Hot-rolled wire rod for 2200MPa bridge cable and manufacturing method of hot-rolled wire rod

Abstract

The invention relates to a hot-rolled wire rod for a 2200MPa bridge cable and a manufacturing method of the hot-rolled wire rod, a high-carbon V-containing chemical component design rolling production line is adopted, after the wire rod is spun into the wire rod at the spinning temperature of more than or equal to 920 DEG C, online molten salt rapid cooling isothermal treatment is carried out, the molten salt treatment time is controlled to be less than or equal to 300s, the wire rod is cooled at the cooling speed of more than or equal to 35 DEG C / s, and enters a sorbite phase region from an austenite state; according to the hot-rolled wire rod, a structure with sorbite as the main part is formed and subjected to isothermal weak tempering to remove stress, finally, roller way slow cooling is conducted, the hot-rolled wire rod with the microscopic structure comprising a mixed structure composed of weak tempered sorbite as the main part and ferrite and fused pearlite as the balance is prepared, the tensile strength can reach 1550-1590 MPa, the percentage reduction of area is 31%-36%, the mechanical property same-circle difference is smaller than or equal to 30 MPa, and the hot-rolled wire rod can be used for manufacturing the steel wire rod. The method is used in the application field of manufacturing of 2200MPa-grade ultrahigh-strength bridge cables and the like, the risk of wire breakage is reduced, and the strength grade of the bridge cables is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of hot-rolled wire rods, and in particular relates to a 2200MPa-grade hot-rolled wire rod for bridge cables and a manufacturing method thereof. Background Art

[0002] With the continuous development of metallurgical technology, the strength level of bridge cables has been continuously improved. Bridge cables are generally made of hot-rolled wire rods through processes such as wire rod unwinding, pickling, multi-pass deep wire drawing, hot-dip galvanizing, and twisting. 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 the advantages of high strength and light weight. In response to the demand for high-strength and high-torsion performance bridge cables for large-span bridges, it is necessary to develop 2200MPa ultra-high-strength hot-rolled wire rods for bridge cables. However, in the existing technology, the improvement of the strength level of hot-rolled wire rods for bridge cables is often achieved through alloying, combined with hot rolling and Stelmor air-cooled line controlled cooling to control the organizational properties. There are still the following technical difficulties: In order to improve the strength of wire rod, the C, Si and Mn contents in the wire rod are relatively high, which are used to improve the hardenability of steel, reduce the critical cooling rate, and refine the pearlite lamellae with strong air cooling after spinning to obtain a sorbite structure with good strength and drawing performance, and increase the sorbite content. For example, patent CN118880169A discloses a high-strength wire rod for bridge cables and its production method, which adopts a high-carbon, high-silicon and high-manganese component system of 87SiMn, combined with the rapid strong cooling of the Stelmor air cooling line after low-temperature rolling and spinning, and the insulation cooling for more than 120 minutes to generate a high-sorbite content wire rod, so that the strength of the hot-rolled wire rod reaches more than 1400MPa. However, on the one hand, based on the cooling capacity of the existing Stelmor air cooling line, the maximum cooling capacity of the air cooling line is generally to make the wire rod temperature drop at about 10℃ / s. As the alloying degree of the wire rod increases, the segregation of carbon and alloy elements in the solidification process of the steel billet will be aggravated. During the process, the wire rod still spends a long time in the precipitation temperature range of secondary cementite, and the cementite precipitated along the grain boundary will form a higher level of network carbide, which affects the uniformity and plastic toughness of the wire rod structure, thereby increasing the risk of wire breakage in the subsequent wire drawing process. In addition, due to the limitation of cooling capacity, it will affect the high-temperature austenite phase transformation speed and full transformation, and lose the strength of the wire rod. On the other hand, the increase in air cooling intensity is accompanied by the increase in the uncontrollability of air volume, air temperature, wind direction, etc. The temperature difference between the edge of the wire rod to the core, the overlap and non-overlap, and the windward side and the leeward side will further increase. Therefore, the higher the degree of alloying, the greater the difficulty of hot rolling controlled cooling due to segregation and temperature difference, and it will be difficult to suppress the generation of hard and brittle martensitic abnormal structure, resulting in a rapid increase in the risk of wire breakage in the wire drawing process of the hot-rolled wire rod for bridge cables, limiting the improvement of the strength level of bridge cables, and reducing the alloy content or air cooling intensity will further lose the strength of the wire rod.

[0003] In order to take into account both the strength and plasticity of the wire rod, although the insulation corridor is used for online aging, the wire rod is still in a continuous slow cooling process due to the insulation capacity of the insulation line, which will affect the sorbite phase transformation. After the phase transformation, the wire rod will be in a lower temperature state. At the same time, the obtained sorbite structure has a larger sheet spacing and higher stress, which will increase the difficulty of plasticity improvement, resulting in insufficient plasticity of the obtained wire rod or too long online time, affecting production efficiency; in the prior art, microalloying or offline salt bath process is also used to improve the strength and plasticity of the wire rod, for example: Patent CN114561 598A discloses a 2200MPa grade wire rod for steel wire and a method for manufacturing the same, which is designed with a C-Si-Mn-Cr-V-Al-Ca composition and is prepared by combining high-wire rolling, Stelmor and salt bath. However, on the one hand, the time for the V element to diffuse and precipitate during the continuous cooling process of the wire rod on the air-cooling line is short and difficult to control, and coarse and fine precipitation will exist at the same time, affecting the uniformity of the structure and losing strength. On the other hand, the preparation of the wire rod requires many processes and steps, and the cycle is long, which limits the production of steel mills or the application of downstream users. Summary of the invention

[0004] The present invention aims to solve at least one of the above-mentioned technical problems to a certain extent. The present invention provides a 2200MPa grade hot-rolled wire rod for bridge cables and a manufacturing method thereof, which can effectively inhibit the generation of network carbides and abnormal 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 of the hot-rolled wire rod during the wire drawing process, so as to improve the strength level of bridge cables.

