1400mpa grade high strength tool steel wire rod and method of manufacturing the same

Abstract

The present application relates to a kind of 1400MPa grade high-strength tool steel wire rod and its manufacturing method, after rolling spinning as wire rod using Cr-V chemical composition design, through on-line molten salt mixed quenching isothermal treatment, first control wire rod with ≥32 ℃ / s cold speed from high temperature austenite state into sorbite phase region, promote part of austenite to sorbite organization transformation, form the quenching organization mainly with residual austenite, then isothermal tempering is carried out to quenching organization, after residual austenite is transformed into martensite, toughening stress relief treatment, finally through roller slow cooling, be made into wire rod with microstructure including isothermal sorbite, tempered martensite and ferrite, can control material cost appropriately, give consideration to wire rod cold working performance and high-strength characteristics, reach the tensile strength of product is 1370~1420MPa, reduction of area is 35~40%, so as to remove the heat treatment process after tool steel cold working, reduce tool steel production energy consumption and cost, improve production efficiency.

Description

Technical Field

[0001] The present invention belongs to the technical field related to hot-rolled wire rods, and specifically relates to a 1400MPa grade high-strength tool steel wire rod and a manufacturing method thereof. Background Art

[0002] With the development of new energy, aerospace technology, medical equipment and other fields, the demand for precision tools under harsh working conditions such as high stress and high speed is constantly increasing. The harsh working conditions of the tools also mean that the overall performance and quality level of tool steel need to be continuously improved, and more attention needs to be paid to the improvement of indicators such as high strengthening, high wear resistance and high toughness of the material. Existing high-strength tool steel generally uses hot-rolled wire rod as the base material. After cold processing in the tool factory, it needs to be combined with heat treatment to adjust the product performance. Although heat treatment can greatly improve the performance of the tool, it is also a high-energy consumption and high-cost process. At the same time, adding too many hardenability elements to the wire rod can easily lead to poor cold working performance, which limits the performance range of the tool that can be adjusted by heat treatment, and has certain restrictions on the expansion of the tool application field. Therefore, it is necessary to develop an ultra-high-strength tool wire rod with excellent cold working performance and no heat treatment.

[0003] Existing tool steel wire rod production lines are usually cooled by Stelmor air cooling lines. The main reasons why they are unable to meet performance requirements are:

[0004] (1) In order to improve the cold working performance of tool steel wire rod, air-cooled wire rod is selected to add hardenability and micro-alloy components to make it into pearlite and ferrite structure. For example, patent CN113737099B discloses tool steel and its preparation method for cold working and forming with large deformation, as well as sleeve and its preparation method. The low carbon composition design of C-Mn-Cr-V-Ti-B-Al is combined with air cooling and heat preservation cooling after spinning to make it into pearlite + ferrite structure. However, on the one hand, due to the limited maximum cooling capacity of the Stelmor air-cooled wire, the wire rod slowly passes through the pearlite phase region to form a soft phase structure. Pearlite is a layered mechanical mixture of ferrite and cementite. The interface bonding force of the layered structure is weak, and interlayer slip is easy to occur under the action of external force. Ferrite has high plasticity but extremely low strength, resulting in insufficient tensile strength. After cold working, it needs to be thermally annealed. Heat treatment improves strength and wear resistance, which causes energy consumption, cost increase and efficiency decrease in tool steel production; on the other hand, in order to adapt to the performance of heat-treated adjustable tools, hardenability elements such as Mn and B are added to the wire rod, but it also aggravates the influence of component segregation. Limited by the cooling capacity of the Stelmor air-cooling line, the temperature difference from the edge to the core of the wire rod will increase the risk of precipitation of brittle structures such as martensite in the core of the wire rod, resulting in a decrease in the uniformity of the structure and the cold working performance of the wire rod. Although V, Ti, etc. can refine the grains and enhance the toughness of the material, they are limited by the minimum cooling capacity of the air-cooling line. The wire rod is easily affected by the temperature difference to produce coarsened carbides. The time that the wire rod passes through the temperature range of microalloy carbide dispersion precipitation is short, which affects its precipitation and requires a large amount of addition. V, B, etc., as expensive alloy components, will significantly increase the cost of the wire rod, which is not conducive to controlling the cost of tool steel.

[0005] (2) In order to improve the hardness and wear resistance of tool steel wire rod, air-cooled wire rod is selected to add high content of Si and other components to make it into martensite or including martensite structure. For example, patent CN105149878A discloses a production process of high alloy tool steel wire rod, which adopts C-Mn-Si-Mo component system combined with low temperature final rolling, air cooling and heat preservation cooling to make the phase transformation zone quickly transition from austenite to martensite to control the martensite ratio. However, on the one hand, in order to promote the martensitic phase transformation, it is necessary to increase the air cooling intensity. However, as the air cooling intensity increases, the temperature difference between the wind-receiving surface and the wind-receiving surface, the overlap and the non-overlap, and the edge to the core of the wire rod will be aggravated, making it difficult to suppress the formation of pearlite and bainite, resulting in mixed phase transformation products, deterioration of organizational uniformity, and increased hardness dispersion, which is not conducive to cold processing. On the other hand, due to the limitation of the maximum cooling capacity of the air-cooled wire, the hardenability of the wire rod is required to be high. It is solid-dissolved in the martensite matrix, increasing the lattice distortion. During cooling, the martensite phase transformation is accompanied by volume expansion, which leads to huge tissue stress inside the wire rod and poor toughness, affecting the cold working performance, and even causing brittle fracture during coiling and transportation, affecting the yield rate of wire rod and tool steel. Therefore, the martensite structure of tool steel wire rod on the air-cooling line is generally regarded as an abnormal structure and is difficult to use. 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 1400MPa grade high-strength tool steel wire rod and a manufacturing method thereof, which can appropriately control material costs and take into account the cold working performance and high strength characteristics of the wire rod, so as to avoid the heat treatment process after cold working of the tool steel, reduce the energy consumption and cost of tool steel production, and improve production efficiency.

