Hot-rolled wire rod for 2200 mpa-grade bridge cable and manufacturing method therefor

Abstract

The present invention relates to a hot-rolled wire rod for a 2200 MPa-grade bridge cable and a manufacturing method therefor. The method comprises: producing a wire by rolling according to a high-carbon V-containing chemical composition design; laying the wire into a wire rod at a laying temperature higher than or equal to 920°C; then carrying out in-line molten salt rapid cooling and isothermal treatment, wherein the molten salt treatment time is controlled to less than or equal to 300 s, and the wire rod is rapidly cooled at a cooling rate of 35°C / s or higher to transition from an austenite state into a sorbitite region so that a sorbite-dominated microstructure is formed; carrying out isothermal weak tempering for stress relief; and finally, carrying out slow cooling on a roller bed to obtain a hot-rolled wire rod having a microstructure mainly composed of weakly tempered sorbite, with the remainder being a mixed microstructure composed of ferrite and fragmented pearlite. The hot-rolled wire rod can reach a tensile strength of 1550-1590 MPa, a percentage reduction of area of 31-36%, and a mechanical property difference of less than or equal to 30 MPa within the same coil. The hot-rolled wire rod is used in application fields such as manufacturing of 2200 MPa-grade ultra-high-strength bridge cables, thereby reducing the risk of wire breakage and improving the strength grade of bridge cables.

Description

A hot-rolled wire rod for bridge cables with a strength of 2200MPa and its manufacturing method Technical Field

[0001] This invention belongs to the field of hot-rolled wire rod technology, specifically relating to a 2200MPa grade hot-rolled wire rod for bridge cables and its manufacturing method. Background Technology

[0002] With the continuous development of metallurgical technology, the strength level of bridge cables is constantly improving. Bridge cables are generally manufactured from hot-rolled wire rods through processes such as unwinding, pickling, multi-pass deep drawing, hot-dip galvanizing, and torsion. Therefore, the improvement of the strength level of bridge cables is based on the improvement of the strength level of hot-rolled wire rods used for bridge cables. Ultra-high strength bridge cables have advantages such as high strength and lightweight. To meet the requirements of long-span bridges for high-strength and high-torsional-performance bridge cables, it is necessary to develop 2200MPa grade ultra-high strength hot-rolled wire rods for bridge cables. However, in existing technologies, the improvement of the strength level of hot-rolled wire rods for bridge cables is often achieved through alloying, combined with hot rolling and Steyrmore air-cooled linear controlled cooling to regulate the microstructure and properties. The following technical challenges remain:

[0003] To improve wire rod strength, the C, Si, and Mn content in the wire rod is relatively high. This improves the hardenability of the steel and reduces the critical cooling rate. Combined with strong air cooling after wire drawing to refine the pearlite lamellae, a sorbitic structure with good strength and drawability is obtained. For example, patent CN118880169A discloses a high-strength bridge cable wire rod and its production method, using an 87SiMn high-carbon, high-silicon, and high-manganese composition system. This is combined with rapid strong cooling on a Steyrmo air-cooling line after low-temperature rolling and wire drawing, followed by holding and cooling for over 120 minutes to generate high-sorbite content wire rod, achieving a hot-rolled wire rod strength of over 1400 MPa. However, based on the existing cooling capacity of the Steyrmo air-cooling line, the maximum cooling capacity is generally only about 10℃ / s for the wire rod temperature drop. As the alloying degree of the wire rod increases, it exacerbates the segregation of carbon and alloying elements during the billet solidification process. During the process, the time spent in the secondary cementite precipitation temperature range of the wire rod is still relatively long. The cementite precipitated along the grain boundaries will form a higher level of network carbides, affecting the uniformity and ductility of the wire rod structure, thereby increasing the risk of wire breakage in the subsequent wire drawing process. In addition, the limited cooling capacity will affect the high-temperature austenitic phase transformation rate and complete transformation, resulting in a loss of wire rod strength. On the other hand, the increase in air cooling strength is accompanied by an increase in the uncontrollability of air volume, air temperature, and air direction. The temperature difference between the edge and core of the wire rod, the overlapping and non-overlapping parts, and the windward and leeward sides will further increase. Therefore, the higher the degree of alloying, the greater the difficulty of hot rolling cooling due to segregation and temperature difference. It will be difficult to suppress the generation of hard and brittle martensite abnormal structure, which will lead to a rapid increase in the risk of wire breakage in the wire drawing process of hot-rolled wire rod for bridge cables, limiting the improvement of the strength level of bridge cables. Reducing the alloy content or air cooling strength will further reduce the wire rod strength.

[0004] To balance the strength and plasticity of the wire rod, although online aging is performed using an insulated corridor, the wire rod remains in a continuous, slow cooling process due to the limited insulation capacity of the insulation line. This affects the sorbitic phase transformation, resulting in a lower temperature state after the transformation. Simultaneously, the resulting sorbite structure has a larger lamellar spacing and higher stress, increasing the difficulty of improving plasticity. This leads to insufficient plasticity in the resulting wire rod or excessively long online aging time, impacting production efficiency. Existing technologies also employ micro-alloying or offline salt bath processes to improve the strength and plasticity of the wire rod, for example, patent CN114561. 598A discloses a 2200MPa grade steel wire rod and its manufacturing method, which adopts a C-Si-Mn-Cr-V-Al-Ca composition design and is prepared by high-speed wire rolling, Stellmore, and salt bath. However, on the one hand, the time for V element dispersion precipitation during the continuous cooling process of the wire rod in the air-cooling line is short and difficult to control, resulting in the simultaneous existence of coarse and fine precipitation, which affects the uniformity of the structure and reduces strength. On the other hand, the wire rod preparation requires many processes and steps and has a long cycle, which limits the production of steel mills or the application of downstream users. Summary of the Invention

[0005] The present invention aims to at least partially solve one of the above-mentioned technical problems. The present invention provides a 2200MPa grade hot-rolled wire rod for bridge cables and its manufacturing method, which can effectively suppress the generation of abnormal network carbides and martensite structures, take into account the strength and plasticity of the wire rod and the uniformity of the structure, and reduce the risk of wire breakage during the wire drawing process of hot-rolled wire rod, so as to improve the strength level of bridge cables.