[0005] The technical solution adopted by the present invention to solve its technical problem is: A method for manufacturing a 2200MPa 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: 0.92% to 0.95%, Si: 0.20% to 0.40%, Mn: 0.70% to 0.90%, Cr: 0.20% to 0.40%, V: 0.025% to 0.035%, Al: 0.02% to 0.04%, P≤0.015%, S≤0.015%, and the rest is Fe and unavoidable impurities; The wire rod is spun into a wire rod at a spinning temperature of ≥920°C, and then is subjected to an online molten salt rapid cooling isothermal treatment, the molten salt treatment time is controlled to be ≤300s, so that the wire rod is cooled at a cooling rate of ≥35°C / s, enters the sorbite phase region from the austenite state, forms a structure mainly composed of sorbite, and isothermally weakly tempered to relieve stress, and finally is slowly cooled by a roller to produce a hot-rolled wire rod whose microstructure includes weakly tempered sorbite with a volume percentage of ≥88%, and the rest is a mixed structure composed of ferrite and fused pearlite.

[0006] The design basis of the chemical composition and mass percentage of the above hot rolled wire rod includes: (1) Carbon: As the most economical and effective element for solid solution strengthening and precipitation strengthening, the carbon element is conducive to expanding the austenite phase region, inhibiting the formation of ferrite, promoting the troostite phase transformation during the online molten salt rapid cooling isothermal treatment, and improving the basic strength of the material. However, as the carbon content increases, it will increase the tendency of carbon segregation during the solidification of the billet, increase the tendency of decarburization and precipitation of network carbides, deteriorate the plasticity and toughness of the material, and increase the difficulty of isothermal weak tempering stress relief, which is not conducive to the control of the matrix structure. Therefore, in order to take into account the high strength requirements of 2200MPa-level bridge cables, reduce the difficulty of controlling network carbides and short-time isothermal stress relief, and control material costs, the mass percentage of C is controlled to be 0.92%~0.95%.

[0007] (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 that a troostite structure with fine interlamellar spacing can be quickly obtained and the difficulty of isothermal stress relief of troostite can be reduced. However, excessive silicon content will make steel easier to decarburize when heated at high temperatures, prolong the transformation time during the phase transformation process, and reduce the toughness of steel. Therefore, in order to reduce the difficulty of improving the plasticity of wire rods and facilitate the phase transformation control during molten salt rapid cooling isothermal treatment, the Si content is appropriately reduced, and the mass percentage of Si is controlled to be 0.20%~0.40%.

[0008] (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 the wire rod. This is beneficial to the rapid nucleation of the sorbite structure with fine interlamellar spacing during the online molten salt rapid cooling isothermal treatment, thereby improving the tensile strength of the wire rod. However, if the Mn content is too high, it will increase the overheating sensitivity of the steel, aggravate the segregation during the solidification process of the billet, increase the risk of precipitation of the martensite structure in the core of the wire rod, and reduce the activity of carbon, which reduces the diffusion rate of carbon, increases the difficulty of tempering softening, and thus loses 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, the mass percentage of Mn is controlled to be 0.70%~0.90%.

[0009] (4) Chromium: As a solid solution strengthening element, Cr can strongly improve the hardenability of the material and regulate the matrix phase composition, which is beneficial to refining the spacing between troostite sheets, improving the drawing performance and increasing the matrix strength. At the same time, it can increase the work hardening rate of the wire rod during the wire drawing process and reduce the strength loss during the subsequent hot-dip galvanizing process of the steel wire. However, too high Cr content will aggravate the component segregation, increase the risk of abnormal martensite structure precipitation, affect the uniformity of the wire rod structure, reduce the activity of carbon in the steel, and significantly increase the difficulty of improving the plasticity of the wire rod. It is not conducive to isothermal weak tempering stress relief and will affect the wire drawing and torsion performance of the steel wire. Therefore, the mass percentage of Cr is controlled to be 0.20%~0.40%.

[0010] (5) Aluminum: Al acts as a deoxidizer during the smelting process and can form fine precipitates during hot rolling, which is beneficial to grain refinement, thereby controlling the uniformity of the structure and improving the toughness of the steel. At the same time, it is cheaper than Mo, which can inhibit the coarsening of cementite, and is beneficial to controlling material costs. However, too high Al content will increase the risk of inclusions and reduce the fatigue performance of the steel. Therefore, the mass percentage of Al is controlled to be 0.20%~0.40%.

[0011] (6) Vanadium: As a microalloying element, V can inhibit the coarsening of high-temperature austenite and refine austenite grains. At the same time, it can be dispersed and precipitated in large quantities in the medium temperature range during the isothermal process of rapid cooling in molten salt, thereby improving the strength level of hot-rolled wire rods. However, the cost of V is relatively high. Excessive addition is not conducive to controlling the cost of wire rods and has the risk of coarsening. Based on the role of V and cost considerations, the present invention controls the V content to 0.025%~0.035%.

[0012] (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%.

[0013] The hot-rolled wire rod adopts the high-carbon, low-silicon, vanadium-containing composition design of C-Si-Mn-Cr-V-Al, appropriately adjusts the proportion of Si, Mn, and Cr components, reduces the influence of alloy element segregation and the difficulty of controlling low-temperature abnormal structures, appropriately controls the hardenability of the wire rod, and adjusts the peak precipitation temperature of sorbite to adapt to the medium temperature range of the dispersion precipitation of vanadium-containing carbides, so as to utilize vanadium to improve the strength level of the hot-rolled wire rod and make up for the strength loss caused by reducing Si and Mn. At the same time, it provides favorable conditions for promoting the rapid formation of a structure dominated by sorbite with fine lamellar spacing during online molten salt rapid cooling isothermal treatment and facilitating weak tempering to relieve stress. On this basis, the wire-spinning temperature is appropriately increased to avoid the formation of network carbides in the wire-spinning stage due to the wire-spinning temperature being too low, so as to prepare for the subsequent formation of a large degree of supercooling and the promotion of sorbite structure nucleation. After the wire is spouted, it is directly subjected to online molten salt rapid cooling isothermal treatment: 1. Compared with the limited maximum cooling capacity of the existing Stelmor air-cooling line, the online molten salt can utilize the high heat exchange capacity of the molten salt to promote the rapid cooling of the wire rod. On the one hand, it can make the wire rod quickly pass the secondary cementite precipitation temperature range of 700~800℃, effectively improve the risk of network carbide precipitation caused by high carbon content, and avoid the deterioration of the plasticity and organizational uniformity of the wire rod; on the other hand, it can promote the wire rod to quickly enter the troostite phase region from the high-temperature austenite state, form a large degree of supercooling, increase the driving force for the nucleation of troostite, and form a structure dominated by troostite with fine lamellar spacing, thereby improving the matrix strength, compensating for the strength loss caused by reducing the Si and Mn contents, and refining the lamellar spacing to prepare for weak tempering stress relief.

