Hot-rolled wire rod for 2100MPa-grade stranded wire and manufacturing method of hot-rolled wire rod

Abstract

The invention relates to a hot-rolled wire rod for a 2100MPa-grade stranded wire and a manufacturing method thereof, after a high-carbon and high-silicon component system is rolled and spun into a wire rod, the wire rod is cooled at a cooling speed of more than or equal to 31 DEG C / s through online molten salt sorbite regulation and control treatment, and enters a sorbite phase region from an austenite state; the method comprises the following steps of: forming a structure mainly comprising a sorbite structure, performing isothermal tempering, promoting fusing of a part of sorbite lamellas, and finally performing roller way cover opening and slow cooling to prepare the hot-rolled wire rod of which the microscopic structure comprises a mixed structure consisting of tempered sorbite, tempered ferrite and fused sorbite, so that alloy components can be simplified, and the strong plasticity matching and the structure uniformity of the wire rod can be improved; the tensile strength is 1420-1470 MPa, the percentage reduction of area is 36%-41%, the composite material is used for the application field of manufacturing 2100 MPa grade stranded wires and the like, off-line heat treatment can be avoided, and the risk of wire breakage during downstream drawing and twisting is reduced.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field related to hot-rolled wire rod, and particularly relates to a 2100MPa-grade hot-rolled wire rod for stranded wire and a manufacturing method thereof. BACKGROUND

[0002] The steel strand takes the hot-rolled wire rod as the base material, is drawn into steel wire, and is stranded by multiple steel wires, and can be used in hoisting, traction, fixing, towing and other working scenes, and is widely used in the fields of railway, bridge, ocean engineering, building, ship, power and the like. With the acceleration of green and intelligent development, energy saving and carbon reduction and light weight become important directions of industrial development, after the strength grade of the steel strand is improved to 1960MPa, the conventional production mode is extremely difficult to meet the further improvement of the strength grade, and usually needs to use the offline heat treatment mode to achieve performance improvement, which not only increases the production cost and energy consumption by a large margin, and further improves the strength to 2100MPa, and there are few developments, therefore, it is necessary to develop a 2100MPa-grade hot-rolled wire rod for stranded wire and a manufacturing method thereof, without offline heat treatment, to meet the development of the iron and steel industry and the market use demand.

[0003] In the prior art, the high-strength steel strand steel hot-rolled wire rod adopts a multi-alloy high-carbon steel composition combined with a Stelmor air cooling line, for example, the patent CN102352469B discloses a super-high-strength vanadium-titanium composite micro-alloyed high-carbon steel wire rod and a preparation method thereof, which adopts a high-carbon composition of C-Si-Mn-V-Ti-Cr-Cu-Ni-B, and combines Stelmor line fast cooling, heat preservation and slow cooling process to prepare sorbite structure wire rod, but there are still the following technical bottlenecks: I. In order to inhibit austenite grains during hot rolling and form precipitation strengthening, V, Ti and other alloying elements are added in the steel grade, but this will also increase the material cost, and in order to reduce the cost, the alloying elements are omitted, which will lose the precipitation strengthening effect, the maximum cooling capacity of the Stelmor air cooling line will affect the nucleation rate of sorbite, and the coarse structure and grains will further affect the strength and toughness performance, and the insufficient strength and toughness of the wire rod will lead to the need for more processing passes in the downstream drawing, and the plasticity loss is fast during the process, and there is a risk of wire breakage during drawing and twisting.

[0004] II. To improve the strength and plasticity of the wire rod, the steel grade is combined with Si, Mn, Cr, Ni, B and other alloying elements, and the high wind cooling treatment after wire drawing is used to improve the content of sorbite in the structure, but it will also increase the material cost and smelting difficulty. After the alloying elements are saved, the hardenability of the wire rod decreases, the critical phase transition temperature moves upward, and coarse pearlite and pre-precipitated ferrite are easily produced during the cooling process of the air cooling line, resulting in a large strength loss. Due to the limitation of the maximum cooling capacity and the segregation and enrichment of high carbon content during solidification, the wire rod stays in the precipitation temperature range of secondary cementite for a long time, and is easy to precipitate and form network carbide, which will cut the matrix and significantly deteriorate the plasticity and toughness. After the air cooling strength is improved, on the one hand, due to the unstable temperature control, the temperature difference between the wind surface and the wind surface, the lap joint and the non-lap joint, and the surface and the core will be further increased, which will cause the surface and the local to form martensite and other low-temperature brittle structures, increase the brittleness of the wire rod, and the core will form coarse cementite lamella, resulting in uneven structure and large fluctuation of mechanical properties. Abnormal structure will also become a crack source and cause brittle fracture during transportation and processing. On the other hand, under the continuous cooling control of the air cooling line, the wire rod is in a low temperature state after phase transition incubation, and the atomic diffusion speed is slow due to the influence of high silicon and chromium alloying elements. The structure stress generated by uneven phase transition will be left in the wire rod, resulting in insufficient plasticity of the wire rod, and the downstream is prone to wire drawing breakage risk, which is difficult to break through the production bottleneck of offline heat treatment. SUMMARY

[0005] The present application aims to at least solve one of the above technical problems to a certain extent, and provides a 2100MPa grade hot rolled wire rod for stranded wire and a manufacturing method thereof, which can simplify the alloying elements, improve the strength and plasticity matching and structure uniformity of the wire rod, and can be offline heat treatment, reduce the risk of downstream drawing and twisting breakage.

[0006] The technical scheme adopted by the present application to solve the technical problems is: A manufacturing method of a 2100MPa grade hot rolled wire rod for stranded wire, the manufacturing method comprising: A wire rod is produced by rolling according to the chemical composition of the hot rolled wire rod, and the chemical composition and mass percentage of the hot rolled wire rod comprises: 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%, and the rest is Fe and unavoidable impurities; after the wire rod is drawn into a wire rod at a wire drawing temperature of≥890℃, it is subjected to online molten salt sorbitizing regulation treatment, so that the wire rod is cooled at a cooling rate of≥31℃ / s from the austenite state into the sorbite phase region, forms a structure mainly composed of sorbite structure and isothermal tempering, promotes the melting of part of the sorbite lamella, and finally is slowly cooled by opening the roller cover to form a hot rolled wire rod with a mixed structure composed of tempered sorbite, tempered ferrite and melted sorbite.

