A 1350mpa grade high strength tool steel wire rod and a manufacturing method thereof

Abstract

The application relates to a 1350MPa-grade high-strength tool steel wire rod and a manufacturing method thereof, after high-Mn-Cr-V medium-high-carbon chemical component design rolling is performed to form the wire rod, and on-line molten salt mixed quenching isothermal treatment is performed, the wire rod is first controlled to enter a sorbite phase region from a high-temperature austenite state at a cold speed of greater than or equal to 30 DEG C / s, a quenched organization mainly formed of sorbite and residual austenite is formed, then isothermal tempering is performed on the quenched organization, residual austenite is converted into martensite, and then stress relieving treatment is performed, finally, after roller slow cooling, the wire rod is prepared, the microstructure of the wire rod includes isothermal sorbite, tempered martensite and ferrite, the strength and plasticity matching of the wire rod can be improved, the tensile strength can reach 1230-1380MPa, the area reduction can be 36%-41%, after cold working, the wire rod can be directly processed into a part, and the tool steel production energy consumption, cost reduction and efficiency improvement are favorable.

Description

Technical Field

[0001] The present invention belongs to the technical field of hot-rolled wire rods, and in particular relates to a 1350MPa grade high-strength tool steel wire rod and a manufacturing method thereof. Background Art

[0002] Tools, as indispensable auxiliary equipment for daily life and production, directly impact the equipment's installation efficiency and functional precision. High-quality tools require durability. Excellent strength, wear resistance, and toughness enhance tool durability. Therefore, existing tool steels, after being cold-formed from hot-rolled wire rods into blanks, often require heat treatment to adjust the tool's mechanical properties to meet operational requirements. This additional heat treatment step also leads to high production costs and energy consumption for tool steel, a problem that urgently needs to be addressed.

[0003] Existing hot-rolled tool steel wire rods are generally produced through alloying and Stelmor air cooling lines. The factors that restrict the improvement of their strength and cold working performance include:

[0004] (1) In order to improve the cold working performance of tool steel wire rod, the existing tool steel wire rod is usually a mixed structure composed of pearlite and ferrite. For example, patent CN107497867A discloses a Stelmor cooling method for improving the uniformity of tool steel 6150 wire rod, which adopts a C-Si-Mn-Cr-V composition design, combined with slow cooling by Stelmor hood cooling after low-temperature spinning, to produce a sorbite structure, achieving a tensile strength of 950~1050MPa and a surface reduction rate of ≥40%. However, on the one hand, the strength performance of the pearlite soft phase is insufficient. In order to further improve the strength of the wire rod, continuing to increase the carbon or alloy component content will increase the difficulty of controlling the air cooling line, which is limited by the minimum cooling capacity and temperature control stability of the air cooling line. The plasticity of the wire rod is limited, and some overcooled positions are prone to form abnormal structures such as brittle martensite, which destroys the uniformity of the structure and the cold working performance, and leads to cracking problems during cold forming processing. On the other hand, due to continuous cooling, the wire rod is in a low-temperature state after phase transformation incubation, and the structure retains large structural stress, resulting in insufficient plasticity of the wire rod. In order to further improve the plasticity of the wire rod, reducing the carbon or alloy content will increase the difficulty of refining the pearlite lamellar layer. Due to the limited maximum cooling capacity and temperature control stability of the air-cooling line, it will bring about a large strength loss, and increasing the air-cooling intensity will increase the risk of precipitation of abnormal structures. It is necessary to adjust the mechanical indicators of the tool through additional heat treatment after cold working, which will increase the energy consumption and cost of tool steel production and reduce efficiency.

[0005] (2) In order to improve the strength of tool steel wire rods, some wire rods are made of high alloy and Stelmor cooling line to form martensitic structure. For example, patent CN103436687A discloses a controlled cooling process for high alloy tool steel, which increases the martensite ratio by low temperature final rolling and rapid air cooling after wire drawing. However, on the one hand, due to the limitation of air cooling line controlled cooling, the required alloy component content is high, resulting in high material cost, and reducing the alloy content will affect the transformation of martensitic structure; on the other hand, martensite as a brittle structure has large distortion and dislocation density, and its brittleness will lead to greater plasticity. Loss affects the cold working performance and even causes brittle fracture during coiling and transportation, affecting the yield rate. For example, patent CN117051308B discloses a method for producing tool steel wire rod, which adopts strong air cooling + slow cooling after low-temperature wire drawing to produce bainite + martensite structure wire rod to improve the wire self-breakage. However, as the air cooling intensity increases, the temperature difference between the wind-receiving and wind-receiving sides of the wire rod and from the edge to the core will be further increased, resulting in uneven phase change of the structure. At the same time, the temperature of the wire rod is low after the phase change incubation, and large residual tissue stress will be lost, which will cause loss of plasticity and cold working performance and increase the risk of cold working cracking. Summary of the Invention

[0006] The present invention aims to solve at least one of the above-mentioned technical problems to a certain extent. The present invention provides a 1350MPa grade high-strength tool steel wire rod and a manufacturing method thereof, which can improve the strength-plasticity matching of the wire rod and can be directly processed into parts after cold forming, which is beneficial to energy consumption and cost reduction and efficiency improvement of tool steel production.

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

[0008] A method for manufacturing a 1350MPa grade high-strength tool steel wire rod, the manufacturing method comprising:

[0009] The steel billet is rolled and spun into a wire rod at a spinning temperature of ≥895°C, and then subjected to an online molten salt mixed quenching isothermal treatment. The wire rod is first controlled to enter the sorbite phase region from the high-temperature austenite state at a cooling rate of ≥30°C / s to form a quenched structure mainly composed of sorbite and retained austenite. The quenched structure is then isothermally tempered to transform the retained austenite into martensite and then subjected to toughening and stress relief treatment. Finally, the steel billet is slowly cooled on a roller to form a wire rod having a microstructure including isothermal sorbite, tempered martensite and ferrite. The chemical composition and mass percentage of the wire rod include: C: 0.58%-0.63%, Si: 0.25%-0.33%, Mn: 0.65%-0.70%, Cr: 0.65%-0.72%, V: 0.050%-0.060%, P≤0.015%, S≤0.015%, and the rest are Fe and unavoidable impurities.

