Hot-rolled wire rod for 2300 MPa bridge cable and manufacturing method of hot-rolled wire rod

Abstract

The invention relates to a hot-rolled wire rod for a 2300MPa-grade bridge cable and a manufacturing method of the hot-rolled wire rod, the hot-rolled wire rod is manufactured by rolling vanadium-containing high-carbon steel components of C-Si-Mn-Cr-V-Al according to the spinning temperature of not less than 900 DEG C, and then the wire rod is subjected to online molten salt rapid cooling toughening treatment, so that the wire rod is cooled at the cooling speed of not less than 33 DEG C / s, enters a sorbite phase region from an austenite state and is subjected to hot rolling at the temperature of not less than 30 DEG C; and finally, a roller way is opened for slow cooling, so that the hot-rolled wire rod of which the microscopic structure comprises a mixed structure consisting of weakly tempered sorbite as the main part and ferrite and fused pearlite as the rest is prepared, the high strength and plasticity matching of the hot-rolled wire rod can be realized, the tensile strength can reach 1595-1635 MPa, and the tensile strength can reach 1595-1635 MPa. The percentage reduction of area can reach 30%-35%, the difference of the same circle of mechanical properties is smaller than or equal to 40 MPa, the structure uniformity and the production efficiency are improved, and stable production is promoted, so that the strength grade of the ultrahigh-strength bridge cable is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of hot-rolled wire rods, and in particular relates to a 2300MPa-grade hot-rolled wire rod for bridge cables and a manufacturing method thereof. Background Art

[0002] Under the guidance of large-span bridge construction and lightweight development, the strength grade of existing bridge cables has been gradually improved to the ultra-high strength grade of 2200MPa. The further improvement of the strength grade of bridge cables will help to further improve the bearing capacity, spanning capacity and service life of bridges, and is suitable for bridges with large traffic flow and frequent load changes. However, the improvement of the strength grade of ultra-high-strength bridge cables is limited by the strength grade of their parent material hot-rolled wire rods. Bridge cables with a higher strength grade of 2300MPa are rarely developed. Therefore, it is necessary to develop a 2300MPa-grade hot-rolled wire rod for bridge cables and a manufacturing method thereof to meet the development needs of the steel industry and market use.

[0003] As the strength level of bridge cables and wire rods for bridge cables continues to rise, wire rods generally use high carbon steel with a carbon content of 0.87% or more, and wire rod production is basically a Stelmor air-cooled line controlled cooling mode. For example, patent CN118880169A discloses a high-strength wire rod for bridge cables and its production method. 87SiMn wire rods are rapidly cooled by a Stelmor air-cooled line after low-temperature rolling and spinning, combined with online aging of insulation corridors for more than 120 minutes, so that the wire rod strength reaches more than 1400MPa. However, there are still the following technical difficulties in the production of hot-rolled wire rods for 2300MPa bridge cables: 1. The insufficient strength of the wire rod parent material will increase the subsequent drawing strength reduction rate, increase the risk of wire breakage, and affect the production efficiency of the bridge cable. In order to further improve the strength grade of the hot-rolled wire rod parent material, the increase of alloying elements such as C, Mn, and Cr in the wire rod will aggravate the segregation tendency during the solidification process of the steel billet. After spinning, before the transformation of austenite to pearlite structure, due to slow cooling, carbides will preferentially nucleate and grow on the grain boundaries and gradually form a network structure. The formed network carbides will seriously reduce the plasticity and toughness of the wire rod, and significantly increase the risk of wire breakage in the bridge cable wire making process. In order to minimize the level of network carbides and promote the refinement of pearlite to obtain better drawing performance For good troostite structure, although strong cooling treatment is adopted after spinning, on the one hand, the maximum cooling capacity of Stelmore air-cooled wire is limited, and the improvement of network carbides is limited. On the other hand, the increase of air cooling intensity makes the uncontrollability of air volume and air temperature further increase, and the temperature difference between the edge to the core of the wire rod and the winded and winded surfaces is further increased, which makes the organization transformation asynchronous and affects the uniformity of the overall performance of the wire. Affected by the segregation of hardenability components, it is also easy to make the cooling rate exceed the critical cooling rate, resulting in the transformation of austenite into non-equilibrium structures such as martensite or bainite, and large thermal stress is generated inside the wire, which in turn aggravates the risk of subsequent wire breakage during drawing or even brittle fracture of coiling.

[0004] Second, in order to improve the strength grade of the base material of the hot-rolled wire rod, micro-alloy elements such as V are added to the wire rod to improve the strength and toughness of the steel, or the online holding time is extended to improve the plasticity of the wire rod. However, it is limited by the minimum cooling capacity of the Stelmore air-cooling line or the holding line. On the one hand, a small degree of supercooling during cooling will affect the precipitation dynamics of vanadium carbonitrides and reduce the precipitation amount. The instability of the continuous cooling and air-cooling control of the wire rod will cause the coarser and finer carbonitrides to exist in the wire rod at the same time, affecting the precipitation strengthening effect and the uniformity of the organization. On the other hand, during the continuous cooling process of the Stelmore air-cooling line, the phase transformation incubation time is short, the phase transformation is easy to be insufficient and the wire rod strength is lost, or the residual austenite forms a low-temperature abnormal organization in the subsequent cooling process, deteriorating the plasticity of the organization. At the same time, the interlamellar spacing of the obtained troostite organization is large and the thermal stress is high. Although it is treated online, the temperature control ability and temperature conditions are limited, the production time is long, and the production efficiency is affected.

