A hot rolled wire rod for 2060mpa class strand and a manufacturing method thereof

Abstract

The present application relates to a kind of 2060MPa grade hot rolled wire rod for strand and its manufacturing method, by the high carbon chemical composition design of Mn-Cr, after wire rod is rolled and wired into wire rod, it is treated by on-line molten salt isothermal phase change, wire rod is first treated by molten salt in front section, from austenite state into sorbite phase region, form the structure mainly with sorbite structure, again after molten salt treatment in rear section, promote the transformation of residual austenite to sorbite structure, while promoting the isothermal tempering of structure, partial sorbite lamella is fused, finally after roller slow cooling, it is made into the hot rolled wire rod of mixed organization including microstructure including tempering sorbite, tempering ferrite and fused sorbite, can control material cost, improve the high strength plastic performance matching of wire rod, reach tensile strength is 1370~1420MPa, reduction of area is 35%~40%, reduce mechanical property fluctuation, so as to reduce the risk of broken wire in strand production, promote high-efficiency and stable production.

Description

Technical Field

[0001] This invention belongs to the technical field of hot-rolled wire rod, specifically relating to a 2060MPa grade hot-rolled wire rod for stranded wire and its manufacturing method. Background Technology

[0002] Steel strand, as an important stress-bearing tool, is widely used in railways, bridges, marine engineering, construction, new energy, and other fields. With technological innovation, industrial restructuring, and the advancement of intelligent and green production, the strength grade of steel strand needs continuous improvement to meet increasingly stringent market demands. Currently, the production of 2060MPa grade steel strand only employs the Stellmore air-cooling method. For example, patent CN117845141A discloses a 1960~2060MPa grade prestressed steel strand and its preparation method, using a C-Mn-Si-Cr-V-Ti-Nb composition design combined with low-speed air cooling to produce pearlitic wire rods. However, this method still has the following technical shortcomings:

[0003] I. To refine the pearlite lamellar spacing and improve the mechanical strength of the alloy in the air-cooled line process, the steel grade contains a relatively high content of alloying elements such as C and Mn. During continuous casting of high-carbon steel, center segregation is exacerbated. Limited by the maximum cooling capacity of the air-cooled line, carbides tend to precipitate along the austenite grain boundaries, forming a network structure. The presence of this network carbide disrupts the continuity of the steel matrix, leading to a significant reduction in toughness and plasticity. It also weakens strength uniformity and increases fluctuations in mechanical properties. When the material is subjected to external forces, stress tends to concentrate at the interface between the carbides and the matrix, leading to brittle fracture and affecting service safety. To minimize... While network carbide levels can improve air-cooling strength, their improvement effect is limited. Furthermore, due to the influence of wire rod hardenability and the limitations of air-cooling capacity and instability, the temperature difference between the air-receiving and air-receiving surfaces, as well as between overlapping and non-overlapping areas, will further increase. This poses a high risk of abnormal microstructure, leading to localized overcooling that can exceed the critical rate of pearlite transformation, resulting in brittle structures such as martensite. This leads to deterioration of plasticity and increased fluctuations in mechanical properties, making it extremely easy for wires to break during downstream wire drawing, making it difficult to meet stable production requirements. If offline heat treatment is combined with production, it will result in more processes and higher energy consumption.

[0004] II. To refine austenite grains and improve austenite deformation energy storage and pearlite transformation driving force, strong carbide-forming elements such as V, Ti, and Nb are added to steel grades. However, the alloying cost of these elements is high, which is not conducive to controlling material costs. On the other hand, omitting these elements results in several problems. First, the austenite grain boundaries lose their pinning force, making the grains prone to coarsening during hot rolling. This coarsening leads to carbon enrichment at the grain boundaries, further exacerbating the risk of network carbides. Second, the maximum cooling capacity of the air-cooling line limits the number of phase deformation nucleation points, affecting the pearlite transformation driving force and leading to microstructure coarsening. Simultaneously, the precipitation strengthening effect of strong carbides is lost. On the one hand, the strength performance will be significantly reduced; on the other hand, due to the decrease in the driving force of pearlite phase transformation, the phase transformation rate will be slowed down due to the limitation of the length of the air-cooling line and continuous cooling. The uneven phase transformation at different positions will increase the phase transformation stress. The pearlite lamellars cannot undergo sufficient phase transformation and refinement, resulting in weak interlamellar bonding and large residual stress in the structure. If the air-cooling strength is further increased, the risk of abnormal structure and structural stress will be further increased, leading to a decrease in wire rod plasticity. When subjected to impact or drawing deformation, it is easy to crack along the lamellars, which will affect the stable production of downstream products. If production is carried out in combination with offline heat treatment, it will lead to problems of multiple processes and high energy consumption.

[0005] Therefore, it is necessary to develop a hot-rolled wire rod for stranded wire of 2060MPa grade and its manufacturing method to promote stable and efficient production of stranded wire and reduce production costs. Summary of the Invention

[0006] The present invention aims to at least partially solve one of the above-mentioned technical problems. The present invention provides a hot-rolled wire rod for stranded wire of 2060MPa grade and its manufacturing method, which can control material costs, improve the matching of high strength and plasticity properties of wire rod, and reduce mechanical property fluctuations, so as to reduce the risk of wire breakage in stranded wire production and promote efficient and stable production.