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

[0011] (1) Carbon: As a carbide strengthening element and austenite forming element, the price of C is relatively low. With the increase of carbon content, carbon acts as the core diffusion medium of sorbite phase transformation, which can promote the refinement of pearlite lamellae to form a strong and tough sorbite structure. During high temperature tempering, the carbon in the retained austenite is concentrated to the grain boundary, which can increase the driving force of martensite phase transformation and provide sufficient carbon content for martensite transformation, giving the tool steel wire rod high strength and wear resistance. However, if the carbon content is too high, it will aggregate to form a network or coarse particles, which will aggravate the volume expansion and increase the internal stress during martensite transformation, causing the difficulty of isothermal tempering to increase, resulting in increased hardness and decreased toughness. Therefore, in order to meet the strength and wear resistance requirements of tool steel and control material costs, and at the same time facilitate the organization control of the wire rod in online molten salt mixed quenching isothermal treatment and improve the strength and toughness matching, the carbon content is appropriately increased, and the mass percentage of C is controlled to be 0.58%~0.63%.

[0012] (2) Silicon: Si is a strong ferrite-forming element that can inhibit grain coarsening during online molten salt mixed quenching isothermal treatment, reduce the diffusion coefficient of carbon in austenite, and is conducive to the refinement of layered troostite. It promotes the high dislocation density when the retained austenite transforms to martensite, improves the toughness of the tempered martensite, and is suitable for the wear resistance of tool steel. However, too high a silicon content will promote inclusions in the steel, reduce the toughness of the wire rod, reduce the plasticity and impact toughness of the material, and increase the deformation resistance of the tool steel wire rod during cold processing. Therefore, in order to adapt to the regulation of the microstructure of online molten salt mixed quenching isothermal treatment and improve the tempering stability of the wire rod, the mass percentage of Si is controlled to be 0.25%~0.33%.

[0013] (3) Manganese: Mn can increase the stability of austenite and the hardenability of wire rod, reduce the phase transformation temperature of austenite to ferrite and pearlite, make the isothermal treatment temperature range closer to the sorbite phase transformation zone, refine the sorbite layer spacing, and at the same time cooperate with the large undercooling of the line molten salt mixed quenching isothermal treatment to inhibit the formation of bainite and promote the transformation of retained austenite to martensite structure. However, when the Mn content is too high, it will promote the growth of austenite grains and form local manganese-rich areas, resulting in uneven structure or coarse martensite grains after quenching, requiring higher energy for stress release, affecting the impact toughness of wire rod. Therefore, in order to make C and Mn partition to produce martensite during the online molten salt mixed quenching isothermal treatment, improve the matrix strength and take into account the toughness of the material, the Mn content is appropriately increased, and the mass percentage of Mn is controlled to be 0.65%~0.70%.

[0014] (4) Chromium: As a carbide-forming element, Cr reduces the diffusion coefficient of carbon when dissolved in austenite, causing the phase transformation curve to shift to the right, broadening the formation temperature range of sorbite, and significantly improving the hardenability of steel. It is beneficial to inhibit the precipitation of ferrite and promote the direct transformation of retained austenite into martensite during rapid cooling, aggravating the lattice distortion and increasing the hardness. At the same time, chromium and carbon form high-hardness carbides that are evenly distributed in the sorbite and martensite matrices, which can improve the wear resistance and tempering softening resistance of tool steel wire rods and help maintain the matrix strength. However, too high Cr content will aggravate composition segregation and there is a risk of coarse and unevenly distributed carbides, which will increase the difficulty of controlling the uniformity of the organization, the difficulty of improving plasticity, and the brittleness of the tool. Therefore, in order to take into account the wear resistance requirements of tool steel and facilitate the control of the isothermal transformation of sorbite and the tempering process of martensite, the Cr content is appropriately increased, and the mass percentage of Cr is controlled to be 0.65%~0.72%.

[0015] (5) Vanadium: The V element forms high-melting-point carbonitrides, which pin the grain boundaries during the austenitization process and prevent the grains from growing. The fine austenite grains provide more nucleation sites for the sorbite phase transformation, promoting the uniform formation of lamellar sorbite. At the same time, the precipitation of fine dispersed carbides during the tempering process can produce a secondary hardening effect, making it easier for the retained austenite to transform into martensite through thermal activation in the isothermal stage, which plays a role in quickly improving the matrix strength. However, the cost of the V element is relatively high, and excessive addition is not conducive to controlling the cost of the wire rod. Therefore, based on the role of the V element, cost and manufacturing control, the mass percentage of V is controlled to be 0.050%~0.060%.

[0016] (6) Phosphorus and sulfur: P and S are impurity elements. The lower the better. Therefore, P is controlled to be ≤ 0.015% and S is controlled to be ≤ 0.015%.

[0017] The above-mentioned wire rod adopts the C-Si-Mn-Cr-V composition system, appropriately increases the C, Mn and Cr contents, and adds a trace amount of V, which can appropriately control the material cost and hardenability, and regulate the tempering stability, providing favorable conditions for making the lamellar sorbite finer, allowing the martensite transformation to proceed at a large undercooling degree, and reducing the strength loss of isothermal tempering toughening. On this basis, a higher spinning temperature, i.e., the quenching temperature, is selected to prepare the organization for increasing the undercooling degree, promoting the refinement of pearlite lamellae to form sorbite structure, and promoting the transformation of retained austenite to martensite. After spinning, the wire rod is directly put into the molten salt for online molten salt mixed quenching isothermal treatment without air cooling:

[0018] 1. Compared with the Stelmor air-cooled line, it is necessary to increase the alloy content and air-cooling intensity to promote the refinement of pearlite lamellae, but it brings about uneven organizational transformation and increased risks of abnormal organizational precipitation. On the one hand, the heat transfer coefficient of molten salt is significantly higher than that of air. The wire rod passing through the molten salt can control the wire rod to quickly enter the bainite phase region from the high-temperature austenite state, forming a bainite structure with finer interlamellar spacing, avoiding the formation of coarse pearlite lamellae that affect the matrix strength, and reducing the demand for wire rod hardenability. The alloy content of high-alloy tool steel wire rod can be appropriately reduced. On the other hand, the temperature of the bainite phase region is higher than that of the bainite phase region. When the wire rod passes through the molten salt, the molten salt covers the surface of the wire rod for uniform heat transfer. There is no temperature difference between the winded side and the winded side, or between the overlap and non-overlap. This can prevent some parts of the wire rod from entering the bainite phase region due to overcooling. The diffusion rate of carbon is reduced by a large cooling rate, which inhibits the bainite transformation and avoids affecting the martensite transformation.

