A hot-rolled wire rod for 2200 MPa-class bridge cables and a manufacturing method thereof

Abstract

The present invention relates to a hot-rolled wire rod for 2200 MPa-class bridge cables and a manufacturing method thereof. High-carbon V-containing chemical compositions are used to design a rolling production line for wire rods. After the wire rods are spun into wire coils at a coiling temperature of ≥920 °C, they are subjected to online molten salt rapid cooling and isothermal treatment. The molten salt treatment time is controlled to be ≤300 s, so that the wire coils are cooled at a cooling rate of ≥35 °C / s, enter the sorbite phase region from the austenite state, form a structure mainly composed of sorbite and isothermally temper weakly to remove stress. Finally, they are slowly cooled through a roller table to obtain a hot-rolled wire rod with a microstructure mainly composed of weakly tempered sorbite, and the rest being a mixed structure composed of ferrite and broken pearlite. The hot-rolled wire rod can achieve a tensile strength of 1550~1590 MPa, an area reduction of 31%~36%, and a within-coil difference in mechanical properties of ≤30 MPa. It is used in application fields such as manufacturing 2200 MPa-class ultra-high-strength bridge cables, reducing the risk of wire breakage, and improving the strength level of bridge cables.

Description

Technical Field

[0001] The present invention belongs to the technical field of hot-rolled wire rods, and particularly relates to a 2200 MPa-class 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 processed from 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 for bridge cables. Ultra-high-strength bridge cables have advantages such as high strength and light weight. In response to the demand for high-strength and high-torsion-performance bridge cables for long-span bridges, it is necessary to develop a 2200 MPa-class ultra-high-strength hot-rolled wire rod for bridge cables. However, in the prior art, the improvement of the strength level of hot-rolled wire rods for bridge cables often relies on alloying, combined with hot rolling and controlled cooling of the Stelmor air-cooling line to regulate the tissue properties. There are still the following technical difficulties:

[0003] In order to improve the strength of the wire rod, the contents of C, Si, and Mn in the wire rod are relatively high, which are used to improve the hardenability of the steel, reduce the critical cooling rate, and cooperate with strong air cooling after wire laying to refine the pearlite lamellae, so as to obtain a sorbite structure with better strength and drawing performance and increase the sorbite content. For example, a wire rod for high-strength bridge cables and its production method disclosed in Patent CN118880169A adopts a high-carbon, high-silicon, and high-manganese composition system of 87SiMn, combined with rapid strong cooling on the Stelmor air-cooling line after low-temperature rolling and wire laying, and holding and cooling for more than 120 minutes to generate a wire rod with a high sorbite content, so that the strength of the hot-rolled wire rod reaches more than 1400 MPa. 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 temperature drop of the wire rod about 10 °C / s. As the alloying degree of the wire rod increases, it will exacerbate the segregation of carbon and alloying elements during the solidification process of the steel billet. During the cooling process, the time for the wire rod to pass through the precipitation temperature range of secondary cementite is still relatively long, and the cementite precipitated along the grain boundaries will form a relatively high-level network carbide, affecting the uniformity, plasticity, and toughness of the wire rod structure, and further increasing the risk of wire breakage during the subsequent wire drawing process of the wire rod. And limited by the cooling capacity, it will affect the high-temperature austenite phase transformation speed and full transformation, resulting in a loss of wire rod strength. On the other hand, with the increase in air-cooling intensity, the uncontrollability of air volume, air temperature, and wind direction increases, and the temperature difference between the edge and the core of the wire rod, the overlapping and non-overlapping parts, and the windward and leeward surfaces will further increase. Therefore, the higher the alloying degree, the greater the difficulty of hot-rolled controlled cooling affected by segregation and temperature difference, and it will be difficult to suppress the generation of abnormal hard and brittle martensite tissues, resulting in a rapid increase in the risk of wire breakage during the wire drawing process of hot-rolled wire rods for bridge cables, restricting the improvement of the strength level of bridge cables. Reducing the alloy content or air-cooling intensity will further result in a loss of wire rod strength.

[0004] In order to balance the strength and plasticity of the wire rod, although an insulated corridor is used for on-line aging, due to the limitation of the heat preservation capacity of the heat preservation line, the wire rod is still in a continuous slow cooling process, which will affect the pearlite transformation. After the transformation, the wire rod will be in a lower temperature state. At the same time, the obtained pearlite structure has a larger lamellar spacing and higher stress, which will increase the difficulty of improving plasticity, resulting in insufficient plasticity of the obtained wire rod or too long on-line time, affecting production efficiency. In the prior art, microalloying or off-line salt bath processes are also used to improve the strength and plasticity of the wire rod. For example, a wire rod for 2200 MPa grade steel wire and its manufacturing method disclosed in Patent CN114561598A adopt a C-Si-Mn-Cr-V-Al-Ca composition design and are prepared by high-speed wire rolling, Stelmor, and salt bath. However, on the one hand, during the continuous cooling process of the wire rod on the air cooling line, the time for the dispersion precipitation of V element is short and difficult to control, resulting in coarser and finer precipitations at the same time, affecting the tissue uniformity and losing the strengthening effect. On the other hand, the wire rod preparation requires more processes and steps and a longer cycle, restricting the production of steel mills or the application of downstream users. Summary of the Invention

[0005] The present invention aims to solve at least one of the above technical problems to some extent. The present invention provides a hot-rolled wire rod for 2200 MPa grade bridge cables and its manufacturing method, which can effectively inhibit the generation of network carbide and abnormal martensite tissue, balance the strength and plasticity of the wire rod and the tissue uniformity, and reduce the risk of wire breakage during the wire drawing process of the hot-rolled wire rod, so as to improve the strength level of bridge cables.

