A high-strength multiphase hot-rolled wire rod for 2060MPa grade stranded wire and its manufacturing method

Abstract

This invention relates to a high-strength multiphase hot-rolled wire rod for 2060MPa grade stranded wire and its manufacturing method. The method involves designing and rolling the high-carbon chemical composition (containing trace amounts of V) into wire rods, followed by online molten salt semi-quenching. This process cools the wire rod at a rate of ≥33℃ / s, transitioning it 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 is then isothermally tempered and finally slowly cooled via a roller conveyor, resulting in a hot-rolled wire rod with a microstructure consisting of tempered sorbite and tempered bainite, comprising a multiphase microstructure. This method simplifies the composition system, reduces material costs, effectively controls network carbides, and achieves multiphase microstructure regulation, improving the balance between high strength and plasticity. The wire rod achieves a tensile strength of 1390~1440MPa and a reduction of area of ​​32%~37%, making it suitable for manufacturing 2060MPa grade stranded wire and other applications, and beneficial for downstream wire drawing and twisting processes.

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 2060MPa grade stranded wire and its manufacturing method. Background Technology

[0002] The improvement of steel strand strength grade can strongly promote the development of large-scale engineering projects towards higher stress service environments, and at the same time, it can also help reduce the use of high-strength strands, achieving the goal of energy conservation and consumption reduction. Steel strand uses hot-rolled wire rod as the base material, which undergoes pretreatment to remove surface defects, multiple drawing into steel wire, and then twisting and stranding. Therefore, the quality of hot-rolled wire rod is directly related to the performance and stable production of steel strand. At present, pearlitic steel strand is the main steel grade and has become the mainstream in the field of steel strand. Other types of steel strand have been less developed because hot-rolled wire rod for steel strand is usually produced by Stellmore air-cooling line. For example, patent CN117845141A discloses a 1960~2060MPa grade prestressed steel strand and its preparation method. Its wire rod adopts a high carbon composition design of C-Mn-Si-Cr-V-Ti-Nb and is combined with low-speed air cooling to form pearlitic wire rod. However, the following technical defects still exist:

[0003] I. To refine the pearlite lamellar spacing and improve the mechanical strength of the alloy, wire rods adopt a high-carbon composition system strengthened by multiple alloys. Based on Mn-Si main alloying, Cr is added as an alloying element. However, this increases material cost and smelting difficulty. Simultaneously, higher Si content increases work hardening sensitivity, leading to concentrated plastic deformation. During solidification, the alloy composition exhibits certain segregation. At high temperatures, Cr tends to segregate towards austenite grain boundaries, reducing grain boundary bonding and exacerbating grain boundary embrittlement. With increased air-cooling strength, the risk of martensite and other abnormal structures precipitating further increases, leading to increased fluctuations in the wire rod's mechanical properties and increasing the risk of subsequent brittle fracture. On the other hand, reducing alloy content and simplifying the composition system to lower material cost, smelting difficulty, and processing sensitivity results in an increased sorbite transformation initiation temperature and a lack of Cr's promoting effect on carbide nucleation and growth. This necessitates low-temperature controlled rolling and rapid cooling. However, low-temperature controlled rolling will affect rolling production efficiency and increase... The rolling line's load requirements are limited by the maximum cooling capacity of the Steyrmore air-cooling line. The wire rod slowly passes through the secondary cementite and pearlite precipitation temperature range. During the wire drawing and subsequent air cooling processes, high carbon enrichment easily forms network carbides. These network carbides disrupt the continuity of the pearlite matrix, affecting the wire rod's ductility and toughness, resulting in uneven deformation transmission. This becomes a source of crack initiation during subsequent wire drawing or twisting. On the other hand, the wire rod's hardenability decreases. As the air cooling intensity of the Steyrmore air-cooling line increases, the difference in cooling rate between the core and surface of the wire rod is further amplified due to unstable temperature control. In particular, as the wire rod diameter decreases, excessively rapid surface or local cooling easily forms a low-temperature brittle structure, while slow core cooling easily coarsens the cementite during the cooling process. As carbon segregation in the core further exacerbates the unevenness of pearlite size, it leads to significant strength loss and mechanical property fluctuations, making it difficult to achieve the target strength and exhibiting significant anisotropy, which is detrimental to downstream wire drawing.

[0004] II. In order to improve the drawing performance, strong carbide-forming elements such as V, Ti, and Nb are added to the wire rod to refine the grains. However, due to the minimum cooling capacity and continuous cooling limitation of the Steyrmo air-cooling line, the precipitation motive is insufficient, which easily leads to insufficient precipitation and uneven coarseness of microalloyed carbides, making it difficult to give full play to their strengthening effect. This results in a large amount of required content and elements. As expensive alloying elements, this will lead to an increase in material cost. On the other hand, after reducing the content of microalloyed alloys and simplifying the composition system, the austenite grains become coarser and the nucleation efficiency decreases. Due to the limitation of the maximum cooling capacity of air cooling, the microstructure is easily coarsened, resulting in a significant loss of strength, which is not conducive to the development of steel strands towards ultra-high strengthening. Summary of the Invention

[0005] The present invention aims to at least partially solve one of the above-mentioned technical problems. The present invention provides a high-strength multiphase hot-rolled wire rod for 2060MPa grade stranded wire and its manufacturing method, which can simplify the composition system, reduce material costs, effectively control network carbides, and at the same time achieve multiphase structure regulation, improve the high strength and plasticity matching of the wire rod, which is beneficial to downstream wire drawing and twisting processing.