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

[0008] A method for manufacturing hot-rolled wire rod for 2060MPa grade stranded wire, the method comprising:

[0009] 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: 0.85%~0.90%, Si: 0.50%~0.65%, Mn: 0.50%~0.70%, Cr: 0.46%~0.55%, 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 ≥930℃, it undergoes online molten salt isothermal phase transformation treatment. The wire rod first undergoes a preliminary molten salt treatment, which cools the wire rod at a rate of ≥34℃ / s, allowing it to transition from the austenitic state to the sorbite phase region, forming a microstructure dominated by sorbite. The wire rod then undergoes a subsequent molten salt treatment, which reduces the amount of molten salt circulating to promote the transformation of untransformed residual austenite into sorbite. At the same time, it promotes isothermal tempering and partial melting of sorbite lamellars. Finally, it undergoes slow cooling on 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 lay the foundation for strength through solid solution strengthening. It is also the core component of cementite in sorbite, which can improve the stability of austenite and prevent austenite from decomposing into coarse pearlite too early. In addition, it can refine the lamellar spacing of sorbite in conjunction with the previous molten salt treatment, slow down the coarsening of cementite during isothermal tempering, and avoid excessive strength loss. However, if the C content is too high, the supersaturation of carbon in austenite will increase significantly, which will lead to increased difficulty in controlling network carbides and abnormal martensite structure, significantly reduce plasticity, and affect processing and forming. Therefore, in order to take into account the high strength requirements of 2060MPa grade strand, reduce the fluctuation of mechanical properties, reduce the difficulty of isothermal tempering control, and promote rapid production, the mass percentage of C is controlled at 0.85%~0.90%.

[0012] (2) Silicon: Si is a ferrite solid solution strengthening element. By dissolving in the matrix phase of sorbite, it can hinder dislocation movement and improve the matrix strength. In the austenite to sorbite phase transformation process of the first stage of molten salt treatment, it can inhibit cementite coarsening and stabilize the sorbite structure. In the isothermal tempering process of the second stage of molten salt treatment, it can hinder cementite lamellar spheroidization and avoid excessive strength loss. However, excessive silicon will promote decarburization, slow down the sorbite phase transformation rate, prolong the incubation period, and increase the difficulty of softening. It is not conducive to rapid tempering and toughness control in the online molten salt isothermal process. Therefore, in order to adapt to the control of phase transformation structure by online molten salt isothermal treatment, the Si content should be appropriately increased and the mass percentage of Si should be controlled at 0.50%~0.65%.

[0013] (3) Manganese: Mn is an austenite stabilizing element that can significantly reduce the pearlite transformation temperature of steel, improve the hardenability of steel, and thus prolong the pearlite transformation incubation period, avoid the precipitation of ferrite or coarse pearlite in the core of the wire rod, and refine the sorbite lamellars formed by subsequent phase transformation, thus promoting the rapid transformation of the structure to sorbite. 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 the cooling process, increasing the difficulty of abnormal structure precipitation and structure uniformity control, thus reducing the plasticity of the wire rod. During subsequent wire drawing, the hard and brittle phase region is prone to become a stress concentration source, leading to an increase in the wire breakage rate. Therefore, in order to take into account the high strength and plasticity of hot-rolled wire rod and reduce the fluctuation of mechanical properties, the Mn content should be appropriately reduced, and the mass percentage of Mn should be controlled at 0.50%~0.70%.

[0014] (4) Chromium: Cr is a strong carbide-forming element. It easily forms carbides and is distributed in the sorbite lamellars to hinder dislocation slip. At the same time, it can enhance the hardenability of austenite, causing the continuous cooling transformation curve of steel to shift to the right. Combined with the first stage of molten salt treatment, it delays the transformation of austenite to pearlite, laying the foundation for the subsequent formation of a structure dominated by sorbite. It also increases the resistance to tempering softening. However, if the Cr content is too high, it will aggravate the segregation of alloying elements, increase the risk of abnormal structures such as martensite precipitation, and reduce the activity of carbon in steel. This is not conducive to sorbite melting and tempering softening, affecting the rapid treatment of the subsequent molten salt, and is not conducive to toughness and drawing plasticity. Therefore, the Cr content should be appropriately increased, and the mass percentage of Cr should be controlled at 0.46%~0.55%.

[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 is designed with a high carbon content of C-Si-Mn-Cr, and does not contain alloying elements such as Nb, V, and Ti. This allows for appropriate control of material costs. Simultaneously, it allows for the regulation of the wire rod's hardenability and sorbite transformation temperature range, providing favorable conditions for delaying pearlite transformation, inhibiting cementite coarsening, reducing the difficulty of controlling brittle abnormal structures and achieving uniform microstructure during online molten salt isothermal transformation treatment, and facilitating rapid tempering. Furthermore, a relatively high wire-drawing temperature is selected to keep the wire rod in a high-temperature austenitizing state, preventing the precipitation of network carbides due to excessively low temperatures. This provides favorable conditions for subsequent refinement of sorbite lamellars through a large temperature difference. After wire drawing, the wire rod undergoes online molten salt isothermal transformation treatment.

[0017] Firstly, compared to the limitations of the Stellmore air-cooled line, which has the highest cooling capacity and unstable temperature control, making it difficult to control network carbides and martensitic abnormal structures, molten salt has a higher thermal conductivity than air. This promotes rapid cooling of the wire rod, allowing it to quickly pass through the secondary cementite precipitation temperature range from a high-temperature austenitic state. This avoids the austenite from remaining in the high-temperature region for too long, leading to carbon enrichment and precipitation at grain boundaries to form network carbides. This also prevents network carbides from adversely affecting the uniformity and ductility of the matrix. Secondly, when the wire rod passes through the molten salt, the molten salt can cover the surface of the wire rod for uniform and rapid heat exchange. There is no temperature difference between the air-receiving and air-receiving surfaces, or between overlapping and non-overlapping areas. This avoids the segregation of alloying elements and localized overcooling that can lead to the formation of brittle martensitic abnormal structures, effectively reducing fluctuations in mechanical properties.

