A high-carbon, ultra-high-hardness powder steel for stamping and its preparation method

Abstract

This application discloses a high-carbon ultra-high hardness powder steel for stamping and its preparation method. The powder steel has the following mass fractions of elements: C 3.2~4.0%, Si 0.5~1.0%, Mn 0.2~0.5%, P≤0.020%, S≤0.0030%, Ni≤0.5%, Cr 3.8~4.8%, Mo 4.5~5.8%, W 8.0~10.0%, V 9.3~11.3%, Co 8.2~9.2%, Al 0.015~0.04%, H≤0.0001%, with the remainder being Fe. The resulting powder steel has a uniform carbide distribution. By employing gradient vacuum quenching and cyclic deep cryogenic processes, the hardness after heat treatment can reach 72~74HRC, with low residual austenite content, exceeding the hardness of existing powder steel heat treatment. This improves the service life of stamping dies. It can achieve a hardness close to that of some cemented carbides, but with much higher toughness. The cost is significantly lower than that of cemented carbides. During the stamping process, the die is less prone to chipping and has better stability.

Description

Technical Field

[0001] This invention belongs to the field of mold manufacturing technology, specifically relating to a high-carbon ultra-high hardness powder steel for stamping and its preparation method. Background Technology

[0002] Molds are known as the "mother of industry," and high-precision stamping dies occupy a key position in the modern mold manufacturing field. In particular, industries such as new energy vehicles, consumer electronics, and semiconductors have very high requirements for stamping dies with long service life and high reliability, such as motor stator and rotor cores, connectors, and sensors used in new energy vehicles. Hardness is a key indicator affecting the lifespan of stamping dies. The heat treatment hardness of conventional M2, M35, and M42 high-speed steel is mostly 64~66 HRC, and the presence of large-sized primary carbides in the steel has a significant impact on the toughness and service life of the dies. The hardness of powder steel such as ASP2060 after heat treatment is usually lower than 68 HRC, which restricts the further improvement of the die life. Although the hardness of cemented carbide can reach 1200~1500 HV (about 71~75 HRC) or even higher, its toughness is extremely low and it is prone to chipping. At the same time, the high price of tungsten (the price of tungsten powder increased more than 6 times from January 2025 to March 2026, exceeding 2300 yuan / kg) and the strategic position of tungsten resources keep the cost of cemented carbide (W accounts for more than 70% of the weight) high, which brings great economic pressure to downstream applications.

[0003] Ultra-high hardness powder steel has become an important alternative to cemented carbide and for improving die life. The applicant's prior invention patent application 202110931400.4 disclosed a high-hardness powder steel and its heat treatment method. This powder steel contained 12-14% W and 1.8-2.5% C, achieving a hardness of over 70 HRC after heat treatment, higher than commercially available powder steels such as ASP2060. However, it was difficult to reach a hardness above 72 HRC, and its high W content also increased costs. While increasing hardness can improve die stamping life, it places higher demands on the quality of the powder steel, heat treatment deformation, and cracking. Increasing the C and alloying element content can improve the hardness of powder steel to some extent, but it brings many problems such as easy carbide accumulation, difficulty in powder preparation and forging, and risks of heat treatment deformation and cracking. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a high-carbon, ultra-high hardness powder steel for stamping and its preparation method, solving problems such as low hardness and poor service life of existing powder steels, and high cost, poor toughness, and easy chipping of cemented carbide. This invention significantly increases the carbon (C) content and optimizes the w and v (W) contents of existing powder steels. By optimizing key production and heat treatment processes, it ultimately obtains an ultra-high hardness powder steel with dispersed carbide distribution and low risk of deformation and cracking during heat treatment. This improves the overall performance of stamping dies, allows for the replacement of some cemented carbide components, and saves costs and stabilizes production for downstream customers.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: The first aspect of this invention provides a high-carbon, ultra-high-hardness powder steel for stamping, wherein the mass fraction of each element is as follows: C 3.2~4.0%, Si 0.5~1.0%, Mn 0.2~0.5%, P≤0.020%, S≤0.0030%, Ni≤0.5%, Cr 3.8~4.8%, Mo 4.5~5.8%, W 8.0~10.0%, V 9.3~11.3%, Co 8.2~9.2%, Al 0.015~0.04%, H≤0.0001%, with the remainder being Fe and unavoidable impurities.

[0006] A second aspect of the present invention provides a method for preparing the high-carbon ultra-high hardness powder steel for stamping as described above, comprising the following steps: S1. Powder metallurgy billet preparation: The refined molten steel is powdered using a high-pressure inert gas of not less than 15 bar. The O content in the molten steel is controlled to be ≤0.0015%, the high-pressure inert gas contains not less than 1% CO, and the contents of O2 and H2O are not higher than 0.05%. The gas flow rate to molten metal flow rate ratio is 3.5~4.5 m³ / s. 3 / kg, powder particle size ≤80μm; then first heat treatment at 720~780℃ for 3~5h, and then hot isostatic pressing at a pressure ≥140Mpa to form the preform; S2. Forging and forming: The billet is upsetting and drawing forging. The forging time for each forging session shall not exceed 10 minutes, the forging ratio shall not be less than 4, and the final forging temperature shall not be less than 850℃. The forged plate is then processed into a die blank. S3. Gradient vacuum quenching: The mold blank is heated to 600~650℃ at a heating rate of ≤300℃ / h under vacuum conditions and held for 1~3h, then heated to 850~950℃ and held for 2~4h, then heated to 1160~1220℃ at a heating rate of ≤200℃ / h and held for 0.5~2h. After the heat preservation is completed, the heat preservation is stopped first, and the temperature is allowed to cool naturally to 930~970℃. Then, high-pressure inert gas is used for cooling. During the cooling stage from 820~880℃ to 670~730℃, the pressure is ≥0.6Mpa. During the cooling stage from 430~470℃ to 280~320℃, the pressure is ≥0.8Mpa. The pressure for the remaining cooling stages is 0.4~0.6Mpa. S4. Cyclic cryogenic and tempering: Cryogenically cryogenically at -140~-190℃ for 3~6 hours. After the workpiece temperature reaches room temperature, heat it to 500~600℃ at a heating rate of ≤300℃ / h and hold it for 4~8 hours. Then air cool it to room temperature. Repeat this operation several times, with the temperature of each subsequent cryogenic cycle being lower than that of the previous cryogenic cycle. Then, a final tempering process is performed to obtain the finished product.