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

[0008] A method for manufacturing a 1400 MPa grade high-strength tool steel wire rod, the manufacturing method comprising:

[0009] The steel billet is rolled and spun into wire rod at a spinning temperature of ≥900℃, and then is subjected to online molten salt mixed quenching isothermal treatment. The wire rod is first controlled to cool from the high temperature austenite state to the sorbite phase at a cooling rate of ≥32℃ / s, promoting the transformation of part of the austenite to the sorbite structure, forming a quenched structure mainly composed of retained austenite, and then the quenched structure is isothermal tempered to transform the retained austenite into martensite and then toughened and stress relieved. Finally, it is slowly cooled on a roller to produce The invention relates to a wire rod having a microstructure including isothermal troostite, tempered martensite and ferrite, wherein the chemical composition and mass percentage of the wire rod include: C: 0.59% to 0.64%, Si: 0.35% to 0.40%, Mn: 0.67% to 0.72%, Cr: 0.75% to 0.80%, V: 0.055% to 0.063%, P≤0.015%, S≤0.015%, and the remainder is 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, C is relatively cheap. With the increase of carbon content, the carbon diffusion driving force during the sorbite phase transformation is enhanced. It can be combined with molten salt treatment to promote the refinement of pearlite lamellae to form sorbite structure. At the same time, the carbon content in the retained austenite increases with the increase of matrix carbon content, which can increase the driving force of martensite phase transformation, provide the initial hardness basis for tool steel, and give tool steel wire rod high strength and wear resistance. However, excessive carbon content will cause the martensite phase transformation stress to surge, 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, control material costs, and facilitate toughening and stress relief treatment to improve strength and toughness matching, the mass percentage of C is controlled to 0.59%~0.64%.

[0012] (2) Silicon: The Si element can inhibit the coarsening of grains during the online molten salt mixed quenching isothermal treatment, and at the same time reduce the carbon diffusion coefficient, reduce the interlamellar spacing of the sorbite, increase the strength, promote the stability of the retained austenite, promote it to maintain a high dislocation density when transforming to martensite, and improve the strength and toughness of the tempered martensite, which is suitable for the wear resistance requirements of tool steel. However, too high a silicon content will lead to an increase in inclusions, reduce the impact toughness of the wire rod, increase the deformation resistance of the tool steel wire rod during cold working, and affect the cold working performance. Therefore, in order to adapt to the online molten salt mixed quenching isothermal treatment of the microstructure and improve the strength and toughness of the tempered martensite, the mass percentage of Si is controlled to be 0.35%~0.40%.

[0013] (3) Manganese: Mn can increase the hardenability of wire rod, lower the temperature range of iso-sorbite phase transformation, and help improve the nucleation rate of sorbite. At the same time, it can be combined with the large undercooling degree of the molten salt mixed quenching isothermal treatment to inhibit the formation of bainite, promote the transformation of retained austenite to martensite structure, and refine the martensite lath. However, when the Mn content is too high, it will increase the risk of austenite grain coarsening, resulting in uneven structure or martensite phase transformation stress concentration, requiring higher energy for stress release, affecting the impact toughness of wire rod and deteriorating the fatigue resistance of tool. 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 maintain good cold working performance, the mass percentage of Mn is controlled to be 0.67%~0.72%.

[0014] (4) Chromium: As a carbide-forming element, Cr will reduce the diffusion coefficient of carbon when it is dissolved in austenite, causing the phase transformation curve to shift to the right, widening the formation temperature range of sorbite, and improving the hardenability of steel, which is beneficial to inhibiting the precipitation of ferrite. Combined with a large degree of undercooling, it promotes the direct transformation of retained austenite into martensite, inhibits the formation of bainite, and improves the matrix strength. At the same time, the high-hardness carbides formed by chromium and carbon are evenly distributed in the sorbite and martensite matrices, which can improve the wear resistance of tool steel wire rods and enhance the high-temperature service stability of tools. However, too high Cr content will aggravate composition segregation. Local Cr-rich areas will increase the difficulty of the organization to control the coarsening carbides, affect uniformity control, increase the difficulty of plasticity improvement, and deteriorate cold working performance. Therefore, in order to take into account the wear resistance requirements of tool steel, facilitate the control of mixed structure and stress relief of quenching structure, the Cr content is appropriately increased, and the mass percentage of Cr is controlled to be 0.75%~0.80%.

