A high-strength duplex hot-rolled wire rod for 2200 MPa-class bridge cables and its manufacturing method

Abstract

The present invention relates to a high-strength dual-phase hot-rolled wire rod for 2200 MPa-class bridge cables and a manufacturing method thereof. After being rolled and spun into wire rods with a C-Si-Mn-Cr chemical composition, the wire rods are subjected to online molten salt critical quenching and isothermal treatment. The wire rods are first subjected to front-stage treatment and cooled at a cooling rate of ≥38 °C / s to enter the mixed phase region of pearlite and martensite from the austenite state, promoting the transformation of part of the austenite into sorbite and martensite. Then, after the back-stage treatment, the molten salt circulation amount is reduced, promoting the transformation of austenite into pearlite and isothermal tempering. Finally, slow cooling is carried out through a roller table to produce hot-rolled wire rods with a dual-phase structure composed of tempered pearlite, tempered sorbite, ferrite, and tempered martensite in the microstructure. It can simplify the composition system, effectively control the deteriorating microstructure, realize the regulation of the dual-phase structure and the matching of high strength and plasticity, with a tensile strength of 1568-1603 MPa and a reduction of area of 29%-34%, which is beneficial to the stable manufacturing 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 high-strength duplex hot-rolled wire rod for 2200 MPa bridge cables and a manufacturing method thereof. Background Art

[0002] With the development of the modern bridge field, bridge cables have gradually developed from the initial 1200 MPa level to 1960 MPa level, and even exceeded the ultra-high strength level of 2000 MPa. The ultra-high strengthening of bridge cables is beneficial to the long-span and lightweight development of bridges, but it is often restricted by the high strengthening of the hot-rolled wire rod base material for bridge cables. In order to meet the market use requirements such as large-span bridges, it is necessary to develop a high-strength duplex hot-rolled wire rod for 2200 MPa bridge cables. However, based on the current industrial development status, the high strengthening of the hot-rolled wire rod base material is often achieved through alloying. There are still the following technical difficulties in manufacturing hot-rolled wire rods with lower material costs, better strength-plasticity properties, and better tissue uniformity by using pearlite tissue to complete wire drawing and cable making of wire rods:

[0003] In order to achieve the high strengthening of hot-rolled wire rods, the existing hot-rolled wire rods mainly increase the content of elements such as C, Si, and Mn to improve the hardenability of the wire rods, and then obtain a refined pearlite tissue, i.e., sorbite tissue, on the air-cooling controlled cooling production line after wire laying, and increase the sorbite content. For example, a production method of a steel wire rod for 2100 MPa bridge cables disclosed in Patent CN114855086A adopts the QS90SiMn composition design of C-Si-Mn-Ti-Cr-V, and combines air cooling + water mist cooling after low-temperature rolling and wire laying to obtain a sorbitization rate of 95%, and the tensile strength of the wire rod reaches more than 1400 Mpa. However, the increase in alloy content and the addition of expensive trace alloys increase the material cost. The fine pearlite tissue has good comprehensive mechanical properties, but it also limits the improvement of the strength grade of the wire rod. For the purpose of reducing material costs, omitting elements such as Ti and V will further reduce the strength of the wire rod. For example, a wire rod for high-strength bridge cables and its production method disclosed in Patent CN118880169A adopts the 87SiMn composition system of high carbon, high silicon, and high manganese, and combines low-temperature rolling and wire laying, strong cooling on the Stelmor air-cooling line, and heat preservation in the heat preservation corridor for more than 120 minutes to obtain a sorbite content of more than 95%, and the wire rod reaches a strength of more than 1400 MPa, but the strength performance is insufficient.

[0004] With the increase in the alloying degree of the wire rod, the segregation of carbon and alloying elements during the solidification of the billet will be aggravated, resulting in the generation of more deteriorated microstructures. For example, in a high-carbon content composition system, higher-level network carbides are likely to form on the air-cooling controlled cooling production line after wire laying, which will destroy the microstructure uniformity and significantly affect the plastic and toughness properties of the wire rod, increasing the risk of wire breakage during subsequent drawing. To minimize the adverse effects of network carbides and promote the refinement of pearlite lamellae to improve the matrix strength, although the air-cooling controlled cooling production line adopts a combination of water mist cooling or strong air cooling, on the one hand, the maximum cooling capacity of the air-cooling line is limited, and the improvement effect on network carbides is limited. Reducing the rolling wire laying temperature is beneficial for grain refinement and matrix strengthening, but it will affect the rolling efficiency, increase the wear on the rolling line, and is prone to form network carbides in the early stage of controlled cooling after wire laying. While increasing the wire laying temperature is beneficial for controlling network carbides, it will affect the grain and microstructure refinement effect, and it is necessary to extend the on-line time of the wire rod to achieve the controlled cooling effect, which is not conducive to high-efficiency production. On the other hand, with the increase in air-cooling intensity, the instability effects of air temperature, air velocity, and air volume increase. Affected by the improvement of wire rod alloying and alloying element segregation, when combined with water mist cooling, martensite is easily formed on the outside of the same cross-section of the wire rod due to rapid cooling, while the core part has a slower cooling rate and is still the cooling effect of the air-cooling line. Due to the further increase in the temperature difference between the windward and leeward sides of the wire rod and the difference between the lapped and non-lapped parts during strong air cooling, abnormal martensite microstructure is also easily formed at some positions due to excessive cooling, or due to incomplete phase transformation of austenite. During the slow cooling process of the wire rod at a temperature below 300°C in the conventional air-cooling line after a long time, the retained austenite in the wire rod microstructure may still transform into martensite, and then the martensite microstructure with high hardness and brittleness remains in the wire rod microstructure, resulting in large fluctuations in the mechanical properties of the wire rod and deterioration of plasticity. At the same time, with the increase in strength level, the control difficulty of deteriorated microstructures becomes greater, which further leads to an increasing risk of wire breakage during the wire drawing and twisting processes of manufacturing bridge cables with the wire rod. 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 high-strength dual-phase hot-rolled wire rod for 2200 MPa-class bridge cables and its manufacturing method, which can simplify the composition system, reduce material costs, effectively control deteriorated microstructures, achieve the regulation of dual-phase microstructures and the matching of high strength and plasticity, and is beneficial to the stable manufacturing of 2200 MPa-class 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 high-strength dual-phase hot-rolled wire rod for 2200 MPa-class bridge cables, the manufacturing method comprising:

[0008] 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: 0.92% - 0.95%, Si: 0.55% - 0.75%, Mn: 0.81% - 0.95%, Cr: 0.35% - 0.50%, P ≤ 0.015%, S ≤ 0.015%, and the rest are Fe and inevitable impurities. After the wire rod is spun into a coil at a spinning temperature of ≥ 950 °C, it undergoes on-line molten salt critical quenching and isothermal treatment. The coil is first subjected to front-stage treatment, causing the coil to cool at a cooling rate of ≥ 38 °C / s, entering the mixed phase region of pearlite and martensite from the austenite state, promoting the transformation of part of the austenite into sorbite and martensite. Then, it undergoes back-stage treatment to reduce the molten salt circulation volume, promote the transformation of austenite into pearlite and isothermal tempering. Finally, it undergoes slow cooling on the roller table to produce a hot-rolled wire rod with a complex-phase structure composed of tempered pearlite, tempered sorbite, ferrite, and tempered martensite in its microstructure.

