A hot-rolled wire rod for 2100MPa grade stranded wire and its manufacturing method

Abstract

This invention relates to a hot-rolled wire rod for 2100MPa grade stranded wire and its manufacturing method. The method involves rolling the wire rod into a high-carbon, high-silicon composition system, followed by online molten salt sorbitization treatment. This process cools the wire rod at a rate of ≥31℃ / s, transitioning it from the austenitic state to the sorbite phase region, forming a predominantly sorbite microstructure. The wire rod is then isothermally tempered to promote partial melting of the sorbite lamellars. Finally, it undergoes slow cooling via a roller conveyor, resulting in a hot-rolled wire rod with a microstructure consisting of tempered sorbite, tempered ferrite, and melted sorbite. This method simplifies the alloy composition, improves the strength-plasticity matching and microstructure uniformity of the wire rod, achieving a tensile strength of 1420~1470MPa and a reduction of area of ​​36%~41%. This method is suitable for manufacturing 2100MPa grade stranded wire and other applications, eliminating the need for offline heat treatment and reducing the risk of wire breakage during downstream drawing and twisting.

Description

Technical Field

[0001] This invention belongs to the technical field of hot-rolled wire rod, specifically relating to a 2100MPa grade hot-rolled wire rod for stranded wire and its manufacturing method. Background Technology

[0002] Steel strand, made from hot-rolled wire rod as the base material, is drawn into steel wire and then stranded into multiple strands. It can be used in hoisting, traction, fixing, and towing operations, and is widely used in railways, bridges, marine engineering, construction, shipbuilding, and power industries. With the accelerated development of green and intelligent technologies, energy conservation, carbon reduction, and lightweighting have become important directions for industrial development. After the strength grade of steel strand was increased to 1960MPa, conventional production methods are extremely difficult to meet further strength increases. Offline heat treatment is usually required to achieve performance improvements, which not only adds multiple processes but also significantly increases production costs and energy consumption. Further strength increases to 2100MPa have been rarely developed. Therefore, there is a need to develop a hot-rolled wire rod for 2100MPa grade strand and its manufacturing method that does not require offline heat treatment to meet the development and market demand of the steel industry.

[0003] In existing technologies, hot-rolled wire rods for high-strength steel strands often employ multi-alloy high-carbon steel compositions, combined with Steyrmo air-cooling line production. For example, patent CN102352469B discloses an ultra-high-strength vanadium-titanium composite microalloyed high-carbon steel wire rod and its preparation method, which uses a high-carbon composition of C-Si-Mn-V-Ti-Cr-Cu-Ni-B, combined with a Steyrmo line rapid cooling, heat preservation, and slow cooling process to prepare sorbitic wire rods. However, the following technical bottlenecks still exist:

[0004] 1. To suppress austenite grains and form precipitation strengthening during hot rolling, alloying elements such as V and Ti are added to steel grades. However, this also increases material costs. If alloying elements are omitted to reduce costs, the precipitation strengthening effect will be lost. The maximum cooling capacity of the Steyrmo air-cooled line will limit the nucleation rate of sorbite. The coarse structure and grains will further affect the strength and toughness. Insufficient strength and toughness of wire rod will lead to more processing passes required for downstream drawing. The plasticity will be lost quickly during the process, and there is a risk of wire breakage during drawing and twisting.

[0005] II. To improve the strength and ductility of wire rod, alloying elements such as Si, Mn, Cr, Ni, and B are used in conjunction with strong air cooling after wire drawing to increase the sorbite content in the microstructure. However, this also increases material costs and smelting difficulty. Omitting alloying elements reduces the hardenability of the wire rod, shifts the critical phase transformation temperature upward, and easily leads to the formation of coarse pearlite and proprecipitated ferrite during air cooling, resulting in significant strength loss. Limited by the maximum cooling capacity and the segregation and enrichment of high carbon content during solidification, the time spent in the secondary cementite precipitation temperature range is longer, easily leading to the formation of network carbides. These network carbides can fracture the matrix, significantly deteriorating ductility and toughness. Increasing air cooling strength, on the one hand, due to... Unstable temperature control will further increase the temperature difference between the wind-receiving and wind-suppressed surfaces, overlapping and non-overlapping areas, and the surface and core. This will lead to the surface and local areas being prone to overcooling, forming low-temperature brittle structures such as martensite, increasing the brittleness of the wire rod. Meanwhile, the core will form coarse cementite lamellars, resulting in uneven structure and greater fluctuations in mechanical properties. Abnormal structures can also become crack initiation sources, causing brittle fracture during transportation and processing. On the other hand, under the continuous cooling control of the air-cooling line, the wire rod is already at a low temperature after phase transformation inoculation. Affected by alloying elements such as high silicon and chromium, the atomic diffusion rate is slow. The structural stress generated by uneven phase transformation will remain in the wire rod, resulting in insufficient plasticity of the wire rod in the end. This can easily lead to the risk of wire breakage during drawing downstream, making it difficult to overcome the production bottleneck of eliminating offline heat treatment. 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 hot-rolled wire rod for stranded wire of 2100MPa grade and its manufacturing method, which can simplify the alloy composition, improve the strength-plasticity matching and microstructure uniformity of the wire rod, and eliminate the need for offline heat treatment, thereby reducing the risk of wire breakage during downstream drawing and twisting.

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

[0008] A method for manufacturing hot-rolled wire rod for 2100MPa grade stranded wire, the method comprising:

[0009] The hot-rolled wire rod is rolled into wire rod according to its chemical composition. The chemical composition and mass percentage of the hot-rolled wire rod include: C: 0.86%~0.90%, Si: 0.75%~0.95%, Mn: 0.64%~0.84%, Cr: 0.55%~0.68%, 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 sorbitization control treatment, which cools the wire rod at a cooling rate of ≥31℃ / s, allowing it to transition from the austenitic state to the sorbite phase region, forming a structure dominated by sorbite. It is then isothermally tempered to promote the melting of some sorbite lamellars. Finally, it undergoes slow cooling through a roller conveyor to produce a hot-rolled wire rod with a microstructure consisting of a mixture of tempered sorbite, tempered ferrite, and melted sorbite.