[0018] Second, compared to omitting microalloying elements and being limited by the cooling capacity and continuous cooling of the Stellmore air-cooling line, which affects the driving force of sorbitic phase transformation and leads to insufficient and uneven transformation of the microstructure, resulting in a loss of strength and toughness, the wire rod undergoes a preliminary molten salt treatment. This process promotes rapid cooling of the wire rod, allowing it to transition from a high-temperature austenitic state to a lower-temperature sorbitic phase region. This breaks the stability of austenite and inhibits the coarsening of pearlite lamellae. By extending the treatment time at the peak sorbitic temperature rather than through continuous cooling, it promotes the transformation of most austenite into a sorbitic microstructure with finer lamellar spacing, forming a microstructure dominated by fine-lamellar sorbite. The subsequent molten salt treatment appropriately reduces the molten salt circulation volume to reduce production energy consumption. At the same time, it promotes the continued transformation of untransformed residual austenite into sorbitic microstructure, thereby increasing the proportion of sorbite and reducing the proportion of ferrite. This compensates for the strength loss and adverse effects on sorbitic phase transformation caused by omitting alloying elements such as Nb, V, and Ti, resulting in a more complete microstructure. This process also prevents the retained austenite from continuing to form a low-temperature brittle structure during subsequent cooling. On the other hand, the molten salt treatment at the beginning can effectively reduce the temperature difference between the wire rod surface and the core, promoting a uniform phase transformation of the structure, thereby reducing thermal stress and structural stress. The thorough refinement of the structure also reduces the difficulty of softening. After isothermal treatment, the wire rod is still in the high-temperature sorbite phase region after phase transformation inoculation, rather than the low-temperature state of continuous treatment. It can further release stress through isothermal tempering, causing a small amount of ferrite to temper, and some cementite lamellars of sorbite to melt and transform into melted sorbite. This not only retains high strength and fully utilizes the strengthening effect of carbon, but also further improves plasticity and structural uniformity. After the wire rod exits the molten salt treatment, it undergoes slow cooling treatment on the roller table, which can promote further toughening of the wire rod structure and improve the tempering softening effect of the wire rod. In this way, the phase transformation and state control of the structure are achieved, improving the overall high strength and plasticity matching and reducing the fluctuation of mechanical properties based on the composition design.

[0019] Before rolling, selecting a higher homogenization temperature and furnace time can promote uniform diffusion of carbon and alloy components, improve component segregation, and enhance rolling plasticity. At the same time, it avoids excessively high temperature and excessively long furnace time, which can lead to coarsening or burning of austenite grains. In the preferred technical solution, before rolling, the homogenization temperature of the heating furnace is controlled at 1165~1210℃ and the furnace time is controlled at 180~240min.

[0020] Because the wire drawing temperature is relatively high, the restrictions on rolling can be reduced. During rolling, an appropriate initial rolling temperature is selected to increase the rolling speed, while breaking the columnar crystals of the billet, providing a basis for subsequent grain refinement. Further control of the final rolling temperature and final rolling reduction promotes dynamic recrystallization and grain refinement during the final rolling process. At the same time, it avoids excessive wear on the rolling line caused by the final rolling temperature being too low, which would affect the load and production efficiency of the rolling mill. In the preferred technical solution, during rolling, the initial rolling temperature is controlled at 1030~1060℃, the final rolling temperature is 930~965℃, and the final rolling reduction is 27%~31.5%.

[0021] During the wire spinning process, the wire spinning temperature can be further controlled to avoid the risk of grain coarsening due to excessively high wire spinning temperature. In a preferred embodiment, the wire spinning temperature is controlled at 930~955℃.

[0022] The molten salt temperature in the initial molten salt treatment is within the sorbite phase region. Lower molten salt temperatures and longer treatment times result in greater supercooling, which helps suppress network carbides, promotes the transformation of high-temperature austenite to sorbite, reduces retained austenite, and makes lamellar growth less coarsened due to carbon diffusion limitations, resulting in finer sorbite lamellar structures and thus improved matrix strength. However, excessively low molten salt temperatures increase the temperature gradient from the wire rod surface to the core, increasing structural stress and the difficulty of isothermal softening, and may even trigger abnormal phase transformations, generating hard and brittle phase structures and causing plasticity loss. Furthermore, longer treatment times, due to higher molten salt circulation, increase production energy consumption. Conversely, higher molten salt temperatures and shorter treatment times reduce the risk of abnormal phase transformations and improve the transformation to sorbite. Stability and uniformity are improved, reducing structural stress, softening difficulty, and production energy consumption. However, excessively high molten salt temperatures and short processing times are detrimental to suppressing network carbides and coarse pearlite, reducing the driving force of sorbite phase transformation, decreasing the nucleation rate, and resulting in more residual austenite, which will lead to strength loss and fluctuations in mechanical properties. Therefore, the molten salt temperature and processing time in the initial stage of molten salt treatment can be appropriately controlled to control the wire rod to quickly transition from the high-temperature austenitic state, quickly bypass the network carbide region, and enter the sorbite phase region, thereby suppressing the formation of network carbides and forming a structure dominated by fine lamellar interlayer sorbite, thus improving the uniformity of the structure. In the preferred technical solution, the molten salt temperature of the initial stage of molten salt treatment is 490~525℃, and the processing time is 80~250s.

[0023] Since the temperature difference between the spinning temperature and the molten salt circulation rate in the front-end molten salt treatment is relatively large, a larger molten salt circulation rate is selected to control the molten salt temperature rise, which can quickly remove the heat from the wire rod, reduce the temperature gradient from the wire rod surface to the core, and promote the formation of a structure dominated by the interlayer spacing of fine flakes in the wire rod. In the preferred technical solution, the molten salt circulation rate in the front-end molten salt treatment is 440~640t / h, and the molten salt temperature rise is ≤8℃.

[0024] The molten salt temperature in the subsequent molten salt treatment is within the sorbite phase region. Higher molten salt temperatures and longer treatment times enhance carbon diffusion, further reducing the temperature gradient between the wire rod surface and core. This promotes isothermal tempering, causing more sorbite cementite lamellars to melt and transform into a smaller surface area morphology, releasing structural stress and improving the wire rod's ductility and toughness. However, excessively high molten salt temperatures and long treatment times can lead to excessive cementite melting and growth, and excessive softening of the wire rod, resulting in significant strength loss and increased production energy consumption. Conversely, lower molten salt temperatures promote the transformation of retained austenite into finer-spaced sorbite, reducing atomic diffusion rates. Shorter treatment times also reduce softening rate and strength loss. While reducing production energy consumption, excessively low molten salt temperatures and short processing times are detrimental to sufficient phase transformation and isothermal tempering, affecting stress release and cementite lamellar melting. Subsequent slow cooling on the roller conveyor may induce martensitic transformation, leading to plasticity loss and fluctuations in mechanical properties. Therefore, the subsequent molten salt treatment allows for control of the molten salt temperature and processing time, promoting the continued transformation of untransformed residual austenite into fine lamellar sorbite, while simultaneously promoting prolonged isothermal tempering of the formed fine lamellar sorbite and causing partial cementite lamellar melting to regulate the strength-plasticity balance of the wire rod. In the preferred technical solution, the molten salt temperature for the subsequent molten salt treatment is 510~530℃, and the processing time is 30~110s.