[0009] The design basis for the chemical composition and mass percentage of the above hot-rolled wire rod includes:

[0010] (1) Carbon: As an effective carbide strengthening element and austenite forming element, the C element has a lower price compared to other alloying elements. With the increase in carbon content, it is beneficial to expand the austenite phase region, inhibit the formation of ferrite, and improve the matrix strength of the material. However, with the increase in carbon content, it will increase the carbon segregation tendency during the solidification of the steel billet, increase the tendency of decarburization and precipitation of network carbide, harm the plasticity and toughness of the steel, and reduce the short-time isothermal tempering effect. Therefore, in order to balance the cost and high-strength requirements of 2200 MPa-class bridge cables and reduce the difficulty of controlling network carbide, the mass percentage of C is controlled at 0.92% - 0.95%.

[0011] (2) Silicon: The Si element is a deoxidizer during the steelmaking process. It can dissolve in ferrite and austenite to increase the strength of the steel. At the same time, it can inhibit the tendency of grain coarsening during front-stage treatment, so as to promote the rapid transformation of part of the high-temperature austenite structure into sorbite structure with a smaller lamellar spacing and acicular martensite, reducing the difficulty of isothermal tempering. However, too high a silicon content will accelerate the diffusion of carbon in the steel, increase the decarburization tendency, promote the growth of columnar crystals in the steel during solidification, and reduce the toughness of the steel. Therefore, in order to facilitate the phase transformation regulation during on-line molten salt critical quenching and isothermal treatment, the mass percentage of Si is controlled at 0.55% - 0.75%.

[0012] (3) Manganese: As an austenite-forming element, Mn can expand the austenite phase region and inhibit the formation of ferrite. At the same time, as an element to improve the hardenability of steel, it is beneficial to reduce the critical transformation temperature and promote the simultaneous occurrence of sorbite structure and acicular martensite phase transformation under a large supercooling degree during the previous treatment process, significantly improving the matrix strength. However, when the content of Mn is too high, it is easy to exacerbate segregation during the solidification of steel billets, which is not conducive to controlling the tissue uniformity. At the same time, it reduces the activity of carbon, decreases the diffusion rate of carbon, increases the difficulty of tempering softening and the tendency of grain coarsening, and then loses the plasticity of wire rods. Therefore, in order to balance the high strength of hot-rolled wire rods, facilitate the regulation of duplex structure, and reduce the difficulty of tempering control, the mass percentage of Mn is controlled at 0.81% - 0.95%.

[0013] (4) Chromium: As a solid solution strengthening element, Cr can strongly improve the hardenability of materials, shift the C curve to the right, reduce the critical cooling rate of quenching, facilitate the refinement of the sorbite plate spacing, promote the transformation of partial austenite structure to acicular martensite during quenching, improve the matrix strength, and at the same time increase the work hardening rate of wire rods during wire drawing, reducing the strength loss during the hot-dip galvanizing process of subsequent wire rods made into bridge cable steel wires. However, too high a Cr content will increase alloy element segregation, affect the tissue uniformity of wire rods, reduce the activity of carbon in steel, significantly increase the difficulty of improving the plasticity of wire rods, and is not conducive to the short-time isothermal tempering of duplex structure, thus affecting wire drawing and torsion properties. Therefore, in order to adapt to the regulation of duplex structure, the mass percentage of Cr is controlled at 0.35% - 0.50%.

[0014] (5) Phosphorus and sulfur: P element and S element belong to impurity elements, and the lower the better. Therefore, P≤0.015% and S≤0.015% are controlled.

[0015] The above hot-rolled wire rods adopt a high-carbon chemical composition design of C-Si-Mn-Cr, which can eliminate alloy elements such as Ti and V. At the same time, cheaper C is used to replace the addition of other alloy elements. The contents of Si and Mn are relatively lower, which can simplify the composition system, reduce the material cost and the influence of alloy element segregation. Combined with the optimization of the contents of Si, Mn, and Cr, the critical transformation temperature can be regulated, providing favorable conditions for the phase transformation of duplex structure and short-time isothermal tempering regulation. On this basis, a higher spinning temperature is selected to avoid the formation of network carbides during the spinning stage due to too low a spinning temperature, and at the same time prepare for the formation of a large supercooling degree later to promote the refinement of pearlite lamellae to obtain sorbite structure and critical quenching. Directly carry out on-line molten salt critical quenching treatment after high-temperature spinning:

[0016] 1. Compared with the conventional Stelmor air-cooled wire, due to the limited cooling capacity, it is unable to effectively control the network carbide and abnormal martensite structure. In the front-stage treatment of the on-line molten salt critical quenching process, the molten salt circulation volume is larger than that in the rear-stage treatment. The high heat transfer capacity of the molten salt can be utilized to promote the rapid cooling of the wire rod. On the one hand, the wire rod can quickly skip the secondary cementite precipitation temperature range of 700-800°C, thereby inhibiting the formation of network carbide and improving the adverse effects of network carbide on the microstructure uniformity and plasticity of the wire rod caused by high carbon content. It also avoids the influence of increasing the spinning temperature on the extension of on-line time and improves production efficiency. On the other hand, it can control the wire rod to quickly enter the narrow pearlite and martensite mixed phase region from the high-temperature austenite state. Due to the relatively fast cooling, a large supercooling degree can be formed, promoting the refinement of pearlite lamellae to obtain a sorbite structure with good drawing performance and strength-plasticity performance. At the same time, the wire rod is cooled to the molten salt temperature in the mixed phase region, controlling the transformation of part of the high-temperature austenite quenching to acicular martensite and improving the matrix strength. When the wire rod passes through the molten salt, the molten salt can cover the surface of the wire rod for uniform and rapid heat transfer, and there is no temperature difference between the windward side and the leeward side. At the same time, a strong air-cooling or combined water mist cooling process can effectively reduce the temperature difference from the edge to the core of the wire rod on the same cross-section. Therefore, the transformation of sorbite and martensite is more uniform. At the same time, the temperature of the wire rod gradually changes to the same as the molten salt temperature, rather than continuous cooling by air-cooling. It can extend the time of the wire rod in the mixed phase region temperature, promote the incubation of phase transformation, and then effectively control the phase transformation of the martensite structure, so as to use the martensite, which is conventionally regarded as an abnormal structure, to improve the matrix strength and make up for the strength loss caused by the simplified composition.