[0005] Compared with stranded wire steel, in order to reduce the strength loss and torsional cracking risk in the subsequent galvanizing process and maintain the strength grade of bridge cables, the wire rod base material for bridge cables has higher requirements on strength and structural uniformity. Although the existing high-strength stranded wire steel wire rod production involves salt baths, it is generally a heat treatment after air-cooled coiling, which is used to refine the interlamellar spacing and increase the austenitization rate and wire rod strength. It involves further salt bath treatment after uncoiling the coils after coiling and heating to austenitizing high temperature, which will increase the production process, processing time and production energy consumption, affecting production efficiency and cost. 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 grade hot-rolled wire rod for bridge cables and a manufacturing method thereof, which can achieve high strength and plasticity matching of the hot-rolled wire rod, improve organizational uniformity and production efficiency, and promote stable production, so as to improve the strength grade 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 grade 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: 0.45%~0.65%, Mn: 0.75%~0.95%, Cr: 0.42%~0.55%, V: 0.038%~0.048%, Al: 0.02%~0.04%, 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 ≥900°C, it is subjected to an online molten salt rapid cooling and toughening treatment, so that the wire rod is cooled at a cooling rate of ≥33°C / s, entering the sorbite phase region from the austenite state, forming a structure mainly composed of sorbite and isothermally toughened to relieve stress, and finally slowly cooled through a roller with an open cover to produce a hot-rolled wire rod with a microstructure mainly composed of weakly tempered sorbite and the rest being a mixed structure composed of ferrite and fused pearlite.

[0008] The design basis of the chemical composition and mass percentage of the above hot rolled wire rod includes: (1) Carbon: C is the main element that improves the strength of steel and can produce a solid solution strengthening effect. With the increase of carbon content, it is beneficial to reduce the critical cooling rate of steel, promote the phase transformation of troostite structure during the online molten salt rapid cooling toughening treatment, improve the strength of the material, and make the hot-rolled wire rod have a higher load-bearing capacity after being drawn into a steel wire bridge cable. However, with the increase of carbon content, the tendency of carbon segregation during the solidification of the steel billet will increase, the tendency of decarburization and precipitation of network carbides will increase, the plasticity and toughness of the material will deteriorate, and it will be unfavorable for the control of the matrix structure. 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 controlling the network carbides and improving the plasticity, the mass percentage of C is controlled to be 0.93%~0.96%.

[0009] (2) Silicon: Si is an effective solid solution strengthening element and a good deoxidizer. It can inhibit grain coarsening during online molten salt rapid cooling toughening treatment so that a troostite structure with fine interlamellar spacing can be quickly obtained, thereby improving matrix strength. At the same time, it can increase the eutectoid transformation temperature so that the phase region temperature can adapt to the dispersion precipitation of vanadium-containing carbides. However, excessive silicon content will make the steel more susceptible to decarburization when heated at high temperatures, increase the risk of abnormal microstructure precipitation, and reduce the toughness and microstructure uniformity of the steel. Therefore, in order to control the phase transformation temperature and promote the rapid offline of online molten salt rapid cooling toughening treatment, the mass percentage of Si is controlled to be 0.45%~0.65%.

[0010] (3) Manganese: As an austenite-forming element, Mn can expand the austenite phase region, inhibit the formation of ferrite, and increase the hardenability of the wire rod. This is beneficial to the rapid nucleation of the troostite structure with fine lamellar spacing during the online molten salt rapid cooling toughening treatment, thereby improving the tensile strength of the 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 and increase the risk of precipitation of martensite structure in the core of the wire rod. At the same time, it will reduce the activity of carbon, increase the difficulty of isothermal toughening stress relief, and then lose the plasticity of the wire rod. Therefore, in order to take into account the high strength of the hot-rolled wire rod, reduce the uniformity of the structure and the difficulty of tempering control, and promote efficient production, the mass percentage of Mn is controlled to be 0.75%~0.95%.

[0011] (4) Chromium: The Cr element can prevent the austenite grains from growing during the heating process and play a role in refining the grains. At the same time, it can strongly improve the hardenability of the material, increase the eutectoid temperature and expand the austenite phase area, reduce the critical cooling rate, and is beneficial to refining the spacing between the troostite sheets and improving the matrix strength. It is also beneficial to reduce the strength loss during the subsequent hot-dip galvanizing process of the steel wire. However, too high a Cr content will aggravate the component segregation, increase the risk of abnormal martensite structure precipitation, affect the uniformity of the wire rod structure, and significantly increase the difficulty of improving the plasticity of the wire rod, affecting the isothermal toughening stress relief effect, and further affecting the wire drawing and torsion performance of the steel wire. Therefore, in order to adapt to the online molten salt rapid cooling toughening treatment control to obtain a uniform high-strength structure, the mass percentage of Cr is controlled to be 0.42%~0.55%.

[0012] (5) Vanadium: The V element can inhibit the coarsening of high-temperature austenite and refine the austenite grains. At the same time, during the isothermal process of rapid cooling in molten salt, a large number of fine dispersed carbonitrides can be formed in the medium temperature range, which can hinder the movement of dislocations, thereby playing a role in precipitation strengthening, and improving the strength level of hot-rolled wire rods 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 0.038%~0.048%.

[0013] (6) Aluminum: Al acts as a deoxidizer during the smelting process and inhibits the growth of austenite grains during hot rolling. Fine austenite grains can form fine troostite structure after cooling transformation, which is beneficial to improving the strength and toughness of steel. At the same time, Al 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 mass percentage of Al is controlled to be 0.02%~0.04%.

[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 adopts the vanadium-containing high-carbon steel composition design of C-Si-Mn-Cr-V-Al, and is matched with the optimized ratio of Si, Mn and Cr, which provides favorable conditions for refining austenite grains, inhibiting grain coarsening during online molten salt rapid cooling toughening treatment, regulating the precipitation of sorbite phase transformation to adapt to the dispersion precipitation temperature of vanadium-containing carbides, and reducing the difficulty of abnormal tissue control. On this basis, the wire-spinning temperature is appropriately increased to avoid excessive temperature causing the grain size to become larger, and to form a large degree of undercooling later, promote the refinement of pearlite lamellae to form sorbite, and increase the precipitation power and nucleation rate of vanadium-containing carbides. The wire-spinning does not use air cooling but directly enters the salt bath for online molten salt rapid cooling toughening treatment: 1. Compared with the Stelmore air-cooled line, which has limited cooling capacity and is difficult to take into account the control of network carbides and low-temperature abnormal structures of high-carbon steel products, the wire rod can be quickly cooled down by using the high heat exchange capacity of the molten salt after passing through the molten salt. On the one hand, rapid and uniform cooling can make the wire rod pass through the secondary cementite precipitation temperature range of 700~800℃ quickly, inhibit the nucleation and growth of network carbides at the grain boundary, and effectively avoid the risk of network carbides caused by increasing the C element content and alloy segregation. On the other hand, when the wire rod passes through the molten salt, the molten salt can cover the surface of the wire rod for uniform heat exchange, and there is no temperature difference problem between the windward side and the leeward side. The temperature difference from the upper edge to the core of the same cross-section of the wire rod can be reduced, avoiding the entry into the bainite or martensite phase region and the formation of hard and brittle low-temperature abnormal structures due to the segregation and supercooling of the wire rod alloy elements, improving the control effect of high carbon manganese and chromium content on the abnormal structure, and then exerting the strengthening effect of carbon elements and improving the uniformity of the wire rod structure.