[0015] (5) Vanadium: The V element forms high-melting-point carbonitrides to pin grain boundaries, which can prevent grain growth. The fine austenite grains can provide more nucleation sites for the sorbite phase transformation, promoting the uniform formation of lamellar sorbite. At the same time, fine and dispersed carbides are precipitated during the tempering process to produce secondary hardening, which plays a role in rapidly improving the matrix strength, which is beneficial to inhibit the initiation of fatigue cracks and improve the fatigue limit of tool steel. However, the cost of the V element is relatively high, and excessive addition is not conducive to controlling the cost of wire rods. The aggregation and coarsening of carbides will lead to a decrease in the toughness of the matrix. Therefore, based on the role of the V element, cost and manufacturing control, the mass percentage of V is controlled to be 0.055%~0.063%.

[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 C-Si-Mn-Cr-V composition design, with relatively high Cr composition and trace addition of V element, which can appropriately control material cost, improve the hardenability of wire rod, reduce the sorbite phase temperature, and provide favorable conditions for the transformation of austenite to sorbite while promoting the dispersion and precipitation of vanadium-containing carbides, promoting the direct transformation of retained austenite to martensite with a large undercooling, inhibiting the formation of bainite, and appropriately controlling the difficulty of tempering. On this basis, a higher spinning temperature, i.e., quenching temperature, is selected to austenitize the structure, so as to prepare the structure for increasing the undercooling degree and promoting the transformation of sorbite and martensite structures in conjunction with molten salt treatment. After spinning, the wire rod is not air-cooled but undergoes online molten salt mixed quenching isothermal treatment:

[0018] 1. Compared with the limitation of the cooling capacity of the Stelmor air-cooled line, which leads to coarse pearlite lamellae, the formation of more ferrite soft phase structure, and uneven precipitation of alloy carbides, on the one hand, the wire rod after spinning passes through the online molten salt, which can utilize the higher heat transfer coefficient of molten salt than air to promote the wire rod to quickly pass through the pearlite phase region and enter the low-temperature sorbite phase region, inhibit the soft phase structure, promote the rapid nucleation phase transformation of part of the austenite, refine the pearlite lamellae to form sorbite structure, improve the matrix strength, and strengthen the interface of the layered structure to maintain the toughness. On the other hand, it can promote rapid cooling of the wire rod, enhance the driving force for the dispersion and precipitation of vanadium-containing carbides, and avoid the loss of strength and plasticity of the wire rod due to slow cooling, resulting in coarsening and uneven precipitation of carbides.

[0019] 2. Compared with the limitation of the maximum cooling capacity and unstable cooling control of the Stelmor air-cooling line, which leads to uncontrollable phase transformation of brittle structures such as martensite, deterioration of organizational uniformity, large hardness dispersion and high brittleness, on the one hand, the quenched structure dominated by retained austenite in the wire rod can form a large degree of supercooling under the strong heat exchange effect of the molten salt. Combined with the hardenability of the wire rod, it can promote the transformation of retained austenite to martensite in the high-temperature isothermal range. When the wire rod passes through the molten salt, the molten salt can cover the surface of the wire rod for uniform heat exchange, and there is no temperature difference on the wind-receiving surface. The temperature difference from the surface of the wire rod to the core can be reduced, and the wire rod can be prevented from entering the bainite phase region with a lower temperature to form a needle-shaped brittle upper bainite structure, thereby making the martensite phase transformation rapid and more uniform and controllable, thereby increasing the carbon element. On the other hand, as the processing time increases, the temperature of the wire rod and the molten salt gradually become consistent, and the wire rod can be controlled to isothermally temper the quenched structure in the high-temperature isothermal range instead of continuous cooling on the air-cooled line, which can toughen the martensite to relieve stress, reduce dislocation density, eliminate martensite brittleness, and form a tempered martensite structure that is both strong and tough, thereby improving the adverse effect of martensite, which is conventionally regarded as an abnormal structure, on cold working performance. The temperature gradient is reduced to make the carbide nucleation more uniform, and then the wire rod is slowly cooled by the roller, which can prevent the wire rod from increasing stress due to excessive cooling rate during the cooling process. At the same time, the temperature of the wire rod after leaving the salt bath is relatively high, which can promote further toughening of the wire rod structure and improve the strength-plasticity matching of the wire rod.

[0020] Before the rolling, selecting appropriate heating furnace soaking temperature and furnace time can promote the full diffusion and homogenization of alloy elements, optimize the austenite matrix, and improve the plasticity of the steel billet, so as to reduce the rolling resistance and the influence of component segregation. In the preferred technical solution, before the rolling, the heating furnace soaking temperature is controlled to be 1155~1200℃, and the furnace time is 145~200min.

[0021] Since the spinning temperature is relatively high, the restrictions on the rolling line can be reduced. The use of higher initial rolling temperature and final rolling temperature during the rolling process can improve the plasticity of the rolled piece, reduce the wear on the rolling line, and improve the rolling efficiency. The defects of the cast structure are eliminated through dynamic recrystallization. With the appropriate final rolling reduction, dynamic recrystallization can be promoted during the final rolling process, the grains can be refined, and deformation energy storage can be retained. In the preferred technical solution, during the rolling process, the initial rolling temperature is controlled to be 1020~1060℃, the final rolling temperature is 910~940℃, and the final rolling reduction is 24%~30%.

