Powder injection molding method for improving performance of maraging steel

Abstract

The invention discloses a powder injection molding method for improving the performance of maraging steel. The powder injection molding method comprises the following steps that maraging steel powder and a binder are kneaded to prepare feed; the prepared feed is subjected to crushing and granulation; carrying out injection molding on the crushed and granulated feed to obtain a green body; performing catalytic degreasing on the prepared green body; sequentially performing negative pressure degreasing, vacuum internal sintering and sintering on the sample subjected to catalytic degreasing to obtain a sintered part; the obtained sintered part is subjected to solid solution and quenching treatment, and a solid solution part of a full-martensite structure is obtained; the obtained solid solution part is subjected to pre-stretching treatment; and aging treatment is conducted on the pre-stretched sample, and the maraging steel is obtained. According to the present invention, the material is subjected to proper pre-stretching so as to introduce the high-density and uniform dislocation to improve the precipitation of the strengthening phase, such that the comprehensive performance of the material is improved, and the density of the dislocation introduced through the pre-stretching is high so as to appropriately reduce the addition of the noble metals such as Co, Mo and the like so as to easily reduce the cost;

Description

Technical Field

[0001] The present invention relates to the technical field of manufacturing methods for maraging steels, and particularly relates to a powder injection molding method for improving the properties of maraging steels. Background Art

[0002] With the rapid development of modern manufacturing industry, the requirements for the properties of metal materials are continuously increasing, especially in the manufacturing field of key components with high precision and high reliability. Maraging steels obtain ultra-high strength by precipitating nano-scale precipitates in the martensite matrix, and at the same time, their alloy compositions can be designed to obtain good plasticity and toughness. They have the advantages of high strength, good toughness, easy machining, and small heat treatment deformation, so they have been widely used. Metal Injection Molding (MIM) technology combines the characteristics of plastic injection molding technology and powder metallurgy process, and has the advantages of strong complex part forming ability, high material utilization rate, and large-scale mass production. Preparing maraging steels by MIM technology can apply them to fields such as consumer electronics, automotive, medical devices, and aerospace, greatly expanding the application scope of maraging steels.

[0003] After obtaining maraging steels by MIM technology, a solution treatment + aging treatment process must be adopted to obtain high strength and high toughness of the materials. During solution treatment, the maraging steel is heated to a specific high temperature to fully dissolve alloying elements, and then rapidly cooled to obtain a martensite structure; aging treatment is to hold at an appropriate temperature to precipitate dispersion-strengthened phases in the martensite structure to improve the strength and hardness of the materials. After solution + aging treatment of maraging steels prepared by traditional MIM, due to insufficient dislocation density and uneven distribution of precipitates, the potential of the materials cannot be fully exerted. Summary of the Invention

[0004] The technical problem to be solved by the present invention is: to provide a powder injection molding method for improving the properties of maraging steels.

[0005] To solve the above technical problem, the technical solution adopted by the present invention is: a powder injection molding method for improving the properties of maraging steels, comprising the following steps: Step 1, kneading maraging steel powder and a binder to obtain a feedstock; Step 2, crushing and granulating the prepared feedstock; Step 3, injection molding the feedstock after crushing and granulating to obtain a green body; Step 4, catalytic debinding the prepared green body; Step 5, sequentially subjecting the sample after catalytic debinding to negative pressure debinding, vacuum internal sintering, and sintering to obtain a sintered part; Step 6: Subject the obtained sintered part to solution treatment and quenching to obtain a solution-treated part with a fully martensitic structure; Step 7: Subject the obtained solution-treated part to pre-stretching treatment; Step 8: Subject the pre-stretched sample to aging treatment to obtain maraging steel.

