A high-strength dual-phase hot-rolled wire rod for 2300 MPa class bridge cables and its manufacturing method

Abstract

The present invention relates to a high-strength duplex hot-rolled wire rod for 2300 MPa-class bridge cables and a manufacturing method thereof. After hot-rolling and coiling the wire rod with a high-carbon steel composition containing Al into a wire rod, through online molten salt critical quenching and isothermal treatment, the wire rod first passes through the front-section molten salt and cools down at a cooling rate of ≥37 °C / s, and part of the austenite structure transforms into a mixed structure of quenched bainite and quenched martensite. Then, it passes through the rear-section molten salt and is heated to the temperature of the sorbite phase region, controlling the untransformed austenite to transform into sorbite and isothermal tempering. Finally, it is slowly cooled through a roller path to produce a hot-rolled wire rod with a duplex structure composed of tempered bainite, tempered sorbite, and tempered martensite in the microstructure, which can take into account the material cost, realize the control of the duplex structure, improve the strength-ductility performance matching and the microstructure uniformity of the wire rod, achieve a tensile strength of 1617~1656 MPa and a reduction of area of 27%~32%, and is conducive to the stable production of ultra-high-strength bridge cables.

Description

Technical Field

[0001] The present invention belongs to the technical field related to hot-rolled wire rods, and particularly relates to a high-strength duplex hot-rolled wire rod for 2300 MPa-class 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 continuously increasing. The higher the bridge cable grade, the greater the load it can bear, and the overall performance, safety, and durability of the bridge can be improved. Bridge cables use hot-rolled wire rods as the base material. After surface treatments such as pickling, they are gradually drawn into wires of the required diameter through multiple passes, and then hot-dip galvanized, post-treated, and twisted and formed. Therefore, it is necessary to improve the performance of the hot-rolled wire rod base material to meet the manufacturing requirements of ultra-high-strength bridge cables.

[0003] Pearlitic steel has relatively high strength, good plasticity, and excellent cold drawing performance, and can be applied to high-stress structural materials such as bridge cables, steel ropes, and spring wires. After cold drawing with different deformation amounts, its products can be applied to fields such as bridges, buildings, transportation, and automobiles. The wire rods for high-strength bridge cable cold-drawn wires in the prior art are generally pearlitic hypereutectoid steels, mainly produced by a Stelmor air-cooling line. For example, a wire rod for high-strength bridge cables and its production method disclosed in Patent CN118880169A uses an 87SiMn composition, combines air cooling by a Stelmor air-cooling line after low-temperature rolling and coiling, and heat preservation in a heat preservation corridor for more than 120 minutes to obtain a wire rod with a high sorbite content, and the strength reaches more than 1400 MPa. However, there are still the following defects:

[0004] First, in order to further improve the strength of the wire rod, in the prior art, the hardenability of the wire rod is improved by increasing the contents of carbon, silicon, manganese, chromium, etc. in the components, in order to obtain refined pearlite lamellae at a lower phase transformation temperature and obtain a better-strength sorbite structure. 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. Due to the limited maximum controlled cooling capacity of the Stelmor air-cooling line, carbon has a greater tendency to precipitate and aggregate in the form of carbides, forming network carbides that affect the tissue uniformity 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 an increase in material cost. Compared with high-strength bainite-based materials, pearlitic steel has the disadvantage of insufficient original strength, resulting in insufficient final strength grade of the wire rod. Subsequently, it is necessary to increase the drawing passes and reduction ratio to improve the material strength, and there is a large loss of plasticity during the process, making it difficult to stably produce 2300 MPa-class bridge cables or unable to reach the corresponding bridge cable grade.

[0005] II. To minimize the reticular carbide level and refine the pearlite lamellar spacing, the existing high-strength bridge cable wire rods generally adopt the Stelmor air-cooling line intensive cooling process. However, on the one hand, affected by the carbon content fluctuation and alloy element segregation of the wire rods, as well as the temperature difference between the windward side and the leeward side of the wire rods under intensive air cooling and the further increase in the temperature difference between the surface and the core, it is easier to form martensite or bainite structures at the positions with fast surface cooling rates. Or due to the continuous cooling of the wire rods through the air-cooling line, the phase transformation time is short and the phase transformation is incomplete, and there will be untransformed austenite in the structure, which will continue to form abnormal structures during subsequent cooling, resulting in uncontrollable bainite or martensite transformation, uneven wire rod structure and large fluctuations in mechanical properties, increasing the risks of drawing wire breakage and torsional cracking. On the other hand, due to the limited controlled cooling capacity of the Stelmor air-cooling line, the bainite structure generated during the production process is quenched bainite, and the quenched bainite has extremely high brittleness. The martensite transformation causes large internal stresses inside the wire rods, and the risk of wire breakage of the hot-rolled wire rod base material during the wire drawing process is extremely high. Therefore, it is difficult to stably develop ultra-high-strength bridge cables.

[0006] III. The precipitation phases of carbonitrides of alloying elements such as vanadium can play roles in precipitation strengthening, grain refinement, and improving toughness and fatigue properties. However, due to the limited controlled cooling capacity of the Stelmor air-cooling line, the wire rods are likely to form coarser phases and finer phases simultaneously due to uncontrollable cooling rates, which not only affects the tissue uniformity, but also the coarsening of the vanadium precipitation phases is unfavorable to the strength and toughness properties of the material. Moreover, during the continuous cooling process, the time for the wire rods to pass through the precipitation temperature range is short, and the precipitation of vanadium-containing carbides is difficult to fully precipitate, affecting the strengthening effect. Summary of the Invention

[0007] The present invention aims to solve at least one of the above technical problems to a certain extent. The present invention provides a high-strength duplex hot-rolled wire rod for 2300 MPa-class bridge cables and a manufacturing method thereof, which can take into account the material cost, realize the regulation of the duplex structure, improve the matching of the strength and plasticity properties of the wire rod and the tissue uniformity, and is conducive to the stable production of ultra-high-strength bridge cables.

