-cooling temperature at 60~100°C and the cooling time at 8~12 seconds. This not only removes the molten salt adhering to the surface of the wire rod but also prevents the temperature from dropping too rapidly.

[0137] (8) Drawing process

[0138] The wire rod is subjected to rough drawing, intermediate drawing, fine drawing, brass electroplating, and final drawing in sequence to obtain the steel wire.

[0139] In one embodiment, heating and salt bath are performed after rough drawing, intermediate drawing, and fine drawing; the uniform heating temperature after rough drawing is 940~950℃, and the salt bath temperature is 600~620℃; the uniform heating temperature after intermediate drawing is 940~950℃, and the salt bath temperature is 580~590℃; the uniform heating temperature after fine drawing is 950~970℃, and the salt bath temperature is 550~560℃.

[0140] Salt bath treatment after rough drawing can control the tensile strength of the intermediate wire to 1400~1450MPa, the area reduction ≥40%, and the grain size to 7~7.5μm. Heating and salt bath treatment after intermediate drawing can control the tensile strength of the intermediate wire to 1460~1480MPa and the area reduction ≥45%. Heating and salt bath treatment after fine drawing can further increase the tensile strength of the intermediate wire to 1520~1540MPa, with an area reduction ≥43% and a grain size to 8.2~8.8μm.

[0141] The salt bath time after rough drawing is 8-10 seconds, the salt bath time after medium drawing is 6-9 seconds, and the salt bath time after fine drawing is 4-8 seconds.

[0142] The heating process after rough drawing includes a preheating section, a heating section, and a homogenizing section, performed sequentially. The temperature of the preheating section is 950~960℃, and the temperature of the heating section is 980~990℃. The heating process after intermediate drawing includes a heating section and a homogenizing section, performed sequentially. The temperature of the heating section is 930~940℃. The heating process after fine drawing includes a heating section and a homogenizing section, performed sequentially. The temperature of the heating section is 940~950℃.

[0143] In one embodiment, the diameter of the intermediate wire obtained after rough drawing is controlled to be 2.2~2.3 mm and the tensile strength is controlled to be 2000~2100 MPa; the diameter of the intermediate wire obtained after intermediate drawing is controlled to be 1.1~1.3 mm and the tensile strength is controlled to be 1800~1850 MPa; and the diameter of the intermediate wire obtained after fine drawing is controlled to be 0.4~0.5 mm and the tensile strength is controlled to be 2420~2480 MPa.

[0144] Specifically, by controlling the reduction rate of the rough drawing pass to be 9-11% and the drawing speed to be 6-8 m / s, the diameter of the intermediate wire after rough drawing can be 2.2-2.3 mm and the tensile strength can be 2000-2100 MPa, based on the tensile strength of the aforementioned wire rod; the reduction rate of the intermediate drawing pass to be 10-12% can be used to obtain an intermediate wire diameter of 1.1-1.3 mm and a tensile strength of 1800-1850 MPa; and the reduction rate of the finish drawing pass to be 8-9% can be used to obtain an intermediate wire diameter of 0.4-0.5 mm and a tensile strength of 2420-2480 MPa.

[0145] In one embodiment, during the electroplating of brass, the current density ratio of copper plating to zinc plating is controlled to be (3.8~4.2):1, and the total thickness of the plating layer formed by electroplating brass is 75~80μm.

[0146] Specifically, the final drawing process uses a water tank to further draw the intermediate wire after electroplating brass into a finished steel wire with a diameter of 28~34μm.

[0147] The detailed descriptions listed above are merely specific descriptions of feasible implementation methods of this application, and are not intended to limit the scope of protection of this application. All equivalent implementation methods or modifications made without departing from the spirit of the art of this application should be included within the scope of protection of this application.

[0148] The beneficial effects of this application will be further illustrated by the following embodiments. Of course, these embodiments are only a part of the many variations contained in this application, and not all of them.

[0149] Examples 1-4 each provide a wire rod, the chemical composition of which is shown in Table 1 by mass percentage, with the remainder being Fe and unavoidable impurities.