[0014] 2. Compared with the existing Stelmor air-cooled line, which weakens the strengthening effect due to the uncontrollable cooling rate during the cooling phase transformation, and causes the appearance of abnormal structures such as martensite, on the one hand, the molten salt can quickly exchange heat with the wire rod to reduce 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 problem of windward side and leeward side, which can avoid the wire rod being affected by segregation and forming martensite structure in the low-temperature phase region. 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 that the wire rod is at the peak precipitation temperature of troostite, promoting the full transformation of austenite structure to troostite structure with fine lamellar spacing, avoiding the continued formation of martensite structure by residual austenite in the subsequent cooling process, thereby improving the strengthening effect of carbon element and the uniformity of the structure; on the other hand, the time that the wire rod is in the large amount of fine precipitation of vanadium-containing carbides can be prolonged during the isothermal process, providing more driving force for the dispersion precipitation of vanadium, thereby exerting a strengthening and toughening effect.

[0015] 3. Compared with air-cooled phase change control or long-term heat preservation online aging, on the one hand, online molten salt can control the wire rod in the high-temperature isothermal zone of the troostite phase region. The wire rod and the molten salt temperature are consistent instead of continuous cooling, which provides more thermal power for tempering, and cooperates with the organization dominated by troostite with fine lamellar spacing to reduce the difficulty of tempering, and perform rapid tempering to relieve stress. At the same time, the molten salt treatment time is controlled to be ≤300s. This short-term weak tempering can control the transition state of weak tempered troostite formed during the transformation of troostite organization to tempered troostite morphology. Part of the troostite melts to form a melted pearlite organization, which appropriately improves the plasticity of the matrix and avoids the coarsening of the troostite organization due to long-term strong tempering. , large-area melting and excessive loss of matrix strength. On the other hand, short-time isothermal weak tempering treatment is used to avoid the precipitation and coarsening of vanadium-containing carbides due to long-term treatment, thereby reducing the strength improvement effect. At the same time, the online time of the wire rod is shortened and the production rhythm is accelerated. Compared with the offline salt bath treatment, the steps of air cooling regulation, repeated winding and unwinding can be omitted. The wire rod that has undergone online molten salt rapid cooling isothermal treatment has a higher temperature after leaving the salt bath tank. Further roller slow cooling can prevent the wire rod from increasing stress due to excessively fast cooling 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 regulation.

[0016] Selecting appropriate heating furnace temperature and furnace time before rolling can promote the homogenization of alloy composition and avoid the risk of decarburization and slight damage caused by excessive temperature, in preparation for reducing the resistance to rolling deformation. In a preferred embodiment, before rolling, the heating furnace is controlled to have a soaking temperature of 1185-1220°C and a furnace time of ≥180min.

[0017] Since the spinning temperature is relatively high, the restrictions on rolling can be reduced, which is beneficial to improving the rolling temperature and efficiency. At the same time, the appropriate rolling temperature and deformation amount are selected to promote dynamic recrystallization in the final rolling process and refine the grains. In a preferred embodiment, during the rolling, the initial rolling temperature is controlled to be 1100~1140℃, the final rolling temperature is 950~1000℃, and the final rolling reduction is 25%~30%.

[0018] In a preferred embodiment, the molten salt temperature of the online molten salt rapid cooling isothermal treatment is 530-560°C, and the molten salt treatment time is controlled to be ≥115s. The temperature is in the medium temperature range of the wire rod troostite phase region and the dispersion precipitation of vanadium-containing carbides. The higher the molten salt temperature and the longer the molten salt treatment time, the more thermal power can be provided for tempering stress relief and the plasticity of the matrix can be improved. However, if the molten salt temperature is too high and the treatment time is too long, the increase in tempering strength will lead to excessive loss of matrix strength, and the precipitation and coarsening of vanadium-containing carbides will affect the strengthening effect. If the temperature exceeds 600°C, it will affect the vanadium-containing The precipitation of vanadium carbides will cause loss of matrix strength. On the contrary, the lower the molten salt temperature, the more favorable it is to form a larger undercooling degree, which promotes the transformation of high-temperature austenite to troostite with finer interlamellar spacing, provides more driving force for the fine precipitation of vanadium-containing carbides, and improves the matrix strength. However, if the molten salt temperature is too low, it will affect the high-temperature isothermal weak tempering stress relief effect of the wire rod and lose the plasticity of the wire rod. Below 500℃ is not conducive to the precipitation of vanadium-containing carbides and affects the matrix strength. Therefore, choosing appropriate molten salt temperature and molten salt treatment time can improve the strength matching of the wire rod and improve production efficiency.

[0019] Since the temperature difference of the wire rod from the spinning temperature to the troostite phase temperature is large, in a preferred embodiment, the online molten salt rapid cooling isothermal treatment is divided into a front-stage treatment and a back-stage treatment. The molten salt circulation volume of the front-stage treatment is greater than that of the back-stage treatment. The treatment time of the front-stage treatment is 60~100s. The front-stage treatment uses a larger molten salt circulation volume to maintain the molten salt temperature, increase the supercooling degree, and promote the wire rod to quickly form a structure dominated by troostite with fine lamellar spacing, reduce austenite residue, and after the front-stage treatment, the temperature difference between the wire rod and the molten salt is small. At the same time, the phase change of the wire rod will release heat energy. Therefore, the molten salt circulation volume can be appropriately reduced in the back-stage treatment, and the treatment time of the back-stage treatment is controlled to be 55~200s. On the one hand, the molten salt temperature can be maintained stable and the production energy consumption can be appropriately reduced. On the other hand, the wire rod can be controlled to be weakly tempered in the high-temperature isothermal zone to relieve stress and improve the strength-plasticity matching of the wire rod.

