A high-strength multiphase hot-rolled wire rod for 2130MPa grade stranded wire and its manufacturing method

Abstract

This invention relates to a high-strength multiphase hot-rolled wire rod for 2130MPa grade stranded wire and its manufacturing method. The method involves rolling the high-carbon, low-silicon wire rod with trace amounts of V into wire rod, followed by online molten salt quenching and isothermal treatment. The wire rod undergoes a pre-treatment molten salt cooling process at a rate of ≥34℃ / s, transitioning it from austenitic to bainitic phase and promoting partial austenite transformation. A subsequent molten salt treatment increases the molten salt temperature, promoting the decomposition of untransformed residual austenite into sorbite, followed by isothermal tempering. Finally, the wire rod undergoes slow cooling on a roller conveyor, resulting in a hot-rolled wire rod with a microstructure comprising tempered bainite, ferrite, and tempered sorbite. This method simplifies the composition system, reduces material costs, achieves multiphase microstructure control, and allows for online control of microstructure and toughness, achieving a tensile strength of 1456~1483MPa and a reduction of area of ​​32%~37%, thus balancing production efficiency and reducing the cracking risk of stranded wire produced by downstream users.

Description

Technical Field

[0001] This invention belongs to the technical field of hot-rolled wire rod, specifically relating to a high-strength multiphase hot-rolled wire rod for 2130MPa grade stranded wire and its manufacturing method. Background Technology

[0002] Steel strand is a stress-bearing structure composed of multiple strands of steel wire twisted together. It is widely used in energy, water conservancy, construction, transportation and other fields. However, with the development of high strength and lightweight steel strand industry, the strength grade of steel strand is constantly increasing, and the strength of the raw material wire rod material is increasingly limiting the improvement of its strength grade. At present, steel strand is mainly made by twisting pearlitic hot-rolled wire rod. The raw material wire rod produced mainly by air-cooled wire rod has a high alloy content, resulting in hot-rolled wire rod containing bainite and martensite, which is extremely brittle and prone to wire breakage during the wire drawing process. Therefore, it is necessary to develop a high-strength multiphase hot-rolled wire rod for 2130MPa grade strand and its manufacturing method, which can control the microstructure and toughness and reduce the risk of wire breakage, in order to meet the development of the steel industry and the needs of market use.

[0003] Existing high-strength hot-rolled wire rods for stranded wire generally employ a high-carbon, high-silicon composition system. For example, patent CN102352469B discloses an ultra-high-strength vanadium-titanium composite microalloyed high-carbon steel wire rod and its preparation method, which uses a C-Si-Mn-V-Ti-Cu-Ni composition and combines a Stellmore air-cooling line with rapid cooling, heat preservation, and slow cooling processes to produce a sorbitic wire rod. However, the development of 2130MPa grade hot-rolled wire rods for stranded wire still faces the following production bottlenecks:

[0004] I. To improve the ferritic strength of wire rod, steel grades contain higher levels of C and Si. However, high carbon and silicon content increases smelting difficulty, increases resistance to rolling deformation, and consequently increases the load and energy consumption of rolling equipment, reducing rolling efficiency. Furthermore, high carbon content increases the tendency for carbon segregation in the steel. During the Stellmore air cooling process after hot rolling, limited by the maximum cooling capacity, high carbon content increases the tendency for carbides to precipitate along austenite grain boundaries, forming network carbides. The presence of network carbides severely deteriorates the mechanical properties of the wire rod, such as reducing plasticity, toughness, and fatigue performance, and also affects the drawing performance of the wire rod. On the other hand, high carbon content lowers the martensitic transformation point of the steel. Silicon increases the critical cooling rate of steel. As the air-cooling strength is increased to suppress network carbides and promote the refinement of pearlite lamellars, the temperature difference between the air-receiving and air-receiving surfaces of the wire rod, and between the surface and the core, will further increase the differences in the microstructure and properties of different parts of the wire rod. During the cooling process, it is easier to form abnormal structures such as bainite or martensite. As a hard and brittle structure, the abnormal structure will increase the hardness and reduce the toughness of the wire rod, increasing its brittleness and making it unfavorable for subsequent processing and use. On the other hand, reducing the carbon or silicon content to reduce the risks of smelting, rolling and microstructure inhomogeneity will result in a significant loss of strength. The initial strength of the base material is too low to quickly achieve the target performance, which will further increase the risk of wire breakage.

[0005] Second, in order to promote grain size and pearlite lamellar refinement and improve wire rod toughness, the steel grades contain a variety of microalloying components with high content. However, this also increases material costs and smelting difficulty. Simplifying the alloy composition and reducing the alloy content will, on the one hand, further increase the risk of pearlite coarsening and loss of matrix strength due to the limitation of the maximum cooling capacity of the air-cooling line. On the other hand, it will lose the deformation nucleation sites of the sorbite phase. With the high silicon content, the phase transformation incubation time is prolonged. Due to the continuous cooling and limited length of the air-cooling line, the wire rod is in a low-temperature state after phase transformation incubation, and the toughness cannot be controlled online. The microstructure has large residual phase transformation stress, or due to the austenite residue, it continues to form a brittle microstructure during subsequent cooling. Under stress, stress concentration is likely to occur, leading to reduced toughness or even premature fracture. On the other hand, the long-term heat preservation on the air-cooling line will significantly affect the production line and production efficiency, which is detrimental to continuous production. Summary of the Invention

[0006] The present invention aims to at least partially solve one of the above-mentioned technical problems. The present invention provides a high-strength multiphase hot-rolled wire rod for 2130MPa grade stranded wire and its manufacturing method, which can simplify the composition system, reduce material costs, realize multiphase structure control, and control the structure toughness online, so as to balance production efficiency and reduce the cracking risk of stranded wire produced by downstream users.

[0007] The technical solution adopted by this invention to solve its technical problem is:

[0008] A method for manufacturing high-strength multiphase hot-rolled wire rod for 2130MPa grade stranded wire, the method comprising:

[0009] The wire rod is rolled into a production line based on the chemical composition of hot-rolled wire rod. The chemical composition and mass percentage of the hot-rolled wire rod include: C: 0.86%~0.90%, Si: 0.18%~0.29%, Mn: 0.60%~0.80%, Cr: 0.33%~0.53%, V: 0.020%~0.040%, P≤0.014%, S≤0.014%, with the remainder being Fe and unavoidable impurities. The wire rod is spun at a spinning temperature of ≥895℃. After being processed into wire rod, the wire rod undergoes online molten salt quenching and isothermal treatment. The wire rod first undergoes a preliminary molten salt treatment and is cooled at a rate of ≥34℃ / s, transitioning from the austenitic state to the bainitic phase region, promoting the transformation of some austenite into bainite. Then, it undergoes a subsequent molten salt treatment, which increases the molten salt temperature, promoting the decomposition of untransformed residual austenite into sorbite and isothermal tempering. Finally, it undergoes slow cooling on a roller conveyor, resulting in a hot-rolled wire rod with a microstructure consisting of tempered bainite, ferrite, and tempered sorbite, forming a multiphase microstructure.