[0017] Second, compared with the conventional Stelmor air-cooled wire which aims to increase the content of sorbite in the structure but has insufficient strength and plasticity and uncontrollable abnormal structures, due to the appropriate reduction of the molten salt circulation volume during the subsequent treatment, on the one hand, the degree of supercooling can be appropriately reduced. At the lower transformation temperature in the mixed-phase region, the transformation of the untransformed high-temperature austenite into a more plastic pearlite structure can be controlled, the duplex structure and the matrix plasticity can be regulated, the full transformation of austenite can be promoted, and the formation of martensite from the retained austenite during subsequent cooling can be avoided, which would otherwise damage the tissue uniformity and the matrix plasticity. On the other hand, the production energy consumption can be appropriately reduced, and the molten salt temperature can be maintained, enabling the mixed structure formed after the phase transformation, including sorbite, acicular martensite, pearlite, and ferrite, to undergo a certain degree of isothermal tempering. Since the temperature of the wire rod is the same as that of the molten salt, rather than the continuous air-cooling process where tempering cannot occur due to low temperature, the molten salt can extend the time of the wire rod in the mixed-phase region, i.e., the high-temperature isothermal range, providing more thermal power for tempering. This further promotes the short-time tempering of the mixed structure, reduces the distortion of the acicular martensite structure, transforms the acicular martensite into a strong and tough tempered martensite structure, reduces the tissue stress between sorbite and pearlite, appropriately improves the tissue plasticity, obtains a tempered structure with better plasticity, enhances the strength-plasticity matching of the wire rod, and then, during the subsequent slow cooling process on the roller table, the stress impact caused by the physical shrinkage of the wire rod can be reduced, and the further toughening of the wire rod structure can be promoted through slow cooling, realizing the regulation of the duplex structure and the properties of the hot-rolled wire rod.

[0018] Selecting an appropriate soaking temperature and soaking time in the heating furnace before rolling can promote the uniform diffusion of alloying elements, reduce the influence of segregation, and at the same time avoid the risk of decarburization caused by too long soaking time. In a preferred embodiment, before rolling, the soaking temperature of the heating furnace is controlled at 1160 - 1210 °C, and the soaking time is 120 - 180 min.

[0019] Due to the relatively high spinning temperature, selecting a relatively high rolling temperature can increase the rolling speed, reduce the deformation resistance of the rolled piece and the wear impact on the rolling line, and at the same time control an appropriate final rolling reduction to promote dynamic recrystallization, refine grains, and strengthen and toughen the matrix during the final rolling process. In a preferred embodiment, during rolling, the initial rolling temperature is controlled at 1110 - 1150 °C, the final rolling temperature is controlled at 1030 - 1050 °C, and the final rolling reduction is 25% - 30%.

[0020] In a preferred embodiment, the molten salt temperature for the online molten salt critical quenching isothermal treatment is 460 - 500 °C, the treatment time for the front-stage treatment is 40 - 70 s, and the treatment time for the back-stage treatment is 50 - 200 s; the molten salt temperature is in the intersection range of the pearlite and martensite phase transformation curves. The lower the molten salt temperature and the longer the treatment time for the front-stage treatment, the more refined the sorbite lamellae can be promoted, the martensite transformation can be increased, and the matrix strength can be improved. However, if the molten salt temperature is too low and the front-stage treatment time is too long, there will be too much martensite transformation, and it will be difficult for the back-stage treatment to provide more thermal power for tempering, which will affect the plasticity of the wire rod and increase the production energy consumption; conversely, the higher the molten salt temperature and the shorter the front-stage treatment time, the supercooling degree can be reduced, which is not conducive to the transformation of austenite to sorbite and acicular martensite, and the matrix strength will be lost, and the pearlite transformation will increase. With the extension of the treatment time for the back-stage treatment, more thermal power can be provided for the tempering of the structure, and the plasticity of the wire rod can be improved. However, if the molten salt temperature is too high and the front-stage treatment time is too short, the critical quenching effect will be affected, the martensite transformation will be too little, and the sorbite lamellae will become coarser, which will significantly reduce the strength of the wire rod; the longer the treatment time for the back-stage treatment, the better the tempering softening effect, and the plasticity of the wire rod will increase. However, if the treatment time for the back-stage treatment is too long, the strength of the wire rod will be excessively lost, and the production energy consumption will increase. On the contrary, if the treatment time for the back-stage treatment is too short, the tempering softening effect will decline. However, if the treatment time for the back-stage treatment is too short, the martensite structure will not be softened, which will significantly increase the brittleness of the wire rod. At the same time, the austenite structure will not be fully transformed, which will increase the risk of rising mechanical fluctuations. Therefore, the molten salt temperature, the front-stage treatment, and the treatment time for the back-stage treatment can be further controlled so that the wire rod can obtain a duplex structure with appropriate strength and plasticity through the regulation of the mixed phase region, reducing the control difficulty and production energy consumption.

[0021] The temperature difference between the wire rod discharged from the spinning temperature and the molten salt temperature is relatively large. Selecting a relatively large molten salt circulation volume for the front-stage treatment can maintain the stability of the molten salt temperature rise, promote the rapid cooling of the wire rod, and carry out short-time phase transformation. In a preferred embodiment, the molten salt circulation volume for the front-stage treatment is 450 - 550 t / h, and the molten salt temperature rise ≤ 8 °C.

[0022] After the wire rod undergoes the front-stage treatment, the temperature difference between the wire rod and the molten salt temperature is relatively small. Appropriately reducing the molten salt circulation volume can appropriately reduce the production energy consumption, while accurately controlling the molten salt temperature, promoting the full phase transformation of the untransformed high-temperature austenite, and experiencing a certain degree of short-time tempering. In a preferred embodiment, the molten salt circulation volume for the back-stage treatment is 255 - 350 t / h, and the molten salt temperature rise ≤ 3 °C.

