A high-strength multiphase hot-rolled wire rod for 1960MPa grade stranded wire and its manufacturing method

Abstract

This invention relates to a high-strength multiphase hot-rolled wire rod for stranded wire of grade 1960MPa and its manufacturing method. The high-carbon composition containing trace amounts of boron is designed and rolled into wire rods. After being rapidly quenched in an online molten salt process, the wire rod undergoes a pre-treatment molten salt cooling process at a rate ≥36℃ / s, transitioning from an austenitic state to a mixed phase region of bainite and pearlite, forming a microstructure dominated by quenched bainite and sorbite. The wire rod then undergoes a post-treatment molten salt process, increasing the molten salt temperature to promote isothermal tempering of the quenched bainite and sorbite microstructures. Finally, it undergoes slow cooling on a roller conveyor, resulting in a hot-rolled wire rod with a microstructure consisting of tempered sorbite, tempered bainite, and ferrite, forming a multiphase microstructure. This method simplifies the composition system, balances the strength and plasticity of the wire rod with rapid production, achieving a tensile strength of 1330~1380MPa and a reduction of area of ​​35%~40%, which helps reduce the risk of wire breakage during wire drawing and twisting.

Description

Technical Field

[0001] This invention belongs to the technical field of hot-rolled wire rod, specifically relating to a high-strength multiphase hot-rolled wire rod for 1960MPa grade stranded wire and its manufacturing method. Background Technology

[0002] With the continuous expansion of fields such as machinery, bridges, highways, and new energy, the market demand for steel strand, as an important connection and anchoring mechanism, is constantly increasing. For large-scale engineering projects, the wire rod can be processed into finished products after drawing, which can greatly enhance the performance of the wire rod and achieve the goal of lightweighting. The improvement of the strength grade of steel wire products can reduce material usage and energy consumption. Based on this, higher requirements are placed on the strength grade of the hot-rolled wire rod base material for stranded steel.

[0003] Currently, 1960MPa grade steel strand is mainly produced using alloy products with 0.87% carbon content combined with Stellmor air-cooled wire. For example, patent CN112301287B discloses prestressed steel strand, wire rod for prestressed steel strand, and its production method. This method uses C-Si-Mn-Cr-V-Al, combined with Stellmor air-cooling for rapid cooling followed by slow cooling, to produce wire rods with a sorbite-based microstructure containing a small amount of pearlite and a diameter of 16mm. The wire rods achieve a tensile strength of 1320~1380MPa and a reduction of area ≥28%. However, its drawbacks include:

[0004] On the one hand, increasing the content of carbon and multiple alloying elements will increase the difficulty of smelting and the cost of alloys. Due to the limitation of the maximum cooling capacity of the air-cooled line, under high carbon content, alloying elements such as Cr and V will further reduce the solubility of carbon in austenite, promote carbon diffusion to grain boundaries, and make it difficult to disperse evenly during the cooling process. They will aggregate along the austenite grain boundaries to form more continuous and coarse network carbides. The network carbides cut the matrix along the grain boundaries, which will cause a significant decrease in the plasticity and toughness of the wire rod. During the subsequent stranding and drawing process, it is easy to fracture along the grain at the stress concentration point. During torsion, it will be brittle and fail due to the inability to withstand shear deformation. However, in order to reduce material costs and control the difficulty of network carbides, choosing to reduce carbon and omit alloying elements will result in a significant loss of strength if only pearlite is used for strengthening, making it difficult to meet the performance requirements of high-strength stranded wire.

[0005] On the other hand, elements such as Cr and Mn, which improve the hardenability of wire rods, will see their local enrichment in carbon and alloying elements generated during continuous casting or rolling become more concentrated as the wire rod diameter decreases. This is exacerbated by the unstable temperature control of the air-cooling line. In particular, to minimize the influence of network carbides and promote lamellar refinement, strong air cooling is required after wire drawing, further intensifying the temperature difference between the wire rod surface and core, or localized temperature differences. This easily leads to the formation of uncontrollable martensite or bainite structures on the surface or in localized areas. Limited by the minimum cooling capacity of the air-cooling line, these abnormal structures will cause significant brittleness in the wire rod. Furthermore, the uneven lamellar structure will further contribute to... Increasing radial differences in strength and mechanical property fluctuations in one step poses a great risk to the production of hot-rolled wire rod. Abnormal structures can also become stress concentration points during subsequent wire drawing or torsion in strand manufacturing, inducing microcracks and causing them to propagate rapidly, affecting the yield and production efficiency of stranded steel. In order to reduce the risk of low-temperature brittle structures such as martensite, choosing to reduce the air-cooling strength will increase the level of network carbides, leading to a surge in material brittleness. The continuous cooling of the air-cooling line and the coarsening of the lamellar structure will result in a loss of strength and toughness. Network carbides and coarse pearlite can also become stress concentration sources during wire drawing, failing to meet the plasticity requirements of torsion processing. Summary of the Invention

[0006] The present invention aims to solve at least one of the above-mentioned technical problems. The present invention provides a high-strength multiphase hot-rolled wire rod for stranded wire of grade 1960MPa and its manufacturing method, which can simplify the composition system, reduce material costs, achieve multiphase structure control, and take into account the matching of strength and plasticity properties of wire rod and rapid production, which helps to reduce the risk of wire breakage during the drawing and twisting process of stranded steel.

[0007] The technical solution adopted by this invention to solve its technical problem is:

[0008] A method for manufacturing high-strength multiphase hot-rolled wire rod for 1960MPa grade stranded wire, the method comprising:

[0009] The wire rod is rolled into production wire according to the chemical composition of hot-rolled wire rod. The chemical composition and mass percentage of the hot-rolled wire rod include: C: 0.79%~0.83%, Si: 0.20%~0.40%, Mn: 0.67%~0.78%, B: 0.001%~0.008%, P≤0.015%, S≤0.015%, with the remainder being Fe and unavoidable impurities. After the wire rod is spun into wire rod at a spinning temperature of ≥890℃, it undergoes online molten salt treatment. Rapid quenching treatment involves first undergoing a preliminary molten salt treatment, which cools the wire rod at a rate of ≥36℃ / s, transforming it from an austenitic state into a mixed phase region of bainite and pearlite, forming a microstructure dominated by quenched bainite and sorbite. The wire rod then undergoes a subsequent molten salt treatment, which increases the molten salt temperature and promotes isothermal tempering of the quenched bainite and sorbite microstructures. Finally, it undergoes slow cooling via a roller conveyor, resulting in a hot-rolled wire rod with a microstructure consisting of a multiphase microstructure composed of tempered sorbite, tempered bainite, and ferrite.