[0022] During the spinning, the spinning temperature can be further controlled to avoid the coarsening of austenite grains due to excessively high spinning temperature. In a preferred technical solution, during the spinning, the spinning temperature is controlled to be 900-930°C.

[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 molten salt circulation volume of the front-stage molten salt treatment is larger, which can enhance convective heat transfer and inhibit soft phase structure. The molten salt circulation volume of the rear-stage molten salt treatment is smaller, which can appropriately reduce production energy consumption.

[0024] The molten salt temperature of the front-stage molten salt treatment is in the bainite phase region. The lower the molten salt temperature and the longer the treatment time, the more conducive it is for the wire rod to quickly pass through the pearlite phase region, inhibit soft phase structures such as ferrite and coarse lamellar pearlite, promote the rapid transformation of austenite to refined bainite structure, and provide suitable precipitation kinetic conditions for vanadium-containing carbides. However, if the molten salt temperature is too low and the treatment time is too long, the retained austenite will decrease, which will affect the martensite transformation and even enter the bainite phase region to cause abnormal structure, while increasing production energy consumption; on the contrary, the higher the molten salt temperature and the shorter the treatment time, the more conducive it is for the retained austenite to provide carbon content storage for the subsequent martensite phase transformation. Preparation, reducing production energy consumption, but the molten salt temperature is too high and the treatment time is too short, which is not conducive to the refinement of the sorbite structure lamellae and the precipitation of carbides, and will lose the strength and plasticity. Therefore, the molten salt temperature and treatment time of the front-end treatment can be controlled to control the wire rod to quickly enter the sorbite phase region from the high-temperature austenite state, so that a small part of the austenite is transformed into a sorbite structure with finer lamellae spacing, promote the dispersion and precipitation of carbides, and form a quenching structure dominated by retained austenite, so as to make organizational preparations for the rear-end molten salt treatment. In the preferred technical solution, the molten salt temperature of the front-end molten salt treatment is 525~555℃, and the treatment time is 50~120s.

[0025] Since the temperature of the wire rod is high when it first enters the molten salt, a larger molten salt circulation rate is selected to control the molten salt temperature rise and further improve the uniformity of the wire rod structure. In the preferred technical solution, the molten salt circulation rate of the front-stage molten salt treatment is 420~580t / h, and the molten salt temperature rise is ≤8℃.

[0026] The latter stage molten salt treatment is in the high temperature isothermal range. The higher the molten salt temperature and the longer the treatment time, the more conducive it is to the transformation of retained austenite into martensite, the lower the dislocation density and the smaller the lattice distortion, so as to achieve the stress relief toughening effect, avoid cracks or brittleness caused by quenching stress, make carbide nucleation more uniform, and improve the plasticity of the matrix. However, if the molten salt temperature is too high and the treatment time is too long, it will be unfavorable to form a large degree of supercooling and promote the transformation of retained austenite into martensite. At the same time, carbides will precipitate and coarsen, and the strength will be lost faster, which will bring about a large strength loss. On the contrary, the lower the molten salt temperature and the shorter the treatment time, the more conducive it is to increase the degree of supercooling of austenite, so as to promote the transformation of retained austenite into martensite in the high temperature isothermal range. Rapid transformation to martensite, control of carbide precipitation coarsening, but the molten salt temperature is too low and the treatment time is too short, it is difficult to provide more thermal power for the tempering of the quenched structure, which will affect the stress release, so that the martensite retains high internal stress, resulting in greater plasticity loss, and increasing the risk of brittle fracture in subsequent processing. Therefore, the molten salt temperature and treatment time of the later molten salt treatment can be controlled, and the wire rod can be controlled to perform isothermal tempering of the quenched structure in the high-temperature isothermal range, and the residual austenite is transformed into martensite for post-toughening stress relief treatment to improve the strength-plasticity matching of the wire rod. In the preferred technical solution, the molten salt temperature of the later molten salt treatment is 550~570℃, and the treatment time is 100~400s.

[0027] Since the wire rod temperature is close to the set temperature of the molten salt during the latter stage of molten salt treatment, appropriately reducing the circulation volume is beneficial to reducing production energy consumption and facilitating precise control of the tempering temperature. In the preferred technical solution, the molten salt circulation volume of the latter stage of molten salt treatment is 150~300t / h.

[0028] Since the wire rod has undergone sufficient phase transformation after online molten salt mixed quenching and isothermal treatment, austenite residue can be avoided and low-temperature structure can be formed in the subsequent cooling. However, in order to prevent the wire rod from increasing shrinkage stress due to excessively fast cooling rate during the cooling process, roller slow cooling treatment is selected. In the preferred technical solution, the roller slow cooling controls the wire rod to slowly cool to below 280°C at a cooling rate of 0.35~0.65°C / s. Preferably, the roller slow cooling adopts a closed insulation cover, and the wire rod is transported into the insulation cover to control the slow cooling. The wire rod can use its own residual heat from the molten salt to slowly cool down, promote further toughening of the wire rod structure, and improve the softening effect of the wire rod.

[0029] A 1400 MPa grade high-strength tool steel wire rod is manufactured by any one of the above-mentioned methods for manufacturing a 1400 MPa grade high-strength tool steel wire rod.