[0150] Table 1

[0151]

[0152] The wire rod diameters of each embodiment are shown in Table 2. The microstructure properties of the wire rods in each embodiment were tested, including:

[0153] (1) In terms of mechanical properties, referring to GB / T 228.1 "Metallic materials - Tensile testing - Part 1: Test at room temperature", the wire rod was sampled and its mechanical properties were tested using a tensile testing machine;

[0154] The tensile strength and reduction of area of ​​the wire rods in each embodiment were measured as shown in Table 2. Two samples were taken from each embodiment for testing.

[0155] (2) Regarding inclusions, the inclusion composition in the wire rods of each embodiment was detected by energy dispersive spectroscopy using scanning electron microscopy, and the number of inclusions per unit area was counted; the microhardness HV test was performed in accordance with ISO 6507-1 "Metallic materials - Vickers hardness test".

[0156] The inclusions in the wire rods of each embodiment were found to be SiO2-MnO-Al2O3 composite inclusions. The Al2O3 content, microhardness, number density, and size of the inclusions within 1 mm of the wire rod surface are shown in Table 3.

[0157] (3) The wire rods were tested in accordance with ISO 16120-1 "Non-alloy steel wire rods for wire making - Part 1: General requirements". The grain boundary carbide levels in the wire rods of each embodiment are shown in Table 3.

[0158] The wire rods were tested according to YB / T 4411 "Evaluation Method of Network Cementite in High Carbon Steel Wire Rods". The martensite level in the wire rods of Examples 1 to 4 was found to be 0.

[0159] Table 2

[0160]

[0161] Table 3

[0162]

[0163] It can be seen that the wire rod in this embodiment has high purity, uniform structure, high tensile strength and good drawing performance.

[0164] The production methods of wire rod in Examples 1-4 specifically include the following steps.

[0165] (1) Converter smelting process

[0166] Raw materials for smelting are added to the converter, and oxygen is blown throughout the process to smelt steel.

[0167] The smelting raw materials include scrap steel and pre-desulfurized molten iron. Scrap steel accounts for 10-18% of the smelting raw materials by mass, and clean scrap steel with low impurity element content is used. The chemical composition of the molten iron before pre-desulfurization, by mass percentage, includes: Si 0.5-0.7%, P≤0.1%, S≤0.035%, Ti≤0.04%, and the slag removal rate of the pre-desulfurized molten iron is ≥99%. The S content in the pre-desulfurized molten iron is ≤0.002%, and the charging temperature of the pre-desulfurized molten iron into the converter is 1350-1400℃.

[0168] Specifically, after adding the smelting raw materials to the converter, oxygen is blown to raise the temperature. During this stage, the height of the oxygen lance from the liquid surface is controlled at 1.12~1.30m, and the oxygen flow rate is 17500~18500m³ / h. 3 The furnace is heated at a rate of 1.5-1.6, and 15-25 kg / t of lime and 6-8 kg / t of dolomite are added to form slag, controlling the slag basicity to 1.5-1.6. When the molten pool temperature rises to 1350-1420℃ and the FeO content in the slag is 13-14%, 80-85% of the slag is poured out.

[0169] Afterwards, perform a slag adjustment, controlling the oxygen lance's height above the liquid surface to be 1.8~1.9m, and the oxygen flow rate to be 15800~16800m³ / h. 3 The process involves adding 16-20 kg / t of lime and 2-3 kg / t of Fe oxide to the molten steel, controlling the slag basicity to 2.6-3.0, the molten pool temperature to 1650-1670℃, and the FeO content in the slag to 17-19%. This ensures that the P content in the molten steel is controlled to ≤0.002%.

[0170] Then, a second slag adjustment is performed, controlling the oxygen lance's height above the liquid surface to be 1.6~1.8m, and the oxygen flow rate to be 15800~16800m³ / h. 3 The steel is then tapped at a rate of 10-20 kg / t of lime and 5-6 kg / t of dolomite per hour. The slag basicity is controlled at 4.0-5.0, the magnesium oxide content at 9-12%, and the FeO content at 23-28%. The steel is then tapped at a temperature of 1640-1660℃, and 10% of the steel is left at the tapping point.