[0010] The chemical composition and mass percentage of the above-mentioned hot-rolled wire rods are designed based on the following:

[0011] (1) Carbon: C is a solid solution strengthening element in steel. It is relatively cheaper. Carbon dissolves in the iron matrix, forms cementite with iron, and forms carbides in quenched bainite or sorbite. It can provide solid solution strengthening effect, hinder dislocation slip, and improve the strength of steel. With appropriate carbon concentration, it can increase the driving force of bainite transformation. It can promote the refinement of pearlite lamellars to form sorbite structure during rapid quenching and cooling, and improve the matrix strength. However, if the C content is too high, it will make it more difficult to control the center segregation, network carbides and coarse carbides in high carbon steel billets. Carbon enrichment in austenite will increase the risk of martensite precipitation, affecting toughness and processing plasticity. Therefore, in order to take into account the high strength requirements of 1960MPa grade strand, reduce the difficulty of controlling the uniformity of the structure and abnormal structure, and adapt to the control of multiphase structure, the carbon content is appropriately reduced. The mass percentage of C is controlled at 0.79%~0.83%.

[0012] (2) Silicon: Si can significantly improve the hardness and strength of the iron matrix through solid solution strengthening. In the phase transformation process from austenite to a mixed structure of quenched bainite and sorbite, silicon can hinder the diffusion of carbon atoms into cementite and inhibit the growth of cementite. It helps to promote the transformation of bainite, maintain the refinement of sorbite lamellae and the uniformity of bainite structure, and avoid the decrease in strength or deterioration of toughness caused by carbide coarsening. However, excessive silicon will promote decarburization, increase the difficulty of softening, and lead to a decrease in the plasticity of steel. In subsequent processing steps such as wire drawing and twisting, it will break due to increased brittleness, affecting the yield of stranded wire. Therefore, in order to adapt to the control of phase transformation structure by online molten salt rapid quenching treatment, the mass percentage of Si is controlled at 0.20%~0.40%.

[0013] (3) Manganese: Mn is an austenite stabilizing element that can expand the stability range of austenite and significantly improve the hardenability of steel. By reducing the critical cooling rate of austenite, it affects the phase transformation kinetics, causing the pearlite transformation temperature to shift to a lower temperature and become closer to the transformation temperature range of bainite. In the rapid quenching stage of the molten salt in the early stage, it avoids coarse pearlite or excessive precipitation of ferrite, thereby promoting the rapid formation of quenched bainite and sorbite mixed structure. At the same time, in the isothermal tempering stage of the molten salt in the later stage, it can stabilize the quenched bainite and sorbite structure, inhibit the coarsening of carbides, and avoid the coarsening of the structure leading to While high Mn content can lead to reduced strength or deteriorated toughness, excessively high Mn content can increase elemental segregation during billet solidification. Austenite in Mn-rich regions has higher stability and is more prone to forming low-temperature martensite during cooling, increasing the risk of abnormal structure precipitation and local brittleness. This can become a stress concentration point during subsequent wire drawing and torsion, leading to microcracks. It also increases the difficulty of tempering and softening, thereby reducing the plasticity of wire rod and hindering rapid production. Therefore, in order to balance the control of multiphase structure of hot-rolled wire rod and reduce the difficulty of abnormal structure and tempering control, the mass percentage of Mn is controlled at 0.67%~0.78%.

[0014] (4) Boron: Trace amounts of boron preferentially accumulate at the austenite grain boundaries in steel, which can effectively improve the hardenability of steel and prevent the precipitation of ferrite at the austenite grain boundaries, so as to form a sufficient proportion of quenched bainite under rapid quenching and cooling, reduce the difference between the surface and core structures, and at the same time inhibit the migration and coarsening of carbides to the grain boundaries during tempering, providing a stable grain boundary basis for the multiphase structure after subsequent tempering. However, boron is expensive, and excessive addition is not conducive to controlling material costs. At the same time, excessive boron will cause brittle phase precipitation, which will damage the plasticity and processing performance of the material. Therefore, the mass percentage of boron is controlled at 0.001%~0.008%.

[0015] (5) Phosphorus and sulfur: P and S are impurity elements, and the lower the better. Therefore, P ≤ 0.015% and S ≤ 0.015%.

[0016] The aforementioned wire rod is designed with a high carbon content and low boron content, eliminating the need for high Cr and V alloying elements. This simplifies the composition system and appropriately reduces material costs, smelting difficulty, and the segregation issues caused by high alloying elements. Simultaneously, the addition of Mn and trace amounts of B elements regulates the wire rod's hardenability. By altering the stability and phase transformation kinetics of austenite, the transformation zones of pearlite and bainite overlap and approach each other, providing favorable conditions for the simultaneous mixing and transformation of bainite and sorbite during quenching, suppressing lamellar coarsening and excessive ferrite precipitation, and facilitating rapid tempering. Furthermore, the wire rod employs a high wire-drawing temperature, keeping the microstructure in a high-temperature austenitic state, suppressing component segregation, and preventing the formation of network carbides at excessively low temperatures. This provides favorable conditions for promoting bainite quenching and lamellar refinement. After wire drawing, the wire rod undergoes online molten salt rapid quenching without air cooling.

[0017] Firstly, compared to air-cooled wire lines, which are limited by their maximum cooling capacity and unstable controlled cooling, making it difficult to effectively control network carbides and abnormal structures, molten salt offers several advantages. Firstly, molten salt has a higher thermal conductivity than air, which is the cooling medium. This efficient heat transfer promotes rapid cooling of the wire rod, quickly bypassing the high-temperature range where carbides easily precipitate from the high-temperature austenitic state. This avoids prolonged stays in the high-temperature range, reducing carbon segregation and precipitation at austenitic grain boundaries, effectively suppressing network carbides and reducing structural brittleness. Secondly, the high cooling rate of the wire rod allows both the surface and core to transition from the high-temperature austenitic state to the lower-temperature bainite-pearlite mixed phase region, avoiding the nose temperature of pearlite transformation, which can lead to significant undercooling and trigger minor... The rapid transformation of quenched bainite and the refinement of pearlite into sorbite with finer lamellar spacing prevent the formation of coarse pearlite or proeutectoid ferrite due to insufficient cooling rate. This enhances the strengthening effect of carbon, compensating for the strength loss caused by reducing carbon and omitting alloying elements. Simultaneously, as the wire rod passes through molten salt, the molten salt can cover the surface of the wire rod. Compared with air or combined water mist cooling and air cooling control, this reduces the temperature gradient between the wire rod surface and the core, while avoiding the formation of brittle martensite due to localized overcooling and segregation. This makes the quenched bainite structure, which is usually considered abnormal, more controllable, effectively controlling abnormal structures, improving structural uniformity, and reducing mechanical property fluctuations, thus providing a foundation for the consistency of subsequent stranding processing.