[0006] The technical solution adopted by this invention to solve its technical problem is:

[0007] A method for manufacturing hot-rolled wire rod for 2200MPa grade bridge cables, the method comprising:

[0008] Production lines are rolled from hot-rolled wire rods according to their chemical composition. The chemical composition and mass percentage of the hot-rolled wire rods include: C: 0.92%–0.95%, Si: 0.20%–0.40%, Mn: 0.70%–0.90%, Cr: 0.20%–0.40%, V: 0.025%–0.035%, Al: 0.02%–0.04%, P≤0.015%, S≤0.015%, with the remainder being Fe and unavoidable impurities. After the wire is spun into coils at a spinning temperature of ≥920℃, it undergoes online molten salt rapid cooling isothermal treatment, with the molten salt treatment time controlled to ≤300s. This allows the coils to cool down at a cooling rate of ≥35℃ / s, transitioning from the austenitic state to the sorbite phase region, forming a structure dominated by sorbite. The coils are then subjected to isothermal weak tempering to relieve stress. Finally, they undergo slow cooling on a roller conveyor to produce a hot-rolled coil with a microstructure consisting of a volume percentage of ≥88% weakly tempered sorbite, with the remainder being a mixture of ferrite and fused pearlite.

[0009] The chemical composition and mass percentage of the above-mentioned hot-rolled wire rods are designed based on the following:

[0010] (1) Carbon: As the most economical and effective element for solid solution strengthening and precipitation strengthening, the carbon content is conducive to expanding the austenite phase region, inhibiting the formation of ferrite, promoting the sorbite phase transformation during the online molten salt rapid cooling isothermal treatment, and improving the basic strength of the material. However, the carbon content will increase the tendency of carbon segregation during the solidification process of the billet, increase the tendency of decarburization and network carbide precipitation, deteriorate the plastic and tough properties of the material, and increase the difficulty of isothermal weak tempering stress relief, which is not conducive to the control of matrix structure. Therefore, in order to take into account the high strength requirements of 2200MPa grade bridge cable, reduce the difficulty of network carbide control and short-time isothermal stress relief, and control the material cost, the mass percentage of C is controlled at 0.92% to 0.95%.

[0011] (2) Silicon: Si is a deoxidizing element in steel. It can dissolve in austenite to increase the strength of steel. At the same time, it can inhibit grain coarsening and cementite precipitation during online molten salt rapid cooling isothermal treatment, so as to quickly obtain sorbite structure with fine lamellar interlayer spacing and reduce the difficulty of sorbite isothermal stress relief. However, excessive silicon content will make steel more prone to decarburization when heated at high temperature, prolong the transformation time in the phase transformation process, and reduce the toughness of steel. Therefore, in order to reduce the difficulty of improving the plasticity of wire rod and facilitate the phase transformation control of molten salt rapid cooling isothermal treatment, the Si content should be appropriately reduced, and the mass percentage of Si should be controlled at 0.20% to 0.40%.

[0012] (3) Manganese: Mn can be added as a deoxidizer during the smelting process. As an austenite forming element, it can expand the austenite phase region, inhibit the formation of ferrite, and increase the hardenability of wire rod. This is beneficial for promoting the rapid nucleation of sorbite structure with fine lamellar interlayer spacing during online molten salt rapid cooling isothermal treatment, thereby improving the tensile strength of wire rod. However, if the Mn content is too high, it will increase the overheating sensitivity of steel, aggravate the segregation during the solidification process of steel billet, increase the risk of precipitation of martensite structure in the core of wire rod, and reduce the activity of carbon, which will reduce the diffusion rate of carbon and increase the difficulty of tempering and softening, thereby losing the plasticity of wire rod. Therefore, in order to balance the high strength of hot-rolled wire rod, reduce the uniformity of structure and the difficulty of tempering control, the mass percentage of Mn is controlled at 0.70% to 0.90%.

[0013] (4) Chromium: As a solid solution strengthening element, Cr can strongly improve the hardenability of materials and regulate the matrix phase composition, which is beneficial to refine the spacing of sorbite lamellars, improve the drawing performance and increase the matrix strength. At the same time, it can increase the work hardening rate of wire rod during the wire drawing process and reduce the strength loss during the subsequent hot-dip galvanizing process of steel wire. However, excessive Cr content will aggravate component segregation, increase the risk of abnormal martensite precipitation, affect the uniformity of wire rod structure, reduce the activity of carbon in steel, significantly increase the difficulty of improving the plasticity of wire rod, and be unfavorable to isothermal weak tempering stress relief. It will affect the drawing and torsion performance of steel wire. Therefore, the mass percentage of Cr is controlled at 0.20% to 0.40%.

[0014] (5) Aluminum: Al is used as a deoxidizer in the smelting process. During hot rolling, it can form fine precipitates, which is beneficial to refine the grains and thus to control the uniformity of the structure and improve the toughness of the steel. At the same time, it is cheaper than Mo, which can inhibit the coarsening of cementite, which is beneficial to control the material cost. However, if the Al content is too high, it will increase the risk of inclusions and thus reduce the fatigue performance of the steel. Therefore, the mass percentage of Al is controlled at 0.20% to 0.40%.

[0015] (6) Vanadium: As a microalloying element, V can suppress high-temperature austenite coarsening and refine austenite grains. At the same time, it can be dispersed and precipitated in large quantities in the medium temperature range during the rapid cooling isothermal process of molten salt, thereby improving the strength level of hot-rolled wire rod. However, V is expensive, and excessive addition is not conducive to controlling wire rod cost and has the risk of coarsening. Based on the role and cost considerations of V, this invention controls the V content to be between 0.025% and 0.035%.

[0016] (7) Phosphorus and sulfur: P and S are impurity elements, and the lower the better. Therefore, P ≤ 0.015% and S ≤ 0.015%.

[0017] The aforementioned hot-rolled wire rod adopts a high-carbon, low-silicon, vanadium-containing composition design (C-Si-Mn-Cr-V-Al). The proportions of Si, Mn, and Cr are appropriately controlled to reduce the influence of alloy element segregation and the difficulty of controlling abnormal microstructure at low temperatures. The hardenability of the wire rod is also appropriately controlled, and the peak precipitation temperature of sorbite is adjusted to match the mid-temperature range of vanadium-containing carbide dispersion precipitation. This allows vanadium to be used to improve the strength level of the hot-rolled wire rod, compensating for the strength loss caused by the reduction of Si and Mn. Simultaneously, it provides favorable conditions for the rapid formation of a microstructure dominated by fine-laminated interlamellar sorbite during online molten salt rapid cooling isothermal treatment, facilitating stress relief through weak tempering. Furthermore, appropriately increasing the wire drawing temperature avoids the formation of network carbides during the wire drawing stage due to excessively low temperatures, preparing for subsequent formation of greater undercooling and promoting sorbite nucleation. After wire drawing, the wire rod undergoes online molten salt rapid cooling isothermal treatment.

