Tungsten-containing high-chromium maraging high-strength steel powder metal injection molding preparation method
By using a water-air combined atomization method to prepare spherical powder, followed by segmented vacuum sintering and composite heat treatment, the problems of densification difficulties and performance instability of high-strength steel were solved. This enabled the preparation of steel parts with high strength, high elongation, and high density, and improved the controllability and repeatability of the process.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-02-02
- Publication Date
- 2026-04-14
AI Technical Summary
In the metal injection molding process of high-strength steel, there are problems such as difficulty in densification, instability of performance due to sensitivity of process parameters, and difficulty in balancing strength and toughness. In particular, for high-Cr systems containing W, there is a lack of a complete process parameter system, which prevents the material potential from being fully realized.
Spherical powders were prepared using a water-air combined atomization method, with polyoxymethylene-based composite binders, combined with segmented vacuum sintering and composite heat treatment, including solution treatment, cryogenic treatment, and aging treatment, forming a closely coordinated preparation method.
It has achieved stable preparation of high-strength (yield ≥1650MPa, tensile ≥1850MPa), high elongation (≥9.0%), high hardness (≥51HRC) and high density (≥98%) steel parts, solved the problem of strength and toughness imbalance, improved the controllability and repeatability of the process, and lowered the industrialization threshold.
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Abstract
Description
Technical Field
[0001] This invention relates to the fields of powder metallurgy and advanced structural materials, specifically to a method for preparing high-strength tungsten-containing high-chromium martensitic aged steel powder by injection molding, which achieves synergistic improvement in high strength and high elongation through composition optimization and process adaptation. This method is suitable for manufacturing precision structural parts with stringent requirements for mechanical properties and microstructure stability. Background Technology
[0002] Metal injection molding (MIM) technology combines the shape flexibility of plastic injection molding with the material property advantages of powder metallurgy, making it particularly suitable for the mass production of small-sized, complex-shaped metal parts. However, several process challenges remain in the application of MIM to high-strength steel: First, high-alloy martensitic aging steel powder faces significant diffusion resistance during sintering, making densification difficult and prone to porosity and microcracks, thus affecting the mechanical properties and reliability of the final parts. Second, traditional debinding and sintering process parameters are highly sensitive to material composition, easily leading to part deformation, cracking, or performance instability. Furthermore, existing heat treatment processes often struggle to balance high strength and high toughness, frequently resulting in an imbalance. While current technologies employ combined water-air atomization and multi-stage sintering to attempt to improve density, the issues of microstructure control and performance stability in high-Cr martensitic aging steel during the MIM process remain unresolved. Particularly for high-Cr systems containing W, a matching full-process parameter system is lacking, preventing the full realization of the material's potential. Summary of the Invention
[0003] To address the existing technological challenges in high-alloy martensitic aging steel during metal injection molding, such as difficulties in densification, performance instability due to sensitivity to process parameters, and the difficulty in balancing strength and toughness, this invention provides a metal injection molding preparation method tailored for tungsten-containing high-chromium martensitic aging high-strength steel powder, with each step closely coordinated. This method has clear process guidance and excellent repeatability, and is key to realizing the industrialization of high-performance materials (steel parts).
[0004] To achieve the above objectives, the present invention provides a method for preparing high-strength tungsten-containing high-chromium martensitic aging steel powder by metal injection molding, comprising the following steps: S1: Powder preparation: After refining the alloy melt, powder is prepared by water-air combined atomization method. After drying the wet powder, spherical powder is obtained by sieving. S2: Feed preparation: Mix the powder with polyoxymethylene-based composite binder, cool and then granulate; S3: Injection molding: Injecting the feed material into a green compact; S4: Degreasing treatment: The green body is degreased to obtain a palm blank; S5: Vacuum sintering: The process is a segmented heating process, which involves degreasing under negative pressure, firing in a vacuum, and sintering under partial pressure, followed by cooling to room temperature in the furnace. S6: Composite heat treatment: After solution treatment, cryogenic treatment, aging treatment, and air cooling to room temperature, the tungsten-containing high-chromium martensitic aging high-strength steel powder is obtained.
[0005] Furthermore, in S1, the alloy melt is refined at 1640-1660℃ for 8-10 minutes, and a deoxidizer is added during the refining process to make the oxygen content ≤0.2wt%.
[0006] Furthermore, the atomizing water pressure is 80-110 MPa, and the gas pressure is 10-15 MPa; the atomizing gas is high-purity nitrogen.
[0007] Further, in S2, the powder and polyoxymethylene-based composite binder are mixed at a weight ratio of 100:(10.2±0.1) and kneaded at 190±5℃ for 45-75 min.
[0008] Furthermore, the mass composition of the polyoxymethylene-based composite adhesive is 87±2% polyoxymethylene, 7±2% high-density polyethylene, 4±1% ethylene-vinyl acetate copolymer, and 2±0.5% stearic acid.
[0009] Furthermore, in S3, the feedstock is injection molded into a green compact at 195±5℃, with an injection pressure of 155±15MPa and a holding time of 5-10s.
[0010] Further, in S4, the brown husk is degreased at 110±5℃ under an oxalic acid atmosphere for 6-8 hours to obtain the brown husk.
[0011] Furthermore, in S5, vacuum sintering includes: negative pressure degreasing stage: room temperature → 600℃, 3℃ / min, holding for 3h, nitrogen gas introduced; vacuum internal firing stage: 600℃ → 1000℃, 3℃ / min, holding for 1h; partial pressure sintering stage: 1000℃ → 1360℃, 3℃ / min, holding for 4h, argon gas introduced.
[0012] Furthermore, in S6, the composite heat treatment includes: solution treatment: holding at 820-840℃ for 2 hours, followed by oil quenching; cryogenic treatment: holding at -196℃ for 1 hour, followed by air cooling to room temperature; aging treatment: holding at 480-550℃ for 4-6 hours, followed by air cooling to room temperature.
[0013] Further, the steel powder comprises, by mass percentage: Ni 14.0-16.0%, Co 10.0-12.0%, Mo 5.0-6.0%, W 1.0-2.0%, Cr 4.5-5.5%, Nb 0.1-0.5%, Si ≤0.3%, Cu ≤0.6%, Al ≤0.4%, C ≤0.03%, with the balance being Fe.