[0018] Second, compared to the limitations of air-cooled lines in terms of minimum cooling capacity and continuous cooling, which prevent improvements in microstructure brittleness, the rapid quenching of the initial molten salt treatment promotes full phase transformation and avoids stress concentration caused by coarse network carbides and coarse pearlite. The higher molten salt temperature in the later stages of the molten salt treatment prevents austenite residue from continuing to form brittle martensite during subsequent cooling. Furthermore, the molten salt temperature allows for isothermal treatment, ensuring the wire rod temperature matches the molten salt temperature, rather than continuous cooling. With extended molten salt treatment times at higher temperatures... Enhanced atomic diffusion allows for the release of transformation stress through dislocation movement and grain boundary slip, reducing the dislocation density of quenched bainite and transforming it into tempered bainite that retains strength but has better toughness, significantly reducing structural brittleness. Simultaneously, it releases stress in the sorbite structure, transforming it into tempered sorbite with better plasticity. Finally, the wire rod undergoes slow cooling treatment via roller conveyor, which further toughens the wire rod structure and improves the tempering softening effect. This, in turn, effectively improves structural brittleness through tempering state control, thereby regulating the strength and plasticity matching of the wire rod and significantly reducing the risk of brittle fracture caused by stress concentration.

[0019] Before rolling, an appropriate heating furnace soaking temperature and furnace time are selected to austenitize the billet, improve compositional uniformity and heating consistency, reduce compositional segregation, and avoid grain coarsening caused by excessively high temperature and excessively long furnace time. In a preferred technical solution, before rolling, the heating furnace soaking temperature is controlled at 1180~1220℃ and the furnace time is controlled at 150~220min.

[0020] During the rolling process, selecting a higher initial rolling temperature can improve the rolling plasticity of the billet, reduce deformation resistance and wear on the rolling line, and increase the rolling speed. Selecting an appropriate final rolling temperature and final rolling reduction will generate a large number of dislocations that provide nucleation sites for recrystallization, promote dynamic recrystallization during the final rolling process, refine grains, and reduce internal defects. In the preferred technical solution, during the rolling process, the initial rolling temperature is controlled at 1080~1100℃, the final rolling temperature is controlled at 900~940℃, and the final rolling reduction is controlled at 25%~30%.

[0021] During the wire spinning process, the wire spinning temperature can be further controlled to provide a suitable starting temperature for online molten salt rapid quenching and avoid the risk of grain coarsening caused by excessively high wire spinning temperature. In the preferred technical solution, the wire spinning temperature is controlled at 890~930℃.

[0022] The molten salt temperature in the initial molten salt treatment is located in the mixed phase region of bainite and pearlite. Lower molten salt temperatures and longer treatment times, in conjunction with the hardenability of boron (B), help suppress network carbides and lamellar coarsening, increasing austenite undercooling. This leads to a dominant shear driving force and accelerated nucleation rate in the transformation of acicular quenched bainite, which is beneficial for refining the lamellar structure of sorbite and improving matrix strength. However, excessively low molten salt temperatures and long treatment times result in increased quenched bainite transformation and internal stress, increasing the difficulty of subsequent tempering and softening, affecting wire rod plasticity and production efficiency, increasing energy consumption, and even causing the formation of abnormal martensitic structures due to undercooling, leading to increased brittleness. Conversely, higher molten salt temperatures and longer treatment times... The shorter the processing time, the stronger the diffusion driving force of the sorbite transformation, making it easier to form sorbite lamellar structures and reducing the difficulty of improving the plasticity of tempering. However, if the molten salt temperature is too high and the processing time is too short, it is not conducive to the formation of quenched bainite, and there is a risk of coarse sorbite lamellars, which in turn leads to a loss of matrix strength. Therefore, the molten salt temperature and processing time of the first stage of molten salt treatment can be controlled to control the wire rod to quickly enter the bainite and pearlite mixed phase region from the high-temperature austenite state, forming a structure dominated by a small amount of quenched bainite and most of fine lamellar sorbite multiphase, which prepares the microstructure for the subsequent molten salt treatment. In the preferred technical solution, the molten salt temperature of the first stage of molten salt treatment is 400~450℃ and the processing time is 30~200s.

[0023] The front-end molten salt treatment uses a large molten salt circulation rate, which can promote rapid cooling and heat transfer of the wire rod, while controlling the molten salt temperature rise and improving the uniformity of continuous processing. In the preferred technical solution, the molten salt circulation rate of the front-end molten salt treatment is 460~660t / h, and the molten salt temperature rise is ≤10℃.

[0024] The molten salt temperature in the subsequent molten salt treatment is appropriately increased compared to the previous molten salt treatment. Higher molten salt temperatures and longer treatment times can increase the carbon atom diffusion rate, providing more driving force for the isothermal tempering and toughening of quenched bainite and sorbite structures. This can reduce internal stress and dislocation density in quenched bainite, improve the ductility and toughness of the microstructure, and enhance the uniformity of tempering on the surface and core. However, excessively high molten salt temperatures and long treatment times accelerate atomic diffusion, causing the cementite in the quenched bainite and sorbite to gradually coarsen and aggregate, resulting in excessive softening and significant loss of matrix strength. This also increases production cycle time and energy consumption. Conversely, lower molten salt temperatures and shorter treatment times result in slower carbon atom diffusion, which is beneficial for reducing... While reducing the risk of carbide coarsening and excessive strength loss, reducing production energy consumption, and improving production efficiency, excessively low molten salt temperature and short processing time make it difficult to provide sufficient thermal power for tempering, which will affect stress release and tempering effect, increase wire rod brittleness, and increase the difference between surface and core structure. Under stress, the core is prone to fracture due to stress concentration. Therefore, the molten salt temperature and processing time of the later stage of molten salt treatment can be further controlled to promote isothermal tempering of the formed quenched bainite and sorbite structures, while taking into account rapid processing and avoiding excessive softening, so as to regulate the strength and plasticity matching of the wire rod. In the preferred technical solution, the molten salt temperature of the later stage of molten salt treatment is 450~480℃, and the processing time is 50~200s.

[0025] Since the temperature difference between the molten salt in the first stage and the second stage is small, the molten salt circulation volume in the second stage is smaller than that in the first stage, which can appropriately reduce production energy consumption. At the same time, it can accurately control the molten salt temperature rise and improve the consistency of wire rod processing in continuous production. In the preferred technical solution, the molten salt circulation volume in the second stage is 320~410t / h, and the molten salt temperature rise is ≤3℃.

[0026] Since the wire rod has undergone sufficient phase transformation through online molten salt rapid quenching, the formation of low-temperature abnormal structures during slow cooling on the roller table can be avoided. Furthermore, since the wire rod is at a relatively high temperature after exiting the molten salt, selecting an appropriate slow cooling rate can prevent insufficient plasticity of the wire rod due to insufficient slow cooling. At the same time, slow cooling promotes further toughening of the wire rod structure and improves the tempering and softening effect of the wire rod. In the preferred technical solution, the slow cooling on the roller table controls the wire rod to cool to below 280°C at a slow cooling rate of ≤0.6°C / s before winding.

