1150MPa-grade high-strength tool steel wire rod and manufacturing method thereof

Abstract

The invention relates to a 1150MPa-grade high-strength tool steel wire rod and a manufacturing method thereof, the wire rod adopts a high-Cr medium-carbon component design, after a steel billet is rolled and spun into the wire rod, on-line molten salt low-temperature quenching isothermal treatment is performed, the wire rod is controlled to be subjected to front-section molten salt treatment firstly, the wire rod enters a lower bainite phase region from a high-temperature austenite state at a cooling speed of more than or equal to 35 DEG C / s, and the steel wire rod is subjected to high-temperature quenching isothermal treatment at a cooling speed of more than or equal to 35 DEG C / s; the method comprises the following steps: quenching bainite to form a structure taking the quenched bainite as a main part, then carrying out rear-section molten salt heating isothermal tempering and toughening destressing treatment, and finally carrying out roller bed cover opening slow cooling to prepare the wire rod with a microscopic structure comprising tempered bainite and ferrite, so that the initiation of an abnormal brittle structure can be inhibited, the structure state of the wire rod is effectively controlled, and the toughness performance matching of the wire rod is improved; the tensile strength is 1050-1100 MPa, and the percentage reduction of area is 59%-64%, so that the alloy can be directly processed into parts after cold forming.

Description

Technical Field

[0001] The present invention belongs to the technical field related to hot-rolled wire rods, and specifically relates to a 1150MPa grade high-strength tool steel wire rod and a manufacturing method thereof. Background Art

[0002] Alloy tool steel is widely used in cutting tools, measuring tools, screwdrivers and other products. As an indispensable basic equipment in the fields of machinery, automobiles, construction, electronics, electrical appliances, energy, etc., its performance directly affects the production efficiency and development speed of related fields. Improving the grade of tool steel is conducive to reducing material consumption through reduction design, improving tool service performance and fatigue limit, etc. In order to improve the performance of tools, the existing high-strength tool steel wire rod as the tool steel base material needs to be combined with quenching and tempering heat treatment after cold forming to improve product performance, but it also increases the production energy consumption and cost of the tool, affecting production efficiency. Therefore, it is necessary to develop a 1150MPa grade high-strength tool steel wire rod and its manufacturing method, so that the wire rod can be directly processed into parts after cold working to meet the manufacturing and market use needs of the steel industry.

[0003] In the prior art, high-strength tool steel wire rods are often manufactured by adding appropriate amounts of alloy elements such as C, Mn, Cr, etc. to improve hardenability, combined with Stelmor air-cooled wire manufacturing after low-temperature rolling and spinning. However, there are still the following technical problems: (1) Although the improvement of alloying elements can improve the performance of tool products, the requirements for production control are also improved simultaneously. For example, patent CN115976407B discloses a low-alloy hand tool steel coil with a tensile strength of 1000 MPa and a uniform structure, and a production method thereof. The coil adopts a medium carbon composition design of C-Si-Mn-Cr-V-Al, combined with the Stelmor air-cooled line insulation cooling to manufacture pearlite + ferrite structure, so that the tensile strength of the wire rod is 1020~1100 MPa, but the Mn and Cr contents are relatively high. On the one hand, excessive Mn and Cr contents will aggravate the component segregation and increase the internal component non-uniformity of the material. Even if the hood cooling control is adopted, the wire rod is in contact with the air for heat exchange. At the edge and center of the wire rod, due to Due to the difference in heat dissipation conditions, the temperature drop rate is different. The high content of hardenability elements makes the effect of this temperature difference on the organizational transformation amplified, and the difficulty of air cooling increases, which easily leads to the initiation of low-temperature brittle organizations such as martensite. In subsequent cold processing, such as cold heading and drawing, when subjected to external forces, stress concentration is very likely to occur in the brittle organization, which in turn leads to cold processing cracking failure; on the other hand, components such as Mn significantly improve the stability of austenite, shift the C curve to the right, and extend the incubation period of austenite to pearlite transformation in disguise. Due to the limited length of the air cooling line, the wire rod continues to cool down, making it more difficult to improve the plasticity of the wire rod in subsequent processing. After the cold processing process, the wire rod needs to be tempered and heat treated to adjust the organizational properties, which affects the production energy consumption, efficiency and cost of the tool.

[0004] (2) In order to improve the problems of high hardness, easy brittle fracture during packing, transportation and user processing of the martensite-containing wire rods on the air-cooling line, although the bainite phase transformation is controlled by using an air-cooling / water-cooling line. For example, an on-line bainite isothermal quenching process for alloy tool steel wire rods disclosed in Patent CN118621099A adopts a composition of C-Si-Mn-Cr-Ni-Mo-V and combines the Stelmor air-cooling line to quickly cool to the bainite phase region and then hold for cooling. However, on the one hand, the maximum cooling capacity of the air-cooling line is limited. Under strong air-cooling, it will enter the upper bainite phase region, which will increase the temperature difference between the windward surface and the leeward surface of the wire rod, from the edge to the core, and between the lapped and non-lapped positions, increase the risk of precipitation of abnormal structures, cause non-uniform phase transformation of the structure, and have a negative impact on the toughness and process stability of the wire rod. At the same time, due to insufficient cooling speed and a relatively high transformation temperature of the upper bainite, the ferrite laths are wider and the cementite distribution is discontinuous. The upper bainite has lower strength and hardness than the lower bainite, but poorer plasticity and toughness, which affects the strong and tough mechanical properties of the tool steel, is prone to cause stress concentration when stressed, and promotes crack propagation. On the other hand, with a relatively high Si content, the solid solution strengthening effect will cause severe distortion of the ferrite lattice. Even with the treatment of a heat preservation cover, the minimum cooling capacity is limited. At the same time, after the wire rod passes through the upper bainite phase transformation temperature range, it is already in a low-temperature state, and the tissue state cannot be regulated, with large residual stresses in the tissue, resulting in an increase in the resistance to dislocation movement, a decrease in the plasticity and toughness of the steel, and easy generation of cracks during cold deformation processing, and it is impossible to directly process into parts after cold forming. 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 1150 MPa grade high-strength tool steel wire rod and its manufacturing method, which can inhibit the generation of abnormal brittle structures, effectively control the tissue state of the wire rod, improve the matching of the strong and tough properties of the wire rod, so that it can be directly processed into parts after cold forming.