[0014] This invention provides a method for preparing high-strength tungsten-containing high-chromium martensitic aged steel powder by metal injection molding, which has the following beneficial effects: 1. By synergistically combining key steps such as water-air combined atomization powder preparation, polyoxymethylene-based composite binder formulation, segmented vacuum sintering and solution-deep cryogenic-aging composite heat treatment, a complete proprietary preparation method has been formed. This method can fully utilize the compositional potential of steel powder to stably prepare steel parts with high strength (yield ≥1650MPa, tensile ≥1850MPa), high elongation (≥9.0%), high hardness (≥51HRC), and high density (≥98%), successfully solving the core problem of strength-toughness imbalance in the MIM process of high alloy steel.
[0015] 2. The process parameters of each step (such as atomization pressure, sintering temperature rise curve, and heat treatment regime) have been optimized and designed, with strong controllability and high repeatability; the characteristics of the steel powder (spherical and fine particle size) and the binder system are fully compatible with the existing MIM production line, and the debinding and sintering regimes are mature and reliable, which greatly reduces the industrialization threshold and makes it easy to achieve large-scale and standardized production of high-performance parts.
[0016] 3. The targeted oxalic acid-catalyzed degreasing and negative pressure degreasing-vacuum internal firing-partial pressure sintering three-stage process effectively avoids green body deformation, cracking and sintering defects, ensuring extremely high sintering density. The exclusive composite heat treatment steps maximize the optimization of the material's microstructure, achieving maximum strength and retention of toughness. Detailed Implementation
[0017] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0018] This invention provides a tungsten-containing high-chromium martensitic aging high-strength steel powder, comprising, by mass percentage: Ni 14.0-16.0%, Co 10.0-12.0%, Mo 5.0-6.0%, W 1.0-2.0%, Cr 4.5-5.5%, Nb 0.1-0.5%, Si ≤0.3%, Cu ≤0.6%, Al ≤0.4%, C ≤0.03%, with the balance being Fe. By controlling the contents of key elements such as Ni, Co, Mo, W, Cr, and Nb within specific ranges and strictly limiting the contents of elements such as Si, Cu, Al, and C, optimized alloy composition design is achieved. This compositional system, while ensuring high strength, effectively suppresses the formation of brittle phases through the solid solution strengthening of W and the synergistic effect of Cr, laying the compositional foundation for excellent strength-toughness matching in the material. Simultaneously, it reduces the amount of precious metals Co and Mo used, resulting in significant cost advantages.
[0019] Preferably, the steel powder is spherical powder with a median diameter D50 of 6.5-7.0 μm, which ensures that the powder has good flowability and high tap density, making it particularly suitable for metal injection molding (MIM) process. This is beneficial for uniform mixing of feedstock, integrity of injection molding, and high densification of the final sintered body.
[0020] Preferably, the oxygen content of the steel powder is ≤0.2wt%, which greatly reduces grain boundary embrittlement and inclusion defects caused by oxygen impurities, and improves the toughness, fatigue performance and uniform stability of the final part.
[0021] This invention also provides a method for preparing high-strength tungsten-containing high-chromium martensitic aged steel powder by metal injection molding, comprising the following steps: S1: Powder preparation: After refining the alloy melt, powder is prepared by water-air combined atomization method. After drying the wet powder, spherical powder is obtained by sieving. S2: Feed preparation: Mix the powder with polyoxymethylene-based composite binder, cool and then granulate; S3: Injection molding: Injecting the feed material into a green compact; S4: Degreasing treatment: The green body is degreased to obtain a palm blank; S5: Vacuum sintering: The process is a segmented heating process, which involves degreasing under negative pressure, firing in a vacuum, and sintering under partial pressure, followed by cooling to room temperature in the furnace. S6: Composite heat treatment: After solution treatment, cryogenic treatment, aging treatment, and air cooling to room temperature, the tungsten-containing high-chromium martensitic aging high-strength steel powder is obtained.
[0022] Preferably, in step S1, the alloy melt is refined at 1640-1660℃ for 8-10 minutes, and a deoxidizer is added during the refining process to ensure an oxygen content ≤0.2wt%. A silicon-calcium alloy is preferred as the deoxidizer. Limiting the refining temperature (1640-1660℃) and time (8-10 minutes) and controlling the oxygen content ensures the purity and compositional uniformity of the alloy melt, providing a prerequisite for preparing high-quality atomized powder. The low oxygen content directly improves the toughness of the final product.
[0023] Preferably, the atomizing water pressure is 80-110 MPa, and the atomizing gas is high-purity nitrogen. This is crucial for obtaining high-quality spherical powder with concentrated particle size distribution, good sphericity, and controllable oxygen content, directly determining the powder's subsequent processing performance and the upper limit of the final part's performance. The gas pressure is 10-15 MPa.
[0024] Preferably, in S2, the powder and polyoxymethylene-based composite binder are mixed at a weight ratio of 100:(10.2±0.1), which ensures that the feed has the best flowability and uniformity; and the mixture is kneaded at 190±5℃ for 45-75 min.
[0025] Preferably, the polyoxymethylene-based composite binder has the following composition by mass: 87±2% polyoxymethylene, 7±2% high-density polyethylene, 4±1% ethylene-vinyl acetate copolymer, and 2±0.5% stearic acid. The polyoxymethylene-based composite binder possesses excellent flowability, compatibility with powders, and rapid catalytic degreasing properties, making it key to achieving high powder loading, good formability, and efficient degreasing.
[0026] Preferably, in step S3, the feedstock is injected into a green compact at 195±5℃, with an injection pressure of 155±15MPa and a holding time of 5-10s. This ensures that the feedstock has good filling capacity in the mold cavity, enabling the molding of green compacts with complex shapes and precise dimensions, while avoiding defects such as underfilling, flash, and internal stress.
[0027] Preferably, in step S4, degreasing is performed at 110±5℃ under an oxalic acid atmosphere for 6-8 hours to obtain a palm blank. The low-temperature degreasing at 110±5℃ can effectively and gently decompose and remove the polyoxymethylene binder matrix, avoiding deformation or cracking of the green blank and providing a structurally intact palm blank for subsequent high-temperature sintering.
[0028] Preferably, in step S5, vacuum sintering includes: a negative pressure degreasing stage: room temperature → 600℃, 3℃ / min, holding for 3 hours, with nitrogen gas introduced; a vacuum internal firing stage: 600℃ → 1000℃, 3℃ / min, holding for 1 hour; and a partial pressure sintering stage: 1000℃ → 1360℃, 3℃ / min, holding for 4 hours, with argon gas introduced. Through the gradual transition from negative pressure degreasing, vacuum internal firing, and partial pressure sintering, the complete removal of residual binder, the cleaning and activation of the powder particle surface, and the final high-temperature densification sintering are achieved, which is crucial for obtaining high-density, high-performance sintered bodies.