[0030] The above-mentioned wire rod is designed with a medium-high carbon chemical composition of Cr-V, and a trace amount of V content is added, which can appropriately control the material cost. At the same time, the organization forms a microstructure including a small amount of isothermal troostite and ferrite, and a large part of tempered martensite. Compared with the existing air-cooled pearlite + ferrite organization of tool steel wire rod, the troostite has finer interlamellar spacing and better toughness than the pearlite. The transitional isothermal troostite that transforms to carbide spheroidization after tempering can further improve the plasticity of the organization. The supersaturated carbon in the tempered martensite forms solid solution strengthening, which is more uniform than the layered strengthening of carbides in pearlite, and the resistance to dislocation movement is increased. At the same time, the proportion of ferrite in the organization is reduced, which can make full use of the strengthening effect of elements such as carbon and vanadium to make up for the strength loss caused by reducing the content of alloys such as V, while taking into account the wear resistance requirements of tool steel. Compared with The existing air-cooled line contains tool steel wire rods containing martensite or martensitic structure, which can avoid the formation of brittle upper bainite structure in the structure. Martensite has higher strength than bainite. After tempering, the structure stress is released and the dislocation density is reduced, and it is transformed into tempered martensite with better strength retention and toughness. The tempered martensite accounts for a high proportion in the structure. The hard and brittle martensite, which is conventionally regarded as an abnormal structure, can be utilized to avoid brittle fracture during transportation or even winding, and improve strength-plasticity matching and structural uniformity. Isothermal troostite is distributed between the martensitic laths as a tough buffer phase. When the material is subjected to external force, the isothermal troostite layer can absorb energy through dislocation slip, taking into account the cold working performance of the wire rod. After cold working, it can be directly processed into parts, so that the tool steel production can avoid the heat treatment process after cold working, reduce production energy consumption and cost, and improve production efficiency.

[0031] The higher the proportion of isothermal sorbite in the microstructure, the improved plasticity of the wire rod can be achieved. The finer the lamellar spacing of the isothermal sorbite, the higher the material strength can be achieved by increasing the resistance to dislocation movement. In the preferred technical solution, the volume percentage of the isothermal sorbite is 25% to 30%, and the lamellar spacing is 85 to 125 nm.

[0032] The higher the proportion of tempered martensite in the microstructure, the more beneficial it is to improving the strength of the wire rod. In the preferred technical solution, the volume percentage of the tempered martensite is 68% to 73%.

[0033] In the preferred technical solution, the diameter of the wire rod is 5.5~10mm, the tensile strength is 1370~1420MPa, the cross-sectional shrinkage rate is 35%~40%, and the mechanical property difference is ≤36MPa. The wire rod is of medium and fine specifications, with good cross-sectional shrinkage rate and small mechanical property difference, showing good plasticity and cold working performance, which can avoid local stress concentration and the risk of cracking during direct cold working. At the same time, the tensile strength is high and can be used for cold working to manufacture cutting tools, drill tools and other wear-resistant scenes, eliminating the additional heat treatment process after cold working, which is beneficial to improving the production efficiency and fatigue limit of tool steel parts and expanding the application field of tools.

[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-cooled line cooling capacity, the addition of too many hardenability elements leads to poor cold working performance, or the soft phase structure leads to insufficient strength, the manufacturing method of the present invention adopts Cr-V chemical composition design combined with online molten salt mixed quenching isothermal technology, and controls the wire rod to quickly enter the sorbite phase region from the high-temperature austenite state after spinning, promotes the transformation of part of the austenite to sorbite with finer lamellar spacing, inhibits coarse lamellar pearlite structure, and forms a quenched structure mainly composed of retained austenite. Then, the wire rod is controlled to be isothermally tempered in the high-temperature isothermal range to transform the retained austenite into martensite and then toughen and relieve stress. Finally, the roller is slowly cooled to avoid stress increase and promote further toughening of the wire rod structure. It can achieve effective regulation of the microstructure, improve the strength and plasticity matching of the wire rod, avoid the hard and brittle martensite that is conventionally regarded as an abnormal structure, which leads to brittle fracture during transportation or even winding, and improve the yield rate. It has good industrial adaptability.

[0036] (2) In view of the current situation that the alloy content or mechanical properties of existing tool steel wire rods fluctuate greatly, and the strength or cold working performance is insufficient, resulting in cold working cracking or the need for additional heat treatment after cold working, which leads to high energy consumption and cost of tool steel, the wire rod of the present invention adopts Cr-V chemical composition design, and V is added in trace amounts, which can appropriately control the material cost. At the same time, the microstructure includes isothermal troostite, tempered martensite and ferrite, which can fully utilize the strengthening effect of elements such as carbon and vanadium to make up for the strength loss caused by reducing the alloy content of V and take into account the wear resistance requirements of tool steel. The martensite structure releases the structural stress and reduces the dislocation density after tempering, and is transformed into tempered martensite with better strength retention and toughness, thereby improving the strength-plasticity matching of the wire rod, achieving a product tensile strength of 1370~1420MPa and a cross-sectional shrinkage rate of 35~40%. It is used in the application fields of manufacturing high-strength tool steel, and can be directly processed into parts after cold working, so as to reduce production energy consumption and cost and improve efficiency, and has good market application prospects. 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 is a metallographic structure diagram of Example 2 of the present invention;

[0040] Figure 3 This is the metallographic structure diagram of Example 3 of the present invention. DETAILED DESCRIPTION

[0041] 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:

[0042] A preferred embodiment of the method for manufacturing 1400MPa grade high-strength tool steel wire rod of the present invention comprises the following chemical compositions and mass percentages: C: 0.59%, Si: 0.39%, Mn: 0.67%, Cr: 0.80%, V: 0.055%, 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:

[0043] 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 1170°C, the time in the furnace is 185min, the initial rolling temperature is 1035°C, the final rolling temperature is 925°C, and the final rolling reduction is 26%; 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 910°C.