[0008] The technical solution adopted by the present invention to solve its technical problems is:

[0009] A manufacturing method of a high-strength duplex hot-rolled wire rod for 2300 MPa-class bridge cables, the manufacturing method comprising:

[0010] The wire rod is rolled according to the chemical composition of the hot-rolled wire rod. 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 inevitable impurities. After the wire rod is spun at a spinning temperature of ≥930°C into a wire rod, it undergoes online molten salt critical quenching and isothermal treatment. The wire rod first passes through the front-section molten salt and cools at a cooling rate of ≥37°C / s, and part of the austenite structure transforms into a mixed structure of quenched bainite and quenched martensite. Then, it passes through the rear-section molten salt and is heated to the temperature in the sorbite phase region, controlling the untransformed austenite to transform into sorbite and isothermal tempering. Finally, it is slowly cooled through the roller path to produce a hot-rolled wire rod with a multiphase structure composed of tempered bainite, tempered sorbite, and tempered martensite in its microstructure.

[0011] The design basis for the chemical composition and mass percentage of the above hot-rolled wire rod includes:

[0012] (1) Carbon: The C element is an effective carbide strengthening element and austenite-forming element, and its price is relatively lower. With the increase of carbon content, it is beneficial to reduce the starting transformation temperature of bainite and martensite, promote short-time quenching during online molten salt critical quenching and isothermal treatment to form a mixed structure including partial quenched bainite and quenched martensite, and reduce the pearlite transformation temperature range. During the rear-section molten salt treatment, it can form pearlite with finer lamellar spacing, that is, sorbite structure, improving the material strength. However, too much carbon content will increase the carbon segregation tendency during the solidification of the steel billet, increase the decarburization sensitivity and the precipitation tendency of network carbide, affecting the plastic and toughness properties of the material. Therefore, in order to meet the high-strength requirements of the 2300MPa-class bridge cable for the hot-rolled wire rod base material, control the material cost, and at the same time reduce the difficulty of multiphase structure regulation and plastic improvement, the mass percentage of C is controlled at 0.93% - 0.96%.

[0013] (2) Silicon: The Si element is the main deoxidizing element in steel, which can improve the strength of steel as a solid-solution hardening element, inhibit the grain coarsening during the front-section molten salt treatment, promote the uniform transformation of the mixed structure during short-time quenching, control the tissue uniformity and improve the matrix strength. However, too high a silicon content will make the steel more prone to decarburization during high-temperature heating and reduce the toughness of the steel. Therefore, in order to refine the grains and facilitate the regulation of the multiphase structure, the mass percentage of Si is controlled at 0.42% - 0.58%.

[0014] (3) Manganese: As an austenite-forming element, Mn can increase the hardenability of the wire rod, shift the bainite and martensite transformations towards lower temperatures. At the same time, Mn 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 lamellar spacing of sorbite. Furthermore, it is conducive to improving the tensile strength of the wire rod, enabling the bridge cable to resist impact and vibration loads while bearing tension. However, when the content of Mn is too high, it will exacerbate alloy element segregation, reduce the activity of carbon, and increase the difficulty of stress relief during isothermal tempering, thereby losing the plasticity of the wire rod. Therefore, in order to facilitate the control of the duplex structure of the hot-rolled wire rod, reduce the tissue uniformity and the difficulty of tempering control, the mass percentage of Mn is controlled at 0.66% - 0.82%.

[0015] (4) Chromium: The Cr element can prevent the growth of austenite grains during heating, playing a role in refining the grains. It can strongly enhance the hardenability of the material. The carbides formed by Cr and carbon can serve as the nucleation cores of bainite and lower the martensite start transformation temperature, which is beneficial to the transformation of the quenched mixed structure. At the same time, it can enhance the stability of austenite, reduce the transformation temperature of sorbite, and is conducive to refining the sorbite lamellar spacing and reducing the strength loss during the subsequent hot-dip galvanizing process of wire rope making. However, when the Cr content is too high, it will exacerbate composition segregation, affect the tissue uniformity of the wire rod, and significantly increase the difficulty of isothermal stress relief of the wire rod, affecting the tempering toughening effect, and further affecting the drawing and torsion properties of the wire. Therefore, in order to facilitate the control of the duplex structure and reduce the difficulty of isothermal tempering, the Cr content is appropriately reduced, and the mass percentage of Cr is controlled at 0.31% - 0.41%.

[0016] (5) Vanadium: The V element can promote grain nucleation and inhibit grain growth. At the same time, during the subsequent molten salt treatment process, it can form fine and dispersed carbonitrides with carbon and nitrogen in the medium-temperature range, which can hinder dislocation movement, thereby playing a role in precipitation strengthening, 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 a risk of coarsening. Based on the role and cost of the V element, the content of the V element in this invention is controlled at 0.015% - 0.030%.

[0017] (6) Aluminum: As a ferrite-forming element, the Al element can inhibit the activity of the C element, inhibit the thickness of cementite lamellae, effectively refine the tissue. The fine austenite grains can form a uniform tissue after cooling transformation, refining the sorbite tissue, which is beneficial to improving the strength and toughness of the steel. At the same time, it has a lower cost compared to the Mo element that can inhibit the coarsening of cementite, which is beneficial to controlling the material cost. However, when the Al content is too high, it will increase the risk of inclusions, thereby reducing the fatigue performance of the steel. Therefore, the Al content is increased, and the mass percentage of Al is controlled at 0.2% - 0.4%.

[0018] (7) Phosphorus and sulfur: The P element and S element belong to impurity elements, and the lower the better. Therefore, P ≤ 0.015% and S ≤ 0.015% are controlled.

