High-strength complex-phase hot-rolled wire rod for 2300 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 2300MPa-grade bridge cable and a manufacturing method of the high-strength complex-phase hot-rolled wire rod. After Al-containing high-carbon steel components are hot-rolled and spun into a wire rod, the wire rod is subjected to online molten salt critical quenching isothermal treatment, so that the wire rod firstly passes through front-section molten salt and is cooled at a cooling speed of greater than or equal to 37 DEG C / s; part of the austenite structure is transformed into a quenched bainite and quenched martensite mixed structure, then the temperature is increased to the sorbite phase region temperature through rear-section molten salt heating, the untransformed austenite is controlled to be transformed into sorbite, isothermal tempering is conducted, and finally slow cooling is conducted through a roller way; the hot-rolled wire rod of which the microscopic structure comprises a complex-phase structure composed of tempered bainite, tempered sorbite and tempered martensite is prepared, the material cost can be considered, complex-phase structure regulation and control are achieved, the strength and plasticity matching and the structure uniformity of the wire rod are improved, the tensile strength is 1617-1656 MPa, the percentage reduction of area is 27%-32%, and the ultrahigh-strength bridge cable can be stably produced.

Description

Technical Field

[0001] The present invention belongs to the technical field related to hot-rolled wire rods, and specifically relates to a high-strength multi-phase hot-rolled wire rod for 2300MPa-grade bridge cables and a manufacturing method thereof. Background Art

[0002] With the construction and development of super-large span bridges, the requirements for the strength grade of bridge cables are constantly increasing. The higher the grade of the bridge cable, the greater the load it can withstand, and the overall performance, safety and durability of the bridge are improved. The bridge cable uses hot-rolled wire rod as the base material. After surface treatment such as pickling, it is gradually drawn into steel wire of the required diameter through multiple passes, and then hot-dip galvanized, post-processed, and twisted into shape. Therefore, it is necessary to improve the performance of the hot-rolled wire rod base material to meet the manufacturing needs of ultra-high strength bridge cables.

[0003] Pearlite steel has high strength, good plasticity and excellent cold drawing performance. It can be used in high stress structural materials such as bridge cables, wire ropes, spring steel wires, etc. After cold drawing with different deformation amounts, its products can be used in bridges, buildings, transportation, automobiles and other fields. The wire rods for high strength bridge cable cold drawn steel wire in the prior art are generally pearlite hypereutectoid steel, which is mainly produced by Stelmor air cooling line. For example, patent CN118880169A discloses a wire rod for high strength bridge cables and its production method, which adopts 87SiMn component combined with Stelmor air cooling line air cooling after low temperature rolling and heat preservation corridor insulation for more than 120 minutes to obtain high troostite content wire rods, and the strength reaches more than 1400MPa, but there are still the following defects: 1. In order to further improve the strength of wire rod, the existing technology will increase the content of carbon, silicon, manganese, chromium and other components to improve the hardenability of wire rod, so as to obtain refined pearlite lamellae at a lower phase transition temperature and obtain a troostite structure with better strength. However, on the one hand, as the carbon content increases, alloying elements such as chromium and manganese will affect the diffusion of carbon and the stability of carbides. Since the maximum cooling control capacity of the Stelmor air-cooled line is limited, carbon has a greater tendency to precipitate and aggregate in the form of carbides, forming a network of carbides that affect the uniformity of the organization and deteriorate the plasticity of the wire rod, increasing the risk of subsequent wire drawing fracture; on the other hand, the increase in alloy content brings about an increase in material costs. Compared with high-strength bainite-based materials, pearlite steel has the disadvantage of insufficient original strength, resulting in insufficient final strength grade of the wire rod. It is necessary to increase the number of drawing passes and the surface reduction rate to improve the material strength. The plasticity loss in the process is large, and it is difficult to stably produce 2300MPa-grade bridge cables or the corresponding bridge cable grade cannot be reached.

[0004] Second, in order to minimize the level of network carbides and refine the pearlite lamellar spacing, the existing high-strength bridge wire rod generally adopts the Stelmor air-cooling line strong cooling process. However, on the one hand, due to the fluctuation of the carbon content of the wire rod, the segregation of alloy elements, and the temperature difference between the windward side and the windward side of the wire rod under strong air cooling, the temperature difference between the surface and the core is further increased, making it easier to form martensite or bainite structure at the position where the surface cooling speed is fast, or because the wire rod is continuously cooled by the air-cooling line, the phase change time is short, the phase change is insufficient, and there will be untransformed in the structure. Austenite continues to form abnormal structure in the subsequent cooling process, resulting in uncontrollable bainite or martensite transformation, uneven wire rod structure, large fluctuations in mechanical properties, and increased risks of wire breakage and torsional cracking during drawing. On the other hand, due to the limited cooling capacity of the Stelmor air-cooled wire, the bainite structure produced in the production process is quenched bainite, which is extremely brittle. The martensitic transformation causes large internal stress inside the wire rod, and the risk of wire breakage in the hot-rolled wire rod base material is extremely high during the wire drawing process. Therefore, it is difficult to stably develop ultra-high strength bridge cables.

