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

Abstract

The invention relates to a 1300 MPa-grade high-strength tool steel wire rod and a manufacturing method thereof, after a Cr-Nb-V medium carbon component design is adopted for rolling and spinning to form a wire rod, the wire rod is subjected to online molten salt micro-quenching tempering treatment, the wire rod is controlled to enter a lower bainite phase region from a high-temperature austenite state at a cooling speed greater than or equal to 31 DEG C / s, and a quenching structure mainly comprising quenching bainite is formed; the steel wire rod with a microscopic structure comprising tempered bainite and ferrite is prepared by carrying out isothermal tempering and toughening destressing treatment on a quenched structure and finally carrying out roller way slow cooling, so that the material cost can be properly controlled, the strength and plasticity matching of the steel wire rod is improved, the tensile strength is 1255-1305MPa, and the percentage reduction of area is 58-63%, so that the steel wire rod can be directly processed into a part after being subjected to cold processing molding, and the service life of the steel wire rod is prolonged. And tool steel production energy consumption, cost reduction and efficiency improvement are facilitated.

Description

Technical Field

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

[0002] Alloy tool steels can improve the toughness and service performance of materials by controlling the carbon content of the materials and adding appropriate amounts of hardenability elements such as Cr, Mn, and Mo. They are suitable for more complex working conditions. Compared with high-speed tool steels, they can appropriately reduce the carbon content, contain no or a small amount of W and V elements, reduce the risk of network carbon caused by high carbon content, sacrifice extreme red hardness in exchange for better toughness and workability, and at the same time greatly reduce costs. They are suitable for tool processing such as turning tools, milling cutters, and screwdrivers. Alloy tool steels generally use hot-rolled wire rods as the base material and are subjected to cold forming processes such as drawing and cold heading. In order to improve the work hardening and residual stress caused by cold working and balance the strength and toughness, heat treatment processes are also required after cold working to improve the service performance of the products, but this also brings problems such as increased production energy consumption, increased processing costs, and reduced efficiency. Therefore, it is necessary to develop a 1300 MPa grade high-strength tool steel wire rod and a manufacturing method thereof, so that it can be directly processed into parts after cold forming to meet the market demand of tool steels.

[0003] Existing alloy tool steel wire rods generally adopt medium-carbon alloy compositions and combine the Stelmor air-cooling line to control the cooling of the wire rods after rolling into pearlite or bainite structures. The main reasons for the difficulty in meeting the requirement of eliminating the heat treatment process after cold working are as follows: First, in order to improve the service performance of the materials, hardenability components are selected and added to the steel in the prior art. For example, a low-alloy hand tool steel wire rod with a uniform through-thickness structure and a tensile strength of 1000 MPa disclosed in Patent CN115976407B adopts a C-Si-Mn-Cr-V-Al composition design and combines low-temperature rolling and heat preservation cooling in the air-cooling line to make it into a pearlite + ferrite structure. However, on the one hand, the pearlite soft-phase structure results in insufficient matrix strength, and continuously 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. In view of the limited controlled cooling ability of the conventional Stelmor air-cooling line, due to insufficient control of the cooling rate, the phase transformation control of the wire rod is difficult, and hardenability elements are likely to induce the generation of brittle phases such as martensite, which is extremely likely to cause cracking problems during subsequent cold working. Reducing the content of hardenability components or the content of V components with fine grain strengthening effect will result in strength loss, limiting the strength improvement of the wire rod.

[0004] II. To improve the adverse effects of martensite structure on the packing, transportation and user processing of wire rods, or to enhance the surface wear resistance of finished tools, medium-carbon high-silicon steel is selected in the prior art, and wire rods with a high bainite content are produced by air cooling or water cooling after spinning. For example, in an online bainite isothermal quenching process for alloy tool steel wire rods disclosed in Patent CN118621099A, rapid cooling is carried out after spinning to the upper bainite transformation region and then heat preservation is carried out in a heat preservation cover to produce a bainite structure with lower hardness; in a high-alloy tool steel wire rod with a high bainite content and its manufacturing method disclosed in Patent CN114134399B, low-temperature rolling and spinning and water bath cooling are used to control the rapid transition of the wire rod to the bainite region, and then coiling is carried out and phase transformation is carried out in the bainite region during heat preservation. However, on the one hand, the maximum cooling capacity of the air-cooling line is limited. As the air-cooling intensity increases, the temperature difference between the windward surface and the leeward surface of the wire rod, and the temperature difference between the overlapping part and the non-overlapping part will increase. Although the cooling capacity of the water-cooling line can be higher than that of the air-cooling line, a large number of bubbles will be generated on the surface of the wire rod during the water-cooling process, affecting the heat transfer uniformity, resulting in an increased risk of precipitation of abnormally brittle tissues at low temperatures, coarsening of carbides and unevenness of the structure. On the other hand, the Si content in the components is relatively high, which will delay the bainite phase transformation kinetics. At the same time, due to the limited minimum cooling capacity of the heat preservation cover, the air-cooling line is restricted by fan cooling and heat preservation cooling, and the water-cooling line is restricted by heat preservation cooling. The wire rod after spinning needs to be quickly cooled to the high-temperature bainite temperature range first, and it is easier to form a feathery upper bainite structure composed of ferrite laths and cementite between the laths. The activation energy for carbide growth is relatively large, resulting in insufficient strength and toughness of the matrix. As the wire rod continues to cool and phase transformation incubation occurs during heat preservation, the wire rod is in a low-temperature state, and there is a large dislocation density and tissue stress in the structure, which will exacerbate the risk of cold working cracking. Summary of the Invention

[0005] The present invention aims to solve at least one of the above technical problems to a certain extent. The present invention provides a 1300 MPa grade high-strength tool steel wire rod and its manufacturing method, which can appropriately control the material cost, improve the strength-plasticity performance matching of the wire rod, so that it can be directly processed into parts after cold forming, which is beneficial to reducing the production energy consumption, cost and improving the efficiency of tool steel.

