A hot-rolled wire rod for bridge cables with a strength level of 2300 MPa and its manufacturing method

Abstract

The present invention relates to a hot-rolled wire rod for 2300 MPa-class bridge cables and a manufacturing method thereof. After being rolled with a vanadium-containing high-carbon steel composition of C-Si-Mn-Cr-V-Al and made into a wire rod at a laying head temperature of ≥900 °C, it undergoes an on-line molten salt rapid cooling and toughening treatment, causing the wire rod to cool at a cooling rate of ≥33 °C / s, enter the sorbite phase region from the austenite state, form a structure mainly composed of sorbite and isothermally toughened to remove stress. Finally, it undergoes slow cooling with the cover opened on the roller table to make a hot-rolled wire rod whose microstructure includes a mixed structure mainly composed of weakly tempered sorbite, with the rest being ferrite and pearlite with melting. It can achieve the high strength and plasticity matching of the hot-rolled wire rod, with a tensile strength of 1595~1635 MPa, an area reduction of 30%~35%, and a difference in mechanical properties within the same coil of ≤40 MPa, improve the tissue uniformity and production efficiency, promote stable production, and thus enhance the strength grade of ultra-high-strength bridge cables.

Description

Technical Field

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

[0002] Under the guidance of the construction of long-span bridges and the development of lightweight, the strength grade of existing bridge cables has been gradually increased to the 2200 MPa-class ultra-high strength grade level. The further improvement of the bridge cable strength grade is beneficial to further improving the bearing capacity, spanning ability and service life of bridges, and is suitable for bridges with large traffic flow and frequent load changes. However, the improvement of the ultra-high strength bridge cable strength grade is limited by the strength grade of its base material hot-rolled wire rod. There is little development of bridge cables with a higher strength grade of 2300 MPa. Therefore, it is necessary to develop a hot-rolled wire rod for 2300 MPa-class bridge cables and a manufacturing method thereof to meet the development of the steel industry and the market use requirements.

[0003] As the strength grades of bridge cables and wire rods for bridge cables continue to climb, high-carbon steel with a carbon content of 0.87% or more is generally used for wire rods. The wire rod production is basically the Stelmor air-cooling line controlled cooling mode. For example, a high-strength bridge cable wire rod and its production method disclosed in Patent CN118880169A, the 87SiMn wire rod is rapidly and strongly cooled by the Stelmor air-cooling line after low-temperature rolling and wire laying, combined with heat preservation in the heat preservation corridor for more than 120 minutes for on-line aging, so that the strength of the wire rod reaches more than 1400 MPa. However, there are still the following technical difficulties in the production of hot-rolled wire rods for 2300 MPa-class bridge cables:

[0004] I. The insufficient strength of the wire rod base material will increase the subsequent drawing strength increase and area reduction rate, increase the risk of wire breakage, and affect the production efficiency of bridge cables. To further improve the strength grade of the hot-rolled wire rod base material, after the addition of alloying elements such as C, Mn, and Cr in the wire rod, the segregation tendency during the solidification of the steel billet will be aggravated. Before the austenite transforms into pearlite structure after wire laying, due to slow cooling, carbides will preferentially nucleate and grow at the grain boundaries and gradually form a network structure. The formed network carbides will seriously reduce the plasticity and toughness of the wire rod, significantly increasing the risk of wire breakage during the wire making process of bridge cables. To minimize the network carbide level and promote pearlite refinement to obtain a better drawing performance sorbite structure, although strong cooling treatment is adopted after wire laying, on the one hand, the maximum cooling capacity of the Stelmor air-cooling line is limited, and the improvement of network carbides is limited. On the other hand, the increase in air-cooling intensity further increases the uncontrollability of air volume and air temperature, and the temperature difference between the edge and the core of the wire rod and between the wind-exposed and wind-receiving surfaces further increases, resulting in asynchronous tissue transformation and affecting the uniformity of the overall performance of the wire. Affected by the segregation of hardenability components, it is also easy for the cooling rate to exceed the critical cooling rate, resulting in the transformation of austenite into non-equilibrium structures such as martensite or bainite, generating large thermal stresses inside the wire rod, and further aggravating the subsequent drawing wire breakage and even the risk of brittle breakage during coiling.

[0005] II. To improve the strength grade of the base material of hot-rolled wire rods, microalloying elements such as V are added to the wire rods to improve the strength and toughness of the steel, or the on-line holding time is extended to improve the plasticity of the wire rods. However, restricted by the minimum cooling capacity of the Stelmor air-cooling line or the holding line, on the one hand, a smaller supercooling degree during cooling will affect the precipitation driving force of vanadium carbonitrides and reduce the precipitation amount. The instability of continuous cooling and air-cooling control of the wire rods will result in the coexistence of relatively coarse and fine carbonitrides in the wire rods, affecting the precipitation strengthening effect and the microstructure uniformity. On the other hand, during the continuous cooling process of the Stelmor air-cooling line, the phase transformation incubation time is short, and the phase transformation is likely to be insufficient, resulting in a loss of the strength of the wire rods, or causing the retained austenite to form abnormal low-temperature microstructures during subsequent cooling, deteriorating the plasticity of the microstructure. At the same time, the obtained sorbite microstructure has a larger lamellar spacing and higher thermal stress. Although on-line aging treatment is carried out, the temperature control ability and temperature conditions are limited, and the production time is long, affecting the production efficiency.

[0006] Compared with stranded wire steel, to reduce the strength loss and the risk of torsional cracking during subsequent galvanizing processing and maintain the strength grade of bridge cables, the base material of the wire rods for bridge cables has higher requirements for strength and microstructure uniformity. Although salt baths are involved in the production of wire rods for existing high-strength stranded wire steel, generally it is the heat treatment after air-cooling coiling, which is used to refine the lamellar spacing, improve the rate of sorbitization and the strength of the wire rods. It involves uncoiling the coiled wire rods after coiling, heating to the high austenitizing temperature and then further salt bath treatment, which will increase the production process, treatment time and production energy consumption, affecting the production efficiency and cost. Summary of the Invention

[0007] 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 bridge cables with a grade of 2300 MPa and a manufacturing method thereof, which can achieve the matching of high strength and plasticity of the hot-rolled wire rod, improve the microstructure uniformity and production efficiency, promote stable production, so as to enhance the strength grade of ultra-high-strength bridge cables.