[0019] The above hot-rolled wire rods adopt a high-carbon steel composition design containing V and Al, and the hardenability of the wire rods is regulated by optimizing the ratios of Si, Mn, and Cr. The starting temperatures of bainite and martensite are appropriately reduced, and the thickening of cementite lamellae and grain coarsening are inhibited, providing favorable conditions for obtaining a partially quenched mixed structure by short-time molten salt quenching in the front stage. The temperature range of the sorbite phase region is appropriately regulated to be at a relatively high temperature and can adapt to the temperature range of a large amount of dispersed precipitation of vanadium carbides, providing favorable conditions for the isothermal phase transformation and tempering of the molten salt in the latter stage. On this basis, a relatively high spinning temperature is selected to keep the wire rods in a high-temperature austenite state, avoiding the formation of network carbides during the spinning stage due to low temperature, and at the same time providing favorable conditions for forming a large supercooling degree later to promote the phase transformation of quenched bainite and quenched martensite. After spinning, direct online molten salt critical quenching is carried out through molten salt:

[0020] I. Compared with the limited maximum cooling capacity, uncontrollable cooling rate, and continuous cooling operation of the Stelmor air-cooling line, when the wire rods pass through the molten salt in the front stage, they can exchange heat with the molten salt more quickly and uniformly. On the one hand, the wire rods can be quickly cooled from the high-temperature austenite state, skipping the secondary cementite precipitation temperature range of 700 - 800 °C, avoiding the formation of network carbides in high-carbon steel wire rods due to the high carbon content and eccentricity, preventing the network carbides from damaging the tissue uniformity and the plasticity of the wire rods, and improving the utilization of carbon elements. On the other hand, the wire rods can be quickly cooled and the temperature difference between the edge and the core of the wire rods can be reduced. Strong air-cooling does not have the problem of temperature difference between the windward side and the leeward side, and can form a large supercooling degree. Combined with Si and Al, it inhibits grain and cementite lamella coarsening, providing more sites for the nucleation of quenched bainite and quenched martensite phase transformation. Through short-time mixed phase transformation, part of the high-temperature austenite structure in the tissue transforms into quenched bainite and quenched martensite, making the phase transformation of the low-temperature quenched structure, which is usually regarded as an abnormal structure, more uniform and controllable, thereby improving the matrix strength, controlling the tissue uniformity, and mechanical property fluctuations.

[0021] II. Compared with the limited minimum cooling capacity and continuous cooling operation of the Stelmor air-cooled line, the wire rod can be heated to the same temperature as the molten salt through heat exchange after passing through the post-section molten salt treatment. On the one hand, it can control the wire rod to rise to the temperature of the sorbite phase region, extend the phase transformation time, control the untransformed high-temperature austenite structure after passing through the pre-section molten salt quenching, and transform it into a sorbite structure with a fine lamellar spacing, promote the full phase transformation of the structure, avoid the formation of martensite structure during the subsequent slow cooling process of the roller table ring due to residual austenite, and at the same time, in the temperature range where a large amount of vanadium carbides are precipitated in a dispersed manner, it can extend the precipitation time of the fine precipitates, promote the uniform and full dispersion precipitation of vanadium carbides, give full play to the strengthening and toughening effect of vanadium, and improve the structural uniformity; on the other hand, the temperature of the sorbite phase region is higher than the molten salt temperature of the pre-section molten salt, which can extend the treatment time of the wire rod in the high-temperature section, provide more thermal power for the tempering of the structure. After isothermal tempering, control the formed duplex structure to undergo a certain degree of short-time tempering, transform the quenched martensite and quenched bainite into a strong and tough tissue state, promote the sorbite structure to reduce internal stress and transform into a tempered state, quickly improve the plasticity of the structure, and enhance the strength-plasticity matching of the wire rod; due to the high temperature of the wire rod after passing through the post-section molten salt and slow cooling through the roller table slow cooling, it can prevent the wire rod from cooling too fast during the cooling process, resulting in increased stress, and can also promote the further toughening of the wire rod structure by continuing the softening effect of the high-temperature treatment, realizing the regulation of the duplex structure and the strength and plasticity performance.

[0022] Before the rolling, selecting appropriate heating furnace parameters can reduce the deformation resistance of the material during rolling, promote the uniform diffusion of components, reduce alloy element segregation, and avoid excessive grain growth and decarburization due to too long time in the furnace. In the preferred technical solution, before the rolling, control the soaking temperature of the heating furnace to be 1190~1240 °C, and the time in the furnace to be 140~200 min.

[0023] Due to the higher spinning temperature and less restriction on the rolling temperature, selecting a higher rolling temperature can reduce the deformation resistance of the wire rod and the wear on the rolling line, adopt a larger reduction ratio and a higher rolling speed, improve production efficiency, eliminate the defects of the as-cast structure, and promote the dynamic recrystallization during the finishing rolling process, making the grains refined and uniform, strengthening and toughening the matrix. In the preferred technical solution, during the rolling, control the initial rolling temperature to be 1090~1140 °C, the finishing rolling temperature to be 1010~1030 °C, and the finishing rolling reduction ratio to be 19%~24%.

[0024] 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 - 35 s. The lower the molten salt temperature of the front-stage molten salt and the longer the treatment time, the more conducive to the transformation of high-temperature austenite into quenched bainite and quenched martensite. Meanwhile, 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 bainite phase transformation during quenching will be affected, and the amount of untransformed high-temperature austenite is too small, which will affect the plasticity of the material. On the contrary, 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 into sorbite, 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 degree of the wire rod will decrease, which will affect the control of network carbide and the efficiency of short-time mixed phase transformation. The proportion of tempered bainite and tempered martensite in the duplex structure is too small, which will affect the strength of the material. Therefore, the molten salt temperature and treatment time of the front-stage molten salt can be further controlled to control the short-time mixed phase transformation of partial high-temperature austenite, regulate the matrix strength, and prepare for the subsequent regulation of the duplex structure.

[0025] In the preferred technical solution, the molten salt temperature of the rear-stage molten salt is 540 - 580 °C, and the treatment time is 60 - 200 s. The lower the molten salt temperature of the rear-stage molten salt, the more conducive to promoting the refinement of the interlamellar spacing of the formed sorbite and providing more driving force for the precipitation of vanadium-containing carbides, so as to improve the matrix strength. However, if the molten salt temperature is too low, the isothermal tempering effect will be affected, and the plasticity of the material will be reduced. If the molten salt temperature is lower than the medium-temperature range of vanadium-containing carbides, the precipitation of vanadium-containing carbides will also be affected, affecting the strength of the material. On the contrary, the higher the molten salt temperature, the more conducive to providing more thermal driving force for isothermal tempering, improving the toughening effect, reducing the tissue stress, and improving the plasticity of the material. However, if the molten salt temperature is too high, it will affect the refinement of the interlamellar spacing of sorbite and the precipitation rate of vanadium-containing carbides. The longer the treatment time of the front-stage molten salt, the more obvious the toughening effect of the duplex structure after isothermal tempering. However, if the treatment time is too long, it will cause a certain loss of strength, and there is also a risk of coarsening of vanadium-containing carbides, resulting in a loss of strength and plasticity. On the contrary, the shorter the treatment time, the worse the isothermal tempering effect and the lower 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 will not precipitate sufficiently, significantly increasing the brittleness of the wire rod. Even due to the remaining austenite, abnormal tissues and mechanical property fluctuations will be caused during subsequent cooling. Therefore, the molten salt temperature and treatment time of the rear-stage molten salt can be further controlled to control the full transformation of the austenite structure, promote the full and uniform precipitation of vanadium-containing carbides, regulate the tempering state and toughening effect of the duplex structure, and improve the strength-plasticity matching of the wire rod.