[0006] The technical solution adopted by this invention to solve its technical problem is:

[0007] A method for manufacturing high-strength multiphase hot-rolled wire rod for 2060MPa grade stranded wire, the method comprising:

[0008] The hot-rolled wire rod is rolled into a production line based on its chemical composition. The chemical composition and mass percentage of the hot-rolled wire rod include: C: 0.84%~0.88%, Si: 0.30%~0.47%, Mn: 0.65%~0.85%, V: 0.01%~0.03%, 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 ≥880℃, it undergoes online molten salt semi-quenching treatment, which cools the wire rod at a cooling rate of ≥33℃ / s, allowing it to transition from the austenitic state to the mixed phase region of bainite and pearlite, forming a microstructure dominated by quenched bainite and sorbite. It is then isothermally tempered and finally slowly cooled on a roller table to produce a hot-rolled wire rod with a microstructure consisting of tempered sorbite and tempered bainite.

[0009] The chemical composition and mass percentage of the above-mentioned hot-rolled wire rods are designed based on the following:

[0010] (1) Carbon: C is a solid solution strengthening element in steel. It is relatively cheaper. It forms interstitial solid solutions in the iron matrix and forms carbides with V, which can hinder dislocation movement and improve the strength of the matrix. During online molten salt semi-quenching, it can reduce the pearlite phase transformation temperature, expand the austenite stable zone and bainite transformation zone, delay the transformation of austenite to pearlite, and promote a small amount of quenched bainite phase transformation. However, if the C content is too high, it will make it more difficult to control the center segregation, network carbides and carbide coarsening of high carbon steel billets. Carbon enrichment in austenite will increase the proportion of bainite in the multiphase structure and the risk of martensite precipitation, affecting toughness and drawing plasticity. Therefore, in order to take into account the high strength requirements of 2060MPa grade strand, reduce the difficulty of controlling the structure uniformity and abnormal structure, and adapt to the control of multiphase structure, the mass percentage of C is controlled at 0.84%~0.88%.

[0011] (2) Silicon: Si can cause lattice distortion when dissolved in the iron matrix through solid solution strengthening, which hinders dislocation movement and increases the hardness and strength of the matrix. During online molten salt semi-quenching, silicon can be enriched at the austenite or cementite interface, hindering the diffusion of carbon atoms into cementite, delaying the transformation kinetics of pearlite, and helping to promote the transformation of bainite. At the same time, it can delay the transformation of carbides from fine dispersed state to coarse aggregated state, so that it can still maintain high strength after tempering. However, excessive silicon will promote decarburization, prolong the phase transformation incubation period, and increase the degree of lattice distortion and dislocation movement resistance, which will increase the difficulty of softening, leading to a decrease in the plasticity and production efficiency of steel. This will then cause breakage in subsequent wire drawing, twisting and other processing steps, affecting the yield of stranded wire. Therefore, in order to adapt to the control of phase transformation structure by online molten salt semi-quenching treatment, the mass percentage of Si is controlled at 0.30%~0.47%.

[0012] (3) Manganese: Mn is a strong austenite stabilizing element. During online molten salt semi-quenching, it can lower the transformation temperature of austenite to pearlite or bainite. The lower phase transformation temperature will make the phase transformation products of sorbite and bainite finer, avoiding coarse pearlite or premature precipitation of ferrite. It hinders dislocation movement through lattice distortion and forms a synergistic effect with the solid solution strengthening of Si, thereby improving the matrix strength. However, if the Mn content is too high, it will increase element segregation during the solidification process of the billet, which will increase the high-temperature strength of the steel. During rolling, it is necessary to... Greater rolling force can easily lead to increased roll wear and excessive rolling load. At high temperatures, Mn tends to segregate at austenite grain boundaries and easily forms low-temperature martensite during cooling, increasing the risk of abnormal precipitation and stress concentration, which in turn increases the risk of brittle fracture during subsequent wire drawing and twisting. It also increases the difficulty of tempering and softening, thereby reducing the plasticity of the wire rod. Therefore, in order to balance the control of the 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 0.65%~0.85%.

[0013] (4) Vanadium: As a microalloying element, V can be precipitated by strain in the high-temperature hot rolling process, pinning grain boundaries to refine grains, increasing the nucleation core of sorbite phase transformation, which helps to obtain fine and uniform sorbite structure, and is conducive to the formation of bainite at lower temperatures, making the bainite structure finer and more dispersed. Excess V can disperse and precipitate nanoscale VC precipitates during the medium-temperature isothermal process, and rapidly strengthen the matrix through solid solution strengthening and precipitation strengthening. However, V is expensive, and excessive addition is not conducive to controlling material costs. Therefore, the mass percentage of V is controlled at 0.01%~0.03%.

[0014] (5) Phosphorus and sulfur: P and S are impurity elements, and the lower the better. Therefore, P ≤ 0.015% and S ≤ 0.015%.

[0015] The aforementioned hot-rolled wire rod adopts a high-carbon composition design of C-Si-Mn-V, free of elements such as Cr, Nb, and Ti, with trace amounts of V added. This simplifies the composition system, reduces material costs, and optimizes the proportions of each element, controlling the hardenability of the wire rod and expanding the bainitic transformation range. This provides favorable conditions for forming a mixed phase region of bainite and pearlite, reducing the risk of compositional segregation, suppressing coarsening of pearlite and ferrite, promoting the synchronous transformation of a small portion of bainite and most of sorbite, and facilitating the control of multiphase structure and microstructure uniformity. Furthermore, a relatively high wire drawing temperature is selected to ensure complete austenitization of the wire rod, avoiding the formation of network carbides during the wire drawing stage due to excessively low temperatures. A temperature difference with the molten salt temperature provides favorable conditions for obtaining sufficient undercooling to promote the synchronous transformation of bainite and sorbite. After wire drawing, the wire rod undergoes online molten salt semi-quenching without air cooling.