[0006] The technical solution adopted by the present invention to solve its technical problems is as follows:

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

[0008] Roll wire rods according to the chemical composition of the hot-rolled wire rod. The chemical composition and mass percentage of the hot-rolled wire rod include: C: 0.92% - 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%, and the rest are Fe and inevitable impurities. After the wire rods are spun into wire rods at a spinning temperature of ≥920°C, they are subjected to on-line molten salt rapid cooling and isothermal treatment, controlling the molten salt treatment time ≤300 s, so that the wire rods cool down at a cooling rate of ≥35°C / s, enter the pearlite phase region from the austenite state, form a structure mainly composed of pearlite and isothermally temper weakly to remove stress, and finally are slowly cooled through a roller table to obtain hot-rolled wire rods with a microstructure including weakly tempered pearlite with a volume percentage of ≥88%, and the rest are a mixed structure composed of ferrite and eutectoid pearlite.

[0009] The chemical composition and mass percentage design basis of the above hot-rolled wire rods include:

[0010] (1) Carbon: As the most economical and effective element for solid solution strengthening and precipitation strengthening, with the increase of carbon content, it is beneficial to expand the austenite phase region, inhibit the formation of ferrite, promote the transformation of sorbite structure during the online molten salt rapid cooling isothermal treatment, and improve the basic strength of the material. However, with the increase of carbon content, it will increase the carbon segregation tendency during the solidification of steel billets, increase the tendency of decarburization and precipitation of network carbide, deteriorate the plastic and toughness properties of the material, and increase the difficulty of isothermal weak tempering stress relief, which is not conducive to the regulation of the matrix structure. Therefore, in order to balance the high-strength requirements of 2200 MPa grade bridge cables, reduce the control of network carbide and the difficulty of short-time isothermal stress relief, and control the material cost, the mass percentage of C is controlled at 0.92% - 0.95%.

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

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

[0013] (4) Chromium: As a solution strengthening element, the Cr element can strongly improve the hardenability of the material, regulate the matrix phase composition, is beneficial to refining the interlamellar spacing of sorbite, is advantageous for improving the drawing processability and increasing the matrix strength. At the same time, it can increase the work hardening rate during the wire drawing process of the wire rod, reduce the strength loss during the subsequent hot-dip galvanizing process of the wire. However, if the Cr content is too high, it will exacerbate composition segregation, increase the risk of abnormal martensite precipitation, affect the uniformity of the wire rod structure, reduce the activity of carbon in the steel, significantly increase the difficulty of improving the plasticity of the wire rod, and is not conducive to isothermal weak tempering stress relief, which will affect the drawing and torsion properties of the wire. Therefore, the mass percentage of Cr is controlled at 0.20% - 0.40%.

[0014] (5) Aluminum: The Al element is used as a deoxidizer during smelting. During hot rolling, it can form fine precipitation phases, which is beneficial to grain refinement, and thus is favorable for controlling the tissue uniformity and improving the toughness of the steel. At the same time, it is lower in cost than the Mo element that can inhibit the coarsening of cementite, which is conducive to controlling the material cost. However, if the Al content is too high, it will increase the risk of inclusions, thereby reducing the fatigue performance of the steel. Therefore, the mass percentage of Al is controlled at 0.20% - 0.40%.

[0015] (6) Vanadium: As a microalloying element, the V element can inhibit the coarsening of austenite at high temperatures, refine austenite grains. At the same time, it can be massively precipitated in a large amount in the medium temperature range during the molten salt rapid cooling isothermal process, improving the strength level of the hot-rolled wire rod. However, the cost of the V element is relatively high. Excessive addition is not conducive to controlling the cost of the wire rod and has a coarsening risk. Considering the role and cost of the V element, the content of the V element in the present invention is controlled at 0.025% - 0.035%.

[0016] (7) Phosphorus and sulfur: The P element and the S element belong to impurity elements, and the lower the better. Therefore, it is controlled that P ≤ 0.015% and S ≤ 0.015%.

[0017] The above hot-rolled wire rod adopts a high-carbon low-silicon vanadium-containing composition design of C-Si-Mn-Cr-V-Al, appropriately regulates the Si, Mn, and Cr component ratios, reduces the influence of alloy element segregation and the control difficulty of abnormal low-temperature structures, appropriately controls the hardenability of the wire rod, and regulates the peak precipitation temperature of sorbite to be compatible with the medium temperature range of massive precipitation of vanadium carbides, so as to use vanadium to improve the strength level of the hot-rolled wire rod, 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 mainly composed of fine lamellar spacing sorbite during the on-line molten salt rapid cooling isothermal treatment and facilitating weak tempering stress relief. On this basis, appropriately increasing the spinning temperature can avoid the formation of network carbides during the spinning stage due to too low spinning temperature, prepare for forming a larger supercooling degree and promoting the nucleation of sorbite structure later. After spinning, it is directly subjected to on-line molten salt rapid cooling isothermal treatment through molten salt:

[0018] 1. Compared with the limited maximum cooling capacity of the existing Stelmor air-cooled line, the on-line molten salt can utilize the high heat transfer capacity of the molten salt to promote the rapid cooling of the wire rod. On the one hand, it enables the wire rod to quickly bypass the secondary cementite precipitation temperature range of 700-800°C, effectively improving the risk of network carbide precipitation caused by high carbon content and avoiding the deterioration of the plasticity and tissue uniformity of the wire rod. On the other hand, it can prompt the wire rod to quickly enter the sorbite phase region from the high-temperature austenite state, forming a large supercooling degree, increasing the nucleation driving force of sorbite, and forming a structure mainly composed of fine lamellar spacing sorbite, thereby improving the matrix strength, compensating for the strength loss caused by reducing the Si and Mn contents, and refining the lamellar spacing, making organizational preparations for weak tempering to relieve stress.