[0007] Preferably, the refined molten steel obtained in step S1 is obtained by sequentially melting in an induction furnace or electric furnace, refining in an LF furnace and a VD furnace.

[0008] Preferably, the temperature of the refined molten steel during powdering in step S1 is not lower than 1600℃; the temperature of the hot isostatic pressing is 1140~1200℃.

[0009] Preferably, step S2 further includes: heating the billet to 1150~1220℃ and holding it at that temperature before upsetting and forging; placing the forged plate in a furnace at 820~880℃ for more than 6 hours; then slowly cooling it to 680~740℃ and holding it at that temperature for more than 10 hours; cooling it to 300~400℃ at a rate not exceeding 25℃ / h before removing it from the furnace; and finally processing the plate into a mold blank.

[0010] Preferably, in step S2, the billet is wrapped in a refractory sleeve during forging.

[0011] Preferably, the carbide inhomogeneity of the plate after forging in step S2 does not exceed grade 1, the hardness does not exceed 400 HB, and the density exceeds 7.91 g / cm³. 3 .

[0012] Preferably, in step S3, the furnace is cooled to 60~100°C using high-pressure inert gas and then air-cooled.

[0013] Preferably, the total number of deep cryogenic cycles in step S4 is 3 to 4, using a cyclic gradient deep cryogenic process. The first deep cryogenic temperature is -140 to -160°C, and the time does not exceed 4 hours. The subsequent deep cryogenic temperatures are 5 to 15°C lower than the previous deep cryogenic temperature, and the deep cryogenic time is extended.

[0014] Preferably, the final tempering temperature in step S4 is 400~450℃, the holding time is 5~10h, and then the furnace is removed and air-cooled.

[0015] The powder steel sheet provided by this invention has a thickness of ≥100mm, a maximum carbide content of ≤1 grade, and a carbide non-uniformity of ≤1 grade; the heat treatment hardness can reach ≥72HRC, the residual austenite content is less than 5%, the die deformation is not higher than 1‰, it can reach a hardness close to that of some cemented carbide, but its toughness is much higher than that of cemented carbide, the cost is significantly lower than that of cemented carbide, and the die is less prone to chipping and has better stability during the stamping process. Attached Figure Description

[0016] Figure 1 This is a microstructure diagram of the powder steel obtained in Example 1 of the present invention after annealing (after step S2 treatment); Figure 2 This is a microstructure diagram of the powder steel obtained in Example 1 of the present invention after heat treatment (after step S4). Figure 3 This is a microstructure diagram of the carbide deposition in the powder steel obtained in Comparative Example 1 of the present invention. Figure 4 This is a comparison chart of the impact properties of powder steel provided in Embodiment 2 of the present invention and existing steel grades. Detailed Implementation

[0017] The first aspect of this application provides a high-carbon, ultra-high-hardness powder steel for stamping, wherein the mass fractions of each element are: C 3.2~4.0%, Si 0.5~1.0%, Mn 0.2~0.5%, P≤0.020%, S≤0.0030%, Ni≤0.5%, Cr 3.8~4.8%, Mo 4.5~5.8%, W 8.0~10.0%, V 9.3~11.3%, Co 8.2~9.2%, Al 0.015~0.04%, H≤0.0001%, with the remainder being Fe and unavoidable impurities.

[0018] Traditional high-speed steels such as M2 and M42 are produced using a smelting-refining-electroslag remelting process, resulting in relatively coarse and unevenly distributed carbides. This often produces plates with a thickness of ≤120mm, and the carbon content is typically less than 1.2%, leading to poor wear resistance during stamping and limiting die life. High-speed steels such as ASP2060 and ASP2023, produced using powder metallurgy, solve the carbide segregation problem, but their carbon content is usually less than 2.5%, making it difficult to achieve a heat-treated hardness above 68HRC. High-hardness cemented carbides, with a W content typically ≥70%, result in high die costs, and their poor toughness makes them prone to chipping and unstable lifespan in some stamping conditions. This invention significantly increases the C content and optimizes the W and V content, enabling powder steel to achieve higher heat-treated hardness.

[0019] Specifically, compared to patent 202110931400.4, this invention significantly increases the C content, which can form more carbides with alloying elements such as W, Mo, and V in steel, further improving the material's hardness and wear resistance. At the same time, it reduces the content of expensive W and Co, and increases the content of V and Si, thereby reducing the production cost of powder steel while meeting the material's hardness requirements. Furthermore, it limits the content of elements such as Al, P, and S to ensure the metallurgical quality of powder steel, enabling it to maintain good and stable toughness even at ultra-high hardness and reducing cracking problems caused by large inclusions.

[0020] However, while increasing the C content and optimizing the content of other alloying elements can improve the hardness of powder steel to a certain extent, the excessively high C and V content in this invention will exacerbate solidification segregation and the formation of more large-sized carbides, and increase the stability of supercooled austenite. This leads to many problems such as easy carbide accumulation, difficulty in powder preparation and forging, and risks of deformation and cracking during heat treatment. Therefore, a reasonable process is needed to solve the above problems.

[0021] The second aspect of this application provides a method for preparing the high-carbon ultra-high hardness powder steel for stamping as described above, comprising the following steps: S1. Powder Metallurgy Billet Preparation: The refined molten steel is powdered using a high-pressure inert gas of not less than 15 bar. The high-pressure inert gas contains not less than 1% CO, and the contents of O2 and H2O are not higher than 0.05%. The gas flow rate to molten metal flow rate ratio is 3.5~4.5 m³ / s. 3 / kg, powder particle size ≤80μm, preferably 30~80μm. The element content in the molten steel must meet the alloy standard. In addition, the O content in the molten steel should be controlled ≤0.0015% to limit the O content in the alloy (the O content will increase after powdering, and the O content in the powder steel can be appropriately controlled by controlling the O content in the molten steel). Then, it is first held at 720~780℃ for 3~5h, and then formed into a billet by hot isostatic pressing. The pressure of hot isostatic pressing is ≥140Mpa; the inert gas can be one or more of N2, Ar, He, etc., mixed together.

[0022] S2. Forging and forming: The billet is heated and forged by upsetting and drawing. The forging time for each forging session shall not exceed 10 minutes, the forging ratio shall not be less than 4, and the final forging temperature shall not be less than 850℃. The forged plate is then processed into a mold blank. Conventional processing methods such as sawing, wire cutting, and grinding can be used.

