High-strength complex-phase hot-rolled wire rod for 2400 MPa bridge cable and manufacturing method of high-strength complex-phase hot-rolled wire rod

Abstract

The invention relates to a high-strength complex-phase hot-rolled wire rod for a 2400 MPa bridge cable and a manufacturing method of the high-strength complex-phase hot-rolled wire rod. After high-carbon chemical components of Mo-Al-V are rolled and spun into a wire rod, the wire rod is subjected to online molten salt tail end quenching toughening treatment, so that the wire rod passes through front-section molten salt and is cooled at the cooling speed of more than or equal to 35 DEG C / s, part of austenite structures are transformed into quenched martensite, and the quenched martensite structure is cooled at the cooling speed of more than or equal to 35 DEG C / s; the method comprises the following steps of: heating to the temperature of a sorbite phase region through rear-section molten salt, controlling unconverted austenite to be converted into sorbite, carrying out isothermal tempering, and finally, slowly cooling through a roller way to prepare a hot-rolled wire rod of which the microscopic structure comprises a complex-phase structure consisting of tempered martensite and tempered sorbite, so that the control of network carbide and other hard and brittle phase structures can be realized, and the service life of the hot-rolled wire rod is prolonged. According to the steel wire rod, the strength and the structure uniformity of the steel wire rod are improved, the material cost and good plasticity are both considered, the tensile strength is 1665-1705MPa, the percentage reduction of area is 26%-31%, the production efficiency is high, and stable production of 2400 MPa bridge cables is facilitated.

Description

Technical Field

[0001] The invention belongs to the technical field of hot-rolled wire rods, and specifically relates to a high-strength multi-phase hot-rolled wire rod for 2400MPa-level bridge cables and a manufacturing method thereof. Background Art

[0002] Cold-drawn pearlite steel has good drawing performance and work hardening ability, and has always been the mainstream steel grade in the steel wire products industry. The strength grade of cold-drawn pearlite steel wire for bridge cables depends on the chemical composition, microstructure and matching drawing process of the parent wire rod. The higher the carbon and alloy element content in the parent wire rod, the higher the strength grade of the cold-drawn pearlite steel wire that can be developed. However, the cold-drawn pearlite steel wire in the existing technology cannot meet the development and application of 2400MPa ultra-high strength bridge cables. The main reasons are: 1. In order to improve the strength of wire rod, the content of alloy elements in the wire rod is relatively high. For example, patent CN110144521B discloses a high-strength and high-toughness bridge cable steel and its preparation method, which uses low-carbon steel wire rod with high alloy content and Co to produce bridge cable steel with tensile strength ≥2400Mpa. However, on the one hand, the alloy content is high and the material cost is high. On the other hand, the existing wire rod is generally produced by Stelmor air-cooling line controlled cooling after wire drawing. Based on the limitations of the microstructure control ability of the existing hot-rolled wire rod production line, after the alloy element content in the parent material wire rod is increased, it is affected by the segregation of alloy elements and the uncontrollable air-cooling cooling rate, which can easily make other hard and brittle phase structures poorly controlled, and the risk of wire breakage during drawing and subsequent cable making is relatively high.

[0003] 2. In order to take into account both material cost and drawing capacity, existing high-strength wire rods for bridge cables mostly use high-carbon pearlite steel. For example, CN118880169A discloses a wire rod for high-strength bridge cables and its production method, which uses 87SiMn combined with low-temperature rolling and spinning, Stelmor air-cooling line and insulation corridor process to increase the troostite content of the wire rod, and is used for 2200~2300MPa strength level bridge cables. However, on the one hand, there is a disadvantage of insufficient original strength of cold-drawn pearlite steel, and the plastic loss and wire breakage risks will increase during the drawing and strengthening process, limiting the development and application of 2400MPa-level bridge cables. If the carbon and alloy element content in the wire rod is further increased, it will be affected by carbon segregation and the maximum cooling capacity of the Stelmor air-cooling line. The grain boundaries of the wire rod are prone to form a network of carbon. Carbides and network carbides will split the matrix, resulting in a significant decrease in the strength of the material, especially the toughness, and easily causing cracks in the carbide network. In order to minimize the level of network carbides and increase the air-cooling intensity, the uncontrollability of the air-cooling line and the temperature difference between the surface and the core of the wire rod will further increase, making the hard and brittle phase structure more difficult to control, affecting the uniformity of the structure, and thus causing the risk of wire breakage during drawing. On the other hand, due to the limitation of the cooling control capacity of the air-cooling line and the influence of the high content of alloy elements, the wire rod has a short time for phase transformation incubation. After the troostite phase transformation, the wire rod is already in a low-temperature state, with high tissue stress and insufficient plasticity. It is also possible that due to the residual austenite, the martensite hard and brittle phase will continue to form in the subsequent cooling, thereby increasing the risk of wire breakage during drawing. Long-term heat preservation treatment will affect the online time, production efficiency and production energy consumption.

[0004] 3. In order to improve the strength of wire rod, micro-alloy elements such as V are added in the prior art. However, due to the uncontrollability and cooling capacity of the air cooling line, on the one hand, the wire rod passes through the precipitation phase for a short time and the precipitation driving force is weak, which affects the full precipitation of the strengthening phase. On the other hand, due to the temperature difference between the wire rod surface and the core, coarser and finer precipitation phases will coexist in the wire rod, affecting the uniformity of the organization. At the same time, the coarsening of the precipitation phase will reduce the plasticity of the wire rod, affecting the strengthening effect and material cost. Summary of the invention

[0005] The present invention aims to solve at least one of the above-mentioned technical problems to a certain extent. The present invention provides a high-strength multi-phase hot-rolled wire rod for 2400MPa-level bridge cables and a manufacturing method thereof, which can achieve control of network carbides and other hard-brittle phase structures, improve the strength and uniformity of the wire rod, take into account both material cost and good plasticity, have high production efficiency, and are conducive to the stable production of 2400MPa-level bridge cables.