[0023] Compared with continuous cooling on the air-cooled line, since the wire rod can undergo full phase transformation through on-line molten salt critical quenching and isothermal treatment, it can effectively inhibit the continued transformation of retained austenite into martensite. However, considering the influence of shrinkage stress, a relatively low cooling rate of the roller table slow cooling is selected before coiling to prevent the stress increase caused by too fast cooling rate during the cooling process of the wire rod. At the same time, the temperature of the wire rod is relatively high after coming out of the molten salt, and the use of roller table slow cooling can continue the isothermal tempering effect, promote the further toughening of the wire rod structure, improve the softening effect of the wire rod. In the preferred embodiment, the roller table slow cooling controls the wire rod to slowly cool at a cooling rate of 0.1~0.3°C / s to below 250°C.

[0024] In the preferred embodiment, the roller table slow cooling is achieved by closing the heat preservation cover, sending the hot gas generated by on-line molten salt critical quenching and isothermal treatment into the heat preservation cover, and transporting the wire rod into the heat preservation cover by the roller table, so as to recycle the production waste heat and reduce the production energy consumption.

[0025] A high-strength duplex hot-rolled wire rod for 2200MPa-class bridge cables, which is manufactured by the manufacturing method of the high-strength duplex hot-rolled wire rod for 2200MPa-class bridge cables described in any one of the above.

[0026] The above hot-rolled wire rod adopts a C-Si-Mn-Cr chemical composition design. Different from the existing hot-rolled wire rods for high-strength bridge cables which are composed of pearlite / sorbite + ferrite structure, the microstructure type of the above hot-rolled wire rod is a composite structure including tempered pearlite, tempered sorbite, ferrite, and tempered martensite. The pearlite has a larger interlamellar spacing and better plasticity than sorbite. After tempering into tempered pearlite, it can further reduce the tissue stress and improve the matrix plasticity. The sorbite has a smaller interlamellar spacing, better strength and drawing performance than pearlite. After short-time tempering of sorbite into tempered sorbite, it can further reduce the tissue stress. Tempered sorbite accounts for the majority, which can appropriately improve the matrix plasticity and is more convenient for subsequent wire drawing work hardening. Needle-shaped martensite has higher hardness but greater brittleness than sorbite structure. After tempering to reduce the tissue distortion and stress and transform into tempered martensite with both strength and plasticity, the martensite, which is conventionally regarded as an abnormal structure, is effectively utilized, which can effectively increase the strength of the wire rod, make up for the adverse effects brought by the simplified composition system, improve the strengthening effect of carbon elements, and improve the overall strength and plasticity of the wire rod.

[0027] The increase in the proportion and interlamellar spacing of tempered pearlite in the duplex structure can improve the matrix plasticity. In the preferred embodiment, the volume percentage of tempered pearlite is 5%~10%, and the interlamellar spacing of tempered pearlite is 155~195mm.

[0028] The smaller the interlamellar spacing of tempered sorbite and the proportion of ferrite in the duplex structure, the higher the matrix strength. In a preferred embodiment, the interlamellar spacing of the tempered sorbite is 70 - 110 mm, and the volume percentage of ferrite ≤ 4%.

[0029] The larger the proportion of tempered martensite in the duplex structure, the higher the matrix strength. In a preferred embodiment, the volume percentage of the tempered martensite is 28% - 32%.

[0030] In a preferred embodiment, the reticulated carbide grade of the hot-rolled wire rod is grade 0, which can effectively avoid the deteriorating effect of reticulated carbide on the microstructure uniformity and plasticity of the wire rod, and improve the strengthening effect of carbon elements.

[0031] Since the reticulated carbide in the hot-rolled wire rod is effectively controlled, the martensite is tempered and regulated, and the duplex structure is relatively evenly distributed, abnormal structures formed by austenite residues can be avoided, and the mechanical property fluctuations of the hot-rolled wire rod structure are lower. In a preferred embodiment, the mechanical property difference within the same coil of the hot-rolled wire rod ≤ 40 MPa.

[0032] In a preferred embodiment, the diameter of the hot-rolled wire rod is 10.0 - 15.0 mm, the tensile strength is 1568 - 1603 MPa, and the reduction of area is 29% - 34%. The hot-rolled wire rod has a high tensile strength, which is beneficial to reducing the drawing area reduction rate and quickly reaching the performance grade of the corresponding bridge cable during the processes of uncoiling, pickling, drawing, hot-dip galvanizing, and twisting to make cables. Combined with a high reduction of area, the risk of wire breakage during the subsequent wire drawing process of the hot-rolled wire rod can be reduced.

[0033] Compared with the prior art, the beneficial effects of the present invention are at least as follows:

[0034] (1) In view of the fact that the existing bridge cable hot-rolled wire rod base material is highly strengthened by alloying, it is often difficult to stably control the generation of deteriorated structure with the existing air-cooled controlled cooling production line, and the strength grade of the wire rod is limited by the pearlite structure, and the risk of wire breakage is continuously increasing, the present invention can simplify the component system and reduce the material cost by combining the C-Si-Mn-Cr chemical composition design with the online molten salt critical quenching isothermal technology, and at the same time control the wire rod after high-temperature spinning to quickly skip the secondary cementite precipitation temperature range from the high-temperature austenite state to the pearlite and martensite mixed phase region, thereby promoting part of the austenite The austenite is transformed into troostite and martensite, the strength of the matrix is ​​improved, and the strength loss caused by the simplified composition system is compensated. At the same time, the circulation amount of molten salt is reduced, and the untransformed austenite is promoted to transform into pearlite after the wire rod is processed in the later stage and undergoes a certain degree of short-term isothermal tempering. The quenched martensite is transformed into tempered martensite with both strength and plasticity, and the tempering state of troostite and pearlite is regulated to improve the strength and plasticity matching of the wire rod. Finally, the wire rod organization is further toughened through slow cooling on a roller, which can effectively control the deterioration of the organization, realize the regulation of complex phase organization and the matching of high strength and plasticity, and has good industrial adaptability.

