Heat treatment method for improving spheroidizing annealing grade of H11 hot work die steel module

Abstract

The invention provides a heat treatment method for improving the spheroidizing annealing grade of an H11 hot work die steel module, and relates to the technical field of metal heat treatment, the heat treatment method for improving the spheroidizing annealing grade of the H11 hot work die steel module with the thickness larger than or equal to 400 mm comprises the following steps that a forged workpiece to be subjected to heat treatment is taken, heat preservation is conducted at the temperature of 980-1020 DEG C for t1, and heat preservation is conducted at the temperature of 740-760 DEG C after cooling is conducted for t2; heating to 980-1020 DEG C, preserving heat for t1, cooling to 740-760 DEG C, preserving heat for t2, and cooling to 200 DEG C or below after heat preservation is finished; heating to 1000-1020 DEG C, keeping the temperature t3, and cooling until the surface temperature is below 200 DEG C after keeping the temperature; heating to 325-425 DEG C, keeping the temperature t4, and cooling to room temperature after keeping the temperature; heating to 850-870 DEG C and preserving heat t5, cooling to 720-740 DEG C and preserving heat t6 after heat preservation is finished, and cooling to room temperature after heat preservation is finished.

Description

Technical Field

[0001] This invention relates to the field of metal heat treatment technology, and more specifically, to a heat treatment method for improving the spheroidizing annealing grade of H11 hot work die steel modules. Background Technology

[0002] Hot work die steel, as a key alloy tool steel, relies primarily on elements such as chromium, molybdenum, and vanadium for strengthening. It operates under extreme conditions of high temperature, high pressure, and high load, thus requiring excellent high-temperature strength, resistance to thermal fatigue, and impact toughness. H11 steel (4Cr5MoSiV), by reducing the vanadium content compared to H13 steel, effectively improves the material's plasticity and toughness, making it widely used in die-casting and forging die manufacturing. Spheroidizing annealing, a core step in the production process of this type of steel, has a decisive influence on its microstructure, affecting subsequent machinability and tempering effects. An ideal spheroidized annealed microstructure should exhibit a uniform and fully distributed spherical carbide structure. A higher annealed microstructure rating results in better machinability and lower internal stress during quenching, significantly reducing the risk of cracking. Therefore, in industrial practice, achieving a high-rated spheroidized annealed microstructure is a key objective for optimizing heat treatment processes.

[0003] However, existing heat treatment technologies face multiple technical bottlenecks for large-size H11 hot-work die steel modules with a thickness of 400 mm or more. During the smelting stage, large steel ingots inevitably experience severe compositional segregation, leading to uneven distribution of alloy element concentrations between positive and negative segregation zones. This inhomogeneity results in significant differences in phase transformation temperatures across different regions, disordered grain size distribution, and consequently, localized anomalies in microstructure and carbide density during heat treatment. Although high-temperature homogenization annealing can partially alleviate segregation, it cannot completely eliminate its effects, and this process often induces abnormal grain coarsening. These coarse grains are directly transferred to the forged module through a microstructure inheritance effect. Furthermore, due to the extreme thickness of the module, heat transfer efficiency is severely limited during heat treatment, resulting in a significant gradient difference in cooling rates between the surface and the core, with the core region cooling much slower than the surface. This uneven cooling condition easily promotes the formation of bainite or a mixed bainite and martensite microstructure in the core. Under conventional heat treatment processes, the spheroidized annealed microstructure rating of such large-scale modules generally only reaches AS6 level or lower, failing to meet the high standard requirements of AS1-4. This low-rated microstructure not only leads to deterioration in machinability, increased tool wear and machining difficulty, but also significantly increases the probability of quenching cracking, severely restricting the production efficiency and application reliability of large-scale hot-work die steel modules. Summary of the Invention

[0004] The present invention aims to solve the problem that the heat treatment process of spheroidizing annealing of large-scale modules is severely limited by heat transfer efficiency, resulting in a significant gradient difference in cooling rates between the surface and the core, which in turn leads to the deterioration of machinability.

[0005] To address the aforementioned problems, this invention provides a heat treatment method for improving the spheroidizing annealing grade of H11 hot work die steel modules.

[0006] This invention provides a heat treatment method for improving the spheroidizing annealing grade of H11 hot work die steel modules, specifically for H11 hot work die steel modules with a thickness ≥ 400 mm, comprising the following steps: S1: Take the H11 hot work die steel module that is to be heat treated after forging, hold it at 980 to 1020℃ for t1, cool it to 740 to 760℃ and hold it for t2; reheat it to 980 to 1020℃ and hold it for t1, cool it to 740 to 760℃ and hold it for t2, and after holding it for t2, cool it to below 200℃; S2: Heat to 1000 to 1020℃ and hold for t3. After holding, cool until the surface temperature is below 200℃. S3: Heat to 325 to 425℃ and hold for t4. After holding, cool to room temperature. S4: Heat to 850 to 870℃ and hold for t5. After holding, cool to 720 to 740℃ and hold for t6. After holding, cool to room temperature. Among them, t1>1h, t2>8h, t3>1h, t4>20h, t5>8h, and t6>10h.

[0007] Optionally, the composition of the H11 hot work die steel module includes C, Si, Mn, Cr, Mo and V.

[0008] Optionally, the composition of the H11 hot work die steel module, by weight, includes C: 0.3 to 0.45 parts, Si: 0.1 to 1.2 parts, Mn: 0.2 to 0.65 parts, Cr: 4.8 to 5.5 parts, Mo: 1.1 to 2.5 parts and V: 0.3 to 1.15 parts.

[0009] Optionally, t1=t 1基础保温 +For H11 hot work die steel modules, for every 40 to 60 mm increase in thickness compared to 400 mm, extend the working time by 40 to 50 minutes. 1基础保温 =1 to 2 hours.

[0010] Alternatively, t2=t 2基础保温 +For H11 hot work die steel modules, for every 40 to 60 mm increase in thickness compared to 400 mm, extend the working time by 40 to 50 minutes. 2基础保温 =8 to 10 hours.

[0011] Alternatively, t3 = t3基础保温 +For H11 hot work die steel modules, for every 40 to 60 mm increase in thickness compared to 400 mm, extend the working time by 40 to 50 minutes. 3基础保温 =1 to 2 hours.

[0012] Optionally, t4 = t 4基础保温 +For H11 hot work die steel modules, for every 40 to 60 mm increase in thickness compared to 400 mm, extend the working time by 40 to 50 minutes. 4基础保温 =20 to 25 hours.

[0013] Alternatively, t5 = t 5基础保温 +For H11 hot work die steel modules, for every 40 to 60 mm increase in thickness compared to 400 mm, extend the working time by 40 to 50 minutes. 5基础保温 =8 to 10 hours.