[0023] S3. Gradient vacuum quenching: Under vacuum conditions, heat the mold blank to 600~650℃ at a heating rate of ≤300℃ / h and hold for 1~3h, then heat to 850~950℃ and hold for 2~4h, then heat to 1160~1220℃ at a heating rate of ≤200℃ / h and hold for 0.5~2h.

[0024] After the heat preservation is completed, the heat preservation is stopped first, and the temperature is allowed to cool naturally to 930~970℃. Then, high-pressure inert gas is used for cooling. During the cooling stage from 820~880℃ to 670~730℃, the high-pressure inert gas pressure is ≥0.6Mpa. During the cooling stage from 430~470℃ to 280~320℃, the high-pressure inert gas pressure is ≥0.8Mpa. During the remaining cooling stages, the high-pressure inert gas pressure is 0.4~0.6Mpa.

[0025] S4. Cyclic cryogenics and tempering: Cryogenically cryogenically at -140~-190℃ for 3~6 hours. After the workpiece temperature reaches room temperature, heat it to 500~600℃ at a heating rate of ≤300℃ / h and hold it for 4~8 hours. Then air cool it to room temperature. Repeat this process several times, with the temperature of each subsequent cryogenic cycle being lower than that of the previous one.

[0026] Then, a final tempering process is performed to obtain the finished product.

[0027] (1) As mentioned above, high C content can react with O in steel to generate CO, forming pores and easily leading to hollow powder formation. At the same time, when the H content in the molten steel is too high, pores will also form during solidification. This invention reduces the problem of hollow coarse powder by controlling O ≤ 0.0015% and H ≤ 0.0001% in the molten steel, while controlling Al ≥ 0.015% to fix O in the steel, and controlling the content of O2 and H2O in the powder-making gas to be no higher than 0.05% and the CO content to be greater than 1%, and controlling an appropriate gas flow rate.

[0028] (2) High C content easily leads to carbide accumulation. To address this issue, the present invention employs the following technical means: under the premise of avoiding powder defects, the cooling rate of the molten metal droplets is appropriately accelerated by optimizing parameters such as gas pressure and flow rate, and the powder particle size is controlled to not exceed 80 μm, so as to reduce the segregation of elements such as C and V and the agglomeration of large carbides; the gas pressure for powder preparation is not less than 15 bar, so as to obtain fine powder, reduce element segregation and refine primary carbides; the hot isostatic pressing pressure is not less than 140 MPa, so as to produce a dense intermediate billet with relatively uniform carbide distribution; the forging ratio during forging is not less than 4, so as to ensure the dispersed distribution of carbides through sufficient deformation and further break up large carbides.

[0029] (3) To solve the problem of forging cracking caused by high C, the present invention anneals the powder before hot isostatic pressing (holding at 720~780℃ for 3~5h) to form a dense intermediate billet. Annealing transforms the non-equilibrium structure such as martensite and supercooled austenite in the powder into the equilibrium structure such as pearlite. At the same time, it reduces the powder hardness, releases internal stress, and reduces powder breakage, morphology and particle size changes caused by powder screening and conveying, thereby improving the powder surface quality and morphology distribution. Annealing reduces the powder resistance during forming, increases the density of the billet, and reduces cracking or substandard quality caused by defects such as looseness and porosity in the intermediate billet. When forging plates, the forging time is limited to no more than 10min and the final forging temperature is no less than 850℃ to prevent forging cracking caused by local low temperature and high deformation resistance.

[0030] (4) Crucially, to obtain a high hardness of 72HRC, rapid quenching and deep cryogenic treatment are required. However, conventional oil cooling and high-pressure air cooling can easily lead to deformation and cracking of the mold, while reducing the air cooling pressure may result in insufficient cooling and low hardness. Deep cryogenic treatment is a common process for improving the hardness of tool and die steel. However, conventional deep cryogenic treatment is prone to cracking due to long time and difficult to improve hardness due to short time. To solve this problem, this invention solves the dual purpose of high hardness and controllable deformation and cracking through vacuum air quenching gradient cooling and cyclic deep cryogenic treatment + tempering. Cooling is strengthened in the pearlite and bainite structure range to avoid the formation of such low-hardness structures from adversely affecting the material properties. Cooling is appropriately reduced in the high temperature (>820~880℃) and low temperature range (<280~320℃) to reduce the risk of deformation and cracking caused by thermal stress. Vacuum air quenching gradient cooling effectively solves the contradiction between quenching deformation and cracking and insufficient quenching hardness. Only by combining cryogenic treatment can the hardness of the invented steel grade be further increased to 72HRC. However, conventional cryogenic treatment is usually a single process. When the temperature is low and the time is long, it is prone to deformation and cracking. When the temperature is high, the purpose of cryogenic treatment cannot be achieved and the hardness is not significantly improved. This invention uses cyclic cryogenic treatment to coordinate the contradiction between cryogenic deformation and cracking and high hardness. After quenching, the mold is prone to deformation and cracking due to high internal stress and high retained austenite content. The initial cryogenic temperature is appropriately increased to minimize the deformation and cracking caused by the initial cryogenic treatment when the retained austenite is transformed into martensite. After tempering, the cryogenic temperature is reduced to further promote the transformation of retained austenite and maximize the martensite content and material hardness.

[0031] The formula and process provided in this application yield powder steel sheets with a thickness ≥100mm, a maximum carbide content ≤1, a carbide non-uniformity ≤1, a heat treatment hardness of ≥72HRC, a residual austenite content of ≤5%, and a die deformation of ≤1‰. This results in high hardness with toughness far exceeding that of cemented carbide, significantly lower cost, and less chipping of the die during stamping, better stability, and a significantly longer stamping life than existing powder steel.

[0032] Step S1: The molten steel can be obtained by conventional refining methods. This invention provides a preferred method in which the refined molten steel is successively melted in an induction furnace or electric furnace, and then refined in an LF furnace and a VD furnace. To ensure the content of Al, O and H in the alloy, the Al content in the molten steel is controlled to be no less than 0.015%, the O content to be no more than 0.0015%, and the H content to be no more than 0.0001%, and the content of other elements also meets the alloy requirements.

[0033] Preferably, the temperature of the refined molten steel in step S1 is not lower than 1600°C during powder production to prevent the low temperature from affecting the spraying and forming of the powder.