[0027] In the preferred technical solution, the slow cooling of the roller conveyor is achieved by controlling the opening of the heat insulation cover, blowing hot air at ≥250℃ during the online molten salt rapid quenching process onto the conveyor roller conveyor, and then conveying the wire rod through the heat insulation cover to control the slow cooling of the wire rod. This can further recover and utilize the heat energy from the online molten salt rapid quenching, reduce production energy consumption, and promote the rapid production of the wire rod.

[0028] A high-strength multiphase hot-rolled wire rod for 1960MPa grade stranded wire, wherein the hot-rolled wire rod is manufactured by the manufacturing method of the high-strength multiphase hot-rolled wire rod for 1960MPa grade stranded wire described in any one of the above-mentioned methods.

[0029] The aforementioned wire rods are designed with a high-carbon composition containing trace amounts of boron. Compared to high-alloy high-carbon steel wire rods used in air-cooled strands, this simplifies the composition system, reduces material costs, and effectively avoids the risk of network carbides caused by high carbon content. Rapid quenching with molten salt allows for the simultaneous transformation of quenched bainite and fine-grained sorbite, reducing the ferrite proportion. The fine acicular structure and high dislocation density of quenched bainite result in higher strength than sorbite. After isothermal tempering, the acicular morphology of tempered bainite is retained, but the substructure is more stable, reducing grain boundary embrittlement, preserving strength, and significantly improving brittle characteristics. The sorbite structure has finer lamellars and better strength and toughness than pearlite. After isothermal tempering to release stress, it transforms into a more oriented... The intermediate transition state of tempered sorbite in the spheroidization transformation further releases structural stress, which can further improve the plasticity of the structure. Furthermore, through the control of the multiphase structure and the tempering state of the structure, the strengthening effect of carbon can be maximized, compensating for the strength loss caused by reducing carbon content and omitting alloying elements. This makes the quenched bainite phase transformation, which is usually considered an abnormal structure, more controllable and usable, and avoids the adverse effects of martensite on the plasticity and toughness of the structure, as well as the adverse effects of coarse pearlite on the strength and uniformity of the matrix. It also reduces the difference in performance between the surface and the core, effectively improving the overall strength and plasticity of the wire rod based on the composition design, reducing the risk of stress concentration and brittle fracture during subsequent drawing and twisting processes, and meeting the manufacturing requirements of high-strength stranded wire.

[0030] In the multiphase structure, the higher the volume percentage of tempered sorbite, the higher the ductility and toughness. The finer the lamellar spacing of the tempered sorbite and the higher the volume percentage of tempered bainite, the stronger the resistance to dislocation movement and the higher the strength. In the preferred technical solution, the volume percentage of tempered sorbite is 68%~78%, the lamellar spacing is 70~115nm, and the volume percentage of tempered bainite is 20%~30%.

[0031] In the preferred technical solution, the hot-rolled wire rod has a network carbide level of 0 and a mechanical property difference of ≤38MPa within the same coil. This can effectively control the adverse effects of network carbides on the matrix's plasticity, toughness, microstructure uniformity, and fatigue performance. At the same time, it suppresses abnormal structures such as martensite and coarse pearlite, resulting in higher microstructure uniformity from the wire rod surface to the core. This can effectively reduce mechanical property fluctuations, thereby improving processing stability and reducing stress concentration and brittle fracture during subsequent wire drawing or twisting.

[0032] In the preferred technical solution, the hot-rolled wire rod has a diameter of 8.0~15.0mm, a tensile strength of 1330~1380MPa, and a section reduction rate of 35%~40%. The hot-rolled wire rod has a smaller size and higher tensile strength, which can reduce the number of subsequent drawing passes and quickly achieve the target diameter and strength of the strand. At the same time, it also has a high section reduction rate, which can meet the deformation requirements during strand drawing and twisting, and improve the stability and yield of large deformation processing.

[0033] Compared with the prior art, the beneficial effects of the present invention are at least as follows:

[0034] (1) In view of the fact that 1960MPa grade steel strand wire rod is mainly produced by alloy products with 0.87% carbon content and air-cooled line, it is easy to generate brittle structures such as network carbides and martensite, which leads to the fracture of hot-rolled wire rod during wire drawing and torsion. This invention adopts a carbon-containing B chemical composition design combined with online molten salt rapid quenching technology, which can control the wire rod to enter the mixed phase region of bainite and pearlite from the high temperature austenite state, forming a structure mainly composed of quenched bainite and fine lamellar interlayer sorbite. Then, the quenched bainite and sorbite structures are appropriately heated to promote isothermal tempering, so as to control the strength and plasticity matching of the wire rod. It can effectively suppress abnormal structures such as network carbides, martensite, and coarse pearlite. Finally, the slow cooling of the roller table promotes the further toughening of the wire rod structure. It takes into account rapid production and can achieve the control of multiphase structure and the high strength and plasticity matching of the wire rod, and has good industrial adaptability.

[0035] (2) In view of the defects of high cost, insufficient strength and plasticity or large fluctuation of mechanical properties of 1960MPa grade steel strand wire rod, the present invention adopts a high carbon composition design with trace amount of B, which can simplify the composition system and reduce material cost. The microstructure includes a multiphase structure composed of tempered sorbite, tempered bainite and ferrite. By controlling the multiphase structure and the tempering state of the structure, the strengthening effect of carbon element is maximized, which makes up for the strength loss caused by reducing carbon content and omitting alloying elements, and avoids the adverse effects of martensite on the plasticity and toughness of the structure, and avoids the adverse effects of coarse pearlite on the strength and uniformity of the matrix, effectively reducing the fluctuation of mechanical properties. Based on the composition design, the overall strength and plasticity of the wire rod are effectively improved, and the tensile strength can reach 1330~1380MPa, and the reduction of area is 35%~40%. It can then be used in fields such as 1960MPa grade steel strand, which is conducive to reducing stress concentration and brittle fracture risk in subsequent wire drawing and torsion processes, and has good market application prospects. Attached Figure Description

[0036] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0037] Figure 1 This is a metallographic diagram of Embodiment 1 of the present invention;

[0038] Figure 2 This is a metallographic diagram of Embodiment 2 of the present invention;

[0039] Figure 3 This is a metallographic diagram of Embodiment 3 of the present invention. Detailed Implementation