[0006] The technical solution adopted by the present invention to solve its technical problems is as follows: A manufacturing method of a 1300 MPa grade high-strength tool steel wire rod, 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 online molten salt micro-quenching and tempering treatment, and the wire rod is controlled to enter the lower bainite phase region from the high-temperature austenite state at a cooling rate of ≥31°C / s to form a quenched structure mainly composed of quenched bainite, and then the quenched structure is subjected to isothermal tempering, toughening and stress relief treatment, 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.

[0007] The design basis of the chemical composition and mass percentage of the above wire rod includes: (1) Carbon: As a carbide strengthening element and austenite forming element, C is relatively cheaper. As the carbon content increases, the carbon concentration in austenite increases, which can reduce the bainite phase transformation temperature and make the phase transformation more easily shift to the low temperature zone. It can delay the pearlite transformation and promote the online molten salt controlled wire rod to form a quenched bainite structure with good toughness, giving the tool steel wire rod high strength and wear resistance. However, excessive carbon content increases the supercooling required for the bainite phase transformation, easily forming coarse cementite or martensite, resulting in a decrease in toughness and an increase in hardness, which increases the difficulty of isothermal tempering. Therefore, in order to meet the strength and wear resistance requirements of tool steel and control material costs, and at the same time facilitate the micro-quenching and tempering treatment of wire rods and improve the strength-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%.

[0008] (2) Silicon: Si is a strong ferrite-forming element. It can inhibit grain coarsening and cementite precipitation during online molten salt micro-quenching and tempering treatment, delay 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 silicon content will lead to excessive strengthening of the ferrite matrix, aggravated lattice distortion, decreased material plasticity and impact toughness, which is not conducive to the fracture resistance of tool steel and affects the tempering plasticity regulation. Therefore, in order to maintain matrix strength, reduce tempering difficulty, and adapt to the regulation of microstructure by online molten salt micro-quenching and tempering, the mass percentage of Si is controlled to be 0.22%~0.37%.

[0009] (3) Manganese: The Mn element can increase the stability of austenite and the hardenability of the wire rod, expand the austenite region, lower the austenite decomposition temperature, delay the transformation of pearlite and bainite, shift the phase transformation to the low-temperature region, increase the dislocation density of bainite ferrite, meet the requirements of micro-quenching, and improve the strength and hardness of the wire rod. However, when the content of Mn is too high, the austenite grains are prone to coarsening during heating, the composition segregation is aggravated, the risk of martensite precipitation increases, higher energy is required for stress release, the tempering softening process is delayed, and the toughness and plasticity of the steel are reduced. Therefore, in order to enable micro-quenching to rapidly form quenched bainite and facilitate the control of tempering softening, the Mn content is appropriately reduced, and the mass percentage of Mn is controlled at 0.38% - 0.43%.

[0010] (4) Chromium: As a carbide-forming element, the Cr element has high-hardness chromium carbides, which can improve the wear resistance of tool steel. At the same time, it can significantly increase the hardenability of the 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 the composition segregation, with the risk of coarse and unevenly distributed carbides, increasing the difficulty of controlling tissue uniformity, the difficulty of improving plasticity, and the brittleness of the tool. Therefore, in order to balance the wear resistance requirements of tool steel and enable micro-quenching tempering to be carried out at a higher temperature, the mass percentage of Cr is controlled at 0.36% - 0.51%.

[0011] (5) Niobium: The Nb element forms high-melting-point carbides, which can precipitate and pin the grain boundaries, strongly inhibit the growth of austenite grains, and obtain a fine-grained structure. Fine-grained austenite can promote the nucleation of bainite ferrite at more grain boundaries, accelerate the phase transformation, and at the same time produce a strong precipitation strengthening effect, improving the high-temperature hardness of tool steel and reducing the crack risk. However, the cost of Nb is relatively high. Therefore, based on the role, cost, and manufacturing control of the Nb element, the mass percentage of Nb is controlled at 0.040% - 0.050%.

[0012] (6) Vanadium: The V element forms high-hardness carbides, which can pin the grain boundaries to inhibit the growth of austenite grains, refine the original structure, promote the formation of high-density dislocations and twins in bainite ferrite, improve the wear resistance of tool steel, and at the same time the dispersion precipitation of carbides plays a role in rapidly increasing the matrix strength. However, the cost of the V element is relatively high, and excessive addition is not conducive to controlling the cost of the wire rod. Therefore, based on the role, cost, and manufacturing control of the V element, the mass percentage of V is controlled at 0.040% - 0.050%.

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

[0014] The above wire rod adopts a medium-carbon composition design of Cr-Nb-V. 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, and Cr, it provides favorable conditions for online molten salt micro quenching and tempering to carry out 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 regulation, and reduce the strength loss during tempering. On this basis, a relatively high spinning temperature, that is, the quenching temperature, is selected to prepare for the rapid cooling of the wire rod after spinning to form a structure mainly composed of quenched bainite. The wire rod after spinning enters the online molten salt for quenching and tempering treatment without passing through air cooling: 1. Compared with the unstable temperature control of the air-cooling line / water-cooling line, which only rapidly cools to the high-temperature temperature range of bainite, resulting in soft phases or abnormal low-temperature structures, and feathery upper bainite structures. On the one hand, the high heat transfer characteristics of molten salt with a thermal conductivity much higher than that of air can be utilized to promote the rapid cooling of the wire rod, pass through the high-temperature temperature range of pearlite and bainite phase transformations, enter the medium-temperature temperature range of bainite phase transformation, inhibit the strength loss caused by the formation of soft pearlite phases, inhibit the loss of strength and toughness caused by the formation of feathery upper bainite, increase the degree of supercooling, promote the wire rod to undergo micro quenching, and transform the high-temperature austenite structure into acicular quenched bainite with better strength and toughness, forming a quenched structure mainly composed of quenched bainite, generating high-density dislocations by shear, and increasing the matrix strength. 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 transfer. There is no problem of temperature difference between the windward side and the leeward side, the overlapping part and the non-overlapping part as in air cooling, and there is no problem of a large number of bubbles interfering with heat transfer as in water cooling. It can reduce the temperature gradient from the surface to the core of the wire rod, promote the uniform tissue transformation of the wire rod. As the treatment time prolongs, it can promote the uniform phase transformation of the entire cross-section, make the tissue fully transform, avoid the generation of abnormal martensite tissue due to entering the low-temperature martensite phase transformation region during the phase transformation process, or the continuous generation of abnormal martensite tissue due to residual austenite during the subsequent phase transformation process, and thus effectively control the tissue phase transformation of the high-strength matrix.