[0014] Alternatively, t6 = t 6基础保温 +For H11 hot work die steel modules, for every 40 to 60 mm increase in thickness compared to 400 mm, extend the working time by 40 to 50 minutes. 6基础保温 =10 to 15 hours.

[0015] Alternatively, cooling can be achieved through water cooling or air cooling.

[0016] The beneficial effects of the heat treatment method for improving the spheroidizing annealing grade of H11 hot work die steel modules of the present invention are as follows: the microstructure originates from the coarse austenite grains formed after high-temperature homogenization annealing and the cast dendritic structure that was not completely broken during forging. This type of microstructure is prone to retaining the original coarse grain characteristics in subsequent heat treatment. In this embodiment, step S1 is refined through two cycles. The first cycle is held at 980 to 1020°C to achieve complete austenitization. The temperature is then lowered to 740 to 760°C and held in the pearlite transformation zone, where austenite transforms into pearlite. Each phase transformation partially destroys the original orientation relationship. After two cycles, the microstructure inheritance can be basically cut off, making the grain size refined and homogenized. The bainitic transformation in step S3 involves prolonged holding at the bainitic transformation temperature range to completely transform the supercooled austenite in the core into bainitic structure. A certain holding time is required to complete the phase transformation. The V content of the H11 hot work die steel module is lower than that of the commonly used H13 hot work die steel module, and the bainitic transformation temperature range of the H11 hot work die steel module is narrower. In this embodiment, the isothermal bainitic treatment involves holding at 325 to 425°C for more than 20 hours to fully complete the bainitic transformation and further homogenize the grain size in the core. The martensite structure generated on the outside due to the rapid cooling rate allows for the full precipitation of carbides within this temperature range, preparing the microstructure for the final spheroidizing annealing. The final step, S4, involves holding the material at 850℃ to 870℃, which is a partial austenitization process. This process retains some carbide nucleation sites as the core for subsequent spheroidization, ensuring a uniform distribution of carbides. The spheroidizing annealing process then begins at 720℃ to 740℃, with a long holding time of over 10 hours. This transforms the carbides from flakes or strips into fine, rounded granular carbides that are evenly dispersed. Therefore, after spheroidizing annealing, a relatively uniform spheroidized structure is obtained, stably achieving an AS1-4 rating. Attached Figure Description

[0017] Figure 1 This is a schematic flowchart of a heat treatment method for improving the spheroidizing annealing grade of H11 hot work die steel modules according to an embodiment of the present invention. Figure 2 This is a microscope image of the surface of the H11 hot work die steel module after heat treatment in Example 1. Figure 3 This is a microscope image of the core of the H11 hot work die steel module after heat treatment in Example 1. Figure 4 This is a microscope image of the surface of the H11 hot work die steel module after heat treatment in Example 2. Figure 5 This is a microscope diagram of the core of the H11 hot work die steel module after heat treatment in Example 2; Figure 6 This is a microscope image of the surface of the H11 hot work die steel module after heat treatment in Example 3. Figure 7 This is a microscope image of the core of the H11 hot work die steel module after heat treatment in Example 3. Figure 8 This is a microscope image of the surface of the H11 hot work die steel module after heat treatment, as shown in Comparative Example 1. Figure 9 This is a microscope image of the core of the H11 hot work die steel module after heat treatment, as shown in Comparative Example 1. Figure 10 This is a microscope image of the surface layer of the H11 hot work die steel module after heat treatment, as shown in Comparative Example 2. Figure 11 This is a microscope image of the core of the H11 hot work die steel module after heat treatment, as shown in Comparative Example 2. Figure 12 This is a microscope image of the surface of the H11 hot work die steel module after heat treatment, as shown in Comparative Example 3. Figure 13 This is a microscope image of the core of the H11 hot work die steel module after heat treatment, as shown in Comparative Example 3. Figure 14 This is a microscope image of the surface of the H11 hot work die steel module after heat treatment, as shown in Comparative Example 4. Figure 15 This is a microscope image of the core of the H11 hot work die steel module after heat treatment, as shown in Comparative Example 4. Figure 16 This is a schematic diagram of the AS rating reference in an embodiment of the present invention. Detailed Implementation

[0018] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Although some embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the present invention. It should be understood that the accompanying drawings and embodiments of the present invention are for illustrative purposes only and are not intended to limit the scope of protection of the present invention.

[0019] Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this invention's description is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "comprising" and its variations as used herein are open-ended inclusion, meaning "including but not limited to"; the term "based on" means "at least partially based on"; the term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment"; the term "some embodiments" means "at least some embodiments"; and the term "optionally" means "optional embodiments". Definitions of other terms will be given in the description below.

[0020] like Figure 1 As shown, the present invention provides a heat treatment method for improving the spheroidizing annealing grade of H11 hot work die steel modules, for H11 hot work die steel modules with a thickness ≥ 400 mm, including the following steps: S1: Cyclic Refinement Process: Take the H11 hot work die steel module to be heat-treated after forging, hold it at 980℃ to 1020℃ for t1, cool it to 740℃ to 760℃ and hold it for t2; reheat it to 980℃ to 1020℃ and hold it for t1, cool it to 740℃ to 760℃ and hold it for t2, and after the holding is completed, cool it to below 200℃; S2: Ultra-fine treatment: Heat to 1000 to 1020℃ and hold for t3. After the holding period, cool to a surface temperature below 200℃. S3: Isothermal bainite treatment: Heat to 325 to 425℃ and hold for t4, then cool to room temperature after holding. S4: Spheroidizing annealing treatment: Heat to 850℃ to 870℃ and hold for t5. After holding, cool to 720℃ to 740℃ and hold for t6. After holding, cool to room temperature. Among them, t1>1h, t2>8h, t3>1h, t4>20h, t5>8h, and t6>10h.

[0021] In the above heat treatment method for improving the spheroidizing annealing grade of H11 hot work die steel modules, all temperature measurements refer to the temperature of the outer surface of the H11 hot work die steel modules.

[0022] Specifically, H11 hot work die steel modules refer to an alloy tool steel with chromium, molybdenum, and vanadium as the main strengthening elements. It possesses high-temperature performance, thermal fatigue resistance, and impact resistance, and is commonly used in die casting and forging processes. The modules targeted in this application have a thickness of not less than 400 mm, which falls into the large-size category.

[0023] Spheroidizing annealing grade refers to the evaluation standard for the degree of spheroidization of carbides in the microstructure of steel after spheroidizing annealing treatment. The higher the grade, the more uniform and complete the spheroidization of carbides, which is more beneficial to subsequent machining performance and quenching crack prevention.