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

[0009] A manufacturing method of a hot-rolled wire rod for bridge cables with a grade of 2300 MPa, the manufacturing method comprising:

[0010] The wire rod is rolled according to the chemical composition of the hot-rolled wire rod. The chemical composition and mass percentage of the hot-rolled wire rod include: C: 0.93% - 0.96%, Si: 0.45% - 0.65%, Mn: 0.75% - 0.95%, Cr: 0.42% - 0.55%, V: 0.038% - 0.048%, Al: 0.02% - 0.04%, P ≤ 0.015%, S ≤ 0.015%, and the rest are Fe and inevitable impurities. After the wire rod is spun at a spinning temperature of ≥900°C into a wire rod, it undergoes an online molten salt rapid cooling and toughening treatment, so that the wire rod cools at a cooling rate of ≥33°C / s, enters the sorbite phase region from the austenite state, forms a sorbite-based structure and isothermally toughened to remove stress. Finally, it is slowly cooled with the cover opened on the roller table to produce a hot-rolled wire rod with a microstructure mainly composed of weakly tempered sorbite, and the rest is a mixed structure composed of ferrite and eutectoid pearlite.

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

[0012] (1) Carbon: The C element is the main element to improve the strength of steel, which can produce a solid solution strengthening effect. With the increase of carbon content, it is beneficial to reduce the critical cooling rate of steel, promote the phase transformation of sorbite structure during the online molten salt rapid cooling and toughening treatment, improve the material strength, so that the hot-rolled wire rod has higher load-bearing capacity after being drawn into steel wire to make bridge cables. However, with the increase of carbon content, it will increase the carbon segregation tendency during the solidification of the steel billet, increase the tendency of decarburization and the precipitation of network carbides, deteriorate the plastic and toughness properties of the material, and is not conducive to the regulation of the matrix structure. Therefore, in order to meet the high-strength requirements of the 2300MPa-class bridge cable for the hot-rolled wire rod base material, control the material cost, and at the same time reduce the difficulty of controlling network carbides and improving plasticity, the mass percentage of C is controlled at 0.93% - 0.96%.

[0013] (2) Silicon: The Si element is an effective solid solution strengthening element and a good deoxidizer, which can inhibit the grain coarsening during the online molten salt rapid cooling and toughening treatment, so as to quickly obtain a sorbite structure mainly with fine lamellar spacing, improve the matrix strength, and at the same time can increase the eutectoid transformation temperature so that the phase region temperature can adapt to the dispersed precipitation of vanadium carbides. However, too high silicon content will make the steel more prone to decarburization during high-temperature heating, increase the risk of abnormal tissue precipitation, and reduce the toughness and tissue uniformity of the steel. Therefore, in order to regulate the phase transformation temperature and promote the rapid offline of the online molten salt rapid cooling and toughening treatment, the mass percentage of Si is controlled at 0.45% - 0.65%.

[0014] (3) Manganese: As an austenite-forming element, Mn can expand the austenite phase region, inhibit the formation of ferrite, and increase the hardenability of the wire rod. Furthermore, it is beneficial for promoting the rapid nucleation of sorbite structure mainly with fine lamellar spacing during on-line molten salt rapid cooling and toughening treatment, thereby increasing the tensile strength of the wire rod. This enables the bridge cable to resist impact and vibration loads while withstanding tension. However, when the Mn content is too high, it will exacerbate alloy element segregation, increase the risk of martensite precipitation in the core of the wire rod, reduce the activity of carbon, and increase the difficulty of isothermal toughening and stress relief, thus resulting in a loss of the plasticity of the wire rod. Therefore, to balance high strength, reduce the difficulty of controlling tissue uniformity and tempering, and promote efficient production of hot-rolled wire rods, the mass percentage of Mn is controlled at 0.75% - 0.95%.

[0015] (4) Chromium: The Cr element can prevent the growth of austenite grains during heating, playing a role in refining the grains. At the same time, it can strongly enhance the hardenability of the material, increase the eutectoid temperature, expand the austenite phase region, and reduce the critical cooling rate, which is beneficial for refining the sorbite lamellar spacing and increasing the matrix strength. It is also conducive to reducing the strength loss during the subsequent hot-dip galvanizing process of wire rope production. However, if the Cr content is too high, it will exacerbate compositional segregation, increase the risk of abnormal martensite precipitation, affect the uniformity of the wire rod structure, and significantly increase the difficulty of improving the plasticity of the wire rod, affecting the isothermal toughening and stress relief effect, and further affecting the drawing and torsion properties of the wire. Therefore, to obtain a uniform high-strength structure through on-line molten salt rapid cooling and toughening treatment regulation, the mass percentage of Cr is controlled at 0.42% - 0.55%.

[0016] (5) Vanadium: The V element can inhibit the coarsening of high-temperature austenite and refine austenite grains. At the same time, during the molten salt rapid cooling and isothermal process, a large number of fine and dispersed carbonitrides can be formed in the medium-temperature range, which can hinder dislocation movement, thus playing a role in precipitation strengthening, improving the strength level of hot-rolled wire rods without reducing plasticity. However, the cost of the V element is relatively high, and excessive addition is not conducive to controlling the cost of wire rods and has a risk of coarsening. Considering the role and cost of the V element, the content of the V element in this invention is controlled at 0.038% - 0.048%.

[0017] (6) Aluminum: The Al element is used as a deoxidizer during smelting and inhibits the growth of austenite grains during hot rolling. The fine austenite grains can form fine sorbite structure after cooling transformation, which is beneficial for improving the strength and 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 beneficial for 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 0.02% - 0.04%.

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

[0019] The above hot-rolled wire rod adopts a vanadium-containing high-carbon steel composition design of C-Si-Mn-Cr-V-Al, combined with the optimized ratio of Si, Mn, and Cr, which provides favorable conditions for refining austenite grains, inhibiting grain coarsening during online molten salt rapid cooling toughening treatment, regulating the precipitation of sorbite phase transformation to be compatible with the dispersion precipitation temperature of vanadium-containing carbides, and reducing the difficulty of controlling abnormal structures. On this basis, the wire drawing temperature is appropriately increased to avoid the increase in grain size caused by too high temperature, and to provide favorable conditions for forming a large supercooling degree later, promoting the refinement of pearlite lamellae to form sorbite, increasing the precipitation driving force and nucleation rate of vanadium-containing carbides. Instead of air cooling, the wire rod directly enters the salt bath for online molten salt rapid cooling toughening treatment:

[0020] First, compared with the Stelmor air-cooling line, due to its limited cooling control ability, it is difficult to balance the control of network carbide and low-temperature abnormal structures in high-carbon steel products. The wire rod can use the high heat transfer capacity of the molten salt to rapidly cool down when passing through the molten salt. On the one hand, the rapid and uniform cooling can enable the wire rod to quickly skip over the secondary cementite precipitation temperature range of 700-800°C throughout the length, inhibiting the nucleation and growth of network carbide at grain boundaries, effectively avoiding the risk of network carbide caused by increasing the C element content and alloy segregation. On the other hand, when the wire rod passes through the molten salt, the molten salt can cover the surface of the wire rod for uniform heat transfer, without the temperature difference problem between the windward side and the leeward side, reducing the temperature difference from the edge to the core of the wire rod cross-section, avoiding the formation of brittle low-temperature abnormal structures due to alloy element segregation and supercooling of the wire rod entering the bainite or martensite phase region, improving the control effect of high carbon manganese chromium content on abnormal structures, and further exerting the strengthening effect of carbon elements to improve the tissue uniformity of the wire rod.