[0015] II. Compared with the carbide coarsening under high-temperature continuous treatment, due to the limited cooling control ability of the heat preservation cover, larger residual stresses are caused. On the one hand, as the treatment time prolongs, the temperature of the wire rod 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 bainite transformation has a lower temperature, which can ensure the nucleation driving force of carbides, promote the full and uniform precipitation of carbides on the matrix, and avoid the coarsening of carbides caused by the long-range diffusion of alloying elements, which has an adverse impact on strength and plasticity and tissue uniformity, thereby compensating for the strength loss caused by tempering. On the other hand, the optimized component ratio enables the wire rod to be bainite quenched at a higher temperature. Compared with the martensite phase region, the medium-temperature range of bainite transformation has a higher temperature, which can provide more thermal power, control the rapid toughening and stress relief treatment of the quenched structure of the wire rod after phase transformation in the isothermal range, reduce the dislocation density, and perform toughening and stress relief treatment, which is beneficial to hindering crack propagation and obtaining a tempered bainite structure that is both strong and tough. Then, the roller table slow cooling is used to prevent the wire rod from physical shrinkage and stress generation due to too fast cooling rate during the cooling process, promote the further toughening of the wire rod structure, and realize the regulation of the tissue state and the matching of strength and plasticity of the wire rod.

[0016] Selecting an appropriate soaking temperature and soaking time in the heating furnace before rolling can promote the full dissolution and homogenization of alloying components, improve the rolling plasticity, and prepare for the subsequent precipitation of Nb and V carbides. In the preferred technical solution, before rolling, the soaking temperature of the heating furnace is controlled at 1130 - 1180 °C, and the soaking time is 100 - 155 min.

[0017] Due to the relatively high spinning temperature, the limitation on the rolling temperature can be reduced. Selecting a higher initial rolling temperature and final rolling temperature can improve the rolling efficiency, reduce the load requirements and energy consumption of the rolling line, and at the same time avoid the premature precipitation of Nb and V carbides due to insufficient solution of Nb and V carbides at too low initial rolling temperature. Promote the precipitation of Nb and V microalloying elements in the initial rolling stage, pin the grain boundaries, select an appropriate final rolling temperature and cooperate with the final rolling reduction to realize dynamic recrystallization during the final rolling process, and play a role in refining grains. In the preferred technical solution, during rolling, the initial rolling temperature is controlled at 1020 - 1070 °C, the final rolling temperature is 900 - 930 °C, and the final rolling reduction is 21% - 26%.

[0018] During spinning, the spinning temperature can be further controlled to inhibit the coarsening of austenite grains and store high deformation energy. In the preferred technical solution, during spinning, the spinning temperature is controlled at 895 - 920 °C.

[0019] In the preferred technical solution, the on-line molten salt micro quenching and tempering treatment is divided into the front-stage molten salt treatment and the 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. Due to the large temperature difference between the wire laying temperature and the lower bainite phase region, a larger molten salt circulation volume can be selected for the front-stage molten salt treatment to control the temperature rise of the molten salt, so that the surface and core of the wire rod quickly pass through the pearlite or upper bainite phase transformation region. As the treatment time prolongs, the temperature difference between the wire rod temperature and the molten salt shrinks. The molten salt circulation volume of the rear-stage molten salt treatment can be appropriately reduced to control the temperature while reducing the production energy consumption.

[0020] The molten salt temperature of the front-stage molten salt treatment is in the lower bainite phase region. The lower the molten salt temperature and the longer the treatment time of the front-stage molten salt treatment, it is beneficial to promote the rapid cooling of the wire rod, inhibit the pearlite or upper bainite structure, and promote the transformation of high-temperature austenite to quenched bainite, so that the core of the wire rod completes the bainite phase transformation and reduces the loss of strength and toughness. However, if the molten salt temperature of the front-stage molten salt treatment is too low, the dislocation density of the structure is relatively large, which will increase the tempering difficulty or even generate abnormal martensite structure due to supercooling. As the treatment time prolongs, the production energy consumption increases; on the contrary, the higher the molten salt temperature and the shorter the treatment time, it is beneficial to reduce the isothermal stress relief difficulty 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 the uniform transformation of the structure. Therefore, the molten salt temperature and treatment time of the front-stage molten salt treatment can be controlled to control the wire rod to enter the lower bainite phase region from the high-temperature austenite state, and micro quenching forms a quenched structure mainly composed of quenched bainite, avoiding too large dislocation density or generating abnormal martensite structure, and reducing the treatment difficulty for the rear-stage molten salt treatment. In the preferred technical solution, the molten salt temperature of the front-stage molten salt treatment is 395-440 °C, and the treatment time is 35-75 s.

[0021] A higher molten salt circulation volume can be selected for the front-stage molten salt treatment to enhance the convective heat transfer efficiency of the molten salt and quickly take away heat, which is beneficial 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 volume of the front-stage molten salt treatment is 550-640 t / h, and the temperature rise of the molten salt ≤ 7 °C.

[0022] The molten salt temperature of the subsequent molten salt treatment is in the lower bainite phase region. The higher the molten salt temperature and the longer the treatment time of the subsequent molten salt treatment, it is beneficial to promote the homogenization of the structure, promote the dislocation slip and rearrangement through thermal activation, reduce the quenching residual stress, and improve the toughness of the material. With the extension of the treatment time, it is beneficial for carbides to precipitate uniformly in nanoscale particles and pin 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 the coarsening of carbides. The excessive softening of the wire rod will cause strength loss and increase the production energy consumption at the same time; on the contrary, the lower the molten salt temperature and the shorter the treatment time, it is beneficial to weaken the diffusion ability of carbides, promote the refinement of carbides, and reduce the 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, affect the release of tissue stress, will cause greater plastic loss, and at the same time, it is not conducive to the full precipitation of microalloy carbides with the shortening of the treatment time. In the preferred technical solution, the molten salt temperature of the subsequent molten salt treatment is 400-425°C, and the treatment time is 100-260 s.