[0019] 2. Compared with the Stelmor air-cooled line, it needs to control the martensite or bainite phase transformation in strong air cooling and slow cooling in the low temperature phase zone, but it brings problems such as uneven organizational transformation, high organizational brittleness and high stress. On the one hand, the wire rod forms a large degree of undercooling through a large cooling rate, and combined with the C, Mn partitioning and the hardenability of the wire rod, the austenite is more stable during the cooling process, which can inhibit the precipitation of ferrite and promote the direct transformation of retained austenite to martensite at high temperature, thereby improving the matrix strength, rather than slowly cooling to the low temperature phase zone to cause the formation of abnormal organizations such as upper bainite. On the other hand, the temperature of the bainite phase zone is higher than that of the low temperature phase zone. As the treatment time increases, the wire rod gradually transforms to isothermal treatment at molten salt temperature instead of continuous cooling, which can extend the time the wire rod is in the high temperature isothermal temperature range, promote isothermal tempering of bainite and martensite, reduce the dislocation density of martensite, transform the high hardness and brittle martensite organization into a toughened organization, reduce organizational stress, and avoid VC caused by unstable controlled cooling. The uneven precipitation can cooperate with the dispersed precipitation of carbides, maintain appropriate tempering stability, reduce strength loss, and finally the roller slow cooling treatment takes advantage of the high temperature state of the wire rod after it comes out of the molten salt to slowly cool down and continue the stress relief effect of the later isothermal stage of online molten salt mixed quenching to achieve uniform control of the organizational state and effectively improve the strength and plasticity matching of the wire rod.

[0020] Selecting an appropriate heating furnace soaking temperature and furnace time before rolling can promote the alloy components to fully melt into austenite, reduce component segregation, and avoid the coarse grains that affect rolling. In the preferred technical solution, before rolling, the heating furnace soaking temperature is controlled to be 1150~1190℃, and the furnace time is 130~186min.

[0021] Since the spinning temperature is relatively high, the restriction on the rolling temperature can be reduced. A higher initial rolling temperature is selected to reduce the deformation resistance of the steel billet and the load demand on the rolling line, thereby improving the rolling efficiency and reducing the risk of surface cracks. At the same time, the appropriate final rolling temperature and final rolling reduction are controlled to promote dynamic recrystallization during the final rolling process, refine the grains, increase the number of grain boundaries, and provide more nucleation sites for subsequent phase transformation. In the preferred technical solution, during the rolling, the initial rolling temperature is controlled to be 1025~1075℃, the final rolling temperature is controlled to be 905~935℃, and the final rolling reduction is controlled to be 23%~29%.

[0022] The spinning temperature can be further controlled during the spinning to avoid grain coarsening caused by excessively high spinning temperature. In a preferred technical solution, the spinning temperature is controlled to be 895-925°C during the spinning.

[0023] In the preferred technical solution, the online molten salt mixed quenching isothermal treatment is divided into a front-stage molten salt treatment and a rear-stage molten salt treatment. The molten salt circulation volume of the front-stage molten salt treatment is greater than the molten salt circulation volume of the rear-stage molten salt treatment. The front-stage molten salt treatment uses a larger molten salt circulation volume to control the molten salt temperature rise, promote the wire rod to quickly cool down to the sorbite phase region, and promote the refinement of the sorbite structure lamellar layer. The rear-stage molten salt treatment appropriately reduces the molten salt circulation volume to control the molten salt temperature rise, which can reduce production energy consumption and promote sufficient and uniform phase transformation and toughening of the structure.

[0024] The molten salt temperature of the front-stage molten salt treatment is in the sorbite phase region. The lower the molten salt temperature and the longer the treatment time, the more it can promote the transformation of austenite to sorbite structure and refine the spacing between sorbite lamellae. However, if the molten salt temperature is too low and the treatment time is too long, the austenite structure will transform too much into sorbite structure or even into bainite structure, which will affect the transformation of martensite structure, lose matrix strength and increase production energy consumption. On the contrary, the higher the molten salt temperature and the shorter the treatment time, the sorbite ratio in the structure can be reduced, so that more residual austenite can be transformed into martensite structure, thereby improving matrix strength. degree, reducing production energy consumption; but if the molten salt temperature is too high and the treatment time is too short, the wire rod will slowly pass through the pearlite phase region, which will affect the sorbite phase transformation and lamellar refinement, and lose the strength and plasticity. Therefore, the front-stage molten salt treatment can select appropriate molten salt temperature and treatment time to control the wire rod to quickly enter the sorbite phase region from the high-temperature austenite state, forming a quenching structure mainly composed of sorbite and retained austenite, and making organizational preparations for subsequent isothermal treatment. In the preferred technical solution, the molten salt temperature of the front-stage molten salt treatment is 560~595℃, and the treatment time is 150~200s.

[0025] The use of a larger molten salt circulation volume in the front-stage molten salt treatment can control the molten salt temperature rise and promote the refinement of the wire rod troostite lamellae, while avoiding excessive molten salt circulation volume that increases production energy consumption and affects austenite retention. In the preferred technical solution, the molten salt circulation volume of the front-stage molten salt treatment is 420~520t / h, and the molten salt temperature rise is ≤9°C.

[0026] The molten salt temperature of the latter molten salt treatment is in the high temperature range. The higher the molten salt temperature and the longer the treatment time, the more thermal power is provided to the quenched structure, the lattice distortion is relieved, the stress of the structure is released, and the matrix plasticity and the uniformity of the structure are improved. However, if the molten salt temperature is too high, the supercooling degree is weakened, the supercooling degree of the wire rod and the nucleation speed of the transformation of the retained austenite to martensite are affected, and the untransformed retained austenite becomes a soft phase, which loses the matrix strength. As the treatment time is too long, the steel is over-softened, the carbides are coarsened, the dispersion strengthening effect is weakened, and the plasticity is reduced due to the weakening of the grain boundaries, which will further lose the strength and plasticity. On the contrary, the lower the molten salt temperature, the more conducive it is to promote the transformation of the retained austenite to martensite. Providing more driving force for the precipitation of microalloy carbides can promote the dispersion and precipitation of carbides, slow down the stress release, and the shorter the treatment time, the lower the softening degree and production energy consumption. However, if the molten salt temperature is too low and the treatment time is too short, it is not conducive to the stress release of the organization, which will significantly lose the plasticity of the wire rod and is not conducive to the full precipitation of carbides, which will lose the matrix strength. Therefore, the post-softening molten salt treatment can select appropriate molten salt temperature and treatment time, and the residual austenite is transformed into martensite and then toughened to relieve stress, control the precipitation of carbides, and improve the strength-plasticity matching of the wire rod. In the preferred technical solution, the molten salt temperature of the post-molten salt treatment is 550~590℃, and the treatment time is 150~300s.

