A 1300MPa grade high-strength tool steel wire rod and its manufacturing method

Abstract

The present invention relates to a 1300MPa-grade high-strength tool steel wire rod and a manufacturing method thereof. The wire rod is designed with a medium-carbon composition of Cr-Nb-V and is rolled and spun into a wire rod. The wire rod is then subjected to an online molten salt micro-quenching and tempering treatment. The wire rod is cooled from a high-temperature austenite state to a lower bainite phase region at a cooling rate of 31°C / s or higher, thereby forming a quenched structure mainly composed of quenched bainite. The quenched structure is then subjected to isothermal tempering and toughening stress relief treatment. Finally, the quenched structure is slowly cooled through a roller to form a wire rod with a microstructure including tempered bainite and ferrite. The method can appropriately control material costs, improve the matching of strength and plasticity of the wire rod, achieve a tensile strength of 1255-1305MPa, and a cross-sectional reduction rate of 58%-63%. The wire rod can then be directly processed into parts after cold forming, thereby reducing energy consumption and costs and improving efficiency in tool steel production.

Description

Technical Field

[0001] The present invention belongs to the technical field related to hot-rolled wire rods, and specifically relates to a 1300MPa grade high-strength tool steel wire rod and a manufacturing method thereof. Background Art

[0002] By controlling the carbon content and adding appropriate amounts of hardenability elements such as Cr, Mn, and Mo, alloy tool steels can improve toughness and performance compared to carbon tool steels, making them suitable for more complex working conditions. Compared to high-speed tool steels, alloy tool steels can have a lower carbon content, with no or limited amounts of W and V, to reduce the risk of carbon buildup associated with high carbon content. This trades extreme red hardness for improved toughness and workability, significantly reducing costs and making them suitable for use in tools such as turning tools, milling cutters, and screwdrivers. Alloy tool steels are typically made from hot-rolled wire rods and then cold-formed through processes such as drawing and cold heading. To mitigate the work hardening and residual stresses caused by cold working and achieve a balance between strength and toughness, post-cold working heat treatment is often required to enhance product performance. However, this also increases production energy consumption, processing costs, and efficiency. Therefore, there is a need to develop 1300MPa-grade high-strength tool steel wire rods and their manufacturing methods, enabling direct processing into parts after cold working to meet market demand for tool steel.

[0003] Existing alloy tool steel wire rods generally use medium carbon alloy components. Combined with the Stelmor air cooling line, the wire rods are cooled to pearlite or bainite structure after rolling. The main reasons for this are that it is difficult to eliminate the need for heat treatment after cold working:

[0004] First, in order to improve the performance of the material, hardenability components are selectively added to the steel in the prior art. For example, patent CN115976407B discloses a low-alloy hand tool steel coil with a uniform tensile strength of 1000 MPa and a production method thereof. The coil adopts a C-Si-Mn-Cr-V-Al composition design and is combined with low-temperature rolling and air-cooled line insulation cooling to form a pearlite + ferrite structure. However, on the one hand, the pearlite soft phase structure makes the matrix strength insufficient, and further increasing the alloy content will increase the cost; on the other hand, the content of hardenability components such as Mn and Cr in the composition is relatively high. Given the limited cooling capacity of conventional Stelmor air-cooled lines, the phase transformation control of the wire rod is difficult due to insufficient cooling rate control. The hardenability elements easily induce the formation of brittle phases such as martensite, which is very likely to cause cracking problems during subsequent cold working. Reducing the content of the hardenability components or the V component content that has a fine grain strengthening effect will result in strength loss, which limits the improvement of the wire rod strength.

[0005] 2. In order to improve the adverse effects of martensite structure on wire rod packaging, transportation and user processing, or to improve the wear resistance of the finished tool surface, medium carbon high silicon steel is selected in the existing technology, and air cooling or water cooling after wire drawing is combined to make high bainite content wire rod. For example: Patent CN118621099A discloses an online bainite isothermal quenching process for alloy tool steel wire rod, which adopts rapid cooling to the upper bainite transformation region after wire drawing and enters the insulation cover for insulation to form a bainite structure with lower hardness; Patent CN114134399B discloses an energy-saving high bainite content high alloy tool steel wire rod and its manufacturing method, which adopts low temperature rolling wire drawing and water bath cooling to control the wire rod to quickly transition to the bainite region, and then coil it and heat-insulate it in the bainite region for phase transformation; but on the one hand, the maximum cooling capacity of the air cooling line is limited. As the air cooling intensity increases, the gap between the windward side and the winded side of the wire rod and the overlap will increase. The temperature difference between the overlapped and non-overlapped parts, although the cooling capacity of the water-cooled line can be higher than that of the air-cooled line, a large number of bubbles will be generated during the water cooling process and attached to the surface of the wire rod, affecting the uniformity of heat transfer, resulting in the risk of precipitation of low-temperature brittle abnormal structure, coarsening of carbides and increased risk of structural inhomogeneity. On the other hand, the high Si content in the component will delay the bainite phase transformation kinetics. At the same time, due to the limited minimum cooling capacity of the insulation cover, the air-cooled line is limited by fan cooling and insulation cooling, and the water-cooled line is limited by insulation cooling. The wire rod after spinning needs to be quickly cooled to the high-temperature temperature range of bainite, which is more likely to form a feathery upper bainite structure composed of ferrite laths and cementite between laths. The carbide growth activation energy is large, which makes the matrix strong and toughness insufficient. As the wire rod continues to cool during the insulation process and is in a low-temperature state after phase transformation incubation, a large dislocation density and structural stress remain in the structure, which will aggravate 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 1300MPa grade high-strength tool steel wire rod and a manufacturing method thereof, which can appropriately control material costs and improve the matching of strength and plasticity of the wire rod so that it can be directly processed into parts after cold forming, which is beneficial to energy consumption and cost reduction and efficiency improvement in tool steel production.