[0023] Appropriately reducing the molten salt circulation amount in the subsequent molten salt treatment can control the molten salt temperature rise and reduce the production energy consumption, provide stable thermodynamic conditions for the precipitation of carbides, and at the same time avoid the too low molten salt circulation amount affecting the temperature accuracy. In the preferred technical solution, the molten salt circulation amount in the subsequent molten salt treatment is 300-500 t / h.

[0024] In the preferred technical solution, the roller table slow cooling controls the wire rod to cool slowly at a cooling rate of 0.3-0.6°C / s to below 280°C, which can prevent the wire rod from increasing stress due to too fast cooling rate during the cooling process, reduce the risk of stress concentration fracture during subsequent cold working, and promote the further toughening of the wire rod structure and improve the softening effect of the wire rod.

[0025] A 1300 MPa grade high-strength tool steel wire rod, which is manufactured by the manufacturing method of the 1300 MPa grade high-strength tool steel wire rod described in any one of the above.

[0026] The above-mentioned wire rod adopts a C-Si-Mn-Cr-Nb-V composition system. The contents of C and Si are relatively low, and Nb and V are added in trace amounts, which can appropriately control the material cost. Combined with the online molten salt micro quenching and tempering technology, the wire rod is made into a wire rod with a mixed structure mainly composed of tempered bainite and containing a small amount of ferrite. Compared with the existing pearlite + ferrite tool steel wire rod, the wire rod is rapidly cooled to the lower bainite phase region for micro quenching, and a high-strength matrix with a high dislocation density can be formed, which can reduce the content requirements of hardenability components such as Cr and Mn, reduce the influence of hardenability and segregation, and avoid the risk of brittle structures such as martensite and Widmanstatten formed by C and Cr elements. At the same time, combined with the precipitation of carbides in a dispersed manner, the high-strength characteristics of the matrix are maintained, the strengthening effect of C and Cr elements is maximally improved, and the strength of the wire rod is effectively improved. Compared with the bainite structure tool steel wire rod produced by the existing air-cooled or water-cooled line, the wire rod undergoes phase transformation and isothermal treatment in the lower bainite phase region, which can avoid the formation of poor-plasticity feathery upper bainite in the high-temperature bainite temperature range of the wire rod. The obtained quenched bainite has better strength and toughness. At the same time, through isothermal tempering treatment, the dislocation density of the quenched bainite decreases, and the tissue stress generated by quenching is released, which can reduce the content requirements of Nb and V microalloys, reduce the material cost and further optimize the plastic and toughness properties, obtain a tempered bainite structure with better strength and toughness, avoid stress concentration cracking during cold processing, effectively control the tissue state, and improve the strength-plasticity performance matching of the wire rod, so that it can be directly processed into tool parts after cold processing.

[0027] The more tempered bainite in the microstructure of the wire rod is beneficial to the formation of a uniform strength and toughness matrix, and the deformation uniformity during cold processing is better. In the preferred technical solution, the volume percentage of the tempered bainite ≥ 95%.

[0028] In the preferred technical solution, the diameter of the wire rod is 5.5 - 11 mm, the tensile strength is 1255 - 1305 MPa, the reduction of area is 58% - 63%, the difference in mechanical properties within the same coil ≤ 38 MPa. The diameter of the wire rod can be applied to the processing fields of medium and small tools such as screwdrivers, drills, and wrenches. The high-strength characteristics of the wire rod can be used to bear greater loads and manufacture parts that require wear resistance and fatigue resistance. The high plasticity of the wire rod can make the wire rod not easily crack during cold deformation processing, reduce the fracture scrap rate during processing, and the smaller difference in mechanical properties within the same coil can further reduce the risk of cold processing cracking and local overload failure, so that it can be directly processed into parts after cold processing forming.

[0029] Compared with the prior art, the beneficial effects of the present invention are at least as follows: (1)For the current situation that the wire rods of tool steel are usually controlled by Stelmor air cooling line, resulting in the generation of brittle phases such as martensite and the difficulty in matching and improving strength and plasticity, the manufacturing method of the present invention combines Cr-Nb-V chemical composition design with on-line molten salt micro quenching and tempering technology. With a relatively high wire laying and quenching temperature and on-line molten salt micro quenching, the wire rods are controlled to quickly enter the lower bainite phase region from the high-temperature austenite state, which can strongly regulate the phase transformation of the wire rods, 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 isothermal tempering of the quenched structure in the lower bainite phase region, perform toughening and stress relief treatment, effectively improve the plasticity of the wire rods, and then slow cooling on the roller table to prevent the stress from increasing due to too fast cooling rate during the cooling process of the wire rods, and promote the further toughening of the wire rod structure, improve the strength and plasticity matching of the wire rods, and have good industrial adaptability.

[0030] (2)For the current situation that the carbon, silicon or hardenability, and microalloy content of the wire rods of tool steel are relatively high, it is difficult to control brittle phases and the strength and plasticity are insufficient, which is extremely easy to cause cracking during subsequent cold processing, or heat treatment regulation is required after cold processing. The C and Si contents of the wire rods of the present invention are relatively low, and Nb and V are added in trace amounts, which can appropriately control the material cost. The microstructure includes a mixed structure mainly composed of tempered bainite and containing a small amount of ferrite, avoiding the risk of brittle structures such as martensite and Widmanstatten structure caused by C and Cr elements, effectively improving the strength of the wire rods. The strength and plasticity of the tempered bainite structure are better, which can effectively regulate the tissue state and improve the strength and plasticity matching of the wire rods, reaching a tensile strength of 1255-1305 MPa and a reduction of area of 58%-63%. It is used in application fields such as manufacturing high-strength tool steel, and the heat treatment process after cold processing can be omitted. After cold processing and forming, it can be directly processed into parts, which is beneficial to reducing production energy consumption, cost and improving efficiency, and has good industrial application prospects. Brief Description of the Drawings