[0035] (2) In view of the current situation that the high-strengthened material cost of the existing hot-rolled wire rod base material of bridge cables is high, the deterioration of the structure is difficult to control, the strength and plasticity are insufficient, and the mechanical properties fluctuate greatly, the microstructure types of the hot-rolled wire rod of the present invention include a complex phase structure composed of tempered pearlite, tempered troostite, ferrite, and tempered martensite, so that the martensitic phase transformation, which is conventionally regarded as an abnormal structure, becomes controllable and can be utilized through isothermal tempering, thereby improving the strengthening effect of the carbon element. Through the combination of component design and complex phase structure regulation, the product tensile strength can reach 1568~1603MPa and the cross-sectional shrinkage rate can reach 29%~34%. It can be used in the manufacture of 2200MPa ultra-high strength bridge cables and other application fields, which is beneficial to reduce the risk of wire breakage and torsional fracture during bridge cable manufacturing, promote stable production of bridge cables, and achieve strength grade improvement, and has good market application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0037] Figure 1 is a metallographic structure diagram of Example 1 of the present invention;

[0038] Figure 2 It is the metallographic structure diagram of Example 2 of the present invention. DETAILED DESCRIPTION

[0039] The embodiments described below with reference to the accompanying drawings are exemplary, merely for purposes of illustration and do not limit the description of the features and characteristics of the present invention. They are intended to present the best mode of carrying out the present invention, for the purpose of explaining the present invention and being sufficient to enable those skilled in the art to implement the present invention. It should not be construed as limiting 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 examples 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 difference in mechanical properties within the same coil: take 2 coils of wire rods at a distance of 5 m from the end of the coil, with the lap area 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 range after the tensile test of the taken tensile specimens is the difference in mechanical properties within the same coil. Example 1:

[0040] A preferred embodiment of the manufacturing method of the 2200MPa grade high-strength duplex 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: 0.55%, Mn: 0.85%, Cr: 0.45%, P: 0.013%, S: 0.013%, 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 critical quenching and isothermal treatment → slow cooling on the roller table → coiling. Specifically:

[0041] 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 plasticity for rolling through a heating furnace. Appropriate heating furnace temperature and residence time in the furnace are selected to promote the uniform diffusion of alloy components, reduce segregation, and control the decarburization risk. After the steel billet exits the heating furnace, the steel billet is rolled into a wire rod with a diameter specification of 10mm through a 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 1160°C, the residence time in the furnace to be 180min, the initial rolling temperature to be 1110°C, the finishing rolling temperature to be 1030°C, and the finishing rolling reduction to be 30%; 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 relatively high wire laying temperature is selected to make the coil 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 obtaining a sorbite structure and critical quenching by forming a large supercooling degree and promoting the refinement of pearlite lamellae. Specifically: control the wire laying temperature to be 950°C.

[0042] The online molten salt critical quenching and isothermal treatment process uses a two-stage salt bath tank with internal molten salt. The wire rod after wire laying is transported through the first-stage salt bath tank by a roller table for pre-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 pearlite and martensite mixed phase region, inhibiting the formation of reticulated carbide. Short-time phase transformation is carried out through large supercooling degrees and lower transformation temperatures, promoting the transformation of part of the austenite into sorbite and acicular martensite. Then the wire rod is transported through the second-stage salt bath tank by a roller table for post-treatment. The molten salt circulation volume in the post-treatment is appropriately reduced to maintain the stability of the molten salt temperature and reduce production energy consumption. At the same time, the supercooling degree is appropriately reduced to promote the transformation of the untransformed high-temperature austenite into pearlite, controlling the mixed structure including sorbite, acicular martensite and pearlite to undergo a certain degree of short-time tempering, improving the strength-plasticity matching of the wire rod. Specifically: the molten salt temperature is 500 °C, the molten salt circulation volume in the pre-treatment is 450 t / h, the molten salt temperature rise ≤ 8 °C, and the treatment time is 40 s; the molten salt circulation volume in the post-treatment is 350 t / h, the molten salt temperature rise ≤ 3 °C, and the treatment time is 50 s.

[0043] In the roller table slow cooling process, the heat preservation cover is closed, and the hot gas generated by the online molten salt critical quenching and isothermal treatment is sent into the heat preservation cover. The wire rod transported by the conveying roller table and passing through the second-stage salt bath tank enters the heat preservation cover, preventing the stress of the wire rod from increasing due to too fast cooling rate during the cooling process, and promoting the further toughening of the wire rod structure and improving the softening effect of the wire rod. Specifically: the wire rod is slowly cooled to 248 °C at a cooling rate of 0.1 °C / s; the coiling process is used to coil the wire rod into a coil by a coiling drum, and after packaging and warehousing, the finished product of the hot-rolled wire rod is obtained, and its metallographic structure diagram is as Figure 1 shown.

[0044] Comparative Example 1:

[0045] A manufacturing method of a hot-rolled wire rod, the difference between its manufacturing method and that of Example 1 lies in: its manufacturing method is manufactured according to the technological process of rolling → wire laying → Stelmor air cooling. Specifically: the soaking temperature of the heating furnace is controlled at 1110 °C, the time in the furnace is 210 min, the initial rolling temperature is 1055 °C, the final rolling temperature is 870 °C, and the wire laying temperature is 840 °C; in the Stelmor forced air cooling, the air volume of each fan is 260,000 m 3 / h, 1-6# fans are turned on at 90%, so that the wire rod cools down at a cooling rate of 8.8 °C / s to 680 °C, and then 7-14# fans are turned on at 25%, so that the wire rod cools down at a cooling rate of 3.3 °C / s to 250 °C. After being taken off the line, the finished product of the hot-rolled wire rod is obtained. The tensile strength of the hot-rolled wire rod is 1382 MPa, the reduction of area is 21%, the microscopic structure includes 86% sorbite by volume percentage, and the rest is ferrite and martensite. The reticulated carbide grade is 3, and the mechanical property difference within the same coil is 103 MPa.