[0006] The technical solution adopted by the present invention to solve its technical problems is: A manufacturing method of a 1150 MPa grade high-strength tool steel wire rod, the manufacturing method includes: After the steel billet is rolled and spun into wire rods at a spinning temperature of ≥905°C, it undergoes on-line molten salt low-temperature quenching and isothermal treatment. The wire rods are first treated with molten salt in the front section, causing the wire rods to enter the lower bainite phase region from the high-temperature austenite state at a cooling rate of ≥35°C / s, forming a structure mainly composed of quenched bainite. Then, they undergo molten salt heating and isothermal tempering and toughening stress relief treatment in the rear section. Finally, they are slowly cooled with the cover opened on the roller path to produce wire rods with a microstructure including tempered bainite and ferrite. The chemical composition and mass percentage of the wire rods are as follows: C: 0.41% - 0.46%, Si: 0.10% - 0.18%, Mn: 0.45% - 0.60%, Cr: 0.52% - 0.60%, Nb: 0.015% - 0.025%, V: 0.025% - 0.035%, P ≤ 0.015%, S ≤ 0.015%, and the rest is Fe and unavoidable impurities.

[0007] The design basis for the chemical composition and mass percentage of the above wire rods includes: (1) Carbon: As a carbide strengthening element and austenite forming element, element C has a relatively lower price. With the increase of carbon content, the stability of supercooled austenite can be improved, the pearlite transformation can be delayed, and the formation of quenched bainite during on-line molten salt low-temperature quenching and isothermal treatment can be promoted. It can promote the finer ferrite needles in quenched bainite, and the intersecting of acicular ferrite can hinder crack propagation. The dispersed distribution of carbides can reduce stress concentration, meeting the requirements of hand tools for wear resistance and toughness. However, too much carbon content will cause the coarsening of bainite acicular structure, increase internal stress, reduce the plasticity improvement difficulty and cold formability of wire rods. Therefore, in order to meet the wear resistance requirements of hand tool steel, control material costs, and at the same time facilitate the control of the microstructure state of hot-rolled wire rods and improve the strength-toughness matching, a medium carbon content is adopted, and the mass percentage of C is controlled at 0.41% - 0.46%.

[0008] (2) Silicon: Element Si can inhibit grain coarsening during on-line molten salt low-temperature quenching and isothermal treatment, improve the stability of supercooled austenite, cause bainite transformation to occur at a lower temperature, compress the pearlite formation range, and slightly strengthen by solid solution without significantly affecting temper softening. However, too high a silicon content will lead to too strong solid solution strengthening effect of silicon, hinder the complete bainite transformation, aggravate lattice distortion, reduce the toughness of steel, affect plasticity regulation, and cause a decrease in plasticity during cold processing. Therefore, the Si content is reduced, and the mass percentage of Si is controlled at 0.10% - 0.18%.

[0009] (3)Manganese: As an austenite-forming element, Mn can expand the austenite region, increase the hardenability of the wire rod, reduce the tendency to form pearlite and ferrite, strongly delay the pearlite transformation, expand the bainite transformation temperature range, enable the bainite transformation to occur at a lower temperature, and at the same time slow down the growth rate of ferrite lamellae, allowing the front-section molten salt to pass through quenching, controlling the wire rod to form a structure mainly composed of quenched bainite, enabling bainite tissue to form in the core of the wire rod cross-section, improving the matrix strength, and meeting the wear resistance requirements of tools. However, when the Mn content is too high, it will exacerbate alloy element segregation, increase the risk of abnormal martensite precipitation, promote austenite grain coarsening, inhibit the recrystallization of ferrite and the aggregation of carbides during tempering, making stress release require higher energy, and reducing the toughness and plasticity of the steel. Therefore, in order to balance the wear resistance of hand tools and facilitate the bainite phase transformation and isothermal toughening stress relief control of the wire rod, the mass percentage of Mn is controlled at 0.45% - 0.60%.

[0010] (4)Chromium: As a strong carbide-forming element, the Cr element can form high-hardness alloy carbides, improve the hardenability of the steel, reduce the diffusion coefficient of carbon in austenite, shift the pearlite transformation kinetics curve to the right, delay the precipitation of ferrite and pearlite, and make quenched bainite the main transformation product during the front-section molten salt treatment. The chromium element is dissolved in bainite ferrite, improving the resistance to tempering softening and preventing a rapid decrease in strength during tempering, which is beneficial to improving the wear resistance and corrosion resistance of the steel. However, too high a Cr content will exacerbate composition segregation, increase the difficulty of controlling tissue uniformity, delay the nucleation and growth of bainite ferrite, require a longer time for quenched bainite to form, increase the difficulty of improving plasticity, and uneven carbide distribution forms coarse particles or a network structure, reducing plasticity and cold workability. Therefore, in order to balance the wear resistance and plastic toughness of hand tools and facilitate the microstructure and tissue state control of the wire rod mainly composed of tempered bainite, the Cr content is appropriately increased, and the mass percentage of Cr is controlled at 0.52% - 0.60%.

[0011] (5)Niobium: The Nb microalloying element can precipitate during the primary rolling stage, pin the grain boundaries, inhibit austenite grain growth, improve strength and toughness through precipitation strengthening and grain refinement strengthening, is beneficial to increasing the nucleation sites of quenched bainite, making the quenched bainite structure finer and more dispersed, and retaining more substructure strengthening effects. However, the price of Nb is relatively high, and coarse precipitation phases will increase the cracking risk during wire rod cold working. Therefore, considering the role, cost, and preparation control of the Nb element, the mass percentage of Nb is controlled at 0.015% - 0.025%.

[0012] (6) Vanadium: As an alloying element, V can pin austenite grain boundaries during the controlled rolling stage, refine the original austenite grains, and promote the formation of high-density dislocations and twins in bainitic ferrite. It can be dispersed and precipitated during the isothermal process of the subsequent molten salt treatment, which can make up for the strength loss of quenched bainite during tempering and softening. It can improve the strength without sacrificing toughness and reduce the crack tendency during cold working of hand tools. However, the cost of V is relatively high, and excessive addition is not conducive to controlling the cost of wire rods. Too much V will also cause element enrichment and rapid coarsening of carbides, resulting in loss of strength and toughness. Therefore, based on the role of V, cost and preparation control, the mass percentage of V is controlled to be 0.025%~0.035%.

[0013] (7) Phosphorus and sulfur: P and S are impurity elements. The lower the better. Therefore, P is controlled to be ≤ 0.015% and S is ≤ 0.015%.