[0005] 3. The carbonitride precipitation phase of alloying elements such as vanadium can play a role in precipitation strengthening, grain refinement, and improvement of toughness and fatigue performance. However, the cooling capacity of the Stelmor air-cooled wire is limited. The wire rod is prone to form both relatively large and relatively fine phases due to the uncontrollable cooling rate, which not only affects the uniformity of the organization, but also the coarse vanadium precipitation phase is not conducive to the strength and toughness of the material. In addition, during the continuous cooling process, the wire rod passes through the precipitation temperature range for a short time, and the vanadium-containing carbide precipitation phase is difficult to fully precipitate, affecting the strengthening effect. Summary of the invention

[0006] The present invention aims to solve at least one of the above-mentioned technical problems to a certain extent. The present invention provides a 2300MPa high-strength complex phase hot-rolled wire rod for bridge cables and a manufacturing method thereof, which can take into account material costs, realize complex phase structure regulation, improve the strength and plasticity matching of the wire rod and the uniformity of the structure, and facilitate the stable production of ultra-high strength bridge cables.

[0007] The technical solution adopted by the present invention to solve its technical problem is: A method for manufacturing a 2300MPa high-strength multiphase hot-rolled wire rod for bridge cables, the manufacturing method comprising: The wire rod is produced by rolling 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: 0.93%~0.96%, Si: 0.42%~0.58%, Mn: 0.66%~0.82%, Cr: 0.31%~0.41%, V: 0.015%~0.030%, Al: 0.2%~0.4%, P≤0.015%, S≤0.015%, and the rest are Fe and unavoidable impurities; the wire rod is ≥93 After spinning into wire rods at a spinning temperature of 0°C, the wire rods are subjected to online molten salt critical quenching isothermal treatment, so that the wire rods first pass through the front section of molten salt and are cooled at a cooling rate of ≥37°C / s, and part of the austenite structure is transformed into a mixed structure of quenched bainite and quenched martensite, and then pass through the rear section of molten salt to raise the temperature to the troostite phase region, control the untransformed austenite to be transformed into troostite and isothermally tempered, and finally pass through roller slow cooling to obtain a hot-rolled wire rod with a microstructure including a complex phase structure composed of tempered bainite, tempered troostite and tempered martensite.

[0008] 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, it is beneficial to reduce the temperature at which bainite and martensite begin to transform, promote the formation of a mixed structure including partially quenched bainite and quenched martensite through short-time quenching during online molten salt critical quenching isothermal treatment, and reduce the pearlite transformation temperature range. In the later molten salt treatment, pearlite with finer interlamellar spacing, namely troostite structure, can be formed, thereby improving the material strength. However, excessive carbon content will increase the tendency of carbon segregation during the solidification process of the steel billet, increase the decarburization sensitivity and the tendency of network carbide precipitation, and affect the plasticity and toughness of the material. Therefore, in order to meet the high strength requirements of the 2300MPa grade bridge cable for the hot-rolled wire rod base material, control the material cost, and reduce the difficulty of complex phase structure regulation and plasticity improvement, the mass percentage of C is controlled to be 0.93%~0.96%.

[0009] (2) Silicon: Si is the main deoxidizing element in steel. It can be used as a solid solution hardening element to improve the strength of steel. It can inhibit the coarsening of grains during the previous molten salt treatment, promote the uniform transformation of the mixed structure after short-time quenching, control the uniformity of the structure and improve the matrix strength. However, too high a silicon content will make the steel more susceptible to decarburization when heated at high temperatures, reducing the toughness of the steel. Therefore, in order to refine the grains and facilitate the control of the complex phase structure, the mass percentage of Si is controlled to be 0.42%~0.58%.

[0010] (3) Manganese: As an austenite-forming element, Mn can increase the hardenability of wire rod and move the transformation of bainite and martensite toward the low temperature direction. At the same time, manganese forms a solid solution in austenite, which can expand the austenite phase region, increase the stability of austenite, inhibit the formation of ferrite, and is beneficial to refining the interlamellar spacing of troostite, thereby improving the tensile strength of wire rod, 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, and then lose the plasticity of wire rod. 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 tempering control, the mass percentage of Mn is controlled to be 0.66%~0.82%.

[0011] (4) Chromium: Cr can prevent austenite grains from growing during heating and refine the grains, which can greatly improve the hardenability of the material. The carbides formed by chromium and carbon can serve as the nucleation core of bainite and reduce the starting transformation temperature of martensite, which is beneficial to the transformation of quenched mixed structure. At the same time, it can enhance the stability of austenite and reduce the transformation temperature of troostite, which is beneficial to refine the spacing between troostite sheets and reduce the strength loss during the subsequent hot-dip galvanizing process of steel wire. However, too high Cr content will aggravate component segregation, affect the uniformity of wire rod structure, and significantly increase the difficulty of isothermal stress relief of wire rod, affecting the tempering toughening effect, and further affecting the wire drawing and torsion performance of steel wire. Therefore, in order to facilitate the control of complex phase structure and reduce the difficulty of isothermal tempering, the Cr content is appropriately reduced, and the mass percentage of Cr is controlled to be 0.31%~0.41%.

[0012] (5) Vanadium: The V element can promote grain nucleation and inhibit grain growth. At the same time, during the later molten salt treatment process, it can form fine dispersed carbonitrides with carbon and nitrogen in the medium temperature range, which can hinder dislocation movement, thereby playing a role in precipitation strengthening, and improving the strength level of the hot-rolled wire rod without reducing plasticity. However, the cost of the V element is relatively high. Excessive addition is not conducive to controlling the cost of the wire rod and has the risk of coarsening. Based on the role of the V element and cost considerations, the present invention controls the V element content to 0.015%~0.030%.