[0029] Preferably, in step S6, the composite heat treatment includes: solution treatment: holding at 820-840℃ for 2 hours, followed by oil quenching; cryogenic treatment: holding at -196℃ for 1 hour, followed by air cooling to room temperature; and aging treatment: holding at 480-550℃ for 4-6 hours, followed by air cooling to room temperature. This composite heat treatment is tailored to the composition of the steel powder of this invention, and can fully realize the solid solution of alloying elements, maximize the martensite transformation, and precipitate a large number of nanoscale strengthening phases, thereby improving the strength, hardness, and toughness of the steel parts to their optimal state.
[0030] The present invention discloses a method for preparing tungsten-containing high-chromium martensitic aging high-strength steel powder by metal injection molding. This method is a complete, precise, and industrially feasible metal injection molding process specifically designed for manufacturing tungsten-containing high-chromium martensitic aging high-strength steel parts. Starting with alloy melting and atomization powder preparation, the method employs optimized feed preparation, injection molding, catalytic debinding, segmented vacuum sintering, and finally, composite heat treatment, with each step working in synergy. Furthermore, this preparation method exhibits high controllability and repeatability, enabling the stable production of tungsten-containing high-chromium martensitic aging high-strength steel parts with complex shapes, precise dimensions, dense internal structure, and no defects. The final product demonstrates excellent and balanced comprehensive mechanical properties, including a yield strength ≥1650 MPa, tensile strength ≥1850 MPa, elongation ≥9.0%, and hardness ≥51 HRC.
[0031] This invention also provides a steel part with a yield strength ≥1650MPa, tensile strength ≥1850MPa, elongation ≥9.0%, hardness ≥51HRC, and sintered density ≥98%. Through innovative compositional design (introducing W and controlling Cr content), combined with specific powder morphology and particle size control, the microstructure and performance potential of the material are fundamentally optimized. The steel part prepared in this way achieves an excellent synergy between high strength (yield strength ≥1650MPa, tensile strength ≥1850MPa) and high plasticity (elongation ≥9.0%), high hardness (≥51HRC), and good density (≥98%), with comprehensive performance far exceeding that of traditional 18Ni-based martensitic aging steel.
[0032] The following examples and comparative examples illustrate the preparation method of the present invention in detail, and verify the performance of the steel parts prepared by the method, so as to demonstrate the beneficial technical effects of the present invention. Example 1
[0033] This example provides a method for preparing high-strength tungsten-containing high-chromium martensitic aged steel powder by metal injection molding, including the following steps: S1: Powder Preparation: The steel powder contains the following components by mass percentage: Ni: 14.5%, Co: 10.5%, Mo: 5.2%, W: 1.2%, Cr: 4.8%, Nb: 0.2%, Si: 0.15%, Cu: 0.3%, Al: 0.2%, C: 0.02%, with the balance being Fe. The batching accuracy error is ±0.03%. The steel powder is fed into an intermediate frequency furnace and heated to 1650℃ in a stepped manner. The alloy melt is refined for 9 minutes. During the refining process, a silicon-calcium alloy is added to ensure that the oxygen content is ≤0.2wt%. The casting temperature is 1645℃. The powder is prepared using a water-gas combined atomization method. The atomizing water pressure is 90MPa, the gas pressure is 10MPa, and the atomizing gas is high-purity nitrogen. The wet powder is dried at 150℃ and under a vacuum of -0.09MPa for 2.5 hours. After grading and sieving, the median diameter of the powder is D50 = 6.7μm.
[0034] S2: Feed Preparation: The powder and polyoxymethylene-based composite binder are mixed at a weight ratio of 100:10.2 and fed into an internal mixer. The mixture is stirred at 190℃ and 25r / min for 1 hour. After cooling and granulation, the particle size is 3-4mm. The mass composition of the polyoxymethylene-based composite binder is 87% polyoxymethylene, 7% high-density polyethylene, 4% ethylene-vinyl acetate copolymer, and 2% stearic acid.
[0035] S3: Injection molding: The feed material is injected into a green body at 195℃, with an injection pressure of 155MPa and a holding time of 8s; the injection rate is 65mm / s, and the dimensional accuracy error is ±0.3%.
[0036] S4: Degreasing treatment: Degrease at 110℃ under oxalic acid atmosphere for 7 hours to obtain palm blank, with residual polyoxymethylene content of 0.8%.
[0037] S5: Vacuum sintering: carried out according to the segmented process. In the negative pressure degreasing stage, the nitrogen flow rate is 2L / min, the temperature is raised from room temperature to 600℃, the temperature is raised at 3℃ / min, and the holding time is 3 hours. In the vacuum internal firing stage, the temperature is raised from 600℃ to 1000℃ at a heating rate of 3℃ / min and the holding time is 1 hour. In the partial pressure sintering stage, the argon flow rate is 2.5L / min, the partial pressure is 20KPa, the temperature is raised from 1000℃ to 1360℃ at 3℃ / min and the holding time is 4 hours. The furnace is then cooled to room temperature at a cooling rate of 8℃ / min.
[0038] S6: Composite heat treatment: solution treatment: hold at 830℃ for 2 hours, then oil quench; cryogenic treatment: hold at -196℃ for 1 hour, then air cool to room temperature; aging treatment: hold at 500℃ for 5 hours, then air cool to room temperature, to obtain the tungsten-containing high-chromium martensitic aging high-strength steel powder. Example 2
[0039] This example provides a method for preparing high-strength tungsten-containing high-chromium martensitic aged steel powder by metal injection molding, including the following steps: S1: Powder Preparation: The steel powder contains the following components by mass percentage: Ni: 15.2%, Co: 11.0%, Mo: 5.6%, W: 1.6%, Cr: 5.2%, Nb: 0.3%, Si: 0.2%, Cu: 0.4%, Al: 0.3%, C: 0.02%, with the balance being Fe. The batching accuracy error is ±0.03%. The steel powder is fed into an intermediate frequency furnace and heated to 1650℃ in a stepped manner. The alloy melt is refined for 9 minutes. During the refining process, a silicon-calcium alloy is added to ensure that the oxygen content is ≤0.2wt%. The casting temperature is 1645℃. The powder is prepared using a water-gas combined atomization method. The atomizing water pressure is 90MPa, the gas pressure is 10MPa, and the atomizing gas is high-purity nitrogen. The wet powder is dried at 150℃ and a vacuum of -0.09MPa for 2.5 hours. After grading and sieving, the median diameter of the powder is D50 = 6.7μm.