[0010] The chemical composition and mass percentage of the above-mentioned hot-rolled wire rods are designed based on the following:

[0011] (1) Carbon: C is an effective strengthening element in steel and is relatively cheaper. Carbon forms interstitial solid solution in austenite, which can increase the lattice distortion energy of austenite and reduce the critical cooling rate of steel, reduce the starting temperature of bainite and sorbite phase transformation, delay the transformation kinetics of austenite to pearlite, promote the preferential formation of bainite quenching and the refinement of sorbite lamellars, thereby improving the matrix strength. However, if the C content is too high, it will cause center segregation of high carbon steel billet, increase the risk of rolling cracks, increase the difficulty of controlling network carbides and martensite, increase the difficulty of isothermal tempering, and lead to a decrease in toughness and affect the efficiency of the line. Therefore, in order to take into account the high strength requirements of 2130MPa grade strand, adapt to the control of multiphase structure, and control the difficulty of isothermal tempering, the mass percentage of C is controlled at 0.86%~0.90%.

[0012] (2) Silicon: Si can slow down the precipitation rate of cementite, inhibit the transformation of austenite to pearlite, help guide the preferential transformation of austenite to bainite, avoid coarse cementite from cutting the matrix, provide sufficient lattice distortion effect to improve strength, and provide solid solution strengthening effect. However, excessive silicon will promote decarburization, increase rolling deformation resistance, affect rolling efficiency, and the dislocation inhibition effect will increase the difficulty of softening. During isothermal tempering, it will delay the decomposition of residual austenite to sorbite, prolong the phase transformation incubation period, and lead to a decrease in the plasticity and production efficiency of steel. In turn, it will cause fracture in subsequent wire drawing, twisting and other processing stages. Therefore, in order to adapt to the control of phase transformation structure by online molten salt quenching isothermal treatment, reduce the difficulty of rolling and isothermal tempering, and improve production stability, the silicon content should be appropriately reduced and the mass percentage of Si should be controlled at 0.18%~0.29%.

[0013] (3) Manganese: Mn is a strong austenite stabilizing element, which can expand the austenite region, improve the stability of the rolling process and the hardenability of the wire rod. During the initial molten salt treatment, it can prevent the austenite from decomposing into pearlite too early during cooling, reduce the transformation temperature of austenite to bainite and the diffusion rate of carbon atoms, and allow bainite to nucleate and grow for a sufficient time. At the same time, it can moderately inhibit the transformation rate of residual austenite to sorbite and the excessive precipitation of ferrite, ensuring that the sorbite precipitation is more uniform and the lamellar is finer. However, if the Mn content is too high, it will increase the element segregation during the solidification process of the billet and the difficulty of controlling martensite, increase the difficulty of tempering and softening, and affect the toughness and uniformity of the wire rod. Therefore, in order to facilitate the control of the multiphase structure of hot-rolled wire rod, the mass percentage of Mn is controlled at 0.60%~0.80%.

[0014] (4) Chromium: Cr is a strong carbide-forming element. The alloy carbides formed by Cr and C can provide dispersion strengthening, improve grain boundary bonding and austenite stability, delay diffusion-type pearlite phase transformation, reduce the bainite transformation initiation temperature, increase the driving force for bainite nucleation at low temperature, and can slowly decompose the residual austenite into sorbite in the later molten salt treatment, improve the resistance to tempering softening, and keep the wire rod with high strength during the drawing process. However, when the Cr content is too high, segregation will occur during solidification, which will increase the difficulty of controlling the uniformity of the structure, and at the same time increase the internal stress of phase transformation, dislocation density and tempering difficulty, affecting the rapid production line. Therefore, in order to take into account the control of the multiphase structure of hot-rolled wire rod, the resistance to tempering softening of wire rod should be appropriately controlled, and the mass percentage of Cr should be controlled at 0.33%~0.53%.

[0015] (5) Vanadium: During the rolling process, V can refine the grains by pinning the austenite grain boundaries. The fine austenite grains provide more nucleation sites for subsequent phase transformation. The fine grain structure not only directly improves the strength but also improves the toughness, providing a strong but not brittle foundation for wire rod drawing. At the same time, fine VC can be precipitated again during the isothermal process, which hinders dislocation movement through the dislocation pinning effect and maintains the dispersion strengthening effect. However, V is relatively expensive, and excessive addition is not conducive to controlling the material cost. Therefore, the mass percentage of V is controlled at 0.020%~0.040%.

[0016] (6) Phosphorus and sulfur: P and S are impurity elements, and the lower the better. Therefore, P ≤ 0.014% and S ≤ 0.014%.

[0017] The aforementioned hot-rolled wire rod adopts a high-carbon, low-silicon composition design of C-Si-Mn-Cr-V, with trace amounts of V added. It contains no alloying elements such as Ni and Ti, simplifying the composition system and reducing material costs, smelting, and rolling difficulties. Simultaneously, Mn and Cr control the wire rod's hardenability, lowering the onset temperature of bainite and sorbite phase transformations, while Cr and V provide appropriate resistance to tempering softening. This provides favorable conditions for suppressing pearlite, promoting the preferential transformation of a small amount of bainite, shortening the phase transformation incubation period, refining the sorbite phase transformation, controlling the dispersed precipitation of carbides, and facilitating rapid production. Furthermore, a higher wire drawing temperature is selected to keep the wire rod in a high-temperature austenitic state, avoiding the formation of network carbides or proeutectoid ferrite at excessively low temperatures, reducing limitations on rolling. This prepares the microstructure for increasing undercooling and promoting the preferential transformation of a small portion of austenite to bainite during the initial molten salt treatment. After wire drawing, the wire rod does not undergo air cooling but directly enters the molten salt for online molten salt quenching and isothermal treatment.

[0018] I. Compared to the limitations imposed by the maximum cooling capacity of the Stellmore air-cooled line, which makes it difficult to suppress network carbides and coarse pearlite and control low-temperature phase transformation, the molten salt treatment of the wire rod at the pre-treatment stage can, on the one hand, utilize the high heat transfer capacity of the molten salt to promote rapid cooling of the wire rod, quickly bypassing the precipitation temperature range of secondary cementite, inhibiting the diffusion and enrichment of carbon atoms to the austenite grain boundaries, and avoiding the adverse effects of network carbides on microstructure uniformity and ductility; on the other hand, the rapid cooling of the wire rod can compress the diffusion process and bypass the pearlite phase from the high-temperature austenite state. The wire rod enters the bainitic phase region at a lower temperature, avoiding the nose region of pearlite transformation, thereby suppressing coarse pearlite. Through quenching, a large degree of undercooling is formed, preferentially promoting the transformation of a small portion of austenite into bainite. The bainitic structure has a higher dislocation density, which compensates for the strength loss caused by simplifying the composition system and reducing the alloy content. At the same time, when the wire rod passes through the molten salt, the molten salt can cover the surface of the wire rod for uniform heat exchange. There is no temperature difference between the wind-receiving and wind-receiving surfaces, which can avoid the formation of brittle martensitic structure due to local undercooling, laying the foundation for the strength and toughness balance of the subsequent multiphase structure.