[0019] 2. Compared with the existing Stelmor air-cooled line, the strengthening effect is weakened due to the uncontrollable cooling rate during the cooling phase change process, and abnormal structures such as martensite appear. 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, without the problem of windward and leeward surfaces, avoiding the formation of martensite tissue in the low-temperature phase region due to the influence of segregation on the wire rod. At the same time, by using on-line molten salt isothermal treatment, the wire rod can be maintained at the molten salt temperature after rapid cooling, extending the time of the wire rod at the peak precipitation temperature of sorbite, promoting the full transformation of austenite tissue into sorbite tissue with fine lamellar spacing, and avoiding the continued formation of martensite tissue by residual austenite during subsequent cooling, thereby improving the strengthening effect of carbon elements and tissue uniformity. On the other hand, during the isothermal process, the time of the wire rod at which a large number of fine vanadium carbides precipitate can be extended, providing more driving force for the dispersed precipitation of vanadium, thereby exerting a strengthening and toughening effect.

[0020] III. Compared with air-cooled phase transformation control or long-time heat preservation online aging, on the one hand, online molten salt can control the high-temperature isothermal range of the wire rod in the sorbite phase region. The temperature of the wire rod is the same as that of the molten salt instead of continuously decreasing, providing more thermal power for tempering. Cooperating with the structure mainly composed of fine lamellar spacing sorbite, it reduces the difficulty of tempering, conducts rapid tempering to remove stress, and at the same time controls the molten salt treatment time ≤ 300 s. This short-term weak tempering can control the transition state of weak tempered sorbite formed during the transformation of sorbite structure to tempered sorbite morphology. Part of the sorbite is melted to form melted pearlite structure, appropriately improving the matrix plasticity and avoiding the coarsening and large-area melting of the sorbite structure due to long-term strong tempering, resulting in excessive loss of matrix strength. On the other hand, through short-term isothermal weak tempering treatment, the precipitation and coarsening of vanadium carbides due to long-term treatment are avoided, reducing the strength improvement effect. At the same time, the online time of the wire rod is shortened, accelerating the production rhythm. Compared with offline salt bath treatment, steps such as air-cooling regulation and repeated winding and unwinding can be omitted. After the wire rod treated by online molten salt rapid cooling and isothermal treatment leaves the salt bath tank, the temperature is relatively high. Further adopting roller table slow cooling can prevent the wire rod from increasing stress due to too fast cooling rate during the cooling process. The slow cooling can be used to promote the further toughening of the wire rod structure, improve the softening effect, and realize the uniformity of the wire rod structure, the matching of strength and plasticity, and the regulation of the mixed structure.

[0021] Selecting appropriate heating furnace temperature and residence time before rolling can promote the homogenization of alloy components and avoid the risks of decarburization and slight loss caused by too high temperature, preparing for reducing the rolling deformation resistance. In the preferred embodiment, before rolling, the soaking temperature of the heating furnace is controlled at 1185 - 1220 °C, and the residence time ≥ 180 min.

[0022] Since the spinning temperature is relatively high, it can reduce the limitation on rolling, which is beneficial to increasing the rolling temperature and efficiency. At the same time, selecting appropriate rolling temperature and reduction can promote dynamic recrystallization during the finishing rolling process, refine the grains. In the preferred embodiment, during rolling, the initial rolling temperature is controlled at 1100 - 1140 °C, the finishing rolling temperature is controlled at 950 - 1000 °C, and the finishing 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 ≥ 115 s. This temperature is in the plate sorbite phase region and the medium temperature range where vanadium-containing carbides precipitate dispersedly. The higher the molten salt temperature and the longer the molten salt treatment time, the more thermal power can be provided for tempering to remove stress, promoting the improvement of matrix plasticity. 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 coarsening of vanadium-containing carbide precipitation will affect the strengthening effect. When the temperature exceeds 600 °C, it will affect the precipitation of vanadium-containing carbides and result in the loss of matrix strength. On the contrary, the lower the molten salt temperature, the more conducive it is to form a larger supercooling degree, promoting the transformation of high-temperature austenite into sorbite tissue with finer lamellar spacing, providing more driving force for the fine precipitation of vanadium-containing carbides, and improving 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 result in the loss of wire rod plasticity. When the temperature is lower than 500 °C, it is not conducive to the precipitation of vanadium-containing carbides and affects the matrix strength. Therefore, by selecting appropriate molten salt temperature and molten salt treatment time, the strength matching of the wire rod can be improved and the production efficiency can be increased.

[0024] Since the temperature difference between the wire rod cooling from the spinning temperature to the sorbite phase region temperature is relatively large, in a preferred embodiment, the online molten salt rapid cooling isothermal treatment is divided into a front-stage treatment and a rear-stage treatment. The molten salt circulation volume in the front-stage treatment is greater than that in the rear-stage treatment. The treatment time for the front-stage treatment is 60 - 100 s. Selecting a larger molten salt circulation volume in the front-stage treatment can maintain the molten salt temperature, increase the supercooling degree, promote the wire rod to quickly form a structure mainly composed of sorbite with fine lamellar spacing, and reduce austenite residue. After the front-stage treatment, the temperature difference between the wire rod and the molten salt is small, and at the same time, the phase transformation of the wire rod will release heat energy. Therefore, the molten salt circulation volume in the rear-stage treatment can be appropriately reduced, and the treatment time for the rear-stage treatment is controlled to be 55 - 200 s. On the one hand, it can maintain the stability of the molten salt temperature and appropriately reduce the production energy consumption. On the other hand, it can control the wire rod to have weak tempering stress relief in the high-temperature isothermal interval and improve the strength-plasticity matching of the wire rod.