[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 an effective strengthening element in steel, and its price is relatively low. It can increase the resistance to dislocation movement through solid solution strengthening. At the same time, by stabilizing austenite, it can increase the critical point of austenite phase transformation, expand the stable region of supercooled austenite, and reduce the starting temperature of austenite to sorbite transformation. This is conducive to promoting rapid transformation and refinement of sorbite to improve the strength of the matrix. However, if the C content is too high, carbon will preferentially diffuse and precipitate along the austenite grain boundaries, forming continuous or semi-continuous network carbides. This will also increase the difficulty of controlling the uniformity of the microstructure and the abnormal martensite structure, leading to material embrittlement, a significant decrease in plasticity, and affecting processing and forming. Therefore, in order to take into account the high strength requirements of 2100MPa grade stranded wire, reduce the fluctuation of mechanical properties, and promote rapid production, the mass percentage of C is controlled at 0.86%~0.90%.

[0012] (2) Silicon: Si is a solid solution strengthening element of ferrite. By dissolving in the sorbite matrix phase, it can hinder dislocation movement and improve matrix strength. During the austenite-to-sorbite phase transformation, it can hinder the migration of carbon atoms into cementite, suppress the formation of coarse carbides during cooling, strongly inhibit the precipitation and coarsening process of Fe3C, delay the pearlite transformation, and widen the sorbite formation range so as to form a structure dominated by sorbite. During isothermal tempering, it can hinder the spheroidization and growth of cementite lamellars and improve the tempering effect. Stability is important to avoid insufficient drawing strength due to softening, and silicon plays a role in refining precipitates and improving material toughness. However, excessive silicon can promote decarburization, prolong the phase transformation incubation period, increase the difficulty of isothermal tempering and softening, increase the dislocation density of the matrix, accelerate the work hardening rate during drawing, and cause brittle fracture during drawing or twisting. Therefore, in order to adapt to the control of phase transformation structure by online molten salt sorbitization and improve the resistance to tempering softening, the Si content should be appropriately increased, and the mass percentage of Si should be controlled at 0.75%~0.95%.

[0013] (3) Manganese: Mn is an austenite stabilizing element that shifts the sorbite phase transformation range downward, slows down the nucleation and growth rate of pearlite, expands the sorbite formation range, and improves the hardenability of wire rod, so that the wire rod can fully complete the sorbite transformation in molten salt and improve the synchronicity of the transformation of the whole cross section. During isothermal tempering, it can also hinder the diffusion and migration of carbon atoms, thereby inhibiting the coarsening of carbides and keeping the wire rod with high strength. However, when the Mn content is too high, it will increase the segregation of alloying elements during the solidification process of the billet, increase the resistance to hot rolling deformation, and easily form low-temperature martensite structure during cooling, resulting in increased hardness, brittleness and mechanical property fluctuations, affecting the toughness of the wire rod, and accelerating the work hardening rate during drawing. Therefore, in order to take into account the high strength and plasticity of hot-rolled wire rod, reduce the fluctuation of mechanical properties, and avoid excessive softening during tempering, the mass percentage of Mn is controlled at 0.64%~0.84%.

[0014] (4) Chromium: Cr is a strong carbide-forming element. It can strengthen through solid solution, form carbides that are dispersed in the sorbite lamellae to hinder dislocation movement, and improve the matrix strength. At the same time, it can enhance hardenability, causing the continuous cooling transformation curve of steel to shift to the right. Combined with online molten salt sorbitization control treatment, it delays the transformation of austenite to pearlite, laying the foundation for the subsequent formation of a sorbite-based structure. Meanwhile, the dispersed Cr-based carbides can continuously pin dislocations, increase the resistance to tempering softening, and enable the wire rod to maintain high strength after tempering. However, excessive Cr content will aggravate the segregation of alloying elements, increase the risk of abnormal structures such as martensite precipitation, and increase the high-temperature deformation resistance of steel during the rolling stage. It also reduces the activity of carbon during isothermal tempering, which is detrimental to sorbite melting and tempering softening, and affects the drawing plasticity of steel. Therefore, the mass percentage of Cr is controlled at 0.55%~0.68%.

[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 hot-rolled wire rod adopts a high-carbon, high-silicon composition system of C-Si-Mn-Cr, without elements such as Ni, Ti, and V. This simplifies the composition system, controls material costs, and simultaneously regulates the wire rod's hardenability, sorbite precipitation temperature range, and resistance to tempering softening. This provides favorable conditions for promoting the full transformation of austenite into fine-laminated sorbite, suppressing coarse pearlite soft phases and abnormal martensite structures, avoiding excessive tempering softening, and increasing the wire rod's running speed. Furthermore, a higher wire drawing temperature is selected to keep the wire rod in a high-temperature austenitizing state, preventing the precipitation of proeutectoid ferrite or network carbides before wire drawing, thus laying the foundation for the sorbitic phase transformation. After wire drawing, the wire rod undergoes online molten salt sorbitizing control treatment without air cooling.