[0016] I. Compared to the simplified composition system, the limitations of the Steyrmore air-cooled line in terms of maximum cooling capacity and unstable temperature control make it difficult to suppress network carbides and regulate multiphase microstructure. On the one hand, the rapid cooling capacity of molten salt can be used to promote the rapid cooling of the wire rod from the high-temperature austenitic state, bypassing the precipitation temperature range of secondary cementite, thus suppressing the network carbides caused by high carbon content. At the same time, rapid cooling increases the undercooling and phase transformation driving force, avoiding premature precipitation of pearlite and ferrite soft phases in the early stage of cooling, which would cause strength loss and mechanical property fluctuations. After expanding the bainite phase region, the temperature of the bainite-pearlite mixed phase region is relatively low, which can promote the synchronous phase transformation of a small amount of bainite and promote the refinement of cementite lamellars to form a large amount of sorbite microstructure with finer lamellar spacing. This process increases the nucleation rate, thereby compensating for the adverse effects of omitting alloying elements and the coarsening of cementite during the process on the phase transformation driving force, thus improving the matrix strength. On the other hand, when the wire rod passes through molten salt, the molten salt can cover the surface of the wire rod for uniform heat exchange, making the bainitic phase transformation, which is usually considered an abnormal structure, controllable. At the same time, the temperature of the mixed bainite and pearlite phase region is higher than that of the martensite phase region. In particular, as the wire rod diameter decreases, it can avoid the formation of brittle martensite structure due to local overcooling under the influence of segregation. With the extension of the processing time, the temperature gradient from the wire rod surface to the core can be further reduced, promoting the full transformation of the structure and avoiding the continued formation of martensite structure due to austenite residue during subsequent cooling, thereby improving the uniformity of the structure and reducing the risk of brittleness.

[0017] Second, compared to the limitations of the Stellmore air-cooling line's minimum cooling capacity and continuous cooling, which prevent it from exerting dispersion strengthening and improving microstructure brittleness, rapid cooling can increase the precipitation motive force of VC, avoiding coarsening of the precipitation due to excessively long high-temperature periods and preventing uneven precipitation size. As the processing time increases, excess VC can fully disperse and precipitate nano-sized VC phases during the medium-temperature isothermal process of online molten salt semi-quenching, thereby fully exerting the dispersion strengthening effect, compensating for the strength loss during isothermal tempering, and providing good cold drawing performance. On the other hand, in online molten salt semi-quenching, the wire rod temperature gradually... The phase transformation is carried out at the same temperature as the molten salt, rather than continuous cooling. After the phase transformation, the wire rod can stay in the medium temperature range for a longer period of time instead of being in a low temperature state. The carbon diffusion ability is enhanced, and metastable carbides can transform into stable cementite, thereby reducing the dislocation density of bainite, refining and stabilizing carbides, eliminating quenching internal stress, and effectively improving bainite brittleness and stress concentration. Finally, the wire rod is slowly cooled on the roller table, continuing the relatively high temperature state after the wire rod exits the molten salt and slowly cooling down to promote further toughening of the microstructure. This controls the multiphase microstructure and tempering state, effectively improving the overall strength and plasticity matching of the wire rod on the basis of simplified composition.

[0018] Before rolling, the heating furnace homogenization temperature and furnace time can be controlled to make the surface and internal temperature of the billet more consistent, reduce segregation, improve rolling plasticity, reduce deformation resistance, provide a good microstructure for subsequent rolling, and avoid overheating caused by excessively high heating furnace homogenization temperature and excessively long furnace time. In the preferred technical solution, before rolling, the heating furnace homogenization temperature is controlled at 1170~1210℃ and the furnace time is controlled at 160~250min.

[0019] Because the wire drawing temperature is relatively high, the limitation on the rolling temperature can be reduced. The use of a higher initial rolling temperature during rolling can reduce wear on the rolling line, increase the rolling speed, control the final rolling temperature and final rolling reduction, and induce V-pinning grain boundary precipitation to refine the grains, strengthen and toughen the matrix, and provide favorable conditions for subsequent cooling to form a refined microstructure. In the preferred technical solution, the initial rolling temperature is controlled at 1065~1100℃, the final rolling temperature is controlled at 890~930℃, and the final rolling reduction is 27%~32%.

[0020] During the wire spinning process, the wire spinning temperature can be further controlled to suppress austenite grain growth. In a preferred embodiment, the wire spinning temperature is controlled to be 880~915℃.

[0021] In the preferred technical solution, the online molten salt semi-quenching treatment is divided into a front-stage molten salt treatment and a rear-stage molten salt treatment. The molten salt circulation volume of the front-stage molten salt treatment is greater than that of the rear-stage molten salt treatment. As the treatment time increases, the temperature difference between the wire rod surface and the core gradually decreases. Appropriately reducing the molten salt circulation volume in the rear-stage molten salt treatment can further reduce production energy consumption and costs.