[0019] Second, compared to the limitations of the Stellmore air-cooling line, which restricts cooling capacity and continuous operation, making it difficult to control the multiphase microstructure and online toughness, the wire rod undergoes a post-treatment molten salt process. By appropriately increasing the molten salt temperature, the diffusion of carbon in the retained austenite is enhanced, promoting its rapid decomposition into finer-laminated sorbite. Combined with a low-silicon design, this shortens the phase transformation incubation period. As the treatment time increases, it promotes the full transformation of austenite, preventing residual austenite from forming martensite during subsequent cooling. Furthermore, compared to the slow passage through the pearlite phase region in air-cooling lines, the lower molten salt temperature in the post-treatment process avoids the coarsening caused by high-temperature Cr and V carbide precipitation. The dispersed precipitation of carbides strengthens the high-strength characteristics and compensates for the strength loss caused by isothermal tempering. On the other hand… In terms of processing time, as the temperature of the wire rod and the molten salt gradually become consistent, the temperature difference between the wire rod surface and the core can be reduced. This allows the wire rod to undergo appropriate isothermal tempering in a high-temperature isothermal range, rather than the low-temperature state after phase transformation inoculation and continuous cooling in an air-cooled line. This improves the tempering thermal dynamics, provides mild conditions for atomic diffusion, promotes the formation of bainite and sorbite structures through dislocation climb, releases phase transformation internal stress, reduces bainite dislocation density, promotes a stable and dispersed distribution of carbides, improves the brittleness of the wire rod caused by bainite and sorbite phase transformation stress, and controls the wire rod toughness online. Finally, the slow cooling on the roller conveyor extends the tempering softening effect of the later stage of molten salt treatment, further toughening the wire rod structure and improving the strength and plasticity matching of the wire rod. This eliminates the need for excessively long heat preservation treatment and improves production efficiency.

[0020] Before rolling, a higher heating furnace temperature and furnace time can be selected to accelerate the diffusion of alloying elements, alleviate the effects of segregation, reduce the temperature difference between the inside and outside of the billet, and improve rolling plasticity. At the same time, excessively high temperature or excessively long furnace time can be avoided, which can lead to grain coarsening. In the preferred technical solution, before rolling, the heating furnace temperature is controlled at 1125~1175℃ and the furnace time is controlled at 125~165min.

[0021] Due to the simplified alloy composition and higher wire drawing temperature, the limitations on rolling can be reduced. During rolling, a higher initial rolling temperature is selected to reduce rolling deformation resistance, avoid overloading of the rolling mill, and improve rolling stability and efficiency. With appropriate final rolling temperature and final rolling reduction, VC precipitation and studded grain boundaries are promoted. Dynamic recrystallization during the final rolling process refines the grains and increases nucleation points for subsequent phase transformation. In the preferred technical solution, the initial rolling temperature is controlled at 1035~1085℃, the final rolling temperature at 905~945℃, and the final rolling reduction at 19%~24%.

[0022] During the wire spinning process, the wire spinning temperature can be further controlled to reduce the risk of austenite grains continuing to grow at high temperatures. In a preferred embodiment, the wire spinning temperature is controlled to be 895~935℃.

[0023] The molten salt temperature in the initial molten salt treatment is within the bainitic phase region. Lower molten salt temperatures promote rapid cooling of the wire rod, increase supercooling, inhibit the formation of network carbides and coarse pearlite, reduce carbon diffusion capacity, promote rapid austenite-to-bainite transformation, and refine the bainitic microstructure. With prolonged treatment time, the bainite nucleation rate can increase, improving matrix strength. However, excessively low molten salt temperatures and prolonged treatment times can increase dislocation density and bainite transformation rate within austenite, reduce carbon sources for sorbite phase transformation, and increase the difficulty of isothermal tempering, which is detrimental to controlling production energy consumption and efficiency. Conversely, higher molten salt temperatures help reduce the temperature difference between the wire rod surface and core, promote slow bainite transformation, and reduce dislocation density and microstructural stress. Shortening the processing time can reduce production energy consumption. However, if the molten salt temperature is too high and the processing time is too short, the short-range diffusion of carbon will be insufficient, and the undercooling will be reduced, which will affect the bainite nucleation rate, reduce the bainite transformation, and result in a loss of matrix strength. It may even be detrimental to the suppression of network carbides and pearlite. Therefore, the molten salt temperature and processing time of the first stage of molten salt treatment can be controlled to control the rapid entry of the wire rod from the high-temperature austenitic state into the bainite phase region, suppress the formation of network carbides and pearlite, and promote the transformation of a small portion of austenite into bainite by quenching. This controls the phase transformation stress and prepares the microstructure for the subsequent molten salt treatment. In the preferred technical solution, the molten salt temperature of the first stage of molten salt treatment is 463~493℃, and the processing time is 42~72s.

[0024] Because the temperature difference between the wire drawing temperature and the molten salt temperature in the front-end molten salt treatment is large, the molten salt circulation rate in the front-end molten salt treatment is high, which can control the molten salt temperature rise, promote rapid cooling of the wire rod, and reduce phase transformation differences. In the preferred technical solution, the molten salt circulation rate in the front-end molten salt treatment is 435~655t / h, and the molten salt temperature rise is ≤9℃.

[0025] The molten salt temperature in the subsequent molten salt treatment is appropriately increased compared to the preceding molten salt treatment. Lower molten salt temperatures promote the decomposition of untransformed residual austenite into a sorbite structure with finer lamellar spacing, and facilitate the dispersed precipitation and strengthening of Cr and V carbides. Shorter treatment times can suppress cementite growth and coarsening of carbide precipitates, reducing production energy consumption. However, excessively low molten salt temperatures are detrimental to the deformation nuclei of the sorbite phase and the precipitation of microalloyed V carbides. Shorter treatment times also make it difficult to provide sufficient thermal power for tempering, affecting residual stress release and potentially causing further transformation into bainitic quenched structures, resulting in a loss of ductility and toughness. Conversely, higher molten salt temperatures and longer treatment times help reduce the temperature difference between the wire rod surface and core, promoting a full transformation of the austenite structure. Tempering promotes the softening of bainite and sorbite, eliminates internal stress, and promotes the uniform distribution of carbide precipitates. However, excessively high molten salt temperatures are detrimental to controlling the refinement of sorbite lamellars and the growth trend of carbides. With prolonged processing time, excessive softening and carbide coarsening will result in a loss of strength and plasticity, while also increasing production energy consumption. Therefore, the molten salt temperature and processing time of the subsequent molten salt treatment can be controlled to promote the decomposition and transformation of most of the untransformed residual austenite into sorbite, and to perform isothermal tempering on the quenched structure dominated by bainite and sorbite, thereby promoting the dispersed precipitation of carbides and inhibiting the aggregation and coarsening of carbides, so as to regulate the strength and plasticity matching of wire rods. In the preferred technical solution, the molten salt temperature of the subsequent molten salt treatment is 503~533℃, and the processing time is 83~156s.