[0025] Since the temperature difference between the molten salt in the front-end molten salt treatment and the back-end molten salt treatment is small, the molten salt circulation volume in the back-end molten salt treatment can be appropriately reduced, thus reducing production energy consumption and controlling the molten salt temperature rise, thereby improving the uniformity of the bar structure. In the preferred technical solution, the molten salt circulation volume in the back-end molten salt treatment is 300~400t / h, and the molten salt temperature rise is ≤3℃.

[0026] Since the temperature of the wire rod is relatively high after the molten salt treatment in the later stage, the slow cooling of the roller can further control the cooling speed, promote the further toughening of the wire rod structure and improve the tempering softening effect. In the preferred technical solution, the slow cooling of the roller controls the wire rod to cool to below 300°C at a slow cooling speed of 0.55~0.85°C / s before winding.

[0027] In the preferred technical solution, the slow cooling of the roller conveyor is achieved by controlling the opening of the heat insulation cover and blowing hot air (≥250℃) from the online molten salt isothermal phase change treatment onto the conveyor roller conveyor. The conveyor roller conveyor then transports the wire rod through the heat insulation cover, which can recover and utilize the heat energy during the production process, further reducing production energy consumption and increasing the wire rod off-line speed.

[0028] A hot-rolled wire rod for stranded wire of 2060MPa grade, wherein the hot-rolled wire rod is manufactured by the manufacturing method for hot-rolled wire rod of 2060MPa grade as described in any one of the above-mentioned methods.

[0029] The aforementioned hot-rolled wire rods are designed with a Mn-Cr chemical composition, free of alloying elements such as Nb and V, which can appropriately reduce material costs. Simultaneously, the microstructure comprises a mixture of tempered sorbite and melted sorbite, with a small amount of tempered ferrite. Compared to existing high-strength stranded wire rods with a pearlitic / sorbitic microstructure and air-cooled wire, this effectively suppresses network carbides and coarse pearlite. The sorbite has a finer lamellar spacing and higher strength and toughness than pearlite, promoting a fully uniform microstructure transformation and effectively suppressing low-temperature brittle abnormal structures such as martensite. After isothermal tempering, some of the cementite lamellars in the sorbite melt and transform into a state with a smaller specific surface area. The transformation of lamellars to a more stable state still has a certain dispersion strengthening effect, resulting in tempered sorbite and melted sorbite in an intermediate transition state towards spheroidized structure. The ferrite content is low and the ferrite is softened by tempering, resulting in a lower dislocation density. This can make the structure uniformity from the surface to the core of the wire rod higher, and the high strength and plasticity are matched. This can make up for the loss of strength and toughness caused by omitting alloying elements such as Nb and V, effectively reduce the fluctuation of mechanical properties, and thus avoid fracture due to abnormal structure or stress concentration during the subsequent drawing, twisting or turning process of strand manufacturing. It also eliminates the need for offline heat treatment to control the microstructure, avoiding the adverse effects of offline heat treatment on production efficiency and cost.

[0030] In the microstructure, the higher the volume percentage of tempered sorbite, the finer the lamellar spacing, and the lower the volume percentage of tempered ferrite, the higher the wire rod strength and toughness. The higher the volume percentage of fused sorbite, the better the wire rod plasticity. In the preferred technical solution, the volume percentage of tempered sorbite is ≥74%, the lamellar spacing is 80~130nm, the volume percentage of tempered ferrite is ≤5%, and the volume percentage of fused sorbite is ≥11%.

[0031] In the preferred technical solution, the hot-rolled wire rod has a network carbide level of 0 and a mechanical property difference of ≤36MPa within the same ring. This avoids the grain boundary brittleness and the effect of network carbide on the microstructure, effectively suppresses abnormal microstructure, improves microstructure uniformity, and reduces the fluctuation of the wire rod's mechanical properties, making it suitable for processing and service performance.

[0032] In the preferred technical solution, the diameter of the hot-rolled wire rod is 6.0~15.0mm, the tensile strength is 1370~1420MPa, and the section reduction rate is 35%~40%. The diameter of the wire for stranding can be achieved by drawing and reducing the diameter through multiple passes. The higher tensile strength can reduce the number of drawing passes, quickly reach the target strength, and adapt to scenarios that bear dynamic loads or complex stresses. The higher section reduction rate can reduce the risk of breakage due to concentrated deformation during drawing and the risk of loose strands and broken wires due to insufficient plasticity during twisting, thus promoting stable production of stranded wire.

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

[0034] (1) In view of the current situation that the production of hot-rolled wire rod for 2060MPa grade steel strand is carried out by only using the Stellmore air cooling method, resulting in high material costs and abnormal structure risks, this invention combines Mn-Cr chemical composition design with online molten salt isothermal phase transformation technology. First, through the front-end molten salt treatment, the wire rod is quickly transformed from the high-temperature austenitic state to the sorbite phase region, which inhibits the formation of network carbides and forms a structure dominated by fine lamellar interlamellar sorbite. Then, through the back-end molten salt treatment, the amount of molten salt circulation is reduced, which reduces production energy consumption and promotes the transformation of untransformed residual austenite into fine lamellar interlamellar sorbite. Isothermal tempering promotes the melting of some sorbite. Finally, slow cooling on the roller table further toughens the wire rod. This invention can improve the high strength and plasticity matching of the wire rod and reduce the fluctuation of mechanical properties without the need for alloying elements such as Nb and V. It has good industrial adaptability.