[0018] First, compared to the limited maximum cooling capacity of existing Stellmore air-cooled lines, online molten salt can utilize the high heat transfer capacity of molten salt to promote rapid cooling of wire rods. On the one hand, it allows the wire rods to quickly bypass the secondary cementite precipitation temperature range of 700-800℃, effectively mitigating the risk of network carbide precipitation caused by high carbon content and avoiding deterioration of wire rod plasticity and microstructure uniformity. On the other hand, it can promote the rapid transition of wire rods from the high-temperature austenitic state to the sorbite phase region, forming a larger degree of undercooling, increasing the driving force for sorbite nucleation, and forming a microstructure dominated by fine lamellar sorbite. This improves the matrix strength, compensates for the strength loss caused by reducing Si and Mn content, and refines the lamellar spacing, preparing the microstructure for stress relief during weak tempering.

[0019] Second, compared to the existing Stellmore air-cooled line, which weakens the strengthening effect due to the uncontrollable cooling rate during the cooling phase transformation process and leads to the appearance of abnormal structures such as martensite, the molten salt can rapidly exchange heat with the wire rod, reducing the temperature difference from the edge to the core of the wire rod. 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 issue of windward and leeward sides. This can avoid the formation of martensite structure in the low-temperature phase region due to segregation of the wire rod. At the same time, by using online molten salt isothermal treatment, the wire rod can be maintained at the molten salt temperature after rapid cooling, prolonging the time when the wire rod is at the peak precipitation temperature of sorbite, promoting the full transformation of austenite structure to fine lamellar sorbite structure, and preventing the residual austenite from continuing to form martensite structure during subsequent cooling, thereby improving the strengthening effect of carbon elements and the uniformity of structure. On the other hand, the isothermal process can prolong the time when the wire rod is in the state of a large number of fine precipitation of vanadium-containing carbides, providing more driving force for the dispersion precipitation of vanadium, thereby exerting a strengthening and toughening effect.

[0020] Third, compared to air-cooled phase transformation control or long-term online aging, online molten salt treatment can control the wire rod within the high-temperature isothermal range of the sorbite phase region. The wire rod and molten salt temperatures are consistent rather than continuously decreasing, providing more thermal power for tempering. Combined with a predominantly sorbite-based microstructure with fine lamellar interlayer spacing, this reduces the difficulty of tempering, enabling rapid stress relief through tempering. Simultaneously, controlling the molten salt treatment time to ≤300s allows for short-term, weak tempering, controlling the transition from sorbite to tempered sorbite, forming a weak tempered sorbite phase. Partial sorbite melts to form melted pearlite, appropriately improving matrix plasticity and preventing coarsening of the sorbite microstructure due to prolonged strong tempering. On the one hand, large-area melting leads to excessive loss of matrix strength. On the other hand, short-time isothermal weak tempering treatment avoids the precipitation and coarsening of vanadium carbides due to long-term treatment, which reduces the strength improvement effect. At the same time, it shortens the online time of the wire rod and speeds up the production rhythm. Compared with offline salt bath treatment, it can save steps such as air cooling control and repeated winding and unwinding. The wire rod that has undergone online molten salt rapid cooling isothermal treatment has a high temperature after exiting the salt bath. Further slow cooling by roller can prevent the wire rod from increasing stress due to excessive cooling rate during the cooling process. Slow cooling can be used to promote further toughening of the wire rod structure, improve the softening effect, and achieve wire rod structure uniformity, strength-plasticity matching and mixed structure control.

[0021] Selecting an appropriate furnace temperature and furnace time before rolling can promote the homogenization of alloy composition and avoid the risk of decarburization and minor damage caused by excessive temperature, thus preparing for reducing the resistance to rolling deformation. In a preferred embodiment, the furnace temperature is controlled to be 1185-1220℃ and the furnace time is ≥180min before rolling.

[0022] Because the wire drawing temperature is relatively high, the restrictions on rolling can be reduced, which is conducive to improving rolling temperature and efficiency. At the same time, by selecting a suitable rolling temperature and deformation amount, dynamic recrystallization is promoted in the final rolling process, and the grains are refined. In the preferred embodiment, during the rolling process, the initial rolling temperature is controlled at 1100-1140°C, the final rolling temperature is controlled at 950-1000°C, and the final rolling reduction is 25%-30%.

[0023] In a preferred embodiment, the molten salt temperature for the online molten salt rapid cooling isothermal treatment is 530–560°C, and the molten salt treatment time is controlled to be ≥115s. This temperature falls within the medium-temperature range of the sorbite phase region of the wire rod and the dispersed precipitation of vanadium-containing carbides. Higher molten salt temperatures and longer treatment times provide more thermal power for tempering stress relief and promote improved matrix plasticity. However, excessively high molten salt temperatures and excessively long treatment times will lead to excessive loss of matrix strength due to increased tempering strength, and the coarsening effect of vanadium-containing carbides will affect the strengthening effect. Temperatures exceeding 600°C will negatively impact the matrix's strength. Vanadium carbide precipitation will reduce the matrix strength. Conversely, the lower the molten salt temperature, the more favorable it is to form a larger undercooling, which promotes the transformation of high-temperature austenite into sorbite with finer lamellar spacing. This provides more driving force for the fine precipitation of vanadium carbides and improves the matrix strength. However, if the molten salt temperature is too low, it will affect the stress relief effect of high-temperature isothermal weak tempering of wire rod and reduce the plasticity of the wire rod. Temperatures below 500℃ are not conducive to the precipitation of vanadium carbides and affect the matrix strength. Therefore, selecting appropriate molten salt temperature and molten salt treatment time can improve the strength matching of wire rod and increase production efficiency.

[0024] Because the temperature difference between the wire rod's coiling temperature and the sorbite phase region temperature is large, in a preferred embodiment, the online molten salt rapid cooling isothermal treatment is divided into a pre-treatment and a post-treatment. The molten salt circulation volume in the pre-treatment is greater than that in the post-treatment. The treatment time for the pre-treatment is 60-100 seconds. Using a larger molten salt circulation volume in the pre-treatment can maintain the molten salt temperature, increase the supercooling, and promote the rapid formation of a microstructure dominated by fine lamellar sorbite in the wire rod, reducing austenite residue. After the pre-treatment, the temperature difference between the wire rod and the molten salt is small, and the phase transformation of the wire rod will release heat energy. Therefore, the molten salt circulation volume in the post-treatment can be appropriately reduced, and the treatment time of the post-treatment can be controlled to be 55-200 seconds. On the one hand, the molten salt temperature can be kept stable, and the production energy consumption can be appropriately reduced. On the other hand, the wire rod can be controlled to undergo weak tempering in the high-temperature isothermal range to relieve stress and improve the strength-plasticity matching of the wire rod.

[0025] The pretreatment process can control the molten salt temperature rise and further improve the uniformity of the microstructure by selecting an appropriate molten salt circulation rate. In a preferred embodiment, the molten salt circulation rate of the pretreatment process is 500-620 t / h, and the molten salt temperature rise is ≤8℃.