[0026] The temperature difference between the molten salt in the front-end molten salt treatment and the back-end molten salt treatment is small. The back-end molten salt treatment can appropriately reduce the molten salt circulation volume, reduce supercooling and production energy consumption, and at the same time control the molten salt temperature rise and improve the uniformity of the structure. In the preferred technical solution, the molten salt circulation volume in the back-end molten salt treatment is 365~465t / h, and the molten salt temperature rise is ≤3℃.

[0027] The roller cooling system further slows down the cooling rate, promoting the gradual cooling of the wire rod and avoiding insufficient plasticity due to inadequate cooling. Slow cooling also promotes further toughening of the wire rod structure, improving the tempering and softening effect. At the same time, the wire rod's plasticity and toughness are significantly improved after the subsequent molten salt treatment. The wire rod exiting the molten salt is at a relatively high temperature, so the roller cooling system does not need to maintain the temperature for a long time, thus avoiding affecting the production line efficiency. In the preferred technical solution, the roller cooling system controls the wire rod to cool to below 280°C at a slow cooling rate of ≤0.7°C / s before winding.

[0028] In the preferred technical solution, the roller conveyor slow cooling adopts the control of the opening of the heat insulation cover, and blows the hot air of ≥240℃ during the online molten salt quenching isothermal treatment into the heat insulation cover. The conveyor roller conveyor transports the wire rod through the heat insulation cover to control the slow cooling of the wire rod, which can further recover and utilize the heat energy of the online molten salt quenching isothermal treatment, reduce production energy consumption, and promote the rapid production of wire rod.

[0029] A high-strength multiphase hot-rolled wire rod for 2130MPa grade stranded wire, characterized in that the hot-rolled wire rod is manufactured by the manufacturing method of the high-strength multiphase hot-rolled wire rod for 2130MPa grade stranded wire described in any one of the above-mentioned methods.

[0030] The aforementioned hot-rolled wire rod adopts a high-carbon, low-silicon composition system containing trace amounts of V. Compared with existing high-strength strand hot-rolled wire rods, this simplifies the composition system, reduces material costs, and smelting and rolling difficulties. Simultaneously, the microstructure comprises a multiphase structure with a small amount of tempered bainite, a large amount of tempered sorbite, and trace amounts of ferrite. Compared with air-cooled pearlitic wire rods, this structure can suppress network carbides and martensite. Bainite has a higher dislocation density than pearlite, and its strength can be improved through grain refinement, dispersion strengthening, and solid solution strengthening. After isothermal tempering, the controllable phase transformation bainite is transformed into tempered bainite, which reduces dislocation density, alleviates internal stress, and stabilizes dispersed carbides. Finely dispersed and stable carbides retain the high strength of bainite while also improving strength through... The pinning effect of carbides inhibits dislocation movement, preventing excessive strength loss and transforming the structure into a strong and tough tempered structure. The lamellar spacing of sorbite is finer than that of pearlite, which can enhance strength through grain boundary strengthening and increase resistance to dislocation movement. After isothermal tempering, sorbite can further release structural stress and improve plasticity and toughness. Combined with the dispersed precipitation of Cr and V carbides, it can compensate for the strength loss caused by omitting alloy components and reducing alloy content. At the same time, through the microstructure control in the tempered state, bainite, which is usually considered an abnormal structure, can be utilized to control the plasticity and toughness of wire rod to match its strength, so as to reduce the risk of wire breakage due to brittleness during subsequent processing and reduce the risk of early fracture due to stress superposition.

[0031] The higher the volume percentage of tempered bainite and the finer the lamellar spacing of tempered sorbite, the higher the matrix strength. The higher the proportion of tempered sorbite, the higher the plasticity. In the preferred embodiment, the volume percentage of tempered bainite is 23%~32%, the volume percentage of ferrite is ≤3%, the volume percentage of tempered sorbite is 65%~76%, and the lamellar spacing of tempered sorbite is 75~130nm.

[0032] In the preferred technical solution, the hot-rolled wire rod has a network carbide level of 0 and a mechanical property difference within the same coil of ≤45MPa. This effectively avoids the adverse effects of network carbides on the continuity and ductility of the matrix, while effectively suppressing abnormal martensite structure and the dispersed precipitation and uniform distribution of carbides. This further reduces the fluctuation of mechanical properties. The lower mechanical property difference within the same coil is beneficial to improving the uniformity of wire rod deformation and the uniformity of strand stress, further reducing the risk of fracture.

[0033] In the preferred technical solution, the diameter of the hot-rolled wire rod is 8.0~15.0mm, the tensile strength is 1456~1483MPa, and the reduction of area is 32%~37%. The hot-rolled wire rod has high tensile strength, which is beneficial as a base material to reduce the number of drawing passes, quickly reach the target strength, reduce plastic loss during the process, and improve production efficiency and load-bearing capacity. The high reduction of area indicates that the hot-rolled wire rod has good plastic deformation ability, which can reduce the risk of cracking during drawing and stranding, and improve the yield and fatigue life of stranded wire.

[0034] Compared with the prior art, the beneficial effects of the present invention are at least as follows:

[0035] (1) In view of the problem that the existing hot-rolled wire rods for high-strength strands are produced by combining high carbon and high silicon content with Stellmore air-cooled line, resulting in abnormal structure that is difficult to control and extremely brittle, the present invention adopts a high carbon and low silicon content design with trace V combined with online molten salt quenching isothermal technology. The wire rod first undergoes a front-end molten salt treatment to enter the bainite phase region from the austenite state, suppressing network carbides and promoting the transformation of some austenite to bainite. Then, it undergoes a rear-end molten salt treatment to increase the molten salt temperature, promote the decomposition of untransformed residual austenite into sorbite and perform isothermal tempering, promote the dispersion and precipitation of carbides and suppress the coarsening of carbides. Finally, it undergoes slow cooling on the roller table to further toughen the structure. It can achieve multiphase structure control and online control of structure toughness. At the same time, it can reduce the restrictions on rolling, take into account production efficiency, and has good industrial adaptability.