[0014] The above-mentioned wire rod adopts the medium carbon composition design of C-Si-Mn-Cr-Nb-V, with low C and Si content, high Cr content, and trace addition of Nb and V, which can appropriately control the material cost and take into account the wear resistance requirements of the tool, and provide favorable conditions for delaying the precipitation of ferrite and pearlite, reducing the temperature of the lower bainite phase region, and promoting the rapid formation of a quenched bainite-based organization in the front-stage molten salt treatment of online molten salt low-temperature quenching, and the rear-stage molten salt treatment can quickly toughen and relieve stress and avoid excessive strength loss. On this basis, a higher wire-spinning temperature can be selected to reduce the temperature limit on the rolling process, and a higher quenching temperature is used to promote the refinement of bainite phase transformation and improve the strength and toughness matching of the material, so as to avoid the low-temperature quenching affecting the diffusion coefficient of carbon and causing the incubation period to be extended. The wire rod after wire-spinning is directly subjected to online molten salt low-temperature quenching isothermal treatment without air cooling: 1. Compared with the limited maximum cooling capacity and unstable temperature control of the Stelmor air-cooled line, which make it difficult to suppress the formation of brittle structures such as martensite, the presence of pearlite soft phase in the structure, and the difficulty in directly entering the lower bainite phase region, when the wire rod undergoes the front-section molten salt treatment, on the one hand, the thermal conductivity of the molten salt is much higher than that of air, which can promote the rapid cooling of the wire rod compared to air cooling, enabling the wire rod to quickly cross the pearlite and upper bainite formation intervals. Combined with composition design, it can avoid the formation of lamellar pearlite structure due to too slow cooling rate, which affects the strength performance, and prevent the prior precipitation of ferrite laths in the upper bainite formation interval, where carbon diffuses between the laths to form discontinuous cementite, thus avoiding the formation of upper bainite that is unfavorable to strength, toughness, and wear resistance. The wire rod rapidly enters the lower bainite phase region from the high-temperature austenite state, restricting the long-range diffusion of carbon and enabling the austenite to be fully transformed into quenched bainite with better strength and toughness in this interval. On the other hand, when the wire rod passes through the front-section molten salt, the molten salt covers the surface of the wire rod, which can reduce the temperature difference problem at different positions such as the windward and leeward sides of the wire rod compared to air cooling, and avoid the attachment of a large number of bubbles on the surface of the wire rod during quenching, which affects the heat transfer stability. It can reduce the temperature difference from the surface to the core of the wire rod, avoid directly entering the martensite region to form hard and brittle martensite, promote the formation of a structure mainly composed of quenched bainite in the wire rod, and avoid the formation of abnormal low-temperature structures during the subsequent cooling process due to residual austenite, resulting in better tissue consistency.

[0015] 2. Compared with the limited minimum cooling capacity and continuous cooling control of the Stelmor air-cooled line's hood cooling, which lead to relatively large tissue stress and insufficient toughness, the wire rod can undergo heating and isothermal treatment after passing through the rear-section molten salt. On the one hand, compared with the slow cooling of the hood cooling in the pearlite / upper bainite phase region, the molten salt can keep the wire rod at the molten salt temperature for isothermal treatment, prolong the time of the wire rod in the high-temperature range, provide more thermal driving force for tissue toughening, promote the formation of a structure mainly composed of quenched bainite, improve the high internal stress generated by the shear mechanism during the formation of quenched bainite, and enable the dislocations in ferrite to move through slip, climb, etc., reducing tissue brittleness, further optimizing the strength-toughness matching, and reducing the cracking tendency. On the other hand, the molten salt can heat the wire rod to the temperature range where fine alloy carbides are diffusely precipitated, increase the precipitation driving force, cause the supersaturated solid solution of fine alloying elements to start to precipitate, form diffusely distributed nano-scale carbides, evenly distributed at the grain boundaries, producing a significant dispersion strengthening effect, while avoiding the coarsening of carbides containing Cr, etc., maximizing the strengthening effect of carbon elements, improving the overall strength and plasticity of the wire rod. Finally, after the wire rod passes through the open hood and slow cooling, the wire rod can use its own residual heat to slowly cool down, continuing the toughening and stress-relieving effect of the rear-section molten salt, avoiding stress increase, while increasing the offline speed and promoting rapid production.

[0016] Before rolling, high-temperature soaking and appropriate soaking time in the furnace are selected, which can fully dissolve carbon and alloying elements in austenite, improve austenite plasticity, lay a foundation for grain refinement control in the subsequent rolling process, and avoid non-uniform microstructure caused by composition segregation during rolling. In the preferred technical solution, before rolling, the soaking temperature of the heating furnace is controlled at 1100-1150°C, and the soaking time in the furnace is 100-150 min.

[0017] Since the spinning temperature is relatively high, which can offset the limitation of the rolling temperature, selecting higher initial rolling temperature and final rolling temperature can increase the rolling speed, reduce the wear impact on the rolling line, inhibit the growth of austenite grains by the solid solution drag effect of microalloying elements, promote dynamic recrystallization during the final rolling process through appropriate deformation, refine grains, provide more nucleation sites for subsequent phase transformation, and refine the microstructure. In the preferred technical solution, during rolling, the initial rolling temperature is controlled at 1020-1060°C, the final rolling temperature is controlled at 915-950°C, and the reduction of the final rolling is 25%-30%.

[0018] During spinning, the spinning temperature can be further controlled to avoid the risk of austenite grain growth caused by too high temperature. In the preferred technical solution, during spinning, the spinning temperature is controlled at 905-940°C.

[0019] The molten salt temperature of the front-stage molten salt is in the lower bainite phase region. The lower the molten salt temperature and the longer the treatment time, the faster the wire rod can be cooled, the supercooling degree can be increased, and the time can be extended to make atomic diffusion sufficient. Through sufficient diffusion, carbon is enriched in the untransformed austenite, inhibiting pearlite transformation, promoting the transformation of enough high-temperature austenite into single quenched bainite, avoiding grain coarsening, and improving the matrix strength. However, if the molten salt temperature is too low and the treatment time is too long, there is a risk of cooling to the martensite phase region to produce abnormal low-temperature microstructure, affecting microstructure uniformity, increasing production energy consumption, and insufficient internal stress elimination; on the contrary, the higher the molten salt temperature and the shorter the treatment time, the production energy consumption and the difficulty of subsequent toughening and stress relief can be reduced. However, if the molten salt temperature is too high and the treatment time is too short, the proportion of quenched bainite in the microstructure is relatively small, and there is a risk of forming soft-phase microstructure during the subsequent heating and isothermal process, which will affect the strength and microstructure control of the wire rod. Therefore, by selecting appropriate front-stage molten salt temperature and treatment time, the wire rod can be controlled to enter the lower bainite phase region from the high-temperature austenite state, form a microstructure mainly composed of quenched bainite, improve the matrix strength, activate the atomic diffusion ability, avoid excessive retained austenite or pearlite / martensite mixed microstructure formed due to insufficient cooling rate, and make organizational preparations for the subsequent back-stage molten salt treatment. In the preferred technical solution, the molten salt temperature of the front-stage molten salt is 270-320°C, and the treatment time is 40-65 s.