[0021] Second, compared with the Stelmor air-cooling line or heat preservation line, due to their limited cooling control ability, it is difficult to regulate the tissue state and give full play to the microalloy strengthening effect. The wire rod can cool down rapidly through online molten salt rapid cooling toughening treatment and enter the sorbite phase region from the high-temperature austenite state. On the one hand, it can form a large supercooling degree, combined with Si and V to inhibit the coarsening of high-temperature austenite grains, providing more nucleation points for phase transformation, promoting the rapid deformation of high-temperature austenite to form a structure mainly composed of fine lamellar spacing sorbite, and improving the matrix strength. On the other hand, as the temperature of the wire rod gradually changes to the same as the molten salt temperature, the high-temperature isothermal interval of the wire rod entering the sorbite phase region can be controlled, prolonging the phase transformation time, promoting the full phase transformation of austenite, avoiding the formation of abnormal structures by retained austenite during subsequent cooling and causing coiling brittle fracture, improving production stability, and at the same time prolonging the precipitation time of vanadium-containing carbides during the isothermal process. Combined with refined grains and a large supercooling degree, the carbonitrides of vanadium can be fully precipitated in this temperature range to obtain fine and dispersed strengthening phases, rather than precipitating with different sizes, which can give full play to the strengthening and toughening effect of V and improve the tissue uniformity.

[0022] 3. Compared with extending the insulation line or post-heat treatment process, which affects production efficiency and organizational regulation, the wire rod can be treated with online molten salt rapid cooling and toughening to promote the full phase transformation of austenite and form appropriate toughening at the same time. On the one hand, the wire rod can prolong the time in the high temperature range in the troostite phase region, provide more thermal power for toughening and stress relief of the organization, quickly improve the plasticity of the wire rod, promote the rapid offline of the wire rod, and improve production efficiency. On the other hand, compared with long-term strong tempering, online molten salt rapid cooling and toughening can form short-term tempering and toughening, avoiding the coarsening of vanadium-containing carbides precipitated due to prolonged high-temperature treatment time, or excessive loss of matrix strength due to large-scale melting and coarsening of troostite lamellae. The wire rod is slowly cooled by the roller cover, and the wire rod's own residual heat can be used to control the slow cooling of the wire rod, avoiding the increase of stress caused by too fast cooling of the wire rod, and using the high temperature state of the wire rod to promote further toughening and stress relief of the wire rod organization, thereby obtaining a weakly tempered troostite-based organization, improving the softening effect and offline efficiency of the wire rod, simplifying the production process and reducing production energy consumption compared with post-treatment.

[0023] Selecting appropriate heating furnace parameters before rolling can promote organizational homogenization, reduce the impact of segregation, and avoid decarburization, burning or coarse grains caused by excessive heating temperature. In a preferred embodiment, before rolling, the heating furnace is controlled to have a soaking temperature of 1190-1230°C, and the time in the furnace is ≥160min.

[0024] Appropriately increasing the start rolling temperature during the rolling process can reduce the deformation resistance of the steel billet, appropriately reduce the final rolling temperature, increase the final rolling reduction, promote dynamic recrystallization during the final rolling process, and refine the grains, so as to provide more nucleation sites for the sorbite phase with fine austenite grains, refine the final structure, and improve the strength and toughness of the steel. In a preferred embodiment, during the rolling process, the initial rolling temperature is controlled to be 1080~1120℃, the final rolling temperature is 890~940℃, and the final rolling reduction is 22%~27%.

[0025] In a preferred embodiment, the molten salt temperature of the online molten salt rapid cooling and toughening treatment is 550~580℃, which is in the medium temperature range of the troostite phase region and the dispersion and precipitation of vanadium-containing carbides. The lower the molten salt temperature, the more conducive it is to improving the supercooling degree, promoting the rapid transformation of high-temperature austenite to a troostite structure with finer lamellae, increasing the power of dispersion and precipitation of vanadium-containing carbides, and thus improving the matrix strength. However, if the molten salt temperature is too low, it is difficult to provide more power for toughening and stress relief in the isothermal interval, which will cause the plasticity of the wire rod to decrease, and even precipitate low-temperature abnormal structure, which will significantly affect the plasticity and uniformity of the wire rod. On the contrary, the higher the molten salt temperature, the greater the troostite lamella spacing and the melting effect, and the plasticity of the wire rod is improved. However, if the molten salt temperature is too high, the troostite lamellae will coarsen and affect the large-scale dispersion and precipitation of vanadium-containing carbides, which will lose the matrix strength and toughness. Therefore, selecting an appropriate molten salt temperature can promote rapid cooling and appropriate toughening of the wire rod, which is convenient for regulating the matrix structure.

[0026] Since the temperature difference between the wire rod when it is discharged from the coiling temperature and the molten salt temperature is relatively large, the on-line molten salt rapid cooling and toughening treatment is divided into a front-stage treatment and a rear-stage treatment. The molten salt circulation volume in the front-stage treatment is larger than that in the rear-stage treatment. Selecting a larger molten salt circulation volume in the front-stage treatment can control the temperature rise, promote the rapid cooling of the wire rod, maintain the stability of the supercooling degree, promote the full phase transformation of high-temperature austenite quickly, improve the matrix strength and tissue uniformity. After undergoing the molten salt treatment for a period of time, the temperature of the wire rod drops to the molten salt temperature, and the difficulty of controlling the molten salt temperature rise decreases. Appropriately reducing the molten salt circulation volume in the rear-stage treatment can precisely control the temperature, control the toughening and stress relief of the wire rod in the high-temperature isothermal range, avoid the influence of too short treatment time in the front-stage treatment on the control of tissue homogenization, avoid the unnecessary increase in production energy consumption due to too long treatment time in the front-stage treatment, avoid the influence of too short treatment time in the front-stage treatment and the rear-stage treatment on the full phase transformation of the tissue and the toughening effect, and avoid the coarsening of vanadium-containing carbide precipitation and excessive toughening resulting in the loss of strength and plasticity due to too long treatment time in the rear-stage treatment. Therefore, by controlling the appropriate treatment time of the front-stage treatment and the rear-stage treatment, the tissue state of the wire rod can be further regulated and the production energy consumption can be appropriately reduced. In the preferred embodiment, the treatment time of the front-stage treatment is 110 - 150 s, and the treatment time of the rear-stage treatment is 80 - 190 s.