[0036] (2) In view of the defects of existing high-strength strand hot-rolled wire rods with complex alloy composition, high content, high brittleness, large fluctuation of mechanical properties or insufficient strength and plasticity, which lead to a high risk of cracking in subsequent processing, the present invention can simplify the composition system, reduce material cost and smelting and rolling difficulty. At the same time, the microstructure includes a multiphase structure composed of tempered bainite, ferrite and tempered sorbite, which can suppress network carbides and martensite structure. The bainite with controllable phase transformation can be transformed into tempered bainite that is both strong and tough after isothermal tempering. The lamellar spacing of sorbite It is finer than pearlite, and with the dispersed precipitation of Cr and V carbides, it can compensate for the strength loss caused by omitting alloy components and reducing alloy content. At the same time, through the microstructure control in the tempered state, the plasticity, toughness and strength of the wire rod can be matched, and the mechanical properties fluctuate less. It can achieve a tensile strength of 1456~1483MPa and a reduction of area of ​​32%~37%. It is used in the manufacture of 2130MPa grade stranded wire and other applications, which can reduce the risk of cracking, improve the yield of stranded wire and fatigue life, and has good industrial adaptability. Attached Figure Description

[0037] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0038] Figure 1 This is a metallographic diagram of Embodiment 1 of the present invention;

[0039] Figure 2 This is a metallographic diagram of Embodiment 2 of the present invention;

[0040] Figure 3 This is a metallographic diagram of Embodiment 3 of the present invention. Detailed Implementation

[0041] The embodiments described below with reference to the accompanying drawings are exemplary and are merely for illustrative purposes and do not limit the description of the features and characteristics of the invention. They are intended to provide the best mode for carrying out the invention, to explain the invention, and to enable those skilled in the art to practice the invention. However, they should not be construed as limiting the scope of the invention in any way, which is defined only by the appended claims. The microstructure and performance testing of the hot-rolled wire rods obtained in the following embodiments and comparative examples includes: tensile testing using GB-T228.1-2021 Metallic Materials - Tensile Testing - Part 1: Room Temperature Test Method, to obtain tensile strength and reduction of area; microstructure testing using the metal microstructure testing method of GB / T13298 standard; and mechanical property same-coil difference test method: two coils of wire rod are taken 5m from the end of the coil. Using the overlap area as the base point, each coil of wire rod is divided into 8 equal segments. One tensile specimen is taken from each segment. The difference in strength of the tensile specimens after tensile testing is the mechanical property same-coil difference.

[0042] Example 1:

[0043] A preferred embodiment of the manufacturing method of the high-strength multiphase hot-rolled wire rod for 2130MPa grade stranded wire according to the present invention, wherein the chemical composition and mass percentage of the hot-rolled wire rod include C: 0.89%, Si: 0.22%, Mn: 0.80%, Cr: 0.39%, V: 0.04%, P: 0.013%, S: 0.012%, with the remainder being Fe and unavoidable impurities; the manufacturing method follows the process flow of rolling → wire drawing → online molten salt quenching isothermal → slow cooling on roller table → coiling, specifically:

[0044] The rolling process is used to heat a 220mm×220mm steel billet in a furnace to a high-temperature steel billet that is rollable and plastic, reducing compositional segregation and avoiding grain coarsening. After exiting the furnace, the billet is rolled into a wire rod with a diameter of 12.5mm through a rolling line. Appropriate rolling temperature and reduction are selected to improve rolling efficiency, promote VC precipitation, and refine grains by anchoring grain boundaries. Specifically, the furnace soaking temperature is controlled at 1165℃, and the furnace dwell time is 13 seconds. The rolling process lasts 5 minutes. The initial rolling temperature is 1075℃, the final rolling temperature is 935℃, and the final rolling reduction is 22%. The wire drawing process is used to convert the wire from the rolling line into coils through the wire drawing mechanism. The coils are spread on the roller table and conveyed along the roller table. A suitable wire drawing temperature is selected to keep the coils in a high-temperature austenitizing state, avoiding the precipitation of network carbides during the wire drawing stage. This prepares the microstructure for the subsequent preferential bainite transformation and residual austenite decomposition. Specifically, the wire drawing temperature is controlled at 920℃.

[0045] The online molten salt quenching isothermal process employs a two-section salt bath with internal molten salt. After coiling, the wire rod is conveyed via roller conveyor through the first section of the salt bath for initial molten salt treatment. This causes the wire rod to cool at a rate of 36°C / s, rapidly transitioning from a high-temperature austenitic state through the network carbide and pearlite phase regions to the bainite phase region. This inhibits the formation of network carbides and pearlite, promotes the transformation of a small portion of austenite into bainite, and retains most of the retained austenite. The wire rod is then conveyed via roller conveyor through the second section of the salt bath for subsequent molten salt treatment, increasing the molten salt temperature. The process involves isothermal tempering to promote the decomposition and transformation of untransformed residual austenite into sorbite, thereby promoting the dispersion and strengthening of Cr and V carbides and preventing carbide coarsening. This helps to control the strength and plasticity of the wire rod. Specifically, the molten salt temperature for the first stage of molten salt treatment is 472℃, the treatment time is 63s, the molten salt circulation rate is 590t / h, and the molten salt temperature rise is ≤9℃. The molten salt temperature for the second stage of molten salt treatment is 511℃, the treatment time is 129s, the molten salt circulation rate is 425t / h, and the molten salt temperature rise is ≤3℃.

[0046] The roller conveyor slow cooling process involves adjusting the opening of the insulation cover to blow hot air (≥240℃) from above the two salt bath tanks undergoing online molten salt quenching isothermal treatment into the insulation cover. The wire rod is then conveyed by the conveyor rollers through the insulation cover for slow cooling, promoting further toughening of the wire rod structure and improving the tempering softening effect. Specifically, the wire rod is cooled to 274℃ at a slow cooling rate of 0.6℃ / s. The coiling process involves coiling the wire rod into coils using a coiling drum. After packaging and warehousing, the hot-rolled wire rod is obtained as a finished product, the metallographic structure of which is shown in the figure below. Figure 1 As shown.

[0047] Comparative Example 1:

[0048] A method for manufacturing hot-rolled wire rod differs from Example 1 in that it follows a process flow of rolling → wire drawing → Steyrmo air cooling. Specifically, the heating furnace homogenization temperature is controlled at 1100℃, the furnace time is 200 min, the initial rolling temperature is 1010℃, the final rolling temperature is 830℃, and the wire drawing temperature is 815℃. The Steyrmo forced air cooling uses an air volume of 260,000 m³ / s per fan. 3 At 75% capacity, fans 1 to 4 are turned on to cool the wire rod to 677℃ at a cooling rate of 7.7℃ / s. Then, fans 5 to 14 are turned on to 20% capacity to cool the wire rod to 285℃ at a cooling rate of 2.3℃ / s. After cooling, the hot-rolled wire rod is obtained.