[0026] Due to the large temperature difference during the cooling and quenching of the wire rod from the high-temperature austenite state, a larger molten salt circulation rate is selected to reduce the temperature rise of the molten salt, increase the supercooling degree, and promote short-time uniform phase transformation. In the preferred technical solution, the molten salt circulation rate of the front-section molten salt is 550 - 760 t / h, and the temperature rise of the molten salt ≤ 7°C;

[0027] Since the temperature difference between the front-section molten salt and the rear-section molten salt is relatively small, as latent heat is released during the phase transformation, the molten salt circulation rate of the rear-section molten salt can be appropriately reduced compared to the front-section molten salt. While accurately controlling the temperature, production energy consumption can be reduced. In the preferred technical solution, the molten salt circulation rate of the rear-section molten salt is 350 - 460 t / h, and the temperature rise of the molten salt ≤ 3°C.

[0028] Since the wire rod enters the conveying roller table at 540 - 580°C after passing through the rear-section molten salt for slow cooling control on the roller table, selecting a lower cooling rate can prevent the stress from increasing due to too fast cooling rate during the cooling process of the wire rod, and promote further toughening of the wire rod structure, improve the softening effect of the wire rod, and also avoid too slow cooling rate resulting in too long online time. In the preferred technical solution, the wire rod is slowly cooled to below 320°C at a cooling rate of 0.3 - 0.7°C / s during the slow cooling control on the roller table.

[0029] A 2300 MPa grade high-strength duplex hot-rolled wire rod for bridge cables, wherein the hot-rolled wire rod is obtained by manufacturing with the manufacturing method of the 2300 MPa grade high-strength duplex hot-rolled wire rod for bridge cables described in any one of the above.

[0030] The above hot-rolled wire rod adopts a 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. Combining with the online molten salt critical quenching isothermal technology, a composite structure composed of tempered bainite, tempered sorbite, and tempered martensite is obtained. Among them, compared with the pearlite structure, quenched bainite has higher hardness and better fatigue resistance. After isothermal tempering, the structure of quenched bainite is finer and more uniform, and carbides are dispersed, transforming into tempered bainite with significantly improved toughness; quenched martensite has high strength and hardness, but poor toughness and a large amount of lattice distortion inside. After high-temperature isothermal tempering, the structure of quenched martensite is more refined, and the internal stress and distortion are significantly improved, transforming into tempered martensite structure with both strength and toughness, having good comprehensive mechanical properties; sorbite has finer lamellar spacing, better strength and hardening ability than pearlite. After high-temperature isothermal tempering, the structure stress of sorbite further decreases, transforming into tempered sorbite structure with better plasticity, and vanadium-containing carbides are evenly dispersed; therefore, compared with traditional pearlitic high-carbon steel, the above hot-rolled wire rod can adjust the tempered state of the duplex structure to maximize the strengthening effect of carbon and vanadium elements, improve the overall strength and plasticity matching of the wire rod, and improve the tissue uniformity of the wire rod.

[0031] In the duplex structure, the higher the volume percentage of the tempered bainite, the higher the matrix strength. In the preferred technical solution, the volume percentage of the tempered bainite is 55% - 65%.

[0032] In the duplex structure, the finer the lamellar spacing of the tempered sorbite, the higher the matrix strength. In the preferred technical solution, the lamellar spacing of the tempered sorbite is 70 - 105 nm.

[0033] In the duplex structure, the higher the proportion of the tempered martensite, the higher the matrix strength. In the preferred technical solution, the volume percentage of the tempered martensite is 25% - 32%.

[0034] In the preferred technical solution, the reticular carbide grade of the hot-rolled wire rod is grade 0, which can reduce the increase in brittleness caused by a large amount of continuous carbides, better exert the mechanical properties of the matrix, improve the strengthening effect of carbon elements and the tissue uniformity.

[0035] Since it can effectively avoid the abnormal structure of reticular carbides formed by carbon elements and transform quenched martensite into tempered martensite with both high strength and plasticity, it can further reduce the mechanical property fluctuation of the hot-rolled wire rod. In the preferred technical solution, the mechanical property difference within the same coil of the hot-rolled wire rod ≤ 42 MPa.

[0036] In the preferred technical solution, the diameter of the hot-rolled wire rod is 11.0 - 15.0 mm, the tensile strength is 1617 - 1656 MPa, and the reduction of area is 27% - 32%. The hot-rolled wire rod has higher tensile strength and good reduction of area, which can reduce the subsequent drawing passes and reduction rate, reduce the plastic loss during the process, reach the performance grade faster, meet the manufacturing requirements of 2300-grade bridge cables, reduce the fracture risk during drawing and torsion, and thus stably develop ultra-high strength bridge cables.

[0037] Compared with the prior art, the beneficial effects of the present invention are at least as follows:

[0038] (1) Aiming at the current situation that the domestic cold-drawn steel wire production mainly uses the Stelmor air-cooling line, but due to the limited controlled cooling ability of the Stelmor air-cooling line, the bainite structure generated during the production process is quenched bainite with extremely high brittleness, and the risk of wire breakage of the hot-rolled wire rod base material during the wire drawing process is extremely high. The present invention combines the Al-containing chemical composition design with the online molten salt critical quenching and isothermal technology to control the rapid cooling of the wire rod from the high-temperature austenite state, promote the transformation of part of the austenite structure into a mixed structure of quenched bainite and quenched martensite, then heat the molten salt in the latter stage to the temperature of the sorbite phase region, control the transformation of the untransformed austenite into sorbite and isothermal tempering, and finally promote the further toughening of the wire rod structure through slow cooling on the roller table, which can take into account the material cost, realize the regulation of the duplex structure, improve the matching of the strength and plasticity of the wire rod and the tissue uniformity, and has good industrial adaptability.