[0040] S2: Feed Preparation: The powder and polyoxymethylene-based composite binder are mixed at a weight ratio of 100:10.2 and fed into an internal mixer. The mixture is stirred at 190℃ and 25r / min for 1 hour. After cooling and granulation, the particle size is 3-4mm. The mass composition of the polyoxymethylene-based composite binder is 87% polyoxymethylene, 7% high-density polyethylene, 4% ethylene-vinyl acetate copolymer, and 2% stearic acid.
[0041] S3: Injection molding: The feed material is injected into a green body at 195℃, with an injection pressure of 155MPa and a holding time of 8s; the injection rate is 65mm / s, and the dimensional accuracy error is ±0.3%.
[0042] S4: Degreasing treatment: Degrease at 110℃ under oxalic acid atmosphere for 7 hours to obtain palm blank, with residual polyoxymethylene content of 0.8%.
[0043] S5: Vacuum sintering: carried out according to the segmented process. In the negative pressure degreasing stage, the nitrogen flow rate is 2L / min, the temperature is raised from room temperature to 600℃, the temperature is raised at 3℃ / min, and the holding time is 3 hours. In the vacuum internal firing stage, the temperature is raised from 600℃ to 1000℃ at a heating rate of 3℃ / min and the holding time is 1 hour. In the partial pressure sintering stage, the argon flow rate is 2.5L / min, the partial pressure is 20KPa, the temperature is raised from 1000℃ to 1360℃ at 3℃ / min and the holding time is 4 hours. The furnace is then cooled to room temperature at a cooling rate of 8℃ / min.
[0044] S6: Composite heat treatment: solution treatment: hold at 830℃ for 2 hours, then oil quench; cryogenic treatment: hold at -196℃ for 1 hour, then air cool to room temperature; aging treatment: hold at 500℃ for 5 hours, then air cool to room temperature, to obtain the tungsten-containing high-chromium martensitic aging high-strength steel powder. Example 3
[0045] This example provides a method for preparing high-strength tungsten-containing high-chromium martensitic aged steel powder by metal injection molding, including the following steps: S1: Powder Preparation: The steel powder contains the following components by mass percentage: Ni: 14.0%, Co: 10.0%, Mo: 5.0%, W: 1.0%, Cr: 4.5%, Nb: 0.1%, Si: 0.1%, Cu: 0.2%, Al: 0.1%, C: 0.02%, with the balance being Fe. The batching accuracy error is ±0.03%. The steel powder is fed into an intermediate frequency furnace and heated to 1650℃ in a stepped manner. The alloy melt is refined for 9 minutes. During the refining process, a silicon-calcium alloy is added to ensure that the oxygen content is ≤0.2wt%. The casting temperature is 1645℃. The powder is prepared using a water-gas combined atomization method. The atomizing water pressure is 90MPa, the gas pressure is 10MPa, and the atomizing gas is high-purity nitrogen. The wet powder is dried at 150℃ and under a vacuum of -0.09MPa for 2.5 hours. After grading and sieving, the median diameter of the powder is D50=6.7μm.
[0046] S2: Feed Preparation: The powder and polyoxymethylene-based composite binder are mixed at a weight ratio of 100:10.2 and fed into an internal mixer. The mixture is stirred at 190℃ and 25r / min for 1 hour. After cooling and granulation, the particle size is 3-4mm. The mass composition of the polyoxymethylene-based composite binder is 87% polyoxymethylene, 7% high-density polyethylene, 4% ethylene-vinyl acetate copolymer, and 2% stearic acid.
[0047] S3: Injection molding: The feed material is injected into a green body at 195℃, with an injection pressure of 155MPa and a holding time of 8s; the injection rate is 65mm / s, and the dimensional accuracy error is ±0.3%.
[0048] S4: Degreasing treatment: Degrease at 110℃ under oxalic acid atmosphere for 7 hours to obtain palm blank, with residual polyoxymethylene content of 0.8%.
[0049] S5: Vacuum sintering: carried out according to the segmented process. In the negative pressure degreasing stage, the nitrogen flow rate is 2L / min, the temperature is raised from room temperature to 600℃, the temperature is raised at 3℃ / min, and the holding time is 3 hours. In the vacuum internal firing stage, the temperature is raised from 600℃ to 1000℃ at a heating rate of 3℃ / min and the holding time is 1 hour. In the partial pressure sintering stage, the argon flow rate is 2.5L / min, the partial pressure is 20KPa, the temperature is raised from 1000℃ to 1360℃ at 3℃ / min and the holding time is 4 hours. The furnace is then cooled to room temperature at a cooling rate of 8℃ / min.
[0050] S6: Composite heat treatment: solution treatment: hold at 830℃ for 2 hours, then oil quench; cryogenic treatment: hold at -196℃ for 1 hour, then air cool to room temperature; aging treatment: hold at 500℃ for 5 hours, then air cool to room temperature, to obtain the tungsten-containing high-chromium martensitic aging high-strength steel powder. Example 4
[0051] This example provides a method for preparing high-strength tungsten-containing high-chromium martensitic aged steel powder by metal injection molding, including the following steps: S1: Powder Preparation: The steel powder contains the following components by mass percentage: Ni: 15.8%, Co: 11.8%, Mo: 5.9%, W: 1.9%, Cr: 5.4%, Nb: 0.45%, Si: 0.28%, Cu: 0.55%, Al: 0.38%, C: 0.02%, with the balance being Fe. The batching accuracy error is ±0.03%. The steel powder is fed into an intermediate frequency furnace and heated in stages to 1650℃. The alloy melt is refined for 9 minutes. During the refining process, a silicon-calcium alloy is added to ensure that the oxygen content is ≤0.2wt%. The casting temperature is 1645℃. The powder is prepared using a water-gas combined atomization method. The atomizing water pressure is 90MPa, the gas pressure is 10MPa, and the atomizing gas is high-purity nitrogen. The wet powder is dried at 150℃ and a vacuum of -0.09MPa for 2.5 hours. After grading and sieving, the median diameter of the powder is D50 = 6.7μm.
[0052] S2: Feed Preparation: The powder and polyoxymethylene-based composite binder are mixed at a weight ratio of 100:10.2 and fed into an internal mixer. The mixture is stirred at 190℃ and 25r / min for 1 hour. After cooling and granulation, the particle size is 3-4mm. The mass composition of the polyoxymethylene-based composite binder is 87% polyoxymethylene, 7% high-density polyethylene, 4% ethylene-vinyl acetate copolymer, and 2% stearic acid.