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

[0008] A method for manufacturing a 1300 MPa 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 micro-quenching and tempering treatment. The wire rod is cooled at a cooling rate of ≥31°C / s from a high-temperature austenite state to a lower bainite phase region to form a quenched structure mainly composed of quenched bainite. The quenched structure is then isothermally tempered and toughened for stress relief, and finally slowly cooled by a roller to form a wire rod with a microstructure including tempered bainite and ferrite. The chemical composition and mass percentage of the wire rod include: C: 0.47%-0.52%, Si: 0.22%-0.37%, Mn: 0.38%-0.43%, Cr: 0.36%-0.51%, Nb: 0.040%-0.050%, V: 0.040%-0.050%, 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, C is relatively cheap. With the increase of carbon content, the carbon concentration in austenite increases, which can reduce the bainite phase transformation temperature and make the phase transformation more likely to shift to the low temperature zone. It can delay the transformation of pearlite and promote the formation of strong and tough quenched bainite structure in the online molten salt controlled wire rod, giving the tool steel wire rod high strength and wear resistance. However, excessive carbon content increases the supercooling required for bainite phase transformation, easily forming coarse cementite or martensite, resulting in a decrease in toughness and an increase in hardness, which makes isothermal tempering more difficult. Therefore, in order to meet the strength and wear resistance requirements of tool steel, control material costs, and facilitate the micro-quenching and tempering treatment of wire rods and improve strength and toughness matching, a medium carbon content is used to balance strength and toughness, and the mass percentage of C is controlled to be 0.47%~0.52%.

[0012] (2) Silicon: Si is a strong ferrite-forming element. It can inhibit the grain coarsening and cementite precipitation during online molten salt micro-quenching and tempering treatment, delay the pearlite transformation, enhance the strength of bainitic ferrite, and delay the precipitation and aggregation of carbides during tempering, so that the wire rod maintains a high strength after tempering, which is suitable for the wear resistance requirements of tool steel. However, too high a silicon content will lead to excessive strengthening of the ferrite matrix, aggravated lattice distortion, decreased material plasticity and impact toughness, which is detrimental to the fracture resistance of tool steel and affects the tempering plasticity control. Therefore, in order to maintain the matrix strength, reduce the difficulty of tempering, and adapt to the control of the microstructure by online molten salt micro-quenching and tempering, the mass percentage of Si is controlled to be 0.22%~0.37%.

[0013] (3) Manganese: Mn can increase the stability of austenite and the hardenability of wire rod, expand the austenite zone, reduce the decomposition temperature of austenite, delay the transformation of pearlite and bainite, move the phase transformation to the low temperature zone, increase the dislocation density of bainitic ferrite, adapt to the needs of micro-quenching, and improve the strength and hardness of wire rod. However, when the Mn content is too high, the austenite grains will be easily coarsened during heating, aggravate the component segregation, increase the risk of martensite precipitation, require higher energy for stress release, delay the tempering softening process, and reduce the toughness and plasticity of steel. Therefore, in order to enable micro-quenching to quickly form quenched bainite and facilitate tempering softening control, the Mn content is appropriately reduced, and the mass percentage of Mn is controlled to be 0.38%~0.43%.

[0014] (4) Chromium: Cr is a carbide-forming element. Chromium carbides have high hardness and can improve the wear resistance of tool steel. At the same time, it can significantly improve the hardenability of steel, reduce the diffusion coefficient of carbon in austenite, expand the bainite transformation range, and make quenched bainite the main transformation product during micro-quenching treatment, which is beneficial to improving the matrix strength. However, too high Cr content will aggravate component segregation and there is a risk of coarse and unevenly distributed carbides, which will increase the difficulty of controlling the uniformity of the structure, the difficulty of improving the plasticity and the brittleness of the tool. Therefore, in order to take into account the wear resistance requirements of tool steel and enable micro-quenching and tempering to be carried out at a higher temperature, the mass percentage of Cr is controlled to be 0.36%~0.51%.

[0015] (5) Niobium: Nb forms high-melting-point carbides that can precipitate and pin grain boundaries, strongly inhibiting the growth of austenite grains and obtaining fine-grained structure. Fine-grained austenite can promote the nucleation of bainitic ferrite at more grain boundaries, accelerate phase transformation, and produce a strong precipitation strengthening effect, thereby improving the high-temperature hardness of tool steel and reducing the risk of cracks. However, the cost of Nb is relatively high. Therefore, based on the role, cost and manufacturing control of Nb, the mass percentage of Nb is controlled to be 0.040%~0.050%.