[0046] Comparative Example 2:

[0047] A manufacturing method of hot-rolled wire rods, the difference between its manufacturing method and that of Example 1 lies in: controlling the soaking temperature of the heating furnace to be 1130 °C, the residence time in the furnace to be 200 min, the rough rolling temperature to be 1075 °C, the finish rolling temperature to be 905 °C, the laying head temperature to be 875 °C, and obtaining the finished hot-rolled wire rods after being taken off the production line. Example 2:

[0048] A preferred implementation of the manufacturing method of the 2200 MPa grade high-strength duplex hot-rolled wire rods for bridge cables of the present invention, the chemical composition and mass percentage of the hot-rolled wire rods include C: 0.94%, Si: 0.75%, Mn: 0.95%, Cr: 0.35%, P: 0.01%, S: 0.012%, and the rest are Fe and inevitable impurities; its manufacturing method is carried out according to the technological process of rolling → laying head → on-line molten salt critical quenching and isothermal treatment → slow cooling on the roller table → coiling, specifically:

[0049] The rolling process is used to heat a billet with a specification of 220 mm × 220 mm into a high-temperature billet that reaches the plasticity for rolling through a heating furnace, select appropriate heating furnace temperature and residence time in the furnace to promote the uniform diffusion of alloy components, reduce segregation, and control the decarburization risk. After the billet exits the heating furnace, the billet is rolled into a wire rod with a diameter specification of 14 mm through the rolling line, select appropriate rolling temperature and reduction ratio to improve the rolling efficiency, and promote dynamic recrystallization and grain refinement during the finish rolling process. Specifically: control the soaking temperature of the heating furnace to be 1195 °C, the residence time in the furnace to be 140 min, the rough rolling temperature to be 1135 °C, the finish rolling temperature to be 1045 °C, and the finish rolling reduction to be 27%; the laying head process is used to make the wire rod exiting the rolling line into a wire coil through a laying head machine, and the wire coil is scattered on the roller table and conveyed along the roller table. Select a higher laying head temperature to make the wire coil in a high-temperature austenite state, avoid the formation of network carbide during the laying head stage due to too low laying head temperature, and prepare for forming a larger supercooling degree, promoting the refinement of pearlite lamellae to obtain a sorbite structure and critical quenching. Specifically: control the laying head temperature to be 960 °C.

[0050] The online molten salt critical quenching and isothermal treatment process uses a two-stage salt bath tank with internal molten salt. 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 40 °C / s, quickly skips the reticular carbide precipitation range from the high-temperature austenite state and enters the pearlite and martensite mixed phase region, inhibiting the formation of reticular carbide. Short-time phase transformation is carried out through large supercooling degrees and lower transformation temperatures, promoting the transformation of part of the austenite into sorbite and acicular martensite. 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, reduce production energy consumption, and at the same time appropriately reduce the supercooling degree, promoting the transformation of the untransformed high-temperature austenite into pearlite, controlling the mixed structure including sorbite, acicular martensite and pearlite to undergo a certain degree of short-time tempering, and improving the strength-plasticity matching of the wire rod. Specifically: the molten salt temperature is 472 °C, the circulation volume of the molten salt in the front-stage treatment is 530 t / h, the temperature rise of the molten salt ≤ 8 °C, and the treatment time is 64 s; the circulation volume of the molten salt in the back-stage treatment is 305 t / h, the temperature rise of the molten salt ≤ 3 °C, and the treatment time is 182 s.

[0051] In the roller table slow cooling process, the heat preservation cover is closed, and the hot gas generated by the online molten salt critical quenching and isothermal treatment is sent into the heat preservation cover. The wire rod transported by the conveying roller table and passing through the second-stage salt bath tank enters the heat preservation cover, preventing the stress of the wire rod from increasing due to too fast cooling rate during the cooling process, and promoting the further toughening of the wire rod structure and improving the softening effect of the wire rod. Specifically: the wire rod is slowly cooled to 240 °C at a cooling rate of 0.2 °C / s; the coiling process is used to coil the wire rod into a coil by a coiling drum, and after packaging and warehousing, the finished product of the hot-rolled wire rod is obtained, and its metallographic structure diagram is as Figure 2 shown.

[0052] Comparative Example 3:

[0053] A manufacturing method of a hot-rolled wire rod, the difference between its manufacturing method and that of Example 2 is that: in the online molten salt critical quenching and isothermal treatment process, the wire rod undergoes the front-stage treatment and cools down at a cooling rate of 42 °C / s, the molten salt temperature is 450 °C, and the finished product of the hot-rolled wire rod is obtained after being taken off the production line.

[0054] Comparative Example 4:

[0055] A manufacturing method of a hot-rolled wire rod, the difference between its manufacturing method and that of Example 2 is that: in the online molten salt critical quenching and isothermal treatment process, the wire rod undergoes the front-stage treatment and cools down at a cooling rate of 37 °C / s, the molten salt temperature is 515 °C, the treatment time of the back-stage treatment is 240 s, and the finished product of the hot-rolled wire rod is obtained after being taken off the production line. Example 3:

[0056] A preferred embodiment of the manufacturing method of the 2200MPa - grade high - strength duplex 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: 0.94%, Si: 0.75%, Mn: 0.81%, Cr: 0.44%, P: 0.015%, S: 0.012%, 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 critical quenching and isothermal treatment → slow cooling on the roller table → coiling. Specifically:

[0057] The rolling process is used to heat a steel billet with a specification of 220mm×220mm into a high - temperature steel billet with rollable plasticity through a heating furnace. Appropriate heating furnace temperature and residence time in the furnace are selected to promote the uniform diffusion of alloying elements, reduce segregation, and control the decarburization risk. After the steel billet leaves the heating furnace, it is rolled into a wire rod with a diameter of 12mm 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 to be 1175°C, the residence time in the furnace to be 165min, the initial rolling temperature to be 1120°C, the finishing rolling temperature to be 1035°C, and the finishing rolling reduction to be 28%. The wire - laying process is used to make the wire rod leaving the rolling line into a coil through a wire - laying machine. The coil is scattered on the roller table and transported along the roller table. A relatively high wire - laying temperature is selected to keep the coil 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 obtaining a larger supercooling degree, promoting the refinement of pearlite lamellae to obtain a sorbite structure and critical quenching. Specifically: control the wire - laying temperature to be 955°C.

[0058] The on - line molten - salt critical quenching and isothermal treatment process uses a two - stage salt - bath tank with molten salt inside. The coil after wire - laying is transported through the first - stage salt - bath tank by the roller table for pre - treatment, so that the coil cools at a cooling rate of 39°C / s, quickly skips the network carbide precipitation range from the high - temperature austenite state and enters the mixed phase region of pearlite and martensite, inhibiting the formation of network carbide, and undergoing short - time phase transformation through a large supercooling degree and a lower transformation temperature, promoting the transformation of part of the austenite into sorbite and acicular martensite. Then the coil is 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 to maintain the stability of the molten - salt temperature, reduce production energy consumption, and at the same time appropriately reduce the supercooling degree, promoting the transformation of the untransformed high - temperature austenite into pearlite, and controlling the mixed structure including sorbite, acicular martensite and pearlite to undergo a certain degree of short - time tempering to improve the strength - plasticity matching of the coil. Specifically: the molten - salt temperature is 487°C, the molten - salt circulation volume in the pre - treatment is 490t / h, the molten - salt temperature rise ≤ 8°C, and the treatment time is 53s; the molten - salt circulation volume in the post - treatment is 275t / h, the molten - salt temperature rise ≤ 3°C, and the treatment time is 126s.