[0040] The embodiments described below with reference to the accompanying drawings are exemplary and are merely for illustrative purposes and do not limit the description of the features and characteristics of the invention. They are intended to provide the best mode for carrying out the invention, to explain the invention, and to enable those skilled in the art to practice the invention. However, they should not be construed as limiting the scope of the invention in any way, which is defined only by the appended claims. The microstructure and performance testing of the hot-rolled wire rods obtained in the following embodiments and comparative examples includes: tensile testing using GB-T228.1-2021 Metallic Materials - Tensile Testing - Part 1: Room Temperature Test Method, to obtain tensile strength and reduction of area; microstructure testing using the metal microstructure testing method of GB / T13298 standard; and mechanical property same-coil difference test method: two coils of wire rod are taken 5m from the end of the coil. Using the overlap area as the base point, each coil of wire rod is divided into 8 equal segments. One tensile specimen is taken from each segment. The difference in strength of the tensile specimens after tensile testing is the mechanical property same-coil difference. Example 1:

[0041] A preferred embodiment of the manufacturing method of the high-strength multiphase hot-rolled wire rod for 1960MPa grade stranded wire according to the present invention, wherein the chemical composition and mass percentage of the hot-rolled wire rod include C: 0.79%, Si: 0.39%, Mn: 0.69%, B: 0.001%, P: 0.013%, S: 0.015%, with the remainder being Fe and unavoidable impurities; the manufacturing method follows the process flow of rolling → wire drawing → online molten salt rapid quenching → roller table slow cooling → coiling, specifically:

[0042] The rolling process is used to heat a 220mm×220mm steel billet in a furnace to a high-temperature steel billet that is rollable and plastic, reducing compositional segregation and avoiding grain coarsening. After exiting the furnace, the billet is rolled into wire rod with a diameter of 11mm through a rolling line. Appropriate rolling temperature and reduction are selected to improve rolling efficiency and control the dynamic recrystallization during the final rolling process to refine the grains. Specifically, the furnace soaking temperature is controlled at 1195℃, and the furnace dwell time is... The rolling time is 200 min, the initial rolling temperature is 1085℃, the final rolling temperature is 920℃, and the final rolling reduction is 28.5%. The wire drawing process is used to convert the wire from the rolling line into coils through the wire drawing mechanism. The coils are distributed on the roller table and conveyed along the roller table. A suitable wire drawing temperature is selected to keep the coils in a high-temperature austenitizing state, avoiding the precipitation of network carbides during the wire drawing stage, and providing favorable conditions for the rapid nucleation of bainite and sorbite. Specifically, the wire drawing temperature is controlled at 905℃.

[0043] The online molten salt rapid quenching process employs a two-stage salt bath with internal molten salt. After wire drawing, the wire rod is conveyed via roller conveyor through the first stage salt bath for initial molten salt treatment, causing the wire rod to cool at a rate of 39°C / s. This rapidly transitions the wire rod from a high-temperature austenitic state, bypassing the network carbide region, into a mixed phase region of bainite and pearlite, inhibiting the formation of network carbides. The high-temperature austenitic phase transformation results in a microstructure dominated by a small portion of quenched bainite and a large portion of fine lamellar interlamellar sorbite. The wire rod is then conveyed via roller conveyor through the second stage salt bath for subsequent molten salt treatment. The process involves increasing the molten salt temperature and reducing the molten salt circulation rate to promote isothermal tempering of the formed quenched bainite and sorbite structures, while ensuring rapid processing and avoiding excessive softening, thereby controlling the strength and plasticity of the wire rod. Specifically: the molten salt temperature for the first stage of molten salt treatment is 432℃, the treatment time is 140s, the molten salt circulation rate is 515t / h, and the molten salt temperature rise is ≤10℃; the molten salt temperature for the second stage of molten salt treatment is 472℃, the treatment time is 170s, the molten salt circulation rate is 345t / h, and the molten salt temperature rise is ≤3℃.

[0044] The slow cooling process on the roller conveyor involves controlling the opening of the insulation cover to blow hot air (≥250℃) from above the two salt bath tanks in the online molten salt rapid quenching treatment onto the conveyor roller conveyor. The conveyor roller conveyor then transports the wire rod through the insulation cover, promoting further toughening of the wire rod structure and improving the tempering softening effect. Specifically, the wire rod is cooled to 274℃ at a slow cooling rate of 0.5℃ / s. The coiling process is used to coil the wire rod into coils using a coiling drum. After packaging and warehousing, the hot-rolled wire rod is obtained as a finished product, the metallographic structure of which is shown in the figure below. Figure 1 As shown.

[0045] Comparative Example 1:

[0046] A method for manufacturing hot-rolled wire rod differs from Example 1 in that it follows a process flow of rolling → wire drawing → Steyrmo air cooling. Specifically, the heating furnace is controlled at a uniform heating temperature of 1150°C, with a furnace time of 215 minutes. The initial rolling temperature is 1060°C, the final rolling temperature is 880°C, and the wire drawing temperature is 860°C. The Steyrmo forced air cooling uses a fan with an air volume of 260,000 m³ / s. 3 At 70% capacity, fans 1 to 5 are turned on to cool the wire rod to 683℃ at a cooling rate of 6.9℃ / s. Then, fans 6 to 14 are turned on to 30% capacity to cool the wire rod to 270℃ at a cooling rate of 2.6℃ / s. After cooling, the hot-rolled wire rod is obtained.

[0047] Comparative Example 2:

[0048] A method for manufacturing hot-rolled wire rod differs from that in Example 1 in that: the heating furnace is heated to a uniform temperature of 1150°C, the furnace time is 215 min, the initial rolling temperature is 1055°C, the final rolling temperature is 860°C, and the wire drawing temperature is 840°C. During the molten salt treatment before the online molten salt rapid quenching process, the wire rod is cooled at a rate of 32°C / s, and the finished hot-rolled wire rod is obtained after the process is completed. Example 2:

[0049] A preferred embodiment of the manufacturing method of the high-strength multiphase hot-rolled wire rod for 1960MPa grade stranded wire according to the present invention, wherein the chemical composition and mass percentage of the hot-rolled wire rod include C: 0.79%, Si: 0.25%, Mn: 0.72%, B: 0.008%, P: 0.014%, S: 0.015%, with the remainder being Fe and unavoidable impurities; the manufacturing method follows the process flow of rolling → wire drawing → online molten salt rapid quenching → roller table slow cooling → coiling, specifically:

[0050] The rolling process is used to heat a 180mm×180mm steel billet in a furnace to a high-temperature steel billet that is rollable and plastic, reducing compositional segregation and avoiding grain coarsening. After exiting the furnace, the billet is rolled into wire rod with a diameter of 8mm through a rolling line. Appropriate rolling temperatures and reductions are selected to improve rolling efficiency and control the dynamic recrystallization and grain refinement during the final rolling process. Specifically, the furnace soaking temperature is controlled at 1180℃, the furnace time at 220min, the initial rolling temperature at 1080℃, the final rolling temperature at 900℃, and the final rolling reduction at 30%. The wire drawing process is used to transfer the wire rod from the rolling line to a wire rod through a wire drawing machine. The wire rod is distributed on a roller conveyor and transported along the roller conveyor. An appropriate wire drawing temperature is selected to keep the wire rod in a high-temperature austenitizing state, preventing the precipitation of network carbides during the wire drawing stage and providing favorable conditions for the rapid nucleation of bainite and sorbite. Specifically, the wire drawing temperature is controlled at 890℃.