[0039] (2) In view of the current situation that the hot-rolled wire rods for high-strength bridge cables have insufficient strength and plasticity, it is difficult to control the tissue uniformity, and it is difficult to stably develop ultra-high-strength bridge cables. The hot-rolled wire rods of the present invention can effectively avoid the abnormal structure of network carbide formed by C element, transform quenched bainite and quenched martensite into tempered bainite and tempered martensite with both strength and plasticity, improve the strengthening effect of carbon element, inhibit the thickness of cementite lamella with Al element, effectively refine the tissue, promote the uniform and dispersed distribution of vanadium carbide, and the microstructure type includes the complex phase structure composed of tempered bainite, tempered sorbite and tempered martensite. Compared with pearlitic steel, it can improve the tensile strength, take into account good plasticity, reach a tensile strength of 1617-1656 MPa and a reduction of area of 27%-32%, and is used in application fields such as manufacturing 2300 MPa grade ultra-high-strength bridge cables, etc., which can effectively reduce the wire breakage risk of the hot-rolled wire rod base material during the wire drawing process and has good market application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The above and / or additional aspects and advantages of the present invention will become obvious and easy to understand from the description of the embodiments in conjunction with the following drawings, wherein:

[0041] Figure 1 is the metallographic structure diagram of Embodiment 1 of the present invention;

[0042] Figure 2 is the metallographic structure diagram of Embodiment 2 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0043] The embodiments described below with reference to the drawings are exemplary, only for illustrative purposes and do not limit the description of the features and characteristics of the present invention. To propose the best way to implement the present invention, it is intended to explain the present invention and is sufficient for those skilled in the art to implement the present invention, and should not be construed as having any limitation on the scope of the present invention. The scope of the present invention is only defined by the appended claims; the tissue and performance detection of the hot-rolled wire rods obtained in the following embodiments and comparative examples include: the tensile test is carried out according to "GB-T 228.1-2021 Metallic materials-Tensile testing-Part 1: Method of test at room temperature" to obtain the tensile strength and reduction of area; the tissue detection is carried out according to the metallic microstructure detection method of the GB / T13298 standard; the method for testing the difference of mechanical properties in the same coil: take 2 coils of wire rods at 5 m from the end of the coil, take the lap area position as the base point, divide each coil of wire rods into 8 equal segments on average, take 1 tensile specimen on each segment, and the strength range of the tensile specimens after the tensile test is the difference of mechanical properties in the same coil. Embodiment 1:

[0044] A preferred embodiment of the manufacturing method of the high-strength duplex hot-rolled wire rod for 2300 MPa-class bridge cables according to 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 inevitable impurities. Its manufacturing method is manufactured according to the technological process of rolling → wire laying → on-line molten salt critical quenching and isothermal treatment → slow cooling on the roller table → coiling. Specifically:

[0045] The rolling process is used to heat the steel billet with a specification of 220 mm × 220 mm into a high-temperature steel billet that reaches the plastic state for rolling, promoting the homogenization of alloy components and reducing segregation. After the steel billet exits the heating furnace, the steel billet is rolled into a wire rod with a diameter specification of 13 mm through the rolling line. A higher rolling temperature is selected to increase the rolling speed, promote dynamic recrystallization in the finishing rolling process, refine grains, and strengthen and toughen the matrix. Specifically: control the soaking temperature of the heating furnace to be 1200 °C, the residence time in the furnace to be 160 min, the initial rolling temperature to be 1105 °C, the finishing rolling temperature to be 1015 °C, and the finishing rolling reduction to be 23%; The wire laying process is used to make the wire rod exiting the rolling line into a coil through the wire laying machine. The coil is scattered on the roller table and conveyed along the roller table, making the coil in the high-temperature austenite state. Appropriately increase the wire laying temperature to provide favorable conditions for forming a larger supercooling degree and promoting the phase transformation of quenched bainite and quenched martensite. Specifically: control the wire laying temperature to be 940 °C.

[0046] The on-line molten salt critical quenching and isothermal treatment process uses a two-stage salt bath tank with molten salt inside. The coil after wire laying is conveyed through the roller table and passes through the first-stage salt bath tank for the front-stage molten salt treatment, so that the coil cools down at a cooling rate of 39 °C / s, quickly skips the network carbide precipitation interval from the high-temperature austenite state, increases the supercooling degree, promotes the transformation of part of the austenite structure into a mixed structure of quenched bainite and quenched martensite, and undergoes short-time mixed phase transformation. Then the coil is conveyed through the roller table and passes through the second-stage salt bath tank for the rear-stage molten salt treatment. The rear-stage molten salt is heated to the temperature of the sorbite phase region, controlling the untransformed austenite to transform into fine lamellar spacing sorbite, promoting the massive dispersion precipitation of vanadium-containing carbides, and after isothermal tempering, controlling the formed mixed structure to undergo a certain degree of short-time tempering, improving the strength-plasticity matching of the coil. Specifically: the molten salt temperature of the front-stage molten salt is 456 °C, the treatment time is 24 s, the molten salt circulation volume is 655 t / h, and the molten salt temperature rise ≤ 7 °C; the molten salt temperature of the rear-stage molten salt is 563 °C, the treatment time is 180 s, the molten salt circulation volume is 440 t / h, and the molten salt temperature rise ≤ 3 °C.

[0047] In the roller table slow cooling process, the heat preservation cover is closed, and the wire rod passing through the second salt bath tank is conveyed into the heat preservation cover by the conveying roller table to prevent the wire rod from cooling too fast during the cooling process, which may cause an increase in stress, promote further toughening of the wire rod structure, and improve the softening effect of the wire rod. Specifically: control the wire rod to cool slowly at a cooling rate of 0.6 °C / s to 310 °C; the coiling process is used to coil the wire rod into coils through a coiling drum, and after packaging and warehousing, the finished hot-rolled wire rod is obtained. Its metallographic structure diagram is as shown in Figure 1 shown.