[0016] 2. Compared with the Stelmore air cooling line or the insulation line, which has limited cooling control capacity and is difficult to control the organizational state and give full play to the strengthening effect of microalloys, the wire rod can be cooled rapidly after online molten salt rapid cooling and toughening treatment, and enter the sorbite phase from the high-temperature austenite state. On the one hand, it can form a large degree of supercooling, cooperate with Si and V to inhibit the coarsening of high-temperature austenite grains, provide more nucleation points for phase transformation, promote the rapid deformation of high-temperature austenite to form a structure dominated by sorbite with fine lamellar spacing, and improve the strength of the matrix. On the other hand, the wire rod temperature gradually changes to the same as the molten salt. The salt temperature is consistent, which can control the wire rod to enter the high-temperature isothermal zone of the sorbite phase region, prolong the phase transformation time, promote the full phase transformation of austenite, avoid the residual austenite from forming abnormal organization in the subsequent cooling process and causing brittle fracture, improve production stability, and also prolong the precipitation time of vanadium-containing carbides in the isothermal process. With the refined grains and large undercooling, the vanadium carbonitrides are fully precipitated in this temperature range to obtain a fine and dispersed strengthening phase, rather than coarse and fine precipitation, which can give full play to the strengthening and toughening effect of V and improve the uniformity of the organization.

[0017] 3. Compared with extending the insulation line or post-heat treatment process, which affects production efficiency and organizational regulation, the wire rod can be treated with online molten salt rapid cooling and toughening to promote the full phase transformation of austenite and form appropriate toughening at the same time. On the one hand, the wire rod can prolong the time in the high temperature range in the troostite phase region, provide more thermal power for toughening and stress relief of the organization, quickly improve the plasticity of the wire rod, promote the rapid offline of the wire rod, and improve production efficiency. On the other hand, compared with long-term strong tempering, online molten salt rapid cooling and toughening can form short-term tempering and toughening, avoiding the coarsening of vanadium-containing carbides precipitated due to prolonged high-temperature treatment time, or excessive loss of matrix strength due to large-scale melting and coarsening of troostite lamellae. The wire rod is slowly cooled by the roller cover, and the wire rod's own residual heat can be used to control the slow cooling of the wire rod, avoiding the increase of stress caused by too fast cooling of the wire rod, and using the high temperature state of the wire rod to promote further toughening and stress relief of the wire rod organization, thereby obtaining a weakly tempered troostite-based organization, improving the softening effect and offline efficiency of the wire rod, simplifying the production process and reducing production energy consumption compared with post-treatment.

[0018] Selecting appropriate heating furnace parameters before rolling can promote organizational homogenization, reduce the impact of segregation, and avoid decarburization, burning or coarse grains caused by excessive heating temperature. In a preferred embodiment, before rolling, the heating furnace is controlled to have a soaking temperature of 1190-1230°C, and the time in the furnace is ≥160min.

[0019] Appropriately increasing the start rolling temperature during the rolling process can reduce the deformation resistance of the steel billet, appropriately reduce the final rolling temperature, increase the final rolling reduction, promote dynamic recrystallization during the final rolling process, and refine the grains, so as to provide more nucleation sites for the sorbite phase with fine austenite grains, refine the final structure, and improve the strength and toughness of the steel. In a preferred embodiment, during the rolling process, the initial rolling temperature is controlled to be 1080~1120℃, the final rolling temperature is 890~940℃, and the final rolling reduction is 22%~27%.

[0020] In a preferred embodiment, the molten salt temperature of the online molten salt rapid cooling and toughening treatment is 550~580℃, which is in the medium temperature range of the troostite phase region and the dispersion and precipitation of vanadium-containing carbides. The lower the molten salt temperature, the more conducive it is to improving the supercooling degree, promoting the rapid transformation of high-temperature austenite to a troostite structure with finer lamellae, increasing the power of dispersion and precipitation of vanadium-containing carbides, and thus improving the matrix strength. However, if the molten salt temperature is too low, it is difficult to provide more power for toughening and stress relief in the isothermal interval, which will cause the plasticity of the wire rod to decrease, and even precipitate low-temperature abnormal structure, which will significantly affect the plasticity and uniformity of the wire rod. On the contrary, the higher the molten salt temperature, the greater the troostite lamella spacing and the melting effect, and the plasticity of the wire rod is improved. However, if the molten salt temperature is too high, the troostite lamellae will coarsen and affect the large-scale dispersion and precipitation of vanadium-containing carbides, which will lose the matrix strength and toughness. Therefore, selecting an appropriate molten salt temperature can promote rapid cooling and appropriate toughening of the wire rod, which is convenient for regulating the matrix structure.