[0025] Selecting an appropriate molten salt circulation volume in the front-stage treatment can control the temperature rise of the front-stage molten salt and further improve the tissue uniformity. In a preferred embodiment, the molten salt circulation volume in the front-stage treatment is 500 - 620 t / h, and the temperature rise of the molten salt is ≤ 8 °C.

[0026] Selecting an appropriate molten salt circulation volume in the rear-stage treatment can control the temperature rise of the rear-stage molten salt and reduce the production energy consumption. In a preferred embodiment, the molten salt circulation volume in the rear-stage treatment is 250 - 345 t / h, and the temperature rise of the molten salt is ≤ 5 °C.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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%.

[0032] 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.

[0033] 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.

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

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

[0036] (1) Aiming at the current situation that the improvement of the strength level of existing hot-rolled wire rods often regulates the tissue properties through alloying combined with hot-rolled controlled cooling. The higher the degree of alloying, the greater the difficulty of hot-rolled controlled cooling, and it is difficult to inhibit the generation of network carbide and martensite tissues, resulting in a rapid increase in the wire breakage risk during the wire drawing process of hot-rolled wire rods for bridge cables, restricting the improvement of the bridge cable strength level. The present invention combines the V-containing chemical composition design with the online molten salt rapid cooling isothermal technology, which can control the wire rod to quickly enter the sorbite phase region from the high-temperature austenite state, inhibit the generation of network carbide and martensite tissues, form a tissue mainly composed of fine lamellar spacing sorbite, improve the strengthening effect of carbon elements, control the wire rod to enter the high-temperature isothermal range, promote the massive dispersion precipitation of vanadium carbides, improve the strength level of the hot-rolled wire rod, make up for the strength loss caused by reducing the Si / Mn content, and at the same time improve the strength-plasticity matching of the wire rod through weak tempering to remove stress, and finally promote the further toughening of the wire rod tissue through slow cooling on the roller table, improve the softening effect of the wire rod, take into account the strength-plasticity performance and tissue uniformity of the wire rod, with a shorter online time and can effectively simplify the process flow compared with offline salt bath treatment, and has good industrial adaptability.

[0037] (2) Aiming at the current situation that the hot-rolled wire rods for existing 2200 MPa grade bridge cables have insufficient strength-plasticity, abnormal tissues and difficult-to-control tissue uniformity, the microstructure type of the hot-rolled wire rod of the present invention includes a mixed tissue mainly composed of weak tempered sorbite, and the rest are ferrite and pearlite with fusing. It can effectively avoid the risk of abnormal tissue precipitation such as network carbon and martensite generated by C elements, improve tissue uniformity, and utilize the transition state of the transformation to tempered sorbite morphology after short-time tempering to improve the strength-plasticity matching of the wire rod, which can reach a tensile strength of 1550 - 1590 MPa, a reduction of area of 31% - 36%, and the mechanical property difference within the same coil ≤ 30 MPa. It is used in application fields such as manufacturing 2200 MPa grade ultra-high strength bridge cables, which is conducive to effectively reducing the wire breakage risk during the wire drawing process of hot-rolled wire rods, so as to improve the bridge cable strength level and meet the application requirements of long-span bridges, and has good application prospects. Description of the Drawings

[0038] The above and / or additional aspects and advantages of the present invention will become obvious and easy to understand from the description of the embodiments in conjunction with the following drawings, where:

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

[0040] Figure 2 It is the metallographic structure diagram of Embodiment 2 of the present invention. Detailed implementation manners

[0041] The embodiments described below by referring to the accompanying drawings are exemplary and are only for illustrative purposes and do not limit the description of the features and characteristics of the present invention. To propose the best mode of implementing the present invention, it is intended to explain the present invention and is sufficient to enable those skilled in the art to implement the present invention, rather than being construed as having any limitation on the scope of the present invention. The scope of the present invention is only defined by the appended claims; the detection of the structure and properties of the hot-rolled wire rods obtained in the following embodiments and comparative examples includes: the tensile test is carried out in accordance with "GB-T 228.1-2021 Metallic materials-Tensile testing-Part 1: Method of test at room temperature" to obtain the tensile strength and reduction of area; the structure detection is carried out in accordance with the metal microstructure detection method of the GB / T13298 standard; the method for testing the difference in mechanical properties within the same coil: take 2 coils of wire rods at 5 m from the end of the coil, take the lap area position as the base point, evenly divide each coil of wire rods into 8 segments on average, take 1 tensile specimen on each segment, and the strength difference after the taken tensile specimens are subjected to the tensile test is the difference in mechanical properties within the same coil. Embodiment 1:

[0042] A preferred implementation manner of the manufacturing method of the 2200 MPa 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 are Fe and inevitable impurities; its manufacturing method is manufactured according to the technological process of rolling → wire laying → online molten salt rapid cooling and isothermal treatment → slow cooling on the roller table → coiling, specifically:

[0043] The rolling process is used to heat a billet with a specification of 220mm×220mm into a high-temperature billet that reaches the plastic state for rolling through a heating furnace. Appropriate heating furnace temperature and residence time in the furnace are selected to promote the homogenization of alloy components, reduce segregation. After the billet exits the heating furnace, it is rolled into wire rods with a diameter specification of 10mm through the rolling line. Appropriate rolling temperature and deformation amount are selected to improve the rolling efficiency, promote dynamic recrystallization and grain refinement during the finishing rolling process. Specifically: control the soaking temperature of the heating furnace to be 1185°C, the residence time in the furnace to be 180min, the initial rolling temperature to be 1100°C, the finishing rolling temperature to be 950°C, and the finishing rolling reduction to be 30%; The wire laying process is used to make the wire rods exiting the rolling line into coiled bars through a wire laying machine. The coiled bars are scattered on the roller table and transported along the roller table. A relatively high wire laying temperature is selected to promote the coiled bars to be in the high-temperature austenite state, avoiding the formation of network carbides during the wire laying stage due to too low wire laying temperature, and preparing for a larger supercooling degree and promoting the nucleation of sorbite structure. Specifically: control the wire laying temperature to be 920°C.