[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 help suppress the formation of network carbides, increase undercooling, inhibit the premature precipitation of coarse pearlite and ferrite, promote preferential nucleation of bainite at austenite grain boundaries and dislocations, and reduce the interlamellar spacing of sorbite. With prolonged treatment time, the dispersion precipitation kinetics of vanadium-containing carbides can be increased, and nanoscale precipitates can be simultaneously precipitated during the bainite and sorbite transformation, improving matrix strength. However, excessively low molten salt temperatures and prolonged treatment times can lead to an increase in bainite in the transformation products, affecting the sorbite transformation, resulting in higher dislocation density and stress in the microstructure, increasing softening difficulty and production energy consumption, and affecting microstructure plasticity and production efficiency. Conversely, higher molten salt temperatures and shorter treatment times help reduce abnormal microstructures such as martensite. To reduce the risk of precipitation, promote sorbite transformation, reduce structural and thermal stress, reduce stress release difficulty, reduce production energy consumption, and promote rapid production, but excessively high molten salt temperature and short processing time are not conducive to suppressing network carbides and abnormal structures. The driving force for the formation of bainite and vanadium-containing carbides decreases, and the matrix strength and structural uniformity decrease. Therefore, the molten salt temperature and processing time of the first stage of treatment can be controlled to allow the wire rod to quickly enter the mixed phase region of bainite and pearlite from the high-temperature austenitic state, forming a structure dominated by quenched bainite and fine lamellar interlamellar sorbite, promoting the precipitation of nano-precipitates, taking into account production energy consumption, and preparing the structure for the subsequent molten salt treatment. In the preferred technical solution, the molten salt temperature of the first stage of molten salt treatment is 455~485℃, and the processing time is 45~150s.

[0023] Since the spinning temperature differs significantly from the molten salt temperature in the preceding molten salt treatment, using a larger molten salt circulation rate can reduce the molten salt temperature rise and improve the uniformity of the strand structure in continuous processing. In the preferred technical solution, the molten salt circulation rate in the preceding molten salt treatment is 450~650t / h, and the molten salt temperature rise is ≤10℃.

[0024] The molten salt temperature in the subsequent molten salt treatment is located in the mixed phase region of bainite and pearlite. Higher molten salt temperatures and longer treatment times are beneficial for improving atomic diffusion, reducing the dislocation density of quenched bainite, promoting stress release, and facilitating the full dispersion and precipitation of vanadium-containing carbides, thus improving overall plasticity and toughness. However, excessively high molten salt temperatures and long treatment times lead to increased atomic diffusion, excessive tempering and softening of the microstructure, resulting in strength loss. Simultaneously, the coarsening of vanadium carbides leads to a loss of strength and plasticity, increasing production energy consumption. Conversely, lower molten salt temperatures and shorter treatment times help reduce softening rate and production energy consumption, shortening the production cycle. Short production time suppresses the coarsening of dispersed precipitates and reduces strength loss. However, if the molten salt temperature is too low and the treatment time is too short, it will be detrimental to isothermal tempering and softening. Vanadium-containing carbides will not be fully precipitated, and the structural stress will not be fully released, resulting in a loss of strength and plasticity. Therefore, the molten salt temperature and treatment time in the later stage can be further controlled to promote isothermal tempering of the formed quenched bainite and sorbite structures and control the dispersed precipitation of carbides, so as to regulate the strength and plasticity matching of the wire rod. In the preferred technical solution, the molten salt temperature in the later stage of molten salt treatment is 450~470℃ and the treatment time is 210~400s.

[0025] Since the temperature difference between the molten salt in the front-end molten salt treatment and the back-end molten salt treatment is small, the molten salt circulation volume in the back-end molten salt treatment can be appropriately reduced to control the molten salt temperature rise and reduce production energy consumption. In the preferred technical solution, the molten salt circulation volume in the back-end molten salt treatment is 200~310t / h, and the molten salt temperature rise is ≤3℃.

[0026] The roller conveyor slow cooling can further control the slow cooling speed of the wire rod, avoiding 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 roller conveyor slow cooling controls the wire rod to cool to below 280°C at a slow cooling speed of ≤0.5°C / s before winding.

[0027] In the preferred technical solution, the slow cooling of the roller conveyor adopts the control of the opening of the heat insulation cover, and blows the hot air of ≥250°C during the online molten salt semi-quenching process to the conveyor roller conveyor. The conveyor roller conveyor transports the wire rod through the heat insulation cover to control the slow cooling of the wire rod, which can further recover and utilize the heat energy of the online molten salt semi-quenching, reduce production energy consumption, and promote the rapid production of wire rod.

[0028] A high-strength multiphase hot-rolled wire rod for 2060MPa 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 2060MPa grade stranded wire described in any one of the above-mentioned methods.

[0029] The aforementioned wire rods, designed with a high-carbon chemical composition containing trace amounts of V, reduce material costs and smelting difficulty. Simultaneously, the microstructure comprises a multiphase structure of tempered sorbite and tempered bainite, which, compared to traditional high-carbon pearlitic wire rods used in high-strength stranded steel, effectively suppresses abnormal structures such as network carbides and martensite. The lamellar spacing of the sorbite is finer than that of pearlite, resulting in higher strength and toughness. After tempering to release stress, it transforms into an intermediate transitional state of tempered sorbite, transitioning towards a spheroidized structure, further improving ductility and toughness, and adapting to multi-pass drawing. Bainite contains distortion and high-density dislocations, resulting in higher strength. After tempering to reduce dislocations and transform into tempered bainite, it retains its strength characteristics. Combined with the dispersed precipitation of VC nanoscale alloy carbides, it has a stronger ability to pin dislocations, fully leveraging the strengthening effects of carbon and vanadium to compensate for the strength loss caused by the simplified composition system. At the same time, the brittleness of bainite, which is conventionally considered an abnormal structure, is effectively improved, enhancing the overall plasticity and strength matching, improving the uniformity of the structure, and making the cold work hardening rate more gradual, thereby reducing the risk of wire breakage during subsequent drawing and twisting processes.