[0027] Appropriately reducing the molten salt circulation rate in the latter molten salt treatment can reduce production energy consumption, while controlling temperature fluctuations in the isothermal zone and improving the consistency of the transformation of retained austenite to martensite. In the preferred technical solution, the molten salt circulation rate in the latter molten salt treatment is 220~350t / h.

[0028] In the preferred technical solution, the roller slow cooling controls the wire rod to be slowly cooled to below 300°C at a cooling rate of 0.7~1°C / s. The roller slow cooling selects an appropriate cooling rate to prevent the wire rod from cooling too fast during the cooling process, which leads to increased stress. Since the temperature of the wire rod is relatively high after it leaves the molten salt, slow cooling can be used to promote further toughening of the wire rod structure and improve the softening effect of the wire rod, while avoiding the cooling rate being too slow to affect the offline speed.

[0029] A 1350MPa grade high-strength tool steel wire rod is manufactured by any one of the above-mentioned methods for manufacturing a 1350MPa grade high-strength tool steel wire rod.

[0030] The above-mentioned wire rod is designed with a medium-high carbon chemical composition of high Mn-Cr-V, and a trace amount of V is added to appropriately control the material cost. Combined with the online molten salt mixed quenching isothermal technology, it is made into a wire rod with a mixed structure composed mainly of isothermal troostite and tempered martensite, and a small amount of ferrite; compared with the air-cooled pearlite + ferrite tool steel wire rod, the interlamellar spacing of troostite is finer than that of pearlite, and has better strength and toughness. After tempering regulation, it is transformed into the intermediate transition state isothermal troostite that transforms to the spheroidized structure, with better plasticity. Combined with the strong and tough tempered martensite, it can significantly improve the matrix strength, make up for the strength loss caused by reducing the alloy component content, and have a more uniform phase. The distribution and interface are matched so as to save additional heat treatment after cold working and directly process into tool parts; compared with air-cooled martensite + bainite tool steel wire rod, isothermal sorbite has better cold working performance, and martensite has a higher dislocation density than bainite. After isothermal regulation and toughening to release stress, the strength characteristics of martensite can be retained, so that the tool has better wear resistance and changes the brittle characteristics. Combined with the dispersion and precipitation of carbides, the matching of strength and toughness is improved, which can not only avoid the brittle fracture temperature during coiling and transportation due to the brittleness of martensite, but also can be used to reduce the cracking risk of direct cold working, thereby improving the yield rate and production efficiency of tool steel and reducing production energy consumption and costs.

[0031] The higher the volume percentage of the isothermal troostite and the larger the interlamellar spacing, the easier it is to release tissue stress and increase the plasticity of the wire rod. In the preferred technical solution, the volume percentage of the isothermal troostite is 30%~35%, and the interlamellar spacing is 90~135nm.

[0032] The higher the volume percentage of the tempered martensite is, the higher the matrix strength is. In a preferred technical solution, the volume percentage of the tempered martensite is 62% to 67%.

[0033] In the preferred technical solution, the diameter of the wire rod is 6~9mm, the tensile strength is 1230~1380MPa, the cross-sectional shrinkage rate is 36%~41%, and the mechanical property same-circle difference is ≤35MPa. The wire rod diameter specification can be used for direct drawing or cold heading and other cold processing into screwdriver heads, punches, mold inserts and other small and medium-sized tool parts. The wire rod has high tensile strength, which can improve the performance of tool steel so that it can withstand greater impact loads. The wire rod has a high cross-sectional shrinkage rate and a low mechanical property same-circle difference, indicating that the wire rod has good plasticity and toughness and organizational consistency, which can reduce the risk of cracking during direct cold processing, improve the yield rate and production stability, and improve the tool's fracture resistance under impact conditions. At the same time, combined with the high strength characteristics, it can eliminate additional heat treatment after cold processing and directly process it into tool parts.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] (1) In view of the current situation that the existing tool steel wire rod is limited by the Stelmor air cooling line, the strength and plasticity are difficult to improve, the alloy content is large or the abnormal structure is difficult to control, the present invention controls the wire rod after spinning to quickly enter the sorbite phase region from the high-temperature austenite state through the design of high Mn-Cr-V chemical composition combined with the online molten salt mixed quenching isothermal technology, which can promote the refinement of the sorbite structure lamellae and form a structure mainly composed of sorbite and residual austenite. Then, the wire rod is controlled to be isothermal tempered in the high-temperature isothermal range of the quenched structure, which can control a large degree of undercooling combined with C, Mn and other distributions to promote the transformation of residual austenite into martensite and then toughening and stress relief treatment. Finally, it is slowly cooled through the roller to prevent stress increase and promote further toughening of the wire rod structure, which can achieve effective regulation of the microstructure and improve the strength and plasticity matching of the wire rod.

[0036] (2) Aiming at the current situation that the existing tool steel wire rod has insufficient strength and plasticity, and has abnormal structure, which leads to cracking during cold forming and high energy consumption of additional heat treatment process, the present invention appropriately increases the content of C, Mn and Cr, and adds a trace amount of V. The alloy content and material cost of the high alloy tool steel wire rod are lower. The wire rod includes a mixed structure composed mainly of isothermal troostite and tempered martensite, and a small amount of ferrite. Compared with the air-cooled pearlite + ferrite tool steel wire rod, it can significantly improve the matrix strength and make up for the strength loss caused by reducing the alloy component content. Compared with the air-cooled martensite + bainite tool steel wire rod, it can not only avoid the brittle fracture temperature during the coiling and transportation process caused by the brittleness of martensite, but also can be used to reduce the cracking risk of direct cold working, effectively improve the strength and plasticity matching of the wire rod, and can achieve a tensile strength of 1230~1380MPa and a cross-sectional shrinkage rate of 36%~41%. After cold forming, it can be directly processed into parts for use in the manufacture of high-strength tool steel and other application fields, which is beneficial to the energy consumption and cost reduction and efficiency improvement of tool steel production. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0038] Figure 1 is a metallographic structure diagram of Example 1 of the present invention;

[0039] Figure 2 This is the metallographic structure diagram of Example 2 of the present invention. DETAILED DESCRIPTION