[0006] The beneficial effects of the present invention are as follows: The powder injection molding method for improving the properties of maraging steel can introduce high-density and uniform dislocations inside the material through appropriate pre-stretching of the material. These dislocations are beneficial to the precipitation of strengthening phases, thereby improving the comprehensive properties of the material. At the same time, due to the high dislocation density introduced by pre-stretching, the addition of precious metals such as Co and Mo can be appropriately reduced, which helps to reduce costs. Description of the Drawings

[0007] Figure 1 It is a flow chart of the powder injection molding method for improving the properties of maraging steel according to Embodiment 1 of the present invention. Detailed Embodiments

[0008] To describe in detail the technical content, achieved objectives and effects of the present invention, the following is described in conjunction with the embodiments and with reference to the drawings.

[0009] Please refer to Figure 1 , a powder injection molding method for improving the properties of maraging steel, comprising the following steps: Step 1: Knead the maraging steel powder and the binder to prepare a feedstock; Step 2: Crush and granulate the prepared feedstock; Step 3: Inject mold the feedstock that has been crushed and granulated to obtain a green compact; Step 4: Subject the prepared green compact to catalytic debinding; Step 5: Subject the sample after catalytic debinding to negative pressure debinding, vacuum internal sintering and sintering in sequence to obtain a sintered part; Step 6: Subject the obtained sintered part to solution treatment and quenching to obtain a solution-treated part with a fully martensitic structure; Step 7: Subject the obtained solution-treated part to pre-stretching treatment; Step 8: Subject the pre-stretched sample to aging treatment to obtain maraging steel.

[0010] As can be seen from the above description, the beneficial effects of the present invention are as follows: The powder injection molding method for improving the properties of maraging steel can introduce high-density and uniform dislocations inside the material through appropriate pre-stretching of the material. These dislocations are beneficial to the precipitation of strengthening phases, thereby improving the comprehensive properties of the material. At the same time, due to the high dislocation density introduced by pre-stretching, the addition of precious metals such as Co and Mo can be appropriately reduced, which helps to reduce costs.

[0011] Furthermore, the weight percentages of Co, Cr, Ni, Mo, and Nb in the maraging steel powder are 7 - 16%, 6 - 8.5%, 6.5 - 8.5%, 6 - 7.5%, and 0 - 0.5% respectively.

[0012] Furthermore, the particle size of the maraging steel powder is less than or equal to 50 μm.

[0013] Furthermore, in step three, the injection temperature of the injection molding machine used for injection molding is 170 - 200 °C, the injection pressure is 100 - 200 MPa, the holding pressure is 80 - 160 MPa, and the mold temperature for injection molding is 90 - 120 °C.

[0014] Furthermore, the specific steps of the negative pressure debinding process in step five are as follows: The ambient temperature is raised from room temperature to 250 - 350 °C at a heating rate of 0.1 - 10 °C / min, held for 0 - 180 min, then continued to be raised to 400 - 500 °C at a heating rate of 0.1 - 10 °C / min, held for 0 - 180 min, and then continued to be raised to 550 - 800 °C at a heating rate of 0.1 - 10 °C / min, held for 0 - 180 min; the atmosphere in the furnace during the negative pressure debinding stage is an inert atmosphere.

[0015] As can be seen from the above description, the negative pressure debinding process can remove the binder, avoiding the reaction between the binder residue and the sample, thus affecting the final properties of the material; the inert atmosphere is used to prevent the sample from oxidizing.

[0016] Furthermore, the specific steps of the vacuum sintering process in step five are as follows: It is raised to 900 - 1200 °C at a heating rate of 0.1 - 10 °C / min, and the furnace pressure is maintained below 10 Pa, and held for 30 - 240 min.

[0017] Furthermore, the specific steps of the sintering process in step five are as follows: The sintering temperature is 1300 - 1400 °C, the holding time is 60 - 360 min, and then it is cooled to room temperature.

[0018] Furthermore, the solution treatment in step six specifically includes: The solution temperature is 1000 - 1100 °C, the holding time is 60 - 180 min, then it is cooled to room temperature, the cooling medium is nitrogen and / or argon, and the cooling rate is ≥50 °C / min.