[0027] To further control the rapid formation of a structure mainly composed of fine lamellar spacing sorbite from the high-temperature austenite state of the wire rod and promote the dispersion precipitation of vanadium-containing carbides, in the preferred embodiment, the molten salt circulation volume in the front-stage treatment is 450 - 600 t / h, and the molten salt temperature rise ≤ 8°C.

[0028] To further control the toughening and stress relief effect and improve the strength-plasticity matching of the wire rod, in the preferred embodiment, the molten salt circulation volume in the rear-stage treatment is 200 - 240 t / h, and the molten salt temperature rise ≤ 3°C.

[0029] After the wire rod exits the salt bath at 550 - 580°C, it enters the conveying roller table. In the preferred embodiment, for the slow cooling with the roller table cover opened, the heat preservation cover is opened to control the wire rod to cool slowly at a cooling rate of 1.2 - 2°C / s to below 320°C. On the one hand, it can prevent the stress increase caused by too fast cooling rate during the cooling process of the wire rod. On the other hand, it can appropriately promote the further toughening of the wire rod tissue by using the residual heat of the wire rod itself, improve the softening effect of the wire rod, reduce the production energy consumption, enable the wire rod to be quickly taken off the production line, and improve the production efficiency.

[0030] A hot-rolled wire rod for 2300 MPa class bridge cables, the hot-rolled wire rod is manufactured by the manufacturing method of the hot-rolled wire rod for 2300 MPa class bridge cables described in any one of the above.

[0031] The above hot-rolled wire rods adopt a chemical composition design containing vanadium, high silicon and high carbon combined with an on-line molten salt rapid cooling and toughening technology to obtain a mixed structure composed of weakly tempered sorbite, ferrite and fused pearlite. The weakly tempered sorbite is a transitional state in which sorbite undergoes a transformation with the cementite lamellae melting and transforming into tempered sorbite during a relatively short tempering time, and a small amount of fused pearlite structure is formed, which appropriately reduces the strength of the sorbite, appropriately improves the plasticity, and toughens the matrix, and avoids excessive loss of matrix strength caused by strong tempering and the influence of extended treatment time on the strengthening effect of vanadium carbides, and cooperates with refined grain size of the structure to improve the overall strength of the wire rod and obtain good plastic properties.

[0032] The higher the proportion of the weakly tempered sorbite and the finer the lamellar spacing, the more beneficial it is to improve the matrix strength. In a preferred embodiment, the volume percentage of the weakly tempered sorbite ≥ 82%, and the lamellar spacing of the weakly tempered sorbite is 75 - 110 nm.

[0033] The more the proportion of the fused pearlite, the more beneficial it is to improve the matrix plasticity. In a preferred embodiment, the volume percentage of the fused pearlite accounts for 11% - 15%.

[0034] In a preferred embodiment, the network carbide grade of the hot-rolled wire rod is grade 0, and no carbides are found to precipitate along the austenite grain boundaries to form a network structure, so that the strength, toughness, plasticity, etc. of the hot-rolled wire rod can be maintained at a relatively good level.

[0035] Since the hot-rolled wire rod will not cause problems such as a decrease in impact toughness and an increase in brittleness due to the presence of network carbides, the tissue phase change is more uniform, avoiding abnormal tissues such as bainite and martensite, and the comprehensive properties of the material are more stable and excellent, and it is not easy to occur brittle fracture. In a preferred embodiment, the mechanical property difference within the same coil of the hot-rolled wire rod ≤ 40 MPa.

[0036] In a preferred embodiment, the diameter of the hot-rolled wire rod is 9.0 - 15.0 mm, the tensile strength is 1595 - 1635 MPa, and the reduction of area is 30% - 35%. The hot-rolled wire rod has a higher tensile strength and good reduction of area, which is beneficial to reducing the drawing reduction rate, quickly reaching the strength grade of the bridge cable, reducing the plastic loss during the process, reducing the drawing wire breakage rate, promoting the stable production of the bridge cable, and at the same time meeting the requirements of the strength loss during the hot-dip galvanizing process for the strength of the base material, thereby improving the strength grade of the bridge cable.

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

[0038] In view of the current situation that the existing Stelmor air-cooled wire is difficult to stably produce high-carbon steel products with a carbon content of 0.87% or more, which restricts the improvement of the strength grade of the base material of ultra-high-strength bridge cables, the present invention combines the C-Si-Mn-Cr-V-Al chemical composition design with the online molten salt rapid cooling toughening technology to inhibit grain coarsening, control the wire rod to quickly enter the sorbite phase region from the high-temperature austenite state, form a structure mainly composed of fine lamellar spacing sorbite, promote the dispersed precipitation of vanadium during the isothermal process, enter the high-temperature isothermal range for toughening and stress relief, and cooperate with the slow cooling of the roller table with the cover opened to improve the softening effect of the wire rod. On the one hand, it can avoid the risk of abnormal structures such as network carbon and martensite caused by C elements, regulate the full and uniform phase transformation of the wire rod, maximize the strengthening effect of carbon elements and the strengthening and toughening effect of microalloying element vanadium, further improve the high strength and tissue uniformity of the hot-rolled wire rod, and form stable production. On the other hand, it controls the weak tempering state of the wire rod structure and the toughening and stress relief effect, improves the plasticity and high-strength matching of the hot-rolled wire rod, can also control production energy consumption, simplifies the manufacturing process, enables the wire rod to be quickly offline, avoids coiling brittle fracture, and thus improves production efficiency, with good industrial adaptability.