[0053] S3: Injection molding: The feed material is injected into a green body at 195℃, with an injection pressure of 155MPa and a holding time of 8s; the injection rate is 65mm / s, and the dimensional accuracy error is ±0.3%.
[0054] S4: Degreasing treatment: Degrease at 110℃ under oxalic acid atmosphere for 7 hours to obtain palm blank, with residual polyoxymethylene content of 0.8%.
[0055] S5: Vacuum sintering: carried out according to the segmented process. In the negative pressure degreasing stage, the nitrogen flow rate is 2L / min, the temperature is raised from room temperature to 600℃, the temperature is raised at 3℃ / min, and the holding time is 3 hours. In the vacuum internal firing stage, the temperature is raised from 600℃ to 1000℃ at a heating rate of 3℃ / min and the holding time is 1 hour. In the partial pressure sintering stage, the argon flow rate is 2.5L / min, the partial pressure is 20KPa, the temperature is raised from 1000℃ to 1360℃ at 3℃ / min and the holding time is 4 hours. The furnace is then cooled to room temperature at a cooling rate of 8℃ / min.
[0056] S6: Composite heat treatment: solution treatment: hold at 830℃ for 2 hours, then oil quench; cryogenic treatment: hold at -196℃ for 1 hour, then air cool to room temperature; aging treatment: hold at 500℃ for 5 hours, then air cool to room temperature, to obtain the tungsten-containing high-chromium martensitic aging high-strength steel powder.
[0057] Comparative Example 1 This example provides a method for preparing steel powder by metal injection molding, including the following steps: S1: Powder preparation: The powder was prepared according to the standard composition of traditional 18Ni(250) martensitic aging steel: Ni: 18%, Co: 8%, Mo: 5%, Ti: 0.4%, Al: 0.1%, with the balance being Fe. The batching accuracy error was ±0.03%. The steel powder was fed into an intermediate frequency furnace and heated to 1650℃ in a stepwise manner. The alloy melt was refined for 9 minutes. During the refining process, a silicon-calcium alloy was added to ensure that the oxygen content was ≤0.2wt%. The casting temperature was 1645℃. The powder was prepared by water-gas combined atomization method. The atomizing water pressure was 90MPa, the gas pressure was 10MPa, and the atomizing gas was high-purity nitrogen. The wet powder was dried at 150℃ and vacuum degree -0.09MPa for 2.5h. After grading and sieving, the median diameter of the powder was D50=6.7μm.
[0058] S2: Feed Preparation: The powder and polyoxymethylene-based composite binder are mixed at a weight ratio of 100:10.2 and fed into an internal mixer. The mixture is stirred at 190℃ and 25r / min for 1 hour. After cooling and granulation, the particle size is 3-4mm. The mass composition of the polyoxymethylene-based composite binder is 87% polyoxymethylene, 7% high-density polyethylene, 4% ethylene-vinyl acetate copolymer, and 2% stearic acid.
[0059] S3: Injection molding: The feed material is injected into a green body at 195℃, with an injection pressure of 155MPa and a holding time of 8s; the injection rate is 65mm / s, and the dimensional accuracy error is ±0.3%.
[0060] S4: Degreasing treatment: Degrease at 110℃ under oxalic acid atmosphere for 7 hours to obtain palm blank, with residual polyoxymethylene content of 0.8%.
[0061] S5: Vacuum sintering: carried out according to the segmented process. In the negative pressure degreasing stage, the nitrogen flow rate is 2L / min, the temperature is raised from room temperature to 600℃, the temperature is raised at 3℃ / min, and the holding time is 3 hours. In the vacuum internal firing stage, the temperature is raised from 600℃ to 1000℃ at a heating rate of 3℃ / min and the holding time is 1 hour. In the partial pressure sintering stage, the argon flow rate is 2.5L / min, the partial pressure is 20KPa, the temperature is raised from 1000℃ to 1360℃ at 3℃ / min and the holding time is 4 hours. The furnace is then cooled to room temperature at a cooling rate of 8℃ / min.
[0062] S6: Composite heat treatment: solution treatment: hold at 830℃ for 2 hours, then oil quench; cryogenic treatment: hold at -196℃ for 1 hour, then air cool to room temperature; aging treatment: hold at 500℃ for 5 hours, then air cool to room temperature, to obtain the tungsten-containing high-chromium martensitic aging high-strength steel powder.
[0063] Comparative Example 2 This example provides a method for preparing steel powder by metal injection molding, including the following steps: S1: Powder Preparation: The steel powder contains the following components by mass percentage: Ni: 14.5%, Co: 10.5%, Mo: 5.2%, Cr: 4.8%, Nb: 0.2%, Si: 0.15%, Cu: 0.3%, Al: 0.2%, C: 0.02%, with the balance being Fe. The batching accuracy error is ±0.03%. The steel powder is fed into an intermediate frequency furnace and heated in stages to 1650℃. The alloy melt is refined for 9 minutes. During the refining process, a silicon-calcium alloy is added to ensure that the oxygen content is ≤0.2wt%. The casting temperature is 1645℃. The powder is prepared using a water-gas combined atomization method. The atomizing water pressure is 90MPa, the gas pressure is 10MPa, and the atomizing gas is high-purity nitrogen. The wet powder is dried at 150℃ and under a vacuum of -0.09MPa for 2.5 hours. After grading and sieving, the median diameter of the powder is D50 = 6.7μm.
[0064] S2: Feed Preparation: The powder and polyoxymethylene-based composite binder are mixed at a weight ratio of 100:10.2 and fed into an internal mixer. The mixture is stirred at 190℃ and 25r / min for 1 hour. After cooling and granulation, the particle size is 3-4mm. The mass composition of the polyoxymethylene-based composite binder is 87% polyoxymethylene, 7% high-density polyethylene, 4% ethylene-vinyl acetate copolymer, and 2% stearic acid.
[0065] S3: Injection molding: The feed material is injected into a green body at 195℃, with an injection pressure of 155MPa and a holding time of 8s; the injection rate is 65mm / s, and the dimensional accuracy error is ±0.3%.
[0066] S4: Degreasing treatment: Degrease at 110℃ under oxalic acid atmosphere for 7 hours to obtain palm blank, with residual polyoxymethylene content of 0.8%.