[0026] The downstream processing can control the molten salt temperature rise and reduce production energy consumption by selecting an appropriate molten salt circulation rate. In a preferred embodiment, the molten salt circulation rate of the downstream processing is 250-345 t / h, and the molten salt temperature rise is ≤5℃.

[0027] In a preferred embodiment, the roller conveyor slow cooling control coil is slowly cooled to below 350°C at a cooling rate of 0.7-1°C / s. The residual heat of the coil at 530-560°C after exiting the salt bath can be used to reduce the energy consumption of the roller conveyor slow cooling, control the slow cooling of the coil, prevent the coil from cooling too quickly during the cooling process, which would lead to an increase in shrinkage stress, and promote further toughening of the coil structure, thereby improving the softening effect of the coil.

[0028] A 2200MPa grade hot-rolled wire rod for bridge cables, wherein the hot-rolled wire rod is manufactured by the manufacturing method of any one of the above-described 2200MPa grade hot-rolled wire rods for bridge cables.

[0029] The aforementioned hot-rolled wire rod adopts a high-carbon, V-containing chemical composition design combined with online molten salt rapid cooling isothermal technology to obtain a mixed microstructure composed of weakly tempered sorbite, ferrite, and fusing pearlite. Weakly tempered sorbite refers to the transitional state of sorbite after short-term tempering to tempered sorbite morphology. After strong tempering, sorbite will coarsen and break in large areas. Although the plasticity is high, the strength is poor. The wire rod microstructure dominated by weakly tempered sorbite can appropriately improve the plasticity of the matrix and avoid excessive strength loss after stress relief. At the same time, with the large amount of dispersed precipitation of V-containing carbides, the amount of precious alloy V can be reduced, the strength level of hot-rolled wire rod can be improved, and by effectively avoiding the risk of abnormal microstructures such as network carbon and martensite generated by C element, the strengthening effect of carbon element can be maximized, thereby improving the overall strength and plasticity of wire rod.

[0030] The higher the volume percentage of the weakly tempered sorbite and the finer the lamellar spacing, the higher the strength of the wire rod matrix. In a preferred embodiment, the volume percentage of the weakly tempered sorbite is ≥88%, and the lamellar spacing of the weakly tempered sorbite is 60-100 mm.

[0031] The higher the volume percentage of the fusing pearlite, the higher the plasticity of the wire rod. In a preferred embodiment, the volume percentage of the fusing pearlite is 7% to 10%.

[0032] In a preferred embodiment, the hot-rolled wire rod has a network carbide level of 0, which can effectively reduce the adverse effects of network carbides on the wire rod's ductility and toughness and the uniformity of its structure.

[0033] The network carbides and martensite structure in the hot-rolled wire rod are effectively controlled. In a preferred embodiment, the mechanical properties of the hot-rolled wire rod have a difference of ≤30MPa between coils, which can effectively reduce the risk of wire breakage during the wire drawing process of bridge cable manufacturing and improve the stability of bridge cable manufacturing.

[0034] In a preferred embodiment, the hot-rolled wire rod has a diameter of 10.0–15.0 mm, a tensile strength of 1550–1590 MPa, and a reduction of area of ​​31%–36%. The hot-rolled wire rod has higher tensile strength and a good reduction of area, which is beneficial for quickly reaching the 2200 MPa bridge cable strength level, reducing the number of wire drawing passes and the risk of wire breakage in bridge cables, thereby stabilizing production and improving the strength level of bridge cables.

[0035] Compared with the prior art, the beneficial effects of the present invention are at least as follows:

[0036] (1) Currently, improving the strength level of hot-rolled wire rod often involves alloying combined with controlled hot rolling cooling to regulate microstructure and properties. The higher the degree of alloying, the more difficult it is to control the hot rolling cooling, making it difficult to suppress the formation of network carbides and martensite. This leads to a rapid increase in the risk of wire breakage during the wire drawing process of hot-rolled wire rod for bridge cables, thus limiting the improvement of the strength level of bridge cables. This invention, through a V-containing chemical composition design combined with online molten salt rapid cooling isothermal technology, can control the wire rod to quickly transition from the high-temperature austenitic state to the sorbite phase region, suppressing the formation of network carbides and martensite. The process forms a microstructure dominated by fine-laminated sorbite, enhancing the strengthening effect of carbon elements and controlling the wire rod to enter the high-temperature isothermal range. This promotes the large-scale dispersion and precipitation of vanadium-containing carbides, improving the strength level of the hot-rolled wire rod and compensating for the strength loss caused by the reduction of Si / Mn content. Simultaneously, weak tempering relieves stress and improves the strength-plasticity balance of the wire rod. Finally, slow cooling on the roller table further toughens the wire rod microstructure and improves the softening effect. This process balances the strength-plasticity and microstructure uniformity of the wire rod. The shorter online time compared to offline salt bath treatment can effectively simplify the process flow and has good industrial adaptability.

[0037] (2) In view of the current situation of insufficient strength and plasticity, abnormal structure and difficulty in controlling the uniformity of structure of existing 2200MPa grade hot-rolled wire rods for bridge cables, the microstructure of the hot-rolled wire rod of the present invention includes a mixed structure composed mainly of weakly tempered sorbite, with the remainder being ferrite and melt-bonded pearlite. This can effectively avoid the risk of abnormal structure precipitation such as carbon network and martensite by carbon element, improve the uniformity of structure, and improve the strength and plasticity matching of wire rod by utilizing the transition state of short-time tempering to tempered sorbite morphology. It can achieve a tensile strength of 1550-1590MPa, a reduction of area of ​​31%-36%, and a mechanical property difference of ≤30MPa between the same rings. It is used in the manufacturing of 2200MPa grade ultra-high strength bridge cables and other application fields. It is beneficial to effectively reduce the risk of wire breakage during the wire drawing process of hot-rolled wire rod, so as to improve the strength level of bridge cables and meet the application requirements of large-span bridges. It has good application prospects. Attached Figure Description

[0038] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0039] Figure 1 is a metallographic diagram of Embodiment 1 of the present invention;

[0040] Figure 2 is a metallographic diagram of Embodiment 2 of the present invention. Detailed Implementation

[0041] The embodiments described below with reference to the accompanying drawings are exemplary and are merely for illustrative purposes and do not limit the description of the features and characteristics of the invention. They are intended to provide the best mode for carrying out the invention, to explain the invention, and are sufficient to enable those skilled in the art to practice the invention. However, they should not be construed as limiting the scope of the invention in any way, which is defined only by the appended claims. The microstructure and performance testing of the hot-rolled wire rods obtained in the following embodiments and comparative examples includes: tensile testing using GB-T 228.1-2021 Metallic Materials - Tensile Testing - Part 1: Room Temperature Test Method, to obtain tensile strength and reduction of area; microstructure testing using the metal microstructure testing method of GB / T13298 standard; and mechanical property same-coil difference test method: two coils of wire rod are taken 5m from the end of the coil. Using the overlap area as the base point, each coil of wire rod is divided into 8 equal segments. One tensile specimen is taken from each segment. The difference in strength of the tensile specimens after tensile testing is the mechanical property same-coil difference.