[0035] (2) In view of the current situation where the cost of hot-rolled wire rod for 2060MPa grade steel strand is high, the strength and plasticity are insufficient, and the mechanical properties fluctuate greatly, resulting in easy wire breakage and difficulty in achieving stable production requirements in downstream applications, this invention, through the design of Mn-Cr chemical composition, does not contain alloying elements such as Nb and V, which can appropriately reduce the material cost. At the same time, the microstructure includes a mixed structure composed of tempered sorbite, tempered ferrite and melted sorbite, which can effectively suppress low-temperature brittle abnormal structures such as network carbides, coarse pearlite and martensite, and improve the high strength and plasticity matching of wire rod, achieving a tensile strength of 1370~1420MPa and a section reduction rate of 35%~40%. When used in the manufacture of 2060MPa grade strand and other application fields, it is beneficial to reduce the risk of wire breakage, improve service performance, and avoid the problems of multiple processes and high energy consumption caused by offline heat treatment, and has good market application prospects. Attached Figure Description

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

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

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

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

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

[0041] A preferred embodiment of the manufacturing method of the 2060MPa 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: 0.60%, Mn: 0.50%, Cr: 0.55%, P: 0.014%, 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 isothermal phase transformation → slow cooling on roller table → coiling, specifically:

[0042] The rolling process is used to heat a 220mm×220mm steel billet in a furnace to a high-temperature steel billet that is rollable and plastic. The furnace parameters are controlled to promote uniform diffusion of alloy components and reduce segregation. After exiting the furnace, the billet is rolled into a 13mm 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 200℃, the furnace time is 185 minutes, the initial rolling temperature is 1050℃, the final rolling temperature is 960℃, and the final rolling reduction is 29%. The wire drawing process is used to convert the wire from the rolling line into coils through the wire drawing mechanism. The coils are distributed on the roller table and conveyed along the roller table. A suitable wire drawing temperature is selected to keep the coils in a high-temperature austenitizing state, avoiding the precipitation of network carbides during the wire drawing stage, and providing favorable conditions for the subsequent refinement of the sorbite structure. Specifically, the wire drawing temperature is controlled at 950℃.

[0043] The online molten salt isothermal phase transformation process employs a two-stage salt bath with internal molten salt. After coiling, the wire rod is conveyed via rollers through the first stage salt bath for initial molten salt treatment, causing the wire rod to cool at a rate of 37°C / s. This rapidly transitions the wire rod from the high-temperature austenitic state, bypassing the network carbide region, into the sorbite phase region, inhibiting the formation of network carbides and coarse pearlite. Most of the high-temperature austenitic structure transforms into a microstructure dominated by fine-laminated sorbite. The wire rod is then conveyed via rollers through the second stage salt bath for final molten salt treatment, with a reduced molten salt circulation rate to promote the transformation of untransformed wire rods. The retained austenite continues to transform into fine lamellar interlamellar sorbite, while simultaneously promoting isothermal tempering of the formed fine lamellar interlamellar sorbite and a small amount of ferrite, and causing some of the cementite lamellars of the sorbite to melt and fracture, thereby controlling the strength-ductility matching of the wire rod. Specifically: the molten salt temperature of the first stage of molten salt treatment is 502℃, the treatment time is 145s, the molten salt circulation rate is 580t / h, and the molten salt temperature rise is ≤8℃; the molten salt temperature of the second stage of molten salt treatment is 522℃, the treatment time is 85s, the molten salt circulation rate is 380t / h, and the molten salt temperature rise is ≤3℃.

[0044] The slow cooling process on the roller conveyor involves controlling the opening of the insulation cover to blow hot air (≥250℃) from the two salt bath tanks of the online molten salt isothermal phase transformation treatment onto the conveyor roller conveyor. The conveyor roller conveyor then transports the wire rod through the insulation cover, promoting further toughening of the wire rod structure and improving the tempering softening effect. Specifically, the wire rod is cooled to 295℃ at a slow cooling rate of 0.75℃ / s. The coiling process is used to coil the wire rod into coils using a coiling drum. After packaging and warehousing, the hot-rolled wire rod is obtained as a finished product, the metallographic structure of which is shown in the figure below. Figure 1 As shown.

[0045] Comparative Example 1:

[0046] A method for manufacturing hot-rolled wire rod differs from Example 1 in that it follows a process flow of rolling → wire drawing → Steyrmo air cooling. Specifically, the heating furnace is controlled at a uniform heating temperature of 1150°C, with a furnace time of 250 min, an initial rolling temperature of 1020°C, a final rolling temperature of 905°C, and a wire drawing temperature of 885°C. The Steyrmo forced air cooling uses a fan with an air volume of 260,000 m³ / s. 3 At 6:00, fans 1 to 6# are turned on at 65% to cool the wire rod to 660℃ at a cooling rate of 6.3℃ / s. Then, fans 7 to 14# are turned on at 30% to cool the wire rod to 280℃ at a cooling rate of 2.9℃ / s. After cooling, the hot-rolled wire rod is obtained.

[0047] Comparative Example 2:

[0048] A method for manufacturing hot-rolled wire rod differs from that in Example 1 in that: the heating furnace is heated to a uniform temperature of 1155°C, the furnace time is 230 min, the initial rolling temperature is 1025°C, the final rolling temperature is 880°C, and the wire drawing temperature is 860°C. During the molten salt treatment before the online molten salt isothermal phase change process, the wire rod is cooled at a rate of 30°C / s, and the finished hot-rolled wire rod is obtained after the process is completed. Example 2:

[0049] A preferred embodiment of the manufacturing method of the 2060MPa 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: 0.85%, Si: 0.54%, Mn: 0.53%, Cr: 0.46%, 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 isothermal phase transformation → slow cooling on roller table → coiling, specifically:

[0050] The rolling process is used to heat a 180mm×180mm steel billet in a furnace to a high-temperature steel billet that is rollable and plastic. Controlling the furnace parameters promotes uniform diffusion of alloy components and reduces segregation. After exiting the furnace, the billet is rolled into a 6mm 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 11... The rolling temperature is 65℃, the furnace time is 240 min, the initial rolling temperature is 1030℃, the final rolling temperature is 930℃, and the final rolling reduction is 31.5%. The wire drawing process is used to convert the wire from the rolling line into coils through the wire drawing mechanism. The coils are distributed on the roller table and conveyed along the roller table. A suitable wire drawing temperature is selected to keep the coils in a high-temperature austenitizing state, avoiding the precipitation of network carbides during the wire drawing stage, and providing favorable conditions for the subsequent refinement of the sorbite structure. Specifically, the wire drawing temperature is controlled at 930℃.