[0040] The embodiments described below with reference to the accompanying drawings are exemplary and are only for illustration and do not limit the description of the features and characteristics of the present invention. They are intended to propose the best way to implement the present invention, are intended to explain the present invention, and are sufficient to enable those skilled in the art to practice the present invention, but should not be understood as limiting the scope of the present invention, which is defined solely by the appended claims. The wire rods obtained in the following embodiments and comparative examples are subjected to microstructure and performance testing, including: tensile testing using "GB-T 228.1-2021 Metallic Materials Tensile Testing Part 1: Room Temperature Test Method" to obtain tensile strength and cross-sectional reduction rate; microstructure testing is performed in accordance with the metal microstructure testing method of GB / T13298 standard; mechanical property same-turn difference test method: 2 turns of wire rod are taken 5m away from the end of the coil, and each turn of wire rod is divided into 8 equal sections with the overlap area as the base point. 1 tensile specimen is taken from each section, and the extreme difference in strength of the tensile specimens after the tensile test is the mechanical property same-turn difference. Example 1:

[0041] A preferred embodiment of the method for manufacturing 1350MPa grade high-strength tool steel wire rod of the present invention comprises the following chemical compositions and mass percentages: C: 0.59%, Si: 0.25%, Mn: 0.65%, Cr: 0.67%, V: 0.06%, P: 0.014%, S: 0.014%, and the remainder being Fe and unavoidable impurities; the manufacturing method is manufactured according to the process flow of rolling → spinning → online molten salt mixed quenching isothermal treatment → roller slow cooling → coiling, specifically:

[0042] The rolling process is used to heat a steel billet with a specification of 180mm×180mm through a heating furnace to achieve a high-temperature steel billet with rollable plasticity, promote the homogenization of alloy composition, and the heating furnace is controlled according to a three-stage temperature rise program of a preheating section, a heating section and a soaking section. The high-temperature steel billet is rolled into a wire rod with a diameter of 6mm through a rolling line. Appropriate rolling temperature and reduction are selected to increase the rolling speed, promote dynamic recrystallization during the final rolling process, and refine the grains. Specifically, the soaking temperature of the heating furnace is controlled to be 1150°C, the time in the furnace is 186min, the initial rolling temperature is 1025°C, the final rolling temperature is 905°C, and the final rolling reduction is 29%; the wire-spinning process is used to convert the wire rod exiting the rolling line into a wire rod through a wire-spinning mechanism, and the wire rod is spread on a roller and transported along the roller, so that the wire rod is in a high-temperature austenite state and is prepared for tissue quenching with a higher quenching temperature; specifically, the wire-spinning temperature is controlled to be 895°C.

[0043] The online molten salt mixed quenching isothermal treatment process adopts a two-stage salt bath tank with molten salt inside. The wire rod after spinning is conveyed by a roller through the first stage salt bath tank for the front stage molten salt treatment, so that the wire rod is cooled at a cooling rate of 35°C / s, entering the sorbite phase region from the high-temperature austenite state, and part of the austenite is transformed into sorbite with finer interlamellar spacing. The quenching is performed to form a quenched structure mainly composed of sorbite and retained austenite. After that, the wire rod is conveyed by a roller through the second stage salt bath tank for the rear stage molten salt treatment, thereby reducing the molten salt circulation amount. The wire rod is controlled to be isothermally tempered in the high-temperature isothermal range to quench the structure, promote the transformation of retained austenite into martensite and then toughen and relieve stress with a large degree of undercooling, control the dispersion and precipitation of carbides, and improve the strength and plasticity matching of the wire rod. Specifically: the molten salt temperature of the front-stage molten salt treatment is 560℃, the treatment time is 200s, the molten salt circulation rate is 420t / h, and the molten salt temperature rise is ≤9℃; the molten salt temperature of the rear-stage molten salt treatment is 588℃, the treatment time is 152s, and the molten salt circulation rate is 220t / h.

[0044] The roller slow cooling process adopts the method of controlling the opening of the heat preservation cover, and the wire rod conveyed by the conveyor roller through the second salt bath tank is slowly cooled through the heat preservation cover to prevent the wire rod from cooling too fast during the cooling process, which leads to an increase in stress, and promotes further toughening of the wire rod structure, thereby improving the softening effect of the wire rod until it is coiled. Specifically: the wire rod is controlled to slowly cool to 293°C at a cooling rate of 1°C / s; the coiling process is used to coil the wire rod into a coil through a coiling drum, and the finished wire rod is obtained after packaging and storage. Its metallographic structure diagram is as follows Figure 1 shown.

[0045] Comparative Example 1:

[0046] A method for manufacturing wire rod, which differs from that of Example 1 in that: the manufacturing method is manufactured according to the process flow of rolling → spinning → Stelmor air cooling line → coiling, specifically: in the rolling process, the heating furnace soaking temperature is controlled to 1080°C, the furnace time is 200 minutes, the initial rolling temperature is 910°C, the final rolling temperature is 825°C, and the spinning temperature is controlled to be 810°C. The Stelmor air cooling line adopts a closed insulation cover, and the wire rod enters the insulation cover and is cooled to 295°C at a rate of 2.9°C / s, and is collected by a coiling drum to obtain a finished wire rod.

[0047] Comparative Example 2:

[0048] A method for manufacturing a wire rod, which differs from Example 1 in that: the soaking temperature of the heating furnace is controlled to 1080°C, the time in the furnace is 200 minutes, the initial rolling temperature is 915°C, the final rolling temperature is 835°C, the spinning temperature is controlled to be 815°C, the wire rod is treated with molten salt in the front section and cooled at a cooling rate of 28°C / s to obtain a finished wire rod. Example 2:

[0049] A preferred embodiment of the method for manufacturing the 1350MPa grade high-strength tool steel wire rod of the present invention comprises the following chemical compositions and mass percentages: C: 0.58%, Si: 0.28%, Mn: 0.70%, Cr: 0.69%, V: 0.05%, P: 0.014%, S: 0.014%, and the remainder being Fe and unavoidable impurities; the manufacturing method is manufactured according to the process flow of rolling → spinning → online molten salt mixed quenching isothermal treatment → roller slow cooling → coiling, specifically:

[0050] The rolling process is used to heat a steel billet with a specification of 180mm×180mm through a heating furnace to achieve a high-temperature steel billet with rollable plasticity, promote the homogenization of alloy composition, and the heating furnace is controlled according to a three-stage temperature rise program of a preheating section, a heating section, and a soaking section. The high-temperature steel billet is rolled into a wire rod with a diameter of 7mm through a rolling line. Appropriate rolling temperature and reduction are selected to increase the rolling speed, promote dynamic recrystallization during the final rolling process, and refine the grains. Specifically, the soaking temperature of the heating furnace is controlled to be 1165°C, the furnace time is 165min, the initial rolling temperature is 1045°C, the final rolling temperature is 915°C, and the final rolling reduction is 27.5%; the wire-spinning process is used to convert the wire rod exiting the rolling line into a wire rod through a wire-spinning mechanism, and the wire rod is spread on a roller and transported along the roller, so that the wire rod is in a high-temperature austenite state and is prepared for tissue quenching with a higher quenching temperature; specifically, the wire-spinning temperature is controlled to be 905°C.