[0013] (6) Aluminum: Al, as a ferrite-forming element, can inhibit the activity of C, inhibit the thickness of cementite lamellae, and effectively refine the structure. The fine austenite grains can form a uniform structure after cooling and transformation, and refine the troostite structure, which is beneficial to improving the strength and toughness of steel. At the same time, it is cheaper than Mo, which can inhibit the coarsening of cementite, and is beneficial to controlling material costs. However, too high Al content will increase the risk of inclusions and thus reduce the fatigue performance of steel. Therefore, the Al content is increased and the mass percentage of Al is controlled to be 0.2%~0.4%.

[0014] (7) 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 is designed with a high-carbon steel composition containing V and Al, and the optimized ratio of Si, Mn and Cr is used to control the hardenability of the wire rod, appropriately reduce the temperature at which bainite and martensite begin to form, inhibit and coarsen the thickness of the cementite layer, and provide favorable conditions for obtaining a partially quenched mixed structure by short-term quenching in the front molten salt. The temperature range of the sorbite phase region is appropriately regulated to be at a higher temperature, and can adapt to the temperature range of a large amount of dispersion and precipitation of vanadium-containing carbides, which provides favorable conditions for the isothermal phase transformation and tempering of the molten salt in the back stage. On this basis, a higher wire-spinning temperature is selected to keep the wire rod in a high-temperature austenite state, avoiding the formation of network carbides in the wire-spinning stage due to low temperature, and at the same time providing favorable conditions for the subsequent formation of a large degree of undercooling and promoting the quenching bainite and quenching martensite phase transformation. After spinning, online molten salt critical quenching is directly carried out through molten salt: 1. Compared with the Stelmore air-cooled line, which has limited maximum cooling capacity, uncontrollable cooling speed and continuous cooling operation, the wire rod can exchange heat with the molten salt more quickly and evenly when passing through the front molten salt. On the one hand, the wire rod can quickly cool down from the high-temperature austenite state, skipping the secondary cementite precipitation temperature range of 700~800℃, avoiding the formation of network carbides due to high carbon content and eccentricity of high carbon steel wire rods, avoiding network carbides that destroy the uniformity of the organization and the plasticity of the wire rod, and improving the utilization of carbon elements; on the other hand, the wire rod can quickly cool down And reduce the temperature difference from the edge to the core of the wire rod. Stronger air cooling does not have the problem of temperature difference between the wind-receiving side and the wind-receiving side, and can form a larger degree of supercooling. Combined with Si and Al, the coarsening of grains and cementite lamellae is suppressed, providing more positions for the deformation nuclei of quenched bainite and quenched martensite phases. After a short mixed phase transformation, part of the high-temperature austenite structure in the organization is transformed into quenched bainite and quenched martensite, making the phase transformation of the low-temperature quenching organization, which is conventionally regarded as an abnormal organization, more uniform and controllable, so as to improve the matrix strength, control the organization uniformity and mechanical property fluctuations.

[0016] 2. Compared with the limited minimum cooling capacity and continuous cooling operation of the Stelmore air-cooled line, the wire rod can be changed to the same temperature as the molten salt through heat exchange after the latter molten salt treatment. On the one hand, the wire rod can be controlled to heat up to the troostite phase temperature, prolong the phase change time, and control the high-temperature austenite structure that has not been transformed after the previous molten salt quenching to be transformed into a troostite structure with fine lamellar spacing, promote the full phase change of the structure, avoid the residual austenite and continue to form the martensite structure in the subsequent roller ring slow cooling process. At the same time, it is in the temperature range where a large amount of vanadium-containing carbides are dispersed and precipitated, which can prolong the precipitation time of the fine precipitation phase, promote the uniform and sufficient dispersion and precipitation of vanadium-containing carbides, give full play to the strengthening and toughening effect of vanadium, and improve the uniformity of the structure; on the other hand On the other hand, the temperature of the troostite phase region is higher than that of the molten salt in the front section, which can extend the processing time of the wire rod in the high temperature section and provide more thermal power for the tempering of the organization. After isothermal tempering, the formed complex phase organization is controlled to undergo a certain degree of short-term tempering, and the quenched martensite and quenched bainite are transformed into a strong and tough organization state, which promotes the troostite organization to reduce the internal stress and transform to the tempered state, quickly improves the organization plasticity, and enhances the strength-plasticity matching of the wire rod. Since the temperature of the wire rod after passing through the molten salt in the rear section is relatively high, it is slowly cooled through roller cooling, which can prevent the wire rod from cooling too fast during the cooling process, resulting in an increase in stress, and can also promote the further toughening of the wire rod organization by continuing the softening effect of high-temperature treatment, thereby realizing the regulation of complex phase organization and strength-plastic properties.

[0017] Before the rolling, selecting appropriate heating furnace parameters can reduce the deformation resistance of the material during the rolling process, while promoting uniform diffusion of components, reducing segregation of alloy elements, and avoiding excessive grain growth and decarburization caused by too long time in the furnace. In the preferred technical solution, before the rolling, the heating furnace is controlled to have a soaking temperature of 1190-1240°C and a furnace time of 140-200 minutes.

[0018] Since the spinning temperature is high and the restriction on the rolling temperature is smaller, the selection of a higher rolling temperature can reduce the deformation resistance of the wire and the wear on the rolling line, adopt a larger reduction and a higher rolling speed, improve production efficiency, eliminate cast structure defects, and promote dynamic recrystallization during the final rolling process, so that the grains are refined and homogenized, and the matrix is ​​strengthened and toughened. In the preferred technical solution, during the rolling, the initial rolling temperature is controlled to be 1090~1140℃, the final rolling temperature is 1010~1030℃, and the final rolling reduction is 19%~24%.