[0020] Since the temperature difference between the wire rod's spinning temperature and the molten salt temperature of the previous section of molten salt is relatively large, a larger molten salt circulation rate is selected to control the temperature rise of the molten salt, which is beneficial to further control the tissue uniformity within the entire length of the wire rod. In the preferred technical solution, the molten salt circulation rate of the previous section of molten salt is 460 - 760 t / h, and the temperature rise of the molten salt ≤ 8°C.

[0021] The molten salt temperature of the latter section of molten salt is in the high-temperature and microalloy dispersion precipitation temperature range. Both Mn and Cr improve the tempering stability of the wire rod. Stress release requires more energy. The higher the molten salt temperature and the longer the treatment time, the more thermal power can be provided, enabling the wire rod to perform isothermal tempering treatment on the quenched structure after the previous section of molten salt treatment in the high-temperature isothermal range, promoting the reduction of dislocation density, contributing to the full release of internal stress in the wire rod, enhancing the plasticity of the wire rod, and promoting the full dispersion precipitation of microalloy carbides. However, if the molten salt temperature is too high and the treatment time is too long, it will soften too quickly, with the risk of excessive softening resulting in a decrease in the load-bearing capacity of the wire rod and the coarsening and aggregation of alloy carbides, thereby losing the strength and plasticity performance. On the contrary, the lower the molten salt temperature, the more driving force is provided for the dispersion precipitation of alloy carbides. With the shortening of the treatment time, the production energy consumption and softening effect can be reduced. However, if the molten salt temperature is too low and the treatment time is too short, the residual stress of the tissue is relatively high, the alloy carbides do not have enough time to fully precipitate, and the stability of the precipitated phase is poor, which will cause the core to be hard and brittle, affecting the strength and plasticity performance of the wire rod. Therefore, an appropriate molten salt temperature and treatment time can be selected for toughening and stress relief treatment, regulating the tissue state and carbide precipitation, and enhancing the strength-plasticity matching of the wire rod. In the preferred technical solution, the molten salt temperature of the latter section of molten salt is 570 - 595°C, and the treatment time is 120 - 280 s.

[0022] Since the temperature difference between the previous section of molten salt and the latter section of molten salt is relatively large, the latter section of molten salt avoids too low a molten salt circulation rate, which helps to maintain the stability of the molten salt temperature of the latter section of molten salt and reduces the production energy consumption by appropriately reducing the molten salt circulation rate. In the preferred technical solution, the molten salt circulation rate of the latter section of molten salt is 350 - 440 t / h.

[0023] In the preferred technical solution, the roller table open-hood slow cooling controls the wire rod to slowly cool at a cooling rate of 0.7 - 1.2°C / s to below 300°C, which can prevent the wire rod from having too fast a cooling rate during cooling, resulting in increased stress, and promote further toughening of the wire rod tissue, improving the softening effect of the wire rod. At the same time, it avoids too slow a cooling rate, which may lead to a slower production rhythm and reduced production efficiency.

[0024] An 1150 MPa grade high-strength tool steel wire rod, which is manufactured by the manufacturing method of the 1150 MPa grade high-strength tool steel wire rod described in any one of the above.

[0025] The above-mentioned wire rod adopts a high-Cr chemical composition design combined with an online molten salt low-temperature quenching and isothermal technology. The obtained wire rod structure is mainly tempered bainite, containing a small amount of ferrite. Compared with the pearlite wire rod structure formed on the air-cooling line, tempered bainite can retain the strength characteristics of quenched bainite, make up for the strength loss caused by reducing the alloy content, and avoid abnormal brittle structures such as martensite. Compared with the upper bainite structure formed on the air-cooling line, the ferrite laths are wide and the cementite is discontinuous. Although the plasticity is slightly better than that of pearlite, the strength is insufficient, and the uneven distribution of cementite is likely to become a crack initiation point. The needles of quenched bainite formed by the molten salt in the front section are thinner and interlaced with each other, and fine and dispersed carbides are distributed on the matrix. Its performance is between that of pearlite and martensite, with a balance of high strength and good toughness, suitable for tool steels that require impact resistance and wear resistance. After molten salt quenching, it is combined with high-temperature isothermal tempering and toughening stress relief treatment to transform into strong and tough tempered bainite. The tempered bainite provides a strong and tough substrate, and the dispersed carbides further strengthen the matrix, avoiding the reduction of toughness caused by relying solely on solid solution strengthening. It can further cooperate with carbide precipitation to optimize the strength-toughness matching, so that it can be directly processed into parts after cold forming.

[0026] The higher the proportion of tempered bainite in the microstructure of the wire rod, the more beneficial it is to maintain a certain toughness while having better strength and wear resistance, making the wire rod not prone to brittle fracture. In the preferred technical solution, the volume percentage of the tempered bainite ≥ 96%.

[0027] In the preferred technical solution, the diameter of the wire rod is 5.5 - 10 mm, the tensile strength is 1050 - 1100 MPa, the reduction of area is 59% - 64%, and the within-coil difference of mechanical properties ≤ 33 MPa. The wire rod diameter is suitable for processing medium and small hand tools such as wrenches, hammers, and screwdriver shafts. The wire rod has good strength, which can avoid the fracture of tools during overload. The reduction of area reflects the plastic deformation ability of the material, has good toughness reserve and cold formability, can absorb impact energy, and reduce the risk of sudden fracture during direct cold processing or use. The within-coil difference of mechanical properties reflects the performance uniformity of the wire rod, which is helpful for mass production. Furthermore, it can be directly processed into parts after cold forming, improving the yield rate and tool life, and reducing production costs.

[0028] Compared with the prior art, the beneficial effects of the present invention are at least as follows: (1)In view of the current situation that in order to improve the use performance of tools, the content of alloying elements for improving hardenability is increased, resulting in difficulty in controlling the microstructure and properties of the wire rod during air cooling after rolling. The present invention combines a high-Cr chemical composition design with an online molten salt low-temperature quenching and isothermal technology. With a relatively high quenching temperature and the molten salt in the front section controlling the wire rod in the high-temperature austenite state, it quickly crosses the formation intervals of pearlite and upper bainite and enters the lower bainite phase region to form a microstructure mainly composed of quenched bainite. Then, the molten salt in the rear section controls the wire rod to perform high-temperature isothermal tempering on the quenched microstructure in the high-temperature isothermal interval, toughening and stress-relieving treatment, controlling the dispersion precipitation of carbides, improving the strength-ductility matching of the wire rod. Finally, slow cooling with the cover opened on the roller table promotes further toughening of the wire rod microstructure, can quickly offline to improve production efficiency, effectively inhibit the generation of abnormal brittle microstructure, control the tempering state of the wire rod microstructure, improve the strength-toughness performance matching of the wire rod, reduce the fluctuation of mechanical properties, and has good industrial adaptability.