[0051] The online molten salt mixed quenching isothermal treatment process adopts a two-stage salt bath tank with molten salt inside. The wire rod after spinning is conveyed by a roller through the first salt bath tank for the front-stage molten salt treatment, so that the wire rod is cooled at a cooling rate of 34°C / s, entering the sorbite phase region from the high-temperature austenite state, and part of the austenite is transformed into sorbite with finer interlamellar spacing. The quenching is performed to form a quenched structure mainly composed of sorbite and retained austenite. After that, the wire rod is conveyed by a roller through the second salt bath tank for the rear-stage molten salt treatment, thereby reducing the molten salt circulation amount. The wire rod is controlled to be isothermally tempered in the high-temperature isothermal range to quench the structure, promote the transformation of retained austenite into martensite and then toughen and relieve stress with a large degree of undercooling, control the dispersion and precipitation of carbides, and improve the strength and plasticity matching of the wire rod. Specifically: the molten salt temperature of the front-stage molten salt treatment is 572°C, the treatment time is 182s, the molten salt circulation rate is 445t / h, and the molten salt temperature rise is ≤9°C; the molten salt temperature of the rear-stage molten salt treatment is 576°C, the treatment time is 195s, and the molten salt circulation rate is 270t / h.

[0052] The roller slow cooling process adopts the method of controlling the opening of the heat preservation cover, and the wire rod conveyed by the conveyor roller through the second salt bath tank is slowly cooled through the heat preservation cover to prevent the wire rod from cooling too fast during the cooling process, which leads to an increase in stress, and promotes further toughening of the wire rod structure, thereby improving the softening effect of the wire rod until it is coiled. Specifically: the wire rod is controlled to slowly cool to 295°C at a cooling rate of 0.95°C / s; the coiling process is used to coil the wire rod into a coil through a coiling drum, and the finished wire rod is obtained after packaging and storage. Its metallographic structure diagram is as follows Figure 2 shown.

[0053] Comparative Example 3:

[0054] A method for manufacturing wire rod, which differs from Example 2 in that: the wire rod is subjected to a front-stage molten salt treatment and cooled at a cooling rate of 29°C / s, the molten salt temperature of the front-stage molten salt treatment is 600°C, and the treatment time is 100s to obtain a finished wire rod.

[0055] Comparative Example 4:

[0056] A method for manufacturing wire rod, which differs from Example 2 in that: the wire rod is subjected to a front-stage molten salt treatment and cooled at a cooling rate of 37°C / s, the molten salt temperature of the front-stage molten salt treatment is 540°C, and the treatment time is 220s to obtain a finished wire rod. Example 3:

[0057] A preferred embodiment of the method for manufacturing 1350MPa grade high-strength tool steel wire rod of the present invention comprises the following chemical compositions and mass percentages: C: 0.62%, Si: 0.33%, Mn: 0.69%, Cr: 0.65%, V: 0.051%, P: 0.015%, S: 0.015%, and the remainder being Fe and unavoidable impurities; the manufacturing method is manufactured according to the process flow of rolling → spinning → online molten salt mixed quenching isothermal treatment → roller slow cooling → coiling, specifically:

[0058] The rolling process is used to heat a steel billet with a specification of 180mm×180mm through a heating furnace to achieve a high-temperature steel billet with rollable plasticity, promote the homogenization of alloy composition, and the heating furnace is controlled according to a three-stage temperature rise program of a preheating section, a heating section and a soaking section. The high-temperature steel billet is rolled into a wire with a diameter of 8mm through a rolling line. Appropriate rolling temperature and reduction are selected to increase the rolling speed, promote dynamic recrystallization during the final rolling process, and refine the grains. Specifically, the soaking temperature of the heating furnace is controlled to be 1180°C, the time in the furnace is 140min, the initial rolling temperature is 1060°C, the final rolling temperature is 925°C, and the final rolling reduction is 25%; the wire-spinning process is used to convert the wire exiting the rolling line into a wire rod through a wire-spinning mechanism, and the wire rod is spread on a roller and transported along the roller, so that the wire rod is in a high-temperature austenite state and is prepared for tissue quenching with a higher quenching temperature; specifically, the wire-spinning temperature is controlled to be 915°C.

[0059] The online molten salt mixed quenching isothermal treatment process adopts a two-stage salt bath tank with molten salt inside. The wire rod after spinning is conveyed by a roller through the first stage salt bath tank for the front stage molten salt treatment, so that the wire rod is cooled at a cooling rate of 33°C / s, entering the sorbite phase region from the high-temperature austenite state, and part of the austenite is transformed into sorbite with finer interlamellar spacing. The quenching forms a quenched structure mainly composed of sorbite and retained austenite. After that, the wire rod is conveyed by a roller through the second stage salt bath tank for the rear stage molten salt treatment, thereby reducing the molten salt circulation amount. The wire rod is controlled to be isothermally tempered in the high-temperature isothermal range to quench the structure, promote the transformation of retained austenite into martensite and then toughen and relieve stress with a large degree of undercooling, control the dispersion and precipitation of carbides, and improve the strength and plasticity matching of the wire rod. Specifically: the molten salt temperature of the front-stage molten salt treatment is 582°C, the treatment time is 167s, the molten salt circulation rate is 482t / h, and the molten salt temperature rise is ≤9°C; the molten salt temperature of the rear-stage molten salt treatment is 563°C, the treatment time is 244s, and the molten salt circulation rate is 310t / h.

[0060] The roller slow cooling process adopts the method of controlling the opening of the insulation cover, and the wire rod transported by the conveyor roller through the second salt bath tank is slowly cooled through the insulation cover to prevent the wire rod from cooling too fast during the cooling process, thereby increasing the stress, promoting further toughening of the wire rod structure, and improving the softening effect of the wire rod until it is coiled. Specifically: the wire rod is controlled to slowly cool to 297°C at a cooling rate of 0.8°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 storage.