[0034] Preferably, the hot isostatic pressing temperature is 1140~1200℃. If the hot isostatic pressing temperature is too low, the porosity of the powder steel will increase and the density will decrease, resulting in a decrease in the strength of the steel, a decrease in impact resistance, and a decrease in service life. If the temperature exceeds 1200℃, the grains will grow and carbide growth and aggregation will occur, resulting in a decrease in strength and toughness and a decrease in wear resistance.

[0035] Preferably, step S2 further includes: heating the billet to 1150~1220℃ and holding it at that temperature before forging; excessively high temperatures will lead to coarse grains or even melting of grain boundaries, and there is a risk of primary carbide coarsening; excessively low temperatures will result in high deformation resistance of powder steel and a risk of cracking; placing the forged plate in a holding furnace at 820~880℃ for more than 6 hours, then slowly cooling it to 680~740℃ and holding it at that temperature for more than 10 hours, and then cooling it to 300~400℃ at a cooling rate not exceeding 25℃ / h before removing it from the furnace, so that the carbides are fully spheroidized, stress is released, and hardness is reduced, and then the plate is processed into a mold blank.

[0036] Preferably, in step S2, the billet is wrapped with a refractory sleeve during forging to slow down the temperature drop, avoid the risk of forging cracks caused by increased deformation resistance due to temperature drop, and at the same time ensure the uniformity of forging temperature and deformation, and improve the internal quality and microstructure uniformity of forging.

[0037] Using the process described in this application, plates of different thicknesses can be produced, especially thick plates with a thickness of ≥100mm. That is, the thickness of the forged plate can be ≥100mm.

[0038] The plates obtained through steps S1-S2 have a carbide non-uniformity of no more than grade 1, a hardness of no more than 400 HB, are easy to process, and have a density exceeding 7.91 g / cm³. 3 It has good density.

[0039] Preferably, in step S3, high-pressure inert gas is used to cool the powder steel to 60-100°C before air cooling to room temperature. The martensitic transformation temperature of the powder steel provided in this application is approximately 150-230°C. Excessive cooling temperature may result in insufficient heat treatment hardness and excessive retained austenite; conversely, insufficient cooling temperature, even with high-pressure cooling, is slow in this low-temperature range, wasting nitrogen with minimal cooling effect. Furthermore, high-pressure cooling within the furnace can lead to a large temperature difference between the inside and outside of the mold, potentially causing mold deformation and other risks.

[0040] Preferably, step S4 involves 3-4 cycles of deep cryogenic treatment, employing a cyclic gradient deep cryogenic process. The first deep cryogenic treatment is at -140 to -160°C for no more than 4 hours. After deep cryogenic and tempering treatments, the residual austenite content gradually decreases. To fully ensure the hardness and dimensional stability of the powder steel, subsequent deep cryogenic treatments are 5-15°C lower than the previous treatment, and the deep cryogenic time is appropriately extended. As the number of cycles increases, the deep cryogenic temperature and time are gradually extended, ensuring the optimal deep cryogenic effect.

[0041] Preferably, the final tempering temperature in step S4 is 400~450℃, the holding time is 5~10h, and then the powder steel is removed from the furnace and air-cooled. The final tempering can further release internal stress, stabilize the microstructure and dimensions of the powder steel, and reduce the risk of deformation and cracking during processing or use.

[0042] Example 1 This embodiment provides a powder steel with the following elemental composition by mass percentage: C 3.8%, Si 0.6%, Mn 0.4%, P 0.017%, S 0.0020%, Ni 0.4%, Cr 4.1%, Mo 5.5%, W 8.5%, V 10.7%, Co 8.4%, Al 0.017%, H 0.00005%, with the remainder being Fe and unavoidable impurities.

[0043] This powder steel is prepared using the following process: S1. Powder Metallurgy Billet Preparation: The refined molten steel is poured into a tundish at a temperature of 1630°C. The main elements of the molten steel meet the requirements of this embodiment, with O at 0.0013% and H at 0.00005%. Then, it is passed through a 19-bar high-pressure mixture of N2 and He inert gas (N2 to He volume ratio 5:1) at a pressure of 4.3 m... 3 The powder was prepared at a flow rate of / Kg. The mixed inert gas contained 1.2% CO, 0.005% O2, and 0.002% H2O. After sieving, the average particle size of the powder was 47μm, and no obvious hollow powder was found (<0.5%). The prepared powder was then vacuum-packed and held at 740℃ for 3 hours, followed by holding at approximately 1190℃ and then hot isostatic pressing at 180MPa to form a billet with a density of 7.91 g / cm³. 3; S2. Forging and forming: The billet is heated to about 1200℃ and held for 12 hours before upsetting and drawing. The upsetting amount is about 30%. Then it is drawn out by a press. When the size exceeds 1.2m, it is covered with an inorganic refractory sleeve to ensure that the billet temperature is not lower than 870℃. It is forged in 4 fires (each fire time is about 7min, 5min, 6min and 9min respectively). The forging ratio / deformation amount exceeds 8. The 200mm wide × 200mm thick plate is placed in an 840℃ holding furnace for 12 hours. Then it is slowly cooled to 700℃ and held for 18 hours. Then it is cooled to 400℃ at a cooling rate of 10℃ / h and removed from the furnace. The plate is then processed into a stamping die blank by sawing, wire cutting, grinding and other processes. S3. Gradient Vacuum Quenching: Place the mold blank in a vacuum quenching furnace, heat it to 650℃ at 200℃ / h and hold it for 2h, then heat it to 880℃ and hold it for 2h, then heat it to 1210℃ at 150℃ / h and hold it for 1h. After holding, turn off the power and let it cool with the furnace. When the temperature drops to 940℃, use nitrogen gas at a pressure of 0.5MPa for cooling. When the temperature drops to 850℃~700℃, the pressure is increased to 0.7MPa. When the temperature drops to 700℃~450℃, the pressure is adjusted to 0.45MPa. When the temperature is 450~300℃, the pressure is 1.0MPa. When the temperature is below 300℃, use 0.5MPa to cool it to 100℃ and then air cool it to room temperature. S4. Cyclic Cryogenic Treatment + Tempering: After quenching, the mold is cryogenically cooled at -160℃ for 3 hours and then removed. Once the workpiece temperature reaches room temperature, it is heated to 540℃ at a rate of 250℃ / h and held for 5 hours before being removed from the furnace and air-cooled to room temperature. Then, it is cryogenically cooled at -170℃ for 4 hours and then removed. Once the workpiece temperature reaches room temperature, it is heated to 550℃ at a rate of 250℃ / h and held for 5 hours before being removed from the furnace and air-cooled to room temperature. Finally, it is cryogenically cooled at -180℃ for 4 hours and then removed. It is heated to 560℃ at a rate of 250℃ / h and held for 5 hours before being removed from the furnace and air-cooled to room temperature.