[0020] The selection of an appropriate molten salt circulation rate in the front-end treatment can control the temperature rise of the molten salt in the front-end treatment and further improve the uniformity of the structure. In a preferred embodiment, the molten salt circulation rate of the front-end treatment is 500-620 t / h, and the temperature rise of the molten salt is ≤8°C.

[0021] The selection of an appropriate molten salt circulation rate in the post-processing can control the temperature rise of the molten salt in the post-processing and reduce production energy consumption. In a preferred embodiment, the molten salt circulation rate in the post-processing is 250-345 t / h, and the temperature rise of the molten salt is ≤5°C.

[0022] In a preferred embodiment, the roller slow cooling controls the wire rod to be slowly cooled to below 350°C at a cooling rate of 0.7~1°C / s. The high temperature waste heat of 530~560°C after the wire rod comes out of the salt bath can be used to reduce the energy consumption of roller slow cooling, control the slow cooling of the wire rod, prevent the wire rod from cooling too fast during the cooling process, resulting in increased shrinkage stress, promote further toughening of the wire rod structure, and improve the softening effect of the wire rod.

[0023] A 2200MPa grade hot-rolled wire rod for bridge cables, the hot-rolled wire rod being manufactured by any one of the above-mentioned methods for manufacturing the 2200MPa grade hot-rolled wire rod for bridge cables.

[0024] The above-mentioned 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 structure composed of weakly tempered troostite, ferrite, and fused pearlite. Weakly tempered troostite refers to the transition state of troostite transforming to tempered troostite after short-time tempering. After strong tempering, the troostite will coarsen and be interrupted on a large scale. Although the plasticity is high, the strength is reduced. The wire rod structure mainly composed of weakly tempered troostite can appropriately improve the plasticity of the matrix and avoid excessive strength reduction 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 the hot-rolled wire rod can be improved, and the risk of abnormal structures such as reticular carbon and martensite produced by C elements can be effectively avoided. The strengthening effect of carbon element can be maximized, thereby improving the overall strength and plasticity of the wire rod.

[0025] The higher the volume percentage of the weakly tempered troostite and the finer the interlamellar spacing, the higher the wire rod matrix strength. In a preferred embodiment, the volume percentage of the weakly tempered troostite is ≥88%, and the interlamellar spacing of the weakly tempered troostite is 60-100 mm.

[0026] The higher the volume percentage of the fusible pearlite is, the higher the plasticity of the wire rod is. In a preferred embodiment, the volume percentage of the fusible pearlite is 7% to 10%.

[0027] In a preferred embodiment, the network carbide grade of the hot-rolled wire rod is grade 0, which can effectively reduce the adverse effects of the network carbide on the plasticity and toughness properties and organizational uniformity of the wire rod.

[0028] The network carbide and martensite structures in the hot-rolled wire rod are effectively controlled. In a preferred embodiment, the mechanical property difference of the hot-rolled wire rod is ≤30MPa, which can effectively reduce the risk of wire breakage of the hot-rolled wire rod during the wire drawing process of bridge cable manufacturing and improve the stability of bridge cable manufacturing.

[0029] In a preferred embodiment, the diameter of the hot-rolled wire rod is 10.0~15.0mm, the tensile strength is 1550~1590MPa, and the cross-sectional shrinkage rate is 31%~36%. The hot-rolled wire rod has higher tensile strength and good cross-sectional shrinkage rate, which is conducive to quickly reaching the 2200MPa bridge cable strength level, reducing the wire drawing passes and wire breakage risks of bridge cables, thereby stabilizing production and improving the strength level of bridge cables.

[0030] Compared with the prior art, the beneficial effects of the present invention are at least: (1) The improvement of the strength level of existing hot-rolled wire rods is often achieved by alloying and hot-rolling controlled cooling to control the microstructure and properties. The higher the degree of alloying, the more difficult it is to control the hot-rolling controlled cooling, and it is difficult to suppress the generation of network carbides and martensite structures, resulting in a rapid increase in the risk of wire breakage during the wire drawing process of the hot-rolled wire rods for bridge cables, which limits the improvement of the strength level of bridge cables. The present invention, through the design of V-containing chemical composition combined with online molten salt rapid cooling isothermal technology, can control the wire rod to quickly enter the troostite phase region from the high-temperature austenite state, thereby suppressing the generation of network carbides and martensite structures. The structure of troostite with fine interlamellar spacing is formed to enhance the strengthening effect of carbon element, and the wire rod is controlled to enter the high temperature isothermal zone to promote the dispersion and precipitation of large amounts of vanadium-containing carbides, thereby improving the strength level of the hot-rolled wire rod and compensating for the strength loss caused by reducing the Si / Mn content. At the same time, the strength-plasticity matching of the wire rod is improved through weak tempering to relieve stress. Finally, the wire rod structure is further toughened through roller slow cooling to enhance the softening effect of the wire rod, taking into account the strength-plasticity and uniformity of the wire rod. The online time is short and the offline salt bath treatment can effectively simplify the process flow and has good industrial adaptability.