[0007] The chemical composition and mass percentage design of the hot-rolled wire rod according to the above include: (1) Carbon: C is an effective strengthening element in steel, and the price is relatively lower. C can improve the resistance to dislocation movement through solid solution strengthening, and can improve the critical point of austenite transformation, expand the stable region of undercooled austenite, and reduce the starting temperature of austenite to sorbite transformation, which is beneficial to promote the rapid transformation and refinement of sorbite to improve the strength of the matrix. However, if the content of C is too high, carbon is easy to diffuse and precipitate along the austenite grain boundary, forming continuous or semi-continuous network carbide, which increases the difficulty of controlling the uniformity of the structure and the abnormal structure of martensite, leading to material embrittlement, significant decrease in plasticity, and affecting the processing forming. Therefore, in order to balance the high strength requirement of 2100MPa grade wire, reduce the fluctuation of mechanical properties, and promote rapid production, the mass percentage of C is controlled to be 0.86%~0.90%.

[0008] (2) Silicon: Si element is a solid solution strengthening element of ferrite. By solid solution in the matrix phase of sorbite, it can hinder dislocation movement and improve the matrix strength. During the transformation of austenite to sorbite, it can hinder the migration of carbon atoms to cementite, inhibit the generation of coarse carbide during cooling, strongly inhibit the precipitation and coarsening process of Fe3C, delay the transformation of pearlite, and expand the sorbite formation interval, so as to form a structure mainly composed of sorbite. During isothermal tempering, it can hinder the spheroidization and growth of cementite lamella, improve the tempering stability, avoid insufficient drawing strength due to softening, refine the precipitated phase, and improve the toughness of the material. However, too high silicon will promote decarburization, prolong the transformation incubation period, increase the difficulty of isothermal tempering 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 regulation of the transformation structure by online molten salt sorbitizing regulation, improve the anti-tempering softening ability, and appropriately increase the Si content, the mass percentage of Si is controlled to be 0.75%~0.95%.

[0009] (3) Manganese: Mn is an austenite stabilizing element, which can make the sorbite transformation interval move down, delay the nucleation and growth speed of pearlite, expand the sorbite formation interval, and improve the hardenability of the wire rod, so that the wire rod can fully complete the sorbite transformation in the molten salt and improve the synchronization of full cross-section structure transformation. During isothermal tempering, it can also hinder the diffusion and migration of carbon atoms, thereby inhibiting the coarsening of carbide, so that the wire rod maintains high strength. However, if the content of Mn is too high, it will increase the alloy element segregation during the solidification process of the steel billet, increase the hot rolling deformation resistance, easily form low-temperature martensite structure during cooling, increase the hardness, increase the brittleness and mechanical property fluctuation, affect the toughness of the wire rod, accelerate the work hardening rate during drawing, and therefore, in order to balance the high strength and plasticity of the hot-rolled wire rod, reduce the fluctuation of mechanical properties, and avoid excessive tempering softening, the mass percentage of Mn is controlled to be 0.64%~0.84%.

[0010] (4) Chromium: Cr is a strong carbide-forming element, which can hinder dislocation movement by solid solution strengthening and forming carbide dispersed in the sorbite lamellar, thereby improving the matrix strength. Meanwhile, it can enhance the hardenability, so that the continuous cooling transformation curve of the steel moves to the right. In combination with the in-line molten salt sorbitizing regulation treatment, the transformation of austenite to pearlite is delayed, which lays the foundation for the subsequent formation of sorbite-based structure. At the same time, the dispersed Cr-based carbide can continuously pin dislocations, increase the resistance to temper softening, and enable the rod to maintain high strength after tempering. However, excessive Cr content will exacerbate alloy element segregation, increase the risk of martensite and other abnormal structure precipitation, and increase the high-temperature deformation resistance of the steel during rolling, thereby reducing the activity of carbon during isothermal tempering, which is not conducive to sorbite melting and temper softening, and affects the drawing plasticity of the steel. Therefore, the mass percentage of Cr is controlled to be 0.55% to 0.68%.

[0011] (5) Phosphorus and sulfur: P and S elements are impurity elements, and the lower the better. Therefore, P is controlled to be ≤0.015%, and S is controlled to be ≤0.015%.

[0012] The above hot-rolled rod adopts a high-carbon high-silicon composition system of C-Si-Mn-Cr, and does not contain elements such as Ni, Ti, and V. This can simplify the composition system and control the material cost. At the same time, it regulates the hardenability of the rod, the sorbite precipitation temperature interval, and the temper softening resistance, which provides favorable conditions for promoting the full transformation of austenite to fine lamellar sorbite, inhibiting coarse pearlite soft phase and martensite abnormal structure, avoiding excessive temper softening, and increasing the offline speed. On this basis, a higher wire laying temperature is selected, so that the rod is in a high-temperature austenitizing state, preventing the precipitation of proeutectoid ferrite or net-shaped carbide before wire laying, and laying the foundation for sorbite transformation. The rod after wire laying is not air-cooled, but directly subjected to in-line molten salt sorbitizing regulation treatment: I. Compared with the alloy elements, the highest cooling capacity and temperature control instability of the Stelmor air cooling line cannot control abnormal organizations such as network carbide, coarse pearlite soft phase and martensite. On the one hand, the high efficient heat transfer characteristics of the molten salt medium can promote the wire rod to slightly pass through the secondary cementite precipitation temperature interval from the high temperature austenite state, so as to inhibit the risk of network carbide caused by high carbon content, and quickly enter the sorbite phase area with lower temperature, inhibit the pro-eutectoid ferrite, cooperate with high silicon content to inhibit the cementite coarsening, cooperate with Mn, Cr and other hardenability elements to promote the synchronous phase change of the wire rod surface and the core, and through increasing the supercooling degree, the incubation period is shortened, the core coarse pearlite soft phase organization is inhibited, and the matrix strength is provided; on the other hand, the molten salt can cover the wire rod surface uniformly when the wire rod passes through the molten salt, and there is no temperature difference between the air cooling surface and the air cooling surface, the lap joint and the non-lap joint, so that the temperature difference between the wire rod surface and the core can be further reduced, the local supercooling and the atomic diffusion of the supercooled austenite are inhibited to form martensite and other low temperature brittle organizations, so as to improve the uniformity of the organization and the internal stress distribution, and reduce the risk of abnormal organizations and mechanical property fluctuation.