[0006] The technical solution adopted by the present invention to solve its technical problem is: A method for manufacturing a 2400MPa high-strength multiphase hot-rolled wire rod for bridge cables, the manufacturing method comprising: The hot rolled wire rod is rolled to produce a wire rod according to the chemical composition of the hot rolled wire rod, wherein the chemical composition and mass percentage of the hot rolled wire rod include: C: 0.94%~0.97%, Si: 0.80%~0.95%, Mn: 0.75%~0.95%, Cr: 0.35%~0.45%, V: 0.050%~0.075%, Mo: 0.30%~0.50%, Al: 0.2%~0.4%, P≤0.015%, S≤0.015%, and the rest are Fe and Inevitable impurities; after the wire is spun into a wire rod at a spinning temperature of ≥880°C, it undergoes an online molten salt terminal quenching and toughening treatment, so that the wire rod first passes through the front section of molten salt and is cooled at a cooling rate of ≥35°C / s, and part of the austenite structure is transformed into quenched martensite, and then passes through the rear section of molten salt to raise the temperature to the bainite phase region, and the untransformed austenite is controlled to be transformed into bainite and isothermally tempered, and finally passes through a roller to slowly cool to produce a hot-rolled wire rod with a microstructure including a complex phase structure composed of tempered martensite and tempered bainite.

[0007] The design basis of the chemical composition and mass percentage of the above hot rolled wire rod includes: (1) Carbon: C is an effective carbide strengthening element and austenite forming element with a relatively low price. With the increase of carbon content, the stability of austenite can be improved, the martensite transformation temperature can be reduced, and the short-term quenching by cooling to below the troostite phase temperature during the front-stage molten salt treatment can be promoted, and part of the austenite structure can be transformed into quenched martensite, which is beneficial to the formation of pearlite with finer interlamellar spacing, i.e. troostite structure, during the rear-stage molten salt treatment, and the amount of cementite in troostite and the material strength can be increased. However, excessive carbon content will increase the tendency of carbon segregation during the solidification of the steel billet, increase the sensitivity of decarburization and the tendency of precipitation of network carbides, and affect the plasticity and toughness of the material. Therefore, in order to improve the strength of the hot-rolled wire rod base material, control the material cost, and reduce the difficulty of controlling the uniformity of the structure and improving the plasticity, the mass percentage of C is controlled to be 0.94%~0.97%.

[0008] (2) Silicon: Si is the main deoxidizing element in steel. It can inhibit the coarsening of grains during the front-end molten salt treatment, promote the nucleation of quenched martensite, and improve the strength of the matrix. During the troostite phase transformation during the back-end molten salt treatment, it can inhibit the growth and aggregation of cementite, making the cementite lamellae in the troostite finer and more uniform. However, excessive silicon content will increase the surface decarburization tendency of the steel when heated at high temperatures, prolong the time required for phase transformation incubation, and reduce the toughness of the steel. Therefore, in order to refine the grains and facilitate the short-term martensitic phase transformation and short-term tempering control of the complex phase structure, the mass percentage of Si is controlled to be 0.80%~0.95%.

[0009] (3) Manganese: As an austenite-forming element, Mn can increase the hardenability of wire rod, inhibit the formation of ferrite, move the martensite transformation toward the low temperature direction, promote the sorbite phase transformation, and increase the strength of sorbite, which is beneficial to improve the tensile strength of wire rod and improve the comprehensive mechanical properties of steel, so that the bridge cable can withstand impact and vibration loads while bearing tension. However, when the Mn content is too high, it will aggravate the segregation of alloy elements, reduce the activity of carbon, increase the difficulty of isothermal tempering stress relief, increase the overheating sensitivity of steel, and reduce the toughness and plasticity of steel. Therefore, in order to facilitate the control of the complex phase structure of hot-rolled wire rod, reduce the uniformity of the structure and the difficulty of short-time tempering control, the mass percentage of Mn is controlled to be 0.75%~0.95%.

[0010] (4) Chromium: Cr can improve the hardenability of steel, reduce the martensite transformation temperature, promote the formation of quenched martensite, increase the amount of quenched martensite transformation during the previous molten salt treatment, and enhance the stability of austenite. In the troostite phase transformation, it can refine the pearlite and cementite lamellae, improve the strength of troostite, and reduce the strength loss during the subsequent hot-dip galvanizing process of steel wire. However, too high Cr content will aggravate the component segregation and increase the difficulty of controlling the uniformity of the organization. The increase in the number of carbides and their uneven distribution will reduce the toughness of the steel, significantly increase the difficulty of isothermal stress relief of the wire rod, affect the short-time tempering toughening effect, and further affect the wire drawing and torsion performance of the steel wire. Therefore, in order to facilitate the complex phase organization, plasticity control and rapid production, the mass percentage of Cr is controlled to be 0.35%~0.45%.

[0011] (5) Vanadium: As a microalloying element, V can effectively inhibit the grain coarsening of wire rod during the rolling process. At the same time, it can be dispersed and precipitated during the online molten salt end quenching and toughening process, providing a strong precipitation strengthening effect, thereby improving the strength level of the hot-rolled wire rod without reducing the plasticity. However, the cost of V is relatively high. Excessive addition is not conducive to controlling the cost of wire rod and has the risk of coarsening. Based on the role and cost of V, the V content is controlled at 0.050%~0.075%.

[0012] (6) Molybdenum: Mo can improve the hardenability of steel, promote the formation of martensite, and inhibit the transformation of bainite. Mo combines with carbon to form carbides, which can play a role in dispersion strengthening. At the same time, it can effectively inhibit the coarsening of strengthening phases such as cementite, Cr and V precipitation phases, and prevent the coarsening of precipitation phases during the online molten salt end quenching and toughening process, thereby reducing the plasticity of the wire rod. However, the cost of Mo is relatively high, and excessive addition is not conducive to controlling the cost of wire rods. Based on the role of Mo and cost considerations, the Mo content is controlled at 0.30%~0.50%.

[0013] (7) Aluminum: Al can prevent austenite grains from growing during heating and rolling, allowing the wire rod to obtain a fine grain structure. The fine austenite grains can form a uniform structure after cooling and transformation. At the same time, it can inhibit the coarsening of cementite and refine the sorbite structure, which is beneficial to improving the strength and toughness of steel. However, too high Al content will increase the risk of inclusions, deteriorate the cold working performance of the wire rod, and reduce the fatigue performance of the steel. Therefore, the Al content is increased and the mass percentage of Al is controlled to be 0.2%~0.4%.

[0014] (8) Phosphorus and sulfur: P and S are impurity elements. The lower the better. Therefore, P is controlled to be ≤ 0.015% and S is ≤ 0.015%.