[0019] In the preferred technical solution, the molten salt temperature of the front-stage molten salt is 450-475°C, and the treatment time is 20-35s; the lower the molten salt temperature of the front-stage molten salt and the longer the treatment time, the higher the transformation of high-temperature austenite to quenched bainite and quenched martensite can be promoted, and at the same time, the proportion of quenched martensite in the mixed structure increases, and the matrix strength increases. However, if the molten salt temperature is too low and the treatment time is too long, the quenched bainite phase transformation is affected, and the untransformed high-temperature austenite is too little, which will affect the plasticity of the material; on the contrary, if the molten salt temperature of the front-stage molten salt is higher and the treatment time is shorter, the quenched martensite in the structure will increase. The reduction of tempered bainite and quenched martensite leaves more space for the subsequent transformation of high-temperature austenite to troostite, which can improve the plasticity of the material. However, the molten salt temperature is too high and the processing time is too short, and the cooling rate and supercooling of the wire rod decrease, which will affect the control of the network carbide and the efficiency of the short-time mixed phase transformation. The proportion of tempered bainite and tempered martensite in the multiphase structure is too small, which will affect the strength of the material. Therefore, the molten salt temperature and processing time of the front molten salt can be further controlled to control part of the high-temperature austenite to undergo short-time mixed phase transformation, regulate the matrix strength, and prepare for the subsequent multiphase structure regulation.

[0020] In the preferred technical scheme, the molten salt temperature of the rear-stage molten salt is 540~580℃, and the processing time is 60~200s; the lower the molten salt temperature of the rear-stage molten salt, the more conducive it is to promote the refinement of the troostite interlamellar spacing and provide more power for the dispersion and precipitation of vanadium-containing carbides, so as to improve the matrix strength, but if the molten salt temperature is too low, it will affect the isothermal tempering effect and reduce the plasticity of the material. If the molten salt temperature is lower than the medium temperature range of vanadium-containing carbides, it will also affect the precipitation of vanadium-containing carbides and affect the material strength; conversely, the higher the molten salt temperature, the more conducive it is to provide more thermal power for isothermal tempering, improve the toughening effect, reduce the tissue stress, and improve the plasticity of the material, but if the molten salt temperature is too high, it will affect the refinement of the troostite interlamellar spacing and the precipitation rate of vanadium-containing carbides; the treatment of the front-stage molten salt The longer the treatment time, the more obvious the toughening effect of the dual-phase structure after isothermal tempering. However, if the treatment time is too long, it will bring a certain strength loss, and there will also be a risk of precipitation and coarsening of vanadium-containing carbides, resulting in loss of strength and plasticity. On the contrary, the shorter the treatment time, the lower the isothermal tempering effect and the plasticity of the wire rod. However, if the treatment time is too short, it will affect the softening effect of quenched bainite and quenched martensite, and the vanadium-containing carbides are not fully precipitated, which significantly increases the brittleness of the wire rod, and even causes abnormal organization and mechanical property fluctuations in subsequent cooling due to residual austenite. Therefore, the molten salt temperature and treatment time of the subsequent molten salt can be further controlled to control the full transformation of the austenite structure, promote the full dispersion and precipitation of vanadium-containing carbides, regulate the tempering state and toughening effect of the dual-phase structure, and improve the strength-plasticity matching of the wire rod.

[0021] Since the temperature difference of the wire rod from the high-temperature austenite state to the quenching is large, a larger molten salt circulation volume is selected to reduce the molten salt temperature rise, increase the supercooling, and promote short-time mixing and uniform phase change. In the preferred technical solution, the molten salt circulation volume of the front stage molten salt is 550~760t / h, and the molten salt temperature rise is ≤7°C; Since the temperature difference between the front-stage molten salt and the rear-stage molten salt is relatively small, as the phase change releases latent heat, the molten salt circulation volume of the rear-stage molten salt can be appropriately reduced compared with the front-stage molten salt. Precise temperature control can also reduce production energy consumption. In the preferred technical solution, the molten salt circulation volume of the rear-stage molten salt is 350~460t / h, and the molten salt temperature rise is ≤3°C.

[0022] Since the wire rod enters the conveyor roller at 540~580℃ for roller slow cooling control after passing through the rear molten salt, selecting a lower cooling rate can prevent the wire rod from cooling too fast during the cooling process, which may cause increased stress, and promote further toughening of the wire rod structure, improve the softening effect of the wire rod, and avoid too long online time due to too slow cooling rate. In the preferred technical solution, the roller slow cooling controls the wire rod to slowly cool to below 320℃ at a cooling rate of 0.3~0.7℃ / s.

[0023] A 2300MPa 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 2300MPa grade high-strength multi-phase hot-rolled wire rod for bridge cables.