[0029] (2)In view of the current situation that in order to improve the use performance of tools, alloying elements such as appropriate amounts of C, Mn, Cr, etc. for improving hardenability are often added, and after cold forming, combined with quenching and tempering heat treatment to improve product performance, resulting in the generation of brittle microstructure, cold working cracking failure, and high energy consumption and cost of quenching and tempering heat treatment. The present invention has relatively low C and Si contents, relatively high Cr content, and trace addition of Nb and V, which can appropriately control the material cost and take into account the wear resistance requirements of tools. At the same time, the microstructure is mainly tempered bainite with a small amount of ferrite microstructure. Compared with the pearlite wire rod microstructure formed on the air cooling line, it can make up for the strength loss caused by reducing the alloy content. Compared with the upper bainite microstructure formed on the air cooling line, tempered bainite is both strong and tough, can maximize the strengthening effect of carbon elements, and cooperate with the precipitation of carbides to optimize the strength-toughness matching, and can reach a tensile strength of 1050 - 1100 MPa and a reduction of area of 59% - 64%. After cold forming, it can be directly processed into hand tool parts, and has good market application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The above and / or additional aspects and advantages of the present invention will become obvious and easy to understand from the description of the embodiments in conjunction with the following drawings, where: Figure 1 is the metallographic microstructure diagram of Embodiment 1 of the present invention; Figure 2 is the metallographic microstructure diagram of Embodiment 2 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0031] The embodiments described below with reference to the accompanying drawings are exemplary and are for illustrative purposes only, without limiting the description of the features and characteristics of the present invention. They are intended to present the best mode of implementing the present invention, to explain the present invention, and 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 defined only by the appended claims. The detection of the structure and properties of the wire rods obtained from the following examples and comparative examples includes: the tensile test is carried out in accordance with "GB-T 228.1-2021 Metallic materials-Tensile testing-Part 1: Method of test at room temperature" to obtain the tensile strength and reduction of area; the structure detection is carried out in accordance with the 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 5 m from the end of the coil. With the lap area as the base point, each coil of wire rod is evenly divided into 8 segments on average, and 1 tensile specimen is taken on each segment. The strength difference after the taken tensile specimens are subjected to the tensile test is the difference in mechanical properties within the same coil. Example 1:

[0032] A preferred embodiment of the manufacturing method of the 1150 MPa grade high-strength tool steel wire rod according to the present invention. The chemical composition and mass percentage of the wire rod include C: 0.46%, Si: 0.17%, Mn: 0.60%, Cr: 0.59%, Nb: 0.025%, V: 0.029%, P: 0.013%, S: 0.012%, and the rest are Fe and unavoidable impurities. Its manufacturing method is manufactured according to the technological process of rolling → wire laying → online molten salt low-temperature quenching and isothermal treatment → slow cooling with the roller path cover opened → coiling. Specifically: 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, reducing the influence of segregation. The heating furnace is controlled according to the three-stage temperature rising program of the preheating section, heating section, and soaking section. The high-temperature steel billet is rolled into a wire rod with a diameter specification of 10 mm through the rolling line. Appropriate rolling temperature and reduction ratio are selected to increase the rolling speed, promote dynamic recrystallization during the finishing rolling process, and refine the grains. Specifically: control the soaking temperature of the heating furnace to be 1150 °C, the residence time in the furnace to be 100 min, the initial rolling temperature to be 1060 °C, the finishing rolling temperature to be 950 °C, and the finishing rolling reduction ratio to be 25%; the wire laying process is used to make the wire rod exiting the rolling line into a coil through the wire laying machine. The coil is scattered on the roller path and conveyed along the roller path, making the coil in the high-temperature austenite state to prepare for quenching the structure at a higher quenching temperature. Specifically: control the wire laying temperature to be 940 °C.

[0033] The online molten salt low-temperature quenching and isothermal 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 the front-stage molten salt treatment, so that the wire rod cools down at a cooling rate of 41 °C / s, quickly crosses the pearlite and upper bainite formation intervals from the high-temperature austenite state, enters the lower bainite phase region, and forms a structure mainly composed of quenched bainite. Then, the wire rod is transported through the second-stage salt bath tank by a roller table for the rear-stage molten salt treatment, controlling the wire rod to perform high-temperature isothermal tempering on the quenched structure in the high-temperature isothermal interval, toughening and stress relief treatment, promoting the dispersion precipitation of microalloy carbides, inhibiting the coarsening of carbides, and improving the strength-plasticity matching of the wire rod. Specifically: the molten salt temperature of the front-stage molten salt is 270 °C, the treatment time is 65 s, the molten salt circulation rate is 760 t / h, and the molten salt temperature rise ≤ 8 °C; the molten salt temperature of the rear-stage molten salt is 594 °C, the treatment time is 280 s, and the molten salt circulation rate is 440 t / h.

[0034] In the slow cooling process with the roller table cover opened, the opening degree of the heat preservation cover is adjusted, and the wire rod transported by the conveying roller table through the second-stage salt bath tank is slowly cooled through the heat preservation cover, preventing the wire rod from having too fast a cooling rate during the cooling process, resulting in an increase in stress, and promoting the further toughening of the wire rod structure, improving the softening effect of the wire rod until coiling. Specifically: controlling the wire rod to slowly cool to 291 °C at a cooling rate of 1.2 °C / s; the coiling process is used to coil the wire rod into a coil through a coiling drum, and after packaging and warehousing, the finished wire rod is obtained, and its metallographic structure diagram is as Figure 1 shown.

[0035] Comparative Example 1: A manufacturing method of a wire rod, the difference between its manufacturing method and that of Example 1 is: its manufacturing method is carried out according to the technological process of rolling → wire laying → Stelmor air-cooling line → coiling. Specifically: in the rolling process, the soaking temperature of the heating furnace is controlled at 1050 °C, the time in the furnace is 175 min, the initial rolling temperature is 1005 °C, the final rolling temperature is 840 °C, the wire laying temperature is controlled at 815 °C, in the Stelmor air-cooling line, the front 1-6# heat preservation covers are opened, the fan is turned on to control the wire rod to cool at a speed of 4.5 °C / s to 675 °C, then the heat preservation cover is closed, the wire rod enters the heat preservation cover and cools at a speed of 2.6 °C / s to 290 °C, and is collected by a coiling drum to obtain the finished wire rod.

