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CN-122007403-A - Hot isostatic pressing preparation method of high-density powder metallurgy die steel

CN122007403ACN 122007403 ACN122007403 ACN 122007403ACN-122007403-A

Abstract

The application relates to the field of powder metallurgy materials, and discloses a hot isostatic pressing preparation method of high-density powder metallurgy die steel and a composite powder premix. The premix comprises H13 die steel powder and trace amorphous boron, manganese nitride and vanadium carbide. The preparation method adopts a step-by-step temperature-pressure coupling process, namely, the amorphous boron reacts with surface oxygen to generate liquid-phase wetting particles in a low-temperature stage, active nitrogen is assisted to replace a surface refractory oxide film in a medium-temperature stage by a liquid-phase channel, and densification is realized in a high-temperature stage. According to the application, through the synergistic effect of low-temperature liquid phase induction and medium-temperature diffusion replacement, the continuously-distributed film-shaped oxide is in-situ converted into the dispersed granular carbonitride, so that the original grain boundary is prevented from splitting the matrix. The method can obtain fine-grain high-density tissues and simultaneously remarkably improve the transverse impact toughness of the die steel.

Inventors

  • Liang Zixun

Assignees

  • 一胜百科技(广东)有限公司

Dates

Publication Date
20260512
Application Date
20260303

Claims (10)

  1. 1. A compound powder premix for preparing die steel by hot isostatic pressing is characterized by comprising, by weight, 0.05% -0.30% of manganese nitride powder, 0.10% -0.50% of vanadium carbide powder, 0.01% -0.05% of amorphous boron powder and the balance of H13 hot work die steel powder.
  2. 2. The composite powder premix for preparing die steel by hot isostatic pressing according to claim 1, which is characterized by comprising, by weight, 0.15% -0.20% of manganese nitride powder, 0.25% -0.30% of vanadium carbide powder, 0.02% -0.03% of amorphous boron powder and the balance of H13 hot work die steel powder.
  3. 3. The composite powder premix for preparing die steel by hot isostatic pressing according to claim 1, wherein the purity of the amorphous boron powder is more than or equal to 95%, the average particle size D50 is less than 1.0 μm, the average particle size of the manganese nitride powder is 2-5 μm, and the average particle size of the vanadium carbide powder is 0.5-0.8 μm.
  4. 4. A method for preparing high-density powder metallurgy die steel by hot isostatic pressing, which adopts the composite powder premix as set forth in any one of claims 1 to 3 as a raw material, and is characterized by comprising the following steps: s1, packaging and degassing, namely filling the composite powder premix into a packaging sleeve, and performing vacuum degassing and sealing after compaction; S2, hot isostatic pressing sintering, namely placing the sealed package in a hot isostatic pressing machine, and executing a step-by-step warm-pressing coupling process, wherein the step-by-step warm-pressing coupling process comprises three steps which are sequentially performed, namely, heating to 500-600 ℃, controlling the pressure to 5-15 MPa, keeping the temperature and the pressure for 30-60 minutes, heating to 700-850 ℃, heating to 40-60 MPa, keeping the temperature and the pressure for 90-120 minutes, heating to 1120-1180 ℃, heating to 120-150 MPa, and keeping the temperature and the pressure for 2-4 hours; S3, cooling and post-treatment, namely cooling along with a furnace after sintering, and removing the sheath to obtain the die steel.
  5. 5. The method for preparing the high-density powder metallurgy die steel by hot isostatic pressing according to claim 4, wherein the method further comprises the step of preparing the composite powder premix before the step S1, wherein manganese nitride powder, vanadium carbide powder, amorphous boron powder and H13 hot work die steel powder are placed in a three-dimensional motion mixer and mixed under the protection of inert gas, and the mixing speed is 20-40r/min, and the mixing time is 4-8 hours.
  6. 6. The method for preparing high-density powder metallurgy die steel according to claim 4, wherein in S1, the vacuum degassing condition is that the heating temperature is 400-450 ℃, the duration is 4-6 hours, and the vacuum degree at the end of degassing is better than 1X 10-3Pa.
  7. 7. The method for preparing the high-density powder metallurgy die steel by hot isostatic pressing according to claim 4, wherein in the step S2, the heating rate of the step-wise warm-pressing coupling process is controlled to be 5-10 ℃ per minute in a first stage, 5-8 ℃ per minute in a second stage and 10-15 ℃ per minute in a third stage.
  8. 8. The hot isostatic pressing preparation method of high-density powder metallurgy die steel according to claim 4 is characterized in that the specific parameters of the step-by-step warm-pressing coupling process are that the temperature is raised to 550 ℃, the pressure is controlled to 10MPa, the temperature and the pressure are kept for 45 minutes in the first stage, the temperature is raised to 800 ℃, the pressure is raised to 50MPa, the temperature and the pressure are kept for 100 minutes in the second stage, the temperature is raised to 1150 ℃, the pressure is raised to 140MPa, and the temperature and the pressure are kept for 3 hours in the third stage.
  9. 9. The method for preparing high-density powder metallurgy die steel according to claim 4, wherein in S3, the post-treatment comprises spheroidizing annealing treatment of the steel ingot after removing the sheath, wherein the process comprises heating to 860-880 ℃, preserving heat for 2-4 hours, and then discharging from the furnace after gradually cooling to below 500 ℃.
  10. 10. The method for preparing high-density powder metallurgy die steel according to claim 4, wherein in the step S1, the material of the sheath is low carbon steel or stainless steel, and the tap density after charging is controlled to be 65% -70% of the theoretical density.