[0044] The on-line molten salt rapid cooling and isothermal treatment process uses a two-stage salt bath tank with molten salt inside. The coiled bars after wire laying are transported through the roller table and pass through the first-stage salt bath tank for pre-treatment, so that the coiled bars cool down at a cooling rate of 37°C / s, quickly skip the network carbide precipitation range from the high-temperature austenite state and enter the sorbite phase region, inhibit the formation of network carbides, increase the supercooling degree, promote the transformation of high-temperature austenite into a structure mainly composed of fine lamellar spacing sorbite, and promote the massive dispersion precipitation of vanadium-containing carbides. Then the coiled bars are transported through the roller table and pass through the second-stage salt bath tank for post-treatment. The molten salt circulation volume in the post-treatment is appropriately reduced to maintain the stability of the molten salt temperature, reduce production energy consumption, and at the same time control the coiled bars to undergo short-time weak tempering to remove stress in the high-temperature isothermal interval, avoid the coarsening of vanadium-containing carbide precipitation, and improve the strength-plasticity matching of the coiled bars. Specifically: the molten salt temperature is 530°C, the molten salt circulation volume in the pre-treatment is 575t / h, the molten salt temperature rise ≤ 8°C, and the treatment time is 100s; the molten salt circulation volume in the post-treatment is 250t / h, the molten salt temperature rise ≤ 5°C, and the treatment time is 200s.

[0045] The roller table slow cooling process uses a non-fully closed heat preservation cover. The coiled bars transported by the conveyor roller table after passing through the second-stage salt bath tank enter the heat preservation cover. The waste heat of the coiled bars is used to prevent the increase of shrinkage stress due to too fast cooling rate during the cooling process of the coiled bars, and promote the further toughening of the coiled bar structure, improving the softening effect of the coiled bars. Specifically: control the coiled bars to cool slowly at a cooling rate of 0.9°C / s to 340°C; The coiling process is used to coil the coiled bars into coils through a coiling drum, and after packaging and warehousing, the finished hot-rolled coiled bars are obtained, and its metallographic structure diagram is as Figure 1 shown.

[0046] Comparative Example 1:

[0047] A manufacturing method of hot-rolled wire rod, the difference between its manufacturing method and that of Example 1 lies in: its manufacturing method is carried out according to the technological process of rolling → spinning → Stelmor air cooling. Specifically: the soaking temperature of the heating furnace is controlled at 1150 °C, the residence time in the furnace is 230 min, the initial rolling temperature is 1050 °C, the final rolling temperature is 900 °C, and the spinning temperature is 865 °C; for the Stelmor forced air cooling, the air volume of each fan is 260,000 m 3 / h, fans 1 - 6# are turned on at 98%, and the wire rod is cooled at a cooling rate of 9.2 °C / s to 675 °C, then fans 7 - 14# are turned on at 30%, and the wire rod is cooled at a cooling rate of 3.6 °C / s to 300 °C. After being taken off the production line, the finished product of hot-rolled wire rod is obtained. The tensile strength of the hot-rolled wire rod is 1466 MPa, the reduction of area is 12%, the microstructure includes 85% sorbite by volume percentage, and the rest is ferrite and martensite. The grade of reticular carbide is 4, and the difference in mechanical properties within the same coil is 118 MPa.

[0048] Comparative Example 2:

[0049] A manufacturing method of hot-rolled wire rod, the difference between its manufacturing method and that of Example 1 lies in: the soaking temperature of the heating furnace is controlled at 1160 °C, the residence time in the furnace is 210 min, the initial rolling temperature is 1060 °C, the final rolling temperature is 905 °C, and the spinning temperature is 875 °C. After the online molten salt rapid cooling and isothermal treatment process undergoes the front-end treatment, the wire rod is cooled at a cooling rate of 32 °C / s, and the finished product of hot-rolled wire rod is obtained after being taken off the production line. Example 2:

[0050] A preferred embodiment of the manufacturing method of the 2200 MPa grade bridge cable hot-rolled wire rod 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 are Fe and unavoidable impurities; its manufacturing method is carried out according to the technological process of rolling → spinning → online molten salt rapid cooling and isothermal treatment → roller table slow cooling → coiling. Specifically:

[0051] The rolling process is used to heat a billet with a specification of 220mm×220mm into a hot billet that reaches the plastic state for rolling. Appropriate heating furnace temperature and residence time in the furnace are selected to promote the homogenization of alloy components, reduce segregation. After the billet exits the heating furnace, it is rolled into wire rods with a diameter specification of 14mm through the rolling line. Appropriate rolling temperature and reduction ratio are selected to improve the rolling efficiency, promote dynamic recrystallization and grain refinement during the finishing rolling process. Specifically: control the soaking temperature of the heating furnace at 1205°C, the residence time in the furnace at 210 min, the initial rolling temperature at 1125°C, the finishing rolling temperature at 970°C, and the finishing rolling reduction at 26%; The wire laying process is used to make the wire rods exiting the rolling line into coiled bars through a wire laying machine. The coiled bars are scattered on the roller table and transported along the roller table. A relatively high wire laying temperature is selected to promote the coiled bars to be in the high-temperature austenite state, avoiding the formation of network carbides during the wire laying stage due to too low wire laying temperature, and preparing for a larger supercooling degree and promoting the nucleation of sorbite structure. Specifically: control the wire laying temperature at 935°C.