[0031] The above and / or additional aspects and advantages of the present invention will become obvious and easy to understand from the description of the embodiments in conjunction with the following drawings, where: Figure 1 is the metallographic structure diagram of Embodiment 1 of the present invention; Figure 2 is the metallographic structure diagram of Embodiment 2 of the present invention. Detailed Embodiments

[0032] The embodiments described below with reference to the accompanying drawings are exemplary, merely for illustrative purposes and do not limit the description of the features and characteristics of the present invention. They are intended to present the best mode of implementing the present invention, for the purpose of explaining the present invention and enabling those skilled in the art to implement the present invention. It should not be construed as limiting the scope of the present invention, which is only defined by the appended claims. The organization and performance testing of the wire rods obtained from the following embodiments and comparative examples include: the tensile test is carried out in accordance with "GB-T 228.1-2021 Metallic materials-Tensile testing-Part 1: Method of test at room temperature" to obtain the tensile strength and reduction of area; the microstructure detection is carried out in accordance with the metallic microstructure detection method of the GB / T13298 standard; the method for testing the difference in mechanical properties within the same coil: take 2 coils of wire rods at 5 m from the end of the coil, take the lap area position as the base point, evenly divide each coil of wire rods into 8 segments on average, take 1 tensile specimen on each segment, and the strength range of the tensile specimens after tensile testing is the difference in mechanical properties within the same coil. Example 1:

[0033] A preferred embodiment of the manufacturing method of the 1300 MPa grade high-strength tool steel wire rod of the present invention, the chemical composition and mass percentage of the wire rod include C: 0.50%, Si: 0.22%, Mn: 0.40%, Cr: 0.44%, Nb: 0.045%, V: 0.05%, P: 0.014%, S: 0.014%, and the rest are Fe and unavoidable impurities; its manufacturing method is manufactured according to the technological process of rolling → wire laying → on-line molten salt micro quenching and tempering treatment → slow cooling on the roller table → coiling, specifically: The rolling process is used to heat the steel billet with a specification of 180 mm × 180 mm into a high-temperature steel billet that reaches the plastic state for rolling, promoting the homogenization of alloy components. The heating furnace is controlled according to the three-stage heating program of the preheating section, heating section, and soaking section. The high-temperature steel billet is rolled into a wire rod with a diameter specification of 5.5 mm through the rolling line. Appropriate rolling temperature and reduction are selected to increase the rolling speed, promote dynamic recrystallization during the finishing rolling process, and refine the grains. Specifically: control the soaking temperature of the heating furnace to be 1130 °C, the residence time in the furnace to be 155 min, the initial rolling temperature to be 1020 °C, the finishing rolling temperature to be 900 °C, and the finishing rolling reduction to be 26%; the wire laying process is used to make the wire rod out of the rolling line into a wire coil through the wire laying machine. The wire coil is scattered on the roller table and conveyed along the roller table, so that the wire coil is in a high-temperature austenite state, preparing for quenching the structure with a relatively high quenching temperature. Specifically: control the wire laying temperature to be 895 °C.

[0034] The online molten salt micro quenching and tempering process uses a two-stage salt bath tank with internal molten salt. The wire rod after wire drawing is transported through the first-stage salt bath tank by a roller table for the front-stage molten salt treatment, so that the wire rod cools down at a cooling rate of 37 °C / s, quickly crosses 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 quenching forms a quenched structure mainly composed of quenched bainite. Then the wire rod is transported through the second-stage salt bath tank by a roller table for the rear-stage molten salt treatment, reducing the molten salt circulation volume, controlling the isothermal tempering of the quenched structure in the lower bainite isothermal range of the wire rod, toughening and stress relieving treatment, inhibiting the coarsening of carbides, and improving the strength-plasticity matching of the wire rod. Specifically: the molten salt temperature for the front-stage molten salt treatment is 427 °C, the treatment time is 57 s, the molten salt circulation volume is 550 t / h, and the molten salt temperature rise ≤ 7 °C; the molten salt temperature for the rear-stage molten salt treatment is 401 °C, the treatment time is 260 s, the molten salt circulation volume is 300 t / h, and the total treatment time is 317 s.

[0035] In the roller table slow cooling process, the heat preservation cover is closed, and the wire rod transported by the conveying roller table through the second-stage salt bath tank is slowly cooled through the heat preservation cover, preventing the wire rod from having too fast a cooling rate during the cooling process, resulting in an increase in stress, and promoting the further toughening of the wire rod structure, improving the softening effect of the wire rod until coiling. Specifically: controlling the wire rod to slowly cool to 271 °C at a cooling rate of 0.6 °C / s; the coiling process is used to coil the wire rod into a coil by a coiling drum, and after packaging and warehousing, the finished wire rod is obtained, and its metallographic structure diagram is as Figure 1 shown.

[0036] Comparative Example 1: A manufacturing method of a wire rod, the difference between its manufacturing method and that of Example 1 lies in: its manufacturing method is manufactured according to the technological process of rolling → wire drawing → Stelmor air cooling line → coiling. Specifically: in the rolling process, the soaking temperature of the heating furnace is controlled at 1050 °C, the time in the furnace is 195 min, the initial rolling temperature is 930 °C, the final rolling temperature is 820 °C, the wire drawing temperature is controlled at 795 °C. In the Stelmor air cooling line, the front 1-5# heat preservation covers are opened, and the fan is turned on to control the wire rod to cool to 690 °C at a speed of 3.2 °C / s. Then the heat preservation cover is closed, the wire rod enters the heat preservation cover and cools to 285 °C at a speed of 1.5 °C / s, and is collected by the coiling drum to obtain the finished wire rod.