[0013] II. Compared with the influence of high silicon, chromium and other alloy elements, and the length and minimum cooling capacity of the Stelmor air cooling line, the final plasticity of the wire rod is insufficient. On the one hand, with the extension of the treatment time, the wire rod temperature can be gradually changed to the isothermal treatment temperature consistent with the molten salt temperature instead of continuous cooling, which can prolong the time of the wire rod in the sorbite phase transformation peak precipitation temperature, promote the untransformed residual austenite to continue to transform into fine interlamellar spacing sorbite organization, compensate for the adverse effects of increasing silicon on prolonging the incubation period, and avoid the formation of brittle abnormal organizations in the subsequent cooling process; on the other hand, the wire rod is still in a high temperature state after phase transformation incubation, which can prolong the time of the wire rod in the high temperature isothermal temperature interval, improve the tempering heat dynamics, provide kinetic energy for atomic diffusion, promote the release of organizational stress, and part of the cementite lamella of sorbite is melted and broken, and is transformed into a better plasticity tempering state, while cooperating with high silicon, chromium and other alloy elements to improve the anti-tempering softening capacity, avoid excessive loss of strength, and finally through the slow cooling of the roller opening cover, promote the wire rod to be further toughened and quickly offline, and regulate the overall strength and plasticity matching of the wire rod.

[0014] Before rolling, a higher heating furnace soaking temperature and a proper furnace time can be selected to reduce the influence of composition segregation and hot rolling deformation resistance, while avoiding the abnormal growth of austenite grains or decarburization caused by too long furnace time. In the preferred technical solution, before rolling, the heating furnace soaking temperature is controlled to be 1180-1220℃, and the furnace time is 120-180min.

[0015] Since the spinning temperature is high, the limitation on the rolling temperature can be reduced, a higher initial rolling temperature is selected to increase the rolling speed, reduce the wear and load demand on the rolling line, realize efficient deformation, cooperate with appropriate finish rolling temperature and finish rolling reduction, promote the dynamic recrystallization in the finish rolling process, refine the grains, and obtain a uniform fine-grained austenite matrix. In the preferred technical solution, during rolling, the initial rolling temperature is controlled to be 1040-1070℃, the finish rolling temperature is 890-920℃, and the finish rolling reduction is 22%-26%.

[0016] During spinning, the spinning temperature can be further controlled to avoid excessive growth of austenite grains. In the preferred technical solution, during spinning, the spinning temperature is controlled to be 890-915℃.

[0017] In the preferred technical solution, the on-line molten salt sorbitizing regulation treatment is divided into a front-stage molten salt treatment and a rear-stage molten salt treatment, and the molten salt circulation amount of the rear-stage molten salt treatment is less than that of the front-stage molten salt treatment. Since the wire rod has a relatively small temperature difference in each part after the front-stage molten salt treatment, the molten salt circulation amount can be appropriately reduced to reduce the production energy consumption.

[0018] The molten salt temperature of the front-stage molten salt treatment is in the sorbite phase region. The lower the molten salt temperature, the more conducive to inhibiting the risk of network carbide precipitation. With the extension of the treatment time, the atomic diffusion speed is slow during low-temperature phase change, the ferrite and cementite lamella are thinner and the spacing is smaller, which is conducive to promoting the synchronous transformation of the core of the wire rod and forming a structure mainly of fine lamella spacing sorbite to improve the strength of the matrix. However, if the molten salt temperature is too low, the temperature difference between the surface and the core of the wire rod will increase, the thermal stress and the organizational stress will increase, and even brittle abnormal organization will be formed due to overcooling. If the treatment time is too long, the molten salt circulation amount of the front-stage molten salt treatment is high, which unnecessarily increases the production energy consumption. On the contrary, the higher the molten salt temperature, the more conducive to reducing the temperature gradient of the wire rod, the difficulty of stress release, and the risk of low-temperature brittle structure precipitation. The shorter the treatment time, the more conducive to reducing the production energy consumption. However, if the molten salt temperature is too high and the treatment time is too short, it is not conducive to inhibiting the network carbide and the coarse pearlite in the core, and the increase of the untransformed residual austenite will affect the rear-stage molten salt treatment, resulting in strength loss and mechanical property fluctuation. Therefore, the molten salt temperature and the treatment time of the front-stage molten salt treatment can be controlled to make the wire rod quickly pass through the network carbide region and enter the sorbite phase region from the high-temperature austenite state, inhibit the formation of network carbide, and form a structure mainly of fine lamella spacing sorbite structure, taking into account the production energy consumption and the uniformity of the structure. In the preferred technical solution, the molten salt temperature of the front-stage molten salt treatment is 530-570℃, and the treatment time is 180-300s.

[0019] Due to the large temperature difference between the spinning temperature and the molten salt temperature of the front-stage molten salt treatment, a large molten salt circulation amount is selected to control the molten salt temperature rise, quickly take away the heat of the wire rod, and avoid the increase of thermal stress caused by uneven cooling. In the preferred technical solution, the molten salt circulation amount of the front-stage molten salt treatment is 350-545 t / h, and the molten salt temperature rise is ≤8℃.

[0020] The molten salt temperature of the rear-stage molten salt treatment is in the sorbite phase region. The lower the molten salt temperature, the more conducive to promoting the untransformed residual austenite to continue to transform into fine lamellar spacing sorbite structure, delaying the diffusion speed of carbon atoms, and avoiding the excessive loss of strength caused by the aggregation and growth of carbides, while reducing the 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 of part of the cementite and stress release, which will lose the plasticity of the wire rod. On the contrary, the higher the molten salt temperature and the longer the treatment time, the more conducive to promoting the fine lamellar sorbite structure to isothermal tempering, lamellar melting, and stress release. However, if the molten salt temperature is too high and the treatment time is too long, it will cause excessive softening and loss of strength, and increase the production energy consumption. Therefore, the molten salt temperature and treatment time of the rear-stage molten salt treatment can be controlled to promote the untransformed residual austenite to continue to transform into fine lamellar spacing sorbite structure, and promote the fine lamellar spacing sorbite structure formed to be tempered for a long time, and part of the cementite lamella to be melted, thereby avoiding the coarsening and excessive softening of carbides, and adjusting the strength and plasticity matching of the wire rod. In the preferred technical solution, the molten salt temperature of the rear-stage molten salt treatment is 540-565℃, and the treatment time is 100-300 s.

[0021] Due to the long treatment time of the front-stage molten salt treatment and the small difference between the molten salt temperatures of the front-stage and rear-stage molten salt treatments, the molten salt circulation amount can be appropriately reduced to control the molten salt temperature rise and isothermal tempering stability, and effectively reduce the production energy consumption. In the preferred technical solution, the molten salt circulation amount of the rear-stage molten salt treatment is 250-370 t / h, and the molten salt temperature rise is ≤3℃.