[0067] S5: Vacuum sintering: carried out according to the segmented process. In the negative pressure degreasing stage, the nitrogen flow rate is 2L / min, the temperature is raised from room temperature to 600℃, the temperature is raised at 3℃ / min, and the holding time is 3 hours. In the vacuum internal firing stage, the temperature is raised from 600℃ to 1000℃ at a heating rate of 3℃ / min and the holding time is 1 hour. In the partial pressure sintering stage, the argon flow rate is 2.5L / min, the partial pressure is 20KPa, the temperature is raised from 1000℃ to 1360℃ at 3℃ / min and the holding time is 4 hours. The furnace is then cooled to room temperature at a cooling rate of 8℃ / min.
[0068] S6: Composite heat treatment: solution treatment: hold at 830℃ for 2 hours, then oil quench; cryogenic treatment: hold at -196℃ for 1 hour, then air cool to room temperature; aging treatment: hold at 500℃ for 5 hours, then air cool to room temperature, to obtain the tungsten-containing high-chromium martensitic aging high-strength steel powder.
[0069] Comparative Example 3 This example provides a method for preparing steel powder by metal injection molding, including the following steps: S1: Powder Preparation: The steel powder, by mass percentage, contains: Ni: 14.5%, Co: 10.5%, Mo: 5.2%, W: 1.2%, Cr: 4.8%, Nb: 0.2%, Si: 0.15%, Cu: 0.3%, Al: 0.2%, C: 0.02%, with the balance being Fe. The batching accuracy error is ±0.03%. The steel powder is fed into an induction furnace and heated in stages to 1650℃. The alloy melt is refined for 9 minutes. During the refining process, a silicon-calcium alloy is added to ensure an oxygen content ≤0.2wt%. The casting temperature is 1645℃. The powder is prepared using a single high-pressure gas atomization at a pressure of 12MPa, with high-purity nitrogen as the atomizing gas. The wet powder is dried at 150℃ and a vacuum of -0.09MPa for 2.5 hours. Subsequently, the powder is sieved to control its median diameter D50 to 6.7μm to eliminate the influence of powder particle size differences on subsequent process comparisons.
[0070] S2: Feed Preparation: The powder and polyoxymethylene-based composite binder are mixed at a weight ratio of 100:10.2 and fed into an internal mixer. The mixture is stirred at 190℃ and 25r / min for 1 hour. After cooling and granulation, the particle size is 3-4mm. The mass composition of the polyoxymethylene-based composite binder is 87% polyoxymethylene, 7% high-density polyethylene, 4% ethylene-vinyl acetate copolymer, and 2% stearic acid.
[0071] S3: Injection molding: The feed material is injected into a green body at 195℃, with an injection pressure of 155MPa and a holding time of 8s; the injection rate is 65mm / s, and the dimensional accuracy error is ±0.3%.
[0072] S4: Degreasing treatment: Degrease at 110℃ under oxalic acid atmosphere for 7 hours to obtain palm blank, with residual polyoxymethylene content of 0.8%.
[0073] S5: Vacuum sintering: carried out according to the segmented process. In the negative pressure degreasing stage, the nitrogen flow rate is 2L / min, the temperature is raised from room temperature to 600℃, the temperature is raised at 3℃ / min, and the holding time is 3 hours. In the vacuum internal firing stage, the temperature is raised from 600℃ to 1000℃ at a heating rate of 3℃ / min and the holding time is 1 hour. In the partial pressure sintering stage, the argon flow rate is 2.5L / min, the partial pressure is 20KPa, the temperature is raised from 1000℃ to 1360℃ at 3℃ / min and the holding time is 4 hours. The furnace is then cooled to room temperature at a cooling rate of 8℃ / min.
[0074] S6: Composite heat treatment: solution treatment: hold at 830℃ for 2 hours, then oil quench; cryogenic treatment: hold at -196℃ for 1 hour, then air cool to room temperature; aging treatment: hold at 500℃ for 5 hours, then air cool to room temperature, to obtain the tungsten-containing high-chromium martensitic aging high-strength steel powder.
[0075] Comparative Example 4 This example provides a method for preparing steel powder by metal injection molding, including the following steps: S1: Powder Preparation: The steel powder contains the following components by mass percentage: Ni: 14.5%, Co: 10.5%, Mo: 5.2%, W: 1.2%, Cr: 4.8%, Nb: 0.2%, Si: 0.15%, Cu: 0.3%, Al: 0.2%, C: 0.02%, with the balance being Fe. The batching accuracy error is ±0.03%. The steel powder is fed into an intermediate frequency furnace and heated to 1650℃ in a stepped manner. The alloy melt is refined for 9 minutes. During the refining process, a silicon-calcium alloy is added to ensure that the oxygen content is ≤0.2wt%. The casting temperature is 1645℃. The powder is prepared using a water-gas combined atomization method. The atomizing water pressure is 90MPa, the gas pressure is 10MPa, and the atomizing gas is high-purity nitrogen. The wet powder is dried at 150℃ and under a vacuum of -0.09MPa for 2.5 hours. After grading and sieving, the median diameter of the powder is D50 = 6.7μm.
[0076] S2: Feed Preparation: The powder and polyoxymethylene-based composite binder are mixed at a weight ratio of 100:10.2 and fed into an internal mixer. The mixture is stirred at 190℃ and 25r / min for 1 hour. After cooling and granulation, the particle size is 3-4mm. The mass composition of the polyoxymethylene-based composite binder is 89% polyoxymethylene, 7% high-density polyethylene, and 4% ethylene-vinyl acetate copolymer.
[0077] S3: Injection molding: The feed material is injected into a green body at 195℃, with an injection pressure of 155MPa and a holding time of 8s; the injection rate is 65mm / s, and the dimensional accuracy error is ±0.3%.
[0078] S4: Degreasing treatment: Degrease at 110℃ under oxalic acid atmosphere for 7 hours to obtain palm blank, with residual polyoxymethylene content of 0.8%.
[0079] S5: Vacuum sintering: carried out according to the segmented process. In the negative pressure degreasing stage, the nitrogen flow rate is 2L / min, the temperature is raised from room temperature to 600℃, the temperature is raised at 3℃ / min, and the holding time is 3 hours. In the vacuum internal firing stage, the temperature is raised from 600℃ to 1000℃ at a heating rate of 3℃ / min and the holding time is 1 hour. In the partial pressure sintering stage, the argon flow rate is 2.5L / min, the partial pressure is 20KPa, the temperature is raised from 1000℃ to 1360℃ at 3℃ / min and the holding time is 4 hours. The furnace is then cooled to room temperature at a cooling rate of 8℃ / min.
[0080] S6: Composite heat treatment: solution treatment: hold at 830℃ for 2 hours, then oil quench; cryogenic treatment: hold at -196℃ for 1 hour, then air cool to room temperature; aging treatment: hold at 500℃ for 5 hours, then air cool to room temperature, to obtain the tungsten-containing high-chromium martensitic aging high-strength steel powder.