[0048] Comparative Example 1:

[0049] A manufacturing method of hot-rolled wire rod, the difference between its manufacturing method and that of Example 1 is: control the soaking temperature of the heating furnace to be 1150 °C, the residence time in the furnace to be 210 min, the rough rolling temperature to be 1085 °C, the finish rolling temperature to be 945 °C, the spinning temperature to be 875 °C, and when the front-section molten salt treatment is carried out, the wire rod cools down at a cooling rate of 33 °C / s, and the hot-rolled wire rod is obtained after being taken off the production line. Example 2:

[0050] A preferred implementation manner of the manufacturing method of the 2300 MPa grade high-strength duplex hot-rolled wire rod for bridge cables according to 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 are Fe and inevitable impurities; its manufacturing method is carried out according to the technological process of rolling → spinning → on-line molten salt critical quenching and isothermal treatment → roller table slow cooling → coiling. Specifically:

[0051] The rolling process is used to heat the steel billet with a specification of 220 mm × 220 mm into a high-temperature steel billet that reaches the plastic state for rolling through a heating furnace, promoting the homogenization of alloy components and reducing segregation. After the steel billet exits the heating furnace, the steel billet is rolled into a wire rod with a diameter specification of 11 mm through a rolling line. A higher rolling temperature is selected to increase the rolling speed, promote dynamic recrystallization and grain refinement during the finish rolling process, and strengthen and toughen the matrix. Specifically: control the soaking temperature of the heating furnace to be 1190 °C, the residence time in the furnace to be 200 min, the rough rolling temperature to be 1090 °C, the finish rolling temperature to be 1010 °C, and the finish rolling reduction to be 24%; the spinning process is used to make the wire rod exiting the rolling line into a wire rod through a spinning machine. The wire rod is scattered on the roller table and conveyed along the roller table, making the wire rod in a high-temperature austenite state. Appropriately increase the spinning temperature to provide favorable conditions for forming a larger supercooling degree and promoting the phase transformation of quenched bainite and quenched martensite. Specifically: control the spinning temperature to be 930 °C.

[0052] The online molten salt critical quenching isothermal treatment process uses a two-stage salt bath tank with internal molten salt. The wire rod after wire drawing is transported through the first-stage salt bath tank by a roller table for the front-stage molten salt treatment, so that the wire rod cools down at a cooling rate of 37 °C / s, quickly skips the reticular carbide precipitation range from the high-temperature austenite state, increases the supercooling degree, promotes the transformation of part of the austenite structure into a mixed structure of quenched bainite and quenched martensite, and undergoes short-term mixed phase transformation. Then, the wire rod is transported through the second-stage salt bath tank by a roller table for the back-stage molten salt treatment. The temperature of the back-stage molten salt is raised to the temperature of the sorbite phase region, and the untransformed austenite is controlled to transform into sorbite with a fine lamellar spacing, promoting the massive dispersion precipitation of vanadium-containing carbides. After isothermal tempering, the formed mixed structure is controlled to undergo a certain degree of short-term tempering, improving the strength-plasticity matching of the wire rod. Specifically: the molten salt temperature of the front-stage molten salt is 467 °C, the treatment time is 31 s, the molten salt circulation rate is 550 t / h, and the molten salt temperature rise is ≤7 °C; the molten salt temperature of the back-stage molten salt is 555 °C, the treatment time is 135 s, the molten salt circulation rate is 380 t / h, and the molten salt temperature rise is ≤3 °C.

[0053] The roller table slow cooling process adopts closing the heat preservation cover. The wire rod transported by the conveying roller table after passing through the second-stage salt bath tank enters the heat preservation cover to prevent the wire rod from increasing stress due to too fast cooling rate during the cooling process, promoting the further toughening of the wire rod structure and improving the softening effect of the wire rod. Specifically: the wire rod is 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 by a coiling drum, and after packaging and warehousing, the finished hot-rolled wire rod is obtained, and its metallographic structure diagram is as Figure 2 shown.

[0054] Comparative Example 2:

[0055] A manufacturing method of a hot-rolled wire rod, the difference in its manufacturing method from that of Example 2 is that: the molten salt temperature of the front-stage molten salt is controlled to be 485 °C, the treatment time is 5 s, and the wire rod cools down at a cooling rate of 36 °C / s during the front-stage molten salt treatment, and the hot-rolled wire rod is obtained after being taken off the production line.

[0056] Comparative Example 3:

[0057] A manufacturing method of a hot-rolled wire rod, the difference in its manufacturing method from that of Example 2 is that: the molten salt temperature of the front-stage molten salt is controlled to be 435 °C, the treatment time is 45 s, and the wire rod cools down at a cooling rate of 41 °C / s during the front-stage molten salt treatment, and the hot-rolled wire rod is obtained after being taken off the production line. Example 3:

[0058] A preferred embodiment of the manufacturing method of the high-strength duplex hot-rolled wire rod for 2300 MPa-class bridge cables according to 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 inevitable impurities. Its manufacturing method is manufactured according to the technological process of rolling → wire laying → on-line molten salt critical quenching and isothermal treatment → slow cooling on the roller table → coiling. Specifically:

[0059] The rolling process is used to heat a steel billet with a specification of 220 mm × 220 mm into a high-temperature steel billet that reaches the plastic state for rolling through a heating furnace, promoting the homogenization of alloy components and reducing segregation. After the steel billet exits the heating furnace, the steel billet is rolled into a wire rod with a diameter specification of 14 mm through a rolling line. A higher rolling temperature is selected to increase the rolling speed, promote dynamic recrystallization and grain refinement in the finishing rolling process, and strengthen and toughen the matrix. Specifically: control the soaking temperature of the heating furnace to be 1240 °C, the residence time in the furnace to be 140 min, the initial rolling temperature to be 1140 °C, the finishing rolling temperature to be 1030 °C, and the finishing rolling reduction to be 21%; The wire laying process is used to make the wire rod exiting the rolling line into a wire coil through a wire laying machine. The wire coil is scattered on the roller table and transported along the roller table, making the wire coil in a high-temperature austenite state. Appropriately increase the wire laying temperature to provide favorable conditions for forming a larger supercooling degree and promoting the phase transformation of quenched bainite and quenched martensite. Specifically: control the wire laying temperature to be 955 °C.