[0061] Comparative Example 5:

[0062] A method for manufacturing a wire rod, which differs from the manufacturing method of Example 3 in that the molten salt temperature of the latter molten salt treatment is 595° C., the treatment time is 320 s, and the finished wire rod is obtained.

[0063] Comparative Example 6:

[0064] A method for manufacturing a wire rod, which differs from the manufacturing method of Example 3 in that the molten salt temperature of the latter molten salt treatment is 540° C., the treatment time is 110 s, and the finished wire rod is obtained. Example 4:

[0065] A preferred embodiment of the method for manufacturing 1350MPa grade high-strength tool steel wire rod of the present invention comprises the following chemical compositions and mass percentages: C: 0.63%, Si: 0.31%, Mn: 0.68%, Cr: 0.72%, V: 0.051%, P: 0.014%, S: 0.014%, and the remainder being Fe and unavoidable impurities; the manufacturing method is manufactured according to the process flow of rolling → spinning → online molten salt mixed quenching isothermal treatment → roller slow cooling → coiling, specifically:

[0066] The rolling process is used to heat a steel billet with a specification of 180mm×180mm through a heating furnace to achieve a high-temperature steel billet with rollable plasticity, promote the homogenization of alloy composition, and the heating furnace is controlled according to a three-stage temperature rise program of a preheating section, a heating section and a soaking section. The high-temperature steel billet is rolled into a wire rod with a diameter of 9mm through a rolling line. Appropriate rolling temperature and reduction are selected to increase the rolling speed, promote dynamic recrystallization during the final rolling process, and refine the grains. Specifically, the soaking temperature of the heating furnace is controlled to be 1190°C, the time in the furnace is 130min, the initial rolling temperature is 1075°C, the final rolling temperature is 935°C, and the final rolling reduction is 23%; the wire-spinning process is used to convert the wire rod exiting the rolling line into a wire rod through a wire-spinning mechanism, and the wire rod is spread on a roller and transported along the roller, so that the wire rod is in a high-temperature austenite state and is prepared for tissue quenching with a higher quenching temperature; specifically, the wire-spinning temperature is controlled to be 925°C.

[0067] The online molten salt mixed quenching isothermal treatment process adopts a two-stage salt bath tank with molten salt inside. The wire rod after spinning is conveyed by a roller through the first stage salt bath tank for the front stage molten salt treatment, so that the wire rod is cooled at a cooling rate of 33°C / s, entering the sorbite phase region from the high-temperature austenite state, and part of the austenite is transformed into sorbite with finer interlamellar spacing. The quenching forms a quenched structure mainly composed of sorbite and retained austenite. After that, the wire rod is conveyed by a roller through the second stage salt bath tank for the rear stage molten salt treatment, thereby reducing the molten salt circulation amount. The wire rod is controlled to be isothermally tempered in the high-temperature isothermal range to quench the structure, promote the transformation of retained austenite into martensite and then toughen and relieve stress with a large degree of undercooling, control the dispersion and precipitation of carbides, and improve the strength and plasticity matching of the wire rod. Specifically: the molten salt temperature of the front-stage molten salt treatment is 594°C, the treatment time is 153s, the molten salt circulation rate is 520t / h, and the molten salt temperature rise is ≤9°C; the molten salt temperature of the rear-stage molten salt treatment is 551°C, the treatment time is 295s, and the molten salt circulation rate is 350t / h.

[0068] The roller slow cooling process adopts the method of controlling the opening of the insulation cover, and the wire rod transported by the conveyor roller through the second salt bath tank is slowly cooled through the insulation cover to prevent the wire rod from cooling too fast during the cooling process, thereby increasing the stress, promoting further toughening of the wire rod structure, and improving the softening effect of the wire rod until it is coiled. Specifically: the wire rod is controlled to slowly cool to 298°C at a cooling rate of 0.7°C / s; the coiling process is used to coil the wire rod into a coil through a coiling drum, and the finished wire rod is obtained after packaging and storage.

[0069] Comparative Example 7:

[0070] A method for manufacturing a wire rod, which differs from Example 4 in that: the manufacturing method is manufactured according to a process flow of rolling → spinning → online molten salt mixed quenching isothermal treatment → air cooling → coiling. Specifically: the air cooling process uses a wire rod transported by a conveyor roller through a second salt bath tank to naturally cool in the air. The wire rod is cooled to 295°C at a cooling rate of 2.1°C / s to obtain a wire rod. The wire rod has a tensile strength of 1391 MPa, a cross-sectional shrinkage rate of 31%, and a mechanical property difference of 47 MPa.

[0071] The structure and performance of the wire rods obtained in Examples 1 to 4 and Comparative Examples 1 to 6 were tested, and the comparative results are shown in Table 1 below:

[0072] Table 1. Comparison of microstructure and properties of different wire rod compositions and manufacturing methods

[0073]

[0074] In the above table, the interlamellar spacing of comparative example 1 is the interlamellar spacing of pearlite, and the interlamellar spacing of other examples is the interlamellar spacing of isothermal sorbite. From the comparison results of Example 1 and comparative example 1, it can be seen that C and Cr, as carbide strengthening elements and austenite forming elements, often weaken the strengthening effect due to the uncontrollable cooling rate during the air-cooling phase transformation process, and cause the generation of abnormal tissues such as martensite. Although the Stelmor air-cooling line adopts heat preservation cooling, it will also affect the refinement of pearlite lamellae, resulting in strength loss, insufficient plasticity, and large fluctuations in mechanical properties. The present invention controls the wire rod after spinning to quickly cool from high temperature by combining the high Mn-Cr-V chemical composition design with the online molten salt mixed quenching isothermal technology. The austenite state enters the sorbite phase region, which can promote the refinement of the sorbite structure lamellae and form a structure mainly composed of sorbite and retained austenite. The wire rod is then controlled to perform isothermal tempering on the quenched structure in the high-temperature isothermal range. The large degree of supercooling can be controlled in combination with the distribution of C, Mn, etc. to promote the transformation of retained austenite into martensite and then toughening and stress relief treatment, thereby effectively improving the matrix strength and plasticity. It can be seen from the results of Examples 1 to 4 that the wire rod can achieve a tensile strength of 1230 to 1380 MPa and a cross-sectional reduction rate of 36% to 41%. It is used in application fields such as the manufacture of high-strength tool steel. After cold working and forming, it can be directly processed into parts, which is beneficial to energy consumption, cost reduction and efficiency improvement in tool steel production.