[0016] (6) Vanadium: The V element forms high-hardness carbides that can pin grain boundaries to inhibit the growth of austenite grains, refine the original structure, promote the formation of high-density dislocations and twins in bainitic ferrite, and improve the wear resistance of tool steel. At the same time, the dispersion and precipitation of carbides can quickly increase the strength of the matrix. However, the cost of the V element is relatively high, and excessive addition is not conducive to controlling the cost of wire rods. Therefore, based on the role, cost and manufacturing control of the V element, the mass percentage of V is controlled to be 0.040%~0.050%.

[0017] (7) Phosphorus and sulfur: P and S are impurity elements. The lower the better. Therefore, P is controlled to be ≤ 0.015% and S is controlled to be ≤ 0.015%.

[0018] The above-mentioned wire rod adopts a medium carbon composition design of Cr-Nb-V, and the contents of C, Si, Mn, Nb and V are relatively low, which can appropriately reduce the material cost. At the same time, by optimizing the content ratio of each component such as Si, Mn, Cr, it provides favorable conditions for online molten salt micro-quenching and tempering to perform bainite quenching at a higher temperature, inhibit the low-temperature brittle structure of martensite, promote the rapid formation of quenched bainite, reduce the difficulty of tempering control, and reduce the strength loss during tempering. On this basis, a higher wire drawing temperature, i.e., quenching temperature, is selected to prepare for the rapid cooling and rapid formation of a structure dominated by quenched bainite during online molten salt micro-quenching. After wire drawing, the wire rod enters the online molten salt for quenching and tempering treatment without air cooling:

[0019] 1. Compared with the air cooling line / water cooling line, the temperature control is unstable and only quickly cooled to the high temperature range of bainite, which brings soft phase or low temperature abnormal structure, feather-like upper bainite structure. On the one hand, the high heat transfer characteristics of molten salt, which has a thermal conductivity much higher than that of air, can be used to promote the rapid cooling of wire rod, pass through the high temperature range of pearlite and bainite phase transformation, and enter the medium temperature range of bainite phase transformation, inhibit the strength loss caused by the formation of pearlite soft phase, inhibit the loss of toughness caused by the formation of feather-like upper bainite, increase the degree of supercooling, promote the wire rod to undergo micro-quenching, and transform the high temperature austenite structure into needle-shaped quenched bainite with better toughness, forming a quenched structure dominated by quenched bainite, and shearing produces high density. On the other hand, when the wire rod passes through the molten salt, the molten salt can cover the surface of the wire rod for uniform and rapid heat exchange. Compared with air cooling, there is no temperature difference problem between the winded surface and the winded surface, and between the overlap and non-overlap, and compared with water cooling, there is no problem of a large number of bubbles interfering with heat transfer. It can reduce the temperature gradient from the surface to the core of the wire rod, and promote the uniform organization transformation of the wire rod. As the processing time increases, it can promote uniform phase transformation of the entire cross section, make the organization fully transformed, avoid the generation of abnormal martensite organization due to entering the low-temperature martensite phase transformation zone during the phase transformation process, or continue to generate abnormal martensite organization in the subsequent phase transformation process due to residual austenite, thereby effectively controlling the organization phase transformation of the high-strength matrix.

[0020] 2. Compared with the coarsening of carbides under high-temperature continuous treatment, the limited cooling control capacity of the insulation cover cooling leads to larger residual stress. On the one hand, as the treatment time increases, the wire rod temperature tends to be consistent with the molten salt temperature, which can extend the isothermal treatment time of the wire rod in the lower bainite phase region. Compared with the pearlite / upper bainite phase region, the medium temperature range of the bainite phase transformation is lower, which can ensure the driving force for carbide nucleation, promote the full dispersion and precipitation of carbides, and evenly distribute them on the matrix, avoid the long-range diffusion of alloy elements leading to carbide coarsening, and bring adverse effects on strength, plasticity and organizational uniformity, thereby compensating for the strength loss caused by tempering. loss; on the other hand, the optimized composition ratio enables the wire rod to be bainite quenched at a higher temperature. Compared with the martensite phase region, the medium temperature range of the bainite phase transformation is higher, which can provide more thermal power, and control the quenching structure of the wire rod after phase transformation to quickly toughen and stress relieve treatment in the isothermal range, reduce dislocation density, toughen and stress relieve treatment, which is beneficial to hinder crack propagation and obtain a tempered bainite structure that is both strong and tough. Afterwards, the roller is used for slow cooling to prevent the wire rod from physical shrinkage and stress generation due to excessive cooling rate during the cooling process, promote further toughening of the wire rod structure, and realize the organization state regulation and strength-plasticity matching of the wire rod.

[0021] Selecting an appropriate heating furnace soaking temperature and furnace time before rolling can promote the full dissolution and homogenization of alloy components, improve rolling plasticity, and prepare for the subsequent precipitation of Nb and V carbides. In the preferred technical solution, before rolling, the heating furnace soaking temperature is controlled to be 1130~1180℃, and the furnace time is 100~155min.