[0022] The slow cooling of the roller opening cover can further control the slow cooling speed, promote the wire rod structure to be further toughened, improve the tempering softening effect of the wire rod, and simultaneously consider the rapid offline. In the preferred technical solution, the slow cooling of the roller opening cover controls the wire rod to be cooled to below 285℃ at a slow cooling speed of 0.8-1.2℃ / s for coiling.

[0023] In the preferred technical solution, the slow cooling of the roller opening cover uses an open insulation cover to blow hot air ≥250℃ in the online molten salt sorbitizing regulation and control to the conveying roller, and the wire rod is conveyed by the conveying roller. The hot air can further reduce the temperature gradient from the surface to the core of the wire rod, reduce the mechanical property fluctuation, and simultaneously recover and utilize the heat energy of the online molten salt sorbitizing regulation and control, and reduce the production energy consumption.

[0024] A hot-rolled wire rod for 2100 MPa grade stranded wire is manufactured by the method for manufacturing a hot-rolled wire rod for 2100 MPa grade stranded wire.

[0025] The hot-rolled wire rod has a high-silicon composition design and does not contain alloying elements such as V, Ti, and Ni, which can reduce material cost and smelting difficulty. Meanwhile, the microstructure of the hot-rolled wire rod mainly includes tempered sorbite and broken sorbite and a small amount of tempered ferrite. Compared with a strand steel air-cooled wire rod pearlite / sorbite structure wire rod, the hot-rolled wire rod can effectively inhibit the adverse effects of network carbide on plasticity and toughness, avoid the formation of brittle abnormal structures such as martensite due to local undercooling, inhibit the coarse pearlite structure in the core and the first-precipitated ferrite soft phase, and utilize the finer interlamellar spacing of full-section sorbite than pearlite, so that the fine lamellar structure can more effectively hinder dislocation movement, the cementite is more uniformly dispersed, the stress concentration effect is weakened, the strength and toughness are better, the mechanical property fluctuation is reduced, and after isothermal tempering, the hot-rolled wire rod is converted into a partially sorbite cementite lamellar broken sorbite and a spherical structure transition state tempered sorbite, which can avoid excessive loss of strength by using the high-silicon tempering softening resistance, can retain the matrix strength by using the carbide pinning grain boundary of Cr, can improve the strengthening effect of carbon elements, can make up for the strength loss due to the omission of alloying elements, can release the tempering stress, and can have better plasticity and toughness, so that the overall strength and plasticity are matched, offline heat treatment is avoided, the risk of fracture in subsequent processing is reduced, and the yield is improved.

[0026] 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 proportion of broken sorbite, the better the plasticity and toughness. In the preferred technical solution, the volume percentage of the tempered sorbite is ≥64%, the lamellar spacing is 75-125 nm, the volume percentage of the tempered ferrite is ≤4%, and the volume percentage of the broken sorbite is ≥22%.

[0027] In the preferred technical solution, the hot-rolled wire rod has a network carbide level of 0, and the mechanical property same circle difference is ≤38 MPa; in cold drawing, twisting, and other processing, the deformation is more uniform, and stress concentration is less likely to occur due to network carbide, local uneven structure, and mechanical property fluctuation, thereby improving the fatigue performance of the stranded wire.

[0028] In the preferred technical solution, the diameter of the hot-rolled wire rod is 5.5-15 mm, the tensile strength is 1420-1470 MPa, and the reduction of area is 36%-41%. The hot-rolled wire rod has high tensile strength, which can reduce the drawing passes and quickly reach the target diameter. The hot-rolled wire rod has high reduction of area and high plasticity, which can avoid offline heat treatment, improve the diameter reduction amount of single drawing, reduce the risk of wire breakage and processing cracking, and further improve the production efficiency of high-strength stranded wire and reduce the processing procedures and production cost.

[0029] Compared with the prior art, the present application has at least the following beneficial effects: (1) For high-strength wire rod, the present application adopts Stelmor air cooling line production, and there is a current situation of insufficient strength and plasticity, difficult to control abnormal organization, and large fluctuation of mechanical properties. The present application controls the wire rod to quickly pass through the interlamellar spacing sorbite organization area from the high-temperature austenite state, suppresses the formation of net-shaped carbide, and forms the main organization of interlamellar spacing sorbite organization, suppresses the coarse pearlite soft phase, and then promotes the untransformed residual austenite to continue to transform into interlamellar spacing sorbite organization through isothermal tempering, suppresses brittle abnormal organizations such as martensite, and at the same time promotes the formed interlamellar spacing sorbite organization to be isothermal tempered for a long time, promotes part of the sorbite sheet to be melted, and finally controls the strength and plasticity matching of the wire rod through slow cooling regulation of the roller opening cover, improves the uniformity of the organization, and has good industrial adaptability.

[0030] (2) For high-strength wire rod, the present application adopts a multi-alloy high-carbon composition system, and there is a current situation of high material cost and the need for offline heat treatment. The present application does not contain elements such as Ni, Ti, and V, can simplify the composition system and control the material cost, the microstructure includes a mixed organization composed of tempered sorbite, tempered ferrite and melted sorbite, can suppress the coarse pearlite organization and the first precipitation ferrite soft phase in the core, avoid carbide coarsening and excessive softening, improve the strengthening effect of carbon elements, make up for the strength loss caused by the omission of alloy elements, at the same time, the stress of the tempered state organization is released, and the plastic and tough properties are better, so as to control the strength and plasticity matching of the wire rod, achieve the tensile strength of 1420-1470 MPa, the reduction of area of 36%-41%, and be used for manufacturing 2100 MPa grade wire and other application fields, without the need for offline heat treatment, reduce the risk of wire breakage in downstream drawing and twisting, and have good market application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0031] The above and / or additional aspects and advantages of the present application will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the following drawings of which: Figure 1 is the metallographic structure diagram of embodiment 1 of the present application; Figure 2 is the metallographic structure diagram of embodiment 2 of the present application; Figure 3 is the metallographic structure diagram of embodiment 3 of the present application. DETAILED DESCRIPTION