[0052] The on-line molten salt rapid cooling and isothermal treatment process uses a two-stage salt bath tank with molten salt inside. The coiled bars after wire laying are transported through the first-stage salt bath tank by the roller table for the front-stage treatment, so that the coiled bars cool down at a cooling rate of 36°C / s, quickly skip the network carbide precipitation range from the high-temperature austenite state and enter the sorbite phase region, inhibit the formation of network carbides, increase the supercooling degree, promote the transformation of high-temperature austenite into a structure mainly composed of fine lamellar spacing sorbite, and promote the massive dispersion precipitation of vanadium-containing carbides. Then the coiled bars are transported through the second-stage salt bath tank by the roller table for the back-stage treatment. The molten salt circulation volume in the back-stage treatment is appropriately reduced to maintain the stability of the molten salt temperature and reduce production energy consumption. At the same time, control the coiled bars to undergo short-time weak tempering to remove stress in the high-temperature isothermal range, avoid the coarsening of vanadium-containing carbide precipitation, and improve the strength-plasticity matching of the coiled bars. Specifically: the molten salt temperature is 553°C, the molten salt circulation volume in the front-stage treatment is 535t / h, the molten salt temperature rise ≤ 8°C, and the treatment time is 74s; the molten salt circulation volume in the back-stage treatment is 320t / h, the molten salt temperature rise ≤ 5°C, and the treatment time is 105s.

[0053] The roller table slow cooling process uses a non-fully closed heat preservation cover. The coiled bars transported by the conveying roller table after passing through the second-stage salt bath tank enter the heat preservation cover. The waste heat of the coiled bars is used to prevent the increase of shrinkage stress due to too fast cooling rate during the cooling process of the coiled bars, and promote the further toughening of the coiled bar structure, improving the softening effect of the coiled bars. Specifically: control the coiled bars to slowly cool to 335°C at a cooling rate of 0.8°C / s; The coiling process is used to coil the coiled bars into coils through a coiling drum, and after packaging and warehousing, the finished hot-rolled coils are obtained, and its metallographic structure diagram is as Figure 2 shown.

[0054] Comparative Example 3:

[0055] A manufacturing method of hot-rolled wire rod, the difference between its manufacturing method and that of Example 2 lies in that: in the online molten salt rapid cooling and isothermal treatment process, after the pre-treatment, 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 being taken off the production line.

[0056] Comparative Example 4:

[0057] A manufacturing method of hot-rolled wire rod, the difference between its manufacturing method and that of Example 2 lies in that: in the online molten salt rapid cooling and isothermal treatment process, after the pre-treatment, the wire rod is cooled at a cooling rate of 39 °C / s, the molten salt temperature is 505 °C, and the hot-rolled wire rod finished product is obtained after being taken off the production line. Example 3:

[0058] A preferred implementation of the manufacturing method of the 2200MPa grade hot-rolled wire rod for bridge cables according to the present invention, the chemical composition and mass percentage of the hot-rolled wire rod include C: 0.92%, Si: 0.37%, Mn: 0.9%, Cr: 0.36%, V: 0.025%, Al: 0.04%, P: 0.013%, S: 0.015%, and the rest are Fe and inevitable impurities; its manufacturing method is manufactured according to the technological process of rolling → wire laying → online molten salt rapid cooling and isothermal treatment → slow cooling on the roller table → coiling, specifically:

[0059] The rolling process is used to heat a steel billet with a specification of 220mm×220mm into a high-temperature steel billet that reaches the plastic state for rolling through a heating furnace. Appropriate heating furnace temperature and residence time in the furnace are selected to promote the homogenization of alloy components and reduce segregation. After the steel billet exits the heating furnace, the steel billet is rolled into a wire rod with a diameter specification of 15mm through the rolling line. Appropriate rolling temperature and reduction ratio are selected to improve the rolling efficiency and promote dynamic recrystallization and grain refinement in the finishing rolling process. Specifically: control the soaking temperature of the heating furnace to be 1220 °C, the residence time in the furnace to be 200min, the initial rolling temperature to be 1140 °C, the finishing rolling temperature to be 1000 °C, and the finishing rolling reduction to be 25%; the wire laying process is used to make the wire rod exiting the rolling line into a wire coil through a wire laying machine. The wire coils are scattered on the roller table and transported along the roller table. A higher wire laying temperature is selected to promote the wire coil to be in a high-temperature austenite state, avoiding the formation of network carbide during the wire laying stage due to too low wire laying temperature, and preparing for forming a larger supercooling degree and promoting the nucleation of sorbite structure. Specifically: control the wire laying temperature to be 945 °C.

[0060] The online molten salt rapid cooling isothermal treatment process uses a two-stage salt bath tank with molten salt inside. The wire rod after wire drawing is transported through the first-stage salt bath tank by a roller table for the front-stage treatment, so that the wire rod cools down at a cooling rate of 38 °C / s, quickly skips the reticulated carbide precipitation range from the high-temperature austenite state and enters the sorbite phase region, inhibits the formation of reticulated carbide, increases the degree of supercooling, promotes the transformation of high-temperature austenite into a structure mainly composed of fine lamellar spacing sorbite, and promotes the massive dispersion precipitation of vanadium-containing carbide. Then the wire rod is transported through the second-stage salt bath tank by a roller table for the back-stage treatment. The circulation volume of the molten salt in the back-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-time weak tempering to remove stress in the high-temperature isothermal range to avoid coarsening of the vanadium-containing carbide precipitation and improve the strength-plasticity matching of the wire rod. Specifically: the molten salt temperature is 542 °C, the circulation volume of the molten salt in the front-stage treatment is 620 t / h, the temperature rise of the molten salt ≤ 8 °C, and the treatment time is 82 s; the circulation volume of the molten salt in the back-stage treatment is 345 t / h, the temperature rise of the molten salt ≤ 5 °C, and the treatment time is 165 s.