[0022] Due to the high spinning temperature, the restriction on rolling temperature can be reduced. Selecting higher initial rolling temperature and final rolling temperature can improve rolling efficiency, reduce the load requirements and energy consumption of the rolling line, and avoid the initial rolling temperature being too low, which may lead to insufficient solid solution of Nb and V carbides and premature precipitation. It promotes the precipitation of Nb and V microalloying elements in the initial rolling stage, pinning the grain boundaries. Selecting an appropriate final rolling temperature and final rolling reduction can dynamically recrystallize the final rolling process, thereby refining the grains. In the preferred technical solution, during the rolling, the initial rolling temperature is controlled to be 1020~1070℃, the final rolling temperature is 900~930℃, and the final rolling reduction is 21%~26%.

[0023] During the spinning, the spinning temperature can be further controlled to inhibit the coarsening of austenite grains and achieve high deformation energy storage. In a preferred technical solution, during the spinning, the spinning temperature is controlled to be 895-920°C.

[0024] In the preferred technical solution, the online molten salt micro-quenching and tempering 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 that of the rear-stage molten salt treatment. Since the temperature difference between the spinning temperature and the lower bainite phase zone is large, the front-stage molten salt treatment can use a larger molten salt circulation volume to control the molten salt temperature rise, so that the surface and core of the wire rod quickly pass through the pearlite or upper bainite phase transformation zone. As the treatment time increases, the temperature difference between the wire rod temperature and the molten salt decreases. The rear-stage molten salt treatment can appropriately reduce the molten salt circulation volume, control the temperature and reduce production energy consumption at the same time.

[0025] The molten salt temperature of the front-stage molten salt treatment is in the lower bainite phase region. The lower the molten salt temperature of the front-stage molten salt treatment and the longer the treatment time, the more conducive it is to promote the rapid cooling of the wire rod, inhibit the pearlite or upper bainite structure, promote the transformation of high-temperature austenite to quenched bainite, complete the bainite phase transformation in the core of the wire rod, and reduce the loss of strength and toughness. However, if the molten salt temperature of the front-stage molten salt treatment is too low and the dislocation density of the structure is large, it will increase the difficulty of tempering and even overcooling to produce abnormal martensite structure. As the treatment time is prolonged, the production energy consumption increases; on the contrary, the higher the molten salt temperature and the shorter the treatment time, the more conducive it is to reduce the difficulty of isothermal stress relief. degree and production energy consumption, but if the molten salt temperature is too high and the treatment time is too short, the risk of precipitation of soft phase structure will be increased, and the temperature difference from the edge to the core of the wire rod will increase, which is not conducive to the uniform transformation of the structure. Therefore, the molten salt temperature and treatment time of the front-stage molten salt treatment can be controlled, and the wire rod can be controlled to enter the lower bainite phase region from the high-temperature austenite state, and micro-quenching can be performed to form a quenched structure mainly composed of quenched bainite, avoiding excessive dislocation density or the generation of abnormal martensite structure, thereby reducing the treatment difficulty for the subsequent molten salt treatment. In the preferred technical solution, the molten salt temperature of the front-stage molten salt treatment is 395~440℃, and the treatment time is 35~75s.

[0026] The front-stage molten salt treatment can use a higher molten salt circulation rate to enhance the convective heat transfer efficiency of the molten salt and quickly take away the heat, which is conducive to the rapid formation of a quenched structure mainly composed of quenched bainite in the wire rod. In the preferred technical solution, the molten salt circulation rate of the front-stage molten salt treatment is 550~640t / h, and the molten salt temperature rise is ≤7°C.

[0027] The molten salt temperature of the latter molten salt treatment is in the lower bainite phase region. The higher the molten salt temperature and the longer the treatment time of the latter molten salt treatment, the more conducive it is to promoting microstructure homogenization, promoting dislocation slip and rearrangement through thermal activation, reducing quenching residual stress, and improving material toughness. As the treatment time increases, it is conducive to the uniform precipitation of carbides in the form of nano-scale particles and pinning them on the dislocation lines. However, if the molten salt temperature is too high and the treatment time is too long, it is not conducive to avoiding carbide coarsening. Excessive softening of the wire rod will lead to strength loss and increased production energy consumption. Conversely, the lower the molten salt temperature and the shorter the treatment time, the more conducive it is to weakening the diffusion ability of carbides, promoting carbide refinement, and reducing production energy consumption. However, if the molten salt temperature is too low and the treatment time is too short, it is difficult to provide high thermal power, affecting the stress release of the tissue, which will lead to greater plasticity loss. At the same time, as the treatment time is shortened, it is not conducive to the full precipitation of microalloy carbides. In the preferred technical solution, the molten salt temperature of the latter molten salt treatment is 400-425°C and the treatment time is 100-260s.

[0028] The latter stage molten salt treatment appropriately reduces the molten salt circulation volume, which can control the molten salt temperature rise, reduce production energy consumption, provide stable thermodynamic conditions for carbide precipitation, and avoid the molten salt circulation volume being too low to affect the temperature accuracy. In the preferred technical solution, the molten salt circulation volume of the latter stage molten salt treatment is 300~500t / h.