[0032] The embodiments described below with reference to the drawings are exemplary, are merely for illustration and do not limit the description of the features and characteristics of the present application, are intended to propose the best mode of carrying out the present application, are intended to serve for explaining the present application, and are sufficient to enable a person skilled in the art to implement the present application, and cannot be understood as any limitation on the scope of the present application, the scope of the present application is limited only by the appended claims; the organization and performance detection of the hot-rolled wire rod obtained in the following examples and comparative examples include: the tensile test is tested according to GB-T228.1-2021 Metal Materials Tensile Test Part 1: Room Temperature Test Method to obtain tensile strength and area reduction; the organization detection is carried out according to the metal microstructure detection method of GB / T13298 standard; the mechanical property same circle difference test method: 2 circles of wire rod are taken at 5m from the end of the coil, the lap joint area position is taken as the base point, each circle of wire rod is equally divided into 8 segments, and 1 tensile sample is taken on each segment, and the strength range of the tensile sample after tensile test is the mechanical property same circle difference. Example 1

[0033] In a preferred embodiment of the manufacturing method of the 2100MPa-grade hot-rolled wire rod for stranded wire provided by the present application, 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%, and the rest is Fe and inevitable impurities; the manufacturing method is manufactured according to the process flow of rolling→ wire laying→ online molten salt sorbite treatment→ slow cooling of roller opening→ coil collecting, and specifically: The rolling process is used to heat the steel billet with a specification of 180mm*180mm to a high-temperature steel billet with a rolling plasticity by a heating furnace, control the heating furnace parameters to promote the uniform diffusion of alloy components, reduce segregation and avoid decarburization, and the steel billet is rolled into a wire rod with a diameter specification of 5.5mm after the steel billet is discharged from the heating furnace through a rolling line, appropriate rolling temperature and reduction are selected to promote rapid rolling deformation of the steel billet, and the dynamic recrystallization of the final rolling process is controlled to refine the grain, and specifically: the soaking temperature of the heating furnace is controlled to be 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 laying process is used to make the wire rod discharged from the rolling line into a wire rod through a wire laying machine, the wire rod is scattered on the roller and conveyed along the roller, and appropriate wire laying temperature is selected to make the wire rod in a high-temperature austenite state, avoid the precipitation of net-shaped carbide or pro-eutectoid ferrite at the wire laying stage, and provide favorable conditions for the subsequent sorbite phase change, and specifically: the wire laying temperature is controlled to be 890℃.

[0034] The online molten salt sorbitizing regulation treatment process adopts two-stage salt bath tanks with molten salt, and the wire rod after spinning is conveyed through the first-stage salt bath tank for the first-stage molten salt treatment, so that the wire rod is cooled at a cooling rate of 31℃ / s, quickly passes through the interlaced carbide zone from the high-temperature austenite state into the sorbite phase zone, inhibits the formation of interlaced carbide and coarse pearlite, most of the high-temperature austenite organization phase changes into the organization mainly of sorbite organization with fine lamellar spacing, reduces the temperature gradient from the surface to the core of the wire rod, and then the wire rod is conveyed through the second-stage salt bath tank for the second-stage molten salt treatment, the molten salt circulation amount is appropriately reduced, the untransformed residual austenite is promoted to continue to transform into sorbite organization with fine lamellar spacing, at the same time, the sorbite organization and a small amount of ferrite formed are promoted to isothermal tempering, and a part of the cementite sheets of the sorbite are promoted to be broken, so as to avoid the coarsening of carbide and excessive softening, so as to regulate the strength and plasticity matching of the wire rod, specifically: the molten salt temperature of the first-stage molten salt treatment is 570℃, the treatment time is 180s, the molten salt circulation amount is 350t / h, and the molten salt temperature rise is ≤8℃; the molten salt temperature of the second-stage molten salt treatment is 560℃, the treatment time is 300s, the molten salt circulation amount is 250t / h, and the molten salt temperature rise is ≤3℃.

[0035] The roller cover opening slow cooling process adopts opening the heat preservation cover, blowing the hot air with a temperature of ≥250℃ above the two-stage salt bath tank of the online molten salt sorbitizing regulation treatment to the conveying roller, conveying the wire rod through the conveying roller, promoting the further toughening of the wire rod organization, and improving the tempering softening effect of the wire rod, specifically: the wire rod is cooled to 275℃ at a slow cooling rate of 1.2℃ / s; and the coiling process is used for coiling the wire rod into a coil through a coiling drum, and obtaining the hot-rolled wire rod product after packaging and storage, and the metallographic structure diagram is as shown in Figure 1 .

[0036] Comparative Example 1 A manufacturing method of a hot-rolled wire rod, which is different from the manufacturing method of Example 1 in that the manufacturing method is manufactured according to the process flow of rolling→spinning→Stelmor strong air cooling, specifically: the heating furnace soaking temperature is controlled to be 1165℃, the furnace time is 200min, the initial rolling temperature is 1010℃, the final rolling temperature is 830℃, and the spinning temperature is 815℃; the Stelmor strong air cooling adopts the air volume of each fan to be 2000000m 3 / h, the 1~6# fans are opened at 60%, the wire rod is cooled to 678℃ at a cooling rate of 5.3℃ / s, the 7~14# fans are opened at 30%, the wire rod is cooled to 275℃ at a cooling rate of 2.3℃ / s, and the hot-rolled wire rod product is obtained after offline.

[0037] Comparative Example 2 A manufacturing method of hot-rolled wire rod, which is different from the manufacturing method of embodiment 1 in that: the soaking temperature of the heating furnace is controlled to be 1165℃, the furnace time is 200min, the rough rolling temperature is 1015℃, the finish rolling temperature is 835℃, the wire drawing temperature is 820℃, and before the online molten salt sorbite treatment regulation process, the wire rod is cooled at a cooling rate of 28℃ / s, and the hot-rolled wire rod product is obtained after being taken offline. Embodiment 2

[0038] In a preferred embodiment of the manufacturing method of the 2100MPa-grade hot-rolled wire rod for stranded wire, 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%, and the rest is Fe and inevitable impurities; and the manufacturing method is manufactured according to the process flow of rolling→wire drawing→online molten salt sorbite treatment regulation→roller opening slow cooling→coiling, specifically: The rolling process is used to heat the steel billet with a specification of 220mm×220mm to a high-temperature steel billet with rolling plasticity through a heating furnace, control the heating furnace parameters to promote uniform diffusion of alloy components, reduce segregation, and avoid decarburization, and after the steel billet is taken out of the heating furnace, the steel billet is rolled into a wire rod with a diameter specification of 12mm through a rolling line, appropriate rolling temperature and reduction are selected to promote rapid rolling deformation of the steel billet, and the dynamic recrystallization of the finish rolling process is controlled to refine the grains, specifically: the soaking temperature of the heating furnace is controlled to be 1205℃, the furnace time is 145min, the rough rolling temperature is 1060℃, the finish rolling temperature is 915℃, and the finish rolling reduction is 23.5%; the wire drawing process is used to make the wire rod out of the rolling line into a wire rod through a wire drawing machine, the wire rod is scattered on the roller way and conveyed along the roller way, appropriate wire drawing temperature is selected to make the wire rod in a high-temperature austenitizing state, avoid the precipitation of net-shaped carbide or pro-eutectoid ferrite at the wire drawing stage, and provide favorable conditions for the subsequent sorbite phase change, specifically: the wire drawing temperature is controlled to be 905℃.