[0021] Since the temperature difference between the wire rod from the spinning temperature to the molten salt temperature is large, the online molten salt rapid cooling and toughening treatment is divided into a front-end treatment and a back-end treatment. The molten salt circulation volume of the front-end treatment is greater than that of the back-end treatment. The front-end treatment uses a larger molten salt circulation volume to control the temperature rise, promote the rapid cooling of the wire rod, maintain the stability of the supercooling, promote the rapid and sufficient phase transformation of the high-temperature austenite, and improve the matrix strength and organizational uniformity. After a period of molten salt treatment, the wire rod temperature drops to the molten salt temperature, and the difficulty of controlling the molten salt temperature rise is reduced. The back-end treatment appropriately reduces the molten salt circulation volume to accurately control the temperature, control the wire rod to toughen and relieve stress in the high-temperature isothermal range, and avoid Avoid too short processing time for the front-stage treatment affecting the control of microstructure homogenization, avoid too long processing time for the front-stage treatment unnecessarily increasing production energy consumption, avoid too short processing time for the front-stage treatment and the back-stage treatment affecting sufficient phase transformation and toughening effect of the microstructure, avoid too long processing time for the back-stage treatment causing precipitation and coarsening of vanadium-containing carbides, excessive toughening and loss of strength and plasticity. Therefore, controlling the appropriate processing time for the front-stage treatment and the back-stage treatment can further regulate the microstructure state of the wire rod and appropriately reduce production energy consumption. In a preferred embodiment, the processing time for the front-stage treatment is 110~150s, and the processing time for the back-stage treatment is 80~190s.

[0022] In order to further control the wire rod to quickly form a structure dominated by fine lamellar spacing troostite from a high-temperature austenite state and promote the dispersion and precipitation of vanadium-containing carbides, in a preferred embodiment, the molten salt circulation rate of the front-stage treatment is 450~600t / h, and the molten salt temperature rise is ≤8°C.

[0023] In order to further control the toughening and stress relief effect and improve the strength-plasticity matching of the wire rod, in a preferred embodiment, the molten salt circulation rate of the later stage treatment is 200-240 t / h, and the molten salt temperature rise is ≤3°C.

[0024] The wire rod comes out of the salt tank at 550-580°C and enters the conveyor roller. In a preferred embodiment, the roller is opened for slow cooling with a heat preservation cover turned on to control the wire rod to slowly cool to below 320°C at a cooling rate of 1.2-2°C / s. On the one hand, it can prevent the wire rod from cooling too fast during the cooling process, resulting in increased stress. On the other hand, the waste heat of the wire rod itself can be used to appropriately promote further toughening of the wire rod structure, improve the softening effect of the wire rod, reduce production energy consumption, enable the wire rod to be quickly offline, and improve production efficiency.

[0025] A 2300MPa grade hot-rolled wire rod for bridge cables, wherein the hot-rolled wire rod is manufactured by any one of the above-mentioned methods for manufacturing a 2300MPa grade hot-rolled wire rod for bridge cables.

[0026] The above-mentioned hot-rolled wire rod adopts a vanadium-containing, high-silicon, high-carbon chemical composition design combined with online molten salt rapid cooling toughening technology to obtain a mixed structure composed of weakly tempered troostite, ferrite, and fused pearlite. The weakly tempered troostite is a transitional state in which the cementite lamellae are melted and transformed into tempered troostite under a relatively short tempering time, and a small amount of fused pearlite structure is formed, so that the strength of the troostite is appropriately reduced, the plasticity is appropriately improved, and the matrix is ​​toughened, and excessive loss of matrix strength caused by strong tempering and prolonged processing time are avoided to affect the strengthening effect of vanadium-containing carbides. The overall strength of the wire rod is improved and good plasticity is obtained in combination with refined organizational grains.

[0027] The higher the proportion of the weakly tempered bainite and the finer the interlamellar spacing, the more beneficial it is to improve the matrix strength. In a preferred embodiment, the volume percentage of the weakly tempered bainite is ≥82%, and the interlamellar spacing of the weakly tempered bainite is 75-110 nm.

[0028] The larger the proportion of the fusible pearlite is, the more beneficial it is to improve the plasticity of the matrix. In a preferred embodiment, the volume percentage of the fusible pearlite is 11% to 15%.

[0029] In a preferred embodiment, the network carbide level of the hot-rolled wire rod is level 0, and no carbides are found to precipitate along the austenite grain boundaries to form a network structure, so that the strength, toughness, plasticity, etc. of the hot-rolled wire rod can be maintained at a good level.

[0030] Since the hot-rolled wire rod will not suffer from problems such as decreased impact toughness and increased brittleness due to the presence of network carbides, the microstructure phase change becomes more uniform, avoiding abnormal bainite and martensite structures, the comprehensive performance of the material is more stable and excellent, and brittle fracture is not prone to occur. In a preferred embodiment, the mechanical properties of the hot-rolled wire rod have a circle difference of ≤40MPa.

[0031] In a preferred embodiment, the diameter of the hot-rolled wire rod is 9.0~15.0mm, the tensile strength is 1595~1635MPa, and the cross-sectional shrinkage rate is 30%~35%. The hot-rolled wire rod has higher tensile strength and good cross-sectional shrinkage rate, which is beneficial to reduce the drawing reduction rate, quickly reach the strength grade of the bridge cable, reduce the plastic loss in the process, reduce the wire breakage rate during drawing, promote stable production of bridge cables, and at the same time meet the demand for parent material strength due to strength loss in the hot-dip galvanizing process, thereby improving the strength grade of bridge cables.

[0032] Compared with the prior art, the beneficial effects of the present invention are at least: In view of the fact that the existing Stelmor air-cooling line is difficult to stably produce high-carbon steel products with a carbon content of 0.87% and above, which limits the improvement of the strength grade of the ultra-high-strength bridge cable base material, the present invention combines the C-Si-Mn-Cr-V-Al chemical composition design with the online molten salt rapid cooling toughening technology to inhibit grain coarsening, control the wire rod to quickly enter the troostite phase region from the high-temperature austenite state, form a structure dominated by troostite with fine lamellar spacing, promote the dispersion and precipitation of vanadium in the isothermal process, enter the high-temperature isothermal interval toughening and stress relief, and cooperate with the roller table open cover slow cooling to improve the softening effect of the wire rod The results show that, on the one hand, it can avoid the risk of abnormal tissues such as network carbon and martensite produced by C elements, regulate the full and uniform phase transformation of the wire rod, maximize the strengthening of carbon elements and the strengthening and toughening effect of the micro-alloying element vanadium, further improve the high strength and uniformity of the hot-rolled wire rod, and form stable production. On the other hand, it controls the weak tempering state and toughening and stress relief effect of the wire rod structure, improves the plasticity and high strength matching of the hot-rolled wire rod, and can also control production energy consumption, simplify the manufacturing process, make the wire rod quickly offline, avoid brittle fracture of coiling, and thus improve production efficiency. It has good industrial adaptability.