[0044] 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 molten salt treatment, so that the wire rod is cooled at a cooling rate of 38°C / s, and enters the sorbite phase region from the high-temperature austenite state, promoting the transformation of part of the austenite to the sorbite structure, forming a quenching structure mainly composed of retained austenite, and promoting the dispersion and precipitation of carbides with a large undercooling degree. After that, the wire rod is conveyed by a roller through the second salt bath tank for the rear molten salt treatment, reducing the molten salt The salt circulation volume controls the wire rod to isothermally temper the quenched structure in the high-temperature isothermal range, promotes the transformation of retained austenite into martensite with a large degree of undercooling, and then toughens and relieves stress, controls the coarsening of carbides, and improves the strength and plasticity matching of the wire rod. Specifically: the molten salt temperature of the front-stage molten salt treatment is 532°C, the treatment time is 95s, the molten salt circulation volume is 460t / h, and the molten salt temperature rise is ≤8°C; the molten salt temperature of the rear-stage molten salt treatment is 564°C, the treatment time is 185s, and the molten salt circulation volume is 195t / h.

[0045] The roller slow cooling process adopts the method of closing 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 275°C at a cooling rate of 0.45°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.

[0046] Comparative Example 1:

[0047] 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 1120°C, the furnace time is 215 minutes, the initial rolling temperature is 980°C, the final rolling temperature is 845°C, the spinning temperature is controlled to be 815°C, the Stelmor air cooling line uses the front fans No. 1 to No. 6 to turn on, control the wire rod to cool to 687°C at a rate of 4.5°C / s, then close the insulation cover, the wire rod enters the insulation cover and is cooled to 290°C at a rate of 1.5°C / s, and is collected by the coiling drum to obtain a finished wire rod.

[0048] Comparative Example 2:

[0049] A method for manufacturing a wire rod, which differs from Example 1 in that: the soaking temperature of the heating furnace is controlled to 1120°C, the time in the furnace is 215 minutes, the initial rolling temperature is 980°C, the final rolling temperature is 850°C, the spinning temperature is controlled to be 820°C, the wire rod is treated with molten salt in the front section and cooled at a cooling rate of 29°C / s to obtain a finished wire rod. Example 2:

[0050] A preferred embodiment of the method for manufacturing 1400MPa grade high-strength tool steel wire rod of the present invention comprises the following chemical compositions and mass percentages: C: 0.62%, Si: 0.35%, Mn: 0.71%, Cr: 0.75%, V: 0.063%, 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:

[0051] 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 5.5mm 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 1155°C, the furnace time is 200min, the initial rolling temperature is 1020°C, the final rolling temperature is 910°C, and the final rolling reduction is 30%; 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 900°C.

[0052] 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 molten salt treatment, so that the wire rod is cooled at a cooling rate of 37°C / s, and enters the sorbite phase region from the high-temperature austenite state, promoting the transformation of part of the austenite to the sorbite structure, forming a quenching structure mainly composed of retained austenite, and promoting the dispersion and precipitation of carbides with a large degree of supercooling. After that, the wire rod is conveyed by a roller through the second salt bath tank for the rear molten salt treatment, reducing the molten salt The circulation volume is used to control the wire rod to isothermally temper the quenched structure in the high-temperature isothermal range, promote the transformation of retained austenite into martensite and then toughen and relieve stress with a large degree of undercooling, control the coarsening 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 525℃, the treatment time is 120s, the molten salt circulation volume is 420t / h, and the molten salt temperature rise is ≤8℃; the molten salt temperature of the rear-stage molten salt treatment is 570℃, the treatment time is 100s, and the molten salt circulation volume is 150t / h.

[0053] The roller slow cooling process adopts the method of closing 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 278°C at a cooling rate of 0.35°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.

[0054] Comparative Example 3:

[0055] 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 31°C / s, the molten salt temperature of the front-stage molten salt treatment is 575°C, and the treatment time is 45s to obtain a finished wire rod.

[0056] Comparative Example 4:

[0057] 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 39°C / s, the molten salt temperature of the front-stage molten salt treatment is 510°C, and the treatment time is 140s to obtain a finished wire rod. Example 3:

[0058] A preferred embodiment of the method for manufacturing 1400MPa grade high-strength tool steel wire rod of the present invention comprises the following chemical compositions and mass percentages: C: 0.62%, Si: 0.4%, Mn: 0.67%, Cr: 0.79%, V: 0.061%, 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:

[0059] 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 1185°C, the time in the furnace is 165min, the initial rolling temperature is 1040°C, the final rolling temperature is 930°C, and the final rolling reduction is 28%; 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.