[0051] The online molten salt rapid quenching process employs a two-stage salt bath with internal molten salt. After wire drawing, the wire rod is conveyed via roller conveyor through the first stage salt bath for initial molten salt treatment, causing the wire rod to cool at a rate of 36°C / s. This rapidly transitions the wire rod from a high-temperature austenitic state, bypassing the network carbide region, into a mixed phase region of bainite and pearlite, inhibiting the formation of network carbides. The high-temperature austenitic phase transformation results in a microstructure dominated by a small portion of quenched bainite and a large portion of fine lamellar interlamellar sorbite. The wire rod is then conveyed via roller conveyor through the second stage salt bath for subsequent molten salt treatment. The process involves increasing the molten salt temperature and reducing the molten salt circulation rate to promote isothermal tempering of the formed quenched bainite and sorbite structures, while ensuring rapid processing and avoiding excessive softening, thereby controlling the strength and plasticity of the wire rod. Specifically: the molten salt temperature for the first stage of molten salt treatment is 450℃, the treatment time is 200s, the molten salt circulation rate is 460t / h, and the molten salt temperature rise is ≤10℃; the molten salt temperature for the second stage of molten salt treatment is 480℃, the treatment time is 50s, the molten salt circulation rate is 320t / h, and the molten salt temperature rise is ≤3℃.

[0052] The slow cooling process on the roller conveyor involves controlling the opening of the insulation cover to blow hot air (≥250℃) from above the two salt bath tanks used in the online molten salt rapid quenching treatment onto the conveyor roller conveyor. The conveyor roller conveyor then transports the wire rod through the insulation cover, promoting further toughening of the wire rod structure and improving the tempering softening effect. Specifically, the wire rod is cooled to 271℃ at a slow cooling rate of 0.6℃ / s. The coiling process involves coiling the wire rod into coils using a coiling drum. After packaging and warehousing, the hot-rolled wire rod is obtained as a finished product, the metallographic structure of which is shown in the figure below. Figure 2 As shown.

[0053] Comparative Example 3:

[0054] A method for manufacturing hot-rolled wire rod differs from that in Example 2 in that: during the initial molten salt treatment of the online molten salt rapid quenching process, the wire rod is cooled at a cooling rate of 40℃ / s, the molten salt temperature of the initial molten salt treatment is 395℃, the treatment time is 210s, and the finished hot-rolled wire rod is obtained after the process is completed.

[0055] Comparative Example 4:

[0056] A method for manufacturing hot-rolled wire rod differs from that in Example 2 in that: during the initial molten salt treatment of the online molten salt rapid quenching process, the wire rod is cooled at a cooling rate of 33°C / s, the molten salt temperature of the initial molten salt treatment is 475°C, the treatment time is 25s, and the finished hot-rolled wire rod is obtained after the process is completed. Example 3:

[0057] A preferred embodiment of the manufacturing method of the high-strength multiphase hot-rolled wire rod for 1960MPa grade stranded wire according to the present invention, wherein the chemical composition and mass percentage of the hot-rolled wire rod include C: 0.81%, Si: 0.4%, Mn: 0.67%, B: 0.005%, P: 0.013%, S: 0.014%, with the remainder being Fe and unavoidable impurities; the manufacturing method follows the process flow of rolling → wire drawing → online molten salt rapid quenching → roller table slow cooling → coiling, specifically:

[0058] The rolling process is used to heat a 220mm×220mm steel billet in a furnace to a high-temperature steel billet that can be rolled into plasticity, reducing compositional segregation and avoiding grain coarsening. After exiting the furnace, the billet is rolled into wire rod with a diameter of 13mm through a rolling line. Appropriate rolling temperature and reduction are selected to improve rolling efficiency and control the dynamic recrystallization and grain refinement during the final rolling process. Specifically, the furnace soaking temperature is controlled at 1210℃, the furnace time is 175min, the initial rolling temperature is 1095℃, the final rolling temperature is 930℃, and the final rolling reduction is 26%. The wire drawing process is used to convert the wire rod exiting the rolling line into wire rod through a wire drawing machine. The wire rod is distributed on the roller conveyor and conveyed along the roller conveyor. An appropriate wire drawing temperature is selected to keep the wire rod in a high-temperature austenitizing state, avoiding the precipitation of network carbides during the wire drawing stage, and providing favorable conditions for the rapid nucleation of bainite and sorbite. Specifically, the wire drawing temperature is controlled at 915℃.

[0059] The online molten salt rapid quenching process employs a two-stage salt bath with internal molten salt. After wire drawing, the wire rod is conveyed via roller conveyor through the first stage salt bath for initial molten salt treatment, causing the wire rod to cool at a rate of 40°C / s. This rapidly transitions the wire rod from a high-temperature austenitic state, bypassing the network carbide region, into a mixed phase region of bainite and pearlite, inhibiting the formation of network carbides. The high-temperature austenitic phase transformation results in a microstructure dominated by a small portion of quenched bainite and a large portion of fine lamellar interlamellar sorbite. The wire rod is then conveyed via roller conveyor through the second stage salt bath for subsequent molten salt treatment. The process involves increasing the molten salt temperature and reducing the molten salt circulation rate to promote isothermal tempering of the formed quenched bainite and sorbite structures, while ensuring rapid processing and avoiding excessive softening, thereby controlling the strength and plasticity of the wire rod. Specifically: the molten salt temperature for the first stage of molten salt treatment is 415℃, the treatment time is 95s, the molten salt circulation rate is 570t / h, and the molten salt temperature rise is ≤10℃; the molten salt temperature for the second stage of molten salt treatment is 465℃, the treatment time is 105s, the molten salt circulation rate is 370t / h, and the molten salt temperature rise is ≤3℃.

[0060] The slow cooling process on the roller conveyor involves controlling the opening of the insulation cover to blow hot air (≥250℃) from above the two salt bath tanks used in the online molten salt rapid quenching treatment onto the conveyor roller conveyor. The conveyor roller conveyor then transports the wire rod through the insulation cover, promoting further toughening of the wire rod structure and improving the tempering softening effect. Specifically, the wire rod is cooled to 276℃ at a slow cooling rate of 0.45℃ / s. The coiling process involves coiling the wire rod into coils using a coiling drum. After packaging and warehousing, the hot-rolled wire rod is obtained as a finished product, the metallographic structure of which is shown in the figure below. Figure 3 As shown.