[0059] In the roller table slow cooling process, the heat preservation cover is closed, and the hot gas generated by the online molten salt critical quenching and isothermal treatment is sent into the heat preservation cover. The wire rods passing through the second salt bath tank are transported into the heat preservation cover by the conveying roller table, preventing the stress of the wire rods from increasing due to too fast cooling rate during the cooling process, promoting the further toughening of the wire rod structure, and improving the softening effect of the wire rods. Specifically: control the wire rods to cool slowly at a cooling rate of 0.15 °C / s to 245 °C; the coiling process is used to coil the wire rods into coils through a coiling drum, and the finished hot-rolled wire rods are obtained after packaging and warehousing.

[0060] Comparative Example 5:

[0061] A manufacturing method of hot-rolled wire rods, the difference between its manufacturing method and that of Example 3 lies in that: the treatment time of the front-stage treatment is 90 s, and the finished hot-rolled wire rods are obtained after being taken off the production line.

[0062] Comparative Example 6:

[0063] A manufacturing method of hot-rolled wire rods, the difference between its manufacturing method and that of Example 3 lies in that: the treatment time of the front-stage treatment is 30 s, and the finished hot-rolled wire rods are obtained after being taken off the production line. Example 4:

[0064] A preferred implementation of the manufacturing method of the 2200 MPa grade high-strength duplex hot-rolled wire rods for bridge cables according to the present invention. The chemical composition and mass percentage of the hot-rolled wire rods include C: 0.92%, Si: 0.62%, Mn: 0.95%, Cr: 0.5%, P: 0.01%, 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 critical quenching and isothermal treatment → roller table slow cooling → coiling. Specifically:

[0065] 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. Select appropriate heating furnace temperature and residence time in the furnace to promote the uniform diffusion of alloy components, reduce segregation, and control the decarburization risk. After the steel billet leaves the heating furnace, the steel billet is rolled into wire rods with a diameter specification of 15 mm through the rolling line. Select appropriate rolling temperature and deformation amount to improve the rolling efficiency and promote dynamic recrystallization and grain refinement during the finish rolling process. Specifically: control the soaking temperature of the heating furnace to be 1210 °C, the residence time in the furnace to be 120 min, the initial rolling temperature to be 1150 °C, the finish rolling temperature to be 1050 °C, and the finish rolling reduction to be 25%; the wire laying process is used to make the wire rods coming out of the rolling line into wire coils through a wire laying machine. The wire coils are scattered on the roller table and transported along the roller table. Select a higher wire laying temperature to make the wire coils 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 forming a larger supercooling degree, promoting the refinement of pearlite lamellae to obtain a sorbite structure and critical quenching. Specifically: control the wire laying temperature to be 965 °C.

[0066] The online molten salt critical quenching and isothermal treatment process uses a two-stage salt bath tank with internal molten salt. The wire rods after wire laying are transported through the first-stage salt bath tank by a roller table for pre-treatment, so that the wire rods cool down at a cooling rate of 42 °C / s, quickly skip the network carbide precipitation range from the high-temperature austenite state and enter the pearlite and martensite mixed phase region, inhibiting the formation of network carbides. Through large supercooling degrees and lower transformation temperatures, short-time phase transformation is carried out to promote the transformation of part of the austenite into sorbite and acicular martensite. Then, the wire rods are transported through the second-stage salt bath tank by a roller table for post-treatment. The circulation volume of the molten salt in the post-treatment is appropriately reduced to maintain the stability of the molten salt temperature and reduce production energy consumption. At the same time, the supercooling degree is appropriately reduced to promote the transformation of the untransformed high-temperature austenite into pearlite, and control the mixed structure including sorbite, acicular martensite and pearlite to undergo a certain degree of short-time tempering to improve the strength-plasticity matching of the wire rods. Specifically: the molten salt temperature is 460 °C, the circulation volume of the molten salt in the pre-treatment is 550 t / h, the temperature rise of the molten salt ≤ 8 °C, and the treatment time is 70 s; the circulation volume of the molten salt in the post-treatment is 255 t / h, the temperature rise of the molten salt ≤ 3 °C, and the treatment time is 200 s.

[0067] The roller table slow cooling process adopts closing the heat preservation cover, sending the hot gas generated by the online molten salt critical quenching and isothermal treatment into the heat preservation cover, and the wire rods transported by the conveying roller table through the second-stage salt bath tank enter the heat preservation cover, preventing the wire rods from increasing stress due to too fast cooling rate during the cooling process and promoting the further toughening of the wire rod structure and improving the softening effect of the wire rods. Specifically: control the wire rods to slowly cool to 237 °C at a cooling rate of 0.3 °C / s; the coiling process is used to coil the wire rods into coils by a coiling drum, and the finished hot-rolled wire rod products are obtained after packaging and warehousing.

[0068] Comparative Example 7:

[0069] A manufacturing method of hot-rolled wire rods, the difference between its manufacturing method and that of Example 4 lies in that: the treatment time of the post-treatment is 45 s, and the finished hot-rolled wire rod products are obtained after being taken off the production line.

[0070] Comparative Example 8:

[0071] A manufacturing method of hot-rolled wire rods, the difference between its manufacturing method and that of Example 4 lies in that: its manufacturing method is carried out according to the technological process of rolling → wire laying → online molten salt critical quenching and isothermal treatment → air cooling. The air cooling adopts opening the heat preservation cover, and the wire rods transported by the conveying roller table through the second-stage salt bath tank are air-cooled, controlling the wire rods to cool to 240 °C at a cooling rate of 1.2 °C / s. The finished hot-rolled wire rod products are obtained after being taken off the production line. The tensile strength of the hot-rolled wire rods is 1611 MPa, the reduction of area is 27%, the network carbide grade is 0 grade, and the mechanical property difference within the same coil is 43 MPa.