[0017] Firstly, compared to omitting alloying elements, which limits the maximum cooling capacity and temperature control instability of the Stellmore air-cooled line and makes it impossible to control abnormal structures such as network carbides, coarse pearlite soft phases, and martensite, the efficient heat transfer characteristics of molten salt can be utilized to promote the wire rod to bypass the precipitation temperature range of secondary cementite from the high-temperature austenitic state, thereby suppressing the risk of network carbides caused by high carbon content. At the same time, it can quickly enter the lower temperature sorbite phase region to suppress proeutectoid ferrite. Combined with high silicon content, it can suppress cementite coarsening, and combined with hardenability elements such as Mn and Cr, it can promote the wire rod to... The surface and core undergo simultaneous phase transformation. By increasing the degree of supercooling, the lamellar structure is forcibly refined and the incubation period is shortened, which suppresses the coarse pearlite soft phase structure in the core and provides matrix strength. On the other hand, when the wire rod passes through the molten salt, the molten salt can cover the surface of the wire rod for uniform heat transfer. Compared with air cooling, there is no temperature difference between the wind-receiving and wind-exposed surfaces, or between overlapping and non-overlapping areas. This can further reduce the temperature difference between the wire rod surface and the core, avoid local supercooling, and prevent the atomic diffusion of supercooled austenite from being suppressed, thus forming low-temperature brittle structures such as martensite. This improves the uniformity of microstructure and internal stress distribution, reduces the risk of abnormal microstructure and fluctuations in mechanical properties.

[0018] Second, compared to the insufficient plasticity of wire rods due to the influence of high silicon and chromium alloying elements, as well as the limitations of the length and minimum cooling capacity of the Steyrmo air-cooling line, the following measures can be taken: First, as the processing time is extended, the wire rod temperature can gradually change to the same temperature as the molten salt for isothermal treatment instead of continuous cooling. This can prolong the time the wire rod is at the peak precipitation temperature of the sorbite phase transformation, promoting the transformation of untransformed residual austenite into fine lamellar sorbite, compensating for the adverse effect of increased silicon on prolonging the phase transformation inoculation, and preventing the austenite residue from continuing to form brittle abnormal structures during subsequent cooling. Second, the wire rod remains at a high temperature after the phase transformation inoculation, which can prolong the time the wire rod is in the high-temperature isothermal temperature range, increase the tempering thermal dynamics, provide kinetic energy for atomic diffusion, promote the release of structural stress, and the melting of some cementite lamellars in the sorbite, transforming it into a tempered state with better plasticity. At the same time, the addition of high silicon and chromium alloying elements can improve the resistance to tempering softening and avoid excessive strength loss. Finally, slow cooling through the roller conveyor can further toughen the wire rod and allow it to be quickly removed from the line, thus controlling the overall strength and plasticity matching of the wire rod.

[0019] Before rolling, a higher heating furnace homogenization temperature and an appropriate furnace dwell time can be selected to reduce the influence of compositional segregation and resistance to hot rolling deformation, while avoiding excessive furnace dwell time that could lead to abnormal austenite grain growth or decarburization. In a preferred embodiment, before rolling, the heating furnace homogenization temperature is controlled at 1180~1220℃ and the furnace dwell time is controlled at 120~180min.

[0020] Because the wire drawing temperature is relatively high, the limitation on the rolling temperature can be reduced. Using a higher initial rolling temperature can increase the rolling speed, reduce the wear and load requirements on the rolling line, and achieve efficient deformation. With appropriate final rolling temperature and final rolling reduction, dynamic recrystallization and grain refinement are promoted in the final rolling process, resulting in a uniform fine-grained austenite matrix. In the preferred technical solution, during the rolling process, the initial rolling temperature is controlled at 1040~1070℃, the final rolling temperature is controlled at 890~920℃, and the final rolling reduction is controlled at 22%~26%.

[0021] During the wire spinning process, the spinning temperature can be further controlled to prevent excessive growth of austenite grains. In a preferred embodiment, the spinning temperature is controlled to be 890~915℃.

[0022] In the preferred technical solution, the online molten salt sorbitization control treatment is divided into a front-stage molten salt treatment and a rear-stage molten salt treatment. The molten salt circulation volume of the rear-stage molten salt treatment is less than that of the front-stage molten salt treatment. Since the temperature difference between different parts of the wire rod is relatively small after the front-stage molten salt treatment, the molten salt circulation volume can be appropriately reduced to reduce production energy consumption.

[0023] The molten salt temperature in the initial molten salt treatment is in the sorbite phase region. Lower molten salt temperatures help suppress the risk of network carbide precipitation. With prolonged treatment time, the atomic diffusion rate during low-temperature phase transformation is slower, resulting in thinner lamellae and smaller spacing between ferrite and cementite layers. This promotes synchronous transformation of the wire rod core, forming a microstructure dominated by fine-lamellar sorbite, thus improving matrix strength. However, excessively low molten salt temperatures increase the temperature difference between the wire rod surface and core, increasing thermal and structural stresses, and may even lead to overcooling and the formation of brittle abnormal structures. Excessively long treatment times, due to the high molten salt circulation volume in the initial molten salt treatment, unnecessarily increase production energy consumption. Conversely, higher molten salt temperatures help reduce the wire rod temperature gradient, decrease stress release difficulty, and prevent low-temperature brittle structures. While shorter processing times can reduce production energy consumption, excessively high molten salt temperatures and short processing times are detrimental to suppressing network carbides and coarse pearlite in the core. Increased untransformed residual austenite affects subsequent molten salt treatment, leading to strength loss and fluctuations in mechanical properties. Therefore, the molten salt temperature and processing time of the initial molten salt treatment can be controlled to allow the wire rod to quickly transition from a high-temperature austenitic state, bypassing the network carbide region and entering the sorbite phase region. This suppresses the formation of network carbides and fosters a microstructure dominated by fine-laminated interlamellar sorbite, balancing production energy consumption and microstructure uniformity. In a preferred embodiment, the molten salt temperature of the initial molten salt treatment is 530~570℃, and the processing time is 180~300s.

[0024] Since there is a large temperature difference between the wire drawing temperature and the molten salt temperature in the previous molten salt treatment, a larger molten salt circulation rate can control the molten salt temperature rise, quickly remove the heat from the wire rod, and avoid increased thermal stress due to uneven cooling. In the preferred technical solution, the molten salt circulation rate in the previous molten salt treatment is 350~545t / h, and the molten salt temperature rise is ≤8℃.