[0031] (2) In view of the current situation that the existing 2200MPa grade hot-rolled wire rod for bridge cables has insufficient strength and plasticity, and the abnormal structure and uniformity of the structure are difficult to control, the microstructure type of the hot-rolled wire rod of the present invention includes a mixed structure composed of weakly tempered troostite as the main body and ferrite and melt pearlite as the rest, which can effectively avoid the risk of precipitation of abnormal structures such as network carbon and martensite produced by the C element, improve the uniformity of the structure, and utilize the transition state of the transformation from the tempered troostite morphology after short-time tempering to improve the strength and plasticity matching of the wire rod, which can achieve a tensile strength of 1550~1590MPa, a cross-sectional shrinkage rate of 31%~36%, and a mechanical property circle difference of ≤30MPa. It is used in the manufacture of 2200MPa grade ultra-high strength bridge cables and other application fields, which is beneficial to effectively reduce the risk of wire breakage of the hot-rolled wire rod during the wire drawing process, so as to improve the strength level of bridge cables and meet the application requirements of large-span bridges, and has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] 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

[0033] 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:

[0034] A preferred embodiment of the manufacturing method of the 2200MPa 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: 0.94%, Si: 0.36%, Mn: 0.7%, Cr: 0.2%, V: 0.031%, Al: 0.025%, P: 0.012%, S: 0.010%, and the rest is Fe and unavoidable impurities; the manufacturing method is manufactured according to the process flow of rolling → spinning → online molten salt rapid cooling isothermal treatment → roller slow cooling → coiling, specifically: The rolling process is used to heat the steel billet with a specification of 220mm×220mm through a heating furnace to achieve a high-temperature steel billet that can be rolled into plasticity. The appropriate heating furnace temperature and furnace time are selected to 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 10mm through a rolling line. The appropriate rolling temperature and deformation amount are selected to improve the rolling efficiency, promote dynamic recrystallization and refine the grains during the final rolling process. Specifically: the heating furnace is controlled to have a soaking temperature of 1185°C The furnace time is 180min, the initial rolling temperature is 1100℃, the final rolling temperature is 950℃, and the final rolling reduction is 30%; the wire-spinning process is used to make the wire rods out of the rolling line through the wire-spinning mechanism into wire rods, which are spread on the rollers and transported along the rollers. A higher wire-spinning temperature is selected to promote the wire rods to be in a high-temperature austenite state, and to avoid the formation of network carbides in the wire-spinning stage caused by too low a wire-spinning temperature, so as to prepare for the subsequent formation of a larger undercooling and promote the nucleation of the sorbite structure. Specifically, the wire-spinning temperature is controlled to be 920℃.

[0035] The online molten salt rapid cooling isothermal 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 stage salt bath tank for front-stage treatment, so that the wire rod is cooled at a cooling rate of 37°C / s, and quickly passes through the network carbide precipitation interval from the high-temperature austenite state to enter the sorbite phase region, inhibiting the formation of network carbides, increasing the degree of supercooling, promoting the transformation of high-temperature austenite to a structure dominated by sorbite with fine lamellar spacing, and promoting the large-scale dispersion and precipitation of vanadium-containing carbides. After that, the wire rod is conveyed by a roller to pass through the second stage salt bath tank The post-stage treatment is carried out, and the molten salt circulation volume of the post-stage treatment is appropriately reduced to maintain the stability of the molten salt temperature and reduce production energy consumption. At the same time, the wire rod is controlled to be subjected to short-term weak tempering in the high-temperature isothermal range to relieve stress, avoid the precipitation and coarsening of vanadium-containing carbides, and improve the strength-plasticity matching of the wire rod. Specifically: the molten salt temperature is 530°C, the molten salt circulation volume of the front-stage treatment is 575t / h, the molten salt temperature rise is ≤8°C, and the treatment time is 100s; the molten salt circulation volume of the post-stage treatment is 250t / h, the molten salt temperature rise is ≤5°C, and the treatment time is 200s.

[0036] The roller slow cooling process adopts an open insulation cover, and the wire rod passing through the second salt bath tank is transported by the conveyor roller into the insulation cover, and the residual heat of the wire rod is used to prevent the wire rod from increasing shrinkage stress due to excessive cooling speed during the cooling process, and promote further toughening of the wire rod structure, thereby improving the softening effect of the wire rod. Specifically: the wire rod is controlled to slowly cool to 340°C at a cooling rate of 0.9°C / s; the coiling process is used to coil the wire rod into a coil through a coiling drum, and the hot-rolled wire rod product is obtained after packaging and storage. Its metallographic structure diagram is as follows Figure 1 shown.

[0037] Comparative Example 1: A method for manufacturing a hot-rolled wire rod, the manufacturing method of which is different from that of Example 1 in that: the manufacturing method is manufactured according to the process flow of rolling → spinning → Stelmor air cooling, specifically: the heating furnace soaking temperature is controlled to be 1150°C, the furnace time is 230min, the initial rolling temperature is 1050°C, the final rolling temperature is 900°C, and the spinning temperature is 865°C; the Stelmor strong air cooling adopts an air volume of 260,000 m per fan 3 / h, open 1~6# fans at 98%, cool the wire rod to 675℃ at a cooling rate of 9.2℃ / s, and then open 7~14# fans at 30%, cool the wire rod to 300℃ at a cooling rate of 3.6℃ / s. The hot-rolled wire rod is obtained after it comes off the line. The tensile strength of the hot-rolled wire rod is 1466MPa, the cross-sectional shrinkage is 12%, the microstructure includes 85% troostite by volume, the rest is ferrite and martensite, the network carbide level is 4, and the mechanical property difference is 118MPa.

[0038] Comparative Example 2: A method for manufacturing a hot-rolled wire rod, which differs from Example 1 in that: the heating furnace soaking temperature is controlled to be 1160°C, the furnace time is 210 min, the initial rolling temperature is 1060°C, the final rolling temperature is 905°C, the spinning temperature is 875°C, and the online molten salt rapid cooling isothermal treatment process is subjected to a front-end treatment to cool the wire rod at a cooling rate of 32°C / s, and a hot-rolled wire rod finished product is obtained after it is off the line. Embodiment 2:

[0039] A preferred embodiment of the manufacturing method of the 2200MPa 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: 0.4%, Mn: 0.85%, Cr: 0.29%, V: 0.03%, Al: 0.02%, P: 0.013%, S: 0.010%, and the rest is Fe and unavoidable impurities; the manufacturing method is manufactured according to the process flow of rolling → spinning → online molten salt rapid cooling isothermal treatment → roller slow cooling → coiling, specifically: The rolling process is used to heat the steel billet with a specification of 220mm×220mm through a heating furnace to achieve a high-temperature steel billet that can be rolled into plasticity. The appropriate heating furnace temperature and furnace time are selected to promote the homogenization of alloy components and reduce segregation. After the steel billet leaves the heating furnace, the steel billet is rolled into a wire with a diameter of 14mm through a rolling line. The appropriate rolling temperature and deformation amount are selected to improve the rolling efficiency, promote dynamic recrystallization and refine the grains during the final rolling process. Specifically: the heating furnace is controlled to have a soaking temperature of 1205°C The furnace time is 210min, the initial rolling temperature is 1125℃, the final rolling temperature is 970℃, and the final rolling reduction is 26%; the wire-spinning process is used to make the wire rod out of the rolling line through the wire-spinning mechanism into a wire rod, and the wire rod is spread on the roller and transported along the roller. A higher wire-spinning temperature is selected to promote the wire rod to be in a high-temperature austenite state, and to avoid the formation of network carbides in the wire-spinning stage caused by too low a wire-spinning temperature, so as to prepare for the subsequent formation of a larger undercooling and promote the nucleation of the sorbite structure. Specifically, the wire-spinning temperature is controlled to be 935℃.

[0040] The online molten salt rapid cooling isothermal 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 stage salt bath tank for front-stage treatment, so that the wire rod is cooled at a cooling rate of 36°C / s, and quickly passes through the network carbide precipitation interval from the high-temperature austenite state to enter the sorbite phase region, inhibiting the formation of network carbides, increasing the degree of supercooling, promoting the transformation of high-temperature austenite to a structure dominated by sorbite with fine lamellar spacing, and promoting the large-scale dispersion and precipitation of vanadium-containing carbides. After that, the wire rod is conveyed by a roller to pass through the second stage salt bath tank The post-stage treatment is carried out, and the molten salt circulation volume of the post-stage treatment is appropriately reduced to maintain the stability of the molten salt temperature and reduce production energy consumption. At the same time, the wire rod is controlled to undergo short-term weak tempering in the high-temperature isothermal range to relieve stress, avoid the precipitation and coarsening of vanadium-containing carbides, and improve the strength-plasticity matching of the wire rod. Specifically: the molten salt temperature is 553°C, the molten salt circulation volume of the front-stage treatment is 535t / h, the molten salt temperature rise is ≤8°C, and the treatment time is 74s; the molten salt circulation volume of the post-stage treatment is 320t / h, the molten salt temperature rise is ≤5°C, and the treatment time is 105s.

[0041] The roller slow cooling process adopts an open insulation cover, and the wire rod passing through the second salt bath tank is transported by the conveyor roller into the insulation cover, and the residual heat of the wire rod is used to prevent the wire rod from increasing shrinkage stress due to excessive cooling speed during the cooling process, and promote further toughening of the wire rod structure, thereby improving the softening effect of the wire rod. Specifically: the wire rod is controlled to slowly cool to 335°C at a cooling rate of 0.8°C / s; the coiling process is used to coil the wire rod into a coil through a coiling drum, and the hot-rolled wire rod product is obtained after packaging and storage. Its metallographic structure diagram is as follows Figure 2 shown.

[0042] Comparative Example 3: A method for manufacturing a hot-rolled wire rod, which differs from Example 2 in that: the online molten salt rapid cooling isothermal treatment process is subjected to a front-end treatment, so that the wire rod is cooled at a cooling rate of 32°C / s, the molten salt temperature is 595°C, and the hot-rolled wire rod finished product is obtained after it comes off the line.

[0043] Comparative Example 4: A method for manufacturing a hot-rolled wire rod, which differs from Example 2 in that: the online molten salt rapid cooling isothermal treatment process is subjected to a front-end treatment, so that the wire rod is cooled at a cooling rate of 39°C / s, the molten salt temperature is 505°C, and a hot-rolled wire rod finished product is obtained after it comes off the line. Embodiment 3:

[0044] A preferred embodiment of the manufacturing method of the 2200MPa 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: 0.92%, Si: 0.37%, Mn: 0.9%, Cr: 0.36%, V: 0.025%, Al: 0.04%, P: 0.013%, 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 rapid cooling isothermal treatment → roller slow cooling → coiling, specifically: The rolling process is used to heat the steel billet with a specification of 220mm×220mm through a heating furnace to achieve a high-temperature steel billet that can be rolled into plasticity. The appropriate heating furnace temperature and furnace time are selected to promote the homogenization of alloy components and reduce segregation. After the steel billet leaves the heating furnace, the steel billet is rolled into a wire with a diameter of 15mm through a rolling line. The appropriate rolling temperature and deformation amount are selected to improve the rolling efficiency, promote dynamic recrystallization and refine the grains during the final rolling process. Specifically: the heating furnace is controlled to have a soaking temperature of 1220°C The furnace time is 200min, the initial rolling temperature is 1140℃, the final rolling temperature is 1000℃, and the final rolling reduction is 25%; the wire-spinning process is used to make the wire rod out of the rolling line into a wire rod through a wire-spinning mechanism, and the wire rod is spread on the roller and transported along the roller. A higher wire-spinning temperature is selected to promote the wire rod to be in a high-temperature austenite state, and to avoid the formation of network carbides in the wire-spinning stage caused by too low a wire-spinning temperature, so as to prepare for the subsequent formation of a larger undercooling and promote the nucleation of the sorbite structure. Specifically, the wire-spinning temperature is controlled to be 945℃.

[0045] The online molten salt rapid cooling isothermal 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 stage salt bath tank for front-stage treatment, so that the wire rod is cooled at a cooling rate of 38°C / s, and quickly passes through the network carbide precipitation interval from the high-temperature austenite state to enter the sorbite phase region, inhibiting the formation of network carbides, increasing the degree of supercooling, promoting the transformation of high-temperature austenite to a structure dominated by sorbite with fine lamellar spacing, and promoting the large-scale dispersion and precipitation of vanadium-containing carbides. After that, the wire rod is conveyed by a roller to pass through the second stage salt bath tank The post-stage treatment is carried out, and the molten salt circulation volume of the post-stage treatment is appropriately reduced to maintain the stability of the molten salt temperature and reduce production energy consumption. At the same time, the wire rod is controlled to undergo short-term weak tempering in the high-temperature isothermal range to relieve stress, avoid the precipitation and coarsening of vanadium-containing carbides, and improve the strength-plasticity matching of the wire rod. Specifically: the molten salt temperature is 542°C, the molten salt circulation volume of the front-stage treatment is 620t / h, the molten salt temperature rise is ≤8°C, and the treatment time is 82s; the molten salt circulation volume of the post-stage treatment is 345t / h, the molten salt temperature rise is ≤5°C, and the treatment time is 165s.