[0024] Post-forging heat treatment refers to the state of H11 hot work die steel modules after forging plastic deformation processing, but before final heat treatment to obtain the required microstructure and properties.

[0025] Heat preservation refers to heating H11 hot work die steel modules to a specific temperature and maintaining that temperature for a period of time to ensure uniform internal temperature and promote specific microstructure transformations or element diffusion.

[0026] Cooling refers to the process of reducing the temperature of H11 hot work die steel modules from a high temperature to a lower temperature. The cooling rate and method have an impact on the final microstructure and properties.

[0027] Surface temperature refers to the temperature of the outer surface of the H11 hot work die steel module.

[0028] Room temperature refers to ambient temperature, which is usually in the range of 20°C to 30°C.

[0029] In this embodiment, the microstructure originates from the coarse austenite grains formed after high-temperature homogenization annealing and the cast dendritic structure that was not completely broken during forging. This type of microstructure tends to retain the original coarse grain characteristics in subsequent heat treatment. In this embodiment, step S1 is refined through two cycles. The first cycle is held at 980 to 1020°C to achieve complete austenitization. The temperature is then lowered to 740 to 760°C, which is in the pearlite transformation zone, where austenite transforms into pearlite. Each phase transformation partially disrupts the original orientation relationship. After two cycles, the microstructure inheritance can be basically cut off, resulting in refined and homogenized grain size. The bainitic transformation in step S3 involves prolonged holding at the bainitic transformation temperature range to completely transform the supercooled austenite in the core into bainitic structure. A certain holding time is required to complete the phase transformation. The V content of the H11 hot work die steel module is lower than that of the commonly used H13 hot work die steel module, and the bainitic transformation temperature range of the H11 hot work die steel module is narrower. In this embodiment, the isothermal bainitic treatment involves holding at 325 to 425°C for more than 20 hours to fully complete the bainitic transformation and further homogenize the grain size in the core. The martensite structure generated on the outside due to the rapid cooling rate allows for the full precipitation of carbides within this temperature range, preparing the microstructure for the final spheroidizing annealing. The final step, S4, involves holding the material at 850℃ to 870℃, which is a partial austenitization process. This process retains some carbide nucleation sites as the core for subsequent spheroidization, ensuring a uniform distribution of carbides. The spheroidizing annealing process then begins at 720℃ to 740℃, with a long holding time of over 10 hours. This transforms the carbides from flakes or strips into fine, rounded granular carbides that are evenly dispersed. Therefore, after spheroidizing annealing, a relatively uniform spheroidized structure is obtained, stably achieving an AS1-4 rating.

[0030] This embodiment effectively solves the problems of severe segregation, uneven microstructure caused by inconsistent internal and external cooling rates, and low spheroidizing annealing rating in large-size H11 hot work die steel modules during heat treatment by using multi-stage temperature cycling and precise holding time control. As a result, it achieves uniform and consistent spheroidizing annealed microstructure on the module surface and in the core, and achieves a high annealed microstructure rating, thereby improving the module's machinability and quenching crack resistance.

[0031] In some specific embodiments, in step S2, after the heat preservation is completed and the surface temperature cools to below 200°C, the core temperature of the H11 hot work die steel module is higher than 200°C, and the temperature gradually decreases from the core to the surface. When furnace cooling / slow cooling (cooling rate ≤ 5°C / min) is used, the temperature difference between the core and the surface is 10 to 50°C; when static air cooling is used, the temperature difference between the core and the surface is 80 to 180°C; when forced air cooling is used, the temperature difference between the core and the surface is 200 to 450°C; and when water cooling is used, the temperature difference between the core and the surface reaches 400 to 700°C.

[0032] Optionally, the composition of the H11 hot work die steel module includes C, Si, Mn, Cr, Mo and V.

[0033] Specifically, carbon is one of the most important alloying elements in steel. Its main role is to increase the hardness and strength of steel, and to influence the microstructure of steel by forming carbides. During spheroidizing annealing, the content and distribution of carbon directly affect the precipitation, growth, and spheroidization morphology of carbides, which is the basis for obtaining a uniform spheroidized carbide microstructure. Silicon mainly acts as a deoxidizer and solid solution strengthening element in steel. Its presence helps reduce harmful impurities in steel, improves the purity of steel, and also improves the hardenability of steel. During heat treatment, silicon has a certain influence on the formation and distribution of carbides, which helps stabilize austenite, thus indirectly affecting the effect of spheroidizing annealing. Manganese is a commonly used alloying element in steel. Its main roles are solid solution strengthening, improving hardenability, and refining grains. The presence of manganese helps suppress grain boundary segregation and improve the plasticity and toughness of steel. During spheroidizing annealing, manganese can affect phase transformation kinetics, promote the uniform distribution of carbides, and thus help obtain a more ideal spheroidized microstructure. Chromium is the main alloying element in H11 hot work die steel, significantly improving its wear resistance, corrosion resistance, and high-temperature strength. As a strong carbide-forming element, chromium's carbides play a crucial role in grain refinement and microstructure homogenization during heat treatment, significantly contributing to austenite stability and promoting carbide spheroidization. Molybdenum improves the steel's hot strength, resistance to tempering softening, and hardenability. Also a carbide-forming element, molybdenum forms highly stable carbides with carbon, helping to suppress grain coarsening and maintain microstructure stability at high temperatures. During spheroidizing annealing, the presence of molybdenum promotes uniform carbide precipitation and spheroidization, enhancing the stability of the annealed microstructure. Vanadium is a strong carbide-forming element, significantly refining the steel's grains and improving its wear resistance and high-temperature strength. Vanadium carbides, dispersed throughout the steel, effectively inhibit grain growth and positively influence the carbide spheroidization process, contributing to the formation of fine, uniform spherical carbides.

[0034] In this optional embodiment, the composition of the H11 hot work die steel module is explicitly defined to include C, Si, Mn, Cr, Mo, and V. This application ensures that the treated steel has a stable chemical basis. The precise presence of these key alloying elements allows for more effective control of the precipitation, dissolution, aggregation, and spheroidization processes of carbides in steps S1 to S4 of the aforementioned heat treatment method. Specifically, carbon provides the basis for carbide formation, silicon and manganese help improve the purity and hardenability of the steel and promote microstructure homogenization, while chromium, molybdenum, and vanadium, as strong carbide-forming elements, can form stable and dispersed carbides, effectively suppressing grain coarsening and promoting the transformation of carbides into a spherical morphology. This explicit composition definition fundamentally solves the problem of aggravated alloy element segregation and microstructure inhomogeneity caused by unclear composition, thereby ensuring that the H11 hot work die steel module can stably obtain a uniform and consistent spheroidized annealed microstructure after the aforementioned heat treatment, achieving a high rating of AS1-4, significantly improving subsequent machinability and quenching stability.