[0051] The online molten salt isothermal phase transformation process employs a two-stage salt bath with internal molten salt. After spinning, the wire rod is conveyed via roller conveyor through the first stage salt bath for initial molten salt treatment, causing the wire rod to cool at a rate of 34°C / s. This rapidly transitions the wire rod from the high-temperature austenitic state, bypassing the network carbide region, into the sorbite phase region, inhibiting the formation of network carbides and coarse pearlite. Most of the high-temperature austenitic structure transforms into a microstructure dominated by fine-laminated sorbite. 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 transformation of untransformed wire rods. The retained austenite continues to transform into fine lamellar sorbite, while simultaneously promoting isothermal tempering of the formed fine lamellar sorbite and a small amount of ferrite, and causing some of the cementite lamellars of the sorbite to melt and fracture, thereby controlling the strength and plasticity matching of the wire rod. Specifically: the molten salt temperature of the first stage of molten salt treatment is 525℃, the treatment time is 250s, the molten salt circulation rate is 440t / h, and the molten salt temperature rise is ≤8℃; the molten salt temperature of the second stage of molten salt treatment is 510℃, the treatment time is 30s, the molten salt circulation rate is 300t / h, and the molten salt temperature rise is ≤3℃.

[0052] The slow cooling process on the roller conveyor involves controlling the opening of the insulation cover to blow hot air (≥250℃) from the two salt bath tanks of the online molten salt isothermal phase transformation treatment onto the conveyor roller conveyor. The conveyor roller conveyor then transports the wire rod through the insulation cover, promoting further toughening of the wire rod structure and improving the tempering and softening effect. Specifically, the wire rod is cooled to 291℃ at a slow cooling rate of 0.85℃ / s. The coiling process is used to coil the wire rod into coils using a coiling drum. After packaging and warehousing, the hot-rolled wire rod is obtained as a finished product, the metallographic structure of which is shown in the figure below. Figure 2 As shown.

[0053] Comparative Example 3:

[0054] A method for manufacturing hot-rolled wire rod differs from that in Example 2 in that: during the initial molten salt treatment of the online molten salt isothermal phase change process, the wire rod is cooled at a cooling rate of 39°C / s, the molten salt temperature of the initial molten salt treatment is 475°C, the treatment time is 260s, and the finished hot-rolled wire rod is obtained after the process is completed.

[0055] Comparative Example 4:

[0056] A method for manufacturing hot-rolled wire rod differs from that in Example 2 in that: during the initial molten salt treatment of the online molten salt isothermal phase change process, the wire rod is cooled at a cooling rate of 31°C / s, the molten salt temperature of the initial molten salt treatment is 540°C, the treatment time is 75s, and the finished hot-rolled wire rod is obtained after the process is completed. Example 3:

[0057] A preferred embodiment of the manufacturing method of the 2060MPa 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: 0.88%, Si: 0.50%, Mn: 0.68%, Cr: 0.49%, 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 isothermal phase transformation → slow cooling on roller table → coiling, specifically:

[0058] The rolling process is used to heat a 220mm×220mm steel billet in a furnace to a high-temperature steel billet that is rollable and plastic. The furnace parameters are controlled to promote uniform diffusion of alloy components and reduce segregation. After exiting the furnace, the billet is rolled into a 10mm diameter wire rod 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 185℃, the furnace time is 220 min, the initial rolling temperature is 1045℃, the final rolling temperature is 955℃, and the final rolling reduction is 30%. The wire drawing process is used to convert the wire from the rolling line into coils through the wire drawing mechanism. The coils are distributed on the roller table and conveyed along the roller table. A suitable wire drawing temperature is selected to keep the coils in a high-temperature austenitizing state, avoiding the precipitation of network carbides during the wire drawing stage, and providing favorable conditions for the subsequent refinement of the sorbite structure. Specifically, the wire drawing temperature is controlled at 940℃.

[0059] The online molten salt isothermal phase transformation process employs a two-stage salt bath with internal molten salt. After spinning, the wire rod is conveyed via roller conveyor through the first stage salt bath for initial molten salt treatment, causing the wire rod to cool at a rate of 36°C / s. This rapidly transitions the wire rod from the high-temperature austenitic state, bypassing the network carbide region, into the sorbite phase region, inhibiting the formation of network carbides and coarse pearlite. Most of the high-temperature austenitic structure transforms into a microstructure dominated by fine-laminated sorbite. The wire rod is then conveyed via roller conveyor through the second stage salt bath for subsequent molten salt treatment, with a slightly reduced molten salt circulation rate to promote the transformation of untransformed wire rods. The retained austenite continues to transform into fine lamellar sorbite, while simultaneously promoting isothermal tempering of the formed fine lamellar sorbite and a small amount of ferrite, and causing some of the cementite lamellars of the sorbite to melt and fracture, thereby controlling the strength and plasticity matching of the wire rod. Specifically: the molten salt temperature of the first stage of molten salt treatment is 515℃, the treatment time is 205s, the molten salt circulation rate is 495t / h, and the molten salt temperature rise is ≤8℃; the molten salt temperature of the second stage of molten salt treatment is 515℃, the treatment time is 60s, the molten salt circulation rate is 325t / h, and the molten salt temperature rise is ≤3℃.