Description

Hot isostatic pressing preparation method of high-density powder metallurgy die steel Technical Field The invention relates to the technical field of powder metallurgy materials, in particular to a hot isostatic pressing preparation method of high-density powder metallurgy die steel. Background The powder metallurgy die steel has uniform structure, no macrosegregation and extremely fine carbide distribution, and is widely applied to the field of manufacturing high-end tools and dies. Especially for hot working die steel with high alloy content, the powder metallurgy process can overcome the serious problems of component segregation and coarse carbide in the traditional casting and forging process, and remarkably improves the isotropy and mechanical properties of the material. However, powder metallurgy die steel faces the difficult problem of controlling the oxidation of the powder surface during the preparation process. Because die steel generally contains high content of alloy elements such as chromium, vanadium, molybdenum and the like with extremely high affinity to oxygen, even if advanced powder making technologies such as vacuum induction melting gas atomization and the like are adopted, the surfaces of powder particles inevitably absorb oxygen or form thermodynamically stable oxide films. These oxide films present on the surface of the particles during the subsequent hot isostatic sintering process, if not effectively removed or broken, will hinder the diffusion and bonding of metal atoms between the powder particles, resulting in a continuously distributed Primary Particle Boundary (PPBs) remaining in the sintered body. The original grain boundaries serve as weak links in the material, the continuity of the matrix is severely ruptured, so that the transverse impact toughness and fatigue life of the material are obviously lower than theoretical expectations, and the application of the powder metallurgy die steel in an extreme service environment is limited. Currently, in order to mitigate the influence of the primary grain boundary, it is common in industry to use a method of increasing the hot isostatic pressure temperature in an attempt to physically break the oxide film by plastic deformation at high temperature. However, too high sintering temperatures can induce abnormal growth of austenite grains, leading to coarsening of the grains of the final product, rather reducing the yield strength and hardness of the material. Another common improvement means is to add carbon powder to the powder for carbothermic reduction, but because of the slow kinetics of the solid-solid reaction between the solid carbon and the surface oxide, it is usually necessary to start the reaction at extremely high temperatures, and it is difficult for trace carbon powder to achieve an ideal uniform distribution in the matrix, which is prone to cause local component fluctuations or carbide segregation. Therefore, how to break the constraint of thermodynamically stable oxide at lower densification temperature, to thoroughly eliminate the good combination of oxide film and interface, and to maintain fine grain structure at the same time, is a problem to be solved in the current powder metallurgy die steel preparation technology. Disclosure of Invention The invention solves the technical problems that in the existing powder metallurgy die steel preparation process, oxide films on the surfaces of powder particles are difficult to eliminate by a conventional means, so that original particle boundaries (PPBs) remain after sintering, the impact toughness and fatigue performance of the material are reduced, and the coarsening of crystal grains is often caused by the improvement of sintering temperature for crushing oxide films, so that the high density and fine grain structure are difficult to be compatible. In order to solve the problems, the invention provides the following technical scheme: First aspect The invention provides a composite powder premix for preparing die steel by hot isostatic pressing, which adopts the following technical scheme: The composite powder premix for preparing the die steel by hot isostatic pressing comprises, by weight, 0.05% -0.30% of manganese nitride powder, 0.10% -0.50% of vanadium carbide powder, 0.01% -0.05% of amorphous boron powder and the balance of H13 hot work die steel powder. By adopting the technical scheme, in-situ modification of the oxide on the particle surface is realized by the grading reaction of the amorphous boron, the manganese nitride and the vanadium carbide in the subsequent hot isostatic pressing process. The amorphous boron has high specific surface area and reactivity, is used as a sacrificial component to be preferentially combined with oxygen on the surface of matrix powder at a lower temperature to generate boron oxide with a lower softening point, forms an infiltration phase on the surface of particles, takes manganese nitride as a solid-phase nitrogen source, decompo