[0044] Finally, it is kept at 450℃ for 5 hours, and then removed from the oven and air-cooled.

[0045] After testing, as Figures 1-2 As shown, the maximum detectable carbide size in the 200mm thick powder steel sheet (referencing GB / T 9943-2025) is 4.3um, the maximum carbide grade is ≤1, the carbide non-uniformity is ≤1, the heat treatment hardness reaches 73.2HRC, the residual austenite content is 4.3%, the mold deformation does not exceed 0.7‰, the unnotched impact test is 6.8J, and none of the three heat-treated pieces in the same batch cracked.

[0046] Example 2 This embodiment provides a powder steel with the following elemental composition by mass percentage: C 3.4%, Si 0.7%, Mn 0.4%, P 0.016%, S 0.0020%, Ni 0.3%, Cr 4.1%, Mo 5.1%, W 9.4%, V 9.5%, Co 8.9%, Al 0.016%, H 0.00009%, with the remainder being Fe and unavoidable impurities.

[0047] This powder steel is prepared using the following process: S1. Powder Metallurgy Billet Preparation: The refined molten steel is poured into a tundish at a temperature of 1620℃. The main elements of the molten steel meet the requirements of this embodiment. The tested molten steel contains 0.0012% O and 0.00009% H. Then, it is passed through a 19 bar high-pressure N2 solution at a flow rate of 4.1 m. 3 The powder was prepared at a flow rate of / Kg. The mixed inert gas contained 1.3% CO, 0.005% O2, and 0.002% H2O. After sieving, the average particle size of the powder was 55μm, and no obvious hollow powder was found (<0.5%). The prepared powder was then vacuum-packed and held at 750℃ for 3 hours, followed by holding at 1200℃ and then hot isostatic pressing at 180MPa to form a billet with a density of 7.91 g / cm³. 3 ; S2. Forging and forming: After heating the billet to about 1180℃ and holding it at that temperature, it is upsetting and drawing forging with an upsetting amount of about 30%. Then it is drawn out by a press. When the size exceeds 1.2m, it is covered with an inorganic refractory sleeve to ensure that the billet temperature is not lower than 860℃. It is forged in 3 fires (each fire lasts for about 6min, 5min and 8min respectively). The forging ratio / deformation amount exceeds 6. The plate with a width of 300mm and a thickness of 200mm is placed in an 850℃ holding furnace for 12h. Then it is slowly cooled to 720℃ and held for 18h. Then it is cooled to 400℃ at a cooling rate of 10℃ / h and then removed from the furnace. The plate is then sawed, ground and processed into a stamping die blank. S3. Gradient Vacuum Quenching: Place the mold blank in a vacuum quenching furnace, heat it to 650℃ at 250℃ / h and hold it for 2 hours, then heat it to 900℃ and hold it for 2 hours, then heat it to 1200℃ at 150℃ / h and hold it for 1 hour. After holding, turn off the power and let it cool with the furnace. When the temperature drops to 950℃, use nitrogen gas at a pressure of 0.4MPa for cooling. When the temperature drops to 880℃~730℃, the pressure is increased to 0.6MPa. When the temperature drops to 730℃~470℃, the pressure is adjusted to 0.45MPa. When the temperature is 470~320℃, the pressure is 0.8MPa. When the temperature is below 320℃, use 0.4MPa to cool it to 60℃ and then air cool it to room temperature. S4. Cyclic Cryogenic Treatment + Tempering: After quenching, the mold is cryogenically cooled at -155℃ for 3 hours and then removed. Once the workpiece temperature reaches room temperature, it is heated to 550℃ at a rate of 260℃ / h and held for 5 hours before being removed from the furnace and air-cooled to room temperature. Then, it is cryogenically cooled at -170℃ for 4 hours and then removed. Once the workpiece temperature reaches room temperature, it is heated to 560℃ at a rate of 260℃ / h and held for 5 hours before being removed from the furnace and air-cooled to room temperature. Then, it is cryogenically cooled at -180℃ for 4 hours and then removed. Once the workpiece temperature reaches room temperature, it is heated to 560℃ at a rate of 260℃ / h and held for 5 hours before being removed from the furnace and air-cooled to room temperature. Finally, it is cryogenically cooled at -185℃ for 4 hours and then held at 550℃ for 6 hours before being removed from the furnace and air-cooled.

[0048] Finally, it is kept at 450℃ for 8 hours, and then removed from the oven and air-cooled. Tests on 200mm thick powder steel plates (referencing GB / T 9943-2025) showed that the maximum detectable carbide size was 4.8µm, the maximum carbide grade was ≤1, the carbide inhomogeneity was ≤1, the heat treatment hardness reached 72.8HRC, the retained austenite content was 3.7%, the die deformation was no more than 0.5‰, the unnotched impact test result was 7.5J, and neither of the two heat-treated pieces from the same batch cracked.

[0049] Example 3 This embodiment provides a powder steel with the following elemental composition by mass percentage: C 3.2%, Si 0.7%, Mn 0.5%, P 0.016%, S 0.0020%, Ni 0.3%, Cr 4.4%, Mo 4.8%, W 8.4%, V 9.6%, Co 8.3%, Al 0.026%, H 0.0001%, with the remainder being Fe and unavoidable impurities.