[0049] Comparative Example 2:

[0050] A method for manufacturing hot-rolled wire rod differs from that in Example 1 in that: the heating furnace is heated to a uniform temperature of 1100°C, the furnace time is 200 min, the initial rolling temperature is 1010°C, the final rolling temperature is 830°C, and the wire drawing temperature is 815°C. During the molten salt treatment before the online molten salt quenching isothermal process, the wire rod is cooled at a rate of 29°C / s, and the finished hot-rolled wire rod is obtained after the process is completed.

[0051] Example 2:

[0052] A preferred embodiment of the manufacturing method of the high-strength multiphase hot-rolled wire rod for 2130MPa grade stranded wire according to the present invention, wherein the chemical composition and mass percentage of the hot-rolled wire rod include C: 0.90%, Si: 0.18%, Mn: 0.66%, Cr: 0.33%, V: 0.025%, P: 0.013%, S: 0.012%, with the remainder being Fe and unavoidable impurities; the manufacturing method follows the process flow of rolling → wire drawing → online molten salt quenching isothermal → slow cooling on roller table → coiling, specifically:

[0053] The rolling process is used to heat a 180mm×180mm steel billet in a furnace to a high-temperature steel billet that is rollable and plastic, reducing compositional segregation and avoiding grain coarsening. After exiting the furnace, the billet is rolled into wire rod with a diameter of 8mm through a rolling line. Appropriate rolling temperature and reduction are selected to improve rolling efficiency and promote VC precipitation, grain refinement, and grain densification. Specifically, the furnace soaking temperature is controlled at 1125℃, and the furnace dwell time is 165 minutes. The initial rolling temperature is 1035℃, the final rolling temperature is 905℃, and the final rolling reduction is 24%. The wire drawing process is used to convert the wire from the rolling line into coils through the wire drawing mechanism. The coils are distributed on the roller table and conveyed along the roller table. A suitable wire drawing temperature is selected to keep the coils in a high-temperature austenitizing state, avoiding the precipitation of network carbides during the wire drawing stage. This prepares the microstructure for the subsequent preferential bainite transformation and residual austenite decomposition. Specifically, the wire drawing temperature is controlled at 895℃.

[0054] The online molten salt quenching isothermal process employs a two-section salt bath with internal molten salt. After coiling, the wire rod is conveyed via roller conveyor through the first section of the salt bath for initial molten salt treatment. This causes the wire rod to cool at a rate of 34°C / s, rapidly transitioning from a high-temperature austenitic state through the network carbide and pearlite phase regions into the bainite phase region. This inhibits the formation of network carbides and pearlite, promotes the transformation of a small portion of austenite into bainite, and retains most of the retained austenite. The wire rod is then conveyed via roller conveyor through the second section of the salt bath for final molten salt treatment, improving the molten salt efficiency. Temperature promotes the decomposition of untransformed residual austenite into sorbite and isothermal tempering, promotes the dispersion and precipitation of Cr and V carbides for strengthening, and avoids carbide coarsening, thereby controlling the strength and plasticity matching of the wire rod. Specifically: the molten salt temperature of the first stage molten salt treatment is 484℃, the treatment time is 42s, the molten salt circulation rate is 435t / h, and the molten salt temperature rise is ≤9℃; the molten salt temperature of the second stage molten salt treatment is 533℃, the treatment time is 83s, the molten salt circulation rate is 365t / h, and the molten salt temperature rise is ≤3℃.

[0055] The roller conveyor slow cooling process employs controlled opening of the insulation cover to blow hot air (≥240℃) from above the two salt bath tanks undergoing online molten salt quenching isothermal treatment into the insulation cover. The wire rod is then conveyed by the conveyor rollers through the insulation cover for slow cooling, promoting further toughening of the wire rod structure and improving the tempering softening effect. Specifically, the wire rod is cooled to 279℃ at a slow cooling rate of 0.45℃ / s. The coiling process uses a coiling drum to coil the wire rod into coils, which are then packaged and stored to obtain the finished hot-rolled wire rod. Its metallographic structure is shown in the figure below. Figure 2 As shown.

[0056] Comparative Example 3:

[0057] A method for manufacturing hot-rolled wire rod differs from that in Example 2 in that: during the initial molten salt treatment of the online molten salt quenching isothermal process, the wire rod is cooled at a rate of 36°C / s, the molten salt temperature of the initial molten salt treatment is 450°C, the treatment time is 80s, and the finished hot-rolled wire rod is obtained after the process is completed.

[0058] Comparative Example 4:

[0059] A method for manufacturing hot-rolled wire rod differs from that in Example 2 in that: during the initial molten salt treatment of the online molten salt quenching isothermal process, the wire rod is cooled at a rate of 33°C / s, the molten salt temperature of the initial molten salt treatment is 500°C, the treatment time is 16s, and the finished hot-rolled wire rod is obtained after the process is completed.

[0060] Example 3:

[0061] A preferred embodiment of the manufacturing method of the high-strength multiphase hot-rolled wire rod for 2130MPa grade stranded wire according to the present invention, wherein the chemical composition and mass percentage of the hot-rolled wire rod include C: 0.86%, Si: 0.26%, Mn: 0.60%, Cr: 0.4%, V: 0.033%, P: 0.014%, S: 0.013%, with the remainder being Fe and unavoidable impurities; the manufacturing method follows the process flow of rolling → wire drawing → online molten salt quenching isothermal → slow cooling on roller table → coiling, specifically:

[0062] The rolling process is used to heat a 220mm×220mm steel billet in a furnace to a high-temperature steel billet that is rollable and plastic, reducing compositional segregation and avoiding grain coarsening. After exiting the furnace, the billet is rolled into wire rod with a diameter of 10mm through a rolling line. Appropriate rolling temperature and reduction are selected to improve rolling efficiency and promote VC precipitation, grain refinement, and grain denaturation. Specifically, the furnace soaking temperature is controlled at 1135℃, and the furnace dwell time is 150 minutes. The initial rolling temperature is 1050℃, the final rolling temperature is 925℃, and the final rolling reduction is 23%. The wire drawing process is used to convert the wire from the rolling line into coils through the wire drawing mechanism. The coils are distributed on the roller table and conveyed along the roller table. A suitable wire drawing temperature is selected to keep the coils in a high-temperature austenitizing state, avoiding the precipitation of network carbides during the wire drawing stage. This prepares the microstructure for the subsequent preferential bainite phase transformation and residual austenite decomposition. Specifically, the wire drawing temperature is controlled at 910℃.