[0039] In view of the current situation that the improvement of the strength grade of the current ultra-high-strength bridge cables is limited by the strength grade of the base material hot-rolled wire rod, the hot-rolled wire rod of the present invention uses vanadium-containing high-carbon steel, and the microscopic tissue type is a mixed tissue composed of weak tempered sorbite, ferrite, and fused pearlite. It can utilize the transition state of the fused cementite lamellae and the transformation into tempered sorbite, the large amount of dispersed precipitation of vanadium carbides, grain refinement, and the effective control of abnormal tissues such as network carbides and martensite, effectively improve the strength-plasticity matching and tissue uniformity of the wire rod. The tensile strength of the product can reach 1595-1635 MPa, the reduction of area can reach 30%-35%, and the difference in mechanical properties within the same coil is ≤40 MPa. It is used in application fields such as manufacturing 2300 MPa grade ultra-high-strength bridge cables, which is beneficial to reducing the risk of drawing wire breakage and torsional cracking, promoting the stable production of bridge cables, and has good market application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

[0043] The embodiments described below with reference to the accompanying drawings are exemplary, merely for illustration purposes and do not limit the description of the features and characteristics of the present invention. They are intended to present the best mode of implementing the present invention, for the purpose of explaining the present invention and being sufficient for those skilled in the art to implement the present invention. It should not be construed as any limitation on the scope of the present invention, which is only defined by the appended claims. The organization and performance testing of the hot-rolled wire rods obtained from the following embodiments and comparative examples include: 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 microstructure detection is carried out in accordance with the metallic microstructure detection method of the GB / T13298 standard; The method for testing the within-coil difference of mechanical properties: Take 2 coils of wire rods at a distance of 5 m from the end of the coil. Taking the lap area position as the base point, each coil of wire rod is evenly divided into 8 segments on average, and 1 tensile specimen is taken on each segment. The strength difference after the tensile test of the taken tensile specimens is the within-coil difference of mechanical properties. Example 1:

[0044] A preferred embodiment of the manufacturing method of the 2300MPa 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: 0.95%, Si: 0.49%, Mn: 0.75%, Cr: 0.45%, V: 0.047%, Al: 0.02%, P: 0.014%, S: 0.015%, and the rest are Fe and unavoidable impurities. Its manufacturing method is manufactured according to the technological process of rolling → wire laying → on-line molten salt rapid cooling and toughening treatment → slow cooling with the rollway cover opened → coiling. Specifically:

[0045] The rolling process is used to heat a steel billet with a specification of 180mm×180mm into a high-temperature steel billet that reaches the plastic state for rolling, promoting the homogenization of alloy components and reducing segregation. After the steel billet exits the heating furnace, the steel billet is rolled into a wire rod with a diameter specification of 9mm through the rolling line. Appropriately reduce the finishing temperature and increase the finishing reduction to promote dynamic recrystallization and grain refinement during the finishing rolling process, so as to provide more nucleation sites for subsequent pearlite and vanadium carbide precipitation phases. Specifically: Control the soaking temperature of the heating furnace to be 1190°C, the residence time in the furnace to be 180min, the rough rolling temperature to be 1080°C, the finishing temperature to be 890°C, and the finishing reduction to be 22%; The wire laying process is used to make the wire rod exiting the rolling line into a coil through the wire laying machine. The coil is scattered on the rollway and transported along the rollway, making the coil in the high-temperature austenite state. Appropriately increase the wire laying temperature to prepare for forming a larger supercooling degree later and promoting the nucleation of pearlite structure and the precipitation of vanadium carbide. Specifically: Control the wire laying temperature to be 900°C.

[0046] The online molten salt rapid cooling and toughening treatment process uses a two-stage salt bath tank with molten salt inside. The wire rod after wire laying 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 33 °C / s, quickly skips the reticular carbide precipitation range from the high-temperature austenite state and enters the sorbite phase region, increases the supercooling degree, promotes the uniform phase transformation of high-temperature austenite, forms a tissue transformation mainly composed of fine lamellar spacing sorbite, and enables a large amount of vanadium-containing carbides to precipitate dispersedly in the medium-temperature range. 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, the temperature is accurately controlled, and the production energy consumption is reduced, so that the wire rod is rapidly isothermally toughened and stress-relieved in the high-temperature isothermal range, avoiding the coarsening of vanadium-containing carbide precipitation, and improving the strength-plasticity matching of the wire rod. Specifically: the molten salt temperature is 571 °C, the circulation volume of the molten salt in the front-stage treatment is 500 t / h, the temperature rise of the molten salt ≤ 8 °C, and the treatment time is 137 s; the circulation volume of the molten salt in the back-stage treatment is 215 t / h, the temperature rise of the molten salt ≤ 3 °C, and the treatment time is 164 s.

[0047] The roller table open-hood slow cooling process uses an open heat preservation hood, and the wire rod passing through the second-stage salt bath tank is transported by the conveying roller table. The residual heat of the wire rod itself is used to appropriately promote the further toughening of the wire rod tissue and improve the softening effect of the wire rod, so that the wire rod can be quickly taken off the line. Specifically: control the wire rod to slowly cool to 305 °C at a cooling rate of 1.6 °C / s; the coiling process is used to coil the wire rod into a coil through a coiling drum, and after packaging and warehousing, the finished hot-rolled wire rod is obtained, and its metallographic structure diagram is as Figure 1 shown.

[0048] Comparative Example 1:

[0049] A manufacturing method of a hot-rolled wire rod, the difference between its manufacturing method and that of Example 1 lies in: controlling the soaking temperature of the heating furnace to be 1200 °C, the time in the furnace to be 180 min, the rough rolling temperature to be 1090 °C, the finish rolling temperature to be 900 °C, and the wire laying temperature to be 865 °C. When the online molten salt rapid cooling and toughening treatment is carried out, the wire rod undergoes the front-stage treatment, so that the wire rod cools down at a cooling rate of 29 °C / s, and the hot-rolled wire rod is obtained after taking off the line.

[0050] Comparative Example 2:

[0051] A manufacturing method of a hot-rolled wire rod, the difference between its manufacturing method and that of Example 1 lies in: when the online molten salt rapid cooling and toughening treatment is carried out, the wire rod undergoes the front-stage treatment, so that the wire rod cools down at a cooling rate of 30 °C / s, the molten salt temperature is 595 °C, and the hot-rolled wire rod is obtained after taking off the line.