[0171] When 1 / 3 of the steel is tapped, a low-phosphorus alloy with a phosphorus content of ≤0.005% is added to the molten steel for alloying. When 1 / 2 of the steel is tapped, 2.8~3.2 kg / t of lime is added to the molten steel to form slag.

[0172] (2) LF refining process

[0173] The molten steel obtained from the converter smelting process is fed into the LF furnace, and argon gas is blown into the bottom of the ladle throughout the process for refining.

[0174] Specifically, after the ladle arrives at the station, bottom-blowing argon gas is turned on, and the ladle is heated electrically. During the heating stage, the flow rate of bottom-blowing argon gas is controlled at 300~350 NL / min. Then, alloying is performed, with the flow rate of bottom-blowing argon gas at 380~450 NL / min during the alloying stage. Next, 5~8 kg / t of lime and 1.3~1.4 kg / t of calcium carbide are added for white slag treatment, with a treatment time of 4~8 minutes. The chemical composition of the white slag, by mass percentage, includes: CaO 70~85%, Al2O3 10~20%, SiO2 5~8%, T.Fe+MnO ≤1%, and the basicity of the white slag is 13~15. The white slag is then removed using a slag remover, with a slag removal rate ≥98%, ensuring the S content in the molten steel is ≤0.0018%. Finally, 7.2~8.6 kg / t of synthetic slag and 0.2~0.3 kg / t of lime are added for slag formation. The chemical composition of the synthetic slag, by mass percentage, includes: CaO 28~33%, SiO2 35~40%, Al2O3 ≤2%, MgO 8~10%, CaF 27~12%, and the remainder is FeO.

[0175] At the end of the LF refining process, the slag basicity is shown in Table 4, and the S content, melting point of inclusions, and tapping temperature of the molten steel are also shown in Table 4.

[0176] Table 4

[0177]

[0178] (3) Continuous casting process

[0179] The molten steel from the LF refining process is fed into a continuous casting machine and cast into small square billets. The superheat during casting of the molten steel in Examples 1 to 4 is 22℃, 21℃, 23℃, and 18℃, respectively. The cross-sectional dimensions of the small square billets in Examples 1 to 4 are 140mm×140mm, 120mm×120mm, 140mm×140mm, and 140mm×140mm, respectively.

[0180] The oxide scale on the surface of the small billet was then removed using a shot blasting machine. The shot blasting machine used two different particle sizes: 1.5~2.5mm and 3.2~4mm. The 1.5~2.5mm particle size accounted for 60% of the mass, and the remainder was 3.2~4mm particle size. The particle speed during shot blasting was 9~10m / s, and the moving speed of the small billet in the shot blasting machine was 5~7m / min.

[0181] (4) Electroslag remelting process

[0182] The small square billets obtained from the continuous casting process are used as electrode rods. Argon is used as the protective atmosphere for electroslag remelting, refining, and resolidification to form remelted ingots. The remelted ingots are cylindrical, and their cross-sectional diameters are shown in Table 5.

[0183] Specifically, after the electrode rod is in place, an arc is ignited to form a slag pool. The current during the slag-forming process is controlled at 5.8~6.0kA, the voltage at 55~60V, and the argon flow rate at 10~15L / min. The chemical composition of the slag material used for slag-forming, expressed as a percentage by mass, is shown in Table 5, as is the amount of slag material added. The slag material is pre-baked and added in two batches. The first batch of slag material is 15~20kg / t, and the remaining slag material is added after the first batch has completely melted.

[0184] After slag formation is completed, the current density is kept constant. The current density is shown in Table 5. The slag pool depth and electrode rod melting rate during remelting are shown in Table 5.

[0185] When the electrode rod is remelted to 10% of its original mass, the control current is reduced in steps at intervals of 8 to 12 minutes. The magnitude of the current reduction is shown in Table 5, until the electrode rod is completely melted and the molten pool solidifies.

[0186] After remelting, the remelted ingot is sent to a slow cooling pit for cooling, with the cooling rate controlled at ≤50℃ / h.