[0024] The hot-rolled wire rod adopts the hypereutectoid high carbon steel composition design of C-Si-Mn-Cr-V-Al, with relatively lower Si, Cr and V contents and relatively higher Al content, which can appropriately reduce the material cost. Combined with the online molten salt critical quenching isothermal technology, a composite structure consisting of tempered bainite, tempered troostite and tempered martensite is obtained. Compared with the pearlite structure, the quenched bainite has higher hardness and better fatigue resistance. After isothermal tempering, the quenched bainite has a finer and more uniform structure, and the carbides are dispersed, and it is transformed into tempered bainite with significantly improved toughness. The quenched martensite has higher strength and hardness, but poor toughness and a large amount of lattice distortion inside. After high-temperature isothermal tempering, the quenched martensite has a more delicate structure, and the internal stress and distortion are significantly improved, and it is transformed into a tempered martensite structure that is both strong and tough, and has good comprehensive mechanical properties; the interlamellar spacing of troostite is finer than that of pearlite, and the strength and hardening ability are better. After high-temperature isothermal tempering, the troostite is transformed into tempered troostite, and the organizational stress is further reduced, and it is transformed into a tempered troostite structure with better plasticity, and the vanadium-containing carbides are evenly dispersed; therefore, compared with traditional pearlite high-carbon steel, the above-mentioned hot-rolled wire rod can be regulated by the tempering state of the complex phase structure, which can maximize the strengthening effect of carbon and vanadium elements, improve the overall strength and plastic matching of the wire rod, and improve the organizational uniformity of the wire rod.

[0025] In the multiphase structure, the higher the volume percentage of the tempered bainite is, the higher the matrix strength is. In a preferred technical solution, the volume percentage of the tempered bainite is 55% to 65%.

[0026] In the multiphase structure, the finer the interlamellar spacing of the tempered troostite, the higher the matrix strength. In a preferred technical solution, the interlamellar spacing of the tempered troostite is 70-105 nm.

[0027] In the multiphase structure, the higher the proportion of the tempered martensite is, the higher the matrix strength is. In a preferred technical solution, the volume percentage of the tempered martensite is 25% to 32%.

[0028] In the preferred technical solution, the network carbide level of the hot-rolled wire rod is level 0, which can reduce the increase in brittleness caused by a large amount of continuous carbides, better exert the mechanical properties of the matrix, and improve the strengthening effect of carbon elements and organizational uniformity.

[0029] Since it can effectively avoid the formation of abnormal network carbide structure of carbon element and transform the quenched martensite into tempered martensite with both strength and plasticity, the fluctuation of mechanical properties of hot-rolled wire rod can be further reduced. In the preferred technical solution, the same-circle difference of the mechanical properties of the hot-rolled wire rod is ≤42MPa.

[0030] In the preferred technical solution, the diameter of the hot-rolled wire rod is 11.0~15.0mm, the tensile strength is 1617~1656MPa, and the cross-sectional shrinkage rate is 27%~32%. The hot-rolled wire rod has higher tensile strength and good cross-sectional shrinkage rate, which can reduce the subsequent drawing passes and exemption rate, reduce plastic loss in the process, and reach the performance level faster. It meets the manufacturing and use of 2300-level bridge cables, and can reduce the risk of fracture during drawing and torsion, thereby stably developing ultra-high-strength bridge cables.

[0031] Compared with the prior art, the beneficial effects of the present invention are at least: (1) In view of the current situation that the domestic cold-drawn steel wire production is mainly based on the Stelmor air-cooling line, but due to the limited cooling control capacity of the Stelmor air-cooling line, the bainite structure produced in the production process is quenched bainite, which is extremely brittle, and the risk of wire breakage in the hot-rolled wire rod base material during the wire drawing process is extremely high. The present invention controls the wire rod to quickly cool down from the high-temperature austenite state through the design of Al-containing chemical composition combined with the online molten salt critical quenching isothermal technology, promotes the transformation of part of the austenite structure into a mixed structure of quenched bainite and quenched martensite, and then raises the temperature to the troostite phase region through the rear-stage molten salt, controls the untransformed austenite to be transformed into troostite and isothermally tempered, and finally promotes further toughening of the wire rod structure through roller slow cooling. It can take into account the material cost, realize the regulation of complex phase structure, improve the matching of strength and plasticity of the wire rod and the uniformity of the structure, and has good industrial adaptability.

[0032] (2) In view of the current situation that the hot-rolled wire rod for high-strength bridge cables has insufficient strength and plasticity, and the uniformity of the organization is difficult to control, and it is difficult to stably develop ultra-high-strength bridge cables, the hot-rolled wire rod of the present invention can effectively avoid the abnormal network carbide organization produced by the C element, transform the quenched bainite and quenched martensite into tempered bainite and tempered martensite with both strength and plasticity, improve the strengthening effect of the carbon element, and use the Al element to inhibit the thickness of the cementite layer, effectively refine the organization, and promote the uniform dispersion distribution of vanadium-containing carbides. The microstructure type includes a complex phase organization composed of tempered bainite, tempered troostite, and tempered martensite. Compared with pearlite steel, the tensile strength can be improved, and good plasticity can be taken into account, reaching a tensile strength of 1617~1656MPa and a cross-sectional reduction rate of 27%~32%. It is used in the manufacture of 2300MPa ultra-high-strength bridge cables and other application fields, and can effectively reduce the risk of wire breakage of the hot-rolled wire rod base material during the wire drawing process, and has good market application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] 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 It is the metallographic structure diagram of Example 2 of the present invention. DETAILED DESCRIPTION

[0034] 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:

[0035] A preferred embodiment of the manufacturing method of the 2300MPa 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: 0.44%, Mn: 0.66%, Cr: 0.35%, V: 0.019%, Al: 0.35%, P: 0.012%, S: 0.013%, and the rest are Fe and unavoidable impurities; the manufacturing method is manufactured according to the process flow of rolling → spinning → online molten salt critical quenching isothermal 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 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 13mm through a rolling line. A higher rolling temperature is selected to increase the rolling speed, promote dynamic recrystallization and grain refinement during the final rolling process, and strengthen the matrix. Specifically: the heating furnace is controlled to have a soaking temperature of 1200°C, a furnace time of 160min, an initial rolling temperature of 1105°C, a final rolling temperature of 1015°C, and a final rolling reduction of 23%; 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 a roller and transported along the roller, so that the wire rod is in a high-temperature austenite state, and the wire-spinning temperature is appropriately increased to provide favorable conditions for the subsequent formation of a large degree of undercooling and the promotion of quenched bainite and quenched martensite phase transformation. Specifically: the wire-spinning temperature is controlled to be 940°C.