[0052] Comparative Example 3:

[0053] A manufacturing method of a hot-rolled wire rod, the difference between its manufacturing method and that of Example 1 lies in: when the online molten salt rapid cooling and toughening treatment is carried out, the wire rod undergoes the front-stage treatment, so that the wire rod cools down at a cooling rate of 38 °C / s, the molten salt temperature is 515 °C, and the hot-rolled wire rod is obtained after taking off the line. Example 2:

[0054] A preferred implementation method of the manufacturing method of the hot-rolled wire rod for 2300MPa-class bridge cables according to the present invention. The chemical composition and mass percentage of the hot-rolled wire rod include C: 0.93%, Si: 0.65%, Mn: 0.9%, Cr: 0.55%, V: 0.038%, Al: 0.036%, P: 0.015%, S: 0.015%, and the rest are Fe and inevitable impurities; its manufacturing method is manufactured according to the technological process of rolling → wire laying → on-line molten salt rapid cooling and toughening treatment → slow cooling with the cover opened on the roller table → coiling. Specifically:

[0055] 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 plastic state for rolling, 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. Appropriately reduce the final rolling temperature and increase the final rolling reduction to promote dynamic recrystallization and grain refinement during the final rolling process, so as to provide more nucleation sites for subsequent sorbite and vanadium-containing carbide precipitation phases. Specifically: control the soaking temperature of the heating furnace to be 1230°C, the residence time in the furnace to be 160min, the initial rolling temperature to be 1120°C, the final rolling temperature to be 940°C, and the final rolling reduction to be 27%; the wire laying process is used to make the wire rod exiting the rolling line into a wire rod through the wire laying machine. The wire rod is scattered on the roller table and transported along the roller table, so that the wire rod is in the high-temperature austenite state. Appropriately increase the wire laying temperature to prepare for forming a large supercooling degree later and promoting the nucleation of sorbite structure and the precipitation of vanadium-containing carbides. Specifically: control the wire laying temperature to be 915°C.

[0056] The on-line molten salt rapid cooling and toughening treatment process uses a two-stage salt bath tank with molten salt inside. The wire rod after wire laying is transported through the roller table and passes through the first-stage salt bath tank for pre-treatment, so that the wire rod 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, increases the supercooling degree, promotes the uniform phase transformation of high-temperature austenite, forms a tissue transformation mainly composed of fine lamellar spacing sorbite, and makes a large amount of vanadium-containing carbides precipitate diffusely in the medium-temperature range. Then the wire rod is transported through the roller table and passes through the second-stage salt bath tank for post-treatment. The molten salt circulation volume in the post-treatment is appropriately reduced, the temperature is accurately controlled and the production energy consumption is reduced, so that the wire rod is quickly isothermally toughened and stress-relieved in the high-temperature isothermal interval, avoiding the coarsening of vanadium-containing carbide precipitation and improving the strength-plasticity matching of the wire rod. Specifically: the molten salt temperature is 563°C, the molten salt circulation volume in the pre-treatment is 600t / h, the molten salt temperature rise ≤ 8°C, and the treatment time is 124s; the molten salt circulation volume in the post-treatment is 225t / h, the molten salt temperature rise ≤ 3°C, and the treatment time is 109s.

[0057] In the process of slow cooling with the roller table cover opened, the heat preservation cover is opened, and the wire rod passing through the second salt bath tank is conveyed by the conveying roller table. The residual heat of the wire rod itself is utilized to appropriately promote the further toughening of the wire rod structure and improve the softening effect of the wire rod, so that the wire rod can be quickly taken off the production line. Specifically: the wire rod is slowly cooled at a cooling rate of 1.4 °C / s to 310 °C; the coiling process is used to coil the wire rod into a coil through a coiling drum. After packaging and warehousing, the finished hot-rolled wire rod is obtained, and its metallographic structure diagram is as shown in Figure 2 shown.

[0058] Comparative Example 4:

[0059] A manufacturing method of hot-rolled wire rod, the difference between its manufacturing method and that of Example 2 is that: during the on-line molten salt rapid cooling and toughening treatment, the treatment time of the front-stage treatment is 200 s, and the hot-rolled wire rod is obtained after taking off the production line.

[0060] Comparative Example 5:

[0061] A manufacturing method of hot-rolled wire rod, the difference between its manufacturing method and that of Example 2 is that: during the on-line molten salt rapid cooling and toughening treatment, the treatment time of the front-stage treatment is 50 s, and the hot-rolled wire rod is obtained after taking off the production line. Example 3:

[0062] A preferred implementation of the manufacturing method of the 2300 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: 0.6%, Mn: 0.95%, Cr: 0.42%, V: 0.046%, Al: 0.029%, P: 0.014%, S: 0.01%, and the rest are Fe and inevitable impurities; its manufacturing method is carried out according to the technological process of rolling → wire laying → on-line molten salt rapid cooling and toughening treatment → slow cooling with the roller table cover opened → coiling. Specifically:

[0063] The rolling process is used to heat the steel billet with a specification of 220 mm × 220 mm into a high-temperature steel billet that reaches the plastic state for rolling through a heating furnace, promoting the homogenization of alloy components and reducing segregation. After the steel billet exits the heating furnace, the steel billet is rolled into a wire rod with a diameter specification of 12 mm through a rolling line, appropriately reducing the final rolling temperature and increasing the final rolling reduction, promoting dynamic recrystallization and grain refinement during the final rolling process, so as to provide more nucleation sites for subsequent sorbite and vanadium carbide precipitation phases. Specifically: control the soaking temperature of the heating furnace to be 1210 °C, the residence time in the furnace to be 175 min, the initial rolling temperature to be 1100 °C, the final rolling temperature to be 910 °C, and the final rolling reduction to be 24%; the wire laying process is used to make the wire rod exiting the rolling line into a wire rod through a wire laying machine. The wire rod is scattered on the roller table and conveyed along the roller table, so that the wire rod is in a high-temperature austenite state, and the wire laying temperature is appropriately increased to prepare for forming a larger supercooling degree and promoting the nucleation of sorbite structure and the precipitation of vanadium carbide. Specifically: control the wire laying temperature to be 900 °C.

[0064] The online molten salt rapid cooling and toughening treatment process uses a two-stage salt bath tank with molten salt inside. The wire rod after spinning 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 35 °C / s, quickly skips the network carbide precipitation range from the high-temperature austenite state and enters the sorbite phase region, increasing the supercooling degree, promoting the uniform phase transformation of high-temperature austenite, forming a tissue transformation mainly composed of fine lamellar spacing sorbite, and enabling a large amount of vanadium-containing carbides to precipitate dispersedly in the medium-temperature range. Then, the wire rod is transported through the second-stage salt bath tank by a roller table for the back-stage treatment. The circulation amount of the molten salt in the back-stage treatment is appropriately reduced, the temperature is precisely controlled, and the production energy consumption is reduced, so that the wire rod is rapidly isothermally toughened and stress-relieved in the high-temperature isothermal range, avoiding the coarsening of vanadium-containing carbide precipitation, and improving the strength-plasticity matching of the wire rod. Specifically: the molten salt temperature is 550 °C, the circulation amount of the molten salt in the front-stage treatment is 580 t / h, the temperature rise of the molten salt ≤ 8 °C, and the treatment time is 150 s; the circulation amount of the molten salt in the back-stage treatment is 200 t / h, the temperature rise of the molten salt ≤ 3 °C, and the treatment time is 190 s.