[0063] The online molten salt quenching isothermal process employs a two-section salt bath with internal molten salt. After coiling, the wire rod is conveyed via roller conveyor through the first section of the salt bath for initial molten salt treatment. This causes the wire rod to cool at a rate of 34°C / s, rapidly transitioning from a high-temperature austenitic state through the network carbide and pearlite phase regions into the bainite phase region. This inhibits the formation of network carbides and pearlite, promotes the transformation of a small portion of austenite into bainite, and retains most of the retained austenite. The wire rod is then conveyed via roller conveyor through the second section of the salt bath for subsequent molten salt treatment, increasing the molten salt temperature. The process involves isothermal tempering to promote the decomposition and transformation of untransformed residual austenite into sorbite, thereby promoting the dispersed precipitation and strengthening of Cr and V carbides and preventing carbide coarsening. This helps to control the strength and plasticity matching of the wire rod. Specifically, the molten salt temperature for the first stage of molten salt treatment is 493℃, the treatment time is 56s, the molten salt circulation rate is 510t / h, and the molten salt temperature rise is ≤9℃. The molten salt temperature for the second stage of molten salt treatment is 526℃, the treatment time is 110s, the molten salt circulation rate is 390t / h, and the molten salt temperature rise is ≤3℃.

[0064] The roller conveyor slow cooling process involves adjusting the opening of the insulation cover to blow hot air (≥240℃) from above the two salt bath tanks undergoing online molten salt quenching isothermal treatment into the insulation cover. The wire rod is then conveyed by the conveyor rollers through the insulation cover for slow cooling, promoting further toughening of the wire rod structure and improving the tempering softening effect. Specifically, the wire rod is cooled to 277℃ at a slow cooling rate of 0.55℃ / s. The coiling process uses a coiling drum to coil the wire rod into coils, which are then packaged and stored to obtain the finished hot-rolled wire rod. Its metallographic structure is shown in the figure below. Figure 3 As shown.

[0065] Comparative Example 5:

[0066] A method for manufacturing hot-rolled wire rod, the difference between the method and Example 3 is that: the molten salt temperature of the subsequent molten salt treatment is 552°C, the treatment time is 180s, and the finished hot-rolled wire rod is obtained after the process is completed.

[0067] Comparative Example 6:

[0068] A method for manufacturing hot-rolled wire rod, the difference between the method and Example 3 is that: the molten salt temperature of the subsequent molten salt treatment is 502°C, the treatment time is 65s, and the finished hot-rolled wire rod is obtained after the process is completed.

[0069] Example 4:

[0070] A preferred embodiment of the manufacturing method of the high-strength multiphase hot-rolled wire rod for 2130MPa grade stranded wire according to the present invention, wherein the chemical composition and mass percentage of the hot-rolled wire rod include C: 0.88%, Si: 0.29%, Mn: 0.72%, Cr: 0.53%, V: 0.02%, P: 0.014%, S: 0.014%, with the remainder being Fe and unavoidable impurities; the manufacturing method follows the process flow of rolling → wire drawing → online molten salt quenching isothermal → slow cooling on roller table → coiling, specifically:

[0071] The rolling process is used to heat a 220mm×220mm steel billet in a furnace to a high-temperature steel billet that is rollable and plastic, reducing compositional segregation and avoiding grain coarsening. After exiting the furnace, the billet is rolled into wire rod with a diameter of 15mm through a rolling line. Appropriate rolling temperature and reduction are selected to improve rolling efficiency and promote VC precipitation, grain refinement, and grain denaturation. Specifically, the furnace soaking temperature is controlled at 1175℃, and the furnace dwell time is 125 minutes. The initial rolling temperature is 1085℃, the final rolling temperature is 945℃, and the final rolling reduction is 19%. The wire drawing process is used to convert the wire from the rolling line into coils through the wire drawing mechanism. The coils are distributed on the roller table and conveyed along the roller table. A suitable wire drawing temperature is selected to keep the coils in a high-temperature austenitizing state, avoiding the precipitation of network carbides during the wire drawing stage. This prepares the microstructure for the subsequent preferential bainite phase transformation and residual austenite decomposition. Specifically, the wire drawing temperature is controlled at 935℃.

[0072] The online molten salt quenching isothermal process employs a two-section salt bath with internal molten salt. After coiling, the wire rod is conveyed via roller conveyor through the first section of the salt bath for initial molten salt treatment. This causes the wire rod to cool at a rate of 38°C / s, rapidly transitioning from a high-temperature austenitic state through the network carbide and pearlite phase regions to the bainite phase region. This inhibits the formation of network carbides and pearlite, promotes the transformation of a small portion of austenite into bainite, and retains most of the retained austenite. The wire rod is then conveyed via roller conveyor through the second section of the salt bath for subsequent molten salt treatment, increasing the molten salt temperature. The process involves isothermal tempering to promote the decomposition of untransformed residual austenite into sorbite and to promote the dispersion and strengthening of Cr and V carbides, while avoiding carbide coarsening. This aims to regulate the strength and plasticity matching of the wire rod. Specifically, the molten salt temperature for the first stage of molten salt treatment is 463℃, the treatment time is 72s, the molten salt circulation rate is 655t / h, and the molten salt temperature rise is ≤9℃. The molten salt temperature for the second stage of molten salt treatment is 503℃, the treatment time is 156s, the molten salt circulation rate is 465t / h, and the molten salt temperature rise is ≤3℃.

[0073] The roller conveyor slow cooling process involves adjusting the opening of the insulation cover to blow hot air (≥240℃) from above the two salt bath tanks undergoing online molten salt quenching isothermal treatment into the insulation cover. The wire rod is then conveyed by the conveyor rollers through the insulation cover for slow cooling, promoting further toughening of the wire rod structure and improving the tempering softening effect. Specifically, the wire rod is controlled to cool to 272℃ at a slow cooling rate of 0.7℃ / s. The coiling process is used to coil the wire rod into coils using a coiling drum. After packaging and warehousing, the hot-rolled wire rod is obtained as a finished product.

[0074] Comparative Example 7:

[0075] A method for manufacturing hot-rolled wire rod differs from that in Example 4 in that the manufacturing method follows the process flow of rolling → wire drawing → online molten salt quenching isothermal → air cooling. The air cooling is achieved by opening the heat insulation cover, conveying the wire rod by the conveyor rollers, and controlling the wire rod to cool to 280°C at a slow cooling rate of 1.4°C / s. After the wire rod is removed from the production line, the finished hot-rolled wire rod is obtained.

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

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

[0078]

[0079] The comparison between Example 1 and Comparative Example 1 shows that, despite simplifying the alloy composition and reducing the content of alloying elements such as Si, compared to the limitations of the Stellmore air-cooling line, the wire rod exhibits a higher level of network carbides, abnormal martensitic structure, and coarse pearlite in the core, leading to significant brittleness, fluctuations in mechanical properties, and strength loss. This invention, combined with online molten salt quenching isothermal technology, allows the wire rod to undergo a preliminary molten salt treatment, transitioning it from the austenitic state to the bainitic phase region, thus suppressing network carbides and pearlite structures and promoting partial austenitic... The transformation from basalt to bainite, followed by molten salt treatment, promotes sorbite transformation, carbide dispersion precipitation, and isothermal tempering, enabling the control of the multiphase microstructure. The microstructure consists of tempered bainite, ferrite, and tempered sorbite, allowing for online control of the microstructure and toughness. As seen in the results of Examples 1-4, the tensile strength can reach 1456-1483 MPa, and the reduction of area can reach 32%-37%. This is suitable for applications such as manufacturing 2130 MPa grade stranded wire, which helps reduce the risk of cracking and improve the yield and fatigue life of stranded wire.