[0042] Example 1:

[0043] A preferred embodiment of the manufacturing method of the 2200MPa grade hot-rolled wire rod for bridge cables of the present invention comprises the following chemical composition and mass percentages: C: 0.94%, Si: 0.36%, Mn: 0.7%, Cr: 0.2%, V: 0.031%, Al: 0.025%, P: 0.012%, S: 0.010%, with the remainder being Fe and unavoidable impurities. The manufacturing method follows a process flow of rolling → wire drawing → online molten salt rapid cooling isothermal treatment → roller table slow cooling → coiling. Specifically:

[0044] The rolling process is used to heat a 220mm×220mm steel billet in a furnace to a high temperature that allows for rolling plasticity. Appropriate furnace temperature and furnace dwell time are selected to promote alloy composition homogenization and reduce segregation. After exiting the furnace, the billet is rolled into a 10mm diameter wire rod on a rolling line. Suitable rolling temperature and deformation are selected to improve rolling efficiency and promote dynamic recrystallization and grain refinement during the final rolling process. Specifically, the furnace soaking temperature is controlled at 1185℃. The furnace time is 180 minutes, the initial rolling temperature is 1100℃, the final rolling temperature is 950℃, and the final rolling reduction is 30%. The wire drawing process is used to convert the wire from the rolling line into coils through the wire drawing mechanism. The coils are spread on the roller table and conveyed along the roller table. A higher wire drawing temperature is selected to promote the coils to be in a high-temperature austenitic state, and to avoid the formation of network carbides during the wire drawing stage due to the wire drawing temperature being too low. This prepares for the formation of a larger degree of undercooling and the promotion of sorbite nucleation. Specifically, the wire drawing temperature is controlled at 920℃.

[0045] The online molten salt rapid cooling isothermal treatment process employs a two-section salt bath with internal molten salt. After coiling, the wire rod is conveyed via roller conveyor through the first section of the salt bath for pre-treatment, causing the wire rod to cool at a rate of 37°C / s. This rapidly transitions the wire rod from the high-temperature austenitic state, bypassing the network carbide precipitation zone, into the sorbite phase region. This inhibits the formation of network carbides, increases the undercooling, and promotes the transformation of high-temperature austenite into a microstructure dominated by fine-laminated sorbite, thus promoting the large-scale dispersion and precipitation of vanadium-containing carbides. Afterward, the wire rod is conveyed via roller conveyor through the second section of the salt bath. The subsequent processing involves appropriately reducing the molten salt circulation rate to maintain stable molten salt temperature and reduce production energy consumption. Simultaneously, the wire rod undergoes short-term weak tempering in the high-temperature isothermal range to relieve stress, preventing vanadium carbide precipitation and coarsening, and improving the strength-plasticity balance of the wire rod. Specifically: the molten salt temperature is 530℃, the molten salt circulation rate for the first-stage processing is 575t / h, the molten salt temperature rise is ≤8℃, and the processing time is 100s; the molten salt circulation rate for the subsequent processing is 250t / h, the molten salt temperature rise is ≤5℃, and the processing time is 200s.

[0046] The slow cooling process of the roller conveyor uses an open insulation cover. The wire rod, which has passed through the second salt bath tank, is conveyed by the conveyor roller conveyor into the insulation cover. The residual heat of the wire rod is used to prevent the wire rod from shrinking and increasing the stress due to excessive cooling rate during the cooling process, and to promote further toughening of the wire rod structure and improve the softening effect of the wire rod. Specifically, the wire rod is slowly cooled to 340°C at a cooling rate of 0.9°C / s. The coiling process is used to coil the wire rod into coils through a coiling drum. After packaging and warehousing, the hot-rolled wire rod product is obtained, and its metallographic structure is shown in Figure 1.

[0047] Comparative Example 1:

[0048] A method for manufacturing hot-rolled wire rod differs from Example 1 in that it follows a process flow of rolling → wire drawing → Steyrmo air cooling. Specifically, the heating furnace is controlled at a uniform heating temperature of 1150°C, with a furnace time of 230 minutes, an initial rolling temperature of 1050°C, a final rolling temperature of 900°C, and a wire drawing temperature of 865°C. The Steyrmo forced air cooling uses a fan with an air volume of 260,000 m³ / s. 3 At 98% capacity, fans 1-6 are turned on to cool the wire rod to 675℃ at a cooling rate of 9.2℃ / s. Then, fans 7-14 are turned on to 30% capacity to cool the wire rod to 300℃ at a cooling rate of 3.6℃ / s. After cooling, the hot-rolled wire rod is obtained. The tensile strength of the hot-rolled wire rod is 1466MPa, the reduction of area is 12%, the microstructure consists of 85% sorbite by volume, the remainder is ferrite and martensite, the network carbide level is 4, and the mechanical property difference between the same ring is 118MPa.

[0049] Comparative Example 2:

[0050] A method for manufacturing hot-rolled wire rod differs from that in Example 1 in that: the heating furnace is heated to a uniform temperature of 1160°C, the furnace time is 210 min, the initial rolling temperature is 1060°C, the final rolling temperature is 905°C, and the wire drawing temperature is 875°C. The online molten salt rapid cooling isothermal treatment process is a pre-treatment step that cools the wire rod at a cooling rate of 32°C / s. After the wire rod is removed from the production line, the finished hot-rolled wire rod is obtained.

[0051] Example 2:

[0052] A preferred embodiment of the manufacturing method of the 2200MPa grade hot-rolled wire rod for bridge cables of the present invention comprises the following chemical composition and mass percentages: C: 0.93%, Si: 0.4%, Mn: 0.85%, Cr: 0.29%, V: 0.03%, Al: 0.02%, P: 0.013%, S: 0.010%, with the remainder being Fe and unavoidable impurities. The manufacturing method follows a process flow of rolling → wire drawing → online molten salt rapid cooling isothermal treatment → roller table slow cooling → coiling. Specifically:

[0053] The rolling process is used to heat a 220mm×220mm steel billet in a furnace to a high temperature that allows for rolling plasticity. Appropriate furnace temperature and furnace dwell time are selected to promote alloy composition homogenization and reduce segregation. After exiting the furnace, the billet is rolled into a 14mm diameter wire rod on a rolling line. Suitable rolling temperature and deformation are selected to improve rolling efficiency and promote dynamic recrystallization and grain refinement during the final rolling process. Specifically, the furnace soaking temperature is controlled at 1205℃. The furnace time is 210 minutes, the initial rolling temperature is 1125℃, the final rolling temperature is 970℃, and the final rolling reduction is 26%. The wire drawing process is used to convert the wire from the rolling line into coils through the wire drawing mechanism. The coils are spread on the roller table and conveyed along the roller table. A higher wire drawing temperature is selected to promote the coils to be in a high-temperature austenitic state, and to avoid the formation of network carbides during the wire drawing stage due to the wire drawing temperature being too low. This prepares for the formation of greater undercooling and the promotion of sorbite nucleation. Specifically, the wire drawing temperature is controlled at 935℃.