[0015] The above-mentioned hot-rolled wire rod adopts the high carbon chemical composition design of Mo-Al-V, combined with the optimized ratio of Si, Mn and Cr components, to regulate the hardenability of the wire rod, the temperature at which martensite begins to transform and the sorbite phase region, so as to provide favorable conditions for the wire rod to undergo a short-term martensite phase transformation below the sorbite phase region, to fully transform and temper in a short time in the sorbite phase region, and to facilitate the control of the precipitation and growth of carbides. On this basis, it avoids the formation of network carbides in the spinning stage due to too low a spinning temperature, improves the uniformity of austenite, and provides favorable conditions for the subsequent short-term uniform martensite phase transformation. After spinning, the wire rod is directly subjected to online molten salt end quenching and toughening treatment without air cooling: 1. Compared with the Stelmor air-cooled line, which has the highest cooling capacity and uncontrollability, resulting in uncontrollable network carbides and hard-brittle phase structures, the wire rod can be quickly cooled by utilizing the high heat exchange capacity of the molten salt when it is treated with molten salt. On the one hand, it can promote the wire rod to quickly pass through the secondary cementite precipitation temperature range of 700~800℃ from the high-temperature austenite state, avoiding the formation of network carbides that are unfavorable to drawing and plasticity. On the other hand, the wire rod can be controlled by the front-stage molten salt treatment. At an ultra-high cooling rate, it quickly enters the troostite phase region from the high-temperature austenite state, forms a certain amount of highly undercooled residual austenite, undergoes a short-term martensite phase transformation, promotes the transformation of part of the austenite to quenched martensite, and improves the matrix strength. At the same time, when the wire rod passes through the molten salt, the molten salt can cover the surface of the wire rod for heat exchange, and there is no temperature difference problem between the wind-receiving side and the winded side. Due to the high heat exchange, the temperature difference from the wire rod surface to the core is also smaller, making the transformation of the hard and brittle phase quenched martensite more uniform and controllable.

[0016] 2. Compared with the limited minimum cooling capacity of the Stelmore air-cooled line and the influence of continuous cooling of the wire rod, which leads to insufficient phase transformation of the wire rod, high organizational stress and poor control of carbide precipitation, the wire rod can enter the latter molten salt after the front-stage molten salt treatment to be treated in the sorbite phase region. On the one hand, the wire rod can be transformed to the same temperature as the molten salt, extending the treatment time of the wire rod in the sorbite phase region, promoting the residual austenite that has not been transformed after the front-stage molten salt treatment to fully transform into the sorbite structure, refining the sorbite structure, and improving the matrix strength, so as to improve the adverse effect of high Si content on the increase of phase transformation incubation time, and avoid the subsequent cooling process. The temperature difference from the surface to the core of the wire rod is also smaller, which can make the sorbite phase transformation uniform and reduce the fluctuation of mechanical properties. On the other hand, the sorbite phase region The higher temperature can prolong the isothermal treatment time of the wire rod at high temperature, provide more thermal power for tempering softening, control the formed quenched martensite and troostite structure to undergo a certain degree of short-term tempering, improve the plasticity and toughness of the quenched martensite, reduce the dislocation density of the quenched martensite, transform it into the tempered martensite which is both strong and tough, reduce the stress of the troostite structure, transform it into the tempered troostite structure, realize the regulation of complex phase structure, and cooperate with Mo to inhibit the coarsening effect of strengthening phases such as cementite, Cr and V precipitation phases, prolong the time that the wire rod is in the dispersed precipitation temperature range of strengthening phases such as Cr and V precipitation phases, promote the sufficient and uniform precipitation of carbide strengthening phases, avoid the coarsening of carbides and the loss of plasticity and toughness, give full play to the strengthening effect, and at the same time, the long-term insulation corridor treatment can also reduce the online time and promote efficient production.

[0017] The wire rod still maintains a relatively high temperature after the latter stage of molten salt treatment. The use of roller slow cooling can extend the high temperature time of the wire rod, prevent the wire rod from losing plasticity due to stress shrinkage due to excessive cooling, promote further toughening of the wire rod structure, and enhance the high strength and plasticity matching of the wire rod.

[0018] Selecting appropriate heating furnace soaking temperature and furnace time before rolling can improve the uniformity and plasticity of the steel billet structure, facilitate rolling, reduce the influence of segregation, and avoid burning, decarburization or degradation of the steel billet surface quality due to too long furnace time. In the preferred technical solution, before rolling, the heating furnace soaking temperature is controlled to be 1180~1250℃, and the furnace time is 150~220min.

[0019] During the rolling, a suitable rolling temperature and deformation amount are selected, and the V element is used to increase the recrystallization temperature of the metal, inhibit grain growth, promote dynamic recrystallization during the final rolling process, and refine and improve the metal structure. In the preferred technical solution, during the rolling, the initial rolling temperature is controlled to be 1060~1110°C, the final rolling temperature is 980~1010°C, and the final rolling reduction is 22%~26%.

[0020] In the preferred technical solution, the molten salt temperature of the front-stage molten salt is 485-505°C, and the treatment time is 8-18s. The molten salt temperature of the front-stage molten salt is below the sorbite phase region. The lower the molten salt temperature of the front-stage molten salt and the longer the treatment time, the more the amount of large undercooling retained austenite increases, the faster the short-term phase transformation of martensite, the more quenched martensite increases, and the matrix strength is higher. However, if the molten salt temperature is too low and the treatment time is too long, the austenite residue is too little, which has a great impact on the subsequent sorbite phase transformation and short-term phase transformation. If tempering is not favorable, it will affect the plasticity of the matrix; on the contrary, the higher the molten salt temperature of the front stage and the shorter the treatment time, it will be unfavorable for the martensitic phase transformation, leaving more residual austenite for the subsequent troostite phase transformation, and the matrix plasticity will increase. However, if the molten salt temperature is too high and the treatment time is too short, the martensitic phase transformation will be affected and the matrix strength will be lost. Therefore, the molten salt temperature and treatment time of the front stage can be controlled to promote the transformation of part of austenite to quenched martensite, so as to make organizational preparation for the subsequent molten salt treatment.

[0021] Since the temperature difference of the wire rod from the high-temperature austenite state to the temperature below the troostite phase region is large, selecting a larger molten salt circulation volume can control the molten salt temperature rise and control the quenching during continuous processing. At the same time, the larger the specification, the greater the molten salt circulation flow rate per unit time, which can further reduce the temperature difference from the surface of the wire rod to the core. In the preferred technical solution, the molten salt circulation volume of the front-stage molten salt is 460~650t / h, and the molten salt temperature rise is ≤5℃.