[0080] As can be seen from the comparison results between Example 1 and Comparative Example 2, using a higher wire drawing temperature to keep the wire rod in a high-temperature austenitic state can avoid the formation of network carbides or proeutectoid ferrite due to excessively low temperature, reduce the restrictions on rolling, and prepare the microstructure for increasing undercooling and promoting the preferential transformation of a small portion of austenite to bainite during the initial molten salt treatment. At the same time, it can reduce the restrictions on rolling and improve production efficiency through high-temperature rapid rolling.

[0081] As can be seen from the comparison results between Example 2 and Comparative Example 3, the lower the molten salt temperature in the initial molten salt treatment, the faster the wire rod cools down, the higher the supercooling, the inhibition of the formation of network carbides and coarse pearlite, the reduction of carbon diffusion ability, the promotion of rapid transformation of austenite to bainite, and the refinement of bainite structure. With the extension of treatment time, the bainite nucleation rate can be increased, and the matrix strength can be improved. However, if the molten salt temperature is too low and the treatment time is too long, the dislocation density and bainite transformation rate in austenite can be increased, the carbon source for sorbite phase transformation can be reduced, and the difficulty of isothermal tempering can be increased, which is detrimental to controlling production energy consumption and efficiency.

[0082] As can be seen from the comparison results between Example 2 and Comparative Example 4, the higher the molten salt temperature in the pre-treatment, the better it is to reduce the temperature difference between the wire rod surface and the core, promote the slow transformation of bainite, reduce dislocation density and structural stress. With the shortening of the treatment time, production energy consumption can be reduced. However, if the molten salt temperature is too high and the treatment time is too short, the short-range diffusion of carbon will be insufficient and the undercooling will be reduced, which will affect the bainite nucleation rate, reduce the bainite transformation, and lose the matrix strength.

[0083] As can be seen from the comparison results between Example 3 and Comparative Example 5, the higher the molten salt temperature and the longer the treatment time in the later stage of molten salt treatment, the better it is to reduce the temperature difference between the wire rod surface and the core, promote the full transformation of austenite structure, promote the tempering and softening of bainite and sorbite, eliminate internal stress, and promote the uniform distribution of carbide precipitates. However, if the molten salt temperature is too high, it is not conducive to controlling the refinement of sorbite lamellars and the growth trend of carbides. As the treatment time is extended, excessive softening and coarsening of carbides will result in a loss of strong and plastic properties, while increasing production energy consumption.

[0084] As can be seen from the comparison results between Example 3 and Comparative Example 6, the lower the molten salt temperature in the later stage of molten salt treatment, the better it is to promote the decomposition of untransformed residual austenite into sorbite with finer lamellar spacing, and to promote the dispersed precipitation and strengthening of Cr and V carbides. With the shortening of the treatment time, the growth of cementite in sorbite and the coarsening of carbide precipitates can be suppressed, thereby reducing production energy consumption. However, if the molten salt temperature is too low, it is not conducive to the deformation nuclei of sorbite phase and the precipitation of microalloyed carbides of V. If the treatment time is too short, it is difficult to provide more thermal power for tempering, affecting the release of residual stress, and may even continue to transform into bainite quenched structure, resulting in the loss of ductile and tough properties.

[0085] As can be seen from the comparison results between Example 4 and Comparative Example 7, the slow cooling of the roller can prolong the tempering and softening effect in the later stage of the molten salt treatment, promote the further toughening of the wire rod structure, and at the same time, it is not necessary to use excessively long heat preservation treatment, which can improve production efficiency.

[0086] The detailed descriptions listed above are merely specific illustrations of feasible embodiments of the present invention and are not intended to limit the scope of protection of the present invention. All equivalent embodiments or modifications made without departing from the spirit of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method of manufacturing high strength multiphase hot-rolled wire rod for 2130 MPa grade strand, characterized by, The manufacturing method comprises the following steps: The manufacturing method of the high-strength complex-phase hot-rolled wire rod for 2130MPa-grade twisted wire comprises the following steps:

2. The process of producing high strength complex phase hot rolled wire rod for 2130 MPa grade strand as claimed in claim 1, wherein, Before the rolling, the soaking temperature of the heating furnace is controlled to be 1125-1175℃, and the furnace time is 125-165min.

3. The process of producing high strength complex phase hot rolled wire rod for 2130 MPa grade strand as claimed in claim 1, wherein, During the rolling, the initial rolling temperature is controlled to be 1035-1085℃, the final rolling temperature is 905-945℃, and the final rolling reduction is 19%-24%.

4. The process of producing high strength complex phase hot rolled wire rod for 2130 MPa grade strand as claimed in claim 1, wherein, During the wire drawing, the wire drawing temperature is controlled to be 895-935℃.

5. The process of producing high strength complex hot rolled wire rod for 2130 MPa grade strand as claimed in claim 1, wherein, The molten salt circulation amount of the first-stage molten salt treatment is 435-655t / h, and the molten salt temperature rise is ≤9℃; the molten salt circulation amount of the second-stage molten salt treatment is 365-465t / h, and the molten salt temperature rise is ≤3℃.

6. The process of producing high strength complex hot rolled wire rod for 2130 MPa grade strand as claimed in claim 1, wherein, The wire rod is cooled to below 280℃ at a cooling speed of ≤0.7℃ / s and then coiled.

7. A high strength multiphase hot rolled wire rod for 2130 MPa grade strand, characterized in that, The hot-rolled wire rod is manufactured by the manufacturing method of the high-strength complex-phase hot-rolled wire rod for 2130MPa-grade twisted wire.

8. The high strength complex phase hot rolled wire rod for 2130 MPa grade strand as claimed in claim 7, wherein, The volume percentage of the tempered bainite is 23%-32%, the volume percentage of the ferrite is ≤3%, and the volume percentage of the tempered sorbite is 65%-76%; the lamellar spacing of the tempered sorbite is 75-130nm; the reticular carbide level of the hot-rolled wire rod is 0 level; and the mechanical property difference between different coils is ≤45MPa.

9. The high strength complex rod for 2130 MPa grade stranded conductor as claimed in claim 7, wherein, The diameter of the hot-rolled wire rod is 8.0-15.0mm, the tensile strength is 1456-1483MPa, and the reduction of area is 32%-37%.

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