[0054] The online molten salt rapid cooling isothermal treatment process employs a two-section salt bath with internal molten salt. After coiling, the wire rod is conveyed via roller conveyor through the first section of the salt bath for pre-treatment, causing the wire rod to cool at a rate of 36℃ / s. This rapidly transitions the wire rod from the high-temperature austenitic state through the network carbide precipitation zone into the sorbite phase region, inhibiting the formation of network carbides, increasing the undercooling, and promoting the transformation of high-temperature austenite into a microstructure dominated by fine lamellar sorbite. This also promotes the large-scale dispersion and precipitation of vanadium-containing carbides. Afterward, the wire rod is conveyed via roller conveyor through the second section of the salt bath. The subsequent processing involves appropriately reducing the molten salt circulation rate to maintain stable molten salt temperature and reduce production energy consumption. Simultaneously, the wire rod undergoes short-term weak tempering in the high-temperature isothermal range to relieve stress, preventing vanadium carbide precipitation and coarsening, and improving the strength-ductility balance of the wire rod. Specifically: the molten salt temperature is 553℃, the molten salt circulation rate for the first-stage processing is 535t / h, the molten salt temperature rise is ≤8℃, and the processing time is 74s; the molten salt circulation rate for the subsequent processing is 320t / h, the molten salt temperature rise is ≤5℃, and the processing time is 105s.

[0055] The slow cooling process of the roller conveyor uses an open insulation cover. The wire rod, which has passed through the second salt bath tank, is conveyed into the insulation cover by the conveyor roller conveyor. The residual heat of the wire rod is used to prevent the wire rod from shrinking and increasing the stress due to excessive cooling rate during the cooling process, and to promote further toughening of the wire rod structure and improve the softening effect of the wire rod. Specifically, the wire rod is slowly cooled to 335°C at a cooling rate of 0.8°C / s. The coiling process is used to coil the wire rod into coils through a coiling drum. After packaging and warehousing, the hot-rolled wire rod product is obtained, and its metallographic structure is shown in Figure 2.

[0056] Comparative Example 3:

[0057] A method for manufacturing hot-rolled wire rod differs from that in Example 2 in that the online molten salt rapid cooling isothermal treatment process involves pretreatment to cool the wire rod at a cooling rate of 32°C / s, with the molten salt temperature being 595°C, resulting in a finished hot-rolled wire rod product after it comes off the production line.

[0058] Comparative Example 4:

[0059] A method for manufacturing hot-rolled wire rod differs from that in Example 2 in that the online molten salt rapid cooling isothermal treatment process involves pretreatment to cool the wire rod at a cooling rate of 39°C / s, with the molten salt temperature at 505°C, resulting in a finished hot-rolled wire rod product after the wire rod is removed from the production line.

[0060] Example 3:

[0061] A preferred embodiment of the manufacturing method of the 2200MPa grade hot-rolled wire rod for bridge cables according to the present invention, wherein the chemical composition and mass percentage of the hot-rolled wire rod include C: 0.92%, Si: 0.37%, Mn: 0.9%, Cr: 0.36%, V: 0.025%, Al: 0.04%, P: 0.013%, S: 0.015%, with the remainder being Fe and unavoidable impurities; the manufacturing method follows the process flow of rolling → wire drawing → online molten salt rapid cooling isothermal treatment → roller table slow cooling → coiling, specifically:

[0062] The rolling process is used to heat a 220mm×220mm steel billet in a furnace to a high temperature that allows for rolling plasticity. Appropriate furnace temperature and furnace dwell time are selected to promote alloy composition homogenization and reduce segregation. After exiting the furnace, the billet is rolled into a 15mm diameter wire rod on a rolling line. Suitable rolling temperature and deformation are selected to improve rolling efficiency and promote dynamic recrystallization and grain refinement during the final rolling process. Specifically, the furnace soaking temperature is controlled at 1220℃. The furnace time is 200 minutes, the initial rolling temperature is 1140℃, the final rolling temperature is 1000℃, and the final rolling reduction is 25%. The wire drawing process is used to convert the wire from the rolling line into coils through the wire drawing mechanism. The coils are spread on the roller table and conveyed along the roller table. A higher wire drawing temperature is selected to promote the coils to be in a high-temperature austenitic state, and to avoid the formation of network carbides during the wire drawing stage due to the wire drawing temperature being too low. This prepares for the formation of a larger degree of undercooling and the promotion of sorbite nucleation. Specifically, the wire drawing temperature is controlled at 945℃.

[0063] The online molten salt rapid cooling isothermal treatment process employs a two-section salt bath with an internal molten salt compartment. After coiling, the wire rod is conveyed via roller conveyor through the first salt bath for pre-treatment, causing the wire rod to cool at a rate of 38°C / s. This rapidly transitions the wire rod from the high-temperature austenitic state, bypassing the network carbide precipitation zone, into the sorbite phase region. This inhibits network carbide formation, increases undercooling, and promotes the transformation of high-temperature austenite into a microstructure dominated by fine-laminated sorbite, facilitating the large-scale dispersion and precipitation of vanadium-containing carbides. The wire rod is then conveyed via roller conveyor through the second salt bath. The subsequent processing involves appropriately reducing the molten salt circulation rate to maintain stable molten salt temperature and reduce production energy consumption. Simultaneously, the wire rod undergoes short-term weak tempering in the high-temperature isothermal range to relieve stress, preventing vanadium carbide precipitation and coarsening, and improving the strength-plasticity balance of the wire rod. Specifically: the molten salt temperature is 542℃, the molten salt circulation rate for the first-stage processing is 620t / h, the molten salt temperature rise is ≤8℃, and the processing time is 82s; the molten salt circulation rate for the subsequent processing is 345t / h, the molten salt temperature rise is ≤5℃, and the processing time is 165s.