[0030] In the microstructure, the higher the volume percentage of tempered sorbite and the finer the lamellar spacing, the better the ductility and toughness. The higher the volume percentage of tempered bainite, the higher the matrix strength. In the preferred embodiment, the volume percentage of tempered sorbite is 65%~75%, the lamellar spacing is 65~110nm, and the volume percentage of tempered bainite is 25%~35%.

[0031] In the preferred technical solution, the network carbide level of the hot-rolled wire rod is grade 0, and the mechanical property difference between the same coil is ≤40MPa. This can effectively prevent the deterioration of the wire rod's toughness by the network carbide, prevent the fracture caused by the carbide cutting the matrix during processing or service, and at the same time avoid the precipitation of abnormal structures such as coarse pearlite and martensite, release structural stress, improve the uniformity of the structure, reduce the fluctuation of mechanical properties, make the overall deformation resistance of the wire rod uniform, and reduce the tension fluctuation during the drawing process, thereby improving the stability of stranding processing and service.

[0032] In the preferred technical solution, the hot-rolled wire rod has a diameter of 5.0~14.0mm, a tensile strength of 1390~1440MPa, and a reduction of area of ​​32%~37%. The smaller diameter and higher tensile strength of the hot-rolled wire rod can reduce the number of drawing passes, quickly achieve the target diameter and strength of the stranded wire, improve production efficiency, reduce plastic loss during the drawing process, and is suitable for stranded wire applications in multiple fields. It has a high reduction of area, which can keep the shape and size of the hot-rolled wire rod stable during processing and transportation, meet the plastic requirements of large deformation in cold drawing, prevent wire breakage during drawing, provide toughness guarantee for stranded wire service, and avoid the risk of brittle fracture.

[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 hot-rolled wire rods for steel strands are usually produced by the Stellmore air-cooling line, resulting in complex material composition, presence of martensite and other structures, and extreme brittleness, this invention uses a V-containing chemical composition design combined with online molten salt semi-quenching technology to control the wire rod after wire drawing to enter the mixed phase region of bainite and pearlite from the high-temperature austenitic state, suppressing network carbides and coarse pearlite, forming a structure dominated by quenched bainite and fine lamellar interlayer sorbite, avoiding the formation of martensite structure, followed by isothermal tempering toughening effect to improve brittleness, promote the dispersion precipitation of vanadium-containing carbides, and finally slow cooling on the roller table to further improve the tempering softening effect of the wire rod, realize the control of the multiphase structure, improve the high strength and plasticity matching of the wire rod, and have good industrial adaptability.

[0035] (2) In view of the high cost of hot-rolled wire rod of pearlitic steel strand and its disadvantage to downstream wire drawing, the present invention has a high carbon chemical composition design with trace amount of V, which can simplify the composition system, reduce material cost, and effectively control network carbides. The microstructure includes a multiphase structure composed of tempered sorbite and tempered bainite, which effectively improves the brittleness of bainite, which is usually regarded as an abnormal structure, so as to regulate the strength and plasticity matching of wire rod and make up for the strength loss caused by the simplified composition system. It can achieve a tensile strength of 1390~1440MPa and a section reduction rate of 32%~37%. It can be used to manufacture 2060MPa grade strand and other application fields, which is beneficial to downstream wire drawing and twisting processing 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 2060MPa grade stranded wire according to the present invention, wherein the chemical composition and mass percentage of the hot-rolled wire rod include C: 0.88%, Si: 0.39%, Mn: 0.65%, V: 0.01%, P: 0.013%, S: 0.013%, with the remainder being Fe and unavoidable impurities; the manufacturing method follows the process flow of rolling → wire drawing → online molten salt semi-quenching → roller table slow cooling → coiling, specifically:

[0042] The rolling process is used to heat a 180mm×180mm steel billet in a furnace to a high-temperature steel billet that can be rolled into plasticity, reducing component segregation and avoiding overheating. After exiting the furnace, the steel billet is rolled into wire rod with a diameter of 5mm through a rolling line. Appropriate rolling temperature and reduction are selected to induce V-pinning grain boundaries and refine the grains. Specifically, the furnace soaking temperature is controlled at 1170℃, the furnace time is 250min, the initial rolling temperature is 1065℃, the final rolling temperature is 890℃, and the final rolling reduction is 32%. The wire drawing process is used to spindle 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 promoting the simultaneous phase transformation of bainite and sorbite. Specifically, the wire drawing temperature is controlled at 880℃.