[0022] In the preferred technical scheme, the molten salt temperature of the rear-stage molten salt is 565~585℃, and the processing time is 78~128s. The molten salt temperature of the rear-stage molten salt is in the troostite phase region of the wire rod. The lower the molten salt temperature, the greater the supercooling can be formed, which promotes the refinement of the troostite lamellae spacing, and provides more driving force for the dispersion and precipitation of vanadium-containing carbides to improve the matrix strength. However, if the molten salt temperature is too low, it is difficult to provide more thermal power for isothermal tempering, which will lead to a decrease in toughening effect and prolonged processing time, which is not conducive to controlling the plasticity and production efficiency of the wire rod. On the contrary, the higher the molten salt temperature of the rear-stage molten salt, the more thermal power can be provided for tempering, which promotes short-term tempering of the complex phase structure and improves the strength-plasticity matching of the wire rod. However, if the molten salt temperature is too high, the troostite lamellae spacing becomes coarser, which affects the precipitation of carbides and loses the strength of the wire rod. As the treatment time is extended, there is a risk of excessive loss of matrix strength, coarsening of carbides and loss of strength and plasticity; the longer the treatment time of the latter molten salt, the more sufficient the carbides will precipitate, the stronger the isothermal toughening effect, and the higher the plasticity of the wire rod. However, if the treatment time is too long, the production energy consumption will increase, and there is a risk of coarsening of carbides. Conversely, the shorter the treatment time, the lower the production energy consumption and the faster the production. However, if the treatment time is too short, the tempering effect of the complex phase structure will decrease, which will lead to greater brittleness. If the carbides are not fully precipitated in time, the strength and plasticity will be lost. Therefore, the molten salt temperature and treatment time of the latter molten salt can be controlled to control the high-temperature austenite of the wire rod to be transformed into troostite. At the same time, after isothermal tempering, the formed complex phase structure can be controlled to undergo a certain degree of short-term tempering to improve the strength and plasticity matching of the wire rod and promote rapid production.

[0023] The rear-stage molten salt can select an appropriate molten salt circulation rate to control the molten salt temperature rise, further reduce the temperature difference from the edge to the core of the wire rod, and improve the uniformity of the structure. In the preferred technical solution, the molten salt circulation rate of the rear-stage molten salt is 400~600t / h, and the molten salt temperature rise is ≤3°C.

[0024] In the preferred technical solution, the roller slow cooling controls the wire rod to slowly cool to below 280°C at a cooling rate of 0.1~0.4°C / s. The roller slow cooling can choose to close the insulation cover or input the hot air in the online molten salt terminal quenching and toughening treatment process into the insulation cover to recycle the heat energy, control the wire rod to cool gradually and slowly, prevent the wire rod from causing excessive internal stress in the wire rod due to too fast cooling rate during the cooling process, promote further toughening of the wire rod structure, and improve the softening effect of the wire rod.

[0025] A 2400MPa grade high-strength multi-phase hot-rolled wire rod for bridge cables, wherein the hot-rolled wire rod is manufactured by any of the above-mentioned methods for manufacturing the 2400MPa grade high-strength multi-phase hot-rolled wire rod for bridge cables.

[0026] The above-mentioned hot-rolled wire rod is designed with Mo-Al-V chemical composition and combined with online molten salt end quenching and toughening technology. Different from general cold-drawn pearlite steel, the microstructure of the hot-rolled wire rod includes a complex phase structure composed of tempered martensite and tempered troostite. The quenched martensite has higher strength, hardness and lattice distortion than the troostite structure. The quenched martensite is tempered to obtain tempered martensite, and the lattice distortion is reduced, while still retaining a high strength. The internal stress is eliminated to a certain extent, and the toughness and plasticity are effectively improved. The structure of troostite is finer and denser than pearlite, the interlamellar spacing is smaller, and the strength is better than pearlite. It has good drawing performance and work hardening ability. After tempering, the carbide distribution of troostite is more uniform, the dislocation movement is easier, and the internal stress is reduced, so that the tempered troostite has good comprehensive mechanical properties. The complex phase structure formed in this way can make up for the disadvantage of insufficient original strength of cold-drawn pearlite steel, further improve the material strength, and take into account good plasticity and uniformity of structure.

[0027] The greater the volume percentage of the tempered martensite is, the higher the wire rod strength is. In a preferred technical solution, the volume percentage of the tempered martensite is 57% to 63%.

[0028] The finer the interlamellar spacing of the tempered troostite is, the higher the wire rod strength is. In a preferred technical solution, the interlamellar spacing of the tempered troostite is 80-110 nm.

[0029] In the preferred technical solution, the network carbide level of the hot-rolled wire rod is level 0, which can prevent the network carbide from splitting the matrix structure, improve the toughness and plasticity of the material, and help improve the drawing performance.

[0030] The hot-rolled wire rod can effectively prevent the C element from generating network carbides, and transform the quenched martensite into tempered martensite with both strong and plastic properties. The carbide strengthening phase is evenly distributed, and the mechanical property fluctuation is smaller, which is beneficial to improving the drawing and torsion properties. In the preferred technical solution, the mechanical property same-circle difference of the hot-rolled wire rod is ≤47MPa.

[0031] In the preferred technical solution, the diameter of the hot-rolled wire rod is 10.0~16.0mm, the tensile strength is 1665~1705MPa, and the cross-sectional shrinkage rate is 26%~31%. The higher initial tensile strength enables the hot-rolled wire rod to reach the strength grade faster after being drawn as the base material. At the same time, the good plasticity enables the wire rod to undergo greater deformation without breaking when subjected to stress, which can reduce the risk of wire breakage during the drawing process, thereby stably developing 2400MPa-level bridge cables.

[0032] Compared with the prior art, the beneficial effects of the present invention are at least: (1) Aiming at the current situation that after the carbon and alloy element contents in the parent material wire rod are increased, the network carbon and other hard and brittle phase structures are poorly controlled and the microstructure control ability is limited, the present invention combines the Mo-Al-V chemical composition design with the online molten salt end quenching and toughening technology, uses the front-stage molten salt to control the wire rod to quickly cool from the high-temperature austenite state at an ultra-high cooling rate, passes through the network carbide formation temperature range and enters below the troostite phase region to undergo a short-term martensitic phase transformation, and uses the rear-stage molten salt to control the wire rod to enter the troostite phase region for isothermal phase transformation. At the same time, after isothermal tempering, the formed complex phase structure is controlled to undergo a certain degree of short-term tempering to improve the strength and plasticity matching of the wire rod. Finally, the roller is slowly cooled to improve the softening effect of the wire rod, which can realize the control of network carbides and other hard and brittle phase structures, improve the strength and organizational uniformity of the wire rod, take into account both material cost and good plasticity, have high production efficiency, and have good industrial adaptability.