[0072] The hot-rolled wire rods obtained from the above Examples 1 to 4 and Comparative Examples 2 to 7 were subjected to microstructure and property tests, and the comparison results obtained are shown in Table 1 below:

[0073] Table 1. Comparison results of microstructure and 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 the improvement of alloying brings about the generation of more deteriorated microstructures. With the existing air-cooled controlled cooling production line, it is difficult to stably control the generation of deteriorated microstructures such as network carbide and martensite. At the same time, the pearlite microstructure limits the improvement of the strength grade of the hot-rolled wire rod. The hot-rolled wire rod has insufficient strength and plasticity, and large fluctuations in mechanical properties. The risk of wire breakage during the wire drawing and torsion processes for manufacturing bridge cables is relatively high. Through the C-Si-Mn-Cr chemical composition design combined with the online molten salt critical quenching isothermal technology of the present invention, the network carbide can be effectively inhibited, the controllable phase transformation of martensite can be controlled, and through a certain degree of short-time isothermal tempering, the quenched martensite can be transformed into tempered martensite with both strength and plasticity, and the tempering state of sorbite and pearlite can be regulated to improve the strength-plasticity matching of the wire rod. From the results of Examples 1 to 4, it can be seen that the tensile strength of the product can reach 1568 - 1603 MPa, and the reduction of area is 29% - 34%, which is beneficial to reducing the risk of wire breakage and torsional fracture during bridge cable manufacturing and realizing the improvement of the strength grade.

[0076] From the comparison results of Example 1 and Comparative Example 2, it can be seen that the online molten salt critical quenching treatment can avoid the influence of increasing the laying head temperature on the extension of the online time. Selecting a higher laying head temperature is beneficial to forming a larger supercooling degree later, promoting the refinement of pearlite lamellae to obtain sorbite microstructure and obtaining a small amount of acicular martensite by critical quenching, and improving the matrix strength.

[0077] From the comparison results of Example 2 and Comparative Example 3, it can be seen that the lower the molten salt temperature and the longer the treatment time of the front-stage treatment, the more beneficial it is to promote the refinement of sorbite lamellae and increase the martensite phase transformation, thereby improving the matrix strength. However, if the molten salt temperature is too low, with the extension of the front-stage treatment time, there will be too much martensite phase transformation, increasing the difficulty of tempering in the later-stage treatment, which will affect the plasticity of the wire rod and increase the production energy consumption at the same time.

[0078] From the comparison results of Example 2 and Comparative Example 4, it can be seen that too high a molten salt temperature is not conducive to the transformation of austenite into sorbite and acicular martensite, but it can provide more thermal driving force for tissue tempering and improve the plasticity of the wire rod. However, if the molten salt temperature is too high, with the extension of the treatment time of the later-stage treatment, the strength of the wire rod will be excessively lost, increasing the production energy consumption.

[0079] From the comparison results of Example 3 and Comparative Example 5, it can be seen that using a larger molten salt circulation volume in the front-stage treatment and extending the treatment time of the front-stage treatment can increase the martensitic phase transformation and improve the matrix strength. However, if the front-stage treatment time is too long and the martensitic phase transformation is too much, the plasticity of the wire rod will be affected.

[0080] From the comparison results of Example 3 and Comparative Example 6, it can be seen that the shorter the treatment time of the front-stage treatment is, the more unfavorable the transformation of austenite to troostite and acicular martensite is, the more pearlite transformation increases, and the matrix strength will be lost.

[0081] From the comparison results of Example 4 and Comparative Example 7, it can be seen that the shorter the treatment time of the later stage treatment, the lower the tempering softening effect. If the treatment time of the later stage treatment is too short, the martensitic structure will not be softened, which will significantly increase the brittleness of the wire rod and increase the risk of increased mechanical fluctuations.

[0082] From the comparison results of Example 4 and Comparative Example 8, it can be seen that selecting a lower roller slow cooling speed before coiling can prevent the wire rod from increasing stress due to excessively fast cooling speed during the cooling process, promote further toughening of the wire rod structure, and improve the softening effect of the wire rod.

[0083] The series of detailed descriptions listed above are only specific descriptions of feasible embodiments of the present invention. They are not intended to limit the scope of protection of the present invention. All equivalent embodiments or changes that do not deviate from the technical spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for manufacturing a 2200MPa grade high-strength multiphase 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: 0.55%~0.75%, Mn: 0.81%~0.95%, Cr: 0.35%~0.50%, 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 ≥950°C, it is subjected to online molten salt critical quenching isothermal treatment, and the wire rod is controlled to undergo a front-end treatment first, so that the wire rod is cooled at a cooling rate of ≥38°C / s. , from the austenite state into the pearlite and martensite mixed phase region, promote the transformation of part of austenite to troostite and martensite, and then through the back-end treatment, reduce the molten salt circulation amount, promote the transformation of austenite to pearlite and isothermal tempering, and finally through roller slow cooling, it is made into a hot-rolled wire rod with a microstructure including tempered pearlite, tempered troostite, ferrite and tempered martensite. The molten salt temperature of the online molten salt critical quenching isothermal treatment is 460~500℃, the processing time of the front-end treatment is 40~70s, and the processing time of the back-end treatment is 50~200s.

2. The method for manufacturing 2200MPa grade high-strength multi-phase 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 1160-1210° C. and a furnace time of 120-180 min.

3. The method for manufacturing 2200MPa grade high-strength multi-phase 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 1110-1150° C., the final rolling temperature is controlled to be 1030-1050° C., and the final rolling reduction is controlled to be 25%-30%.

4. The method for manufacturing 2200MPa grade high-strength multi-phase hot-rolled wire rod for bridge cables according to claim 1, characterized in that: The molten salt circulation volume of the front-end treatment is 450-550 t / h, and the molten salt temperature rise is ≤8°C; the molten salt circulation volume of the back-end treatment is 255-350 t / h, and the molten salt temperature rise is ≤3°C.

5. The method for manufacturing 2200MPa grade high-strength multi-phase 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 250° C. at a cooling rate of 0.1-0.3° C. / s.

6. A 2200MPa grade high-strength multiphase hot-rolled wire rod for bridge cables, characterized in that: The hot-rolled wire rod is manufactured by the method for manufacturing 2200MPa-grade high-strength multi-phase hot-rolled wire rod for bridge cables as described in any one of claims 1 to 5.

7. The 2200MPa grade high-strength multi-phase hot-rolled wire rod for bridge cables according to claim 6, characterized in that: The volume percentage of the tempered pearlite is 5% to 10%, the interlamellar spacing of the tempered pearlite is 155 to 195 mm, the interlamellar spacing of the tempered bainite is 70 to 110 mm, the volume percentage of the ferrite is ≤4%, and the volume percentage of the tempered martensite is 28% to 32%.

8. The 2200MPa high-strength multi-phase 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 ≤40MPa.

9. The 2200MPa high-strength multi-phase 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 1568-1603 MPa, and a cross-sectional shrinkage of 29%-34%.

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