[0064] The slow cooling process of the roller conveyor uses an open insulation cover. The wire rod, which has passed through the second salt bath tank, is conveyed by the conveyor roller conveyor into the insulation cover. The residual heat of the wire rod is used to prevent the wire rod from shrinking and increasing the stress due to excessive cooling rate during the cooling process, and to promote further toughening of the wire rod structure and improve the softening effect of the wire rod. Specifically, the wire rod is slowly cooled to 328°C at a cooling rate of 1°C / s. The coiling process is used to coil the wire rod into coils through a coiling drum. After packaging and warehousing, the hot-rolled wire rod is obtained as a finished product.

[0065] Comparative Example 5:

[0066] A method for manufacturing hot-rolled wire rod differs from that in Example 3 in that the processing time for the first stage of the online molten salt rapid cooling isothermal treatment process is 50 seconds, and the processing time for the second stage is 40 seconds, after which the finished hot-rolled wire rod is obtained.

[0067] Comparative Example 6:

[0068] A method for manufacturing hot-rolled wire rod differs from that in Example 3 in that the processing time for the first stage of the online molten salt rapid cooling isothermal treatment process is 135s, and the processing time for the second stage is 320s, after which the finished hot-rolled wire rod is obtained.

[0069] Example 4:

[0070] A preferred embodiment of the manufacturing method of the 2200MPa grade hot-rolled wire rod for bridge cables of the present invention comprises the following chemical composition and mass percentages: C: 0.95%, Si: 0.2%, Mn: 0.76%, Cr: 0.4%, V: 0.035%, Al: 0.034%, P: 0.015%, S: 0.013%, with the remainder being Fe and unavoidable impurities. The manufacturing method follows a process flow of rolling → wire drawing → online molten salt rapid cooling isothermal treatment → roller table slow cooling → coiling. Specifically:

[0071] The rolling process is used to heat a 220mm×220mm steel billet in a furnace to a high temperature that allows for rolling plasticity. Appropriate furnace temperature and furnace time are selected to promote alloy composition homogenization and reduce segregation. After exiting the furnace, the billet is rolled into 11mm diameter wire rod on a rolling line. Suitable rolling temperature and deformation are selected to improve rolling efficiency and promote dynamic recrystallization and grain refinement during the final rolling process. Specifically, the furnace soaking temperature is controlled at 1195℃. The furnace time is 195 minutes, the initial rolling temperature is 1110℃, the final rolling temperature is 960℃, and the final rolling reduction is 29%. The wire drawing process is used to convert the wire from the rolling line into coils through the wire drawing mechanism. The coils are spread on the roller table and conveyed along the roller table. A higher wire drawing temperature is selected to promote the coils to be in a high-temperature austenitic state, and to avoid the formation of network carbides during the wire drawing stage due to the wire drawing temperature being too low. This prepares for the formation of a larger degree of undercooling and the promotion of sorbite nucleation. Specifically, the wire drawing temperature is controlled at 930℃.

[0072] The online molten salt rapid cooling isothermal treatment process employs a two-stage salt bath with an internal molten salt compartment. After coiling, the wire rod is conveyed via roller conveyor through the first salt bath for pre-treatment, causing the wire rod to cool at a rate of 35°C / s. This rapidly transitions the wire rod from the high-temperature austenitic state, bypassing the network carbide precipitation zone, into the sorbite phase region. This inhibits network carbide formation, increases undercooling, and promotes the transformation of high-temperature austenite into a microstructure dominated by fine-laminated sorbite, facilitating the large-scale dispersion and precipitation of vanadium-containing carbides. The wire rod is then conveyed via roller conveyor through the second salt bath. The molten salt circulation rate in the downstream processing tank is appropriately reduced to maintain stable molten salt temperature and reduce production energy consumption. At the same time, the wire rod is subjected to short-term weak tempering in the high-temperature isothermal range to relieve stress, avoid vanadium carbide precipitation and coarsening, and improve the strength-plasticity matching of the wire rod. Specifically: the molten salt temperature is 560℃, the molten salt circulation rate in the upstream processing tank is 500t / h, the molten salt temperature rise is ≤8℃, and the processing time is 60s; the molten salt circulation rate in the downstream processing tank is 300t / h, the molten salt temperature rise is ≤5℃, and the processing time is 55s.

[0073] The slow cooling process of the roller conveyor uses an open insulation cover. The wire rod, which has passed through the second salt bath tank, is conveyed into the insulation cover by the conveyor roller conveyor. The residual heat of the wire rod is used to prevent the wire rod from shrinking and increasing the stress due to excessive cooling rate during the cooling process, and to promote further toughening of the wire rod structure and improve the softening effect of the wire rod. Specifically, the wire rod is slowly cooled to 345°C at a cooling rate of 0.7°C / s. The coiling process is used to coil the wire rod into coils through a coiling drum. After packaging and warehousing, the hot-rolled wire rod is obtained as a finished product.

[0074] Comparative Example 7:

[0075] A method for manufacturing hot-rolled wire rod differs from that in Example 4 in that the manufacturing method follows a process flow of rolling → wire drawing → online molten salt rapid cooling isothermal treatment → air cooling. The air cooling is achieved by opening an insulation cover and conveying the wire rod through the second salt bath tank via a conveyor roller. The wire rod is cooled to 285°C at a cooling rate of 1.7°C / s, and the finished hot-rolled wire rod is obtained after exiting the production line.

[0076] The microstructure and properties of the hot-rolled wire rods obtained in Examples 1-4 and Comparative Examples 2-7 were tested, and the comparative results are shown in Table 1 below:

[0077] Table 1. Comparison of microstructure and properties of hot-rolled wire rods with different compositions and manufacturing methods

[0078] The comparison between Example 1 and Comparative Example 1 shows that, compared to the Stellmore air-cooled line, which weakens the strengthening effect due to the uncontrollable cooling rate during the cooling phase transformation process and leads to the formation of abnormal structures such as network carbon and martensite, and makes it difficult to control the fine precipitation of vanadium-containing carbides, resulting in poor microstructure uniformity, this invention, through the design of a V-containing chemical composition combined with online molten salt rapid cooling isothermal technology, can effectively avoid the risk of abnormal structures such as network carbon and martensite precipitation of C element, maximize the strengthening effect of carbon element, control the diffuse precipitation of vanadium-containing carbides during the isothermal process, and improve the microstructure uniformity. The microstructure includes a mixed microstructure mainly composed of weakly tempered sorbite, with the remainder being ferrite and fused pearlite. This improves the overall strength, plasticity, and microstructure uniformity of the wire rod. As can be seen from the results of Examples 1 to 4, the hot-rolled wire rod can achieve a tensile strength of 1550-1590 MPa, a reduction of area of ​​31%-36%, and a mechanical property difference of ≤30 MPa between coils. It is suitable for applications such as manufacturing 2200 MPa grade ultra-high strength bridge cables, which helps to effectively reduce the risk of wire breakage during the wire drawing process of hot-rolled wire rod and improve the strength level of bridge cables.