[0035] Optionally, the composition of the H11 hot work die steel module, by weight, includes C: 0.3 to 0.45 parts, Si: 0.1 to 1.2 parts, Mn: 0.2 to 0.65 parts, Cr: 4.8 to 5.5 parts, Mo: 1.1 to 2.5 parts and V: 0.3 to 1.15 parts.

[0036] Specifically, carbon content can affect the quantity, morphology, and distribution of carbides, thereby regulating the wear resistance and toughness of steel. For example, within a certain range, slightly higher carbon content can enhance hardness and wear resistance, while slightly lower carbon content may improve plasticity and toughness. Silicon in steel mainly acts as a deoxidizer and solid solution strengthening element. Its content can affect the purity of molten steel and the strength of the matrix. For example, higher silicon content can more effectively deoxidize and improve the strength of steel, but too much may affect plasticity; lower silicon content may require other deoxidation measures, but helps maintain good toughness. Manganese can improve the hardenability of steel and acts as a deoxidizer and desulfurizer. Its content is crucial to the balance between the hardening ability and toughness of steel. For example, increasing manganese content can significantly improve the hardenability of steel, allowing for a uniform microstructure even in large-sized modules; while appropriately reducing manganese content may optimize toughness performance in some cases. Chromium is a key alloying element in H11 hot work die steel, mainly improving the high-temperature strength, wear resistance, and oxidation resistance of steel by forming stable carbides. The content of chromium directly affects the performance stability of steel under high-temperature service conditions. For example, a higher chromium content can form more stable carbides, further improving high-temperature strength and wear resistance; while a lower chromium content may improve processing performance to some extent. Molybdenum can significantly improve the high-temperature strength, creep resistance, and tempering stability of steel, and helps prevent temper brittleness. Its content has an important impact on the creep performance and microstructure stability of steel at high temperatures. For example, increasing the molybdenum content can further enhance the high-temperature strength and tempering resistance of steel; adjusting the molybdenum content can also affect the precipitation kinetics of carbides, thereby optimizing the overall mechanical properties. Vanadium in steel mainly refines grains by forming fine carbides and produces a secondary hardening effect, thereby improving the strength, toughness, and wear resistance of steel. Its content is crucial for controlling grain size and carbide distribution. For example, a higher vanadium content can more effectively refine grains and promote secondary hardening, improving the overall mechanical properties of steel; while a lower vanadium content may optimize cost or processing performance while ensuring certain performance.

[0037] In this optional embodiment, the specific weight percentage range of each element in the H11 hot work die steel module is precisely defined, ensuring that the steel composition remains within the optimized range during heat treatment. This effectively solves the problem of increased segregation or impaired microstructure due to compositional fluctuations. This precise elemental ratio promotes the uniform formation and distribution of carbides, refines grains, and balances the steel's strength, toughness, hardenability, and high-temperature performance. Therefore, in the aforementioned heat treatment method, this precise compositional control significantly improves the uniformity and rating of the spheroidizing annealed microstructure, ensuring that both the surface and core microstructure of the H11 hot work die steel module reach ideal levels after heat treatment. This provides a superior microstructure foundation for subsequent machining and tempering processes, effectively avoiding the risk of quenching cracking.

[0038] Optionally, t1=t 1基础保温 +For H11 hot work die steel modules, for every 40 to 60 mm increase in thickness compared to 400 mm, extend the working time by 40 to 50 minutes. 1基础保温 =1 to 2 hours.

[0039] Specifically, "t 1基础保温 "" refers to the initial holding time of the H11 hot work die steel module in the temperature range of 980℃ to 1020℃ during heat treatment step S1. Its purpose is to provide the module with a minimum time for heat penetration and microstructure transformation, ensuring that the module achieves initial microstructure homogenization during subsequent cooling and reheating cycles. For example, t can be set... 1基础保温 The initial heat treatment time is set to 1 hour to meet the basic heat treatment requirements of modules with smaller thicknesses; or it is set to 2 hours to provide more thorough initial heat treatment for modules with general thicknesses.

[0040] The statement, "For every 40 to 60 mm increase in thickness of the H11 hot-work die steel module exceeding 400 mm, extend the holding time by 40 to 50 minutes," describes a mechanism for adjusting the holding time based on the thickness of the H11 hot-work die steel module. Because larger modules have a relatively slower heat conduction rate, the core takes longer to reach the set temperature; therefore, the holding time needs to be extended to ensure sufficient heat penetration. For example, when the module thickness exceeds 400 mm, the holding time can be extended by 40 minutes for every 40 mm increase in thickness; or by 50 minutes for every 60 mm increase in thickness. This extension mechanism can be calculated using linear interpolation, for example, extending by 45 minutes for every 50 mm increase in thickness; or it can be done using a stepped increase, that is, uniformly extending the holding time by a fixed duration within a specific thickness range.

[0041] "t1" represents the total holding time of the H11 hot work die steel module within the temperature range of 980℃ to 1020℃ in heat treatment step S1. It is "t 1基础保温 "The sum of the holding time and the extended holding time based on the module thickness. The purpose is to ensure that H11 hot work die steel modules of varying thicknesses, especially large modules with a thickness ≥ 400mm, receive sufficient heat and time during the high-temperature stage to promote carbide dissolution and austenite homogenization, thereby laying a good microstructure foundation for the subsequent spheroidizing annealing process. For example, for a module with a thickness of 480mm, if t..." 1基础保温 The time is 1.5 hours, and for every 40 mm increase, the time is extended by 40 minutes. Therefore, t1 will be 1.5 hours + (480-400) / 40×40 minutes = 1.5 hours + 80 minutes = 2 hours and 50 minutes.

[0042] In this optional embodiment, for H11 hot work die steel modules with a thickness ≥ 400mm, the holding time t1 in step S1 is set to t1基础保温 The sum of this and the extended insulation time due to the increase in module thickness. Specifically, t 1基础保温 The system provides the minimum holding time required for the initial microstructure transformation of the modules. Furthermore, by extending the holding time by 40 to 50 minutes for every 40 to 60 mm increase in thickness compared to 400 mm for H11 hot work die steel modules, it effectively compensates for insufficient heat penetration caused by the long heat conduction path and large internal and external temperature differences in large-sized modules. This dynamically adjusted holding strategy ensures that the modules absorb heat fully from the surface to the core, promoting uniform dissolution of carbides and complete austenitization, thus avoiding microstructure inhomogeneity caused by a fixed holding time that cannot adapt to dimensional changes. Therefore, this solution significantly improves the microstructure uniformity and heat treatment efficiency of large-sized H11 hot work die steel modules at high temperatures, providing a more ideal initial microstructure for the subsequent spheroidizing annealing process, thereby contributing to obtaining a higher grade of spheroidized annealed microstructure.