[0061] In the roller table slow cooling process, the heat preservation cover is not fully closed. The wire rod transported by the conveying roller table after passing through the second-stage salt bath tank enters the heat preservation cover. The residual heat of the wire rod is used to prevent the increase of shrinkage stress caused by too fast cooling rate during the cooling process of the wire rod, and promote the further toughening of the wire rod structure and improve the softening effect of the wire rod. Specifically: the wire rod is controlled to slowly cool at a cooling rate of 1 °C / s to 328 °C; the coiling process is used to coil the wire rod into a coil by a coiling drum, and the finished hot-rolled wire rod is obtained after packaging and warehousing.

[0062] Comparative Example 5:

[0063] A manufacturing method of a hot-rolled wire rod, the difference between its manufacturing method and that of Example 3 is that: the treatment time of the front-stage treatment in the online molten salt rapid cooling isothermal treatment process is 50 s, and the treatment time of the back-stage treatment is 40 s. The finished hot-rolled wire rod is obtained after offline.

[0064] Comparative Example 6:

[0065] A manufacturing method of a hot-rolled wire rod, the difference between its manufacturing method and that of Example 3 is that: the treatment time of the front-stage treatment in the online molten salt rapid cooling isothermal treatment process is 135 s, and the treatment time of the back-stage treatment is 320 s. The finished hot-rolled wire rod is obtained after offline. Example 4:

[0066] A preferred embodiment of the manufacturing method of the hot-rolled wire rod for 2200MPa-class bridge cables according to 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 are Fe and inevitable impurities. Its manufacturing method is manufactured according to the technological process of rolling → wire laying → on-line molten salt rapid cooling and isothermal treatment → slow cooling on the roller table → coiling. Specifically:

[0067] The rolling process is used to heat the steel billet with a specification of 220mm×220mm into a high-temperature steel billet that reaches the plasticity for rolling through a heating furnace. Appropriate heating furnace temperature and residence time in the furnace are selected to promote the homogenization of alloy components and reduce segregation. After the steel billet exits the heating furnace, it is rolled into a wire rod with a diameter specification of 11mm through the rolling line. Appropriate rolling temperature and reduction ratio are selected to improve the rolling efficiency and promote dynamic recrystallization and grain refinement during the finishing rolling process. Specifically: control the soaking temperature of the heating furnace to be 1195°C, the residence time in the furnace to be 195min, the initial rolling temperature to be 1110°C, the finishing rolling temperature to be 960°C, and the finishing rolling reduction to be 29%; The wire laying process is used to make the wire rod exiting the rolling line into a coil through a wire laying machine. The coil is scattered on the roller table and conveyed along the roller table. A higher wire laying temperature is selected to promote the coil to be in the high-temperature austenite state, avoiding the formation of network carbide during the wire laying stage due to too low wire laying temperature, and preparing for the formation of a larger supercooling degree and promoting the nucleation of sorbite structure. Specifically: control the wire laying temperature to be 930°C.

[0068] The on-line molten salt rapid cooling and isothermal treatment process uses a two-stage salt bath tank with molten salt inside. The coil after wire laying is conveyed through the first-stage salt bath tank by the roller table for the front-stage treatment, so that the coil cools down at a cooling rate of 35°C / s, quickly skips the network carbide precipitation interval from the high-temperature austenite state and enters the sorbite phase region, inhibiting the formation of network carbide, increasing the supercooling degree, promoting the transformation of high-temperature austenite into a structure mainly composed of fine lamellar spacing sorbite, and promoting the massive dispersion precipitation of vanadium-containing carbides. Then the coil is conveyed through the second-stage salt bath tank by the roller table for the back-stage treatment. The molten salt circulation volume of the back-stage treatment is appropriately reduced to maintain the stability of the molten salt temperature and reduce production energy consumption. At the same time, the coil is controlled to be short-time and weakly tempered in the high-temperature isothermal interval to remove stress, avoiding the coarsening of vanadium-containing carbide precipitation and improving the strength-plasticity matching of the coil. Specifically: the molten salt temperature is 560°C, the molten salt circulation volume of the front-stage treatment is 500t / h, the molten salt temperature rise ≤ 8°C, and the treatment time is 60s; the molten salt circulation volume of the back-stage treatment is 300t / h, the molten salt temperature rise ≤ 5°C, and the treatment time is 55s.

[0069] In the roller table slow cooling process, the heat preservation cover is not fully closed. The wire rod passing through the second salt bath tank is conveyed into the heat preservation cover by the conveying roller table. The residual heat of the wire rod is utilized to prevent the increase of shrinkage stress caused by too fast cooling rate during the cooling process of the wire rod, and to promote the further toughening of the wire rod structure, improving the softening effect of the wire rod. Specifically: control the wire rod to cool slowly at a cooling rate of 0.7 °C / s to 345 °C; the coiling process is used to coil the wire rod into coils by the coiling drum, and the finished hot-rolled wire rod is obtained after packaging and warehousing.

[0070] Comparative example 7:

[0071] A manufacturing method of hot-rolled wire rod, the difference between its manufacturing method and that of Example 4 is that: its manufacturing method is carried out according to the technological process of rolling → spinning → online molten salt rapid cooling and isothermal treatment → air cooling. The air cooling is carried out with the heat preservation cover open, and the wire rod passing through the second salt bath tank is air-cooled by the conveying roller table. Control the wire rod to cool at a cooling rate of 1.7 °C / s to 285 °C, and the finished hot-rolled wire rod is obtained after being taken off the production line.