[0037] Comparative Example 2: A manufacturing method of a wire rod, the difference between its manufacturing method and that of Example 1 lies in: controlling the soaking temperature of the heating furnace at 1050 °C, the time in the furnace at 195 min, the initial rolling temperature at 930 °C, the final rolling temperature at 820 °C, controlling the wire drawing temperature at 795 °C, and the wire rod undergoes the front-stage molten salt treatment and cools down at a cooling rate of 30 °C / s to obtain the finished wire rod. Example 2:

[0038] A preferred embodiment of the manufacturing method of the 1300 MPa grade high-strength tool steel wire rod. The chemical composition and mass percentage of the wire rod include 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 rest are Fe and inevitable impurities. Its manufacturing method is manufactured according to the technological process of rolling → wire laying → on-line molten salt micro quenching and tempering treatment → slow cooling on the roller table → coiling. Specifically: The rolling process is used to heat the steel billet with a specification of 220 mm × 220 mm into a high-temperature steel billet that reaches the plastic state for rolling, promoting the homogenization of alloy components. The heating furnace is controlled according to the three-stage temperature rise program of the preheating section, heating section, and soaking section. The high-temperature steel billet is rolled into a wire rod with a diameter specification of 11 mm through the rolling line. Appropriate rolling temperature and reduction are selected to increase the rolling speed, promote dynamic recrystallization during the finishing rolling process, and refine the grains. Specifically: control the soaking temperature of the heating furnace to be 1180 °C, the residence time in the furnace to be 100 min, the initial rolling temperature to be 1070 °C, the finishing rolling temperature to be 930 °C, and the finishing rolling reduction to be 21%; The wire laying process is used to make the wire rod exiting the rolling line into a wire rod through the wire laying machine. The wire rod is scattered on the roller table and conveyed along the roller table, making the wire rod in the high-temperature austenite state, preparing for quenching the structure with a relatively high quenching temperature. Specifically: control the wire laying temperature to be 920 °C.

[0039] The on-line molten salt micro quenching and tempering treatment process uses a two-stage salt bath tank with molten salt inside. The wire rod after wire laying is conveyed through the roller table and passes through the first-stage salt bath tank for the front-stage molten salt treatment, making the wire rod cool at a cooling rate of 41 °C / s, quickly crossing the pearlite phase region from the high-temperature austenite state and entering the lower bainite phase region, inhibiting the formation of pearlite and martensite, and micro quenching to form a quenched structure mainly composed of quenched bainite. Then the wire rod is conveyed through the roller table and passes through the second-stage salt bath tank for the rear-stage molten salt treatment, reducing the molten salt circulation volume, controlling the wire rod to perform isothermal tempering on the quenched structure in the lower bainite isothermal range, toughening and stress relieving treatment, inhibiting the coarsening of carbides, and improving the strength-plasticity matching of the wire rod. Specifically: the molten salt temperature for the front-stage molten salt treatment is 395 °C, the treatment time is 75 s, the molten salt circulation volume is 640 t / h, and the molten salt temperature rise ≤ 7 °C; the molten salt temperature for the rear-stage molten salt treatment is 425 °C, the treatment time is 100 s, the molten salt circulation volume is 500 t / h, and the total treatment time is 175 s.

[0040] In the process of slow cooling on the roller table, the heat preservation cover is closed, and the hot air above the salt bath tank is input into the heat preservation cover. The wire rod transported by the conveying roller table and passing through the second salt bath tank is slowly cooled in the heat preservation cover to prevent the wire rod from having too fast cooling rate during the cooling process, which may lead to an increase in stress, and to promote further toughening of the wire rod structure, improve the softening effect of the wire rod, until coiling. Specifically: control the wire rod to be slowly cooled at a cooling rate of 0.3 °C / s to 276 °C; the coiling process is used to coil the wire rod into a coil by a coiling drum, and after packaging and storing in the warehouse, the finished wire rod is obtained. Its metallographic structure diagram is as Figure 2 shown.

[0041] Comparative Example 3: A manufacturing method of a wire rod, the difference between its manufacturing method and that of Example 2 is that: the wire rod is subjected to pre-stage molten salt treatment and cooled at a cooling rate of 34 °C / s. The molten salt temperature of the pre-stage molten salt treatment is 455 °C, the treatment time is 25 s, and the total treatment time of the on-line molten salt micro quenching and tempering treatment process is 125 s to obtain the finished wire rod.

[0042] Comparative Example 4: A manufacturing method of a wire rod, the difference between its manufacturing method and that of Example 2 is that: the wire rod is subjected to pre-stage molten salt treatment and cooled at a cooling rate of 43 °C / s. The molten salt temperature of the pre-stage molten salt treatment is 325 °C, the treatment time is 100 s, and the total treatment time of the on-line molten salt micro quenching and tempering treatment process is 200 s to obtain the finished wire rod. Example 3:

[0043] A preferred implementation manner of the manufacturing method of the 1300 MPa grade high-strength tool steel wire rod of the present invention. The chemical composition and mass percentage of the wire rod include C: 0.52%, Si: 0.30%, Mn: 0.38%, Cr: 0.51%, Nb: 0.044%, V: 0.040%, P: 0.015%, S: 0.015%, and the rest are Fe and inevitable impurities; its manufacturing method is manufactured according to the technological process of rolling → wire laying → on-line molten salt micro quenching and tempering treatment → slow cooling on the roller table → coiling. Specifically: The rolling process is used to heat a billet with a specification of 180mm×180mm into a hot billet with rollable plasticity through a heating furnace, promoting the homogenization of alloy components. The heating furnace is controlled according to a three-stage temperature rising program of a preheating section, a heating section, and a soaking section. The hot billet is rolled into wire rods with a diameter specification of 9mm through a rolling line. Appropriate rolling temperature and reduction are selected to increase the rolling speed, promote dynamic recrystallization during the finish rolling process, and refine the grains. Specifically: control the soaking temperature of the heating furnace to be 1160°C, the residence time in the furnace to be 135min, the initial rolling temperature to be 1055°C, the finish rolling temperature to be 925°C, and the finish rolling reduction to be 22.5%; The wire laying process is used to make the wire rods exiting the rolling line into coils through a wire laying machine. The coils are scattered on the roller table and transported along the roller table, keeping the coils in a high-temperature austenite state to prepare for quenching the structure at a relatively high quenching temperature. Specifically: control the wire laying temperature to be 915°C.