[0061] Comparative Example 5:

[0062] A method for manufacturing hot-rolled wire rod, the difference between the method and Example 3 is that: the molten salt temperature of the subsequent molten salt treatment is 490℃, the treatment time is 210s, and the finished hot-rolled wire rod is obtained after the process is completed.

[0063] Comparative Example 6:

[0064] A method for manufacturing hot-rolled wire rod, the difference between the method and Example 3 is that: the molten salt temperature of the subsequent molten salt treatment is 440°C, the treatment time is 45s, and the finished hot-rolled wire rod is obtained after the process is completed. Example 4:

[0065] A preferred embodiment of the manufacturing method of the high-strength multiphase hot-rolled wire rod for 1960MPa grade stranded wire according to the present invention, wherein the chemical composition and mass percentage of the hot-rolled wire rod include C: 0.83%, Si: 0.35%, Mn: 0.78%, B: 0.004%, P: 0.015%, S: 0.014%, with the remainder being Fe and unavoidable impurities; the manufacturing method follows the process flow of rolling → wire drawing → online molten salt rapid quenching → roller table slow cooling → coiling, specifically:

[0066] The rolling process is used to heat a 220mm×220mm steel billet in a furnace to a high-temperature steel billet that is rollable and plastic, reducing compositional segregation and avoiding grain coarsening. After exiting the furnace, the billet is rolled into wire rod with a diameter of 15mm through a rolling line. Appropriate rolling temperatures and reductions are selected to improve rolling efficiency and control the dynamic recrystallization and grain refinement during the final rolling process. Specifically, the furnace soaking temperature is controlled at 1220℃, the furnace time at 150min, the initial rolling temperature at 1100℃, the final rolling temperature at 940℃, and the final rolling reduction at 25%. The wire drawing process is used to convert the wire rod exiting the rolling line into coil through a wire drawing machine. The coil is distributed on a roller conveyor and transported along the roller conveyor. An appropriate wire drawing temperature is selected to keep the coil in a high-temperature austenitizing state, preventing the precipitation of network carbides during the wire drawing stage and providing favorable conditions for the rapid nucleation of bainite and sorbite. Specifically, the wire drawing temperature is controlled at 930℃.

[0067] The online molten salt rapid quenching process employs a two-stage salt bath with internal molten salt. After wire drawing, the wire rod is conveyed via roller conveyor through the first stage salt bath for initial molten salt treatment, causing the wire rod to cool at a rate of 42℃ / s. This rapidly transitions the wire rod from a high-temperature austenitic state, bypassing the network carbide region, into a mixed phase region of bainite and pearlite, inhibiting the formation of network carbides. The high-temperature austenitic phase transformation results in a microstructure dominated by a small portion of quenched bainite and a large portion of fine lamellar interlamellar sorbite. The wire rod is then conveyed via roller conveyor through the second stage salt bath for subsequent molten salt treatment. The process involves increasing the molten salt temperature and reducing the molten salt circulation rate to promote isothermal tempering of the formed quenched bainite and sorbite structures, while ensuring rapid processing and avoiding excessive softening, thereby controlling the strength and plasticity of the wire rod. Specifically: the molten salt temperature for the first stage of molten salt treatment is 400℃, the treatment time is 30s, the molten salt circulation rate is 660t / h, and the molten salt temperature rise is ≤10℃; the molten salt temperature for the second stage of molten salt treatment is 450℃, the treatment time is 200s, the molten salt circulation rate is 410t / h, and the molten salt temperature rise is ≤3℃.

[0068] The slow cooling process of the roller conveyor involves controlling the opening of the insulation cover to blow hot air (≥250℃) from the two salt bath tanks of the online molten salt rapid quenching treatment onto the conveyor roller conveyor. The conveyor roller conveyor then transports the wire rod through the insulation cover, promoting further toughening of the wire rod structure and improving the tempering and softening effect of the wire rod. Specifically, the wire rod is cooled to 278℃ at a slow cooling rate of 0.2℃ / s. The coiling process is used to coil the wire rod into coils using a coiling drum. After packaging and warehousing, the hot-rolled wire rod is obtained as a finished product.

[0069] Comparative Example 7:

[0070] A method for manufacturing hot-rolled wire rod differs from that in Example 4 in that the method follows a process flow of rolling → wire drawing → online molten salt rapid quenching → air cooling. The air cooling process involves opening the insulation cover and controlling the wire rod to cool to 270°C at a slow cooling rate of 1.3°C / s. After the wire rod is removed from the production line, the finished hot-rolled wire rod is obtained.

[0071] The microstructure and properties of the hot-rolled wire rods obtained in Examples 1-4 and Comparative Examples 1-7 were tested, and the comparative results are shown in Table 1 below:

[0072] Table 1. Comparison of microstructure and properties of hot-rolled wire rods with different compositions and manufacturing methods

[0073]

[0074] In the table above, the lamellar spacing of Comparative Example 2 refers to the lamellar spacing of pearlite, while the others refer to the lamellar spacing of tempered sorbite. As can be seen from the comparison between Example 1 and Comparative Example 1, even after reducing carbon content and omitting alloying elements, a higher level of network carbides is still generated under air-cooling conditions, which adversely affects the fluctuations in the matrix's ductility, toughness, and mechanical properties. Simultaneously, the weak cooling rate weakens the strengthening effect, and the strong air-cooling after wire drawing further increases the radial difference in strength and ductility and the fluctuations in mechanical properties. This invention employs a carbon-containing B-based chemical composition design combined with online molten salt rapid quenching technology to form a quenched... The microstructure, dominated by a mixture of bainite and fine lamellar sorbite, is effectively improved by isothermal tempering at appropriate temperatures, resulting in the formation of abnormal microstructures such as network carbides, martensite, and coarse pearlite. As can be seen from the results of Examples 1-4, this invention simplifies the composition system, reduces material costs, and achieves multiphase microstructure control. It also balances the strength and plasticity of the wire rod with rapid production. The wire rod can achieve a tensile strength of 1330-1380 MPa and a reduction of area of ​​35%-40%, which can then be used in fields such as 1960 MPa grade steel strand, thereby reducing the risk of wire breakage during the drawing and twisting process of the stranded steel.

[0075] As can be seen from the comparison results between Example 1 and Comparative Example 2, using a higher wire rod spinning temperature keeps the microstructure in a high-temperature austenitic state, which can suppress component segregation, avoid the formation of network carbides due to excessively low temperature, provide favorable conditions for promoting bainite quenching and lamellar refinement, and at the same time reduce the limitation on rolling temperature.