[0060] 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 molten salt treatment, so that the wire rod is cooled at a cooling rate of 38°C / s, and enters the sorbite phase region from the high-temperature austenite state, promoting the transformation of part of the austenite to the sorbite structure, forming a quenching structure mainly composed of retained austenite, and promoting the dispersion and precipitation of carbides with a large undercooling degree. After that, the wire rod is conveyed by a roller through the second salt bath tank for the rear molten salt treatment, reducing the molten salt The salt circulation volume controls the wire rod to isothermally temper the quenched structure in the high-temperature isothermal range, promotes the transformation of retained austenite into martensite with a large degree of undercooling, and then toughens and relieves stress, controls the coarsening of carbides, and improves the strength and plasticity matching of the wire rod. Specifically: the molten salt temperature of the front-stage molten salt treatment is 547°C, the treatment time is 65s, the molten salt circulation volume is 515t / h, and the molten salt temperature rise is ≤8°C; the molten salt temperature of the rear-stage molten salt treatment is 558°C, the treatment time is 250s, and the molten salt circulation volume is 260t / h.

[0061] The roller slow cooling process adopts the method of closing 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 273°C at a cooling rate of 0.50°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 3 shown.

[0062] Comparative Example 5:

[0063] 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 585° C., the treatment time is 410 s, and the finished wire rod is obtained.

[0064] Comparative Example 6:

[0065] 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 535° C., the treatment time is 90 seconds, and the finished wire rod is obtained. Example 4:

[0066] A preferred embodiment of the method for manufacturing 1400MPa grade high-strength tool steel wire rod of the present invention comprises the following chemical compositions and mass percentages: C: 0.64%, Si: 0.37%, Mn: 0.72%, Cr: 0.76%, V: 0.060%, 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:

[0067] The rolling process is used to heat a steel billet with a specification of 220mm×220mm 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 10mm 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 1200°C, the time in the furnace is 145min, the initial rolling temperature is 1060°C, the final rolling temperature is 940°C, and the final rolling reduction is 24%; 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 930°C.

[0068] 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 molten salt treatment, so that the wire rod is cooled at a cooling rate of 37°C / s, and enters the sorbite phase region from the high-temperature austenite state, promoting the transformation of part of the austenite to the sorbite structure, forming a quenching structure mainly composed of retained austenite, and promoting the dispersion and precipitation of carbides with a large undercooling degree. After that, the wire rod is conveyed by a roller through the second salt bath tank for the rear molten salt treatment, reducing the molten salt The salt circulation volume controls the wire rod to perform isothermal tempering on the quenched structure in the high-temperature isothermal range, promotes the transformation of retained austenite into martensite with a large degree of undercooling, and then performs toughening and stress relief treatment, controls the coarsening of carbides, and improves the strength-plasticity matching of the wire rod. Specifically: the molten salt temperature of the front-stage molten salt treatment is 555°C, the treatment time is 50s, the molten salt circulation volume is 580t / h, and the molten salt temperature rise is ≤8°C; the molten salt temperature of the rear-stage molten salt treatment is 550°C, the treatment time is 400s, and the molten salt circulation volume is 300t / h.

[0069] The roller slow cooling process adopts the method of closing 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, which leads to increased 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 271°C at a cooling rate of 0.65°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.

[0070] Comparative Example 7:

[0071] 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 270°C at a cooling rate of 1.8°C / s to obtain a wire rod. The wire rod has a tensile strength of 1424 MPa, a cross-sectional shrinkage rate of 31%, and a mechanical property difference of 47 MPa.

[0072] 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:

[0073] Table 1. Comparison of microstructure and properties of different wire rod compositions and manufacturing methods

[0074]

[0075] In the above table, the interlamellar spacing of comparative example 1 is the pearlite interlamellar spacing, and the interlamellar spacing of other examples is the isothermal sorbite interlamellar spacing; from the comparison results of Example 1 and Comparative Example 1, it can be seen that C and Cr, as relatively low-priced and effective 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 the mechanical properties fluctuate greatly. In order to reduce the precipitation risk of low-temperature structure in the wire rod, after reducing the air-cooling strength, the wire rod slowly passes through the pearlite phase region to form a soft phase structure, resulting in insufficient tensile strength and a certain amount of tissue stress that is difficult to release. The present invention adopts the Cr-V chemical composition design combined with the The wire molten salt mixed quenching isothermal technology controls the wire rod to quickly enter the troostite phase region from the high-temperature austenite state after spinning, which can suppress the coarse lamellar pearlite structure, and then controls the wire rod to isothermal temper the quenched structure in the high-temperature isothermal range, so that the residual austenite is transformed into martensite and then toughened and stress relieved to form a microstructure including a small amount of isothermal troostite and ferrite and most of tempered martensite. It can be seen from the results of Examples 1 to 4 that the present invention can achieve a product tensile strength of 1370~1420MPa and a cross-sectional reduction rate of 35~40%, which is used in application fields such as manufacturing high-strength tool steel, so that it can be directly processed into parts after cold forming.

[0076] From the comparison results of Example 1 and Comparative Example 2, it can be seen that a higher spinning temperature, i.e., quenching temperature, is selected to austenitize the structure, which can be combined with molten salt treatment to increase the supercooling degree and promote the phase transformation of sorbite and martensite structures. At the same time, the restrictions on the rolling line can be reduced. When rolling, higher initial rolling temperature and final rolling temperature are selected, which can improve the plasticity of the rolled piece, reduce the wear on the rolling line, and improve the rolling efficiency.