[0044] The online molten salt micro quenching and tempering treatment process uses a two-stage salt bath tank with molten salt inside. The coils after wire laying are transported through the roller table and pass through the first-stage salt bath tank for the front-stage molten salt treatment, cooling the coils at a cooling rate of 38°C / s, quickly crossing the pearlite phase region from the high-temperature austenite state and entering the lower bainite phase region, inhibiting the formation of pearlite and martensite, and micro quenching to form a quenched structure mainly composed of quenched bainite. Then the coils are transported through the roller table and pass through the second-stage salt bath tank for the rear-stage molten salt treatment, reducing the molten salt circulation volume, controlling the coils to perform isothermal tempering on the quenched structure in the lower bainite isothermal range, toughening and stress relieving treatment, inhibiting the coarsening of carbides, and improving the strength-ductility matching of the coils. Specifically: the molten salt temperature for the front-stage 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 ≤ 7°C; the molten salt temperature for the rear-stage 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.

[0045] The roller table slow cooling process uses a closed heat preservation cover, inputs the hot air above the salt bath tank into the heat preservation cover, and the coils transported by the conveying roller table passing through the second-stage salt bath tank are slowly cooled in the heat preservation cover, preventing the coils from having too fast a cooling rate during the cooling process, which may lead to an increase in stress, and promoting further toughening of the coil structure, improving the softening effect of the coils until coiling. Specifically: control the coils to be slowly cooled to 275°C at a cooling rate of 0.4°C / s; The coiling process is used to coil the coils into coil packages through a coiling drum, and the coil products are obtained after being packaged and stored in the warehouse.

[0046] Comparative Example 5: A manufacturing method of coils, the difference between its manufacturing method and that of Example 3 lies in that: the molten salt temperature for the rear-stage 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 coil products.

[0047] Comparative Example 6: A manufacturing method of wire rod, the difference between the manufacturing method and that of Example 3 lies in that: the molten salt temperature in the latter-stage molten salt treatment is 409 °C, the treatment time is 235 s, and the total treatment time of the on-line molten salt micro quenching and tempering treatment process is 152 s, obtaining the wire rod finished product. Example 4:

[0048] A preferred implementation manner of the manufacturing method of the 1300 MPa grade high-strength tool steel wire rod of the present invention, the chemical composition and mass percentage of the wire rod include C: 0.47%, Si: 0.31%, Mn: 0.43%, Cr: 0.36%, Nb: 0.050%, V: 0.047%, P: 0.014%, S: 0.014%, and the rest are Fe and inevitable impurities; its manufacturing method is manufactured according to the technological process of rolling → wire laying → on-line molten salt micro quenching and tempering treatment → slow cooling on the roller table → coiling, specifically: The rolling process is used to heat the steel billet with a specification of 180 mm × 180 mm into a high-temperature steel billet that reaches the plastic state for rolling through a heating furnace, promoting the homogenization of alloy components. The heating furnace is controlled according to the three-stage temperature rising program of the preheating section, heating section, and soaking section. The high-temperature steel billet is rolled into a wire rod with a diameter specification of 7 mm through the rolling line, and appropriate rolling temperature and reduction are selected to increase the rolling speed, promote dynamic recrystallization during the finishing rolling process, and refine the grains. Specifically: control the soaking temperature of the heating furnace to be 1145 °C, the time in the furnace to be 115 min, the initial rolling temperature to be 1035 °C, the finishing rolling temperature to be 915 °C, and the finishing rolling reduction to be 24%; the wire laying process is used to make the wire rod exiting the rolling line into a wire rod through a wire laying machine, and the wire rod is scattered on the roller table and transported along the roller table, so that the wire rod is in a high-temperature austenite state, preparing for quenching the structure with a relatively high quenching temperature. Specifically: control the wire laying temperature to be 905 °C.

[0049] The on-line molten salt micro quenching and tempering treatment process adopts a two-stage salt bath tank with molten salt inside. The wire rod after wire laying is transported through the first-stage salt bath tank by the roller table for the first-stage molten salt treatment, so that the wire rod cools down at a cooling rate of 34 °C / s, quickly crosses 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 quenched structure mainly composed of quenched bainite. Then the wire rod is transported through the second-stage salt bath tank by the roller table for the latter-stage molten salt treatment, reducing the molten salt circulation volume, controlling the isothermal tempering of the quenched structure in the lower bainite isothermal range, toughening and stress relieving treatment, inhibiting the coarsening of carbides, and improving the strength-plasticity matching of the wire rod. Specifically: the molten salt temperature in the first-stage molten salt treatment is 440 °C, the treatment time is 35 s, the molten salt circulation volume is 580 t / h, and the molten salt temperature rise ≤ 7 °C; the molten salt temperature in the latter-stage molten salt treatment is 409 °C, the treatment time is 235 s, the molten salt circulation volume is 385 t / h, and the total treatment time is 270 s.

[0050] The roller slow cooling process adopts closing the insulation cover, and the wire rod conveyed by the conveying 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, resulting in increased stress, and promote further toughening of the wire rod structure, improve the softening effect of the wire rod, until coiling. 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 through a coiling drum, and the finished wire rod is obtained after packaging and storage.

[0051] Comparative Example 7: A method for manufacturing a wire rod, which differs from Example 4 in that: the manufacturing method is manufactured according to the process flow of rolling → spinning → online molten salt micro-quenching and tempering treatment → air cooling → coiling. Specifically: the air cooling process adopts the wire rod transported by a conveyor roller through a second salt bath tank to be naturally cooled 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.

[0052] The structure and performance of the wire rods obtained in the above examples 1 to 4 and comparative examples 1 to 7 were tested, and the comparison results obtained are shown in Table 1 below: Table 1. Comparison of the microstructure and properties of different wire rod compositions and manufacturing methods

[0053] From the comparison results of Example 1 and Comparative Example 1, it can be seen that compared with the Stelmore air-cooled line, the cooling rate is uncontrollable during the cooling phase transformation process, resulting in the production 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 can control the wire rod to quickly enter the lower bainite phase region from the high-temperature austenite state through the Cr-Nb-V chemical composition design combined with online molten salt micro-quenching and tempering, and strongly regulate the wire rod phase transformation to avoid the formation of pearlite soft phase, low-strength brittle upper bainite structure or martensite abnormal structure. After isothermal tempering toughening and 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 is 58%~63%, which is used in the manufacture of high-strength tool steel and other application fields, so as to save the heat treatment process after cold working, and can be directly processed into parts after cold working.