[0029] 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 0.3~0.6°C / s, which can prevent the wire rod from cooling too fast during the cooling process, resulting in increased stress, reduce the risk of stress concentration fracture during subsequent cold processing, and promote further toughening of the wire rod structure, thereby improving the softening effect of the wire rod.

[0030] A 1300 MPa grade high-strength tool steel wire rod is manufactured by any one of the above-mentioned methods for manufacturing a 1300 MPa grade high-strength tool steel wire rod.

[0031] The above-mentioned wire rod adopts the C-Si-Mn-Cr-Nb-V composition system, with relatively low C and Si contents and trace additions of Nb and V, which can appropriately control the material cost. It is made into a wire rod with a mixed structure mainly composed of tempered bainite and a small amount of ferrite by combining with the online molten salt micro-quenching and tempering technology. Compared with the existing pearlite + ferrite tool steel wire rod, the wire rod is micro-quenched in the lower bainite phase region after rapid cooling to form a high-strength matrix with a high dislocation density, which can reduce the content demand for hardenability components such as Cr and Mn, reduce the influence of hardenability and segregation, avoid the risk of C and Cr elements producing brittle structures such as martensite and widmanstattensite, and at the same time, combine the dispersion and precipitation of carbides to maintain the high strength characteristics of the matrix, and maximize the strength of C and Cr elements. The quenching bainite is a kind of bainite structure that is easy to oxidize and deform, and the bainite structure of the wire rod is a kind of bainite structure that is easy to oxidize and deform. The bainite structure of the wire rod is a kind of bainite structure that is easy to oxidize and deform. The bainite structure of the wire rod is a kind of bainite structure that is easy to oxidize and deform. The bainite structure of the wire rod is a kind of bainite structure that is easy to oxidize and deform. The bainite structure of the wire rod is a kind of bainite structure that is easy to oxidize and deform. The bainite structure of the wire rod is a kind of bainite structure that is easy to oxidize and deform. The bainite structure of the wire rod is a kind of bainite structure that is easy to oxidize and deform. The bainite structure of the wire rod is a kind of bainite structure that is easy to oxidize and deform. The bainite structure of the wire rod is a kind of bainite structure that is easy to oxidize and deform. The bainite structure of the wire rod is a kind of bainite structure that is easy to oxidize and deform.

[0032] The more tempered bainite in the wire rod microstructure, the more conducive it is to forming a uniform strong and tough matrix, and the better the deformation uniformity during cold working. In the preferred technical solution, the volume percentage of the tempered bainite is ≥95%.

[0033] In the preferred technical solution, the diameter of the wire rod is 5.5~11mm, the tensile strength is 1255~1305MPa, the cross-sectional shrinkage rate is 58%~63%, the mechanical property circle difference is ≤38MPa, and the wire rod diameter can be used in the manufacturing of screwdrivers, drills, wrenches and other small and medium-sized tool processing fields. The high strength characteristics of the wire rod can be used to withstand larger loads and manufacture parts that require wear resistance and fatigue resistance. The high plasticity of the wire rod can make the wire rod less likely to crack during cold deformation processing, reducing the fracture scrap rate during processing. The smaller mechanical property circle difference further reduces the risk of cold working cracking and local overload failure, so that it can be directly processed into parts after cold working forming.

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

[0035] (1) Aiming at the current situation that tool steel wire rods are usually cooled by Stelmor air cooling line, which leads to the formation of brittle phases such as martensite and difficulty in matching and improving strength and plasticity, the manufacturing method of the present invention combines the Cr-Nb-V chemical composition design with the online molten salt micro-quenching and tempering technology, uses a higher wire drawing quenching temperature and online molten salt micro-quenching to control the wire rods to quickly enter the lower bainite phase region from the high-temperature austenite state, can strongly regulate the wire rod phase transformation, form a quenched structure mainly composed of quenched bainite, avoid the formation of pearlite soft phase and low-strength brittle upper bainite structure, control the wire rods to perform isothermal tempering on the quenched structure in the lower bainite phase region, toughen and relieve stress, effectively improve the plasticity of the wire rods, and then slowly cool the wire rods by rollers to prevent the wire rods from cooling too fast during the cooling process, resulting in stress increase, and promote further toughening of the wire rod structure, thereby improving the strength and plasticity matching of the wire rods, and having good industrial adaptability.