[0060] The slow cooling process on the roller conveyor involves controlling the opening of the insulation cover to blow hot air (≥250℃) from above the two salt bath tanks in the online molten salt isothermal phase transformation treatment onto the conveyor roller conveyor. The conveyor roller conveyor then transports the wire rod through the insulation cover, promoting further toughening of the wire rod structure and improving the tempering softening effect. Specifically, the wire rod is cooled to 296℃ at a slow cooling rate of 0.6℃ / s. The coiling process is used to coil the wire rod into coils using a coiling drum. After packaging and warehousing, the hot-rolled wire rod is obtained as a finished product, the metallographic structure of which is shown in the figure below. Figure 3 As shown.

[0061] Comparative Example 5:

[0062] A method for manufacturing hot-rolled wire rod, the difference between the method and Example 3 is that: the molten salt temperature of the subsequent molten salt treatment is 565℃, the treatment time is 150s, and the finished hot-rolled wire rod is obtained after the process is completed.

[0063] Comparative Example 6:

[0064] A method for manufacturing hot-rolled wire rod, the difference between the method and Example 3 is that: the molten salt temperature of the subsequent molten salt treatment is 485°C, the treatment time is 25s, and the finished hot-rolled wire rod is obtained after the process is completed. Example 4:

[0065] A preferred embodiment of the manufacturing method of the 2060MPa 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: 0.65%, Mn: 0.70%, Cr: 0.51%, P: 0.014%, S: 0.015%, with the remainder being Fe and unavoidable impurities; the manufacturing method follows the process flow of rolling → wire drawing → online molten salt isothermal phase transformation → slow cooling on roller table → coiling, specifically:

[0066] The rolling process is used to heat a 220mm×220mm steel billet in a furnace to a high-temperature steel billet that is rollable and plastic. Controlling the furnace parameters promotes uniform diffusion of alloy components and reduces segregation. 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 210℃, the furnace time is 180min, the initial rolling temperature is 1060℃, the final rolling temperature is 965℃, and the final rolling reduction is 27%. The wire drawing process is used to convert the wire from the rolling line into coils through the wire drawing mechanism. The coils are distributed on the roller table and conveyed along the roller table. A suitable wire drawing temperature is selected to keep the coils in a high-temperature austenitizing state, avoiding the precipitation of network carbides during the wire drawing stage, and providing favorable conditions for the subsequent refinement of the sorbite structure. Specifically, the wire drawing temperature is controlled at 955℃.

[0067] The online molten salt isothermal phase transformation process employs a two-stage salt bath with internal molten salt. After spinning, the wire rod is conveyed via rollers through the first stage salt bath for initial molten salt treatment, causing the wire rod to cool at a rate of 40°C / s. This rapidly transitions the wire rod from the high-temperature austenitic state, bypassing the network carbide region, into the sorbite phase region, inhibiting the formation of network carbides and coarse pearlite. Most of the high-temperature austenitic structure transforms into a microstructure dominated by fine-laminated sorbite. The wire rod is then conveyed via rollers through the second stage salt bath for final molten salt treatment, with a reduced molten salt circulation rate to promote the transformation of untransformed wire rods. The retained austenite continues to transform into fine lamellar interlamellar sorbite, while simultaneously promoting isothermal tempering of the formed fine lamellar interlamellar sorbite and a small amount of ferrite, and causing some of the cementite lamellars of the sorbite to melt and fracture, thereby controlling the strength and plasticity matching of the wire rod. Specifically: the molten salt temperature of the first stage of molten salt treatment is 490℃, the treatment time is 80s, the molten salt circulation rate is 640t / h, and the molten salt temperature rise is ≤8℃; the molten salt temperature of the second stage of molten salt treatment is 530℃, the treatment time is 110s, the molten salt circulation rate is 400t / h, and the molten salt temperature rise is ≤3℃.

[0068] The slow cooling process of the roller conveyor involves controlling the opening of the insulation cover to blow hot air (≥250℃) from the two salt bath tanks of the online molten salt isothermal phase change treatment onto the conveyor roller conveyor. The conveyor roller conveyor then transports the wire rod through the insulation cover, promoting further toughening of the wire rod structure and improving the tempering and softening effect of the wire rod. Specifically, the wire rod is cooled to 280℃ at a slow cooling rate of 0.55℃ / s. The coiling process is used to coil the wire rod into coils using a coiling drum. After packaging and warehousing, the hot-rolled wire rod is obtained as a finished product.

[0069] Comparative Example 7:

[0070] A method for manufacturing hot-rolled wire rod differs from that in Example 4 in that the manufacturing method follows the process flow of rolling → wire drawing → online molten salt isothermal phase transformation → air cooling. The air cooling process involves opening the heat insulation cover and controlling the wire rod to cool to 290°C at a slow cooling rate of 1.5°C / s. After the wire rod is removed from the production line, the finished hot-rolled wire rod is obtained.

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

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

[0073]

[0074] As can be seen from the comparison results of Example 1 and Comparative Example 1, C, as an effective strengthening element in high-carbon steel, often suffers from weakened strengthening effect and increased fluctuations in mechanical properties due to the difficulty in suppressing network carbides, the risk of abnormal structure, and the impact on the driving force of pearlite phase transformation during the Stellmore air-cooling phase transformation process. This invention, through Mn-Cr chemical composition design, without alloying elements such as Nb and V, combined with online molten salt isothermal phase transformation technology, can effectively suppress abnormal low-temperature brittle structures such as network carbides, coarse pearlite, and martensite, thereby improving the high strength and plasticity matching of wire rods. As can be seen from the results of Examples 1 to 4, the microstructure includes a mixed structure composed of tempered sorbite, tempered ferrite, and melted sorbite, achieving a tensile strength of 1370~1420MPa and a reduction of area of ​​35%~40%, which is beneficial for reducing the risk of wire breakage when used in applications such as manufacturing 2060MPa grade stranded wire.

[0075] As can be seen from the comparison between Example 1 and Comparative Example 2, selecting a higher spinning temperature to keep the wire rod in a high-temperature austenitizing state can prevent the precipitation of network carbides due to excessively low temperature, and at the same time provide favorable conditions for subsequent refinement of sorbite lamellars through a large temperature difference.