[0187] Table 5

[0188]

[0189] (5) Blank preparation and grinding process

[0190] After heating the remelted ingot, it is slab-rolled into steel billets, the cross-sectional dimensions of which are shown in Table 6. During heating, the heating rate is controlled at 60~70℃ / h when the temperature is ≤700℃, and at 120~160℃ / h when the temperature is above 700℃. The soaking temperatures are shown in Table 6. The slab rolling process uses seven passes, with the reduction rate for each pass shown in Table 6. The surface temperature of the rolled piece is controlled to be ≥1100℃ for the first three passes and ≥950℃ for the last four passes.

[0191] Then, the steel billet is fully re-grinded using a 24-mesh grinding wheel. The single-sided grinding depth during full re-grinding is ≥2mm, the decarburization layer removal rate on the steel billet surface is ≥90%, and the traveling speed of the re-grinding trolley is 30~35m / min.

[0192] After full grinding, shot blasting is performed. The shot size used in shot blasting is 3.5~5.0mm, the shot velocity is 9.5~12m / s, and the billet moves at a speed of 4~6m / min in the shot blasting machine.

[0193] Magnetic particle inspection was performed, controlling the concentration of fluorescent magnetic powder to be 0.8~0.9 g / L. An aqueous solution of the mixed fluorescent magnetic powder was sprayed onto the surface of the steel billet through a nozzle, using an intensity of 980~1200 μW / cm². 2 Ultraviolet light was used for observation, and the defect density of the steel billet was measured to be ≤0.02 defects / m.

[0194] Table 6

[0195]

[0196] (6) High-speed wire rolling process

[0197] The steel billet is rolled into wire rod at a rolling temperature of 1150~1180℃ and a wire drawing temperature of 910~930℃.

[0198] The steel billet is rolled into wire rod through a 26-stand sequential process of roughing, intermediate rolling, pre-finishing, finishing, and sizing. The diameter of the wire rod is shown in Table 7. The 26-stand mill includes 6 stands for roughing, 6 stands for intermediate rolling, 4 stands for pre-finishing, 8 stands for finishing, and 2 sizing mills for sizing.

[0199] The initial rolling temperature, finishing rolling inlet temperature, finishing rolling outlet temperature, and wire drawing temperature are shown in Table 7. The temperature difference between the core and surface of the workpiece during finishing rolling should be controlled to be ≤6℃.

[0200] Table 7

[0201]

[0202] Examples 1-4 also provide a steel wire, which is prepared by further processing the aforementioned wire rod through salt bath cooling and drawing processes. Details are as follows.

[0203] (7) Salt bath cooling process

[0204] After the wire rod is ejected from the spinning machine, it immediately enters the conveyor roller conveyor, with the roller conveyor speed controlled at 0.65~0.72m / s. It is then fed into three salt bath tanks arranged sequentially for three-stage salt bath cooling. The three salt bath tanks correspond to the first, second, and third stages of the salt bath, respectively. The distance between the spinning machine and the nearest salt bath tank is 9m.

[0205] The salt bath temperatures and roller speeds of the wire rod during the first, second, and third salt baths are shown in Table 8. After the first and second salt baths, the wire rod is air-cooled at a temperature of 60-100℃ for 8-12 seconds.

[0206] After exiting the salt bath, the residual molten salt on the surface of the wire rod is washed off before winding and packaging.

[0207] Table 8

[0208]

[0209] (8) Drawing process

[0210] The wire rod is sequentially drawn into rough, intermediate, and fine sections, then electroplated with brass, and finally drawn to obtain steel wire. Each of the rough, intermediate, and fine drawing processes involves heating and a salt bath.

[0211] The reduction in area per pass during rough drawing was controlled at 9-11%, and the drawing speed was 6-8 m / s. The diameter and tensile strength of the intermediate wire after rough drawing are shown in Table 9. Heating after rough drawing included a preheating section, a heating section, and a soaking section, performed sequentially. The temperature of the preheating section was 950-960℃, the temperature of the heating section was 980-990℃, and the temperature of the soaking section was 940-950℃. The salt bath temperature was 600-620℃, and the salt bath time was 8-10 s. The tensile strength, reduction in area, and grain size of the intermediate wire after the salt bath are shown in Table 9.