[0081] Comparative Example 5 This example provides a method for preparing steel powder by metal injection molding, including the following steps: S1: Powder Preparation: The steel powder contains the following components by mass percentage: Ni: 14.5%, Co: 10.5%, Mo: 5.2%, W: 1.2%, Cr: 4.8%, Nb: 0.2%, Si: 0.15%, Cu: 0.3%, Al: 0.2%, C: 0.02%, with the balance being Fe. The batching accuracy error is ±0.03%. The steel powder is fed into an intermediate frequency furnace and heated to 1650℃ in a stepped manner. The alloy melt is refined for 9 minutes. During the refining process, a silicon-calcium alloy is added to ensure that the oxygen content is ≤0.2wt%. The casting temperature is 1645℃. The powder is prepared using a water-gas combined atomization method. The atomizing water pressure is 90MPa, the gas pressure is 10MPa, and the atomizing gas is high-purity nitrogen. The wet powder is dried at 150℃ and under a vacuum of -0.09MPa for 2.5 hours. After grading and sieving, the median diameter of the powder is D50 = 6.7μm.
[0082] S2: Feed Preparation: The powder and polyoxymethylene-based composite binder are mixed at a weight ratio of 100:10.2 and fed into an internal mixer. The mixture is stirred at 190℃ and 25r / min for 1 hour. After cooling and granulation, the particle size is 3-4mm. The mass composition of the polyoxymethylene-based composite binder is 87% polyoxymethylene, 7% high-density polyethylene, 4% ethylene-vinyl acetate copolymer, and 2% stearic acid.
[0083] S3: Injection molding: The feed material is injected into a green body at 195℃, with an injection pressure of 155MPa and a holding time of 8s; the injection rate is 65mm / s, and the dimensional accuracy error is ±0.3%.
[0084] S4: Degreasing treatment: Degrease at 110℃ under oxalic acid atmosphere for 7 hours to obtain palm blank, with residual polyoxymethylene content of 0.8%.
[0085] S5: Vacuum sintering: The temperature is increased from room temperature to 1360℃ at a rate of 5℃ / min, held for 4 hours, and then cooled with the furnace.
[0086] S6: Composite heat treatment: solution treatment: hold at 830℃ for 2 hours, then oil quench; cryogenic treatment: hold at -196℃ for 1 hour, then air cool to room temperature; aging treatment: hold at 500℃ for 5 hours, then air cool to room temperature, to obtain the tungsten-containing high-chromium martensitic aging high-strength steel powder.
[0087] Comparative Example 6 This example provides a method for preparing steel powder by metal injection molding, including the following steps: S1: Powder Preparation: The steel powder contains the following components by mass percentage: Ni: 14.5%, Co: 10.5%, Mo: 5.2%, W: 1.2%, Cr: 4.8%, Nb: 0.2%, Si: 0.15%, Cu: 0.3%, Al: 0.2%, C: 0.02%, with the balance being Fe. The batching accuracy error is ±0.03%. The steel powder is fed into an intermediate frequency furnace and heated to 1650℃ in a stepped manner. The alloy melt is refined for 9 minutes. During the refining process, a silicon-calcium alloy is added to ensure that the oxygen content is ≤0.2wt%. The casting temperature is 1645℃. The powder is prepared using a water-gas combined atomization method. The atomizing water pressure is 90MPa, the gas pressure is 10MPa, and the atomizing gas is high-purity nitrogen. The wet powder is dried at 150℃ and under a vacuum of -0.09MPa for 2.5 hours. After grading and sieving, the median diameter of the powder is D50 = 6.7μm.
[0088] S2: Feed Preparation: The powder and polyoxymethylene-based composite binder are mixed at a weight ratio of 100:10.2 and fed into an internal mixer. The mixture is stirred at 190℃ and 25r / min for 1 hour. After cooling and granulation, the particle size is 3-4mm. The mass composition of the polyoxymethylene-based composite binder is 87% polyoxymethylene, 7% high-density polyethylene, 4% ethylene-vinyl acetate copolymer, and 2% stearic acid.
[0089] S3: Injection molding: The feed material is injected into a green body at 195℃, with an injection pressure of 155MPa and a holding time of 8s; the injection rate is 65mm / s, and the dimensional accuracy error is ±0.3%.
[0090] S4: Degreasing treatment: Degrease at 110℃ under oxalic acid atmosphere for 7 hours to obtain palm blank, with residual polyoxymethylene content of 0.8%.
[0091] S5: Vacuum sintering: carried out according to the segmented process. In the negative pressure degreasing stage, the nitrogen flow rate is 2L / min, the temperature is raised from room temperature to 600℃, the temperature is raised at 3℃ / min, and the holding time is 3 hours. In the vacuum internal firing stage, the temperature is raised from 600℃ to 1000℃ at a heating rate of 3℃ / min and the holding time is 1 hour. In the partial pressure sintering stage, the argon flow rate is 2.5L / min, the partial pressure is 20KPa, the temperature is raised from 1000℃ to 1360℃ at 3℃ / min and the holding time is 4 hours. The furnace is then cooled to room temperature at a cooling rate of 8℃ / min.
[0092] S6: Composite heat treatment: solution treatment: hold at 830℃ for 2 hours, then oil quench; aging treatment: hold at 500℃ for 5 hours, then air cool to room temperature, to obtain the tungsten-containing high-chromium martensitic aging high-strength steel powder.
[0093] Table 1 Performance parameters of steel parts obtained in various embodiments and comparative examples
[0094] in conclusion: 1. Examples 1-4 use the tungsten-containing high-chromium martensitic aging high-strength steel powder composition described in this invention and are prepared by metal injection molding. The steel parts obtained have stable properties: yield strength ≥1650MPa, tensile strength ≥1850MPa, elongation ≥9.0%, hardness ≥51HRC, and sintering density ≥98%. This demonstrates that the steel powder of this invention has the advantages of high strength, high toughness, high hardness, and high density.
[0095] 2. Comparative Example 1 uses a traditional 18Ni(250) martensitic aging steel composition (high Ni, low Co, no W). Its yield strength (1420 MPa), tensile strength (1630 MPa), elongation (7.1%), and hardness (48 HRC) are all significantly lower than those of the embodiments of the present invention, demonstrating the decisive role of the composition system of the present invention, which adjusts the Ni and Co content and introduces W, in improving the comprehensive mechanical properties. Comparative Example 2 does not contain W. Its yield strength (1580 MPa), tensile strength (1750 MPa), and hardness (50 HRC) are all significantly reduced, and its elongation (8.2%) is also lower than that of the embodiments. This shows that W is the key to achieving high strength and high hardness.