[0033] (2) Aiming at the disadvantage of insufficient original strength of existing cold-drawn pearlite steel, which gradually limits the current situation of development and application of ultra-high strength bridge cables, the microstructure of the present invention includes a complex phase structure composed of tempered martensite and tempered troostite, which can effectively avoid the generation of network carbides by C element, transform the quenched martensite into tempered martensite with both strength and plasticity, use the dispersed precipitation of V element to provide a strong precipitation strengthening effect, use the Mo element to prevent the coarsening of the precipitate phase and reduce the plasticity of the wire rod, and maximize the strengthening effect of the carbon element, so that the carbide strengthening phase is evenly distributed. Combined with the tempering state regulation of the complex phase structure, the strength and plasticity matching of the wire rod can be improved, and the tensile strength can reach 1665~1705MPa, and the cross-sectional shrinkage rate can reach 26%~31%. It is used in the manufacture of 2400MPa ultra-high strength bridge cables and other application fields, and has good market application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which: Figure 1 is a metallographic structure diagram of Example 1 of the present invention; Figure 2 is the metallographic structure diagram of Example 2 of the present invention; Figure 3 It is the metallographic structure diagram of Example 3 of the present invention. DETAILED DESCRIPTION

[0035] The embodiments described below with reference to the accompanying drawings are exemplary and are only for illustration and do not limit the description of the features and characteristics of the present invention, so as to propose the best way to implement the present invention, and are intended to be used to explain the present invention and are sufficient to enable those skilled in the art to implement the present invention, but cannot be understood as any limitation on the scope of the present invention, which is limited only by the appended claims; the organization and performance testing of the hot-rolled wire rods obtained in the following embodiments and comparative examples include: the tensile test is carried out using "GB-T 228.1-2021 Metallic Material Tensile Test Part 1: Room Temperature Test Method" to obtain the tensile strength and cross-sectional reduction rate; the organization test is carried out according to the metal microstructure detection method of GB / T13298 standard; the mechanical property same circle difference test method: take 2 circles of wire rod 5m away from the end of the coil, take the overlap area position as the base point, divide each circle of wire rod into 8 sections on average, take 1 tensile specimen on each section, and the strength extreme difference of the tensile specimen after the tensile test is the mechanical property same circle difference. Embodiment 1:

[0036] A preferred embodiment of the manufacturing method of the 2400MPa grade high-strength multiphase hot-rolled wire rod for bridge cables of the present invention, the chemical composition and mass percentage of the hot-rolled wire rod include C: 0.95%, Si: 0.88%, Mn: 0.95%, Cr: 0.38%, V: 0.05%, Mo: 0.45%, Al: 0.39%, P: 0.012%, S: 0.013%, and the rest are Fe and unavoidable impurities; the manufacturing method thereof is manufactured according to the process flow of rolling → spinning → online molten salt end quenching and toughening treatment → roller slow cooling → coiling, specifically: The rolling process is used to heat the steel billet with a specification of 220mm×220mm through a heating furnace to achieve a high-temperature steel billet that can be rolled into plastic, promote the homogenization of alloy components and reduce segregation. After the steel billet comes out of the heating furnace, it is rolled into a wire with a diameter of 16mm through a rolling line. Appropriate rolling temperature and deformation are selected to promote dynamic recrystallization, grain refinement, and matrix toughening during the final rolling process. Specifically: the heating furnace is heated to 1250°C, the furnace time is 150min, the initial rolling temperature is 1100°C, the final rolling temperature is 1010°C, and the final rolling reduction is 22%; the wire-spinning process is used to convert the wire coming out of the rolling line into a wire rod through a wire-spinning mechanism, and the wire rod is spread on the roller and transported along the roller, so that the wire rod is in a high-temperature austenite state, the uniformity of austenite is improved, and favorable conditions are provided for the subsequent short-term uniform phase transformation of martensite. Specifically: the wire-spinning temperature is controlled to be 920°C.

[0037] The online molten salt terminal quenching and toughening treatment process adopts a two-stage salt bath tank with molten salt inside. The wire rod after spinning is conveyed by a roller through the first salt bath tank for the front molten salt treatment, so that the wire rod is cooled at a cooling rate of 38°C / s, and quickly passes through the network carbide precipitation interval from the high-temperature austenite state to below the sorbite phase region, forming a certain amount of large undercooling residual austenite, promoting the transformation of part of the austenite structure to quenched martensite, and performing a short-time martensitic phase transformation. After that, the wire rod is conveyed by a roller through the second salt bath tank for the rear molten salt treatment, and the rear molten salt is heated to the sorbite phase Zone temperature, control the transformation of untransformed austenite into troostite and isothermal tempering, promote the dispersion and precipitation of large amounts of vanadium-containing carbides, control the growth of carbide strengthening phases, and after isothermal tempering, control the formed complex phase structure to undergo a certain degree of short-term tempering to improve the strength-plasticity matching of the wire rod. Specifically: the molten salt temperature of the front section is 492°C, the processing time is 16s, the molten salt circulation volume is 650t / h, and the molten salt temperature rise is ≤5°C; the molten salt temperature of the rear section is 579°C, the processing time is 95s, the molten salt circulation volume is 600t / h, and the molten salt temperature rise is ≤3°C.

[0038] The roller slow cooling process adopts closing the insulation cover, inputting the hot air above the two salt bath tanks into the insulation cover, and conveying the wire rods through the second salt bath tank by the conveying roller into the insulation cover to prevent the wire rods from cooling too fast during the cooling process, resulting in increased stress, promoting further toughening of the wire rod structure, and improving the softening effect of the wire rod. Specifically: the wire rod is controlled to slowly cool to 274°C at a cooling rate of 0.4°C / s; the coiling process is used to coil the wire rods into coils through the coiling drum, and obtain the hot-rolled wire rod products after packaging and storage. Its metallographic structure diagram is as follows Figure 1 shown.