[0079] As can be seen from the comparison results between Example 1 and Comparative Example 2, appropriately increasing the wire drawing temperature can avoid the formation of network carbides during the wire drawing stage due to excessively low wire drawing temperature, thus preparing for the formation of greater undercooling and promoting the nucleation of sorbite structure. At the same time, it can reduce the restrictions on rolling, which is conducive to increasing the rolling temperature, reducing the rolling deformation resistance, and thus improving the rolling efficiency.

[0080] As can be seen from the comparison results of Example 2 and Comparative Example 3, the higher the molten salt temperature of the online molten salt rapid cooling isothermal treatment, the more thermal power can be provided for tempering stress relief and the improvement of matrix plasticity. However, if the molten salt temperature is too high, as the treatment time is extended, the increase in tempering strength will lead to excessive loss of matrix strength, and the precipitation of vanadium carbides will coarsen the matrix and affect the strengthening effect.

[0081] As can be seen from the comparison results of Example 2 and Comparative Example 4, the lower the molten salt temperature of the online molten salt rapid cooling isothermal treatment, the better it is to form a larger degree of undercooling, promote the transformation of high-temperature austenite into sorbite with finer lamellar spacing, provide more driving force for the fine precipitation of vanadium carbides, and improve the matrix strength. However, if the molten salt temperature is too low, it will affect the stress relief effect of high-temperature isothermal weak tempering of wire rod and lose the plasticity of wire rod.

[0082] As can be seen from the comparison results between Example 3 and Comparative Example 5, the shorter the processing time of the online molten salt rapid cooling isothermal treatment, the lower the stress relief effect of weak tempering, the higher the strength and the lower the plasticity of the wire rod. However, if the initial treatment time is too short, it will affect the control of the uniformity of the microstructure. At the same time, if the subsequent treatment time is too short, it will affect the full precipitation of vanadium carbides and the stress relief effect of weak tempering, which is detrimental to the plasticity of the wire rod.

[0083] As can be seen from the comparison results of Example 3 and Comparative Example 6, the longer the processing time of online molten salt rapid cooling isothermal treatment, the more thermal power can be provided for tempering stress relief, and the plasticity of the matrix can be improved. However, if the processing time is too long, the increase in tempering strength will lead to excessive loss of matrix strength, and the precipitation of vanadium carbides will coarsen the matrix, affecting the strengthening effect and increasing production energy consumption.

[0084] As can be seen from the comparison results of Example 3 and Comparative Example 7, the use of roller conveyor slow cooling control to slowly cool the wire rod can prevent the wire rod from cooling too quickly during the cooling process, which would lead to an increase in shrinkage stress and promote further toughening of the wire rod structure, thereby improving the softening effect of the wire rod.

[0085] The detailed descriptions listed above are merely specific illustrations of feasible embodiments of the present invention and are not intended to limit the scope of protection of the present invention. All equivalent embodiments or modifications made without departing from the spirit of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for manufacturing hot-rolled wire rod for 2200MPa grade bridge cables, characterized in that, Its manufacturing methods include: Production lines are rolled from hot-rolled wire rods according to their chemical composition. The chemical composition and mass percentage of the hot-rolled wire rods include: C: 0.92%–0.95%, Si: 0.20%–0.40%, Mn: 0.70%–0.90%, Cr: 0.20%–0.40%, V: 0.025%–0.035%, Al: 0.02%–0.04%, P≤0.015%, S≤0.015%, with the remainder being Fe and unavoidable impurities. After the wire is spun into coils at a spinning temperature of ≥920℃, it undergoes online molten salt rapid cooling isothermal treatment, with the molten salt treatment time controlled to ≤300s. This allows the coils to cool down at a cooling rate of ≥35℃ / s, transitioning from the austenitic state to the sorbite phase region, forming a structure dominated by sorbite. The coils are then subjected to isothermal weak tempering to relieve stress. Finally, they undergo slow cooling on a roller conveyor to produce a hot-rolled coil with a microstructure consisting of a volume percentage of ≥88% weakly tempered sorbite, with the remainder being a mixture of ferrite and fused pearlite.

2. The method for manufacturing hot-rolled wire rod for 2200MPa grade bridge cables according to claim 1, characterized in that, Before rolling, the heating furnace temperature is controlled at 1185-1220℃, and the furnace time is ≥180min.

3. The method for manufacturing 2200MPa grade hot-rolled wire rod for bridge cables according to claim 1, characterized in that, During the rolling process, the initial rolling temperature is controlled at 1100–1140°C, the final rolling temperature at 950–1000°C, and the final rolling reduction at 25%–30%.

4. The method for manufacturing hot-rolled wire rod for 2200MPa grade bridge cables according to claim 1, characterized in that, The molten salt temperature in the online molten salt rapid cooling isothermal treatment is 530–560°C. The online molten salt rapid cooling isothermal treatment is divided into a pre-treatment and a post-treatment. The molten salt circulation volume in the pre-treatment is greater than that in the post-treatment. The treatment time for the pre-treatment is 60–100 s, and the treatment time for the post-treatment is 55–200 s.

5. The method for manufacturing hot-rolled wire rod for 2200MPa grade bridge cables according to claim 4, characterized in that, The molten salt circulation rate of the pre-treatment stage is 500-620 t / h, and the molten salt temperature rise is ≤8℃; the molten salt circulation rate of the post-treatment stage is 250-345 t / h, and the molten salt temperature rise is ≤5℃.

6. The method for manufacturing hot-rolled wire rod for 2200MPa grade bridge cables according to claim 4, characterized in that, The roller conveyor slow cooling control strip is slowly cooled to below 350°C at a cooling rate of 0.7 to 1°C / s.

7. A hot-rolled wire rod for bridge cables with a strength of 2200MPa, characterized in that... The hot-rolled wire rod is manufactured by the method for manufacturing 2200MPa grade hot-rolled wire rod for bridge cables as described in any one of claims 1 to 6.

8. The hot-rolled wire rod for bridge cables of 2200MPa grade according to claim 7, characterized in that, The lamellar spacing of the weakly tempered sorbite is 60–100 mm, and the volume percentage of the melt-fractured pearlite is 7%–10%.

9. The hot-rolled wire rod for bridge cables of 2200MPa grade according to claim 7, characterized in that, The hot-rolled wire rod has a network carbide grade of 0 and a mechanical property difference of ≤30MPa between the same rings.

10. The hot-rolled wire rod for bridge cables of 2200MPa grade according to claim 7, characterized in that, The hot-rolled wire rod has a diameter of 10.0–15.0 mm, a tensile strength of 1550–1590 MPa, and a reduction of area of ​​31%–36%.

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