[0050] This powder steel is prepared using the following process: S1. Powder Metallurgy Billet Preparation: The refined molten steel is poured into a tundish at a temperature of 1620°C. The main elements of the molten steel meet the requirements of this embodiment. The tested molten steel contains 0.0013% O and 0.0001% H. Then, it is passed through a 17-bar high-pressure N2 solution at 3.9m³. 3 The powder was prepared at a flow rate of / Kg. The mixed inert gas contained approximately 1.2% CO, 0.003% O2, and 0.002% H2O. After sieving, the average particle size of the powder was approximately 65μm, and no obvious hollow powder was found (<0.5%). The prepared powder was then vacuum-packed and held at 750℃ for 3 hours, followed by holding at 1160℃ and then hot isostatic pressing at 160MPa to form a billet with a density of 7.90 g / cm³. 3 ; S2. Forging and forming: The billet is heated to about 1170℃ and held for 8 hours, then upsetting and drawing forging is carried out. The upsetting amount is about 35%. Then it is drawn out by a press. When the size exceeds 1.2m, it is covered with an inorganic refractory sleeve to ensure that the billet temperature is not lower than 860℃. It is forged in 4 fires (each fire time is about 7min, 5min, 6min and 7min respectively). The forging ratio / deformation amount exceeds 6. The plate with a width of 400mm and a thickness of 300mm is placed in an 860℃ holding furnace for 8 hours. Then it is slowly cooled to 720℃ and held for 18 hours. Then it is cooled to 400℃ at a cooling rate of 10℃ / h and then removed from the furnace. The plate is then sawed, ground and processed into a stamping die blank. S3. Gradient Vacuum Quenching: Place the mold blank in a vacuum quenching furnace, heat it to 600℃ at 280℃ / h and hold for 2 hours, then heat it to 850℃ and hold for 2 hours, then heat it to 1180℃ at 150℃ / h and hold for 1 hour. After holding, turn off the power and let it cool with the furnace. When the temperature drops to 970℃, use nitrogen gas at a pressure of 0.6MPa for cooling. When the temperature drops to 830℃~680℃, the pressure is increased to 0.8MPa. When the temperature drops to 680℃~430℃, the pressure is adjusted to 0.6MPa. When the temperature drops to 430~280℃, the pressure is 0.9MPa. When the temperature drops below 280℃, use 0.6MPa to cool to 80℃ and then air cool to room temperature. S4. Cyclic Cryogenic Treatment + Tempering: After quenching, the mold is cryogenically cooled to -160℃ for 3 hours and then removed. Once the workpiece temperature reaches room temperature, it is heated to 540℃ at a rate of 280℃ / h and held for 5 hours before being removed from the furnace and air-cooled to room temperature. Then, it is cryogenically cooled to -175℃ for 4 hours and then removed. Once the workpiece temperature reaches room temperature, it is heated to 540℃ at a rate of 280℃ / h and held for 5 hours before being removed from the furnace and air-cooled to room temperature. Finally, it is cryogenically cooled to -190℃ for 4 hours and then removed. Once the workpiece temperature reaches room temperature, it is heated to 550℃ at a rate of 280℃ / h and held for 5 hours before being removed from the furnace and air-cooled to room temperature.

[0051] Finally, it is kept at 420℃ for 10 hours, and then removed from the oven and air-cooled. Tests on 300mm thick powder steel plates (referencing GB / T 9943-2025) showed that the maximum detectable carbide size was 5.2µm, the maximum carbide grade was 1, the carbide inhomogeneity was 1, the heat treatment hardness reached 72.2HRC, the retained austenite content was 4.1%, the die deformation was no more than 0.5‰, the unnotched impact test result was 8.1J, and neither of the two heat-treated pieces from the same batch cracked.

[0052] Comparative Example 1 The refined molten steel from Example 1 was processed according to the following process: S1. Powder metallurgy billet preparation (compared to Example 1, the powder-making gas flow rate is larger): using 22 bar high-pressure N2 at a flow rate of 4.9 m... 3 The N2 to He mixture was prepared by grinding at a flow rate of / Kg (N2 to He volume ratio of 5:1). The mixed inert gas contained 1.2% CO, 0.005% O2, and 0.002% H2O. After sieving, the average particle size of the powder was 46μm, with approximately 1.2% hollow powder present. The powder was then vacuum-packed and held at 740℃ for 3 hours, followed by holding at approximately 1190℃ and then hot isostatic pressing at 180MPa to form a billet with a density of 7.90 g / cm³. 3 ; S2. Forging and forming (compared to Example 1, the final forging temperature is lower and no insulation is used): The billet is heated to about 1200°C and held for a period of time before upsetting and drawing. The upsetting amount is about 30%. Then it is drawn out by a press. The temperature at both ends of the billet is lower than 830°C. There are some cracks on the surface of the plate. After three deformations, when the deformation amount exceeds 6, the 200mm×200mm plate is placed in an 850°C holding furnace for 12 hours. Then it is slowly cooled to 700°C and held for 18 hours. Then it is cooled to 400°C at a cooling rate of 10°C / h and taken out of the furnace. Then the plate is sawed and processed into a stamping die blank. S3. Vacuum quenching (compared to Example 1, gradient pressure cooling was not used): The mold blank was placed in a vacuum quenching furnace, heated to 650°C at 200°C / h and held for 2 hours, then heated to 880°C and held for 2 hours, then heated to 1210°C at 150°C / h and held for 1 hour. After the holding period, the power was turned off and the furnace was cooled. When the temperature dropped to 940°C, nitrogen gas at a pressure of 0.6 MPa was used for cooling. The mold blank was then removed from the furnace at approximately 100°C. S4. Deep Cryogenic Treatment + Tempering (compared to Example 1, cyclic deep cryogenic treatment was not used): The quenched mold was deep-cryogenically treated at -160℃ for 3 hours and then removed. After the workpiece temperature reached room temperature, it was heated to 540℃ at a heating rate of 250℃ / h and held for 5 hours before being removed from the furnace and air-cooled to room temperature. Then, it was held at 550℃ twice for 5 hours before being removed from the furnace and air-cooled to room temperature.

[0053] Finally, it is kept at 450℃ for 5 hours and then removed from the furnace and air-cooled. After testing, as Figure 3As shown, the maximum detectable carbide size (referring to GB / T 9943-2025) in the 200mm thick powder steel sheet is 4.9µm, and the maximum carbide grade is ≤1. However, there is localized carbide accumulation and the carbide inhomogeneity reaches grade 2. The heat treatment hardness is 71.7HRC, the retained austenite content is 6.7%, the maximum mold deformation is 1.3‰, and one of the three heat-treated pieces in the same batch cracked. The average unnotched impact test value is 6.4J, and some test values ​​are lower than 3J. Compared with Example 1, the powder steel provided in this comparative example has a lower impact under the premise of lower hardness, proving that the hollow powder generated when producing powder steel using ordinary processes and the lack of optimization of S3 and S4 lead to a reduction in the hardness, impact and processing (deformation, heat treatment cracking, etc.) performance of powder steel.