[0212] The reduction in area per pass during intermediate drawing is 10-12%. The diameter and tensile strength of the intermediate wire obtained after intermediate drawing are shown in Table 10. The heating after intermediate drawing includes a heating section and a soaking section. The temperature of the heating section is 930-940℃, and the temperature of the soaking section is 940-950℃. The salt bath temperature is 580-590℃, and the salt bath time is 6-9s. The tensile strength and reduction in area of ​​the intermediate wire after the salt bath are shown in Table 10.

[0213] The reduction in area per pass during fine drawing is 8-9%. The diameter and tensile strength of the intermediate wire obtained after fine drawing are shown in Table 10. The heating after fine drawing includes a heating section and a soaking section. The temperature of the heating section is 940-950℃, and the temperature of the soaking section is 950-970℃. The salt bath temperature is 550-560℃, and the salt bath treatment time is 4-8 seconds. The tensile strength, reduction in area, and grain size of the intermediate wire after the salt bath are shown in Table 10.

[0214] Table 9

[0215]

[0216] Table 10

[0217]

[0218] When electroplating brass, the current density ratio of copper plating to zinc plating is controlled at 4:1, and the total thickness of the brass plating layer is 75~80μm.

[0219] The final drawing process uses a water tank to further draw the intermediate brass-plated wire into finished steel wire. Without welding, the length of a single steel wire can reach 450 km or more. The diameter, tensile strength, torsion cycles, and elongation of the finished steel wire are shown in Table 11.

[0220] Table 11

[0221]

[0222] In summary, this application has the following advantages over existing technologies: Through a chemical composition design scheme, combined with three-stage salt bath cooling and salt bath temperature control of the wire rod, precise coordination between the phase transformation process and the salt bath temperature is achieved. This enables a phase transformation path of high-density nucleation, full diffusion transformation, and rapid phase transformation, resulting in a uniform sorbitic structure in the wire rod with smaller lamellar spacing. This effectively suppresses the formation of abnormal structures such as grain boundary cementite, significantly reducing the wire breakage rate and laying the foundation for the preparation of high-strength steel wire. Furthermore, the drawing process of the steel wire... By controlling the heating and salt bath treatment, the brittleness caused by work hardening during drawing is eliminated, and the steel wire is endowed with better microstructure and plasticity. This achieves a balance between ultra-high strength and excellent ductility and toughness, thus enabling the preparation of ultra-high strength steel wires with a diameter of 28~34μm and a tensile strength ≥5500MPa. The steel wire can be twisted ≥130 times and the length of a single steel wire is ≥450km. It not only has excellent comprehensive performance, but also enables stable industrial production, which far meets the market demand for good drawing performance, low wire breakage rate and high strength steel wire.

[0223] It should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This way of describing the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0224] The detailed descriptions listed above are merely specific descriptions of feasible implementation methods of this application, and are not intended to limit the scope of protection of this application. All equivalent implementation methods or modifications made without departing from the spirit of the art of this application should be included within the scope of protection of this application.

Claims

1. A method for producing 5500MPa grade diamond wire busbar steel wire, characterized in that, The method for producing the steel wire includes: The billet is formed into wire rods, and the wire rods are wound at a temperature of 910~930℃. The chemical composition of the billet, by mass percentage, includes: C 0.97~0.99%, Si 0.38~0.42%, Mn 0.65~0.75%, Cr 0.30~0.35%, Ni 0.16~0.25%, and any one of La 0.010~0.030% and Ce 0.005~0.02%; the remainder is Fe and unavoidable impurities, wherein the impurities include Al≤0.001%, Ti≤0.0005%, S≤0.002%, P≤0.003%, O≤0.0010%, and N≤0.0010%. The wire rod is subjected to a three-stage salt bath cooling process. The salt bath temperature in the first stage is 600~620℃, and the roller speed of the wire rod is 0.30~0.40m / s. The salt bath temperature in the second stage is 580~600℃, and the roller speed of the wire rod is 0.25~0.30m / s. The salt bath temperature in the third stage is 570~580℃, and the roller speed of the wire rod is 0.40~0.45m / s. The wire rod is sequentially subjected to rough drawing, intermediate drawing, fine drawing, brass plating, and final drawing to obtain the steel wire. Each of the rough drawing, intermediate drawing, and fine drawing processes involves heating and a salt bath. The uniform heating temperature after rough drawing is 940-950℃, and the salt bath temperature is 600-620℃. The uniform heating temperature after intermediate drawing is 940-950℃, and the salt bath temperature is 580-590℃. The uniform heating temperature after fine drawing is 950-970℃, and the salt bath temperature is 550-560℃.