[0060] The on-line molten salt critical quenching and isothermal treatment process uses a two-stage salt bath tank with molten salt inside. The wire coil after wire laying is transported through the first-stage salt bath tank by the roller table for the front-stage molten salt treatment, so that the wire coil cools down at a cooling rate of 41 °C / s, quickly skips the reticular carbide precipitation interval from the high-temperature austenite state, increases the supercooling degree, promotes the transformation of part of the austenite structure into a mixed structure of quenched bainite and quenched martensite, and undergoes a short-time mixed phase transformation. Then the wire coil is transported through the second-stage salt bath tank by the roller table for the rear-stage molten salt treatment. The temperature of the rear-stage molten salt is raised to the temperature of the sorbite phase region, controlling the untransformed austenite to transform into fine lamellar-spacing sorbite, promoting the massive dispersion precipitation of vanadium-containing carbides, and after isothermal tempering, controlling the formed mixed structure to undergo a certain degree of short-time tempering to improve the strength-plasticity matching of the wire coil. Specifically: the molten salt temperature of the front-stage molten salt is 450 °C, the treatment time is 35 s, the molten salt circulation volume is 760 t / h, and the molten salt temperature rise ≤ 7 °C; the molten salt temperature of the rear-stage molten salt is 580 °C, the treatment time is 200 s, the molten salt circulation volume is 460 t / h, and the molten salt temperature rise ≤ 3 °C.

[0061] In the roller table slow cooling process, the heat preservation cover is closed, and the wire rods passing through the second salt bath tank are transported into the heat preservation cover by the conveying roller table to prevent the wire rods from cooling too fast during the cooling process, which may lead to an increase in stress, promote further toughening of the wire rod structure, and improve the softening effect of the wire rods. Specifically: control the wire rods to cool slowly at a cooling rate of 0.7 °C / s to 318 °C; the coiling process is used to coil the wire rods into coils through a coiling drum, and after packaging and warehousing, the finished hot-rolled wire rods are obtained.

[0062] Comparative Example 4:

[0063] A manufacturing method of hot-rolled wire rods, the difference between its manufacturing method and that of Example 3 lies in: controlling the molten salt temperature of the latter-stage molten salt to be 595 °C, the treatment time to be 250 s, and obtaining hot-rolled wire rods after offline.

[0064] Comparative Example 5:

[0065] A manufacturing method of hot-rolled wire rods, the difference between its manufacturing method and that of Example 3 lies in: controlling the molten salt temperature of the latter-stage molten salt to be 525 °C, the treatment time to be 50 s, and obtaining hot-rolled wire rods after offline. Example 4:

[0066] A preferred implementation of the manufacturing method of the 2300 MPa grade high-strength duplex hot-rolled wire rods for bridge cables described in the present invention. The chemical composition and mass percentage of the hot-rolled wire rods 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 inevitable impurities; its manufacturing method is carried out according to the technological process of rolling → wire laying → on-line molten salt critical quenching and isothermal treatment → roller table slow cooling → coiling. Specifically:

[0067] The rolling process is used to heat the steel billet with a specification of 220 mm × 220 mm into a high-temperature steel billet that reaches the plastic state for rolling through a heating furnace, promoting the homogenization of alloy components and reducing segregation. After the steel billet exits the heating furnace, the steel billet is rolled into wire rods with a diameter specification of 15 mm through a rolling line. A relatively high rolling temperature is selected to increase the rolling speed, promote dynamic recrystallization during the finishing rolling process, refine the grains, and strengthen and toughen the matrix. Specifically: control the soaking temperature of the heating furnace to be 1220 °C, the time in the furnace to be 180 min, the initial rolling temperature to be 1125 °C, the finishing rolling temperature to be 1025 °C, and the finishing rolling reduction to be 19%; the wire laying process is used to make the wire rods exiting the rolling line into wire coils through a wire laying machine. The wire coils are scattered on the roller table and transported along the roller table, making the wire coils in a high-temperature austenite state. Appropriately increase the wire laying temperature to provide favorable conditions for forming a large supercooling degree and promoting the phase transformation of quenched bainite and quenched martensite. Specifically: control the wire laying temperature to be 950 °C.

[0068] The online molten salt critical quenching isothermal treatment process uses a two-stage salt bath tank with internal molten salt. The wire rod after wire drawing is transported through the first-stage salt bath tank by a roller table for the front-stage molten salt treatment, so that the wire rod cools down at a cooling rate of 38 °C / s, quickly skips the network carbide precipitation range from the high-temperature austenite state, increases the supercooling degree, promotes the transformation of part of the austenite structure into a mixed structure of quenched bainite and quenched martensite, and undergoes short-term mixed phase transformation. Then, the wire rod is transported through the second-stage salt bath tank by a roller table for the back-stage molten salt treatment. The temperature of the back-stage molten salt is raised to the temperature of the sorbite phase region, controlling the untransformed austenite to transform into sorbite with a fine lamellar spacing, promoting the massive dispersion precipitation of vanadium carbides, and after isothermal tempering, controlling the formed mixed structure to undergo a certain degree of short-term tempering, improving the strength-plasticity matching of the wire rod. Specifically: the molten salt temperature of the front-stage molten salt is 475 °C, the treatment time is 20 s, the molten salt circulation rate is 590 t / h, and the molten salt temperature rise ≤ 7 °C; the molten salt temperature of the back-stage molten salt is 540 °C, the treatment time is 60 s, the molten salt circulation rate is 350 t / h, and the molten salt temperature rise ≤ 3 °C.

[0069] The roller table slow cooling process adopts closing the heat preservation cover. The wire rod transported by the conveying roller table through the second-stage salt bath tank enters the heat preservation cover to prevent the wire rod from having too fast a cooling rate during the cooling process, resulting in an increase in stress, promoting the further toughening of the wire rod structure, and improving the softening effect of the wire rod. Specifically: controlling the wire rod 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 after packaging and warehousing, the finished product of the hot-rolled wire rod is obtained.