[0025] The molten salt temperature in the subsequent molten salt treatment is within the sorbite phase region. Lower molten salt temperatures promote the transformation of untransformed residual austenite into fine lamellar sorbite, slowing carbon atom diffusion. Shorter treatment times prevent excessive strength loss due to carbide aggregation and growth, while also reducing energy consumption. However, excessively low molten salt temperatures and short treatment times hinder partial cementite melting and stress release, resulting in a loss of wire rod plasticity. Conversely, higher molten salt temperatures and longer treatment times promote isothermal tempering of fine lamellar sorbite, lamellar melting, and stress release. However, molten salt... Excessive temperature and processing time can lead to over-softening, strength loss, and increased energy consumption. Therefore, the molten salt temperature and processing time of the subsequent molten salt treatment can be controlled to promote the transformation of untransformed residual austenite into fine lamellar interlamellar sorbite. At the same time, the formed fine lamellar interlamellar sorbite is subjected to long-term isothermal tempering, and some cementite plates are melted to prevent carbide coarsening and over-softening, thereby regulating the strength and plasticity matching of the wire rod. In the preferred technical solution, the molten salt temperature of the subsequent molten salt treatment is 540~565℃, and the processing time is 100~300s.

[0026] Since the processing time of the first stage molten salt treatment is relatively long, and the temperature difference between the first stage and the second stage molten salt treatment is small, the molten salt circulation volume can be appropriately reduced to control the molten salt temperature rise and isothermal tempering stability, while effectively reducing production energy consumption. In the preferred technical solution, the molten salt circulation volume of the second stage molten salt treatment is 250~370t / h, and the molten salt temperature rise is ≤3℃.

[0027] The roller conveyor opening and slow cooling can further control the slow cooling speed, promote further toughening of the wire rod structure, improve the tempering and softening effect of the wire rod, and at the same time take into account rapid unloading. In the preferred technical solution, the roller conveyor opening and slow cooling controls the wire rod to cool to below 285°C at a slow cooling speed of 0.8~1.2°C / s before winding.

[0028] In the preferred technical solution, the slow cooling of the roller conveyor is achieved by opening the heat preservation cover and blowing hot air at ≥250°C during the online molten salt sorbitization control treatment onto the conveyor roller conveyor. The conveyor roller conveyor transports the wire rod. The hot air can further reduce the temperature gradient from the surface of the wire rod to the core, reduce the fluctuation of mechanical properties, and at the same time recover and utilize the heat energy of the online molten salt sorbitization control to reduce production energy consumption.

[0029] A hot-rolled wire rod for stranded wire of 2100MPa grade, wherein the hot-rolled wire rod is manufactured by the manufacturing method for hot-rolled wire rod of 2100MPa grade as described in any one of the above-mentioned methods.

[0030] The aforementioned hot-rolled wire rods are designed with a high silicon content and do not contain alloying elements such as V, Ti, and Ni, which reduces material costs and smelting difficulty. Simultaneously, the microstructure comprises a mixed structure mainly composed of tempered sorbite and melted sorbite, with a very small amount of tempered ferrite. Compared to air-cooled pearlitic / sorbitic wire rods used for stranded steel, this simplified composition effectively suppresses the adverse effects of network carbides on ductility and toughness, avoids the formation of brittle abnormal structures such as martensite due to localized overcooling, suppresses the coarse pearlitic structure in the core and the premature precipitation of soft ferrite phases, and utilizes the finer lamellar spacing of full-section sorbite compared to pearlite, the fine lamellar structure more effectively hinders dislocation movement. This process results in more uniform cementite dispersion, reduced stress concentration, and improved strength and toughness. It can reduce fluctuations in mechanical properties. After isothermal tempering, the cementite transforms into a transitional state of tempered sorbite and melted sorbite, which partially melts into sorbite lamellars and transitions to spheroidized structure. The high silicon content helps prevent excessive strength loss due to tempering softening, while Cr carbides anchor grain boundaries, preserving matrix strength and enhancing the strengthening effect of carbon. This compensates for the strength loss caused by omitting alloying elements. Simultaneously, the stress in the tempered structure is released, resulting in better ductility and toughness. This ensures a good balance between overall strength and ductility, eliminating the need for offline heat treatment and reducing the risk of fracture during subsequent processing, thus improving yield.

[0031] In the microstructure, the higher the proportion of tempered sorbite, the finer the lamellar spacing, and the lower the proportion of tempered ferrite, the higher the strength; the higher the volume percentage of fused sorbite, the better the ductility and toughness. In the preferred technical solution, the volume percentage of tempered sorbite is ≥64%, the lamellar spacing is 75~125nm, the volume percentage of tempered ferrite is ≤4%, and the volume percentage of fused sorbite is ≥22%.

[0032] In the preferred technical solution, the hot-rolled wire rod has a network carbide level of 0 and a mechanical property difference of ≤38MPa between coils; it deforms more uniformly during cold drawing, twisting and other processing, and is less prone to stress concentration due to network carbides, uneven local structure and fluctuations in mechanical properties, thereby improving the fatigue performance of the stranded wire.

[0033] In the preferred technical solution, the diameter of the hot-rolled wire rod is 5.5~15mm, the tensile strength is 1420~1470MPa, and the reduction of area is 36%~41%. The wire rod has high tensile strength, which can reduce the number of drawing passes and quickly reach the target diameter. The wire rod has high reduction of area and high plasticity, which can eliminate the need for offline heat treatment, increase the diameter reduction of a single drawing, reduce the risk of wire breakage and processing cracking, thereby improving the production efficiency of high-strength stranded wire and reducing processing steps and production costs.