[0065] The roller table open-hood slow cooling process adopts an open heat preservation hood, and the wire rod passing through the second-stage salt bath tank is transported by the conveying roller table. The residual heat of the wire rod itself is used to appropriately promote the further toughening of the wire rod structure, improve the softening effect of the wire rod, and enable the wire rod to be quickly taken off the production line. Specifically: the wire rod is controlled to slowly cool to 300 °C at a cooling rate of 2 °C / s; the coiling process is used to coil the wire rod into a coil by a coiling drum, and the finished hot-rolled wire rod is obtained after packaging and warehousing.

[0066] Comparative Example 6:

[0067] A manufacturing method of a hot-rolled wire rod, the difference between its manufacturing method and that of Example 3 lies in that: during the online molten salt rapid cooling and toughening treatment, the treatment time of the back-stage treatment is 230 s, and the hot-rolled wire rod is obtained after taking off the production line.

[0068] Comparative Example 7:

[0069] A manufacturing method of a hot-rolled wire rod, the difference between its manufacturing method and that of Example 3 lies in that: during the online molten salt rapid cooling and toughening treatment, the treatment time of the back-stage treatment is 30 s, and the hot-rolled wire rod is obtained after taking off the production line. Example 4:

[0070] A preferred implementation manner of the manufacturing method of the 2300 MPa grade bridge cable hot-rolled wire rod according to the present invention. The chemical composition and mass percentage of the hot-rolled wire rod include C: 0.96%, Si: 0.45%, Mn: 0.86%, Cr: 0.5%, V: 0.048%, Al: 0.04%, P: 0.015%, S: 0.012%, and the rest are Fe and unavoidable impurities; its manufacturing method is manufactured according to the technological process of rolling → spinning → online molten salt rapid cooling and toughening treatment → roller table open-hood slow cooling → coiling. Specifically:

[0071] The rolling process is used to heat a billet with a specification of 220 mm × 220 mm into a high-temperature billet with rollable plasticity through a heating furnace, promoting the homogenization of alloy components and reducing segregation. After the billet exits the heating furnace, it is rolled into wire rods with a diameter specification of 13 mm through a rolling line. Appropriately reducing the finishing temperature and increasing the finishing reduction promotes dynamic recrystallization and grain refinement during the finishing rolling process, so as to provide more nucleation sites for subsequent pearlite and vanadium carbide precipitation phases. Specifically: control the soaking temperature of the heating furnace to be 1220 °C, the residence time in the furnace to be 170 min, the rough rolling temperature to be 1110 °C, the finishing temperature to be 930 °C, and the finishing reduction to be 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, keeping the coiled bars in a high-temperature austenite state. Appropriately increasing the wire laying temperature prepares for a larger supercooling degree, promoting the nucleation of pearlite tissue and the precipitation of vanadium carbide. Specifically: control the wire laying temperature to be 910 °C.

[0072] The on-line molten salt rapid cooling and toughening 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 pre-treatment, cooling the coiled bars at a cooling rate of 33 °C / s, quickly skipping the network carbide precipitation interval from the high-temperature austenite state into the pearlite phase region, increasing the supercooling degree, promoting the uniform phase transformation of high-temperature austenite, forming a tissue transformation mainly composed of fine lamellar spacing pearlite, and enabling a large amount of vanadium carbide to precipitate diffusely in the medium-temperature range. Then the coiled bars are transported through the second-stage salt bath tank by the roller table for post-treatment. The molten salt circulation volume in the post-treatment is appropriately reduced, precisely controlling the temperature and reducing production energy consumption, enabling the coiled bars to be rapidly isothermally toughened and stress-relieved in the high-temperature isothermal interval, avoiding the coarsening of vanadium carbide precipitation, and improving the strength-plasticity matching of the coiled bars. Specifically: the molten salt temperature is 580 °C, the molten salt circulation volume in the pre-treatment is 535 t / h, the molten salt temperature rise ≤ 8 °C, and the treatment time is 110 s; the molten salt circulation volume in the post-treatment is 240 t / h, the molten salt temperature rise ≤ 3 °C, and the treatment time is 80 s.

[0073] The roller table open cover slow cooling process uses an open insulation cover and transports the coiled bars passing through the second-stage salt bath tank by the conveying roller table, appropriately promoting the further toughening of the coiled bar tissue and improving the softening effect of the coiled bars by using the residual heat of the coiled bars themselves, and enabling the coiled bars to quickly exit the line. Specifically: control the coiled bars to slowly cool to 318 °C at a cooling rate of 1.2 °C / s; The coiling process is used to coil the coiled bars into coils through a coiling drum, and the finished hot-rolled coiled bars are obtained after packaging and warehousing.

[0074] Comparative Example 8:

[0075] A manufacturing method of hot-rolled wire rod, the difference between the manufacturing method and Example 4 lies in: in the process of slow cooling with the roller table cover opened, the wire rod is slowly cooled to 310°C at a cooling rate of 2.5°C / s, and the hot-rolled wire rod is obtained after being taken off the production line.

[0076] The hot-rolled wire rods obtained from the above Examples 1 to 4 and Comparative Examples 1 to 8 were subjected to microstructure and property tests, and the comparison results obtained are shown in Table 1 below:

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

[0078]

[0079] From the results of Examples 1 to 4, it can be seen that the present invention adopts the chemical composition design of C-Si-Mn-Cr-V-Al combined with the online molten salt rapid cooling toughening technology. The tensile strength of the product can reach 1595 - 1635 MPa, the reduction of area can reach 30% - 35%, and the difference in mechanical properties within the same coil is ≤ 40 MPa, effectively improving the strength-plasticity matching and microstructure uniformity of the wire rod.