[0070] Comparative Example 6:

[0071] A manufacturing method of a hot-rolled wire rod, the difference in its manufacturing method from that of Example 4 lies in: controlling the roller table slow cooling to adopt opening the heat preservation cover, transporting the wire rod transported by the conveying roller table through the second-stage salt bath tank, and controlling the wire rod to slowly cool to 290 °C at a cooling rate of 1.1 °C / s; after being taken off the production line, the hot-rolled wire rod is obtained. The tensile strength of the hot-rolled wire rod is 1661 MPa, the reduction of area is 25%, and the mechanical property difference within the same coil is 47 MPa.

[0072] The hot-rolled wire rods obtained from the above Examples 1 to 4 and Comparative Examples 1 to 5 were subjected to microstructure and property tests, and the comparison results obtained are shown in Table 1 below:

[0073] Table 1. Comparison results of the microstructure and properties of different hot-rolled wire rod compositions and manufacturing methods

[0074]

[0075] As can be seen from the results of Examples 1 to 4, the present invention adopts an Al-containing chemical composition design combined with an online molten salt critical quenching isothermal technology. The microstructure type of the hot-rolled wire rod includes a duplex structure composed of tempered bainite, tempered sorbite, and tempered martensite, with a tensile strength of 1617-1656 MPa and a reduction of area of 27%-32%. It can be used in application fields such as manufacturing 2300 MPa grade ultra-high strength bridge cables, which is beneficial to reducing the wire breakage risk of the hot-rolled wire rod base material during the wire drawing process.

[0076] As can be seen from the comparison results of Example 1 and Comparative Example 1, choosing a higher wire laying temperature, on the one hand, can avoid the formation of network carbides during the wire laying stage due to low temperature, and at the same time provide favorable conditions for forming a larger supercooling degree in the subsequent stage to promote the phase transformation of quenched bainite and quenched martensite. On the other hand, it can reduce the limitation on the rolling temperature, which is beneficial to improving the rolling efficiency and reducing the wear of the rolling line.

[0077] As can be seen from the comparison results of Example 2 and Comparative Example 2, the higher the molten salt temperature and the shorter the treatment time of the front-stage molten salt, the less quenched bainite and quenched martensite in the structure, leaving more space for the subsequent transformation of high-temperature austenite to sorbite, 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 degree of the wire rod will decrease, affecting the efficiency of short-time mixed phase transformation and the strength of the material.

[0078] As can be seen from the comparison results of Example 2 and Comparative Example 3, the lower the molten salt temperature and the longer the treatment time of the front-stage molten salt, the more favorable it is to promote the transformation of high-temperature austenite to quenched bainite and quenched martensite, increasing the matrix strength. However, if the molten salt temperature is too low and the treatment time is too long, there will be too little untransformed high-temperature austenite, and the tempered sorbite in the duplex structure will decrease, increasing the difficulty of isothermal tempering and affecting the plasticity of the material.

[0079] As can be seen from the comparison results of Example 3 and Comparative Example 4, the higher the molten salt temperature and the longer the treatment time of the rear-stage molten salt, it is beneficial to provide more thermal power for isothermal tempering, improve the toughening effect, reduce the tissue stress, and improve the plasticity of the material. However, if the molten salt temperature of the rear-stage molten salt is too high, it will affect the refinement of the sorbite lamellar spacing and the precipitation rate of vanadium-containing carbides. If the treatment time is too long, there will be a certain strength loss, and there will also be a risk of coarsening of the vanadium-containing carbides, resulting in a loss of strength and plasticity.

[0080] As can be seen from the comparison results of Example 3 and Comparative Example 5, the lower the molten salt temperature and the shorter the treatment time of the rear-stage molten salt, it is beneficial to promote the refinement of the formed sorbite lamellar spacing and provide more driving force for the dispersion precipitation of vanadium-containing carbides, increasing the matrix strength. However, if the molten salt temperature is too low and the treatment time is too short, the softening effect of isothermal tempering will be reduced, significantly increasing the brittleness of the wire rod. At the same time, if the treatment time is too short, the vanadium-containing carbides will not precipitate sufficiently, resulting in a loss of strength and plasticity.

[0081] From the comparison results of Example 4 and Comparative Example 6, it can be seen that selecting a lower cooling rate for slow cooling on the roller table can prevent the cooling rate of the wire rod from being too fast during cooling, resulting in increased stress, and improve the softening effect of the wire rod.

[0082] The series of detailed descriptions listed above are only specific descriptions of the feasible embodiments of the present invention, and they are not intended to limit the protection scope of the present invention. Any equivalent embodiments or changes made without departing from the technical spirit of the present invention should be included in the protection scope 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% to 0.96%, Si: 0.42% to 0.58%, Mn: 0.66% to 0.82%, Cr: 0.31% to 0.41%, V: 0.015% to 0.030%, Al: 0.2% to 0.4%, P≤0.015%, S≤0.015%, and the rest are Fe and unavoidable impurities; after the wire rod is spun into a wire rod at a spinning temperature of ≥930°C, it is subjected to an online molten salt critical quenching isothermal treatment, so that the wire rod is first subjected to The steel wire is passed through the front section molten salt and cooled at a cooling rate of ≥37°C / s, so that part of the austenite structure is transformed into a mixed structure of quenched bainite and quenched martensite, and then the temperature is raised to the troostite phase temperature through the rear section molten salt, and the untransformed austenite is controlled to be transformed into troostite and isothermally tempered, and finally 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; the molten salt temperature of the front section molten salt is 450-475°C, and the processing time is 20-35s; the molten salt temperature of the rear section molten salt is 540-580°C, and the processing time is 60-200s.

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 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.

5. 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 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.

6. 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 5.

7. The 2300MPa grade high-strength multi-phase hot-rolled wire rod for bridge cables according to claim 6, 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%.

8. The 2300MPa high-strength multi-phase hot-rolled wire rod for bridge cables according to claim 6, characterized in that: The network carbide grade of the hot-rolled wire rod is grade 0, and the mechanical property difference is ≤42MPa.

9. The 2300MPa grade high-strength multi-phase hot-rolled wire rod for bridge cables according to claim 6, 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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