[0043] Alternatively, t2=t 2基础保温 +For H11 hot work die steel modules, for every 40 to 60 mm increase in thickness compared to 400 mm, extend the working time by 40 to 50 minutes. 2基础保温 =8 to 10 hours.

[0044] Specifically, t 2基础保温 This refers to the baseline holding time for H11 hot work die steel modules in the aforementioned heat treatment method, within the temperature range of 740℃ to 760℃, where the holding temperature falls within the pearlite transformation zone. This basic holding time is set to 8 to 10 hours, providing an initial and sufficient time window for the dissolution, diffusion, and transformation of carbides into pearlite within the austenitic matrix. Under standard conditions, this ensures that the carbides can transform from austenite to pearlite, and after two cycles, the microstructure inheritance is essentially severed, resulting in uniform grain size and laying a good foundation for subsequent processing and performance. Possible implementation methods include: precisely controlling the temperature and time in the heat treatment furnace to maintain the module at the target temperature for 8 hours; or, depending on specific equipment and process requirements, setting the holding time to 9 or 10 hours to optimize the grain refinement effect.

[0045] Furthermore, for every 40 to 60 mm increase in thickness of the H11 hot work die steel module compared to 400 mm, the holding time is extended by 40 to 50 minutes. This technical feature describes a mechanism for dynamically adjusting the holding time t2, that is, based on the actual thickness of the H11 hot work die steel module, the holding time t2 is adjusted within the base holding time. 2基础保温The holding time is extended further. Specifically, when the module thickness exceeds 400mm, the holding time t2 is extended by 40 to 50 minutes for every additional 40 to 60mm of thickness. This extension mechanism aims to compensate for the inconsistent internal and external temperature differences and cooling rates caused by differences in heat conduction rates during the heat treatment of large-sized modules, especially the significantly reduced cooling rate in the core region, which may lead to insufficient pearlite transformation. By extending the holding time, more time is provided to the module core, allowing sufficient opportunity for the carbides to dissolve, diffuse, and transform into pearlite, thereby ensuring a uniform and sufficient grain structure throughout the entire module cross-section, including the core. Possible implementation methods include: calculating the total holding time based on the actual size of the module during heat treatment process planning; or, using an automated control system to monitor the module thickness in real time and dynamically adjust the holding parameters, for example, extending the basic 8-hour holding time by 40 minutes for a 460mm thick module; and extending it by 80 minutes for a 500mm thick module.

[0046] In this optional embodiment, for H11 hot work die steel modules with a thickness exceeding 400mm, the problem of insufficient spheroidization of the core structure, which may be caused by a decrease in the core cooling rate due to the increased module thickness, can be effectively solved. This is achieved by setting a basic holding time t. 2基础保温 The holding time t2 was dynamically extended according to the module thickness, ensuring temperature uniformity from the surface to the core of the module. This provided sufficient time for the carbides to fully dissolve, diffuse, and transform from austenite to pearlite throughout the entire cross-section. By cyclically cutting off the microstructure inheritance through "austenitization + pearlite phase transformation," the grains were refined, significantly improving the uniformity and rating of the spheroidized annealed microstructure of large-size H11 hot work die steel modules. Ultimately, this resulted in a uniform spheroidized annealed microstructure on the surface and core of large-size modules, achieving an annealed microstructure rating of AS1-4. This improved the subsequent machinability of the die steel and reduced internal stress during quenching, thus lowering the risk of quenching cracking.

[0047] Alternatively, t3 = t 3基础保温 +For H11 hot work die steel modules, for every 40 to 60 mm increase in thickness compared to 400 mm, extend the working time by 40 to 50 minutes. 3基础保温 =1 to 2 hours.

[0048] Specifically, t 3基础保温The initial holding time, set to 1 to 2 hours, is the initial holding time after heating to 1000 to 1020°C in step S2. Its purpose is to ensure that the surface and near-surface areas of the H11 hot work die steel module can fully absorb heat, achieving a uniform temperature distribution and laying the foundation for the subsequent cooling process. For example, in actual operation, a shorter initial holding time of 1 hour can be selected to improve efficiency, or a longer initial holding time of 2 hours can be selected to ensure more thorough heating uniformity, depending on the initial temperature of the H11 hot work die steel module or the heating rate of the furnace. Simultaneously, the holding time is extended by 40 to 50 minutes for every 40 to 60 mm increase in thickness beyond 400 mm. This technical feature aims to dynamically adjust the holding time (t3) based on the actual thickness of the H11 hot work die steel module. Its core function is to compensate for the delay in heat transfer to the core caused by the increased module thickness, ensuring that even the core of a thick module can fully reach the target temperature and complete the necessary microstructural transformation. Specifically, this extension mechanism can be achieved through a preset calculation formula or a lookup table. For example, when the module thickness exceeds 400mm, the t3 heat preservation time can be extended by 40 minutes for every 40mm increase in thickness; or by 50 minutes for every 60mm increase in thickness. This adjustment ensures that heat can fully penetrate to the module core, avoiding insufficient heating of the core due to thickness differences.

[0049] In this optional embodiment, the t3 holding time in step S2 is dynamically adjusted to address the thickness differences of the H11 hot work die steel module. Specifically, the holding time is extended proportionally for portions of the module exceeding 400mm in thickness, beyond the base holding time. This adjustment mechanism effectively solves the problem of insufficient microstructure transformation caused by delayed heat transfer in the core of thick modules. By extending the holding time, sufficient time is allowed for heat to penetrate deep into the module, ensuring that the module core also reaches and maintains a temperature range of 1000 to 1020°C. This promotes the complete dissolution and refinement of carbides, providing a uniform initial microstructure for subsequent cooling and spheroidizing annealing. Ultimately, this solution significantly improves the overall uniformity of the spheroidizing annealed microstructure of the H11 hot work die steel module and helps achieve a higher annealed microstructure rating, thereby improving its machinability and quenching stability.

[0050] Optionally, t4 = t 4基础保温 +For H11 hot work die steel modules, for every 40 to 60 mm increase in thickness compared to 400 mm, extend the working time by 40 to 50 minutes. 4基础保温 =20 to 25 hours.