[0039] Comparative Example 1: A method for manufacturing a hot-rolled wire rod, which differs from Example 1 in that: the heating furnace soaking temperature is controlled to be 1150°C, the furnace time is 200 min, the initial rolling temperature is 1020°C, the final rolling temperature is 920°C, the spinning temperature is 830°C, the wire rod is cooled at a cooling rate of 30°C / s during the front-stage molten salt treatment, and the hot-rolled wire rod is obtained after it is off the line. Embodiment 2:

[0040] A preferred embodiment of the manufacturing method of the 2400MPa grade high-strength multiphase hot-rolled wire rod for bridge cables of the present invention, the chemical composition and mass percentage of the hot-rolled wire rod include C: 0.95%, Si: 0.95%, Mn: 0.78%, Cr: 0.35%, V: 0.062%, Mo: 0.5%, Al: 0.28%, P: 0.012%, S: 0.012%, and the rest are Fe and unavoidable impurities; the manufacturing method is manufactured according to the process flow of rolling → spinning → online molten salt end quenching and toughening treatment → roller slow cooling → coiling, specifically: The rolling process is used to heat the steel billet with a specification of 220mm×220mm through a heating furnace to achieve a high-temperature steel billet with rollable plasticity, promote the homogenization of alloy components and reduce segregation. After the steel billet comes out of the heating furnace, it is rolled into a wire with a diameter of 14mm through a rolling line. Appropriate rolling temperature and deformation are selected to promote dynamic recrystallization, grain refinement, and matrix toughening during the final rolling process. Specifically: the heating furnace is heated to 1235°C, the furnace time is 180min, the initial rolling temperature is 1090°C, the final rolling temperature is 1000°C, and the final rolling reduction is 23%; the wire-spinning process is used to make the wire coming out of the rolling line into a wire rod through a wire-spinning mechanism, and the wire rod is spread on the roller and transported along the roller, so that the wire rod is in a high-temperature austenite state, the uniformity of austenite is improved, and favorable conditions are provided for the subsequent short-term uniform phase transformation of martensite. Specifically: the wire-spinning temperature is controlled to be 910°C.

[0041] The online molten salt terminal quenching and toughening treatment process adopts a two-stage salt bath tank with molten salt inside. The wire rod after spinning is conveyed by a roller through the first salt bath tank for the front molten salt treatment, so that the wire rod is cooled at a cooling rate of 37°C / s, and quickly passes through the network carbide precipitation interval from the high-temperature austenite state to below the sorbite phase region, forming a certain amount of large undercooling residual austenite, promoting the transformation of part of the austenite structure to quenched martensite, and performing a short-time martensitic phase transformation. After that, the wire rod is conveyed by a roller through the second salt bath tank for the rear molten salt treatment, and the rear molten salt is heated to the sorbite phase region. Temperature, control the transformation of untransformed austenite into troostite and isothermal tempering, promote the dispersion and precipitation of large amounts of vanadium-containing carbides, control the growth of carbide strengthening phases, and after isothermal tempering, control the formed complex phase structure to undergo a certain degree of short-term tempering, and improve the strength-plasticity matching of the wire rod. Specifically: the molten salt temperature of the front section is 498°C, the processing time is 12s, the molten salt circulation volume is 615t / h, and the molten salt temperature rise is ≤5°C; the molten salt temperature of the rear section is 569°C, the processing time is 107s, the molten salt circulation volume is 530t / h, and the molten salt temperature rise is ≤3°C.

[0042] The roller slow cooling process adopts closing the insulation cover, inputting the hot air above the two salt bath tanks into the insulation cover, and conveying the wire rods through the second salt bath tank by the conveying roller into the insulation cover to prevent the wire rods from cooling too fast during the cooling process, resulting in increased stress, promoting further toughening of the wire rod structure, and improving the softening effect of the wire rod. Specifically: the wire rod is controlled to slowly cool to 271°C at a cooling rate of 0.25°C / s; the coiling process is used to coil the wire rods into coils through the coiling drum, and obtain the hot-rolled wire rod products after packaging and storage. Its metallographic structure diagram is as follows Figure 2 shown.

[0043] Comparative Example 2: A method for manufacturing a hot-rolled wire rod, which differs from Example 2 in that: during the front-stage molten salt treatment, the wire rod is cooled at a cooling rate of 36°C / s, the molten salt temperature of the front-stage molten salt is 510°C, the treatment time is 5s, and the hot-rolled wire rod is obtained after going offline.

[0044] Comparative Example 3: A method for manufacturing a hot-rolled wire rod, which differs from Example 2 in that: during the front-stage molten salt treatment, the wire rod is cooled at a cooling rate of 39°C / s, the molten salt temperature of the front-stage molten salt is 480°C, the treatment time is 25s, and the hot-rolled wire rod is obtained after going offline. Embodiment 3:

[0045] A preferred embodiment of the manufacturing method of the 2400MPa grade high-strength multiphase hot-rolled wire rod for bridge cables of the present invention, the chemical composition and mass percentage of the hot-rolled wire rod include C: 0.94%, Si: 0.8%, Mn: 0.82%, Cr: 0.42%, V: 0.075%, Mo: 0.39%, Al: 0.2%, P: 0.015%, S: 0.015%, and the rest are Fe and unavoidable impurities; the manufacturing method is manufactured according to the process flow of rolling → spinning → online molten salt end quenching and toughening treatment → roller slow cooling → coiling, specifically: The rolling process is used to heat the steel billet with a specification of 220mm×220mm through a heating furnace to achieve a high-temperature steel billet that can be rolled into plastic, promote the homogenization of alloy components and reduce segregation. After the steel billet comes out of the heating furnace, it is rolled into a wire with a diameter of 10mm through a rolling line. Appropriate rolling temperature and deformation are selected to promote dynamic recrystallization, grain refinement, and matrix toughening during the final rolling process. Specifically: the heating furnace is heated to 1180°C, the furnace time is 220min, the initial rolling temperature is 1060°C, the final rolling temperature is 980°C, and the final rolling reduction is 26%; the wire-spinning process is used to convert the wire coming out of the rolling line into a wire rod through a wire-spinning mechanism, and the wire rod is spread on the roller and transported along the roller, so that the wire rod is in a high-temperature austenite state, the uniformity of austenite is improved, and favorable conditions are provided for the subsequent short-term uniform phase transformation of martensite. Specifically: the wire-spinning temperature is controlled to be 880°C.

[0046] The online molten salt terminal quenching and toughening treatment process adopts a two-stage salt bath tank with molten salt inside. The wire rod after spinning is conveyed by a roller through the first salt bath tank for the front molten salt treatment, so that the wire rod is cooled at a cooling rate of 35°C / s, and quickly passes through the network carbide precipitation interval from the high-temperature austenite state to below the sorbite phase region, forming a certain amount of large undercooling residual austenite, promoting the transformation of part of the austenite structure to quenched martensite, and performing a short-time martensitic phase transformation. After that, the wire rod is conveyed by a roller through the second salt bath tank for the rear molten salt treatment, and the rear molten salt is heated to the sorbite phase Zone temperature, control the transformation of untransformed austenite into sorbite and isothermally tempered, promote the dispersion and precipitation of large amounts of vanadium-containing carbides, control the growth of carbide strengthening phases, and after isothermal tempering, control the formed complex phase structure to undergo a certain degree of short-term tempering to improve the strength-plasticity matching of the wire rod. Specifically: the molten salt temperature of the front section is 505°C, the processing time is 8s, the molten salt circulation volume is 460t / h, and the molten salt temperature rise is ≤5°C; the molten salt temperature of the rear section is 565°C, the processing time is 128s, the molten salt circulation volume is 400t / h, and the molten salt temperature rise is ≤3°C.