[0043] The online molten salt semi-quenching process employs a two-section salt bath with internal molten salt. After coiling, the wire rod is conveyed via roller conveyor through the first section of the salt bath for initial molten salt treatment. This causes the wire rod to cool at a rate of 33°C / s, rapidly transitioning from a high-temperature austenitic state through the network carbide region into a mixed bainite and pearlite phase region. This suppresses the formation of network carbides and coarse pearlite, resulting in a high-temperature austenitic phase transformation that forms a microstructure dominated by a small portion of quenched bainite and a large portion of fine lamellar interlamellar sorbite. This promotes the dispersed precipitation of vanadium-containing carbides. The wire rod is then conveyed via roller conveyor... The wire rod undergoes a second-stage molten salt treatment in a salt bath. This reduces the molten salt circulation rate and promotes isothermal tempering of the formed quenched bainite and sorbite structures, preventing carbide coarsening and thus controlling the strength-plasticity balance of the wire rod. Specifically, the molten salt temperature for the first-stage molten salt treatment is 483℃, the treatment time is 45s, the molten salt circulation rate is 450t / h, and the molten salt temperature rise is ≤10℃. The molten salt temperature for the second-stage molten salt treatment is 450℃, the treatment time is 400s, the molten salt circulation rate is 200t / 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 semi-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 278℃ at a slow cooling rate of 0.25℃ / 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 265 minutes, an initial rolling temperature of 1040°C, a final rolling temperature of 825°C, and a wire drawing temperature of 810°C. The Steyrmo forced air cooling uses a fan with an air volume of 260,000 m³ / s. 3 At 65% speed, fans 1 to 4 are turned on to cool the wire rod to 695℃ at a cooling rate of 5.8℃ / s. Then, fans 5 to 14 are turned on to 35% speed to cool the wire rod to 270℃ at a cooling rate of 3.2℃ / 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 265 min, the initial rolling temperature is 1040°C, the final rolling temperature is 850°C, and the wire drawing temperature is 825°C. During the molten salt treatment before the online molten salt semi-quenching process, the wire rod is cooled at a rate of 30°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 2060MPa grade stranded wire according to the present invention, wherein the chemical composition and mass percentage of the hot-rolled wire rod include C: 0.85%, Si: 0.30%, Mn: 0.77%, V: 0.017%, P: 0.015%, S: 0.013%, with the remainder being Fe and unavoidable impurities; the manufacturing method follows the process flow of rolling → wire drawing → online molten salt semi-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 can be rolled into plasticity, reducing component segregation and avoiding overheating. After exiting the furnace, the steel billet is rolled into wire rod with a diameter of 8mm through a rolling line. Appropriate rolling temperature and reduction are selected to induce V-pinning grain boundaries and refine the grains. Specifically, the furnace soaking temperature is controlled at 1185℃, the furnace time is 215min, the initial rolling temperature is 1085℃, the final rolling temperature is 905℃, and the final rolling reduction is 30%. The wire drawing process is used to draw the wire rod from 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 promoting the simultaneous phase transformation of bainite and sorbite. Specifically, the wire drawing temperature is controlled at 895℃.

[0051] The online molten salt semi-quenching process employs a two-stage salt bath with internal molten salt. After coiling, the wire rod is conveyed via roller conveyor through the first stage of the salt bath for initial molten salt treatment. This causes the wire rod to cool at a rate of 35°C / s, rapidly transitioning it from a high-temperature austenitic state, bypassing the network carbide region, and entering a mixed phase region of bainite and pearlite. This suppresses the formation of network carbides and coarse pearlite, resulting in a high-temperature austenitic phase transformation that forms a microstructure dominated by a small portion of quenched bainite and a large portion of fine lamellar interlamellar sorbite. This promotes the dispersed precipitation of vanadium-containing carbides. The wire rod is then conveyed via roller conveyor... The wire rod undergoes a second-stage molten salt treatment in a salt bath. This reduces the molten salt circulation rate and promotes isothermal tempering of the formed quenched bainite and sorbite structures, preventing carbide coarsening and thus controlling the strength-plasticity balance of the wire rod. Specifically, the molten salt temperature for the first-stage molten salt treatment is 470℃, the treatment time is 75s, the molten salt circulation rate is 510t / h, and the molten salt temperature rise is ≤10℃. The molten salt temperature for the second-stage molten salt treatment is 460℃, the treatment time is 315s, the molten salt circulation rate is 245t / 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 in the online molten salt semi-quenching process 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 275℃ at a slow cooling rate of 0.35℃ / 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 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 semi-quenching process, the wire rod is cooled at a cooling rate of 37°C / s, the molten salt temperature of the initial molten salt treatment is 450°C, the treatment time is 155s, 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 semi-quenching process, the wire rod is cooled at a cooling rate of 33℃ / s, the molten salt temperature of the initial molten salt treatment is 500℃, the treatment time is 40s, 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 2060MPa grade stranded wire according to the present invention, wherein the chemical composition and mass percentage of the hot-rolled wire rod include C: 0.85%, Si: 0.47%, Mn: 0.81%, V: 0.024%, 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 semi-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 is rollable and plastic, reducing component segregation and avoiding overheating. 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 induce V-pinning grain boundaries and refine the grains. Specifically, the furnace soaking temperature is controlled at 1200℃, the furnace time at 185min, the initial rolling temperature at 1095℃, the final rolling temperature at 915℃, and the final rolling reduction at 28.5%. The wire drawing process is used to transfer the wire rod from the rolling line to a wire rod through a wire drawing mechanism. 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, avoiding the precipitation of network carbides during the wire drawing stage, and providing favorable conditions for the subsequent simultaneous phase transformation of bainite and sorbite. Specifically, the wire drawing temperature is controlled at 905℃.