[0033] In view of the improvement of the strength grade of the current ultra-high strength bridge cables, which is limited by the current strength grade of the hot-rolled wire rod of its parent material, the hot-rolled wire rod of the present invention adopts vanadium-containing high-carbon steel, and the microstructure type is a mixed structure composed of weakly tempered troostite, ferrite, and fused pearlite. The transition state of cementite lamellar melting and transformation to tempered troostite, the large-scale dispersion and precipitation of vanadium-containing carbides, grain refinement and effective control of abnormal structures such as network carbides and martensite can be utilized to effectively improve the strength-plasticity matching and organizational uniformity of the wire rod. The product has a tensile strength of 1595~1635MPa, a cross-sectional shrinkage rate of 30%~35%, and a mechanical property difference of ≤40MPa. It is used in the manufacture of 2300MPa ultra-high strength bridge cables and other application fields, which is beneficial to reduce the risk of wire breakage and torsional cracking during drawing, promote the stable production of bridge cables, and has good market application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0036] A preferred embodiment of the manufacturing method of the 2300MPa grade hot-rolled wire rod for bridge cables of the present invention, the chemical composition and mass percentage of the hot-rolled wire rod include C: 0.95%, Si: 0.49%, Mn: 0.75%, Cr: 0.45%, V: 0.047%, Al: 0.02%, P: 0.014%, S: 0.015%, and the rest is Fe and unavoidable impurities; the manufacturing method is manufactured according to the process flow of rolling → spinning → online molten salt fast cooling toughening treatment → roller table open cover slow cooling → coiling, specifically: The rolling process is used to heat the steel billet with a specification of 180mm×180mm 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 9mm through a rolling line, and the final rolling temperature is appropriately reduced and the final rolling reduction is increased to promote dynamic recrystallization and grain refinement during the final rolling process, so as to provide more nucleation sites for the subsequent sorbite and vanadium-containing carbide precipitation phases. Specifically: control the heating furnace The soaking temperature is 1190°C, the furnace time is 180min, the initial rolling temperature is 1080°C, the final rolling temperature is 890°C, and the final rolling reduction is 22%; the wire-spinning process is used to make the wire rods coming out of the rolling line into wire rods through a wire-spinning mechanism, and the wire rods are spread on the rollers and transported along the rollers to make the wire rods in a high-temperature austenite state, and appropriately increase the wire-spinning temperature to prepare for the subsequent formation of a larger degree of undercooling, promote the nucleation of the sorbite structure and the precipitation of vanadium-containing carbides, specifically: the wire-spinning temperature is controlled to be 900°C.

[0037] The online molten salt rapid cooling and toughening treatment process adopts a two-stage salt bath tank with molten salt inside. The wire rod after spinning is conveyed by a roller to pass through the first salt bath tank for front-end treatment, so that the wire rod is cooled at a cooling rate of 33°C / s, and quickly passes through the network carbide precipitation interval from the high-temperature austenite state to enter the sorbite phase region, thereby increasing the degree of supercooling, promoting the uniform phase transformation of the high-temperature austenite, forming a microstructure transformation dominated by fine lamellar spacing sorbite, and allowing vanadium-containing carbides to be dispersed and precipitated in large quantities in the medium temperature range. After that, the wire rod is conveyed by a roller to pass through the second The post-processing is carried out in a salt bath tank. The circulation volume of the molten salt in the post-processing is appropriately reduced, the temperature is accurately controlled and the production energy consumption is reduced, so that the wire rod can be quickly isothermally toughened and stress-relieved in the high-temperature isothermal zone, the precipitation and coarsening of vanadium-containing carbides can be avoided, and the strength and plasticity matching of the wire rod can be improved. Specifically: the molten salt temperature is 571°C, the circulation volume of the molten salt in the front-stage treatment is 500t / h, the temperature rise of the molten salt is ≤8°C, and the processing time is 137s; the circulation volume of the molten salt in the post-processing is 215t / h, the temperature rise of the molten salt is ≤3°C, and the processing time is 164s.

[0038] The roller open cover slow cooling process adopts the method of opening the heat preservation cover, and conveying the wire rod through the second salt bath tank by the conveyor roller, using the residual heat of the wire rod itself to appropriately promote the further toughening of the wire rod structure and improve the softening effect of the wire rod, so that the wire rod can be quickly offline. Specifically: the wire rod is controlled to slowly cool to 305°C at a cooling rate of 1.6°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.

[0039] Comparative Example 1: A method for manufacturing a hot-rolled wire rod, the manufacturing method differs from Example 1 in that: the heating furnace soaking temperature is controlled to be 1200°C, the furnace time is 180min, the initial rolling temperature is 1090°C, the final rolling temperature is 900°C, the spinning temperature is 865°C, the wire rod is subjected to a front-end treatment during the online molten salt rapid cooling and toughening treatment, so that the wire rod is cooled at a cooling rate of 29°C / s, and the hot-rolled wire rod is obtained after it is off the line.

[0040] Comparative Example 2: A method for manufacturing a hot-rolled wire rod, the manufacturing method differs from that of Example 1 in that: during the online molten salt rapid cooling and toughening treatment, the wire rod undergoes a front-end treatment, so that the wire rod is cooled at a cooling rate of 30°C / s, the molten salt temperature is 595°C, and the hot-rolled wire rod is obtained after going offline.