[0039] The online molten salt sorbitizing regulation treatment process adopts two-stage salt bath tanks with molten salt inside. The wire rod after spinning is conveyed through the first-stage salt bath tank for front-stage molten salt treatment, so that the wire rod is cooled at a cooling rate of 34℃ / s, quickly passes through the intercritical region of the net-shaped carbide from the high-temperature austenite state into the sorbite phase region, inhibits the formation of the net-shaped carbide and coarse pearlite, most of the high-temperature austenite organization phase changes into the organization mainly with the sorbite organization with fine lamellar spacing, reduces the temperature gradient from the surface to the core of the wire rod, and then the wire rod is conveyed through the second-stage salt bath tank for rear-stage molten salt treatment. The molten salt circulation amount is appropriately reduced to promote the untransformed residual austenite to continue to transform into the sorbite organization with fine lamellar spacing, promote the sorbite organization with fine lamellar spacing and a small amount of ferrite formed to be isothermal tempered, and promote the cementite sheets of part of the sorbite to be melted off to avoid the coarsening of the carbide and excessive softening, so as to regulate the strength and plasticity matching of the wire rod. Specifically, the molten salt temperature of the front-stage molten salt treatment is 544℃, the treatment time is 265s, the molten salt circulation amount is 485t / h, and the molten salt temperature rise is ≤8℃; the molten salt temperature of the rear-stage molten salt treatment is 548℃, the treatment time is 175s, the molten salt circulation amount is 315t / h, and the molten salt temperature rise is ≤3℃.

[0040] The roller cover opening slow cooling process blows the hot air with a temperature of ≥250℃ above the two-stage salt bath tanks of the online molten salt sorbitizing regulation treatment to the conveying roller, and the wire rod is conveyed by the conveying roller to promote the further toughening of the wire rod organization and improve the tempering softening effect of the wire rod. Specifically, the wire rod is cooled to 280℃ at a slow cooling rate of 0.95℃ / s. Figure 2

[0041] Comparative Example 3 A manufacturing method of a hot-rolled wire rod, which is different from that of Example 2 in that, in the front-stage molten salt treatment of the online molten salt sorbitizing regulation treatment process, the wire rod is cooled at a cooling rate of 40℃ / s, the molten salt temperature of the front-stage molten salt treatment is 500℃, and the treatment time is 310s. The hot-rolled wire rod product is obtained after being discharged.

[0042] Comparative Example 4 A manufacturing method of a hot-rolled wire rod, which is different from that of Example 2 in that, in the front-stage molten salt treatment of the online molten salt sorbitizing regulation treatment process, the wire rod is cooled at a cooling rate of 29℃ / s, the molten salt temperature of the front-stage molten salt treatment is 580℃, and the treatment time is 150s. The hot-rolled wire rod product is obtained after being discharged. Example 3

[0043] ​A preferred embodiment of the manufacturing method of the hot-rolled wire rod for 2100MPa grade stranded wire provided by the application has the chemical composition and mass percentage of the hot-rolled wire rod including C: 0.86%, Si: 0.95%, Mn: 0.64%, Cr: 0.57%, P: 0.013%, S: 0.015%, and the rest being Fe and inevitable impurities; and the manufacturing method is manufactured according to the process flow of rolling → wire drawing → on-line molten salt sorbite treatment → slow cooling with the opening of the roller table → coiling, and specifically: The rolling process is used to heat the steel billet with the specification of 180mm*180mm to a high-temperature steel billet with the rollable plasticity through the heating furnace, control the heating furnace parameters to promote the uniform diffusion of alloy components, reduce segregation, and avoid decarburization, and roll the steel billet into a wire rod with the diameter specification of 8mm through the rolling line after the steel billet is out of the heating furnace, select the appropriate rolling temperature and reduction, promote the rapid rolling deformation of the steel billet, control the dynamic recrystallization grain refinement in the final rolling process, and specifically: the soaking temperature of the heating furnace is controlled to be 1195℃, the in-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 draw the wire rod out of the rolling line into a wire rod through the wire drawing machine, the wire rod is scattered on the roller table and conveyed along the roller table, the appropriate wire drawing temperature is selected to make the wire rod in the high-temperature austenitizing state, avoid the precipitation of net-shaped carbide or pro-eutectoid ferrite in the wire drawing stage, and provide favorable conditions for the subsequent sorbite phase change, and specifically: the wire drawing temperature is controlled to be 895℃.

[0044] The on-line molten salt sorbite treatment process adopts two-stage salt bath tanks with molten salt, the wire rod after wire drawing is conveyed through the first-stage salt bath tank for the front-stage molten salt treatment, the wire rod is cooled at the cooling rate of 32℃ / s, quickly passes through the net-shaped carbide interval from the high-temperature austenite state into the sorbite phase interval, inhibits the formation of net-shaped carbide and coarse pearlite, most of the high-temperature austenite organization phase change forms the organization mainly with the fine lamellar spacing sorbite organization, reduces the temperature gradient from the surface to the core of the wire rod, and then is conveyed through the second-stage salt bath tank for the rear-stage molten salt treatment, appropriately reduces the molten salt circulation amount, promotes the untransformed residual austenite to continue to transform into the fine lamellar spacing sorbite organization, at the same time promotes the fine lamellar spacing sorbite organization and a small amount of ferrite formed to be isothermal tempered, and promotes part of the sorbite cementite sheet to be melted, avoids the coarsening of carbide and excessive softening, and adjusts the strength and plasticity matching of the wire rod, and specifically: the molten salt temperature of the front-stage molten salt treatment is 561℃, the treatment time is 220s, the molten salt circulation amount is 395t / h, and the molten salt temperature rise is ≤8℃; the molten salt temperature of the rear-stage molten salt treatment is 555℃, the treatment time is 260s, the molten salt circulation amount is 285t / h, and the molten salt temperature rise is ≤3℃.