[0036] (2) Aiming at the current situation that tool steel wire rod has high carbon silicon or hardenability and microalloy content, brittle phase is difficult to control, and strength and plasticity are insufficient, which easily leads to cracking during subsequent cold working or requires heat treatment after cold working, the wire rod of the present invention has relatively low C and Si content, and trace amounts of Nb and V are added, which can appropriately control the material cost. The microstructure includes a mixed structure mainly composed of tempered bainite and a small amount of ferrite, avoiding the risk of brittle structures such as martensite and widmanstattenite produced by C and Cr elements, effectively improving the strength of the wire rod, and the strength and plasticity of the tempered bainite structure are better. It can effectively control the organizational state and improve the matching of the strength and plasticity of the wire rod, achieving a tensile strength of 1255~1305MPa and a cross-sectional shrinkage rate of 58%~63%. It is used in the manufacture of high-strength tool steel and other application fields, and can save the heat treatment process after cold working. After cold working, it can be directly processed into parts, which is beneficial to production energy consumption, cost reduction and efficiency improvement, and has good industrial 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 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 1300MPa grade high-strength tool steel wire rod of the present invention comprises the following chemical compositions and mass percentages: C: 0.50%, Si: 0.22%, Mn: 0.40%, Cr: 0.44%, Nb: 0.045%, 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 micro-quenching and tempering 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 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 1130°C, the time in the furnace is 155min, the initial rolling temperature is 1020°C, the final rolling temperature is 900°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 895°C.

[0043] The online molten salt micro-quenching and tempering 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, quickly passes through the pearlite phase region from the high-temperature austenite state, enters the lower bainite phase region, inhibits the formation of pearlite and martensite, and micro-quenches to form a quenching structure mainly composed of quenched bainite. 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 of the quenched structure in the lower bainite isothermal range, toughening and stress relief treatment, inhibiting carbide coarsening, and improving the strength-plasticity matching of the wire rod. Specifically: the molten salt temperature of the front-stage molten salt treatment is 427°C, the treatment time is 57s, the molten salt circulation volume is 550t / h, and the molten salt temperature rise is ≤7°C; the molten salt temperature of the rear-stage molten salt treatment is 401°C, the treatment time is 260s, the molten salt circulation volume is 300t / h, and the total treatment time is 317s.

[0044] 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 271°C at a cooling rate of 0.6°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 1050°C, the furnace time is 195 minutes, the initial rolling temperature is 930°C, the final rolling temperature is 820°C, and the spinning temperature is controlled to 795°C. The Stelmor air cooling line adopts the front 1~5# insulation covers to be opened, and the fan is turned on to control the wire rod to be cooled to 690°C at a rate of 3.2°C / s. Thereafter, the insulation cover is closed, the wire rod enters the insulation cover and is cooled to 285°C at a rate of 1.5°C / s, and is collected by the 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 1050°C, the time in the furnace is 195 minutes, the initial rolling temperature is 930°C, the final rolling temperature is 820°C, the spinning temperature is controlled to 795°C, the wire rod is treated with molten salt in the front section and cooled at a cooling rate of 30°C / s to obtain a finished wire rod. Example 2:

[0049] A preferred embodiment of the method for manufacturing 1300MPa grade high-strength tool steel wire rod of the present invention comprises the following chemical compositions and mass percentages: C: 0.51%, Si: 0.37%, Mn: 0.40%, Cr: 0.47%, Nb: 0.04%, V: 0.048%, 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 micro-quenching and tempering treatment → roller slow cooling → coiling, specifically:

[0050] 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 specification of 11mm 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 furnace time is 100min, the initial rolling temperature is 1070°C, the final rolling temperature is 930°C, and the final rolling reduction is 21%; 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 920°C.

[0051] The online molten salt micro-quenching and tempering 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 41°C / s, quickly passes through the pearlite phase region from the high-temperature austenite state, enters the lower bainite phase region, inhibits the formation of pearlite and martensite, and micro-quenches to form a quenching structure mainly composed of quenched bainite. 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 lower bainite isothermal range, toughens and relieves stress, inhibits carbide coarsening, and improves the strength-plasticity matching of the wire rod. Specifically: the molten salt temperature of the front molten salt treatment is 395°C, the treatment time is 75s, the molten salt circulation volume is 640t / h, and the molten salt temperature rise is ≤7°C; the molten salt temperature of the rear molten salt treatment is 425°C, the treatment time is 100s, the molten salt circulation volume is 500t / h, and the total treatment time is 175s.

[0052] The roller slow cooling process adopts the method of closing the insulation cover, inputting the hot air above the salt bath tank into the insulation cover, and conveying the wire rod through the second section of the salt bath tank by the conveyor roller to slowly cool through the insulation cover, so as 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 276°C at a cooling rate of 0.3°C / s; the coiling process is used to coil the wire rod into a coil by a coiling drum, and obtain the finished wire rod 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 undergoes a front-stage molten salt treatment and is cooled at a cooling rate of 34°C / s, the molten salt temperature of the front-stage molten salt treatment is 455°C, the treatment time is 25s, and the total treatment time of the online molten salt micro-quenching and tempering treatment process is 125s to obtain a finished wire rod.

[0055] Comparative Example 4:

[0056] A method for manufacturing a wire rod, which differs from Example 2 in that: the wire rod undergoes a front-stage molten salt treatment and is cooled at a cooling rate of 43°C / s, the molten salt temperature of the front-stage molten salt treatment is 325°C, the treatment time is 100s, and the total treatment time of the online molten salt micro-quenching and tempering treatment process is 200s to obtain a finished wire rod. Example 3:

[0057] A preferred embodiment of the method for manufacturing 1300MPa grade high-strength tool steel wire rod of the present invention comprises the following chemical compositions and mass percentages: C: 0.52%, Si: 0.30%, Mn: 0.38%, Cr: 0.51%, Nb: 0.044%, V: 0.040%, 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 micro-quenching and tempering 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 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 1160°C, the time in the furnace is 135min, the initial rolling temperature is 1055°C, the final rolling temperature is 925°C, and the final rolling reduction is 22.5%; 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 915°C.