[0054] 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, so as to prepare for rapid cooling of online molten salt micro-quenching and rapid formation of a structure dominated by quenched bainite. 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.

[0055] From the comparison results between Example 2 and Comparative Example 3, it can be seen that the molten salt temperature in 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, it is beneficial to reduce 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, it will increase the risk of precipitation of soft-phase tissues and the temperature difference from the edge to the core of the wire rod, which is not conducive to the uniform transformation of the structure.

[0056] From the comparison results between Example 2 and Comparative Example 4, it can be seen that the molten salt temperature in the front-stage molten salt treatment is in the lower bainite phase region. The lower the molten salt temperature and the longer the treatment time in the front-stage molten salt treatment, it is beneficial to promote the rapid cooling of the wire rod, inhibit pearlite or upper bainite tissues, promote the transformation of high-temperature austenite to quenched bainite, enable the core of the wire rod to complete bainite phase transformation, and reduce strength and toughness losses. However, if the molten salt temperature in the front-stage molten salt treatment is too low, the dislocation density of the structure is relatively large, which will increase the difficulty of tempering or even generate abnormal martensite due to undercooling. Due to the large molten salt circulation volume and extended treatment time in the front-stage molten salt treatment, the production energy consumption increases.

[0057] From the comparison results between Example 3 and Comparative Example 5, it can be seen that the molten salt temperature in the rear-stage molten salt treatment is in the lower bainite phase region. The higher the molten salt temperature and the longer the treatment time in the rear-stage molten salt treatment, it is beneficial to promote tissue homogenization, promote dislocation slip and rearrangement through thermal activation, reduce quenching residual stress, and improve material toughness. With the extension of the treatment time, it is beneficial for carbides to precipitate uniformly in the form of nano-scale particles and pin on 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, and excessive softening of the wire rod will cause strength loss, and at the same time, the production energy consumption increases.

[0058] From the comparison results between Example 3 and Comparative Example 6, it can be seen that the molten salt temperature in the rear-stage molten salt treatment is in the lower bainite phase region. The lower the molten salt temperature and the shorter the treatment time, it is beneficial to weaken the diffusion ability of carbides, promote carbide refinement, and reduce 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 release of tissue stress, will cause greater plastic loss, and at the same time, it is not conducive to the full precipitation of microalloy carbides with the shortening of the treatment time.

[0059] From the comparison results between Example 4 and Comparative Example 7, it can be seen that slow cooling on the roller table can prevent the wire rod from increasing stress due to too fast cooling rate during the cooling process, and promote further toughening of the wire rod structure, improving the softening effect of the wire rod.

[0060] The series of detailed descriptions listed above are only specific descriptions of the feasible embodiments of the present invention, and they are not intended to limit the protection scope of the present invention. Any equivalent embodiments or changes made without departing from the technical spirit of the present invention should be included within the protection scope of the present invention.

Claims

1. A manufacturing method of a 1300MPa grade high-strength tool steel wire rod, characterized in that, The manufacturing method includes: After the steel billet is rolled and spun into wire rods at a spinning temperature of ≥895°C, it undergoes on-line molten salt micro quenching and tempering treatment. The wire rods are controlled to enter the lower bainite phase region from the high-temperature austenite state at a cooling rate of ≥31°C / s, forming a quenched structure mainly composed of quenched bainite. Then, the quenched structure is subjected to isothermal tempering and toughening stress relief treatment, and finally slowly cooled on the roller table to produce wire rods with a microstructure including tempered bainite and ferrite. The chemical composition and mass percentage of the wire rods include: C: 0.47% - 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 is Fe and unavoidable impurities.

2. The manufacturing method of the 1300 MPa grade high-strength tool steel wire rod according to claim 1, characterized in that, Before the rolling, the soaking temperature of the heating furnace is controlled at 1130 - 1180°C, and the residence time in the furnace is 100 - 155 min.

3. The manufacturing method of the 1300 MPa grade high-strength tool steel wire rod according to claim 1, characterized in that, During the rolling, the initial rolling temperature is controlled at 1020 - 1070°C, the final rolling temperature is 900 - 930°C, and the final rolling reduction is 21% - 26%; during the spinning, the spinning temperature is controlled at 895 - 920°C.

4. The manufacturing method of the 1300 MPa grade high-strength tool steel wire rod according to claim 1, characterized in that, The on-line molten salt micro quenching and tempering treatment is divided into the front-section molten salt treatment and the rear-section molten salt treatment, and the molten salt circulation volume of the front-section molten salt treatment is greater than that of the rear-section molten salt treatment.

5. The manufacturing method of the 1300 MPa grade high-strength tool steel wire rod according to claim 4, characterized in that, The molten salt temperature of the front-section molten salt treatment is 395 - 440°C, and the treatment time is 35 - 75 s. The molten salt temperature of the rear-section molten salt treatment is 400 - 425°C, and the treatment time is 100 - 260 s.

6. The manufacturing method of the 1300 MPa grade high-strength tool steel wire rod according to claim 5, characterized in that, The molten salt circulation volume of the front-section molten salt treatment is 550 - 640 t / h, and the molten salt temperature rise ≤7°C; the molten salt circulation volume of the rear-section molten salt treatment is 300 - 500 t / h.

7. The manufacturing method of the 1300 MPa grade high-strength tool steel wire rod according to claim 5, characterized in that, The slow cooling on the roller table controls the wire rods to be slowly cooled at a cooling rate of 0.3 - 0.6°C / s to below 280°C.

8. A wire rod of 1300 MPa grade high-strength tool steel, characterized in that, The wire rods are manufactured by the manufacturing method of the 1300 MPa grade high-strength tool steel wire rods described in any one of claims 1 - 7.

9. The wire rod of 1300 MPa grade high-strength tool steel according to claim 8, wherein, The volume percentage of the tempered bainite ≥95%.

10. The wire rod of 1300 MPa grade high-strength tool steel according to claim 8, characterized in that, The diameter of the wire rods is 5.5 - 11 mm, the tensile strength is 1255 - 1305 MPa, the reduction of area is 58% - 63%, and the difference in mechanical properties within the same coil ≤38 MPa.

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