[0096] 3. Comparative Example 3 uses single gas atomization instead of water-air combined atomization. Although the powder particle size (D50=6.7μm) was controlled by sieving and was the same as in Example 1, all its mechanical properties (yield strength 1600MPa, tensile strength 1780MPa, elongation 8.0%, hardness 49HRC) and density (97.0%) were lower than those in Example 1. This shows that the water-air combined atomization process itself is crucial for obtaining a powder structure with high sphericity and low porosity, which is the basis for obtaining high performance. Controlling the particle size alone cannot make up for its shortcomings.
[0097] 4. Comparative Example 4 changed the binder composition (containing only polyoxymethylene, high-density polyethylene, and ethylene-vinyl acetate copolymer), and its properties (yield strength 1550 MPa, tensile strength 1700 MPa, elongation 7.5%, hardness 48 HRC, density 96.5%) showed a significant overall decline, indicating that the polyoxymethylene-based composite binder formulation is the basis for achieving good feeding performance, complete debinding, and high-density sintering.
[0098] 5. Comparative Example 5, which uses simple direct heating sintering, exhibits the most severe performance degradation (yield strength 1450 MPa, tensile strength 1650 MPa, elongation 6.5%, hardness 46 HRC, density 96.0%), highlighting the importance of the three-stage segmented vacuum sintering process (negative pressure debinding, vacuum internal firing, and partial pressure sintering) of this invention for thoroughly removing binders, activating the powder surface, and achieving sufficient densification.
[0099] 6. Comparative Example 6 omitted the cryogenic treatment step, resulting in a significant decrease in its yield strength (1580 MPa) and hardness (48 HRC). Although its elongation (10.0%) was relatively high, it could not meet the requirements for high strength and high hardness. This demonstrates the crucial role of cryogenic treatment in promoting the transformation of retained austenite and improving the strength of the material in the "solution-cryogenic-aging" composite heat treatment method.
[0100] In summary, this invention provides a metal injection molding preparation method tailored for tungsten-containing high-chromium martensitic aging high-strength steel powder, with each step closely coordinated. This method has clear process guidance and excellent repeatability, and is the key to realizing the industrialization of high-performance materials (steel parts).
[0101] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.
Claims
1. A method for preparing high-strength tungsten-containing high-chromium martensitic aged steel powder by metal injection molding, characterized in that: Includes the following steps: S1: Powder preparation: After refining the alloy melt, powder is prepared by water-air combined atomization method. After drying the wet powder, spherical powder is obtained by sieving. S2: Feed preparation: Mix the powder with polyoxymethylene-based composite binder, cool and then granulate; S3: Injection molding: Injecting the feed material into a green compact; S4: Degreasing treatment: The green body is degreased to obtain a palm blank; S5: Vacuum sintering: The process is a segmented heating process, which involves degreasing under negative pressure, firing in a vacuum, and sintering under partial pressure, followed by cooling to room temperature in the furnace. S6: Composite heat treatment: After solution treatment, cryogenic treatment, aging treatment, and air cooling to room temperature, the tungsten-containing high-chromium martensitic aging high-strength steel powder is obtained.
2. The method for preparing high-strength tungsten-containing high-chromium martensitic aged steel powder by metal injection molding according to claim 1, characterized in that: In S1, the alloy melt is refined at 1640-1660℃ for 8-10 minutes, and a deoxidizer is added during the refining process to make the oxygen content ≤0.2wt%.
3. The method for preparing high-strength tungsten-containing high-chromium martensitic aged steel powder by metal injection molding according to claim 2, characterized in that: The atomizing water pressure is 80-110 MPa, and the gas pressure is 10-15 MPa; the atomizing gas is high-purity nitrogen.
4. The method for preparing high-strength tungsten-containing high-chromium martensitic aged steel powder by metal injection molding according to claim 1, characterized in that: In S2, the powder and polyoxymethylene-based composite binder are mixed at a weight ratio of 100:(10.2±0.1) and kneaded at 190±5℃ for 45-75 min.
5. The method for preparing high-strength tungsten-containing high-chromium martensitic aged steel powder by metal injection molding according to claim 4, characterized in that: The mass composition of the polyoxymethylene-based composite adhesive is 87±2% polyoxymethylene, 7±2% high-density polyethylene, 4±1% ethylene-vinyl acetate copolymer, and 2±0.5% stearic acid.
6. The method for preparing high-strength tungsten-containing high-chromium martensitic aged steel powder by metal injection molding according to claim 1, characterized in that: In S3, the feedstock is injected into a green compact at 195±5℃, with an injection pressure of 155±15MPa and a holding time of 5-10s.
7. The method for preparing high-strength tungsten-containing high-chromium martensitic aged steel powder by metal injection molding according to claim 1, characterized in that: In S4, the brown bismuth was degreased at 110±5℃ under an oxalic acid atmosphere for 6-8 hours to obtain the brown bismuth preform.
8. The method for preparing high-strength tungsten-containing high-chromium martensitic aged steel powder by metal injection molding according to claim 1, characterized in that: In S5, vacuum sintering includes: Negative pressure degreasing stage: room temperature → 600℃, 3℃ / min, keep warm for 3h, and introduce nitrogen gas; Vacuum firing stage: 600℃→1000℃, 3℃ / min, hold for 1 hour; Partial pressure sintering stage: 1000℃→1360℃, 3℃ / min, hold for 4h, argon gas introduced.
9. The method for preparing high-strength tungsten-containing high-chromium martensitic aged steel powder by metal injection molding according to claim 1, characterized in that: In S6, the composite heat treatment includes: Solution treatment: Hold at 820-840℃ for 2 hours, then oil quench and cool; Cryogenic treatment: Hold at -196℃ for 1 hour, then air cool to room temperature; Aging treatment: Keep at 480-550℃ for 4-6 hours, then air cool to room temperature.
10. The method for preparing high-strength tungsten-containing high-chromium martensitic aged steel powder by metal injection molding according to any one of claims 1-9, characterized in that: The steel powder comprises, by mass percentage: Ni 14.0-16.0%, Co 10.0-12.0%, Mo 5.0-6.0%, W 1.0-2.0%, Cr 4.5-5.5%, Nb 0.1-0.5%, Si ≤0.3%, Cu ≤0.6%, Al ≤0.4%, C ≤0.03%, with the balance being Fe.