[0080] From the comparison results between Example 1 and Comparative Example 1, it can be seen that appropriately increasing the spinning temperature can provide favorable conditions for forming a larger supercooling degree later, promoting the refinement of pearlite lamellae to form sorbite, increasing the precipitation driving force and nucleation rate of vanadium carbide, thereby improving the matrix strength. At the same time, increasing the cooling rate is beneficial for controlling network carbide and reducing mechanical property fluctuations.

[0081] From the comparison results between Example 1 and Comparative Example 2, it can be seen that the higher the molten salt temperature, the increase in sorbite lamellar spacing and fusing effect, and the improvement of the plasticity of the wire rod. However, when the molten salt temperature is too high, the sorbite lamellae coarsen and affect the massive dispersion precipitation of vanadium carbide. At the same time, the amount of fused pearlite increases, resulting in a loss of matrix strength and a decrease in the plasticity improvement effect.

[0082] From the comparison results between Example 1 and Comparative Example 3, it can be seen that the lower the molten salt temperature, the more beneficial it is to increase the supercooling degree, promote the rapid transformation of high-temperature austenite into sorbite with finer lamellae, and increase the dispersion precipitation driving force of vanadium carbide, thereby improving the matrix strength. However, when the molten salt temperature is too low, it is difficult to provide more driving force for stress relief during isothermal toughening, resulting in a decrease in the plasticity of the wire rod.

[0083] From the comparison results between Example 2 and Comparative Example 4, it can be seen that as the treatment time of the front-end treatment is extended, it can promote the full and uniform phase transformation of the austenite structure of the wire rod, increase the total treatment time of the online molten salt rapid cooling toughening treatment, and promote stress relief during toughening. However, too long treatment time of the front-end treatment will cause a certain strength loss and unnecessarily increase production energy consumption.

[0084] It can be seen from the comparison results of Example 2 and Comparative Example 5 that too short processing time in the front-stage treatment affects the sufficient phase transformation and toughening effect of the tissue, resulting in loss of strength and plasticity and increased mechanical property fluctuations.

[0085] It can be seen from the comparison results of Example 3 and Comparative Example 6 that as the processing time of the rear-stage treatment increases, the interlamellar spacing of sorbite and the fusing effect increase, and the plasticity of the wire rod improves. However, if the processing time of the rear-stage treatment is too long, more sorbite lamellae will fuse, the precipitation of vanadium carbides will coarsen, and over-toughening will occur, resulting in loss of strength and plasticity. It can be seen from the comparison results of Example 3 and Comparative Example 7 that too short processing time in the rear-stage treatment affects the toughening effect, resulting in obvious loss of the plasticity of the wire rod.

[0086] It can be seen from the comparison results of Example 4 and Comparative Example 8 that by further controlling the cooling rate of the wire rod with slow cooling under the open hood of the roller table, it is possible to prevent the stress from increasing due to too fast cooling rate during the cooling process of the wire rod, promote further toughening of the wire rod structure, and improve the softening effect of the wire rod.

[0087] The series of detailed descriptions listed above are only specific descriptions of the feasible embodiments of the present invention, and they are not intended to limit the protection scope of the present invention. Any equivalent embodiments or changes made without departing from the technical spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A manufacturing method for hot-rolled wire rods for 2300 MPa-class bridge cables, characterized in that, The manufacturing method includes: Rolling wire rods according to the chemical composition of hot-rolled wire rods. The chemical composition and mass percentage of the hot-rolled wire rods include: C: 0.93% - 0.96%, Si: 0.45% - 0.65%, Mn: 0.75% - 0.95%, Cr: 0.42% - 0.55%, V: 0.038% - 0.048%, Al: 0.02% - 0.04%, P ≤ 0.015%, S ≤ 0.015%, and the rest are Fe and inevitable impurities. After the wire rods are spun into wire coils at a spinning temperature of ≥ 900 °C, they are subjected to on-line molten salt rapid cooling and toughening treatment, so that the wire coils are cooled at a cooling rate of ≥ 33 °C / s, enter the sorbite phase region from the austenite state, form a structure mainly composed of sorbite and isothermally toughened to remove stress, and finally are slowly cooled with the hood opened on the roller table to produce hot-rolled wire rods with a mixed microstructure composed of weakly tempered sorbite, ferrite, and eutectoid pearlite. The molten salt temperature for the on-line molten salt rapid cooling and toughening treatment is 550 - 580 °C. The on-line molten salt rapid cooling and toughening treatment is divided into a front-stage treatment and a rear-stage treatment. The molten salt circulation rate in the front-stage treatment is greater than that in the rear-stage treatment. The treatment time for the front-stage treatment is 110 - 150 s, and the treatment time for the rear-stage treatment is 80 - 190 s. The molten salt circulation rate in the front-stage treatment is 450 - 600 t / h, and the molten salt circulation rate in the rear-stage treatment is 200 - 240 t / h. For the slow cooling with the hood opened on the roller table, the heat preservation hood is opened, and the wire coils are slowly cooled at a cooling rate of 1.2 - 2 °C / s to below 320 °C.

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

3. The manufacturing method of the hot-rolled wire rod for 2300MPa-class bridge cables according to claim 1, characterized in that, During rolling, control the initial rolling temperature to be 1080 - 1120 °C, the final rolling temperature to be 890 - 940 °C, and the final rolling reduction to be 22% - 27%.

4. The manufacturing method of the hot-rolled wire rod for 2300 MPa-class bridge cables according to claim 1, characterized in that The temperature rise of the molten salt in the front-stage treatment ≤ 8 °C; the temperature rise of the molten salt in the rear-stage treatment ≤ 3 °C.

5. A hot-rolled wire rod for 2300 MPa class bridge cables, characterized in that, The hot-rolled wire rods are obtained by the manufacturing method of the 2300 MPa-class bridge cable hot-rolled wire rods according to any one of claims 1 - 4.

6. The hot-rolled wire rod for 2300 MPa class bridge cables according to claim 5, characterized in that, The volume percentage of the weakly tempered sorbite ≥ 82%, the lamellar spacing of the weakly tempered sorbite is 75 - 110 nm, and the volume percentage of the eutectoid pearlite accounts for 11% - 15%.

7. The hot-rolled wire rod for 2300 MPa class bridge cables according to claim 5, characterized in that, The reticular carbide grade of the hot-rolled wire rods is grade 0, and the difference in mechanical properties within the same coil ≤ 40 MPa.

8. The hot-rolled wire rod for 2300 MPa class bridge cables according to claim 5, characterized in that The diameter of the hot-rolled wire rods is 9.0 - 15.0 mm, the tensile strength is 1595 - 1635 MPa, and the reduction of area is 30% - 35%.

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