[0045] The roller opening cover slow cooling process adopts opening the heat preservation cover, blowing the hot air above 250 DEG C of the two section salt bath tank of on-line molten salt sorbitizing regulation treatment to the conveying roller, conveying the wire rod by the conveying roller, promoting the further toughening of the wire rod organization, improving the wire rod tempering softening effect, specifically: controlling the wire rod to cool to 279 DEG C at 1.1 DEG C / s slow cooling speed;The coiling process is used for coiling the wire rod into a coil by the coiling drum, and the hot rolled wire rod product is obtained after packaging and warehousing, and the metallographic structure diagram is as shown in Figure 3

[0046] Comparative example 5: A kind of hot rolled wire rod manufacturing method, its manufacturing method is different from example 3 in that: the molten salt temperature of the latter section molten salt treatment is 585 DEG C, and the processing time is 310 s, and the hot rolled wire rod product is obtained after offline.

[0047] Comparative example 6: A kind of hot rolled wire rod manufacturing method, its manufacturing method is different from example 3 in that: the molten salt temperature of the latter section molten salt treatment is 525 DEG C, and the processing time is 90 s, and the hot rolled wire rod product is obtained after offline. Example 4:

[0048] A preferred embodiment of the manufacturing method of the 2100 MPa grade hot rolled wire rod for the twisted wire of the application, 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%, the rest is Fe and unavoidable impurities;Its manufacturing method is manufactured according to the process flow of rolling→ wire drawing→ on-line molten salt sorbitizing regulation treatment→ roller opening cover slow cooling→ coiling, specifically: The rolling process is used for heating the steel billet with a specification of 220mm*220mm to a high-temperature steel billet with a rolling plasticity by a heating furnace, controlling the heating furnace parameters to promote the uniform diffusion of alloy components, reduce segregation and avoid decarburization, and the steel billet is rolled into a wire rod with a diameter specification of 15mm after the steel billet is discharged from the heating furnace through a rolling line, appropriate rolling temperature and reduction are selected to promote rapid rolling deformation of the steel billet, and the dynamic recrystallization of the final rolling process is controlled to refine the grains, specifically: the soaking temperature of the heating furnace is controlled to be 1220 DEG C, the in-furnace time is 120 min, the initial rolling temperature is 1070 DEG C, the final rolling temperature is 920 DEG C, and the final rolling reduction is 22%;The wire drawing process is used for forming the wire rod discharged from the rolling line into a wire rod through a wire drawing machine, and the wire rod is scattered on the roller and conveyed along the roller, and appropriate wire drawing temperature is selected to make the wire rod in a high-temperature austenitizing state, avoid the precipitation of network carbide or proeutectoid ferrite at the wire drawing stage, and provide favorable conditions for the subsequent sorbite phase change, specifically: the wire drawing temperature is controlled to be 915 DEG C.

[0049] ​The online molten salt sorbitizing regulation treatment process adopts two-stage salt bath tanks with built-in molten salt. The wire rod after spinning is conveyed through the first-stage salt bath tank for front-stage molten salt treatment, so that the wire rod is cooled at a cooling rate of 37 ℃ / s, quickly passes through the interlaced carbide zone from the high-temperature austenite state into the sorbite phase zone, inhibits the formation of interlaced carbide and coarse pearlite, most of the high-temperature austenite organization phase changes into the organization mainly with fine lamellar spacing sorbite organization, reduces the temperature gradient from the surface to the core of the wire rod, and then is conveyed through the second-stage salt bath tank for rear-stage molten salt treatment. The molten salt circulation amount is appropriately reduced to promote the untransformed residual austenite to continue to transform into fine lamellar spacing sorbite organization, promote the fine lamellar spacing sorbite organization and a small amount of ferrite formed to isothermal tempering, and promote the partial sorbite cementite sheet to be melted off to avoid the coarsening of carbide and excessive softening, so as to regulate the strength and plasticity matching of the wire rod. Specifically, the molten salt temperature of the front-stage molten salt treatment is 530 ℃, the treatment time is 300 s, the molten salt circulation amount is 545 t / h, and the molten salt temperature rise is ≤8 ℃; the molten salt temperature of the rear-stage molten salt treatment is 540 ℃, the treatment time is 100 s, the molten salt circulation amount is 370 t / h, and the molten salt temperature rise is ≤3 ℃.

[0050] The roller cover opening slow cooling process blows hot air at ≥250 ℃ above the two-stage salt bath tanks of the online molten salt sorbitizing regulation treatment to the conveying roller, and the wire rod is conveyed by the conveying roller to promote the further toughening of the wire rod organization and improve the tempering softening effect of the wire rod. Specifically, the wire rod is cooled to 282 ℃ at a slow cooling rate of 0.8 ℃ / s. The coiling process is used to coil the wire rod into a coil by a coiling drum, and the hot-rolled wire rod product is obtained after packaging and storage.

[0051] Comparative Example 7: A manufacturing method of a hot-rolled wire rod, which is different from that of Example 4 in that the manufacturing method is manufactured according to the process flow of rolling→spinning→online molten salt sorbitizing regulation treatment→air cooling. The air cooling process adopts opening of the heat preservation cover, and the wire rod is cooled to 270 ℃ at a slow cooling rate of 1.8 ℃ / s. The hot-rolled wire rod product is obtained after offline.

[0052] The hot-rolled wire rods obtained in Examples 1-4 and Comparative Examples 1-7 are subjected to organization and performance detection, and the comparison results are shown in Table 1 as follows: Table 1. Comparison results of organization and performance of different hot-rolled wire rod compositions and manufacturing methods

[0053] From the comparison results of Example 1 and Comparative Example 1, compared with not adding alloying elements such as V and Ti, using the high-carbon high-silicon component system of C-Si-Mn-Cr, the high-carbon steel is difficult to inhibit the network carbon during the Stelmor air cooling phase change process, which weakens the strengthening effect, affects the nucleation rate of sorbite, forms coarse cementite lamella in the core, causes uneven structure, and increases the fluctuation of mechanical properties. The structure stress generated by uneven phase change will be left in the wire rod, resulting in insufficient plasticity of the wire rod. The present application combines the online molten salt sorbitizing regulation technology to control the wire rod to quickly pass through the network carbide interval into the sorbite phase interval from the high-temperature austenite state, and then promotes the untransformed residual austenite to continue to transform into fine interlamellar spacing sorbite structure by isothermal tempering, and promotes the melting of part of the sorbite sheet. The results of Examples 1-4 show that the tensile strength is 1420-1470 MPa, the reduction of area is 36%-41%, and the wire rod is used to manufacture 2100 MPa grade twisted wire for application fields, without offline heat treatment, and is also conducive to reducing the risk of wire breakage during downstream drawing and twisting.