[0077] 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 more conducive it is to the retention of austenite, providing a carbon content reserve for the subsequent martensitic phase transformation and reducing production energy consumption. However, if the molten salt temperature is too high and the treatment time is too short, it is not conducive to the refinement of the sorbite structure lamellae and the precipitation of carbides, which will result in a loss of strength and plasticity, especially plasticity.

[0078] 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 more conducive it is to suppressing soft phase structures such as ferrite and coarse lamellar pearlite, promoting the rapid transformation of austenite to refined sorbite structure, and providing suitable precipitation kinetic conditions for vanadium-containing carbides. However, if the molten salt temperature is too low and the treatment time is too long, the retained austenite will be reduced, which will affect the martensite transformation and increase production energy consumption.

[0079] From the comparison results of Example 3 and Comparative Example 5, it can be seen that the latter molten salt treatment is in the high-temperature isothermal range. The higher the molten salt temperature and the longer the treatment time, the more conducive it is to stress relief and toughening after the retained austenite is transformed into martensite, thereby improving the plasticity of the matrix. However, if the molten salt temperature is too high and the treatment time is too long, it will be unfavorable to form a large degree of supercooling and promote the transformation of retained austenite to martensite. At the same time, carbides will precipitate and coarsen, and the strength loss will be faster, which will result in a large strength loss.

[0080] From the comparison results of Example 3 and Comparative Example 6, it can be seen that the lower the molten salt temperature and the shorter the treatment time of the later molten salt treatment, the more conducive it is to increasing the supercooling of austenite, prompting the retained austenite to quickly transform into martensite in the high-temperature isothermal range, and controlling the precipitation and coarsening of carbides. However, if the molten salt temperature is too low and the treatment time is too short, it is difficult to provide more thermal power for the tempering of the quenched structure, which will affect the stress release, causing the martensite to retain high internal stress, resulting in greater plasticity loss and increasing the risk of brittle fracture in subsequent processing.

[0081] From the comparison results of Example 4 and Comparative Example 7, it can be seen that the roller slow cooling treatment can prevent the increase of shrinkage stress of the wire rod due to too fast cooling rate during the cooling process, and utilize the wire rod's own residual heat insulation through the molten salt to slowly cool down, thereby promoting further toughening of the wire rod structure and improving the softening effect of the wire rod.

[0082] 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 1400MPa grade high strength tool steel wire rod, characterized in that: The manufacturing method includes: The steel billet is rolled and spun into a wire rod at a spinning temperature of ≥900°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 ≥32°C / s to promote the transformation of part of the austenite into the sorbite structure, forming a quenched structure mainly composed of 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, it is slowly cooled by a roller to form a wire rod with a microstructure including isothermal sorbite, tempered martensite and ferrite. The chemical composition and mass percentage of the wire rod include: C: 0.59%~0.64%, Si: 0.35%~0.40% , Mn: 0.67%~0.72%, Cr: 0.75%~0.80%, V: 0.055%~0.063%, P≤0.015%, S≤0.015%, and the rest are Fe and unavoidable impurities; the online molten salt mixed quenching isothermal treatment is divided into a front-end molten salt treatment and a rear-end molten salt treatment, the molten salt temperature of the front-end molten salt treatment is 525~555℃, and the treatment time is 50~120s, the molten salt temperature of the rear-end molten salt treatment is 550~570℃, and the treatment time is 100~400s, and the roller slow cooling controls the wire rod to slowly cool to below 280℃ at a cooling rate of 0.35~0.65℃ / s.

2. The method for manufacturing 1400MPa 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 1155-1200° C., and the soaking time in the furnace is 145-200 minutes.

3. The method for manufacturing 1400MPa 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 1020-1060° C., the final rolling temperature is controlled to be 910-940° C., and the final rolling reduction is controlled to be 24%-30%. During the spinning, the spinning temperature is controlled to be 900-930° C.

4. The method for manufacturing 1400 MPa grade high strength tool steel wire rod according to claim 1, characterized in that: The molten salt circulation amount of the front-stage molten salt treatment is greater than the molten salt circulation amount of the back-stage molten salt treatment.

5. The method for manufacturing 1400MPa 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 420~580t / h, and the molten salt temperature rise is ≤8°C; the molten salt circulation rate of the back-stage molten salt treatment is 150~300t / h.

6. A 1400MPa grade high strength tool steel wire rod, characterized in that: The wire rod is manufactured by the manufacturing method of 1400MPa grade high-strength tool steel wire rod according to any one of claims 1 to 5.

7. The 1400 MPa grade high strength tool steel wire rod according to claim 6, characterized in that: The volume percentage of the isothermal troostite is 25% to 30%, and the interlamellar spacing is 85 to 125 nm; the volume percentage of the tempered martensite is 68% to 73%.

8. The 1400 MPa grade high strength tool steel wire rod according to claim 6, characterized in that: The diameter of the wire rod is 5.5-10 mm, the tensile strength is 1370-1420 MPa, the cross-sectional shrinkage rate is 35%-40%, and the mechanical property difference within the same circle is ≤36 MPa.

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