[0041] Comparative Example 3: A method for manufacturing a hot-rolled wire rod, the manufacturing method differs from that of Example 1 in that: during the online molten salt rapid cooling and toughening treatment, the wire rod undergoes a front-end treatment, so that the wire rod is cooled at a cooling rate of 38°C / s, the molten salt temperature is 515°C, and the hot-rolled wire rod is obtained after going offline. Embodiment 2:

[0042] A preferred embodiment of the manufacturing method of the 2300MPa grade 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: 0.65%, Mn: 0.9%, Cr: 0.55%, V: 0.038%, Al: 0.036%, 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 fast cooling toughening treatment → roller table open cover 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, and the final rolling temperature is appropriately reduced and the final rolling reduction is increased to promote dynamic recrystallization and grain refinement during the final rolling process, so as to provide more nucleation sites for the subsequent sorbite and vanadium-containing carbide precipitation phases. Specifically: control the heating The furnace average heating temperature is 1230°C, the furnace time is 160min, the initial rolling temperature is 1120°C, the final rolling temperature is 940°C, and the final rolling reduction is 27%; the wire-spinning process is used to make the wire rods coming out of the rolling line into wire rods through the wire-spinning mechanism, and the wire rods are spread on the rollers and transported along the rollers to make the wire rods in a high-temperature austenite state, and appropriately increase the wire-spinning temperature to prepare for the subsequent formation of a larger degree of supercooling, promote the nucleation of the sorbite structure and the precipitation of vanadium-containing carbides, specifically: the wire-spinning temperature is controlled to be 915°C.

[0043] The online molten salt rapid cooling and toughening treatment process adopts a two-stage salt bath tank with molten salt inside. The wire rod after spinning is conveyed by a roller to pass through the first salt bath tank for front-end treatment, so that the wire rod is cooled at a cooling rate of 35°C / s, and quickly passes through the network carbide precipitation interval from the high-temperature austenite state to enter the sorbite phase region, thereby increasing the degree of supercooling, promoting the uniform phase transformation of the high-temperature austenite, forming a microstructure transformation dominated by fine lamellar spacing sorbite, and allowing vanadium-containing carbides to be dispersed and precipitated in large quantities in the medium temperature range. After that, the wire rod is conveyed by a roller to pass through the second The post-processing is carried out in a salt bath tank. The circulation volume of the molten salt in the post-processing is appropriately reduced, the temperature is accurately controlled and the production energy consumption is reduced, so that the wire rod can be quickly isothermally toughened and stress-relieved in the high-temperature isothermal zone, the precipitation and coarsening of vanadium-containing carbides can be avoided, and the strength and plasticity matching of the wire rod can be improved. Specifically: the molten salt temperature is 563℃, the circulation volume of the molten salt in the front-stage treatment is 600t / h, the temperature rise of the molten salt is ≤8℃, and the processing time is 124s; the circulation volume of the molten salt in the post-processing is 225t / h, the temperature rise of the molten salt is ≤3℃, and the processing time is 109s.

[0044] The roller open cover slow cooling process adopts the method of opening the heat preservation cover, and conveying the wire rod through the second salt bath tank by the conveyor roller, using the residual heat of the wire rod itself to appropriately promote further toughening of the wire rod structure and improve the softening effect of the wire rod, so that the wire rod can be quickly offline. Specifically: the wire rod is controlled to slowly cool to 310°C at a cooling rate of 1.4°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.

[0045] Comparative Example 4: A method for manufacturing a hot-rolled wire rod, the manufacturing method of which is different from that of Example 2 in that: during the online molten salt rapid cooling toughening treatment, the processing time of the front-stage treatment is 200s, and the hot-rolled wire rod is obtained after going offline.

[0046] Comparative Example 5: A method for manufacturing a hot-rolled wire rod, the manufacturing method of which is different from that of Example 2 in that: during the online molten salt rapid cooling toughening treatment, the processing time of the front stage treatment is 50s, and the hot-rolled wire rod is obtained after going offline. Embodiment 3:

[0047] A preferred embodiment of the manufacturing method of the 2300MPa grade 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: 0.6%, Mn: 0.95%, Cr: 0.42%, V: 0.046%, Al: 0.029%, P: 0.014%, S: 0.01%, and the rest are Fe and unavoidable impurities; the manufacturing method thereof is manufactured according to the process flow of rolling → spinning → online molten salt fast cooling toughening treatment → roller table open cover 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 leaves the heating furnace, it is rolled into a wire with a diameter of 12mm through a rolling line, and the final rolling temperature is appropriately reduced and the final rolling reduction is increased to promote dynamic recrystallization and grain refinement during the final rolling process, so as to provide more nucleation sites for subsequent sorbite and vanadium-containing carbide precipitation phases. Specifically: control the heating The furnace average heating temperature is 1210°C, the furnace time is 175min, the initial rolling temperature is 1100°C, the final rolling temperature is 910°C, and the final rolling reduction is 24%; the wire-spinning process is used to make the wire rods coming out of the rolling line into wire rods through a wire-spinning mechanism, and the wire rods are spread on the rollers and transported along the rollers to make the wire rods in a high-temperature austenite state, and appropriately increase the wire-spinning temperature to prepare for the subsequent formation of a larger undercooling, promote the nucleation of the sorbite structure and the precipitation of vanadium-containing carbides, specifically: the wire-spinning temperature is controlled to be 900°C.

[0048] The online molten salt rapid cooling and toughening treatment process adopts a two-stage salt bath tank with molten salt inside. The wire rod after spinning is conveyed by a roller to pass through the first salt bath tank for front-end treatment, so that the wire rod is cooled at a cooling rate of 35°C / s, and quickly passes through the network carbide precipitation interval from the high-temperature austenite state to enter the sorbite phase region, thereby increasing the degree of supercooling, promoting the uniform phase transformation of the high-temperature austenite, forming a microstructure transformation dominated by fine lamellar spacing sorbite, and allowing vanadium-containing carbides to be dispersed and precipitated in large quantities in the medium temperature range. After that, the wire rod is conveyed by a roller to pass through the second The post-processing is carried out in a salt bath tank. The circulation volume of the molten salt in the post-processing is appropriately reduced, the temperature is accurately controlled and the production energy consumption is reduced, so that the wire rod can be quickly isothermally toughened and stress-relieved in the high-temperature isothermal zone, the precipitation and coarsening of vanadium-containing carbides can be avoided, and the strength and plasticity matching of the wire rod can be improved. Specifically: the molten salt temperature is 550℃, the circulation volume of the molten salt in the front-stage treatment is 580t / h, the temperature rise of the molten salt is ≤8℃, and the processing time is 150s; the circulation volume of the molten salt in the post-processing is 200t / h, the temperature rise of the molten salt is ≤3℃, and the processing time is 190s.