[0036] The online molten salt critical quenching isothermal 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 39°C / s, and quickly passes through the network carbide precipitation interval from the high-temperature austenite state, thereby increasing the degree of supercooling, promoting the transformation of part of the austenite structure to the mixed structure of quenched bainite and quenched martensite, and performing a short-time mixed 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 troostite phase region. Temperature, control the transformation of untransformed austenite into troostite with fine lamellar spacing, promote the dispersion and precipitation of large amounts of vanadium-containing carbides, and after isothermal tempering, control the formed mixed 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 456°C, the processing time is 24s, the molten salt circulation volume is 655t / h, and the molten salt temperature rise is ≤7°C; the molten salt temperature of the rear section is 563°C, the processing time is 180s, the molten salt circulation volume is 440t / h, and the molten salt temperature rise is ≤3°C.

[0037] The roller slow cooling process adopts the method of closing the heat preservation cover, and the wire rod passing through the second salt bath tank is transported by the conveying roller into the heat preservation cover to prevent the wire rod from cooling too fast during the cooling process, thereby increasing the 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 be slowly cooled to 310°C at a cooling rate of 0.6°C / s; the coiling process is used to coil the wire rod into a coil through a coiling drum, and obtain the hot-rolled wire rod product after packaging and storage. Its metallographic structure diagram is as follows Figure 1 shown.

[0038] 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 210min, the initial rolling temperature is 1085°C, the final rolling temperature is 945°C, the spinning temperature is 875°C, the wire rod is cooled at a cooling rate of 33°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:

[0039] A preferred embodiment of the manufacturing method of the 2300MPa 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: 0.93%, Si: 0.42%, Mn: 0.78%, Cr: 0.31%, V: 0.03%, Al: 0.2%, P: 0.012%, S: 0.012%, and the rest is Fe and unavoidable impurities; the manufacturing method is manufactured according to the process flow of rolling → spinning → online molten salt critical quenching isothermal 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 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 11mm through a rolling line. A higher rolling temperature is selected to increase the rolling speed, promote dynamic recrystallization and grain refinement during the final rolling process, and strengthen the matrix. Specifically: the heating furnace is controlled to have a soaking temperature of 1190°C, the furnace time is 200min, the initial rolling temperature is 1090°C, the final rolling temperature is 1010°C, and the final rolling reduction is 24%; 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, and the wire-spinning temperature is appropriately increased to provide favorable conditions for the subsequent formation of a large degree of undercooling and the promotion of quenched bainite and quenched martensite phase transformation. Specifically: the wire-spinning temperature is controlled to be 930°C.

[0040] The online molten salt critical quenching isothermal 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 front-stage 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, thereby increasing the degree of supercooling, promoting the transformation of part of the austenite structure to the mixed structure of quenched bainite and quenched martensite, and performing a short-time mixed phase transformation. After that, the wire rod is conveyed by a roller through the second salt bath tank for rear-stage molten salt treatment, and the rear-stage molten salt is heated to the troostite phase region. Temperature, control the transformation of untransformed austenite into troostite with fine lamellar spacing, promote the dispersion and precipitation of large amounts of vanadium-containing carbides, and after isothermal tempering, control the formed mixed 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 467°C, the processing time is 31s, the molten salt circulation volume is 550t / h, and the molten salt temperature rise is ≤7°C; the molten salt temperature of the rear section is 555°C, the processing time is 135s, the molten salt circulation volume is 380t / h, and the molten salt temperature rise is ≤3°C.

[0041] The roller slow cooling process adopts the method of closing the heat preservation cover, and the wire rod passing through the second salt bath tank is transported by the conveying roller into the heat preservation cover to prevent the wire rod from cooling too fast during the cooling process, thereby increasing the 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 be slowly cooled to 305°C at a cooling rate of 0.4°C / s; the coiling process is used to coil the wire rod into a coil through a coiling drum, and obtain the hot-rolled wire rod product after packaging and storage. Its metallographic structure diagram is as follows Figure 2 shown.

[0042] Comparative Example 2: A method for manufacturing a hot-rolled wire rod, which differs from Example 2 in that: the molten salt temperature of the front-stage molten salt is controlled to be 485°C, the treatment time is 5s, the wire rod is cooled at a cooling rate of 36°C / s during the front-stage molten salt treatment, and the hot-rolled wire rod is obtained after it is off the line.