[0047] The roller slow cooling process adopts closing the insulation cover, inputting the hot air above the two salt bath tanks into the insulation cover, and conveying the wire rod passing through the second salt bath tank by the conveying roller into the insulation cover to prevent the wire rod from cooling too fast during the cooling process, resulting in increased stress, promoting further toughening of the wire rod structure, and improving the softening effect of the wire rod. Specifically: the wire rod is controlled to slowly cool to 279°C at a cooling rate of 0.13°C / s; the coiling process is used to coil the wire rod into a coil through a coiling drum, and obtain a hot-rolled wire rod product after packaging and storage. Its metallographic structure diagram is as follows Figure 3 shown.

[0048] Comparative Example 4: A method for manufacturing a hot-rolled wire rod, the manufacturing method of which is different from that of Example 3 in that the molten salt temperature of the rear-stage molten salt is 590° C., the processing time is 200 s, and the hot-rolled wire rod is obtained after going offline.

[0049] Comparative Example 5: A method for manufacturing a hot-rolled wire rod, the manufacturing method of which is different from that of Example 3 in that the molten salt temperature of the rear-stage molten salt is 535° C., the processing time is 55 s, and the hot-rolled wire rod is obtained after going offline. Embodiment 4:

[0050] A preferred embodiment of the manufacturing method of the 2400MPa grade high-strength multiphase hot-rolled wire rod for bridge cables of the present invention, the chemical composition and mass percentage of the hot-rolled wire rod include C: 0.97%, Si: 0.92%, Mn: 0.75%, Cr: 0.45%, V: 0.065%, Mo: 0.3%, Al: 0.4%, P: 0.015%, S: 0.012%, and the rest are Fe and unavoidable impurities; the manufacturing method thereof is manufactured according to the process flow of rolling → spinning → online molten salt end quenching and toughening treatment → roller slow cooling → coiling, specifically: The rolling process is used to heat the steel billet with a specification of 220mm×220mm through a heating furnace to achieve a high-temperature steel billet with rollable plasticity, promote the homogenization of alloy components and reduce segregation. After the steel billet comes out of the heating furnace, it is rolled into a wire with a diameter of 12mm through a rolling line. Appropriate rolling temperature and deformation are selected to promote dynamic recrystallization, grain refinement, and matrix toughening during the final rolling process. Specifically: the heating furnace is heated to 1210°C, the furnace time is 200min, the initial rolling temperature is 1070°C, the final rolling temperature is 990°C, and the final rolling reduction is 25%; the wire-spinning process is used to convert the wire coming out of the rolling line into a wire rod through a wire-spinning mechanism, and the wire rod is spread on the roller and transported along the roller, so that the wire rod is in a high-temperature austenite state, the uniformity of austenite is improved, and favorable conditions are provided for the subsequent short-term uniform phase transformation of martensite. Specifically: the wire-spinning temperature is controlled to be 895°C.

[0051] The online molten salt terminal quenching and toughening treatment process adopts a two-stage salt bath tank with molten salt inside. The wire rod after spinning is conveyed by a roller through the first salt bath tank for the front molten salt treatment, so that the wire rod is cooled at a cooling rate of 36°C / s, and quickly passes through the network carbide precipitation interval from the high-temperature austenite state to below the sorbite phase region, forming a certain amount of large undercooling residual austenite, promoting the transformation of part of the austenite structure to quenched martensite, and performing a short-time martensitic phase transformation. After that, the wire rod is conveyed by a roller through the second salt bath tank for the rear molten salt treatment, and the rear molten salt is heated to the sorbite phase The zone temperature is controlled to control the transformation of untransformed austenite into sorbite and isothermally tempered, which promotes the dispersion and precipitation of a large number of vanadium-containing carbides, controls the growth of carbide strengthening phases, and after isothermal tempering, controls the formed complex phase structure to undergo a certain degree of short-term tempering to improve the strength and plasticity matching of the wire rod. Specifically: the molten salt temperature of the front section is 485℃, the processing time is 18s, the molten salt circulation volume is 545t / h, and the molten salt temperature rise is ≤5℃; the molten salt temperature of the rear section is 585℃, the processing time is 78s, the molten salt circulation volume is 470t / h, and the molten salt temperature rise is ≤3℃.

[0052] The roller slow cooling process adopts closing the insulation cover, inputting the hot air above the two salt bath tanks into the insulation cover, and conveying the wire rod passing through the second salt bath tank by the conveying roller into the insulation cover, so as to prevent the wire rod from cooling too fast during the cooling process, resulting in increased stress, promote further toughening of the wire rod structure, and improve the softening effect of the wire rod. Specifically: the wire rod is controlled to be slowly cooled to 268°C at a cooling rate of 0.3°C / s; the coiling process is used to coil the wire rod into a coil by a coiling drum, and obtain the hot-rolled wire rod finished product after packaging and storage.

[0053] Comparative Example 6: A method for manufacturing a hot-rolled wire rod, which differs from Example 4 in that: the roller slow cooling process uses an open insulation cover to control the wire rod to slowly cool to 280°C at a cooling rate of 0.9°C / s, and the hot-rolled wire rod is obtained after it comes off the line. The tensile strength of the hot-rolled wire rod is 1713MPa, the cross-sectional shrinkage rate is 24%, and the mechanical property difference is 48MPa.

[0054] The hot rolled wire rods obtained in the above examples 1 to 4 and comparative examples 1 to 5 were subjected to microstructure and performance tests, and the comparative results obtained are shown in Table 1 below: Table 1. Comparison of microstructure and performance of hot rolled wire rods with different compositions and manufacturing methods

[0055] It can be seen from the results of Examples 1 to 4 that the present invention can effectively avoid the generation of network carbides by the C element through the Mo-Al-V chemical composition design combined with the online molten salt end quenching and toughening technology, and transform the quenched martensite into tempered martensite with both strong and plastic properties. The microstructure includes a complex phase structure composed of tempered martensite and tempered bainite, which can maximize the strengthening effect of the carbon element and make the carbide strengthening phase evenly distributed, achieving a tensile strength of 1665~1705MPa and a cross-sectional shrinkage rate of 26%~31%, which is conducive to the stable production of 2400MPa-level bridge cables.