[0034] Compared with the prior art, the beneficial effects of the present invention are at least as follows:

[0035] (1) In view of the current situation that the hot-rolled wire rod for high-strength strand is produced by the Stellmore air-cooling line, there are insufficient strength and plasticity, the abnormal structure is difficult to control, and the mechanical properties fluctuate greatly. This invention uses high Si chemical composition design combined with online molten salt sorbitization control technology to control the wire rod to quickly bypass the network carbide region from the high-temperature austenitic state and enter the sorbite phase region, suppressing the formation of network carbides and forming a structure dominated by fine lamellar interlamellar sorbite structure, suppressing the coarse pearlite soft phase, and then promoting the transformation of untransformed residual austenite into fine lamellar interlamellar sorbite structure through isothermal tempering, suppressing brittle abnormal structures such as martensite, and promoting the formation of fine lamellar interlamellar sorbite structure to undergo long-term isothermal tempering, causing some sorbite plates to melt. Finally, the roller table opening and slow cooling control the strength and plasticity matching of the wire rod, improve the uniformity of the structure, and has good industrial adaptability.

[0036] (2) In view of the current situation that the hot-rolled wire rod for high-strength strand uses a multi-alloy high-carbon composition system, the material cost is high and offline heat treatment is required. This invention does not contain elements such as Ni, Ti, and V, which can simplify the composition system and control the material cost. The microstructure includes a mixed structure composed of tempered sorbite, tempered ferrite and melted sorbite, which can suppress the coarse pearlite structure in the core and the pre-precipitation of soft ferrite phase, avoid carbide coarsening and excessive softening, enhance the strengthening effect of carbon elements, make up for the strength loss caused by omitting alloy elements, and at the same time, the stress of the tempered structure is released and the ductility and toughness are better, so as to control the strength and ductility matching of the wire rod, achieving a tensile strength of 1420~1470MPa and a section reduction rate of 36%~41%. It can be used to manufacture 2100MPa grade stranded wire and other application fields without offline heat treatment, reducing the risk of wire breakage during downstream drawing and twisting, and has good market application prospects. Attached Figure Description

[0037] 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:

[0038] Figure 1 This is a metallographic diagram of Embodiment 1 of the present invention;

[0039] Figure 2 This is a metallographic diagram of Embodiment 2 of the present invention;

[0040] Figure 3 This is a metallographic diagram of Embodiment 3 of the present invention. Detailed Implementation

[0041] 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:

[0042] A preferred embodiment of the manufacturing method of the 2100MPa grade hot-rolled wire rod for stranded wire according to the present invention, wherein the chemical composition and mass percentage of the hot-rolled wire rod include C: 0.87%, Si: 0.75%, Mn: 0.69%, Cr: 0.55%, P: 0.014%, 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 sorbitization control treatment → roller table opening and slow cooling → coiling, specifically:

[0043] The rolling process is used to heat a 180mm×180mm steel billet in a furnace to a high temperature that allows for rolling plasticity. Controlling the furnace parameters promotes uniform diffusion of alloy components, reduces segregation, and prevents decarburization. After exiting the furnace, the billet is rolled into a 5.5mm diameter wire rod on a rolling line. Appropriate rolling temperatures and reductions are selected to promote rapid rolling deformation of the billet. The final rolling process is controlled to dynamically recrystallize and refine the grains. Specifically, the furnace soaking temperature is controlled to be... The rolling temperature is 1180℃, the furnace time is 180min, the initial rolling temperature is 1040℃, the final rolling temperature is 890℃, and the final rolling reduction is 26%. 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 or proeutectoid ferrite during the wire drawing stage, thus providing favorable conditions for the subsequent sorbitic phase transformation. Specifically, the wire drawing temperature is controlled at 890℃.

[0044] The online molten salt sorbitization control 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 salt bath for initial molten salt treatment. This causes the wire rod to cool at a rate of 31°C / s, rapidly transitioning from a high-temperature austenitic state through the network carbide region into the sorbite phase region. This inhibits the formation of network carbides and coarse pearlite, resulting in a high-temperature austenitic microstructure dominated by fine-laminated sorbite, reducing the temperature gradient from the wire rod surface to the core. The wire rod is then conveyed via roller conveyor through the second stage salt bath for final molten salt treatment, with a reduced molten salt circulation rate to promote the development of the remaining wire rod. The residual austenite is transformed into fine lamellar sorbite, while the formed fine lamellar sorbite and a small amount of ferrite undergo isothermal tempering. This also promotes the melting of some of the cementite lamellars, preventing carbide coarsening and excessive softening, thus controlling the strength-ductility balance of the wire rod. Specifically: the molten salt temperature for the first stage of the molten salt treatment is 570℃, the treatment time is 180s, the molten salt circulation rate is 350t / h, and the molten salt temperature rise is ≤8℃; the molten salt temperature for the second stage of the molten salt treatment is 560℃, the treatment time is 300s, the molten salt circulation rate is 250t / h, and the molten salt temperature rise is ≤3℃.

[0045] The slow cooling process of the roller conveyor involves opening the insulation cover and blowing hot air (≥250℃) from the two salt bath tanks of the online molten salt sorbitization control treatment onto the conveyor roller conveyor. The conveyor roller conveyor transports the wire rod, 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 1.2℃ / 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, and its metallographic structure is shown in the figure below. Figure 1 As shown.

[0046] Comparative Example 1:

[0047] 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 1165°C, with a furnace time of 200 min, an initial rolling temperature of 1010°C, a final rolling temperature of 830°C, and a wire drawing temperature of 815°C. The Steyrmo forced air cooling uses a fan with an air volume of 200,000 m³ / s. 3 At 60% capacity, fans 1 to 6 are turned on to cool the wire rod to 678℃ at a cooling rate of 5.3℃ / s. Then, fans 7 to 14 are turned on to 30% capacity to cool the wire rod to 275℃ at a cooling rate of 2.3℃ / s. After cooling, the hot-rolled wire rod is obtained.