[0072] The tissues and properties of the hot-rolled wire rods obtained in the above Examples 1-4 and Comparative Examples 2-7 were detected, and the comparison results are shown in Table 1 below:

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

[0074]

[0075] From the comparison results of Example 1 and Comparative Example 1, it can be seen that compared with the Stelmor air-cooling line, due to the uncontrollable cooling rate during the cooling phase transformation, the strengthening effect is weakened, and abnormal tissues such as network carbon and martensite appear, and it is difficult to control the fine precipitation of vanadium carbides, and the tissue uniformity is poor. Through the V-containing chemical composition design combined with the online molten salt rapid cooling and isothermal technology, the present invention can effectively avoid the risk of precipitation of abnormal tissues such as network carbon and martensite in C elements, maximize the strengthening effect of carbon elements, control the dispersed precipitation of vanadium carbides during the isothermal process, so that the microstructure type includes a mixed structure mainly composed of weak tempered sorbite, and the rest are ferrite and eutectoid pearlite, improving the overall strength, plasticity and tissue uniformity of the wire rod. From the results of Examples 1-4, it can be seen that the hot-rolled wire rod can reach a tensile strength of 1550-1590 MPa, a reduction of area of 31%-36%, and the mechanical property difference within the same coil ≤ 30 MPa, which is used in application fields such as manufacturing 2200 MPa grade ultra-high strength bridge cables, etc., and is beneficial to effectively reduce the wire breakage risk during the wire drawing process of the hot-rolled wire rod and improve the strength level of the bridge cable.

[0076] It can be seen from the comparison results of Example 1 and Comparative Example 2 that appropriately increasing the wire drawing temperature can avoid the formation of network carbide during the wire drawing stage due to too low wire drawing temperature, prepare for forming a larger supercooling degree and promoting the nucleation of sorbite structure later, and at the same time can reduce the limitation on rolling, which is beneficial to increasing the rolling temperature, reducing the rolling deformation resistance, and further improving the rolling efficiency.

[0077] It can be seen from the comparison results of Example 2 and Comparative Example 3 that the higher the molten salt temperature of the on-line molten salt rapid cooling isothermal treatment, the more thermal power can be provided for tempering to remove stress and promote the improvement of matrix plasticity. However, if the molten salt temperature is too high, with the extension of the treatment time, 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.

[0078] It can be seen from the comparison results of Example 2 and Comparative Example 4 that the lower the molten salt temperature of the on-line molten salt rapid cooling isothermal treatment, the more beneficial it is to form a larger supercooling degree, promote the transformation of high-temperature austenite into sorbite structure with finer lamellar 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 result in the loss of wire rod plasticity.

[0079] It can be seen from the comparison results of Example 3 and Comparative Example 5 that the shorter the treatment time of the on-line molten salt rapid cooling isothermal treatment, the weaker the weak tempering stress relief effect, the increase in wire rod strength and the decrease in plasticity. However, if the front-stage treatment time is too short, it will affect the regulation of tissue uniformity. At the same time, if the back-stage treatment time is too short, it will affect the full precipitation of vanadium-containing carbides and the weak tempering stress relief effect, which is not beneficial to the plasticity of the wire rod.

[0080] It can be seen from the comparison results of Example 3 and Comparative Example 6 that the longer the treatment time of the on-line molten salt rapid cooling isothermal treatment, the more thermal power can be provided for tempering to remove stress 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 precipitation and coarsening of vanadium-containing carbides will affect the strengthening effect and increase the production energy consumption.

[0081] It can be seen from the comparison results of Example 3 and Comparative Example 7 that adopting roller table 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 an increase in shrinkage stress, and promote the further toughening of the wire rod structure and improve the softening effect of the wire rod.

[0082] The series of detailed descriptions listed above are only specific descriptions of the feasible embodiments of the present invention, and they are not intended to limit the protection scope of the present invention. Any equivalent embodiments or modifications made without departing from the technical spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for manufacturing a 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%-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%, and the rest are Fe and unavoidable impurities; after the wire rod is spun into a wire rod at a spinning temperature of ≥920°C, it is subjected to an online molten salt rapid cooling isothermal treatment, and the molten salt treatment time is controlled to be ≤300s, so that the wire rod is ≥3 The temperature is lowered at a cooling rate of 5°C / s, from the austenite state into the sorbite phase region, forming a structure dominated by sorbite and isothermally weakly tempered to relieve stress, and finally slowly cooled through a roller to be made into a hot-rolled wire rod with a microstructure including weakly tempered sorbite with a volume percentage of ≥88%, and the rest being a mixed structure composed of ferrite and fused pearlite; the molten salt temperature of the online molten salt rapid cooling isothermal treatment is 530~560°C, and the online molten salt rapid cooling isothermal treatment is divided into a front-stage treatment and a rear-stage treatment, the molten salt circulation amount of the front-stage treatment is greater than the molten salt circulation amount of the rear-stage treatment, the processing time of the front-stage treatment is 60~100s, and the processing time of the rear-stage treatment is 55~200s.

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 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.

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

6. 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 5.

7. The 2200MPa grade hot rolled wire rod for bridge cables according to claim 6, 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%.

8. The 2200MPa grade hot rolled wire rod for bridge cables according to claim 6, characterized in that: The network carbide grade of the hot-rolled wire rod is grade 0, and the mechanical property difference is ≤30MPa.

9. The 2200MPa grade hot rolled wire rod for bridge cables according to claim 6, 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%.

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