[0019] Furthermore, the pre - stretching treatment in step seven uses a universal material testing machine, and the pre - stretching strain is 0.3 - 1.2%.

[0020] Furthermore, the aging temperature of the aging treatment in step eight is 480 - 610 °C, and the holding time is 180 - 360 min.

[0021] Please refer to Figure 1 , Embodiment 1 of the present invention is: A powder injection molding method for improving the properties of maraging steel, comprising the following steps: Step 1, knead the maraging steel powder and the binder to obtain a feedstock. Specifically, the weight percentage of Co in the maraging steel powder is 15.2%, the weight percentage of Cr is 8.1%, the weight percentage of Ni is 6.7%, the weight percentage of Mo is 6.3%, the weight percentage of Nb is 0.3%, and the balance is Fe; the particle size of the maraging steel powder is <30 μm; the components of the binder are 84% polyoxymethylene, 8% polyethylene, 3% paraffin wax, 3% ethylene-vinyl acetate copolymer, and the balance stearic acid.

[0022] Step 2, crush and granulate the prepared feedstock. Step 2 is specifically: add the metal powder and the binder into a mixer at a mass ratio of 10:1, knead evenly to obtain a feedstock and granulate it.

[0023] Step 3, injection mold the feedstock after crushing and granulating to obtain a green body. Specifically, inject the granulated feedstock into an injection molding machine and a mold for injection molding. The injection temperature of the injection molding machine is 195°C, the injection pressure is 200 MPa, the holding pressure is 120 MPa, and the mold temperature is 100°C.

[0024] Step 4, catalytically debind the prepared green body. Specifically, use nitric acid for catalytic debinding, the acid feeding rate is 4 g / min, the debinding temperature is 100°C, the debinding time is 8.5 h; the relative debinding rate > 96%.

[0025] Step Five: Subject the sample after catalytic debinding to negative pressure debinding, vacuum internal sintering, and sintering in sequence to obtain a sintered part. Specifically, Step Five is as follows: Place the debound sample in a sintering furnace for negative pressure debinding. Argon is introduced into the furnace at a flow rate of 40 L / min. The temperature in the furnace is raised to 260 °C at a heating rate of 4 °C / min and held for 60 min. Then, the temperature in the furnace is raised to 450 °C at a heating rate of 2 °C / min and held for 90 min. Next, the temperature in the furnace is raised to 600 °C at a heating rate of 5 °C / min and held for 120 min. Finally, the temperature in the furnace is raised to 800 °C at a heating rate of 3 °C / min and held for 60 min to complete the negative pressure debinding process, ensuring that all the remaining binders after catalytic debinding are thermally decomposed. Keep the pressure in the furnace < 10 Pa, and raise the temperature in the furnace to 1050 °C at a heating rate of 4 °C / min and hold for 80 min to complete the vacuum internal sintering process. Keep the argon flow rate in the furnace at 30 L / min, raise the temperature in the furnace to 1300 °C at a heating rate of 2 °C / min and hold for 60 min, then raise the temperature in the furnace to 1340 °C at a heating rate of 1 °C / min and hold for 300 min, and then cool the furnace to room temperature to complete the sintering process.

[0026] Step Six: Subject the obtained sintered part to solution treatment and quenching to obtain a solution-treated part with a fully martensitic structure. The specific solution treatment process in Step Six is as follows: Keep the sintered part at 1050 °C for 60 min under vacuum conditions, and then quickly cool it to room temperature. The cooling medium is nitrogen at 800 KPa, and the cooling rate ≥ 50 °C / min.

[0027] Step Seven: Perform pre-tensioning treatment on the obtained solution-treated part. Specifically, Step Seven is as follows: Place the solution-treated part on a universal material testing machine for pre-tensioning. The tensile speed is 2 mm / min, and the pre-tensile strain is 0.55%.

[0028] Step Eight: Perform aging treatment on the pre-tensioned sample to obtain maraging steel. Specifically, Step Eight is as follows: Keep the pre-tensioned sample at 570 °C for 240 min under vacuum conditions, and then quickly cool it to room temperature. The cooling medium is nitrogen at 200 KPa to obtain ultra-high-strength maraging steel.