[0048] Comparative Example 2:

[0049] 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 1165°C, the furnace time is 200 min, the initial rolling temperature is 1015°C, the final rolling temperature is 835°C, and the wire drawing temperature is 820°C. During the molten salt treatment before the online molten salt sorbitization control process, the wire rod is cooled at a rate of 28°C / s, and the finished hot-rolled wire rod is obtained after the process is completed. Example 2:

[0050] A preferred embodiment of the manufacturing method of the 2100MPa grade hot-rolled wire rod for stranded wire according to the present invention, wherein the chemical composition and mass percentage of the hot-rolled wire rod include C: 0.90%, Si: 0.88%, Mn: 0.74%, Cr: 0.61%, 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 sorbitization control treatment → roller conveyor opening and slow cooling → coiling, specifically:

[0051] 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. Controlling the furnace parameters promotes uniform diffusion of alloy components, reduces segregation, and prevents decarburization. After exiting the furnace, the billet is rolled into a 12mm diameter wire rod on a rolling line. Appropriate rolling temperature and reduction are selected to promote rapid rolling deformation of the billet. The final rolling process is controlled to dynamically recrystallize and refine the grains. Specifically, the furnace soaking temperature is controlled at 12... The rolling temperature is 0.05℃, the furnace time is 145 min, the initial rolling temperature is 1060℃, the final rolling temperature is 915℃, and the final rolling reduction is 23.5%. 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 or proeutectoid ferrite during the wire drawing stage, thus providing favorable conditions for the subsequent sorbitic phase transformation. Specifically, the wire drawing temperature is controlled at 905℃.

[0052] The online molten salt sorbitization 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 salt bath for initial molten salt treatment. This causes the wire rod to cool at a rate of 34°C / s, rapidly transitioning from a high-temperature austenitic state through the network carbide region into the sorbite phase region. This inhibits the formation of network carbides and coarse pearlite, resulting in a microstructure dominated by fine-laminated sorbite with narrow lamellar spacing. This reduces the temperature gradient from the wire rod surface to the core. The wire rod is then conveyed via roller conveyor through the second stage salt bath for final molten salt treatment, with a reduced molten salt circulation rate to promote the development of the remaining wire rod. The retained austenite is transformed into fine lamellar sorbite, while the formed fine lamellar sorbite and a small amount of ferrite undergo isothermal tempering. This also promotes the melting of some of the cementite lamellars, preventing carbide coarsening and excessive softening, thus controlling the strength-ductility balance of the wire rod. Specifically: the molten salt temperature for the first stage of the molten salt treatment is 544℃, the treatment time is 265s, the molten salt circulation rate is 485t / h, and the molten salt temperature rise is ≤8℃; the molten salt temperature for the second stage of the molten salt treatment is 548℃, the treatment time is 175s, the molten salt circulation rate is 315t / h, and the molten salt temperature rise is ≤3℃.

[0053] The slow cooling process of the roller conveyor involves opening the insulation cover and blowing hot air (≥250℃) from the two salt bath tanks undergoing online molten salt martensitization control onto the conveyor roller conveyor. The conveyor roller conveyor then transports the wire rod, promoting further toughening of the wire rod structure and improving the tempering softening effect. Specifically, the wire rod is cooled to 280℃ at a slow cooling rate of 0.95℃ / 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, and its metallographic structure is shown in the figure below. Figure 2 As shown.

[0054] Comparative Example 3:

[0055] 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 sorbitization control process, the wire rod is cooled at a rate of 40°C / s, the molten salt temperature of the initial molten salt treatment is 500°C, the treatment time is 310s, and the finished hot-rolled wire rod is obtained after the process is completed.

[0056] Comparative Example 4:

[0057] 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 sorbitization control process, the wire rod is cooled at a rate of 29°C / s, the molten salt temperature of the initial molten salt treatment is 580°C, the treatment time is 150s, and the finished hot-rolled wire rod is obtained after the process is completed. Example 3:

[0058] A preferred embodiment of the manufacturing method of the 2100MPa grade hot-rolled wire rod for stranded wire according to the present invention, wherein the chemical composition and mass percentage of the hot-rolled wire rod include C: 0.86%, Si: 0.95%, Mn: 0.64%, Cr: 0.57%, 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 sorbitization control treatment → roller table opening and slow cooling → coiling, specifically:

[0059] 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. Controlling the furnace parameters promotes uniform diffusion of alloy components, reduces segregation, and avoids decarburization. After exiting the furnace, the billet is rolled into a wire rod with a diameter of 8mm via a rolling line. Appropriate rolling temperature and reduction are selected to promote rapid rolling deformation of the billet. The final rolling process is controlled to dynamically recrystallize and refine the grains. Specifically, the furnace soaking temperature is controlled at 1... The rolling temperature is 195℃, the furnace time is 165min, the initial rolling temperature is 1055℃, the final rolling temperature is 900℃, and the final rolling reduction is 25%. 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 or proeutectoid ferrite during the wire drawing stage, thus providing favorable conditions for the subsequent sorbitic phase transformation. Specifically, the wire drawing temperature is controlled at 895℃.

[0060] The online molten salt sorbitization 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 salt bath for initial molten salt treatment. This causes the wire rod to cool at a rate of 32°C / s, rapidly transitioning from a high-temperature austenitic state through the network carbide region into the sorbite phase region. This inhibits the formation of network carbides and coarse pearlite, resulting in a microstructure dominated by fine-laminated sorbite with narrow lamellar spacing. This reduces the temperature gradient from the wire rod surface to the core. The wire rod is then conveyed via roller conveyor through the second stage salt bath for final molten salt treatment, with a reduced molten salt circulation rate to promote the development of the remaining wire rod. The retained austenite is transformed into fine lamellar sorbite, while the formed fine lamellar sorbite and a small amount of ferrite undergo isothermal tempering. This also promotes the melting of some of the cementite lamellars, preventing carbide coarsening and excessive softening, thus controlling the strength-ductility balance of the wire rod. Specifically: the molten salt temperature for the first stage of the molten salt treatment is 561℃, the treatment time is 220s, the molten salt circulation rate is 395t / h, and the molten salt temperature rise is ≤8℃; the molten salt temperature for the second stage of the molten salt treatment is 555℃, the treatment time is 260s, the molten salt circulation rate is 285t / h, and the molten salt temperature rise is ≤3℃.