[0051] Specifically, t 4基础保温The holding time is set to 20 to 25 hours to provide a basic, minimum holding time for the H11 hot work die steel module during the holding phase at 325 to 425°C. This basic holding time aims to ensure that, at a typical thickness, the module receives sufficient heat and time to promote the complete dissolution of carbides and the transformation of bainite, allowing the supercooled austenite to completely transform into bainite. To address the issues of internal and external temperature differences and thermal conduction hysteresis in large-sized modules, this embodiment further specifies a dynamic adjustment mechanism that extends the holding time by 40 to 50 minutes for every 40 to 60 mm increase in thickness of the H11 hot work die steel module beyond 400 mm. When the thickness of the H11 hot work die steel module exceeds 400 mm, the time required for its internal region to reach and maintain the target temperature increases significantly. By dynamically extending the holding time according to the thickness increment, it is possible to ensure that the module core receives an effective holding time similar to that of the surface region, thereby promoting the uniformity of the microstructure transformation throughout the module. In practice, a functional relationship or lookup table between thickness and extended insulation time can be established in advance, and the specific time to be extended can be calculated based on the actual thickness of the module to be processed; or, by monitoring the internal temperature of the module in real time, the additional insulation time can be calculated after the internal temperature reaches the set value and is maintained for a period of time.

[0052] In this optional embodiment, the holding time t4 is dynamically adjusted to ensure that even for H11 hot work die steel modules with a thickness exceeding 400 mm, the core receives sufficient holding time. This solves the problem of insufficient core transformation that may occur with a fixed holding time, allowing the supercooled austenite to completely transform into bainite. This thickness-adaptive holding time adjustment mechanism promotes the full dissolution, dispersion, and bainitization of carbides within the module, resulting in a more uniform microstructure throughout the module. This avoids insufficient bainitization and inconsistent grading caused by thickness differences. Ultimately, this helps improve the overall spheroidizing annealing grade of the H11 hot work die steel module, enhances its subsequent machinability and hardening properties, and effectively reduces the risk of quenching cracking.

[0053] Alternatively, t5 = t 5基础保温 +For H11 hot work die steel modules, for every 40 to 60 mm increase in thickness compared to 400 mm, extend the working time by 40 to 50 minutes. 5基础保温 =8 to 10 hours.

[0054] Specifically, the heat preservation time of t5 is set to t 5基础保温In addition, the holding time is extended by 40 to 50 minutes for every 40 to 60 mm increase in thickness of the H11 hot work die steel module beyond 400 mm. This aims to dynamically adjust the holding time t5 within the temperature range of 850℃ to 870℃ based on the actual thickness of the H11 hot work die steel module. Its function is to compensate for the heat conduction lag and reduced core cooling rate caused by the increased module thickness, thereby ensuring that the module's interior, especially the core area, achieves the same sufficient spheroidizing annealing effect as the external areas. Specific implementation methods may include: for example, installing multiple temperature sensors in the heat treatment furnace to monitor the temperature at different locations of the module in real time and adjusting the total holding time based on the accumulated time after the set temperature is reached; or, before heat treatment, calculating the precise extended holding time based on the module's dimensional data using a preset algorithm or lookup table, and inputting this value into the control system of the heat treatment equipment.

[0055] t 5基础保温 The technical feature specifies a base holding time t5 for H11 hot work die steel modules within a temperature range of 850°C to 870°C, ranging from 8 to 10 hours. This base holding time is set for modules with a thickness of 400 mm and aims to provide sufficient starting conditions for the spheroidizing annealing process, ensuring that carbides can begin to dissolve and spheroidize. Specific implementation methods can include: for example, setting the base holding time to 8 hours to improve production efficiency while ensuring spheroidization effect; or setting the base holding time to 10 hours to pursue more thorough carbide spheroidization and a higher annealing grade; or any value between 8 and 10 hours can be selected as the base holding time depending on the specific material batch and performance requirements.

[0056] In this optional embodiment, for H11 hot work die steel modules with a thickness greater than 400mm, the holding time t5 at 850℃ to 870℃ is dynamically adjusted, i.e., the basic holding time t 5基础保温 Based on the previous holding time of 8 to 10 hours, the holding time was extended by 40 to 50 minutes for every 40 to 60 mm increase in module thickness beyond 400 mm. This effectively solved the problem that a fixed holding time could not ensure sufficient transformation of the core microstructure in thick modules, leading to inconsistent spheroidizing annealing grades. This solution compensates for the thermal conduction lag caused by increased thickness, allowing both the core and surface of the module to receive sufficient holding time. This promotes uniform dissolution and spheroidization of carbides, ensuring a uniform and consistent spheroidizing annealed microstructure throughout the H11 hot work die steel module. It also significantly improves the annealed microstructure rating and avoids differences in subsequent processing performance and the risk of quenching cracking caused by uneven microstructure.

[0057] Alternatively, t6 = t 6基础保温 +For H11 hot work die steel modules, for every 40 to 60 mm increase in thickness compared to 400 mm, extend the working time by 40 to 50 minutes.6基础保温 =10 to 15 hours.

[0058] Specifically, t6 refers to the holding time performed on the H11 hot work die steel module after cooling to 720°C to 740°C in step S4 above. This holding stage aims to promote further spheroidization of carbides and eliminate residual stress, preparing for subsequent cooling to room temperature. This holding time can be precisely controlled by the temperature control system of the heat treatment furnace, or implemented by manually timing and monitoring the furnace temperature. 6基础保温 This refers to the minimum holding time required to ensure that H11 hot work die steel modules achieve basic spheroidizing annealing effects, before considering the influence of module thickness. This basic holding time is 10 to 15 hours, providing a baseline and sufficient holding time for the spheroidizing annealing process to ensure that carbides can fully spheroidize under normal conditions. This basic holding time can be preset in the control program of the heat treatment equipment or determined experimentally or empirically based on the material properties of H11 hot work die steel and the target spheroidization grade. Furthermore, for H11 hot work die steel modules with a thickness exceeding 400 mm, the t6 holding time is dynamically adjusted, specifically by extending it by 40 to 50 minutes for every 40 to 60 mm increase in thickness beyond 400 mm. Because the internal heat conduction rate is slower in thick modules, the core temperature change lags behind the surface, thus requiring additional holding time to ensure that the core microstructure also fully completes the spheroidization transformation. The heat treatment control system can integrate this calculation logic to automatically calculate and add the extension amount based on the input module thickness, or the operator can manually calculate the required extension amount according to this rule based on the actual thickness of the module and add it to the t. 6基础保温 In terms of time.

[0059] In this optional embodiment, the problem of insufficient microstructure transformation in the core of the thick H11 hot work die steel module is solved by dynamically adjusting the t6 holding time. Specifically, a t6 holding time of 10 to 15 hours is set. 6基础保温 The time provided by the standard allows for a basic spheroidizing annealing duration for the module. Building upon this, for modules thicker than 400mm, the holding time is extended by 40 to 50 minutes for every additional 40 to 60mm of thickness. This thickness-dependent extension mechanism effectively compensates for the hysteresis effect of heat conduction within thick modules, ensuring sufficient time for the module core to achieve complete carbide spheroidization during the 720℃ to 740℃ holding stage. Therefore, this approach significantly improves the overall uniformity of the spheroidized annealed microstructure in thick H11 hot work die steel modules, avoiding microstructure inhomogeneity and a decrease in annealing grade due to insufficient core spheroidization, thereby improving the subsequent machinability and quenching stability of the die steel.