[0036] Comparative Example 2: A manufacturing method of a wire rod, the difference between its manufacturing method and that of Example 1 is: controlling the soaking temperature of the heating furnace at 1065 °C, the time in the furnace at 165 min, the initial rolling temperature at 1010 °C, the final rolling temperature at 875 °C, controlling the wire laying temperature at 855 °C, the wire rod undergoes the front-stage molten salt treatment and cools down at a cooling rate of 34 °C / s to obtain the finished wire rod. Example 2:

[0037] A preferred embodiment of the manufacturing method of the 1150 MPa grade high-strength tool steel wire rod described in the present invention. The chemical composition and mass percentage of the wire rod include C: 0.42%, Si: 0.10%, Mn: 0.49%, Cr: 0.52%, Nb: 0.015%, V: 0.025%, P: 0.015%, S: 0.015%, and the rest are Fe and inevitable impurities. Its manufacturing method is carried out according to the technological process of rolling → wire laying → online molten salt low-temperature quenching and isothermal treatment → slow cooling with the roller path cover open → coiling. Specifically: The rolling process is used to heat a steel billet with a specification of 180 mm × 180 mm into a high-temperature steel billet that reaches the plastic state for rolling through a heating furnace, reducing the influence of segregation. The heating furnace is controlled according to the three-stage temperature-rising program of the preheating section, heating section, and soaking section. The high-temperature steel billet is rolled into a wire rod with a diameter specification of 5.5 mm through the rolling line. Appropriate rolling temperature and reduction are selected to increase the rolling speed, promote dynamic recrystallization during the finishing rolling process, and refine the grains. Specifically: control the soaking temperature of the heating furnace to be 1100 °C, the residence time in the furnace to be 150 min, the initial rolling temperature to be 1020 °C, the finishing rolling temperature to be 915 °C, and the finishing rolling reduction to be 30%. The wire laying process is used to make the wire rod coming out of the rolling line into a wire coil through a wire laying machine. The wire coil is scattered on the roller path and conveyed along the roller path, making the wire coil in the high-temperature austenite state to prepare for quenching the structure at a relatively high quenching temperature. Specifically: control the wire laying temperature to be 905 °C.

[0038] The online molten salt low-temperature quenching and isothermal treatment process uses a two-stage salt bath tank with molten salt inside. The wire coil after wire laying is conveyed through the roller path and passes through the first-stage salt bath tank for the front-stage molten salt treatment, making the wire coil cool down at a cooling rate of 35 °C / s, quickly crossing the pearlite and upper bainite formation intervals from the high-temperature austenite state and entering the lower bainite phase region to form a structure mainly composed of quenched bainite. Then the wire coil is conveyed through the roller path and passes through the second-stage salt bath tank for the rear-stage molten salt treatment, controlling the wire coil to carry out high-temperature isothermal tempering on the quenched structure in the high-temperature isothermal interval, toughening and stress-relieving treatment, promoting the dispersion precipitation of microalloy carbides, inhibiting the coarsening of carbides, and improving the strength-plasticity matching of the wire coil. Specifically: the molten salt temperature of the front-stage molten salt is 320 °C, the treatment time is 40 s, the molten salt circulation volume is 460 t / h, and the molten salt temperature rise ≤ 8 °C; the molten salt temperature of the rear-stage molten salt is 570 °C, the treatment time is 120 s, and the molten salt circulation volume is 350 t / h.

[0039] In the slow cooling process with the roller table cover opened, the opening degree of the heat preservation cover is adjusted, and the wire rod passing through the second salt bath tank is slowly cooled by the conveying roller table through the heat preservation cover, preventing the wire rod from having too fast a cooling rate during the cooling process, which may lead to an increase in stress, promoting further toughening of the wire rod structure, improving the softening effect of the wire rod, until coiling. Specifically: control the wire rod to be slowly cooled at a cooling rate of 0.7 °C / s to 298 °C; the coiling process is used to coil the wire rod into a coil by a coiling drum, and after packaging and warehousing, the finished wire rod is obtained, and its metallographic structure diagram is as Figure 2 shown.

[0040] Comparative Example 3: A manufacturing method of a wire rod, the difference between its manufacturing method and that of Example 2 is that: the wire rod is treated by molten salt in the front stage and cooled at a cooling rate of 32 °C / s, the molten salt temperature of the front-stage molten salt is 335 °C, and the treatment time is 25 s to obtain the finished wire rod.

[0041] Comparative Example 4: A manufacturing method of a wire rod, the difference between its manufacturing method and that of Example 2 is that: the wire rod is treated by molten salt in the front stage and cooled at a cooling rate of 29 °C / s, the molten salt temperature of the front-stage molten salt is 265 °C, and the treatment time is 68 s to obtain the finished wire rod. Example 3:

[0042] A preferred implementation manner of the manufacturing method of the 1150 MPa grade high-strength tool steel wire rod of the present invention, the chemical composition and mass percentage of the wire rod include C: 0.41%, Si: 0.18%, Mn: 0.55%, Cr: 0.60%, Nb: 0.02%, V: 0.035%, P: 0.012%, S: 0.012%, 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 low-temperature quenching and isothermal treatment → slow cooling with the roller table cover opened → coiling. Specifically: The rolling process is used to heat a steel billet with a specification of 180 mm × 180 mm into a high-temperature steel billet that reaches the plastic state for rolling through a heating furnace, reducing the influence of segregation. The heating furnace is controlled according to the three-stage heating program of the preheating section, heating section, and soaking section. The high-temperature steel billet is rolled into a wire rod with a diameter specification of 9 mm through the rolling line. Appropriate rolling temperature and reduction are selected to increase the rolling speed and promote dynamic recrystallization during the finishing rolling process, refining the grains. Specifically: control the soaking temperature of the heating furnace to be 1135 °C, the residence time in the furnace to be 120 min, the initial rolling temperature to be 1050 °C, the finishing rolling temperature to be 945 °C, and the finishing rolling reduction to be 26%; the wire laying process is used to make the wire rod coming out of the rolling line into a wire rod through a wire laying machine, and the wire rod is scattered on the roller table and conveyed along the roller table, so that the wire rod is in a high-temperature austenite state, preparing for quenching with a relatively high quenching temperature. Specifically: control the wire laying temperature to be 928 °C.