[0061] The slow cooling process of the roller conveyor involves opening the insulation cover and blowing hot air (≥250℃) from the two salt bath tanks undergoing online molten salt martensitization control onto the conveyor roller conveyor. The conveyor roller conveyor then transports the wire rod, promoting further toughening of the wire rod structure and improving the tempering softening effect. Specifically, the wire rod is cooled to 279℃ at a slow cooling rate of 1.1℃ / 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, and its metallographic structure is shown in the figure below. Figure 3 As shown.

[0062] Comparative Example 5:

[0063] 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 585℃, the treatment time is 310s, and the finished hot-rolled wire rod is obtained after the process is completed.

[0064] Comparative Example 6:

[0065] 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 525°C, the treatment time is 90s, and the finished hot-rolled wire rod is obtained after the process is completed. Example 4:

[0066] A preferred embodiment of the manufacturing method of the 2100MPa grade hot-rolled wire rod for stranded wire according to the present invention, wherein the chemical composition and mass percentage of the hot-rolled wire rod include C: 0.87%, Si: 0.91%, Mn: 0.84%, Cr: 0.68%, 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 sorbitization control treatment → roller conveyor opening and slow cooling → coiling, specifically:

[0067] 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. Controlling the furnace parameters promotes uniform diffusion of alloy components, reduces segregation, and avoids decarburization. After exiting the furnace, the billet is rolled into a 15mm diameter wire rod on a rolling line. Appropriate rolling temperature and reduction are selected to promote rapid rolling deformation of the billet. The final rolling process is controlled to dynamically recrystallize and refine the grains. Specifically, the furnace soaking temperature is controlled at 1... The rolling temperature is 220℃, the furnace time is 120min, the initial rolling temperature is 1070℃, the final rolling temperature is 920℃, and the final rolling reduction is 22%. 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 or proeutectoid ferrite during the wire drawing stage, thus providing favorable conditions for the subsequent sorbitic phase transformation. Specifically, the wire drawing temperature is controlled at 915℃.

[0068] The online molten salt sorbitization 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 salt bath for initial molten salt treatment. This causes the wire rod to cool at a rate of 37°C / s, rapidly transitioning from a high-temperature austenitic state through the network carbide region into the sorbite phase region. This inhibits the formation of network carbides and coarse pearlite, resulting in a microstructure dominated by fine-laminated sorbite with narrow lamellar spacing. This reduces the temperature gradient from the wire rod surface to the core. The wire rod is then conveyed via roller conveyor through the second stage salt bath for final molten salt treatment, with a reduced molten salt circulation rate to promote the development of the remaining wire rod. The residual austenite is transformed into fine lamellar sorbite, while the formed fine lamellar sorbite and a small amount of ferrite undergo isothermal tempering. This also promotes the melting of some of the cementite lamellars, preventing carbide coarsening and excessive softening, thus controlling the strength-ductility balance of the wire rod. Specifically: the molten salt temperature for the first stage of the molten salt treatment is 530℃, the treatment time is 300s, the molten salt circulation rate is 545t / h, and the molten salt temperature rise is ≤8℃; the molten salt temperature for the second stage of the molten salt treatment is 540℃, the treatment time is 100s, the molten salt circulation rate is 370t / h, and the molten salt temperature rise is ≤3℃.

[0069] The slow cooling process of the roller conveyor involves opening the insulation cover and blowing hot air (≥250°C) from the two salt bath tanks of the online molten salt sorbitization control treatment onto the conveyor roller conveyor. The conveyor roller conveyor transports the wire rod, 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 282°C at a slow cooling rate of 0.8°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.

[0070] Comparative Example 7:

[0071] A method for manufacturing hot-rolled wire rod differs from that in Example 4 in that the manufacturing method follows a process flow of rolling → wire drawing → online molten salt sorbitization control treatment → air cooling. The air cooling process involves opening the heat insulation cover and controlling the wire rod to cool to 270°C at a slow cooling rate of 1.8°C / s. After the wire rod is removed from the production line, the finished hot-rolled wire rod is obtained.

[0072] 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:

[0073] Table 1. Comparison of microstructure and properties of hot-rolled wire rods with different compositions and manufacturing methods

[0074]

[0075] The comparison between Example 1 and Comparative Example 1 shows that, compared to the absence of V, Ti, and other alloying elements, the high-carbon, high-silicon composition system using C-Si-Mn-Cr often results in a weakening of the strengthening effect of high-carbon steel during the Stellmore air-cooling phase transformation due to the difficulty in suppressing the carbon matrix. This affects the nucleation rate of sorbite, leading to the formation of coarse cementite lamellae in the core, resulting in uneven microstructure and increased fluctuations in mechanical properties. The microstructure stress generated by the uneven phase transformation remains in the wire rod, leading to insufficient plasticity in the final wire rod. This invention addresses this issue by combining online molten salt sorbitization control technology. The wire rod is controlled to quickly transition from the high-temperature austenitic state, bypassing the network carbide region and entering the sorbite phase region. Then, isothermal tempering promotes the transformation of untransformed residual austenite into fine lamellar interlamellar sorbite, causing some sorbite plates to melt. This allows for the control of the wire rod's strength and plasticity. As seen in the results of Examples 1-4, a tensile strength of 1420-1470 MPa and a reduction of area of ​​36%-41% are achieved. This wire rod is suitable for applications such as manufacturing 2100 MPa grade stranded wire, eliminating the need for offline heat treatment and reducing the risk of wire breakage during downstream drawing and twisting.