[0054] Comparative Example 2 Steps S1, S2, and S4 are the same as in Comparative Example 1, and step S3 is the same as in Example 1 (compared to Comparative Example 1, gradient vacuum quenching as in Example 1 is used): S3. Gradient vacuum quenching: The aforementioned process is the same as that in Comparative Example 1. After the heat preservation is completed, the power is turned off and the furnace is cooled. When the temperature drops to 940℃, nitrogen gas at a pressure of 0.5MPa is used for cooling. When the temperature drops to the range of 850℃ to 700℃, the pressure is increased to 0.7MPa. When the temperature drops to the range of 700℃ to 450℃, the pressure is adjusted to 0.45MPa. When the temperature drops to the range of 450℃ to 300℃, the pressure is 1.0MPa. When the temperature drops below 300℃, the furnace is cooled to 100℃ using 0.5MPa. S4. Deep Cryogenic + Tempering: After the quenched mold is deep-cryogenically cooled at -160℃ for 3 hours, it is taken out and after the workpiece temperature reaches room temperature, it is heated to 540℃ at a heating rate of 250℃ / h and held for 5 hours. Then it is taken out of the furnace and air-cooled to room temperature. Then it is held at 560℃ twice for 5 hours and then taken out of the furnace and air-cooled to room temperature. Finally, it is held at 450℃ for 5 hours and then taken out of the furnace and air-cooled. The heat-treated material was tested to have a hardness of 72.1 HRC, a residual austenite content of 5.3%, and a maximum mold deformation of 1‰. None of the three heat-treated pieces from the same batch cracked, but one piece cracked during the processing of the stamping die. The average unnotched impact strength was 6.2 J, with some test values ​​still below 3 J.

[0055] Comparative Example 3 The steps S1, S2, and S3 are the same as in Comparative Example 2, but step S4 is different (compared to Comparative Example 2, the cyclic cryogenic process in Example 1 is used): S4. Cyclic Cryogenic Treatment + Tempering: After quenching, the mold is cryogenically cooled at -160℃ for 3 hours and then removed. After the workpiece temperature reaches room temperature, it is heated to 540℃ at a heating rate of 250℃ / h and held for 5 hours before being removed from the furnace and air-cooled to room temperature. Then, it is cryogenically cooled at -170℃ for 4 hours and then removed from the furnace and held at 550℃ for 5 hours. Next, it is cryogenically cooled at -180℃ for 4 hours and then removed from the furnace and held at 560℃ for 5 hours. Finally, it is held at 450℃ for 5 hours before being removed from the furnace and air-cooled.

[0056] The heat-treated material was tested to have a hardness of 72.9 HRC, a residual austenite content of 4.1%, and a maximum mold deformation of 0.8‰. No cracking occurred in the three heat-treated pieces from the same batch, nor did any cracking occur during the processing of the stamping die. The average unnotched impact test value was 6J, with a few test values ​​still below 3J.

[0057] Comparative Example 4 The steps S2, S3, and S4 are the same as in Example 1, except that step S1 is different: S1. Powder metallurgy billet preparation (compared to Example 1, the gas content was not effectively controlled): A mixture of N2 and He inert gas (N2 to He volume ratio 5:1) was prepared at 19 bar pressure at a speed of 4.3 m... 3 The powder was produced at a flow rate of / Kg. The mixed inert gas contained <0.1% CO, 0.5% O2, and 0.8% H2O. After sieving, the average particle size of the powder was approximately 48µm, with noticeable hollow particles (1.0%). The powder was then vacuum-packed and held at approximately 1190℃ before being hot isostatically pressed into blanks at 180MPa. The blank density was approximately 7.90 g / cm³. 3 .

[0058] Tests on 200mm thick powder steel plates (referencing GB / T 9943-2025) showed that the maximum detectable carbide size was 4.5µm, the maximum carbide grade was ≤1, the carbide non-uniformity was ≤1, the heat treatment hardness was 73.0HRC, the retained austenite content was 4.3%, and the mold deformation was no more than 0.8‰. Some localized porosity defects were found in the powder steel produced in the same batch. The average unnotched impact strength was 6.4J, with some test values ​​below 5J. However, none of the three pieces of material cracked during heat treatment and mold processing.

[0059] Comparative Example 5 The steps S1 and S2 are the same as in Example 1, but steps S3 and S4 are different: S3. Vacuum quenching (compared to Example 1, gradient pressure cooling was not used): The mold blank was placed in a vacuum quenching furnace, heated to 650°C at 200°C / h and held for 2 hours, then heated to 880°C and held for 2 hours, then heated to 1210°C at 150°C / h and held for 1 hour. After the holding period, the power was turned off and the furnace was cooled. When the temperature dropped to 940°C, nitrogen gas at a pressure of 0.6 MPa was used for cooling. The mold blank was then removed from the furnace at approximately 100°C. S4. Deep Cryogenic Treatment + Tempering (compared to Example 1, cyclic deep cryogenic treatment was not used): The quenched mold was deep-cryogenically treated at -160℃ for 3 hours and then removed. After the workpiece temperature dropped to room temperature, it was heated to 540℃ at a heating rate of 250℃ / h and held for 5 hours before being removed from the furnace and air-cooled to room temperature. Then, it was held at 560℃ twice for 5 hours before being removed from the furnace and air-cooled to room temperature.

[0060] Tests on 200mm thick powder steel plates (referencing GB / T 9943-2025) showed the following maximum carbide size: 4.4µm; maximum carbide grade: ≤1; carbide inhomogeneity: ≤1; heat treatment hardness: 71.8HRC; retained austenite content: 6.8%; mold deformation: 1.6‰; unnotched impact strength: 7.4J; and one of the two heat-treated plates showed cracks.

[0061] The powder steel provided in Example 2 of this invention was subjected to stamping tests with existing ASP2060 powder steel and a certain cemented carbide. The results are shown in Table 1.

[0062] Table 1. Comparison of stamping service life between the powder steel of this invention, ASP2060 powder steel, and a certain cemented carbide.

[0063] As can be seen from Table 1, although a certain high-W content cemented carbide has a similar hardness to that of this application (both are relatively high), it is prone to chipping and has poor toughness during use. ASP2060, with its lower hardness, has better toughness and is less prone to chipping, but its lower hardness results in poor wear resistance and a shorter service life. In contrast, the powder steel provided in this application not only has high hardness but also good toughness and stability, resulting in a longer service life.