[0046] The roller slow cooling process uses an open insulation cover, and the wire rod that has passed through the second salt bath tank is transported by the conveyor roller into the insulation cover. The residual heat of the wire rod is used to prevent the increase of shrinkage stress of the wire rod due to excessive cooling speed during the cooling process, and promote further toughening of the wire rod structure, thereby improving the softening effect of the wire rod. Specifically: the wire rod is controlled to be slowly cooled to 328°C at a cooling rate of 1°C / s; the coiling process is used to coil the wire rod into a coil by a coiling drum, and the hot-rolled wire rod product is obtained after packaging and storage.

[0047] Comparative Example 5: A method for manufacturing a hot-rolled wire rod, which differs from Example 3 in that the processing time of the front-end processing of the online molten salt rapid cooling isothermal treatment process is 50 seconds, and the processing time of the back-end processing is 40 seconds, and the hot-rolled wire rod finished product is obtained after going offline.

[0048] Comparative Example 6: A method for manufacturing a hot-rolled wire rod, which differs from Example 3 in that the processing time of the front-end processing of the online molten salt rapid cooling isothermal treatment process is 135 seconds, and the processing time of the back-end processing is 320 seconds, and the hot-rolled wire rod finished product is obtained after going offline. Embodiment 4:

[0049] A preferred embodiment of the manufacturing method of the 2200MPa 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: 0.2%, Mn: 0.76%, Cr: 0.4%, V: 0.035%, Al: 0.034%, P: 0.015%, S: 0.013%, and the rest is Fe and unavoidable impurities; the manufacturing method is manufactured according to the process flow of rolling → spinning → online molten salt rapid cooling isothermal treatment → roller slow cooling → coiling, specifically: The rolling process is used to heat the steel billet with a specification of 220mm×220mm through a heating furnace to achieve a high-temperature steel billet that can be rolled into plasticity. The appropriate heating furnace temperature and furnace time are selected to promote the homogenization of alloy components and reduce segregation. After the steel billet leaves the heating furnace, the steel billet is rolled into a wire with a diameter specification of 11mm through a rolling line. The appropriate rolling temperature and deformation amount are selected to improve the rolling efficiency, promote dynamic recrystallization and refine the grains during the final rolling process. Specifically: the heating furnace is controlled to have a soaking temperature of 1195°C The furnace time is 195min, the initial rolling temperature is 1110℃, the final rolling temperature is 960℃, and the final rolling reduction is 29%; the wire-spinning process is used to make the wire rod out of the rolling line into a wire rod through a wire-spinning mechanism, and the wire rod is spread on the roller and transported along the roller. A higher wire-spinning temperature is selected to promote the wire rod to be in a high-temperature austenite state, and to avoid the formation of network carbides in the wire-spinning stage caused by too low a wire-spinning temperature, so as to prepare for the subsequent formation of a larger undercooling and promote the nucleation of the sorbite structure. Specifically, the wire-spinning temperature is controlled to be 930℃.

[0050] The online molten salt rapid cooling isothermal treatment process adopts a two-stage salt bath tank with molten salt inside. The wire rod after spinning is conveyed by a roller through the first stage salt bath tank for front-stage 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, inhibiting the formation of network carbides, increasing the degree of supercooling, promoting the transformation of high-temperature austenite to a structure dominated by sorbite with fine lamellar spacing, and promoting the large-scale dispersion and precipitation of vanadium-containing carbides. After that, the wire rod is conveyed by a roller through the second stage salt bath The tank is used for post-processing. The circulation volume of the molten salt in the post-processing is appropriately reduced to maintain the stability of the molten salt temperature and reduce production energy consumption. At the same time, the wire rod is controlled to undergo short-term weak tempering in the high-temperature isothermal range to relieve stress, avoid the precipitation and coarsening of vanadium-containing carbides, and improve the strength-plasticity matching of the wire rod. Specifically, the molten salt temperature is 560°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 60s; the circulation volume of the molten salt in the post-processing is 300t / h, the temperature rise of the molten salt is ≤5°C, and the processing time is 55s.

[0051] The roller slow cooling process uses an open insulation cover, and the wire rod that has passed through the second salt bath tank is transported by the conveyor roller into the insulation cover. The residual heat of the wire rod is used to prevent the increase of shrinkage stress of the wire rod due to excessive cooling speed during the cooling process, and promote further toughening of the wire rod structure, thereby improving the softening effect of the wire rod. Specifically: the wire rod is controlled to slowly cool to 345°C at a cooling rate of 0.7°C / s; the coiling process is used to coil the wire rod into a coil by a coiling drum, and the hot-rolled wire rod product is obtained after packaging and storage.

[0052] Comparative Example 7: A method for manufacturing a hot-rolled wire rod, which differs from Example 4 in that: the method is manufactured according to a process flow of rolling → spinning → online molten salt rapid cooling isothermal treatment → air cooling, wherein the air cooling is performed by opening a heat preservation cover, and air cooling the wire rod that has passed through a second salt bath tank is performed by a conveyor roller, and the wire rod is controlled to be cooled to 285°C at a cooling rate of 1.7°C / s, and a hot-rolled wire rod finished product is obtained after it comes off the line.