[0054] From the comparison results of Example 1 and Comparative Example 2, a higher wire laying temperature is selected to make the wire rod in a high-temperature austenitizing state, prevent the precipitation of proeutectoid ferrite or network carbide before wire laying, and lay a foundation for sorbite phase change. The wire rod after wire laying does not pass through air cooling, which can reduce the limitation on rolling temperature.

[0055] From the comparison results of Example 2 and Comparative Example 3, the lower the molten salt temperature of the front-stage molten salt treatment is, the more conducive to inhibiting the risk of network carbide precipitation. With the extension of the treatment time, the atomic diffusion speed is slow during low-temperature phase change, the lamella of ferrite and cementite is thinner and the spacing is smaller, which is conducive to promoting the synchronous transformation of the core of the wire rod and forming a structure mainly of fine interlamellar spacing sorbite, and improving the strength of the matrix. However, too low molten salt temperature will increase the temperature difference between the surface and the core of the wire rod, increase the thermal stress and the structure stress, and too long treatment time will unnecessarily increase the production energy consumption due to the high molten salt circulation amount of the front-stage molten salt treatment.

[0056] From the comparison results of Example 2 and Comparative Example 4, the higher the molten salt temperature of the front-stage molten salt treatment is, the more conducive to reducing the temperature gradient of the wire rod, the stress release difficulty and the risk of low-temperature brittle structure precipitation. The shorter the treatment time is, the more conducive to reducing the production energy consumption. However, too high molten salt temperature and too short treatment time are not conducive to inhibiting network carbide and coarse pearlite in the core, and the increase of untransformed residual austenite will affect the rear-stage molten salt treatment, resulting in strength loss and fluctuation of mechanical properties.

[0057] From the comparison results of Example 3 and Comparative Example 5, it can be seen that the higher the molten salt temperature and the longer the treatment time in the later molten salt treatment, the more conducive it is to promote the isothermal tempering of the fine lamellar troostite structure, the melting of the lamellar layers, and the release of stress. 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.

[0058] From the comparison results of Example 3 and Comparative Example 6, it can be seen that the lower the molten salt temperature of the latter molten salt treatment, the more conducive it is to promoting the continued transformation of the untransformed residual austenite into a fine-lamellar spacing sorbite structure, slowing down the diffusion rate of carbon atoms, and as the treatment time shortens, it can avoid the excessive loss of strength due to the aggregation and growth of carbides, and at the same time 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 of some cementite and stress release, and the plasticity of the wire rod will be lost.

[0059] From the comparison results of Example 4 and Comparative Example 7, it can be seen that the slow cooling with the roller cover open 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 offline.

[0060] The series of detailed descriptions listed above are only specific descriptions of feasible embodiments of the present invention. They are not intended to limit the scope of protection of the present invention. Any equivalent embodiments or changes that do not deviate from the technical spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for manufacturing a 2100 MPa grade hot-rolled wire rod for stranded wire, characterized in that: The manufacturing method includes: The wire rod is produced by rolling according to the chemical composition of the hot-rolled wire rod, and 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%, and the rest are Fe and unavoidable impurities; after the wire rod is spun into a wire rod at a spinning temperature of ≥890°C, it undergoes an online molten salt sorbitization control treatment, so that the wire rod is cooled at a cooling rate of ≥31°C / s, entering the sorbite phase region from the austenite state, forming a structure mainly composed of sorbite structure, and isothermally tempered to promote the melting of some sorbite lamellae. Finally, it is slowly cooled through a roller with an open hood to produce a hot-rolled wire rod with a microstructure including a mixed structure consisting of tempered sorbite, tempered ferrite and fused sorbite.

2. The method for manufacturing the 2100 MPa grade hot-rolled wire rod for stranded wire according to claim 1, characterized in that: Before the rolling, the soaking temperature of the heating furnace is controlled to be 1180-1220° C., and the soaking time in the furnace is 120-180 minutes.

3. The method for manufacturing the 2100 MPa grade hot rolled wire rod for stranded wire according to claim 1, wherein: During the rolling, the initial rolling temperature is controlled to be 1040-1070° C., the final rolling temperature is controlled to be 890-920° C., and the final rolling reduction is controlled to be 22%-26%; during the wire drawing, the wire drawing temperature is controlled to be 890-915° C.

4. The method for manufacturing the 2100 MPa grade hot rolled wire rod for stranded wire according to claim 1, wherein: The online molten salt sorbitization control treatment is divided into a front-stage molten salt treatment and a rear-stage molten salt treatment, and the molten salt circulation amount of the rear-stage molten salt treatment is smaller than that of the front-stage molten salt treatment.

5. The method for manufacturing the 2100 MPa grade hot rolled wire rod for stranded wire according to claim 4, characterized in that: The molten salt temperature of the front-stage molten salt treatment is 530-570° C., and the treatment time is 180-300 s; the molten salt temperature of the back-stage molten salt treatment is 540-565° C., and the treatment time is 100-300 s.

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

7. The method for manufacturing the 2100 MPa grade hot rolled wire rod for stranded wire according to claim 5, characterized in that: The roller table opens the cover and slowly cools the wire rod to a slow cooling rate of 0.8-1.2°C / s and cools it to below 285°C for coiling.

8. A 2100 MPa grade hot rolled wire rod for stranded wire, characterized in that: The hot-rolled wire rod is manufactured by the method for manufacturing the 2100 MPa grade hot-rolled wire rod for stranded wire according to any one of claims 1 to 7.

9. The 2100 MPa grade hot-rolled wire rod for stranded wire according to claim 8, characterized in that: The volume percentage of the tempered bainite is ≥64%, the interlamellar spacing is 75~125nm, the volume percentage of the tempered ferrite is ≤4%, the volume percentage of the fused bainite is ≥22%, the network carbide grade of the hot-rolled wire rod is grade 0, and the mechanical property same-circle difference is ≤38MPa.

10. The 2100 MPa grade hot rolled wire rod for stranded wire according to claim 8, characterized in that: The hot-rolled wire rod has a diameter of 5.5-15 mm, a tensile strength of 1420-1470 MPa, and a cross-sectional shrinkage rate of 36%-41%.

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