[0059] The online molten salt micro-quenching and tempering 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, quickly passes through the pearlite phase region from the high-temperature austenite state, enters the lower bainite phase region, inhibits the formation of pearlite and martensite, and micro-quenches to form a quenching structure mainly composed of quenched bainite. 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 lower bainite isothermal range, toughens and relieves stress, inhibits carbide coarsening, and improves the strength-plasticity matching of the wire rod. Specifically: the molten salt temperature of the front molten salt treatment is 406°C, the treatment time is 62s, the molten salt circulation volume is 610t / h, and the molten salt temperature rise is ≤7°C; the molten salt temperature of the rear molten salt treatment is 415°C, the treatment time is 165s, the molten salt circulation volume is 430t / h, and the total treatment time is 227s.

[0060] The roller slow cooling process adopts the method of closing the insulation cover, inputting the hot air above the salt bath tank into the insulation cover, and conveying the wire rod through the second section of the salt bath tank by the conveyor roller to be slowly cooled through the insulation cover, so as to prevent the wire rod from cooling too fast and causing stress increase during the cooling process, promote further toughening of the wire rod structure, and improve 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 0.4°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 Example 3 in that the molten salt temperature of the latter molten salt treatment is 465°C, the treatment time is 300s, and the total treatment time of the online molten salt micro-quenching and tempering treatment process is 362s to obtain a finished wire rod.

[0063] Comparative Example 6:

[0064] A method for manufacturing a wire rod, which differs from Example 3 in that the molten salt temperature of the latter molten salt treatment is 409°C, the treatment time is 235s, and the total treatment time of the online molten salt micro-quenching and tempering treatment process is 152s to obtain a finished wire rod. Example 4:

[0065] A preferred embodiment of the method for manufacturing 1300MPa grade high-strength tool steel wire rod of the present invention comprises the following chemical compositions and mass percentages: C: 0.47%, Si: 0.31%, Mn: 0.43%, Cr: 0.36%, Nb: 0.050%, V: 0.047%, 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 micro-quenching and tempering 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 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 1145°C, the time in the furnace is 115min, the initial rolling temperature is 1035°C, the final rolling temperature is 915°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 905°C.

[0067] The online molten salt micro-quenching and tempering 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 34°C / s, quickly passes through the pearlite phase region from the high-temperature austenite state, enters the lower bainite phase region, inhibits the formation of pearlite and martensite, and micro-quenches to form a quenching structure mainly composed of quenched bainite. 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 lower bainite isothermal range, toughens and relieves stress, inhibits carbide coarsening, and improves the strength-plasticity matching of the wire rod. Specifically: the molten salt temperature of the front-stage molten salt treatment is 440°C, the treatment time is 35s, the molten salt circulation volume is 580t / h, and the molten salt temperature rise is ≤7°C; the molten salt temperature of the rear-stage molten salt treatment is 409°C, the treatment time is 235s, the molten salt circulation volume is 385t / h, and the total treatment time is 270s.

[0068] 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 273°C at a cooling rate of 0.55°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.

[0069] Comparative Example 7:

[0070] A method for manufacturing a wire rod, which differs from that of Example 4 in that: the manufacturing method is manufactured according to a process flow of rolling → spinning → online molten salt micro-quenching and tempering 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, and the wire rod is cooled to 285°C at a cooling rate of 1.5°C / s to obtain the wire rod.

[0071] The structure and performance of the wire rods obtained in Examples 1 to 4 and Comparative Examples 1 to 7 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] From the comparison results of Example 1 and Comparative Example 1, it can be seen that compared with the Stelmor air-cooled line, the cooling rate is uncontrollable during the cooling phase transformation, resulting in the generation of abnormal structures such as martensite. Although reducing the contents of C, Cr, Mn, etc. can reduce the control difficulty and the risk of martensite precipitation, the strengthening effect will be weakened due to the uncontrollable cooling rate. The present invention combines the Cr-Nb-V chemical composition design with online molten salt micro-quenching and tempering to control the wire rod to quickly enter the lower bainite phase region from the high-temperature austenite state, strongly regulate the wire rod phase transformation, and avoid the formation of pearlite soft phase, low-strength brittle upper bainite structure or martensite abnormal structure. After isothermal tempering and toughening stress relief treatment, the strength-plasticity matching of the wire rod can be improved. It can be seen from the results of Examples 1 to 4 that the tensile strength is 1255~1305MPa and the cross-sectional shrinkage rate is 58%~63%. It is used in application fields such as the manufacture of high-strength tool steel, so as to eliminate the heat treatment process after cold working, and can be directly processed into parts after cold working.