[0043] Comparative Example 3: A method for manufacturing a hot-rolled wire rod, which differs from Example 2 in that: the molten salt temperature of the front-stage molten salt is controlled to be 435°C, the treatment time is 45s, the wire rod is cooled at a cooling rate of 41°C / s during the front-stage molten salt treatment, and the hot-rolled wire rod is obtained after it comes off the line. Embodiment 3:

[0044] A preferred embodiment of the manufacturing method of the 2300MPa 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: 0.96%, Si: 0.58%, Mn: 0.82%, Cr: 0.39%, V: 0.025%, Al: 0.29%, 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 critical quenching isothermal 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 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. A higher rolling temperature is selected to increase the rolling speed, promote dynamic recrystallization and grain refinement during the final rolling process, and strengthen the matrix. Specifically: the heating furnace is controlled to have a soaking temperature of 1240°C, the furnace time is 140min, the initial rolling temperature is 1140°C, the final rolling temperature is 1030°C, and the final rolling reduction is 21%; 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, and the wire-spinning temperature is appropriately increased to provide favorable conditions for the subsequent formation of a large degree of undercooling and the promotion of quenched bainite and quenched martensite phase transformation. Specifically: the wire-spinning temperature is controlled to be 955°C.

[0045] The online molten salt critical quenching isothermal 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 front-stage molten salt treatment, so that the wire rod is cooled at a cooling rate of 41°C / s, and quickly passes through the network carbide precipitation interval from the high-temperature austenite state, thereby increasing the degree of supercooling, promoting the transformation of part of the austenite structure to the mixed structure of quenched bainite and quenched martensite, and performing a short-time mixed phase transformation. After that, the wire rod is conveyed by a roller through the second salt bath tank for rear-stage molten salt treatment, and the rear-stage molten salt is heated to the troostite phase region. Temperature, control the transformation of untransformed austenite into troostite with fine lamellar spacing, promote the dispersion and precipitation of large amounts of vanadium-containing carbides, and after isothermal tempering, control the formed mixed 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 450°C, the processing time is 35s, the molten salt circulation volume is 760t / h, and the molten salt temperature rise is ≤7°C; the molten salt temperature of the rear section is 580°C, the processing time is 200s, the molten salt circulation volume is 460t / h, and the molten salt temperature rise is ≤3°C.

[0046] The roller slow cooling process adopts closing the insulation cover, and the wire rod passing through the second salt bath tank is transported by the conveyor 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 318°C at a cooling rate of 0.7°C / s; the coiling process is used to coil the wire rod into a coil by a coiling drum, and the hot-rolled wire rod product is obtained after packaging and storage.

[0047] 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 controlled to be 595° C., the processing time is 250 s, and the hot-rolled wire rod is obtained after going offline.

[0048] 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 controlled to be 525° C., the processing time is 50 s, and the hot-rolled wire rod is obtained after going offline. Embodiment 4:

[0049] A preferred embodiment of the manufacturing method of the 2300MPa 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: 0.96%, Si: 0.52%, Mn: 0.73%, Cr: 0.41%, V: 0.015%, Al: 0.4%, P: 0.015%, 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 critical quenching isothermal 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 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 15mm through a rolling line. A higher rolling temperature is selected to increase the rolling speed, promote dynamic recrystallization and grain refinement during the final rolling process, and strengthen the matrix. Specifically: the heating furnace is controlled to have a soaking temperature of 1220°C, the furnace time is 180min, the initial rolling temperature is 1125°C, the final rolling temperature is 1025°C, and the final rolling reduction is 19%; 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, and the wire-spinning temperature is appropriately increased to provide favorable conditions for the subsequent formation of a large degree of undercooling and the promotion of quenched bainite and quenched martensite phase transformation. Specifically: the wire-spinning temperature is controlled to be 950°C.

[0050] The online molten salt critical quenching isothermal 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 front-stage 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, thereby increasing the degree of supercooling, promoting the transformation of part of the austenite structure to the mixed structure of quenched bainite and quenched martensite, and performing a short-time mixed phase transformation. After that, the wire rod is conveyed by a roller through the second salt bath tank for rear-stage molten salt treatment, and the rear-stage molten salt is heated to the troostite phase The zone temperature is controlled to control the transformation of untransformed austenite into troostite with fine lamellar spacing, promote the dispersion and precipitation of large amounts of vanadium-containing carbides, and after isothermal tempering, control the formed mixed 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 475°C, the processing time is 20s, the molten salt circulation volume is 590t / h, and the molten salt temperature rise is ≤7°C; the molten salt temperature of the rear section is 540°C, the processing time is 60s, the molten salt circulation volume is 350t / h, and the molten salt temperature rise is ≤3°C.

[0051] The roller slow cooling process adopts closing the insulation cover, and the wire rod passing through the second salt bath tank is transported by the conveyor roller into the insulation cover 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 slowly cool to 295°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 the hot-rolled wire rod product is obtained after packaging and storage.

[0052] Comparative Example 6: A method for manufacturing a hot-rolled wire rod, the manufacturing method of which differs from that of Example 4 in that: a roller is controlled to slowly cool by opening a heat preservation cover, and the wire rod is transported by a conveyor roller through a second salt bath tank, and the wire rod is controlled to slowly cool to 290°C at a cooling rate of 1.1°C / s; after the hot-rolled wire rod is off the line, the hot-rolled wire rod has a tensile strength of 1661MPa, a cross-sectional shrinkage rate of 25%, and a mechanical property same-circle difference of 47MPa.