[0043] The online molten salt low-temperature quenching and isothermal 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 front-stage molten salt treatment, so that the wire rod cools at a cooling rate of 39 °C / s, quickly crosses the pearlite and upper bainite formation intervals from the high-temperature austenite state, enters the lower bainite phase region, and forms a structure mainly composed of quenched bainite. Then the wire rod is transported through the second-stage salt bath tank by a roller table for post-stage molten salt treatment, controlling the wire rod to perform high-temperature isothermal tempering, toughening and stress-relieving treatment in the high-temperature isothermal interval, promoting the dispersion precipitation of microalloy carbides, inhibiting the coarsening of carbides, and improving the strength-plasticity matching of the wire rod. Specifically: the molten salt temperature of the front-stage molten salt is 279 °C, the treatment time is 58 s, the molten salt circulation rate is 675 t / h, and the molten salt temperature rise ≤ 8 °C; the molten salt temperature of the post-stage molten salt is 583 °C, the treatment time is 245 s, and the molten salt circulation rate is 415 t / h.

[0044] The roller table open-hood slow cooling process adopts adjusting the opening degree of the heat preservation hood, and the wire rod transported by the conveying roller table after passing through the second-stage salt bath tank is slowly cooled through the heat preservation hood, preventing the wire rod from increasing stress due to too fast cooling rate during the cooling process, and promoting the further toughening of the wire rod structure, improving the softening effect of the wire rod until coiling. Specifically: controlling the wire rod to slowly cool to 295 °C at a cooling rate of 1.1 °C / s; the coiling process is used to coil the wire rod into a coil by a coiling drum, and the finished wire rod is obtained after packaging and warehousing.

[0045] Comparative Example 5: A manufacturing method of a wire rod, the difference between its manufacturing method and that of Example 3 is that: the molten salt temperature of the post-stage molten salt is 600 °C, the treatment time is 360 s, and the finished wire rod is obtained.

[0046] Comparative Example 6: A manufacturing method of a wire rod, the difference between its manufacturing method and that of Example 3 is that: the molten salt temperature of the post-stage molten salt is 560 °C, the treatment time is 100 s, and the finished wire rod is obtained. Example 4:

[0047] A preferred implementation of the manufacturing method of the 1150 MPa grade high-strength tool steel wire rod of the present invention, the chemical composition and mass percentage of the wire rod include C: 0.43%, Si: 0.12%, Mn: 0.45%, Cr: 0.54%, Nb: 0.022%, V: 0.03%, P: 0.014%, 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 → online molten salt low-temperature quenching and isothermal → roller table open-hood slow cooling → coiling. Specifically: The rolling process is used to heat a billet with a specification of 180mm×180mm into a high-temperature billet that reaches the rollable plasticity through a heating furnace, reducing the influence of segregation. The heating furnace is controlled according to a three-stage temperature-rising program of a preheating section, a heating section, and a soaking section. The high-temperature billet is rolled into wire rods with a diameter specification of 7mm through a rolling line. Appropriate rolling temperature and reduction are selected to increase the rolling speed, promote dynamic recrystallization during the finishing rolling process, and refine the grains. Specifically: control the soaking temperature of the heating furnace to be 1115°C, the residence time in the furnace to be 135min, the initial rolling temperature to be 1035°C, the finishing rolling temperature to be 925°C, and the finishing rolling reduction to be 28%; The wire laying process is used to make the wire rods exiting the rolling line into coils through a wire laying machine. The coils are scattered on the roller table and transported along the roller table, keeping the coils in a high-temperature austenite state to prepare for quenching the structure at a relatively high quenching temperature. Specifically: control the wire laying temperature to be 915°C.

[0048] The on-line molten salt low-temperature quenching and isothermal process uses a two-stage salt bath tank with molten salt inside. The coils after wire laying are transported through the roller table and pass through the first-stage salt bath tank for the front-stage molten salt treatment, cooling the coils at a cooling rate of 37°C / s, quickly crossing the pearlite and upper bainite formation intervals from the high-temperature austenite state, entering the lower bainite phase region, and forming a structure mainly composed of quenched bainite. Then the coils are transported through the roller table and pass through the second-stage salt bath tank for the rear-stage molten salt treatment, controlling the coils to perform high-temperature isothermal tempering on the quenched structure in the high-temperature isothermal interval, toughening and stress-relieving treatment, promoting the dispersion precipitation of microalloy carbides, inhibiting the coarsening of carbides, and improving the strength-plasticity matching of the coils. Specifically: the molten salt temperature of the front-stage molten salt is 298°C, the treatment time is 46s, the molten salt circulation rate is 565t / h, and the molten salt temperature rise ≤ 8°C; the molten salt temperature of the rear-stage molten salt is 576°C, the treatment time is 183s, and the molten salt circulation rate is 380t / h.

[0049] The slow cooling process with the roller table cover open uses an adjustable heat preservation cover opening. The coils passing through the second-stage salt bath tank by the conveying roller table are slowly cooled through the heat preservation cover, preventing the coils from cooling too quickly during the cooling process, which may lead to an increase in stress, and promoting further toughening of the coil structure, improving the softening effect of the coils until coiling. Specifically: control the coils to be slowly cooled to 297°C at a cooling rate of 0.85°C / s; The coiling process is used to coil the coils into coil reels through a coiling drum, and the coil reel products are obtained after packaging and warehousing.

[0050] Comparative Example 7: A manufacturing method of coils, the difference between its manufacturing method and that of Example 4 is that: its manufacturing method is carried out according to the technological process of rolling → wire laying → on-line molten salt low-temperature quenching and isothermal → air cooling → coiling. Specifically: the air cooling process uses the coils passing through the second-stage salt bath tank by the conveying roller table to be naturally cooled in the air, and the coils are cooled to 290°C at a cooling rate of 2.2°C / s to obtain the coils.

[0051] The wire rods obtained from the above Examples 1-4 and Comparative Examples 1-7 were subjected to microstructure and property tests, and the comparison results obtained are shown in Table 1 below: Table 1. Comparison results of microstructure and properties of different wire rod compositions and manufacturing methods

[0052] From the comparison results of Example 1 and Comparative Example 1, it can be seen that compared with the air-cooled wire rod, which often weakens the strengthening effect due to uncontrollable cooling rates during the cooling phase transformation and leads to the appearance of abnormal structures such as martensite, the present invention can effectively avoid the risk of brittle structures such as martensite and Widmanstatten in C and Cr elements through the online molten salt isothermal toughening technology, maximize the strengthening effect of carbon elements, and improve the overall strength and plasticity of the wire rod; from the results of Examples 1-4, it can be seen that the present invention adopts a high-Cr chemical composition design combined with the online molten salt low-temperature quenching and isothermal technology. The obtained wire rod microstructure is mainly tempered bainite, containing a small amount of ferrite, effectively controlling the wire rod microstructure state, improving the strength and toughness performance matching of the wire rod, with a tensile strength of 1050-1100 MPa and a reduction of area of 59%-64%, so that it can be directly processed into parts after cold forming, eliminating the tempering heat treatment after cold working, improving production efficiency and reducing production costs.