[0053] The hot rolled wire rods obtained in the above examples 1 to 4 and comparative examples 2 to 7 were subjected to microstructure and performance testing, and the comparative results obtained are shown in Table 1 below: Table 1. Comparison of microstructure and performance of hot rolled wire rods with different compositions and manufacturing methods

[0054] It can be seen from the comparison results of Example 1 and Comparative Example 1 that compared with the Stelmore air-cooled line, the cooling rate is uncontrollable during the cooling phase transition process, which weakens the strengthening effect and leads to the generation of abnormal structures such as reticular carbon and martensite. It is difficult to control the fine precipitation of vanadium-containing carbides, and the uniformity of the structure is poor. The present invention can effectively avoid the risk of abnormal structure precipitation such as reticular carbon and martensite produced by C elements through the design of V-containing chemical composition combined with online molten salt rapid cooling isothermal technology, maximize the strengthening effect of carbon elements, control the dispersion precipitation of vanadium-containing carbides in the isothermal process, and make the microstructure The weave type includes a mixed structure composed mainly of weakly tempered troostite and the rest of ferrite and fused pearlite, which improves the overall strength, plasticity and structural uniformity of the wire rod. It can be seen from the results of Examples 1 to 4 that the hot-rolled wire rod can achieve a tensile strength of 1550 to 1590 MPa, a cross-sectional shrinkage rate of 31% to 36%, and a mechanical property difference of ≤30 MPa. It is used in the manufacture of 2200 MPa ultra-high strength bridge cables and other application fields, which is beneficial to effectively reduce the risk of wire breakage of the hot-rolled wire rod in the wire drawing process and improve the strength level of the bridge cables.

[0055] From the comparison results of Example 1 and Comparative Example 2, it can be seen that appropriately increasing the spinning temperature can avoid the formation of network carbides during the spinning stage due to the spinning temperature being too low, preparing for the subsequent formation of a larger degree of undercooling and promoting the nucleation of the sorbite structure. At the same time, it can reduce the restrictions on rolling, which is beneficial to increasing the rolling temperature, reducing the rolling deformation resistance, and thus improving the rolling efficiency.

[0056] From the comparison results of Example 2 and Comparative Example 3, it can be seen that 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 promote the improvement of matrix plasticity. However, if the molten salt temperature is too high, as the treatment time increases, the tempering strength increases, which will lead to excessive loss of matrix strength, and the vanadium-containing carbides will precipitate and coarsen, affecting the strengthening effect.

[0057] From the comparison results of Example 2 and Comparative Example 4, it can be seen that the lower the molten salt temperature of the online molten salt rapid cooling isothermal treatment, the more favorable it is to form a larger degree of supercooling, promote the transformation of high-temperature austenite to a troostite structure with finer interlamellar spacing, provide more driving force for the fine precipitation of vanadium-containing carbides, and improve the matrix strength. However, if the molten salt temperature is too low, it will affect the high-temperature isothermal weak tempering stress relief effect of the wire rod and lose the plasticity of the wire rod.

[0058] From the comparison results of Example 3 and Comparative Example 5, it can be seen that the shorter the treatment time of the online molten salt rapid cooling isothermal treatment, the lower the weak tempering stress relief effect, the wire rod strength increases and the plasticity decreases, but the front-stage treatment time is too short, which affects the regulation of organizational uniformity. At the same time, the back-stage treatment time is too short, which affects the full precipitation of vanadium-containing carbides and the weak tempering stress relief effect, which is not good for the plasticity of the wire rod.

[0059] From the comparison results of Example 3 and Comparative Example 6, it can be seen that the longer the treatment time of the online molten salt rapid cooling isothermal treatment is, the more thermal power can be provided for tempering stress relief and promote the improvement of matrix plasticity. However, if the treatment time is too long, the increase in tempering strength will lead to excessive loss of matrix strength, and the vanadium-containing carbides will precipitate and coarsen, affecting the strengthening effect and increasing production energy consumption.

[0060] From the comparison results of Example 3 and Comparative Example 7, it can be seen that the use of roller slow cooling to control the slow cooling of the wire rod can prevent the wire rod from cooling too fast during the cooling process, resulting in increased shrinkage stress, and promote further toughening of the wire rod structure, thereby improving the softening effect of the wire rod.

[0061] The series of detailed descriptions listed above are only specific descriptions of feasible embodiments of the present invention. They are not intended to limit the scope of protection of the present invention. All equivalent embodiments or changes that do not deviate from the technical spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for manufacturing a 2200MPa grade hot-rolled wire rod for bridge cables, characterized in that: The manufacturing method thereof comprises: The wire rod is produced by rolling according to the chemical composition of the hot-rolled wire rod, wherein the chemical composition and mass percentage of the hot-rolled wire rod include: C: 0.92% to 0.95%, Si: 0.20% to 0.40%, Mn: 0.70% to 0.90%, Cr: 0.20% to 0.40%, V: 0.025% to 0.035%, Al: 0.02% to 0.04%, P≤0.015%, S≤0.015%, and the rest is Fe and unavoidable impurities; The wire rod is spun into a wire rod at a spinning temperature of ≥920°C, and then is subjected to an online molten salt rapid cooling isothermal treatment, the molten salt treatment time is controlled to be ≤300s, so that the wire rod is cooled at a cooling rate of ≥35°C / s, enters the sorbite phase region from the austenite state, forms a structure mainly composed of sorbite, and isothermally weakly tempered to relieve stress, and finally is slowly cooled by a roller to produce a hot-rolled wire rod whose microstructure includes weakly tempered sorbite with a volume percentage of ≥88%, and the rest is a mixed structure composed of ferrite and fused pearlite.

2. The method for manufacturing the 2200MPa 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 1185-1220° C. and the time in the furnace is ≥180 min.

3. The method for manufacturing the 2200MPa 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 1100-1140° C., the final rolling temperature is controlled to be 950-1000° C., and the final rolling reduction is controlled to be 25%-30%.

4. The method for manufacturing the 2200MPa 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 isothermal treatment is 530~560℃, and the online molten salt rapid cooling isothermal treatment is divided into front-end treatment and back-end treatment. The molten salt circulation volume of the front-end treatment is greater than the molten salt circulation volume of the back-end treatment. The processing time of the front-end treatment is 60~100s, and the processing time of the back-end treatment is 55~200s.

5. The method for manufacturing the 2200MPa 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 500-620 t / h, and the molten salt temperature rise is ≤8°C; the molten salt circulation volume of the back-stage treatment is 250-345 t / h, and the molten salt temperature rise is ≤5°C.

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

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

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

9. The 2200MPa 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 ≤30MPa.

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

Images