[0056] From the comparison results of Example 1 and Comparative Example 1, it can be seen that the selection of a suitable spinning temperature can avoid the formation of network carbides during the spinning stage due to the spinning temperature being too low, improve the uniformity of austenite, and provide favorable conditions for the subsequent short-term uniform phase transformation of martensite.

[0057] From the comparison results of Example 2 and Comparative Example 2, it can be seen that the molten salt temperature of the front-stage molten salt is below the troostite phase region. The higher the molten salt temperature of the front-stage molten salt and the shorter the treatment time, the smaller the proportion of tempered martensite in the structure, the greater the proportion of tempered troostite, and the higher the plasticity of the matrix. However, if the molten salt temperature of the front-stage molten salt is too high and the treatment time is too short, the martensitic phase transformation will be affected and the matrix strength will be lost.

[0058] From the comparison results of Example 2 and Comparative Example 3, it can be seen that the lower the molten salt temperature of the front-stage molten salt and the longer the treatment time, the more the amount of retained austenite with a large degree of supercooling increases, the faster the short-term phase transformation of martensite, the more quenched martensite increases, and the matrix strength is higher. However, if the molten salt temperature is too low and the treatment time is too long, it is not conducive to the subsequent troostite phase transformation and short-term tempering. The proportion of tempered troostite in the organization is too small, which will affect the matrix plasticity.

[0059] From the comparison results of Example 3 and Comparative Example 4, it can be seen that the higher the molten salt temperature of the latter molten salt and the longer the treatment time, the more thermal power can be provided for tempering, the carbide precipitation is sufficient, the isothermal toughening effect is enhanced, and the plasticity of the wire rod increases. However, if the molten salt temperature is too high and the treatment time is too long, the spacing between the troostite lamellae becomes coarser, and there is a risk of excessive loss of matrix strength and coarsening of carbide precipitation, resulting in loss of strength and plasticity.

[0060] From the comparison results of Example 3 and Comparative Example 5, it can be seen that the lower the molten salt temperature of the latter molten salt, the finer the spacing between the troostite lamellae can be, providing more driving force for the dispersion and precipitation of vanadium-containing carbides. The shorter the processing time, the lower the production energy consumption can be, and rapid production can be promoted. However, if the molten salt temperature is too low and the processing time is too short, the tempering effect of the complex phase structure will decrease, resulting in greater brittleness, and the carbides will not be fully precipitated in time, resulting in a loss of strength and plasticity.

[0061] From the comparison results of Example 4 and Comparative Example 6, it can be seen that the roller slow cooling controls the gradual and slow cooling of the wire rod, which can prevent the wire rod from having excessive internal stress due to too fast cooling rate during the cooling process, promote further toughening of the wire rod structure, and improve the softening effect of the wire rod.

[0062] 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. All 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 2400MPa grade high-strength multiphase hot-rolled wire rod for bridge cables, characterized in that: The manufacturing method thereof comprises: The hot rolled wire rod is rolled to produce a wire rod according to the chemical composition of the hot rolled wire rod, wherein the chemical composition and mass percentage of the hot rolled wire rod include: C: 0.94%~0.97%, Si: 0.80%~0.95%, Mn: 0.75%~0.95%, Cr: 0.35%~0.45%, V: 0.050%~0.075%, Mo: 0.30%~0.50%, Al: 0.2%~0.4%, P≤0.015%, S≤0.015%, and the rest are Fe and Inevitable impurities; after the wire is spun into a wire rod at a spinning temperature of ≥880°C, it undergoes an online molten salt terminal quenching and toughening treatment, so that the wire rod first passes through the front section of molten salt and is cooled at a cooling rate of ≥35°C / s, and part of the austenite structure is transformed into quenched martensite, and then passes through the rear section of molten salt to raise the temperature to the bainite phase region, and the untransformed austenite is controlled to be transformed into bainite and isothermally tempered, and finally passes through a roller to slowly cool to produce a hot-rolled wire rod with a microstructure including a complex phase structure composed of tempered martensite and tempered bainite.

2. The method for manufacturing 2400MPa grade high-strength multi-phase hot-rolled wire rod for bridge cables according to claim 1, characterized in that: Before the rolling, the soaking temperature of the heating furnace is controlled to be 1180-1250° C., and the time in the furnace is 150-220 min.

3. The method for manufacturing the 2400MPa grade high-strength multi-phase hot-rolled wire rod for bridge cables according to claim 1, characterized in that: During the rolling, the initial rolling temperature is controlled to be 1060-1110° C., the final rolling temperature is controlled to be 980-1010° C., and the final rolling reduction is controlled to be 22%-26%.

4. The method for manufacturing 2400MPa grade high-strength multi-phase hot-rolled wire rod for bridge cables according to claim 1, characterized in that: The molten salt temperature of the front-stage molten salt is 485-505° C., and the processing time is 8-18 seconds; the molten salt temperature of the rear-stage molten salt is 565-585° C., and the processing time is 78-128 seconds.

5. The method for manufacturing 2400MPa grade high-strength multi-phase hot-rolled wire rod for bridge cables according to claim 4, characterized in that: The molten salt circulation volume of the front-stage molten salt is 460-650 t / h, and the molten salt temperature rise is ≤5°C; the molten salt circulation volume of the rear-stage molten salt is 400-600 t / h, and the molten salt temperature rise is ≤3°C.

6. The method for manufacturing 2400MPa grade high-strength multi-phase hot-rolled wire rod for bridge cables according to claim 4, characterized in that: The roller slow cooling controls the wire rod to be slowly cooled to below 280° C. at a cooling rate of 0.1-0.4° C. / s.

7. A 2400MPa grade high-strength multiphase hot-rolled wire rod for bridge cables, characterized in that: The hot-rolled wire rod is manufactured by the method for manufacturing 2400MPa-grade high-strength multi-phase hot-rolled wire rod for bridge cables as described in any one of claims 1 to 6.

8. The 2400MPa grade high-strength multi-phase hot-rolled wire rod for bridge cables according to claim 7, characterized in that: The volume percentage of the tempered martensite is 57% to 63%, and the interlamellar spacing of the tempered troostite is 80 to 110 nm.

9. The 2400MPa grade high-strength multi-phase hot-rolled wire rod for bridge cables according to claim 7, characterized in that: The network carbide grade of the hot-rolled wire rod is grade 0, and the mechanical property difference is ≤47MPa.

10. The 2400MPa grade high-strength multi-phase hot-rolled wire rod for bridge cables according to claim 7, characterized in that: The hot-rolled wire rod has a diameter of 10.0-16.0 mm, a tensile strength of 1665-1705 MPa, and a cross-sectional shrinkage of 26%-31%.

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