[0060] The present invention will be further described below with reference to specific embodiments.

[0061] Example 1: A heat treatment method for improving the spheroidizing annealing grade of H11 hot work die steel module. A 400mm thick H11 hot work die steel module is used, and the following steps are included: 1. Cyclic Refinement Process: The H11 hot work die steel module workpiece to be heat-treated after forging is held at 1000℃ for 2 hours (basic heat preservation). After the heat preservation is completed, it is furnace cooled to 740℃ and held for 10 hours (basic heat preservation). Then the workpiece is reheated to 1000℃ and held for 2 hours (basic heat preservation). After the heat preservation is completed, it is furnace cooled to 740℃ and held for 10 hours (basic heat preservation). After the heat preservation is completed, it is air-cooled to below 200℃.

[0062] 2. Ultrafine treatment: Heat the workpiece to 1000℃ and hold for 2 hours (basic heat preservation). After the heat preservation is completed, cool it with water until the surface temperature is below 200℃.

[0063] 3. Isothermal bainite treatment: Transfer the workpiece whose surface has been cooled to below 200°C in step 2 into a 425°C heat treatment furnace and keep it at that temperature for 25 hours (basic heat treatment). After the heat treatment is completed, air cool it to room temperature.

[0064] 4. Spheroidizing annealing treatment: After cooling in step 3, the workpiece is heated to 850℃ and held for 10 hours (basic heat preservation). After the heat preservation is completed, it is air-cooled to 740℃ and held for 15 hours (basic heat preservation). After the heat preservation is completed, it is air-cooled.

[0065] Samples are taken from the surface and core of the workpiece, such as Figure 2 and Figure 3 As shown, both exhibit uniform carbide distribution, consistent annealing microstructure, and are rated AS1-4.

[0066] Example 2: A heat treatment method for improving the spheroidizing annealing grade of H11 hot work die steel modules. A 400mm thick H11 hot work die steel module is used, and the following steps are included: 1. Cyclic Refinement Process: Hold the forged workpiece at 1020℃ for 2 hours (basic holding). After holding, furnace cool to 740℃ and hold for 8 hours (basic holding). Then reheat the workpiece to 1020℃ and hold for 2 hours (basic holding). After holding, furnace cool to 740℃ and hold for 8 hours (basic holding). After holding, air cool to below 200℃.

[0067] 2. Ultrafine treatment: Heat the workpiece to 1000℃ and hold for 2 hours (basic heat preservation). After the heat preservation is completed, cool it with water until the surface temperature is below 200℃.

[0068] 3. Isothermal bainite treatment: Transfer the workpiece whose surface has been cooled to below 200°C in step 2 into a 325°C heat treatment furnace and keep it at that temperature for 20 hours (basic heat treatment). After the heat treatment is completed, air cool it to room temperature.

[0069] 4. Spheroidizing annealing treatment: After cooling in step 3, the workpiece is heated to 850℃ and held for 10 hours (basic heat preservation). After the heat preservation is completed, it is air-cooled to 740℃ and held for 15 hours (basic heat preservation). After the heat preservation is completed, it is air-cooled.

[0070] Samples are taken from the surface and core of the workpiece, such as Figure 4 and Figure 5 As shown, the annealed microstructure is uniform and consistent, and the ratings are all in AS1-4.

[0071] Example 3: A heat treatment method for improving the spheroidizing annealing grade of H11 hot work die steel module. An H11 hot work die steel module with a thickness of 400 mm is used, and the following steps are included: 1. Cyclic Refinement Process: The forged workpiece to be heat-treated is held at 1000℃ for 2 hours (basic heat preservation). After the heat preservation is completed, it is furnace cooled to 740℃ and held for 10 hours (basic heat preservation). The workpiece is then reheated to 1000℃ and held for 2 hours (basic heat preservation). After the heat preservation is completed, it is furnace cooled to 740℃ and held for 10 hours (basic heat preservation). After the heat preservation is completed, it is air-cooled to below 200℃.

[0072] 2. Ultrafine treatment: Heat the workpiece to 1000℃ and hold for 2 hours (basic heat preservation). After the heat preservation is completed, cool it with water until the surface temperature is below 200℃.

[0073] 3. Isothermal bainite treatment: Transfer the workpiece whose surface has been cooled to below 200°C in step 2 into a 390°C heat treatment furnace and keep it at that temperature for 20 hours (basic heat treatment). After the heat treatment is completed, air cool it to room temperature.

[0074] 4. Spheroidizing annealing treatment: After cooling in step 3, the workpiece is heated to 850℃ and held for 10 hours (basic heat preservation). After the heat preservation is completed, it is air-cooled to 740℃ and held for 15 hours (basic heat preservation). After the heat preservation is completed, it is air-cooled.

[0075] Samples are taken from the surface and core of the workpiece, such as Figure 6 and Figure 7 As shown, the annealed microstructure is uniform and consistent, and the ratings are all in AS1-4.

[0076] Comparative Example 1: A 400mm thick H11 hot work die steel module was taken and heat-treated according to the same method as in Example 1, but step 1 and the cyclic refinement process were omitted, and heat treatment started directly from step 2.

[0077] Samples are taken from the surface and core of the workpiece, such as Figure 8 and Figure 9 As shown, the carbide distribution is uneven, there are areas without carbides, and the annealed structure still maintains the original orientation of the coarse laths, with a rating within AS6-AS8.

[0078] Comparative Example 2: A 400mm thick H11 hot work die steel module was taken and heat-treated according to the same method as in Example 2, but step 3 was different, as follows: 3. Isothermal bainite treatment: Transfer the workpiece whose surface has been cooled to below 200°C in step 2 into a 325°C heat treatment furnace and keep it at that temperature for 10 hours (basic heat treatment). After the heat treatment is completed, air cool it to room temperature.

[0079] Comparative Example 2: Reduce the isothermal bainite treatment time by taking samples from the workpiece surface and core, such as... Figure 10 and Figure 11 As shown, the core structure exhibits uneven carbide distribution, with both dense and sparse carbide regions.

[0080] Comparative Example 3: A 400mm thick H11 hot work die steel module was taken and heat-treated according to the same method as in Example 3, but step 4 was different, as follows: 4. Spheroidizing annealing treatment: After cooling in step 4, the workpiece is heated to 890℃ and held for 10 hours (basic heat preservation). After the heat preservation is completed, it is air-cooled to 740℃ and held for 15 hours (basic heat preservation). After the heat preservation is completed, it is air-cooled.