[0059] The online molten salt semi-quenching process employs a two-section salt bath with internal molten salt. After coiling, the wire rod is conveyed via roller conveyor through the first section of the salt bath for initial molten salt treatment. This causes the wire rod to cool at a rate of 37°C / s, rapidly transitioning it from a high-temperature austenitic state, bypassing the network carbide region, and entering a mixed phase region of bainite and pearlite. This suppresses the formation of network carbides and coarse pearlite, resulting in a high-temperature austenitic phase transformation that forms a microstructure dominated by a small portion of quenched bainite and a large portion of fine lamellar interlamellar sorbite. This promotes the dispersed precipitation of vanadium-containing carbides. The wire rod is then conveyed via roller conveyor... The wire rod undergoes a second-stage molten salt treatment in a second salt bath. This reduces the molten salt circulation rate and promotes isothermal tempering of the formed quenched bainite and sorbite structures, preventing carbide coarsening and thus controlling the strength-plasticity balance of the wire rod. Specifically, the molten salt temperature for the first-stage molten salt treatment is 463℃, the treatment time is 115s, the molten salt circulation rate is 590t / h, and the molten salt temperature rise is ≤10℃. The molten salt temperature for the second-stage molten salt treatment is 465℃, the treatment time is 270s, the molten salt circulation rate is 275t / 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 in the online molten salt semi-quenching process 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 272℃ at a slow cooling rate of 0.4℃ / 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 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 495°C, the treatment time is 405s, 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 430°C, the treatment time is 200s, 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 2060MPa grade stranded wire according to the present invention, wherein the chemical composition and mass percentage of the hot-rolled wire rod include C: 0.84%, Si: 0.45%, Mn: 0.85%, V: 0.03%, 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 semi-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 can be rolled into plasticity, reducing component segregation and avoiding overheating. After exiting the furnace, the steel billet is rolled into wire rod with a diameter of 14mm through a rolling line. Appropriate rolling temperature and reduction are selected to induce V-pinning grain boundaries and refine the grains. Specifically, the furnace soaking temperature is controlled at 1210℃, the furnace time is 160min, the initial rolling temperature is 1100℃, the final rolling temperature is 930℃, and the final rolling reduction is 27%. The wire drawing process is used to transfer 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 promoting the simultaneous phase transformation of bainite and sorbite. Specifically, the wire drawing temperature is controlled at 915℃.

[0067] The online molten salt semi-quenching process employs a two-stage salt bath with internal molten salt. After coiling, the wire rod is conveyed via roller conveyor through the first stage of the salt bath for initial molten salt treatment. This causes the wire rod to cool at a rate of 40°C / s, rapidly transitioning from a high-temperature austenitic state through the network carbide region into a mixed phase region of bainite and pearlite. This suppresses the formation of network carbides and coarse pearlite, resulting in a high-temperature austenitic phase transformation that forms a microstructure dominated by a small portion of quenched bainite and a large portion of fine lamellar interlamellar sorbite. This promotes the dispersed precipitation of vanadium-containing carbides. The wire rod is then conveyed via roller conveyor... The wire rod undergoes a second-stage molten salt treatment in a salt bath. This reduces the molten salt circulation rate and promotes isothermal tempering of the formed quenched bainite and sorbite structures, preventing carbide coarsening and thus controlling the strength-plasticity balance of the wire rod. Specifically, the molten salt temperature for the first-stage treatment is 455℃, the treatment time is 150s, the molten salt circulation rate is 650t / h, and the molten salt temperature rise is ≤10℃. The molten salt temperature for the second-stage treatment is 470℃, the treatment time is 210s, the molten salt circulation rate is 310t / 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 at ≥250°C above the two salt bath tanks of the online molten salt semi-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 controlled to be cooled to 270°C at a slow cooling rate of 0.5°C / s. The coiling process is used to coil the wire rod into coils through 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 semi-quenching → air cooling. The air cooling process involves opening the insulation cover and controlling the wire rod to cool to 265°C at a slow cooling rate of 1.4°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] The comparison between Example 1 and Comparative Example 1 shows that, compared to the simplified composition system, the hardenability of the wire rod decreases. Due to the limited cooling capacity of the Stellmore air-cooling line, the wire rod slowly passes through the precipitation temperature range of secondary cementite and pearlite, easily forming network carbides. In particular, as the wire rod diameter decreases, excessively rapid surface or local cooling easily forms a low-temperature brittle structure. Slow cooling of the core easily causes the cementite to coarsen during the cooling process. Insufficient precipitation and uneven coarseness of microalloyed carbides make it difficult to fully exert their strengthening effect, resulting in a significant loss of strength and ductility. To mitigate fluctuations in mechanical properties, this invention combines online molten salt semi-quenching technology with the compositional basis to suppress network carbides and coarse pearlite. The microstructure comprises a multiphase structure composed of tempered sorbite and tempered bainite, which can compensate for the strength loss caused by the simplified composition system and regulate the strength-plasticity matching of the wire rod. As can be seen from the results of Examples 1-4, a tensile strength of 1390-1440 MPa and a reduction of area of ​​32%-37% can be achieved. This is suitable for applications such as manufacturing 2060 MPa grade stranded wire, and is beneficial for downstream wire drawing and twisting processes.

[0075] As can be seen from the comparison results between Example 1 and Comparative Example 2, a higher wire drawing temperature is selected to ensure complete austenitization of the wire rod, avoid the formation of network carbides during the wire drawing stage due to excessively low temperature, and create a temperature difference with the molten salt temperature. This provides favorable conditions for obtaining sufficient undercooling to promote the synchronous phase transformation of bainite and sorbite, and reduces the limitation on rolling temperature.