[0049] The roller open cover slow cooling process adopts the method of opening the heat preservation cover, and conveying the wire rod through the second section of the salt bath tank by the conveyor roller, and utilizing the residual heat of the wire rod itself to appropriately promote further toughening of the wire rod structure and improve the softening effect of the wire rod, so that the wire rod can be quickly offline. Specifically: the wire rod is controlled to be slowly cooled to 300°C at a cooling rate of 2°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 finished product is obtained after packaging and storage.

[0050] Comparative Example 6: A method for manufacturing a hot-rolled wire rod, the manufacturing method of which is different from that of Example 3 in that: during the online molten salt rapid cooling toughening treatment, the processing time of the rear-stage treatment is 230s, and the hot-rolled wire rod is obtained after going offline.

[0051] Comparative Example 7: A method for manufacturing a hot-rolled wire rod, the manufacturing method of which is different from that of Example 3 in that: during the online molten salt rapid cooling toughening treatment, the processing time of the rear-stage treatment is 30 seconds, and the hot-rolled wire rod is obtained after going offline. Embodiment 4:

[0052] A preferred embodiment of the manufacturing method of the 2300MPa grade 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: 0.45%, Mn: 0.86%, Cr: 0.5%, V: 0.048%, Al: 0.04%, 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 fast cooling toughening treatment → roller cover open 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 leaves the heating furnace, it is rolled into a wire with a diameter of 13mm through a rolling line, and the final rolling temperature is appropriately reduced and the final rolling reduction is increased to promote dynamic recrystallization and grain refinement during the final rolling process, so as to provide more nucleation sites for subsequent sorbite and vanadium-containing carbide precipitation phases. Specifically: control the heating The furnace average heating temperature is 1220°C, the furnace time is 170min, the initial rolling temperature is 1110°C, the final rolling temperature is 930°C, and the final rolling reduction is 26%; the wire-spinning process is used to make the wire rods coming out of the rolling line into wire rods through the wire-spinning mechanism, and the wire rods are spread on the rollers and transported along the rollers to make the wire rods in a high-temperature austenite state, and appropriately increase the wire-spinning temperature to prepare for the subsequent formation of a larger degree of supercooling, promote the nucleation of the sorbite structure and the precipitation of vanadium-containing carbides, specifically: the wire-spinning temperature is controlled to be 910°C.

[0053] The online molten salt rapid cooling and toughening treatment process adopts a two-stage salt bath tank with molten salt inside. The wire rod after spinning is conveyed by a roller to pass through the first salt bath tank for front-end treatment, so that the wire rod is cooled at a cooling rate of 33°C / s, and quickly passes through the network carbide precipitation interval from the high-temperature austenite state to enter the sorbite phase region, thereby increasing the degree of supercooling, promoting the uniform phase transformation of the high-temperature austenite, forming a microstructure transformation dominated by fine lamellar spacing sorbite, and allowing vanadium-containing carbides to be dispersed and precipitated in large quantities in the medium temperature range. After that, the wire rod is conveyed by a roller to pass through the second The post-processing is carried out in a salt bath tank. The circulation volume of the molten salt in the post-processing is appropriately reduced, the temperature is accurately controlled and the production energy consumption is reduced, so that the wire rod can be quickly isothermally toughened and stress-relieved in the high-temperature isothermal zone, the precipitation and coarsening of vanadium-containing carbides can be avoided, and the strength and plasticity matching of the wire rod can be improved. Specifically: the molten salt temperature is 580℃, the circulation volume of the molten salt in the front-stage treatment is 535t / h, the temperature rise of the molten salt is ≤8℃, and the processing time is 110s; the circulation volume of the molten salt in the post-processing is 240t / h, the temperature rise of the molten salt is ≤3℃, and the processing time is 80s.

[0054] The roller open cover slow cooling process adopts the method of opening the heat preservation cover, and conveying the wire rod through the second section of the salt bath tank by the conveyor roller, and utilizing the residual heat of the wire rod itself to appropriately promote further toughening of the wire rod structure and improve the softening effect of the wire rod, so that the wire rod can be quickly offline. Specifically: the wire rod is controlled to be slowly cooled to 318°C at a cooling rate of 1.2°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.

[0055] Comparative Example 8: A method for manufacturing a hot-rolled wire rod, which differs from Example 4 in that in the roller open cover slow cooling process, the wire rod is controlled to slowly cool to 310°C at a cooling rate of 2.5°C / s, and the hot-rolled wire rod is obtained after it comes off the line.

[0056] The hot rolled wire rods obtained in the above examples 1 to 4 and comparative examples 1 to 8 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

[0057] It can be seen from the results of Examples 1 to 4 that the present invention adopts the C-Si-Mn-Cr-V-Al chemical composition design combined with the online molten salt rapid cooling toughening technology, the product tensile strength can reach 1595~1635MPa, the cross-sectional shrinkage rate can reach 30%~35%, and the mechanical property difference is ≤40MPa, which effectively improves the strength-plasticity matching and organizational uniformity of the wire rod.

[0058] From the comparison results of Example 1 and Comparative Example 1, it can be seen that appropriately increasing the spinning temperature can provide favorable conditions for forming a larger degree of supercooling later, promoting the refinement of pearlite lamellae to form troostite, increasing the precipitation kinetics and nucleation rate of vanadium-containing carbides, thereby improving the matrix strength. At the same time, increasing the cooling rate is beneficial to controlling the network carbides and reducing the fluctuation of mechanical properties.