[0081] Comparative Example 3: Increase the annealing temperature and take samples from the workpiece surface and core, such as... Figure 12 and Figure 13 As shown, the core structure exhibits uneven carbide distribution, with both dense and sparse carbide regions.

[0082] Comparative Example 4: A 400mm thick H11 hot work die steel module was taken and heat-treated according to the same method as in Example 3, but step 3 was omitted. After step 2, the workpiece with a surface temperature below 200°C was directly subjected to step 4.

[0083] Samples are taken from the surface and core of the workpiece, such as Figure 14 and Figure 15 As shown, the core carbides are extremely uneven, with large areas of no carbides and undissolved lamellar pearlite structures, and the rating is AS16.

[0084] It is evident that this application employs large-size H11 die steel modules that undergo post-forging heat treatment. Firstly, by employing two refinement processes, the large grain size, mixed grains, and inherited microstructure phenomena caused by the high-temperature homogenization treatment and forging of the original steel ingot can be effectively eliminated. Secondly, through ultra-refinement and isothermal bainite treatment, the microstructure differences caused by the inconsistent cooling rates between the surface and core of the large workpiece can be effectively prevented. In particular, the core cools more slowly, often remaining between 400°C and 500°C while the surface cools to below 200°C. At this point, a large amount of untransformed supercooled austenite still exists in the core. If spheroidizing annealing is directly performed at this stage, AS will form in the core. The H11 mold steel module has a grade 16 microstructure. After ultra-fine processing, the core of the workpiece is transferred to a furnace at 325°C to 425°C for a long period of isothermal treatment, which allows the core to form a complete bainitic microstructure. Meanwhile, the martensite microstructure formed on the outside due to the rapid cooling rate allows for the full precipitation of carbides within this temperature range, preparing the microstructure for the final spheroidizing annealing. Finally, by isothermal treatment at 850°C to 870°C, followed by air cooling to 720°C to 740°C, and then air cooling again, the internal and external annealing microstructures of the large-sized H11 mold steel module can be made uniform and consistent, avoiding the phenomenon of low core annealing microstructure rating caused by large size.

[0085] The AS rating mentioned above is based on NADCA#207, "Structure Rating Standard for Die Casting Mold Steels." This standard is specifically for the spheroidized annealed microstructure of hot work die steels (such as H11 and H13). The core evaluation indicators are "carbide size, uniformity of distribution, and grain size." The smaller the rating number, the better the microstructure quality. See the grading image for reference. Figure 16 The specific classifications are as follows: AS1-4 grade: Carbides are fine, uniformly dispersed, and without agglomeration or network carbides; AS6-8 grade: Carbide distribution is basically uniform, with slight local aggregation or thin strips; AS16 grade: Carbide is severely uneven, with obvious areas without carbide or dense areas, and the grains are coarse.

[0086] While the present invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, and all such changes and modifications will fall within the scope of protection of the present invention.

Claims

1. A heat treatment method for improving the spheroidizing annealing grade of H11 hot work die steel modules, characterized in that, For H11 hot work die steel modules with a thickness ≥ 400mm, the following steps are included: S1: Take the H11 hot work die steel module that is to be heat treated after forging, hold it at 980 to 1020°C for t1, cool it to 740 to 760°C and hold it for t2; reheat it to 980 to 1020°C and hold it for t1, cool it to 740 to 760°C and hold it for t2, and after the holding is completed, cool it to below 200°C; S2: Heat to 1000 to 1020℃ and hold for t3. After holding, cool until the surface temperature is below 200℃. S3: Heat to 325 to 425℃ and hold for t4. After holding, cool to room temperature. S4: Heat to 850 to 870℃ and hold for t5. After holding, cool to 720 to 740℃ and hold for t6. After holding, cool to room temperature. Among them, t1>1h, t2>8h, t3>1h, t4>20h, t5>8h, and t6>10h.

2. The heat treatment method for improving the spheroidizing annealing grade of H11 hot work die steel modules according to claim 1, characterized in that, The composition of the H11 hot work die steel module includes C, Si, Mn, Cr, Mo and V.

3. The heat treatment method for improving the spheroidizing annealing grade of H11 hot work die steel modules according to claim 2, characterized in that, The H11 hot work die steel module comprises, by weight, 0.3 to 0.45 parts of C, 0.1 to 1.2 parts of Si, 0.2 to 0.65 parts of Mn, 4.8 to 5.5 parts of Cr, 1.1 to 2.5 parts of Mo, and 0.3 to 1.15 parts of V.

4. The heat treatment method for improving the spheroidizing annealing grade of H11 hot work die steel modules according to claim 1, characterized in that, t1=t 1基础保温 +For each 40 to 60 mm increase in thickness of the H11 hot work die steel module compared to 400 mm, the extension time is 40 to 50 minutes. 1基础保温 =1 to 2 hours.

5. The heat treatment method for improving the spheroidizing annealing grade of H11 hot work die steel modules according to claim 1, characterized in that, t2=t 2基础保温 +For each 40 to 60 mm increase in thickness of the H11 hot work die steel module compared to 400 mm, the extension time is 40 to 50 minutes. 2基础保温 =8 to 10 hours.

6. The heat treatment method for improving the spheroidizing annealing grade of H11 hot work die steel modules according to claim 1, characterized in that, t3=t 3基础保温 +For each 40 to 60 mm increase in thickness of the H11 hot work die steel module compared to 400 mm, the extension time is 40 to 50 minutes. 3基础保温 =1 to 2 hours.

7. The heat treatment method for improving the spheroidizing annealing grade of H11 hot work die steel modules according to claim 1, characterized in that, t4=t 4基础保温 +For each 40 to 60 mm increase in thickness of the H11 hot work die steel module compared to 400 mm, the extension time is 40 to 50 minutes. 4基础保温 =20 to 25 hours.

8. The heat treatment method for improving the spheroidizing annealing grade of H11 hot work die steel modules according to claim 1, characterized in that, t5=t 5基础保温 +For each 40 to 60 mm increase in thickness of the H11 hot work die steel module compared to 400 mm, the extension time is 40 to 50 minutes. 5基础保温 =8 to 10 hours.

9. The heat treatment method for improving the spheroidizing annealing grade of H11 hot work die steel modules according to claim 1, characterized in that, t6=t 6基础保温 +For each 40 to 60 mm increase in thickness of the H11 hot work die steel module compared to 400 mm, the extension time is 40 to 50 minutes. 6基础保温 =10 to 15 hours.

10. The heat treatment method for improving the spheroidizing annealing grade of H11 hot work die steel modules according to claim 1, characterized in that, The cooling method is either water cooling or air cooling.

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