[0064] Figure 4The sample of this invention (66~68HRC) is a powder steel with a hardness of 66~68HRC obtained by adjusting the heat treatment parameters in steps S3 and S4 of Example 2. The sample of this invention (72~74HRC) is a powder steel with a hardness of 72~74HRC obtained by using the method of Example 2 (the required hardness can be adjusted by adjusting the heat treatment parameters; 72~74HRC is the highest heat treatment hardness of this invention, while the highest heat treatment hardness of ASP2060 is 66~68HRC). Generally, hardness and toughness cannot be simultaneously achieved in metal alloy materials. Figure 3 As can be seen (with the vertical axis set at ASP2060 impact as 100%), the high-hardness powder steel (72~74HRC) obtained using the method of this invention exhibits approximately three times the impact performance compared to cemented carbide (72~74HRC), and its toughness is significantly improved. The powder steel (66~68HRC) obtained by changing the heat treatment parameters shows only slightly inferior impact performance compared to the equivalent low-hardness ASP2060 steel. Therefore, the powder steel obtained using the method of this application achieves high hardness while also possessing good toughness, resulting in superior stamping die performance compared to conventional powder steel. Although lower than cemented carbide, the powder steel of this invention is less prone to chipping, more stable in use, and its cost is only about 25%~35% of that of cemented carbide, demonstrating superior cost-effectiveness.

[0065] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention. Clearly, those skilled in the art can make various alterations and modifications to the invention without departing from its spirit and scope. Thus, if these modifications and modifications of the invention fall within the scope of the claims and their equivalents, the invention is also intended to include these modifications and modifications.

Claims

1. A high-carbon, ultra-high-hardness powder steel for stamping, characterized in that, The mass fraction of each element is: C 3.2~4.0%, Si 0.5~1.0%, Mn 0.2~0.5%, P≤0.020%, S≤0.0030%, Ni≤0.5%, Cr 3.8~4.8%, Mo 4.5~5.8%, W 8.0~10.0%, V 9.3~11.3%, Co 8.2~9.2%, Al 0.015~0.04%, H≤0.0001%, with the remainder being Fe and unavoidable impurities.

2. The method for preparing high-carbon ultra-high hardness powder steel for stamping as described in claim 1, characterized in that, Includes the following steps: S1. Powder metallurgy billet preparation: The refined molten steel is powdered using a high-pressure inert gas of not less than 15 bar. The O content in the molten steel is controlled to be ≤0.0015%, the high-pressure inert gas contains not less than 1% CO, and the contents of O2 and H2O are not higher than 0.05%. The gas flow rate to molten metal flow rate ratio is 3.5~4.5 m³ / s. 3 / kg, powder particle size ≤80μm; then first heat treatment at 720~780℃ for 3~5h, and then hot isostatic pressing at a pressure ≥140Mpa to form the preform; S2. Forging and forming: The billet is upsetting and drawing forging. The forging time for each forging session shall not exceed 10 minutes, the forging ratio shall not be less than 4, and the final forging temperature shall not be less than 850℃. The forged plate is then processed into a die blank. S3. Gradient vacuum quenching: The mold blank is heated to 600~650℃ at a heating rate of ≤300℃ / h under vacuum conditions and held for 1~3h, then heated to 850~950℃ and held for 2~4h, then heated to 1160~1220℃ at a heating rate of ≤200℃ / h and held for 0.5~2h. After the heat preservation is completed, the heat preservation is stopped first, and the temperature is allowed to cool naturally to 930~970℃. Then, high-pressure inert gas is used for cooling. During the cooling stage from 820~880℃ to 670~730℃, the pressure is ≥0.6Mpa. During the cooling stage from 430~470℃ to 280~320℃, the pressure is ≥0.8Mpa. The pressure for the remaining cooling stages is 0.4~0.6Mpa. S4. Cyclic cryogenic and tempering: Cryogenically cryogenically at -140~-190℃ for 3~6 hours. After the workpiece temperature reaches room temperature, heat it to 500~600℃ at a heating rate of ≤300℃ / h and hold it for 4~8 hours. Then air cool it to room temperature. Repeat this operation several times, with the temperature of each subsequent cryogenic cycle being lower than that of the previous cryogenic cycle. Then, a final tempering process is performed to obtain the finished product.

3. The method for preparing high-carbon ultra-high hardness powder steel for stamping as described in claim 2, characterized in that, The refined molten steel described in step S1 is obtained by sequentially melting in an induction furnace or electric furnace, refining in an LF furnace and a VD furnace.

4. The method for preparing high-carbon ultra-high hardness powder steel for stamping as described in claim 2, characterized in that, The temperature of the refined molten steel during powdering in step S1 shall not be lower than 1600℃; the temperature of the hot isostatic pressing shall be 1140~1200℃.

5. The method for preparing high-carbon ultra-high hardness powder steel for stamping as described in claim 2, characterized in that, Step S2 further includes: heating the billet to 1150~1220℃ and holding it at that temperature before upsetting and forging; placing the forged plate in a furnace at 820~880℃ for more than 6 hours; then slowly cooling it to 680~740℃ and holding it at that temperature for more than 10 hours; cooling it to 300~400℃ at a rate not exceeding 25℃ / h before removing it from the furnace; and finally processing the plate into a mold blank.

6. The method for preparing high-carbon ultra-high hardness powder steel for stamping as described in claim 5, characterized in that, In step S2, the billet is wrapped in a refractory sleeve during forging.

7. The method for preparing high-carbon ultra-high hardness powder steel for stamping as described in claim 2, characterized in that, The carbide inhomogeneity of the forged plate after step S2 shall not exceed grade 1, the hardness shall not exceed 400 HB, and the density shall exceed 7.91 g / cm³. 3 .

8. The method for preparing high-carbon ultra-high hardness powder steel for stamping as described in claim 2, characterized in that, Step S3 involves cooling the furnace to 60-100°C using high-pressure inert gas before air cooling.

9. The method for preparing high-carbon ultra-high hardness powder steel for stamping as described in claim 2, characterized in that, Step S4 involves a total of 3 to 4 cycles of deep cryogenic treatment, using a cyclic gradient deep cryogenic process. The first deep cryogenic treatment is at a temperature of -140 to -160°C and lasts for no more than 4 hours. Subsequent deep cryogenic treatments are performed at temperatures 5 to 15°C lower than the previous treatment, and the deep cryogenic treatment time is appropriately extended.

10. The method for preparing high-carbon ultra-high hardness powder steel for stamping as described in claim 2, characterized in that, The final tempering temperature in step S4 is 400~450℃, the holding time is 5~10h, and then the furnace is removed and air-cooled.

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