[0076] As can be seen from the comparison results between Example 2 and Comparative Example 3, the lower the molten salt temperature and the longer the treatment time in the initial molten salt treatment, the greater the supercooling, which is beneficial to suppress network carbides, promote the transformation of high-temperature austenite to sorbite, reduce residual austenite, and make lamellar growth difficult to coarsen due to carbon diffusion, resulting in finer sorbite lamellar structure and thus improving matrix strength. However, if the molten salt temperature is too low, it will increase the temperature gradient from the wire rod surface to the core, increase the structural stress and the difficulty of isothermal softening, and cause plasticity loss. As the treatment time is too long, the production energy consumption will increase due to the higher molten salt circulation volume.

[0077] As can be seen from the comparison results between Example 2 and Comparative Example 4, the higher the molten salt temperature and the shorter the treatment time in the initial molten salt treatment, the lower the risk of abnormal phase transformation, the better the stability and uniformity of sorbite transformation, and the lower the structural stress, softening difficulty and production energy consumption. However, if the molten salt temperature is too high and the treatment time is too short, it will be detrimental to suppressing network carbides and coarse pearlite, reduce the driving force of sorbite phase transformation, decrease the nucleation rate, and result in more residual austenite, which will lead to strength loss and fluctuations in mechanical properties.

[0078] As can be seen from the comparison results between Example 3 and Comparative Example 5, the higher the molten salt temperature and the longer the treatment time in the later stage of molten salt treatment, the stronger the carbon diffusion ability, further reducing the temperature gradient between the wire rod surface and the core, which is conducive to promoting isothermal tempering of the structure, causing more sorbite cementite lamellars to melt and transform into a morphology with a smaller specific surface area and releasing structural stress, thereby improving the plasticity and toughness of the wire rod. However, if the molten salt temperature is too high and the treatment time is too long, excessive melting and growth of cementite and excessive softening of the wire rod will result in a significant loss of strength and increase production energy consumption.

[0079] As can be seen from the comparison results between 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 retained austenite into sorbite with finer lamellar spacing, reduce the atomic diffusion rate, and reduce the softening rate and strength loss as the treatment time is shortened, thus reducing production energy consumption. However, if the molten salt temperature is too low and the treatment time is too short, it will be detrimental to the full phase transformation of the microstructure and isothermal tempering, affecting stress release and cementite lamellar melting, which will lead to plasticity loss and mechanical property fluctuations.

[0080] As can be seen from the comparison results of Example 4 and Comparative Example 7, the slow cooling treatment of the wire rod after exiting the molten salt can promote further toughening of the wire rod structure and improve the tempering and softening effect of the wire rod.

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

Claims

1. A method of manufacturing a hot-rolled wire rod for a 2060 MPa grade strand, characterized by, The manufacturing method comprises the following steps: The chemical composition of the hot-rolled wire rod comprises the following components in percentage by mass: C: 0.85% to 0.90%, Si: 0.50% to 0.65%, Mn: 0.50% to 0.70%, Cr: 0.46% to 0.55%, P: ≤0.015%, S: ≤0.015%, and the balance of Fe and inevitable impurities; after the wire rod is spun into a wire rod at a spinning temperature of ≥930°C, the wire rod is subjected to on-line molten salt isothermal phase transformation treatment; the wire rod is first subjected to front-stage molten salt treatment, so that the wire rod is cooled at a cooling rate of ≥34°C / s and enters a sorbite phase region from an austenite state, thereby forming a structure mainly composed of sorbite structure; the wire rod is then subjected to rear-stage molten salt treatment, so as to reduce molten salt circulation amount, promote residual untransformed austenite to transform into sorbite structure, and promote the structure to be isothermal tempered and partially melt sorbite lamination; and finally, the wire rod is subjected to slow cooling on a roller bed, thereby obtaining a hot-rolled wire rod with a microstructure composed of a mixture of tempered sorbite, tempered ferrite and melt sorbite.

2. The method of producing a hot rolled wire rod for a 2060 MPa grade strand according to claim 1, characterized by, Before the rolling, the soaking temperature of a heating furnace is controlled to be 1165-1210°C, and the furnace time is 180-240 min.

3. The method of producing a hot rolled wire rod for a 2060 MPa grade strand according to claim 1, characterized by, During the rolling, the initial rolling temperature is controlled to be 1030-1060°C, the final rolling temperature is controlled to be 930-965°C, and the final rolling reduction is 27%-31.5%.

4. The method of producing a hot rolled wire rod for a 2060 MPa grade strand according to claim 1, characterized by, During the spinning, the spinning temperature is controlled to be 930-955°C.

5. The method of producing a hot rolled wire rod for a 2060 MPa grade strand according to claim 1, characterized by, The molten salt circulation amount of the front-stage molten salt treatment is 440-640 t / h, and the molten salt temperature rise is ≤8°C; the molten salt circulation amount of the rear-stage molten salt treatment is 300-400 t / h, and the molten salt temperature rise is ≤3°C.

6. The method of producing a hot rolled wire rod for a 2060 MPa grade strand according to claim 1, characterized by, The roller bed slow cooling controls the wire rod to be cooled to below 300°C at a slow cooling rate of 0.55-0.85°C / s for coiling.

7. A hot rolled wire rod for 2060 MPa class strand, characterized by, The hot-rolled wire rod is obtained by the manufacturing method of the hot-rolled wire rod for a 2060 MPa grade twisted wire rod according to any one of claims 1-6.

8. The hot rolled wire rod for 2060 MPa class strand according to claim 7, characterized by, The volume percentage of the tempered sorbite is ≥74%, the interlamination spacing is 80-130 nm, the volume percentage of the tempered ferrite is ≤5%, the volume percentage of the melt sorbite is ≥11%, the reticulated carbide level of the hot-rolled wire rod is 0 level, and the mechanical property difference between turns is ≤36 MPa.

9. The hot rolled wire rod for 2060 MPa class strand according to claim 7, characterized by, The diameter of the hot-rolled wire rod is 6.0-15.0 mm, the tensile strength is 1370-1420 MPa, and the reduction of area is 35%-40%.

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