[0076] The comparison results between Example 2 and Comparative Example 3 show that the lower the molten salt temperature and the longer the treatment time in the initial molten salt treatment, the better it works in conjunction with the hardenability of B to suppress network carbides and lamellar coarsening, increase the undercooling of austenite, and make the shear driving force of acicular quenched bainite transformation dominant and accelerate the nucleation rate, which is beneficial to promoting the refinement of sorbite lamellar structure and can improve the matrix strength. However, if the molten salt temperature is too low and the treatment time is too long, the quenched bainite transformation will increase and the internal stress of the structure will increase the difficulty of subsequent tempering and softening, affect the plasticity of wire rod and production efficiency, and increase production energy consumption.

[0077] As can be seen from the comparison results between Example 2 and Comparative Example 4, the higher the molten salt temperature and the shorter the treatment time in the first stage of molten salt treatment, the stronger the diffusion driving force of sorbite transformation, making it easier to form sorbite lamellar structure and reducing the difficulty of improving the plasticity of tempering. However, if the molten salt temperature is too high and the treatment time is too short, it is not conducive to the formation of quenched bainite, and there is a risk of coarse sorbite lamellars, which in turn leads to a loss of matrix strength.

[0078] As can be seen from the comparison results between Example 3 and Comparative Example 5, the higher the molten salt temperature and the longer the treatment time in the later stage of molten salt treatment, the higher the carbon atom diffusion rate can be, providing more driving force for the isothermal tempering and toughening of quenched bainite and sorbite structures. This can reduce the stress and dislocation density in quenched bainite, improve the ductility and toughness of the structure, and enhance the uniformity of tempering of the surface and core structures. However, if the molten salt temperature is too high and the treatment time is too long, the atomic diffusion rate will accelerate, and the cementite in quenched bainite and sorbite will gradually coarsen and aggregate, resulting in excessive softening and significant loss of matrix strength. At the same time, it will lead to an increase in production cycle and energy consumption.

[0079] As can be seen from the comparison results between Example 3 and Comparative Example 6, the lower the molten salt temperature and the shorter the processing time in the later stage of molten salt treatment, the slower the carbon atom diffusion rate, which is beneficial to reduce the risk of carbide coarsening and excessive strength loss, reduce production energy consumption, and improve production efficiency. However, if the molten salt temperature is too low and the processing time is too short, it is difficult to provide more thermal power for tempering, which will affect stress release and tempering effect, increase the brittleness of the wire rod, the difference between the surface and core structure, and the core is prone to fracture due to stress concentration when under stress.

[0080] As can be seen from the comparison results of Example 4 and Comparative Example 7, the temperature of the wire rod after exiting the molten salt is relatively high. The use of roller table slow cooling can avoid insufficient wire rod plasticity due to insufficient slow cooling. At the same time, slow cooling promotes further toughening of the wire rod structure and improves the tempering and softening effect of the wire rod.

[0081] The detailed descriptions listed above are merely specific illustrations of feasible embodiments of the present invention and are not intended to limit the scope of protection of the present invention. All equivalent embodiments or modifications made without departing from the spirit of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for manufacturing high-strength multiphase hot-rolled wire rod for 1960MPa grade stranded wire, characterized in that, Its manufacturing methods include: The wire rod is rolled into production line according to the chemical composition of hot-rolled wire rod. The chemical composition and mass percentage of the hot-rolled wire rod include: C: 0.79%~0.83%, Si: 0.20%~0.40%, Mn: 0.67%~0.78%, B: 0.001%~0.008%, P≤0.015%, S≤0.015%, with the remainder being Fe and unavoidable impurities. After the wire rod is spun into wire rod at a spinning temperature of ≥890℃, it undergoes online molten salt rapid quenching treatment. The wire rod first undergoes a pre-treatment molten salt treatment, which cools the wire rod at a cooling rate of ≥36℃ / s. The austenitic state enters the mixed phase region of bainite and pearlite, forming a microstructure mainly composed of quenched bainite and sorbite. The wire rod then undergoes a subsequent molten salt treatment to increase the molten salt temperature and promote isothermal tempering of the quenched bainite and sorbite microstructures. Finally, it is slowly cooled by roller conveyors to produce a hot-rolled wire rod with a microstructure consisting of a multiphase microstructure composed of tempered sorbite, tempered bainite, and ferrite. The molten salt temperature of the first stage molten salt treatment is 400~450℃, and the treatment time is 30~200s. The molten salt temperature of the second stage molten salt treatment is 450~480℃, and the treatment time is 50~200s.

2. The method for manufacturing high-strength multiphase hot-rolled wire rod for 1960MPa grade stranded wire according to claim 1, characterized in that, Before rolling, the heating furnace temperature is controlled at 1180~1220℃ and the furnace time is 150~220min.

3. The method for manufacturing high-strength multiphase hot-rolled wire rod for 1960MPa grade stranded wire according to claim 1, characterized in that, During the rolling process, the initial rolling temperature is controlled at 1080~1100℃, the final rolling temperature at 900~940℃, and the final rolling reduction at 25%~30%.

4. The method for manufacturing high-strength multiphase hot-rolled wire rod for 1960MPa grade stranded wire according to claim 1, characterized in that, During the spinning process, the spinning temperature is controlled at 890~930℃.

5. The method for manufacturing high-strength multiphase hot-rolled wire rod for 1960MPa grade stranded wire according to claim 1, characterized in that, The molten salt circulation rate of the front-end molten salt treatment is 460~660t / h, and the molten salt temperature rise is ≤10℃; the molten salt circulation rate of the rear-end molten salt treatment is 320~410t / h, and the molten salt temperature rise is ≤3℃.

6. The method for manufacturing high-strength multiphase hot-rolled wire rod for 1960MPa grade stranded wire according to claim 1, characterized in that, The roller conveyor slow cooling control strip is cooled to below 280°C at a slow cooling rate of ≤0.6°C / s before being wound up.

7. A high-strength multiphase hot-rolled wire rod for 1960MPa grade stranded wire, characterized in that, The hot-rolled wire rod is manufactured by the manufacturing method of high-strength multiphase hot-rolled wire rod for 1960MPa grade strand as described in any one of claims 1 to 6.

8. The high-strength multiphase hot-rolled wire rod for 1960MPa grade stranded wire according to claim 7, characterized in that, The volume percentage of the tempered sorbite is 68%~78%, the lamellar spacing is 70~115nm, the volume percentage of the tempered bainite is 20%~30%, the network carbide grade of the hot-rolled wire rod is 0, and the mechanical property difference between the same ring is ≤38MPa.

9. The high-strength multiphase hot-rolled wire rod for 1960MPa grade stranded wire according to claim 7, characterized in that, The hot-rolled wire rod has a diameter of 8.0~15.0mm, a tensile strength of 1330~1380MPa, and a reduction of area of ​​35%~40%.

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