[0059] From the comparison results of Example 1 and Comparative Example 2, it can be seen that the higher the molten salt temperature, the greater the spacing between the troostite lamellae and the melting effect, and the improved plasticity of the wire rod. However, when the molten salt temperature is too high, the troostite lamellae coarsen and affect the large-scale dispersion and precipitation of vanadium-containing carbides. At the same time, the amount of melted pearlite increases, the matrix strength will be lost, and the plasticity improvement effect will decrease.

[0060] From the comparison results of Example 1 and Comparative Example 3, it can be seen that the lower the molten salt temperature, the more conducive it is to improving the degree of supercooling, promoting the rapid transformation of high-temperature austenite to a troostite structure with finer lamellar layers, increasing the kinetic energy of the dispersion and precipitation of vanadium-containing carbides, and thus improving the matrix strength. However, if the molten salt temperature is too low, it is difficult to provide more power for toughening and stress relief in the isothermal zone, which will cause the plasticity of the wire rod to decrease.

[0061] From the comparison results of Example 2 and Comparative Example 4, it can be seen that as the treatment time of the front-stage treatment is extended, the austenite structure of the wire rod can be fully and uniformly transformed, the total treatment time of the online molten salt rapid cooling toughening treatment is increased, and toughening and stress relief are promoted. However, the treatment time of the front-stage treatment is too long, which brings a certain strength loss and unnecessarily increases the production energy consumption.

[0062] From the comparison results of Example 2 and Comparative Example 5, it can be seen that if the treatment time of the previous stage is too short, the sufficient phase transformation and toughening effect of the structure will be affected, the strong plasticity will be lost, and the fluctuation of mechanical properties will be increased.

[0063] From the comparison results of Example 3 and Comparative Example 6, it can be seen that as the treatment time of the later stage treatment is extended, the spacing between the troostite lamellae and the melting effect increase, and the plasticity of the wire rod is improved. However, if the treatment time of the later stage treatment is too long, the melting of the troostite lamellae increases, and the vanadium-containing carbides precipitate coarsen and over-toughen, which will lead to a loss of strength and plasticity. From the comparison results of Example 3 and Comparative Example 7, it can be seen that if the treatment time of the later stage treatment is too short, the toughening effect is affected, and the plasticity of the wire rod will be obviously lost.

[0064] From the comparison results of Example 4 and Comparative Example 8, it can be seen that further controlling the cooling speed of the wire rod in the roller open cover slow cooling can 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.

[0065] 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 hot-rolled wire rod for bridge cables, characterized in that: The manufacturing method thereof comprises: The hot-rolled wire rod is rolled to produce a wire rod according to its chemical composition, wherein the chemical composition and mass percentage of the hot-rolled wire rod include: C: 0.93% to 0.96%, Si: 0.45% to 0.65%, Mn: 0.75% to 0.95%, Cr: 0.42% to 0.55%, V: 0.038% to 0.048%, Al: 0.02% to 0.04%, P≤0.015%, S≤0.015%, The rest is Fe and unavoidable impurities; after the wire rod is spun into a wire rod at a spinning temperature of ≥900°C, it is subjected to an online molten salt rapid cooling and toughening treatment, so that the wire rod is cooled at a cooling rate of ≥33°C / s, entering the sorbite phase region from the austenite state, forming a sorbite-based structure and isothermally toughened to relieve stress, and finally slowly cooled through a roller with an open hood to produce a hot-rolled wire rod with a microstructure including a mixed structure consisting of weakly tempered sorbite, ferrite and fused pearlite.

2. The method for manufacturing the 2300MPa grade hot rolled wire rod for bridge cables according to claim 1, characterized in that: Before the rolling, the heating furnace is controlled to have a soaking temperature of 1190-1230° C. and the time in the furnace is ≥160 min.

3. The method for manufacturing the 2300MPa grade 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 1080-1120° C., the final rolling temperature is controlled to be 890-940° C., and the final rolling reduction is controlled to be 22%-27%.

4. The method for manufacturing the 2300MPa grade hot rolled wire rod for bridge cables according to claim 1, characterized in that: The molten salt temperature of the online molten salt rapid cooling and toughening treatment is 550~580℃, and the online molten salt rapid cooling and toughening treatment is divided into a front-stage treatment and a back-stage treatment. The molten salt circulation amount of the front-stage treatment is greater than the molten salt circulation amount of the back-stage treatment. The processing time of the front-stage treatment is 110~150s, and the processing time of the back-stage treatment is 80~190s.

5. The method for manufacturing the 2300MPa grade hot rolled wire rod for bridge cables according to claim 4, characterized in that: The molten salt circulation volume of the front-stage treatment is 450-600 t / h, and the molten salt temperature rise is ≤8°C; the molten salt circulation volume of the back-stage treatment is 200-240 t / h, and the molten salt temperature rise is ≤3°C.

6. The method for manufacturing the 2300MPa grade hot rolled wire rod for bridge cables according to claim 4, characterized in that: The roller open cover slow cooling adopts opening the heat preservation cover to control the wire rod to slowly cool to below 320°C at a cooling speed of 1.2~2°C / s.

7. A 2300MPa grade hot-rolled wire rod for bridge cables, characterized in that: The hot-rolled wire rod is manufactured by the method for manufacturing 2300MPa-grade hot-rolled wire rod for bridge cables according to any one of claims 1 to 6.

8. The 2300MPa grade hot rolled wire rod for bridge cables according to claim 7, characterized in that: The volume percentage of the weakly tempered bainite is ≥82%, the interlamellar spacing of the weakly tempered bainite is 75-110 nm, and the volume percentage of the fused pearlite is 11%-15%.

9. The 2300MPa grade 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 ≤40MPa.

10. The 2300MPa grade hot rolled wire rod for bridge cables according to claim 7, characterized in that: The hot-rolled wire rod has a diameter of 9.0-15.0 mm, a tensile strength of 1595-1635 MPa, and a cross-sectional shrinkage of 30%-35%.

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