[0075] From the comparison results of Example 1 and Comparative Example 2, it can be seen that the selection of a higher spinning temperature, i.e., the quenching temperature, can make organizational preparations for increasing the degree of supercooling, promoting the refinement of pearlite lamellae to form sorbite structure, and promoting the transformation of retained austenite to martensite. At the same time, it can reduce the restriction on the rolling temperature, which is beneficial to improving the rolling efficiency and reducing the wear on the rolling line.

[0076] From the comparison results of Example 2 and Comparative Example 3, it can be seen that the molten salt temperature of the front-stage molten salt treatment is in the sorbite phase region. The higher the molten salt temperature and the shorter the treatment time, the sorbite proportion in the structure can be reduced, so that more residual austenite can be transformed into martensite structure, the matrix strength is improved, and the production energy consumption is reduced; but if the molten salt temperature is too high and the treatment time is too short, the wire rod slowly passes through the pearlite phase region, which will affect the sorbite phase transformation and lamellar refinement, lose the sorbite strength, increase the martensite transformation, increase the difficulty of softening, and affect the plasticity of the wire rod.

[0077] From the comparison results of Example 2 and Comparative Example 4, it can be seen that the lower the molten salt temperature and the longer the treatment time of the front-stage molten salt treatment, the transformation of austenite to sorbite structure can be promoted and the spacing between sorbite lamellae can be refined. However, if the molten salt temperature is too low and the treatment time is too long, the austenite structure will transform too much to the sorbite structure, which will affect the transformation of martensite structure, lose matrix strength and increase production energy consumption.

[0078] From the comparison results of Example 3 and Comparative Example 5, it can be seen that the molten salt temperature of the latter molten salt treatment is in the high temperature range. The higher the molten salt temperature and the longer the treatment time, the more beneficial it is to provide more thermal power to the quenched structure, promote the alleviation of lattice distortion, release of tissue stress, and improve the matrix plasticity and tissue uniformity. However, if the molten salt temperature is too high, the supercooling will be weakened, and the martensitic transformation will be affected. As the treatment time is too long, excessive softening and carbide coarsening will occur, the dispersion strengthening effect will be weakened, and the strong and plastic properties will be lost.

[0079] 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 molten salt treatment, the more conducive it is to promoting the transformation of retained austenite to martensite, providing more driving force for the precipitation of microalloy carbides. However, if the molten salt temperature is too low, the stress release tends to slow down. As the treatment time is too short, it is not conducive to the stress release of the organization, which will significantly lose the plasticity of the wire rod, is not conducive to the full precipitation of carbides, and will lose the matrix strength.

[0080] From the comparison results of Example 4 and Comparative Example 7, it can be seen that slow roller cooling can prevent the wire rod from cooling too fast during the cooling process, which leads to increased stress. Slow cooling is used to promote further toughening of the wire rod structure and improve the softening effect of the wire rod.

[0081] The series of detailed descriptions listed above are only specific descriptions of feasible embodiments of the present invention. They are not intended to limit the scope of protection of the present invention. Any equivalent embodiments or changes that do not deviate from the technical spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for manufacturing 1350MPa grade high strength tool steel wire rod, characterized in that: The manufacturing method includes: The steel billet is rolled and spun into wire rod at a spinning temperature of ≥895°C, and then subjected to online molten salt mixed quenching isothermal treatment. The online molten salt mixed quenching isothermal treatment is divided into a front-stage molten salt treatment and a rear-stage molten salt treatment. The molten salt circulation amount of the front-stage molten salt treatment is greater than the molten salt circulation amount of the rear-stage molten salt treatment. The wire rod is first controlled to undergo the front-stage molten salt treatment and enter the sorbite phase region from the high-temperature austenite state at a cooling rate of ≥30°C / s to form a quenching structure mainly composed of sorbite and retained austenite. The molten salt temperature of the front-stage molten salt treatment is 560~595°C, and the treatment time is 150~200s. The quenching structure is then isothermally tempered in the rear-stage molten salt treatment to transform the retained austenite into martensite for toughening and stress relief. The wire rod is subjected to roller cooling, wherein the molten salt temperature of the latter molten salt treatment is 550-590°C, the treatment time is 150-300s, and the wire rod is slowly cooled by a roller. The roller cooling controls the wire rod to be slowly cooled to below 300°C at a cooling rate of 0.7-1°C / s, and is made into a wire rod having a microstructure including isothermal troostite, tempered martensite and ferrite. The chemical composition and mass percentage of the wire rod include: C: 0.58%-0.63%, Si: 0.25%-0.33%, Mn: 0.65%-0.70%, Cr: 0.65%-0.72%, V: 0.050%-0.060%, P≤0.015%, S≤0.015%, and the rest are Fe and unavoidable impurities.

2. The method for manufacturing 1350 MPa grade high strength tool steel wire rod according to claim 1, characterized in that: Before the rolling, the soaking temperature of the heating furnace is controlled to be 1150-1190° C., and the soaking time in the furnace is 130-186 minutes.

3. The method for manufacturing 1350 MPa grade high strength tool steel wire rod according to claim 1, characterized in that: During the rolling, the initial rolling temperature is controlled to be 1025-1075° C., the final rolling temperature is controlled to be 905-935° C., and the final rolling reduction is controlled to be 23%-29%; during the wire drawing, the wire drawing temperature is controlled to be 895-925° C.

4. The method for manufacturing 1350 MPa grade high strength tool steel wire rod according to claim 1, characterized in that: The molten salt circulation rate of the front-stage molten salt treatment is 420~520t / h, and the molten salt temperature rise is ≤9°C; the molten salt circulation rate of the back-stage molten salt treatment is 220~350t / h.

5. A 1350MPa grade high strength tool steel wire rod, characterized in that: The wire rod is manufactured by the manufacturing method of 1350MPa grade high-strength tool steel wire rod according to any one of claims 1 to 4.

6. The 1350 MPa grade high strength tool steel wire rod according to claim 5, characterized in that: The volume percentage of the isothermal troostite is 30% to 35%, and the interlamellar spacing is 90 to 135 nm; the volume percentage of the tempered martensite is 62% to 67%.

7. The 1350 MPa grade high strength tool steel wire rod according to claim 5, characterized in that: The diameter of the wire rod is 6-9 mm, the tensile strength is 1230-1380 MPa, the cross-sectional shrinkage rate is 36%-41%, and the mechanical property difference within the same circle is ≤35 MPa.

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