2. The method for producing 5500MPa grade diamond wire busbar steel wire according to claim 1, characterized in that, During the three-stage salt bath cooling process of the wire rod, the wire rod is air-cooled after the first and second salt baths, with the air-cooling temperature being 60~100℃ and the cooling time being 8~12s.

3. The method for producing 5500MPa grade diamond wire busbar steel wire according to claim 1, characterized in that, The salt bath time after rough drawing is 8-10 seconds, the salt bath time after medium drawing is 6-9 seconds, and the salt bath time after fine drawing is 4-8 seconds.

4. The method for producing 5500MPa grade diamond wire busbar steel wire according to claim 1, characterized in that, The heating process after rough drawing includes a preheating section, a heating section, and a homogenizing section, performed sequentially. The temperature of the preheating section is 950~960℃, and the temperature of the heating section is 980~990℃. The heating process after intermediate drawing includes a heating section and a homogenizing section, performed sequentially. The temperature of the heating section is 930~940℃. The heating process after fine drawing includes a heating section and a homogenizing section, performed sequentially. The temperature of the heating section is 940~950℃.

5. The method for producing 5500MPa grade diamond wire busbar steel wire according to claim 1, characterized in that, The diameter of the wire rod is 4.5~5.0mm and the tensile strength is 1280~1350MPa; the diameter of the intermediate wire obtained after rough drawing is 2.2~2.3mm and the tensile strength is 2000~2100MPa; the diameter of the intermediate wire obtained after intermediate drawing is 1.1~1.3mm and the tensile strength is 1800~1850MPa; the diameter of the intermediate wire obtained after fine drawing is 0.4~0.5mm and the tensile strength is 2420~2480MPa.

6. The method for producing 5500MPa grade diamond wire busbar steel wire according to claim 5, characterized in that, The surface area reduction rate for rough drawing is 9-11%, and the drawing speed is 6-8 m / s; the surface area reduction rate for intermediate drawing is 10-12%; and the surface area reduction rate for finish drawing is 8-9%.

7. The method for producing 5500MPa grade diamond wire busbar steel wire according to claim 1, characterized in that, When electroplating brass, the current density ratio of copper plating to zinc plating is (3.8~4.2):1, and the total thickness of the plating layer formed by electroplating brass is 75~80μm.

8. The method for producing 5500MPa grade diamond wire busbar steel wire according to claim 1, characterized in that, The process of forming the billet into wire rod includes: The billet is used as an electrode rod for electroslag remelting to obtain a remelted ingot; The remelted ingot is slabred or forged into a steel billet, and the steel billet is then ground. The steel billet is rolled into wire rod.

9. The method for producing 5500MPa grade diamond wire busbar steel wire according to claim 1, characterized in that, During electroslag remelting, the billet is remelted, refined, and resolidified under a protective atmosphere to form a remelted ingot. The melting rate of the electrode rod is 55~58 kg / h. After remelting, the remelted ingot is cooled, and the cooling rate is controlled to be ≤50℃ / h.

10. A 5500MPa grade diamond wire busbar steel wire, characterized in that, The steel wire is prepared using the production method of 5500MPa grade diamond wire busbar steel wire as described in any one of claims 1 to 9.

11. The 5500MPa grade diamond wire busbar steel wire according to claim 10, characterized in that, The steel wire has a diameter of 28~34μm, a tensile strength of ≥5500MPa, an elongation of ≥3.8%, a torsion count of ≥130 times, and a length of ≥450km for a single steel wire.

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