[0075] From the comparison results of Example 1 and Comparative Example 2, it can be seen that a higher spinning temperature, i.e., quenching temperature, can be selected to avoid premature initiation of phase transformation and prepare for rapid cooling and rapid formation of a structure dominated by quenched bainite during online molten salt micro-quenching. At the same time, a higher spinning temperature can reduce the restriction on rolling temperature, improve rolling efficiency, and reduce the load requirements and energy consumption of 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 lower bainite phase region. The higher the molten salt temperature and the shorter the treatment time, the more conducive to reducing the difficulty of isothermal stress relief and production energy consumption. However, if the molten salt temperature is too high and the treatment time is too short, the risk of precipitation of soft phase structure will increase and the temperature difference from the edge to the core of the wire rod will increase, which is not conducive to uniform transformation of the structure.

[0077] From the comparison results of Example 2 and Comparative Example 4, it can be seen that the molten salt temperature of the front-stage molten salt treatment is in the lower bainite phase region. The lower the molten salt temperature of the front-stage molten salt treatment and the longer the treatment time, the more conducive it is to promote rapid cooling of the wire rod, inhibit pearlite or upper bainite structure, promote the transformation of high-temperature austenite to quenched bainite, complete the bainite phase transformation in the core of the wire rod, and reduce the loss of strength and toughness. However, the molten salt temperature of the front-stage molten salt treatment is too low, and the dislocation density of the structure is large, which will increase the difficulty of tempering and even overcooling to produce abnormal martensite structure. Due to the large molten salt circulation volume of the front-stage molten salt treatment, the treatment time is extended and the production energy consumption increases.

[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 lower bainite phase region. The higher the molten salt temperature of the latter molten salt treatment and the longer the treatment time, the more conducive it is to promote organizational homogenization, promote dislocation slip and rearrangement through thermal activation, reduce quenching residual stress, and improve material toughness. As the treatment time increases, it is beneficial for carbides to precipitate uniformly in the form of nano-scale particles and pin them on the dislocation lines. However, if the molten salt temperature is too high and the treatment time is too long, it is not conducive to avoiding carbide coarsening. Excessive softening of the wire rod will lead to strength loss, and at the same time, production energy consumption will increase.

[0079] From the comparison results of Example 3 and Comparative Example 6, it can be seen that the molten salt temperature of the latter molten salt treatment is in the lower bainite phase region. The lower the molten salt temperature and the shorter the treatment time, the more conducive it is to weakening the diffusion ability of carbides, promoting carbide refinement, and reducing production energy consumption. However, if the molten salt temperature is too low and the treatment time is too short, it is difficult to provide high thermal power, which affects the stress release of the tissue and will bring about a large plastic loss. At the same time, as the treatment time is shortened, it is not conducive to the full precipitation of microalloy carbides.

[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, and promotes further toughening of the wire rod structure, thereby improving 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 1300MPa 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 ≥895°C, and then subjected to an online molten salt micro-quenching and tempering treatment. The wire rod is cooled at a rate of ≥31°C / s from a high-temperature austenite state to a lower bainite phase region to form a quenched structure mainly composed of quenched bainite. The quenched structure is then isothermally tempered and toughened to relieve stress, and finally slowly cooled on a roller to form a wire rod with a microstructure including tempered bainite and ferrite. The chemical composition and mass percentage of the wire rod include: C: 0.47%~0.52%, Si: 0.22%~0.37%, Mn: 0.38%~0.43%, Cr: 0.36%. ~0.51%, Nb: 0.040%~0.050%, V: 0.040%~0.050%, P≤0.015%, S≤0.015%, and the rest are Fe and unavoidable impurities; the online molten salt micro quenching and tempering treatment is divided into a front-stage molten salt treatment and a rear-stage molten salt treatment, the molten salt temperature of the front-stage molten salt treatment is 395~440℃, and the treatment time is 35~75s, and the molten salt temperature of the rear-stage molten salt treatment is 400~425℃, and the treatment time is 100~260s; the roller slow cooling controls the wire rod to slowly cool to below 280℃ at a cooling rate of 0.3~0.6℃ / s.

2. The method for manufacturing 1300MPa 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 1130-1180° C., and the soaking time in the furnace is 100-155 minutes.

3. The method for manufacturing 1300MPa 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 1020-1070° C., the final rolling temperature is controlled to be 900-930° C., and the final rolling reduction is controlled to be 21%-26%; during the spinning, the spinning temperature is controlled to be 895-920° C.

4. The method for manufacturing 1300 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 1300 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 550~640t / h, and the molten salt temperature rise is ≤7°C; the molten salt circulation rate of the back-stage molten salt treatment is 300~500t / h.

6. A 1300MPa grade high strength tool steel wire rod, characterized in that: The wire rod is manufactured by the manufacturing method of 1300MPa grade high-strength tool steel wire rod according to any one of claims 1 to 5.

7. The 1300 MPa grade high strength tool steel wire rod according to claim 6, characterized in that: The volume percentage of the tempered bainite is ≥95%.

8. The 1300 MPa grade high strength tool steel wire rod according to claim 6, characterized in that: The diameter of the wire rod is 5.5-11 mm, the tensile strength is 1255-1305 MPa, the cross-sectional shrinkage rate is 58%-63%, and the mechanical property difference within the same circle is ≤38 MPa.

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