[0053] 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

[0054] It can be seen from the results of Examples 1 to 4 that the present invention adopts an Al-containing chemical composition design combined with online molten salt critical quenching isothermal technology. The microstructure type of the hot-rolled wire rod includes a complex phase structure composed of tempered bainite, tempered troostite, and tempered martensite. The tensile strength can reach 1617~1656MPa, and the cross-sectional shrinkage rate is 27%~32%. It can be used to manufacture 2300MPa-level ultra-high strength bridge cables and other application fields, which is beneficial to reduce the risk of wire breakage of the hot-rolled wire rod base material during the wire drawing process.

[0055] From the comparison results of Example 1 and Comparative Example 1, it can be seen that by selecting a higher spinning temperature, on the one hand, the formation of network carbides due to low temperature in the spinning stage can be avoided, while providing favorable conditions for the subsequent formation of a large degree of undercooling and promoting the quenching bainite and quenching martensite phase transformation. On the other hand, the restriction on the rolling temperature can be reduced, which is beneficial to improving the rolling efficiency and reducing the wear of the rolling line.

[0056] From the comparison results of Example 2 and Comparative Example 2, it can be seen that the higher the molten salt temperature of the front stage molten salt and the shorter the treatment time, the less quenched bainite and quenched martensite in the structure, leaving more room for the subsequent transformation of high-temperature austenite to troostite, which can improve the plasticity of the material. However, if the molten salt temperature is too high and the treatment time is too short, the cooling rate and supercooling of the wire rod will decrease, which will affect the efficiency of the short-time mixed phase transformation and the material strength.

[0057] 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 transformation of high-temperature austenite to quenched bainite and quenched martensite can be promoted, and the matrix strength can be increased. However, if the molten salt temperature is too low and the treatment time is too long, there is too little untransformed high-temperature austenite, the tempered troostite in the complex phase structure is reduced, and the difficulty of isothermal tempering is increased, which will affect the plasticity of the material.

[0058] 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 is provided for isothermal tempering, the toughening effect is improved, the tissue stress is reduced, and the plasticity of the material is improved. However, if the molten salt temperature of the latter molten salt is too high, the refinement of the troostite interlamellar spacing and the precipitation rate of vanadium-containing carbides will be affected. If the treatment time is too long, a certain strength loss will be caused. At the same time, there is also the risk of coarsening of vanadium-containing carbides and loss of strength and plasticity.

[0059] 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 and the shorter the treatment time, the more conducive it is to promote the refinement of the interlamellar spacing of the formed troostite, provide more power for the dispersion and precipitation of vanadium-containing carbides, and improve the matrix strength. However, if the molten salt temperature is too low and the treatment time is too short, the isothermal tempering softening effect will be reduced and the brittleness of the wire rod will be significantly increased. At the same time, if the treatment time is too short, the vanadium-containing carbides will not be fully precipitated, resulting in a loss of strength and plasticity.

[0060] From the comparison results of Example 4 and Comparative Example 6, it can be seen that the use of a lower cooling rate for roller slow cooling can prevent the wire rod from cooling too fast during the cooling process, which will cause an increase in stress and improve the softening effect of the wire rod.

[0061] 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 2300MPa grade high-strength multiphase hot-rolled wire rod for bridge cables, characterized in that: The manufacturing method thereof comprises: The wire rod is produced by rolling 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: 0.93%~0.96%, Si: 0.42%~0.58%, Mn: 0.66%~0.82%, Cr: 0.31%~0.41%, V: 0.015%~0.030%, Al: 0.2%~0.4%, P≤0.015%, S≤0.015%, and the rest are Fe and unavoidable impurities; the wire rod is ≥93 After spinning into wire rod at a spinning temperature of 0°C, it is subjected to online molten salt critical quenching isothermal treatment, so that the wire rod first passes through the front section of molten salt and is cooled at a cooling rate of ≥37°C / s, and part of the austenite structure is transformed into a mixed structure of quenched bainite and quenched martensite, and then is heated to the troostite phase region temperature through the rear section of molten salt, and the untransformed austenite is controlled to be transformed into troostite and isothermally tempered, and finally is slowly cooled through a roller to obtain a hot-rolled wire rod with a microstructure including a complex phase structure composed of tempered bainite, tempered troostite and tempered martensite.

2. The method for manufacturing 2300MPa 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 1190-1240° C., and the time in the furnace is 140-200 min.

3. The method for manufacturing 2300MPa 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 1090-1140° C., the final rolling temperature is controlled to be 1010-1030° C., and the final rolling reduction is controlled to be 19%-24%.

4. The method for manufacturing 2300MPa 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 450-475° C., and the processing time is 20-35 seconds; the molten salt temperature of the rear-stage molten salt is 540-580° C., and the processing time is 60-200 seconds.

5. The method for manufacturing 2300MPa 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 550-760 t / h, and the molten salt temperature rise is ≤7°C; the molten salt circulation volume of the rear-stage molten salt is 350-460 t / h, and the molten salt temperature rise is ≤3°C.

6. The method for manufacturing 2300MPa 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 320° C. at a cooling rate of 0.3-0.7° C. / s.

7. A 2300MPa 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 2300MPa-grade high-strength multi-phase hot-rolled wire rod for bridge cables as described in any one of claims 1 to 6.

8. The 2300MPa 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 bainite is 55% to 65%, the interlamellar spacing of the tempered troostite is 70 to 105 nm, and the volume percentage of the tempered martensite is 25% to 32%.

9. The 2300MPa 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 ≤42MPa.

10. The 2300MPa 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 11.0-15.0 mm, a tensile strength of 1617-1656 MPa, and a cross-sectional shrinkage of 27%-32%.

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