[0076] As can be seen from the comparison results between Example 1 and Comparative Example 2, selecting a higher wire drawing temperature keeps the wire rod in a high-temperature austenitizing state, preventing the precipitation of proeutectoid ferrite or network carbides before wire drawing, laying the foundation for sorbitic phase transformation. The wire rod after wire drawing does not need to be air-cooled, and the limitation on rolling temperature can be reduced.

[0077] As can be seen from the comparison results between Example 2 and Comparative Example 3, the lower the molten salt temperature in the initial molten salt treatment, the better it is to suppress the risk of network carbide precipitation. As the treatment time is extended, the atomic diffusion rate is slow during the low-temperature phase transformation, and the ferrite and cementite lamellae are thinner and the spacing is smaller, which is conducive to promoting the synchronous transformation of the wire rod core and forming a structure dominated by fine lamellar spacing sorbite, thereby improving the matrix strength. However, if the molten salt temperature is too low, it will increase the temperature difference between the wire rod surface and the core, increasing thermal stress and structural stress. If the treatment time is too long, the molten salt circulation volume in the initial molten salt treatment will be high, which will unnecessarily increase the production energy consumption.

[0078] As can be seen from the comparison results between Example 2 and Comparative Example 4, the higher the molten salt temperature of the first stage of molten salt treatment, the better it is to reduce the temperature gradient of the wire rod, the difficulty of stress release, and the risk of precipitation of low-temperature brittle structure. The shorter the treatment time, the better it is to reduce production energy consumption. 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 coarse pearlite in the core. The increase of untransformed residual austenite affects the subsequent molten salt treatment, resulting in strength loss and fluctuation of mechanical properties.

[0079] As can be seen from the comparison results of 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 better it is to promote isothermal tempering of fine lamellar sorbite structure, lamellar melting, and stress release. However, if the molten salt temperature is too high and the treatment time is too long, there will be problems of excessive softening, loss of strength, and increased production energy consumption.

[0080] As can be seen from the comparison results of Example 3 and Comparative Example 6, the lower the molten salt temperature in the later stage of molten salt treatment, the better it is to promote the transformation of untransformed residual austenite into fine lamellar interlamellar sorbite structure, and slow down the diffusion rate of carbon atoms. With the shortening of the treatment time, it is possible to avoid excessive loss of strength due to the aggregation and growth of carbides, and at the same time, it can reduce production energy consumption. However, if the molten salt temperature is too low and the treatment time is too short, it is not conducive to the melting and stress release of some cementite, and the plasticity of wire rod will be lost.

[0081] As can be seen from the comparison results between Example 4 and Comparative Example 7, the slow cooling with the roller conveyor can further control the cooling speed, promote the further toughening of the wire rod structure, improve the tempering and softening effect of the wire rod, and at the same time take into account the rapid unloading.

[0082] 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 hot-rolled wire rod for 2100MPa grade stranded wire, characterized in that, Its manufacturing methods include: The wire rod is rolled into wire rod according to the chemical composition of hot-rolled wire rod. The chemical composition and mass percentage of the hot-rolled wire rod include: C: 0.86%~0.90%, Si: 0.75%~0.95%, Mn: 0.64%~0.84%, Cr: 0.55%~0.68%, 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 sorbitization control treatment. This process involves cooling the wire rod at a cooling rate of ≥31℃ / s after the initial molten salt treatment, causing it to transition from the austenitic state to the sorbite phase region. The process involves forming a microstructure dominated by sorbite, followed by isothermal tempering in the subsequent molten salt treatment to promote the melting of some sorbite lamellars, and finally slow cooling via a roller conveyor to produce a hot-rolled wire rod with a microstructure consisting of a mixture of tempered sorbite, tempered ferrite, and melted sorbite. The molten salt temperature in the initial molten salt treatment is 530~570℃, and the treatment time is 180~300s. The molten salt temperature in the subsequent molten salt treatment is 540~565℃, and the treatment time is 100~300s. The slow cooling via the roller conveyor controls the wire rod to cool to below 285℃ at a slow cooling rate of 0.8~1.2℃ / s before coiling.

2. The method for manufacturing hot-rolled wire rod for 2100MPa 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 120~180min.

3. The method for manufacturing hot-rolled wire rod for 2100MPa grade stranded wire according to claim 1, characterized in that, During the rolling process, the initial rolling temperature is controlled at 1040~1070℃, the final rolling temperature is controlled at 890~920℃, and the final rolling reduction is controlled at 22%~26%; during the wire drawing process, the wire drawing temperature is controlled at 890~915℃.

4. The method for manufacturing hot-rolled wire rod for 2100MPa grade stranded wire according to claim 1, characterized in that, The molten salt circulation volume in the subsequent molten salt treatment is less than that in the preceding molten salt treatment.

5. The method for manufacturing hot-rolled wire rod for 2100MPa grade stranded wire according to claim 1, characterized in that, The molten salt circulation rate of the front-end molten salt treatment is 350~545t / h, and the molten salt temperature rise is ≤8℃; the molten salt circulation rate of the rear-end molten salt treatment is 250~370t / h, and the molten salt temperature rise is ≤3℃.

6. A hot-rolled wire rod for 2100MPa grade stranded wire, characterized in that, The hot-rolled wire rod is manufactured by the manufacturing method of hot-rolled wire rod for 2100MPa grade strand as described in any one of claims 1 to 5.

7. The hot-rolled wire rod for 2100MPa grade stranded wire according to claim 6, characterized in that, The volume percentage of tempered sorbite is ≥64%, the lamellar spacing is 75~125nm, the volume percentage of tempered ferrite is ≤4%, the volume percentage of melted sorbite is ≥22%, the network carbide grade of the hot-rolled wire rod is 0, and the mechanical property difference between the same ring is ≤38MPa.

8. The hot-rolled wire rod for 2100MPa grade stranded wire according to claim 6, characterized in that, The hot-rolled wire rod has a diameter of 5.5~15mm, a tensile strength of 1420~1470MPa, and a reduction of area of ​​36%~41%.

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