[0076] The comparison results between Example 2 and Comparative Example 3 show that the lower the molten salt temperature in the initial molten salt treatment, the better it is to suppress the formation of network carbides, while also suppressing the premature precipitation of coarse pearlite and ferrite, promoting the preferential nucleation of bainite, and reducing the interlamellar spacing of sorbite. With the extension of the treatment time, the dispersion precipitation kinetics of vanadium-containing carbides can be increased, and nanoscale precipitates can be precipitated simultaneously during the transformation of bainite and sorbite, thereby improving the matrix strength. However, if the molten salt temperature is too low or the treatment time is too long, it will lead to an increase in bainite in the transformation products, affecting the transformation of sorbite, resulting in a larger dislocation density and stress in the microstructure, increasing the difficulty of softening and production energy consumption, and affecting the plasticity of the microstructure and production efficiency.

[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 better it is to reduce the risk of precipitation of abnormal structures such as martensite, promote the transformation of sorbite, reduce structural stress and thermal stress, reduce the difficulty of stress release, reduce production energy consumption, and promote rapid production. However, if the molten salt temperature is too high and the treatment time is too short, it is not conducive to suppressing network carbides and abnormal structures, the driving force for the formation of bainite and vanadium-containing carbides decreases, and the matrix strength and structural uniformity decrease.

[0078] As can be seen from the comparison results of Example 3 and Comparative Example 4, the higher the molten salt temperature and the longer the treatment time in the later stage of molten salt treatment, the better it is to reduce the dislocation density of quenched bainite, promote the release of structural stress, promote the full dispersion and precipitation of vanadium-containing carbides, and improve the overall plasticity and toughness. However, if the molten salt temperature is too high and the treatment time is too long, the atomic diffusion ability will be enhanced, the structure will be excessively tempered and softened, which will lead to a loss of strength. At the same time, VC is easy to coarsen, which will lead to a loss of strong plasticity and increase production energy consumption.

[0079] As can be seen from the comparison results between Example 3 and Comparative Example 5, the lower the molten salt temperature and the shorter the treatment time in the later stage of molten salt treatment, the better it is to reduce the softening rate and production energy consumption, shorten the production time, inhibit the coarsening of the dispersed precipitate phase, and reduce the strength loss. However, if the molten salt temperature is too low and the treatment time is too short, it will be detrimental to isothermal tempering and softening. Vanadium-containing carbides will not be fully precipitated, and the structural stress will not be fully released, which will lead to a loss of strength and plasticity.

[0080] As can be seen from the comparison results of Example 4 and Comparative Example 7, the slow cooling of the roller can avoid 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.

[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 2060MPa 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: 0.84%~0.88%, Si: 0.30%~0.47%, Mn: 0.65%~0.85%, V: 0.01%~0.03%, 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 ≥880℃, it undergoes online molten salt semi-quenching treatment. This process involves first undergoing a preliminary molten salt treatment and then cooling the wire rod at a cooling rate of ≥33℃ / s, transitioning it from the austenitic state to a mixed phase region of bainite and pearlite, forming a... The hot-rolled wire rod, with a microstructure mainly composed of quenched bainite and sorbite, undergoes isothermal tempering via molten salt treatment in the later stage, and finally slow cooling via roller conveyor, resulting in a microstructure consisting of a multiphase structure of tempered sorbite and tempered bainite. The molten salt temperature of the first stage molten salt treatment is 455~485℃, and the treatment time is 45~150s. The molten salt circulation rate of the first stage molten salt treatment is greater than that of the second stage molten salt treatment. The molten salt temperature of the second stage molten salt treatment is 450~470℃, and the treatment time is 210~400s. The slow cooling via roller conveyor controls the wire rod to cool to below 280℃ at a slow cooling rate of ≤0.5℃ / s before coiling.

2. The method for manufacturing high-strength multiphase hot-rolled wire rod for 2060MPa grade stranded wire according to claim 1, characterized in that, Before rolling, the heating furnace temperature is controlled at 1170~1210℃ and the furnace time is 160~250min.

3. The method for manufacturing high-strength multiphase hot-rolled wire rod for 2060MPa grade stranded wire according to claim 1, characterized in that, During the rolling process, the initial rolling temperature is controlled at 1065~1100℃, the final rolling temperature at 890~930℃, and the final rolling reduction at 27%~32%.

4. The method for manufacturing high-strength multiphase hot-rolled wire rod for 2060MPa grade stranded wire according to claim 1, characterized in that, During the spinning process, the spinning temperature is controlled at 880~915℃.

5. The method for manufacturing high-strength multiphase hot-rolled wire rod for 2060MPa grade stranded wire according to claim 1, characterized in that, The molten salt circulation rate of the front-end molten salt treatment is 450~650t / h, and the molten salt temperature rise is ≤10℃; the molten salt circulation rate of the rear-end molten salt treatment is 200~310t / h, and the molten salt temperature rise is ≤3℃.

6. A high-strength multiphase hot-rolled wire rod for 2060MPa 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 2060MPa grade strand as described in any one of claims 1 to 5.

7. The high-strength multiphase hot-rolled wire rod for 2060MPa grade stranded wire according to claim 6, characterized in that, The volume percentage of the tempered sorbite is 65%~75%, the lamellar spacing is 65~110nm, the volume percentage of the tempered bainite is 25%~35%, the network carbide grade of the hot-rolled wire rod is 0, and the mechanical property difference between the same ring is ≤40MPa.

8. The high-strength multiphase hot-rolled wire rod for 2060MPa grade stranded wire according to claim 6, characterized in that, The hot-rolled wire rod has a diameter of 5.0~14.0mm, a tensile strength of 1390~1440MPa, and a reduction of area of ​​32%~37%.

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