[0053] From the comparison results of Example 1 and Comparative Example 2, it can be seen that low-temperature quenching affects the carbon diffusion coefficient and causes an extended incubation period. Under the same front-section molten salt treatment conditions, it affects the amount of quenched bainite phase transformation. A higher quenching temperature is beneficial to promoting bainite phase transformation refinement and improving the strength and toughness of the material.

[0054] From the comparison results of Example 2 and Comparative Example 3, it can be seen that if the molten salt temperature of the front-section molten salt is too high and the treatment time is too short, the production energy consumption and the difficulty of subsequent toughening and stress relief can be reduced. However, if the molten salt temperature is too high and the treatment time is too short, the proportion of quenched bainite in the microstructure is relatively small, and there is a risk of forming soft-phase structures during the subsequent heating and isothermal process, which will affect the wire rod strength and microstructure control.

[0055] From the comparison results of Example 2 and Comparative Example 4, it can be seen that if the molten salt temperature of the front-section molten salt is lower and the treatment time is longer, it can promote the full transformation of the wire rod from high-temperature austenite to quenched bainite and improve the matrix strength. However, if the molten salt temperature is too low and the treatment time is too long, there is a risk of generating low-temperature abnormal structures when cooling to the martensite phase region, affecting the microstructure uniformity, increasing the production energy consumption and insufficient internal stress elimination.

[0056] From the comparison results of Example 3 and Comparative Example 5, it can be seen that the higher the molten salt temperature and the longer the treatment time of the latter-stage molten salt, the more thermal power can be provided, which helps to fully release the internal stress of the wire rod, improve the plasticity of the wire rod, and promote the full and uniform precipitation of microalloy carbides. However, if the molten salt temperature is too high and the treatment time is too long, there is a risk of excessive softening, resulting in a decrease in the load-bearing capacity of the wire rod and coarsening of alloy carbides, thus losing the strength and plasticity performance.

[0057] From the comparison results of Example 3 and Comparative Example 6, it can be seen that the lower the molten salt temperature of the latter-stage molten salt, the more conducive it is to the dispersed precipitation of alloy carbides. However, if the molten salt temperature is too low and the treatment time is too short, the residual stress of the structure is relatively high, and the alloy carbides do not have enough time to fully precipitate, and the stability of the precipitated phase is poor, which will cause the core to be hard and brittle, affecting the plasticity and tissue uniformity of the wire rod.

[0058] From the comparison results of Example 4 and Comparative Example 7, it can be seen that slow cooling with the roller table cover opened is better than air cooling in controlling the slow cooling of the wire rod, promoting the further toughening of the wire rod structure, improving the softening effect of the wire rod, avoiding stress increase caused by too fast cooling, and at the same time, compared with fully closing the heat preservation cover, it can also promote the rapid offline of the wire rod, improving the production rhythm and efficiency.

[0059] The series of detailed descriptions listed above are only specific descriptions of the feasible embodiments of the present invention, and they are not intended to limit the protection scope of the present invention. Any equivalent embodiments or changes made without departing from the technical spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A manufacturing method of a 1150MPa grade high-strength tool steel wire rod, characterized in that, The manufacturing method includes: After the steel billet is rolled and spun into wire rods at a wire-spinning temperature of ≥905°C, it undergoes on-line molten salt low-temperature quenching and isothermal treatment. The wire rods are first treated with molten salt in the front section, so that the wire rods enter the lower bainite phase region from the high-temperature austenite state at a cooling rate of ≥35°C / s, forming a structure mainly composed of quenched bainite. Then, they undergo molten salt heating and isothermal tempering and toughening stress relief treatment in the rear section. Finally, they are slowly cooled with the cover opened on the roller table to produce wire rods with a microstructure including tempered bainite and ferrite. The chemical composition and mass percentage of the wire rods include: C: 0.41% - 0.46%, Si: 0.10% - 0.18%, Mn: 0.45% - 0.60%, Cr: 0.52% - 0.60%, Nb: 0.015% - 0.025%, V: 0.025% - 0.035%, P≤0.015%, S≤0.015%, and the rest is Fe and unavoidable impurities.

2. The manufacturing method of the 1150 MPa grade high-strength tool steel wire rod according to claim 1, characterized in that, Before rolling, the soaking temperature of the heating furnace is controlled at 1100 - 1150°C, and the residence time in the furnace is 100 - 150 min.

3. The manufacturing method of the 1150MPa grade high-strength tool steel wire rod according to claim 1, characterized in that, During rolling, the initial rolling temperature is controlled at 1020 - 1060°C, the final rolling temperature is 915 - 950°C, and the final rolling reduction is 25% - 30%.

4. The manufacturing method of the 1150 MPa grade high-strength tool steel wire rod according to claim 1, characterized in that, During wire-spinning, the wire-spinning temperature is controlled at 905 - 940°C.

5. The manufacturing method of the 1150 MPa grade high-strength tool steel wire rod according to claim 1, characterized in that, The molten salt temperature of the front-section molten salt is 270 - 320°C, and the treatment time is 40 - 65 s; the molten salt temperature of the rear-section molten salt is 570 - 595°C, and the treatment time is 120 - 280 s.

6. The manufacturing method of the 1150MPa grade high-strength tool steel wire rod according to claim 5, characterized in that, The molten salt circulation volume of the front-section molten salt is 460 - 760 t / h, and the molten salt temperature rise ≤8°C; the molten salt circulation volume of the rear-section molten salt is 350 - 440 t / h.

7. The manufacturing method of the 1150 MPa grade high-strength tool steel wire rod according to claim 5, characterized in that, During slow cooling with the cover opened on the roller table, the wire rods are slowly cooled at a cooling rate of 0.7 - 1.2°C / s to below 300°C.

8. A 1150 MPa grade high-strength tool steel wire rod, characterized in that, The wire rods are manufactured by the manufacturing method of 1150 MPa grade high-strength tool steel wire rods described in any one of claims 1 - 7.

9. The wire rod of 1150MPa grade high-strength tool steel according to claim 8, characterized in that, The volume percentage of the tempered bainite ≥96%.

10. The wire rod of 1150 MPa grade high-strength tool steel according to claim 8, characterized in that, The diameter of the wire rods is 5.5 - 10 mm, the tensile strength is 1050 - 1100 MPa, the cross-sectional shrinkage rate is 59% - 64%, and the difference in mechanical properties within the same coil ≤33 MPa.

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