[0029] Conduct a tensile test on the maraging steel obtained in Step Eight to test its mechanical properties. The tensile test method refers to the national standard GB / T228.1 - 2021. Through the tensile test, the yield strength of the maraging steel sample obtained by the powder injection molding method for improving the properties of maraging steel in Example One of the present invention reaches 1615 MPa, and the elongation rate reaches 6%.

[0030] Please refer to Figure 1 , Example Two of the present invention is: A powder injection molding method for improving the properties of maraging steel, including the following steps: Step 1: Knead maraging steel powder with a binder to prepare a feedstock. Specifically, the weight percentage of Co in the maraging steel powder is 15.2%, the weight percentage of Cr is 7.95%, the weight percentage of Ni is 6.56%, the weight percentage of Mo is 6.36%, the weight percentage of Nb is 0.34%, and the balance is Fe; the particle size of the maraging steel powder is <30 μm; the components of the binder are 84% polyoxymethylene, 8% polyethylene, 3% paraffin wax, 3% ethylene-vinyl acetate copolymer, and the balance stearic acid.

[0031] Step 2: Crush and granulate the prepared feedstock. Specifically, in Step 2, the metal powder and the binder are added to a mixer at a mass ratio of 10:1, kneaded evenly to obtain a feedstock, and then granulated.

[0032] Step 3: Injection mold the feedstock after crushing and granulating to obtain a green compact. Specifically, the granulated feedstock is injection molded in an injection molding machine and a mold. The injection temperature is 195 °C, the injection pressure is 200 MPa, the holding pressure is 120 MPa, and the mold temperature is 100 °C.

[0033] Step 4: Catalytically debind the prepared green compact. Specifically, nitric acid is used for catalytic debinding. The acid flow rate is 4 g / min, the debinding temperature is 100 °C, and the debinding time is 8.5 h; the relative debinding rate > 96%.

[0034] Step 5: Sequentially subject the sample after catalytic debinding to negative pressure debinding, vacuum internal firing, and sintering to obtain a sintered part. Specifically, in Step 5, the sample after debinding is placed in a sintering furnace for negative pressure debinding. Argon is introduced into the furnace, and the argon flow rate is 40 L / min. The temperature in the furnace is increased to 300 °C at a heating rate of 6 °C / min and held for 90 min, then the temperature in the furnace is increased to 450 °C at a heating rate of 2 °C / min and held for 90 min, and then the temperature in the furnace is increased to 600 °C at a heating rate of 2 °C / min and held for 90 min to complete the negative pressure debinding process, ensuring that all the remaining binder after catalytic debinding is thermally decomposed; keep the pressure in the furnace < 10 Pa, and increase the temperature in the furnace to 1050 °C at a heating rate of 4.5 °C / min and hold for 90 min to complete the vacuum internal firing process; keep the argon flow rate in the furnace at 40 L / min, increase the temperature in the furnace to 1250 °C at a heating rate of 3 °C / min and hold for 60 min, then increase the temperature in the furnace to 1380 °C at a heating rate of 2 °C / min and hold for 300 min, and then cool the furnace to room temperature to complete the sintering process.

[0035] Step Six: Subject the obtained sintered part to solution treatment followed by quenching to obtain a solution-treated part with a fully martensitic structure. The specific solution treatment process in Step Six is as follows: Keep the sintered part at 1070°C for 150 min under vacuum conditions, and then rapidly cool it to room temperature. The cooling medium is nitrogen at 800 KPa, and the cooling rate is ≥50°C / min.

[0036] Step Seven: Perform pre-stretching treatment on the obtained solution-treated part. Specifically, in Step Seven: Place the solution-treated part on a universal material testing machine for pre-stretching. The stretching speed is 2 mm / min, and the pre-stretching strain is 0.5%.

[0037] Step Eight: Perform aging treatment on the pre-stretched sample to obtain maraging steel. Specifically, in Step Eight: Keep the pre-stretched sample at 530°C for 240 min under vacuum conditions, and then rapidly cool it to room temperature. The cooling medium is nitrogen at 200 KPa to obtain ultra-high strength maraging steel.

[0038] Conduct a tensile test on the maraging steel obtained in Step Eight to test its mechanical properties. The tensile test method refers to the national standard GB / T228.1-2021. Through the tensile test, the yield strength of the maraging steel sample obtained by the powder injection molding method for improving the properties of maraging steel in Example Two reaches 2100 MPa, and the elongation reaches 4%.

[0039] Comparative Example One: A powder injection molding method for maraging steel, comprising the following steps: Step One: Knead the maraging steel powder with a binder to prepare a feedstock. Specifically, in the maraging steel powder, the weight percentage of Co is 15.2%, the weight percentage of Cr is 8.1%, the weight percentage of Ni is 6.7%, the weight percentage of Mo is 6.3%, the weight percentage of Nb is 0.3%, and the balance is Fe; the particle size of the maraging steel powder is <30 μm; the components of the binder are 84% polyoxymethylene, 8% polyethylene, 3% paraffin wax, 3% ethylene-vinyl acetate copolymer, and the balance stearic acid.

[0040] Step Two: Crush and granulate the prepared feedstock. Specifically, in Step Two: Add the metal powder and the binder to a mixer at a mass ratio of 10:1, knead them evenly to obtain the feedstock, and then granulate it.

[0041] Step Three: Inject mold the feedstock that has been crushed and granulated to obtain a green body. Specifically, inject mold the granulated feedstock in an injection molding machine and a mold. The injection temperature is 195°C, the injection pressure is 200 MPa, the holding pressure is 120 MPa, and the mold temperature is 100°C.

[0042] Step 4: Catalytic debinding is carried out on the obtained green body. Specifically, nitric acid is used for catalytic debinding, the acid flow rate is 4 g / min, the debinding temperature is 100 °C, the debinding time is 8.5 h; the relative debinding rate > 96%.

[0043] Step 5: The samples after catalytic debinding are successively subjected to negative pressure debinding, vacuum internal sintering and sintering to obtain sintered parts. Step 5 is specifically as follows: The samples after debinding are placed in a sintering furnace for negative pressure debinding. Argon is introduced into the furnace, and the argon flow rate is 40 L / min. The temperature in the furnace is raised to 260 °C at a heating rate of 4 °C / min and held for 60 min, then the temperature in the furnace is raised to 450 °C at a heating rate of 2 °C / min and held for 90 min, then the temperature in the furnace is raised to 600 °C at a heating rate of 5 °C / min and held for 120 min, and finally the temperature in the furnace is raised to 800 °C at a heating rate of 3 °C / min and held for 60 min to complete the negative pressure debinding process, ensuring that all the remaining binders after catalytic debinding are thermally decomposed; keeping the pressure in the furnace < 10 Pa, the temperature in the furnace is raised to 1050 °C at a heating rate of 4 °C / min and held for 80 min to complete the vacuum internal sintering process; keeping the argon flow rate in the furnace at 30 L / min, the temperature in the furnace is raised to 1300 °C at a heating rate of 2 °C / min and held for 60 min, then the temperature in the furnace is raised to 1340 °C at a heating rate of 1 °C / min and held for 300 min, and then the furnace is cooled to room temperature to complete the sintering process.

[0044] Step 6: The obtained sintered parts are subjected to solution treatment and quenching to obtain solution parts with a fully martensitic structure. The solution process of Step 6 is specifically as follows: The sintered parts are held at 1050 °C for 60 min under vacuum conditions and then rapidly cooled to room temperature. The cooling medium is nitrogen at 800 KPa, and the cooling rate ≥ 50 °C / min.

[0045] Step 7: The solution parts are subjected to aging treatment to obtain maraging steel. Step 7 is specifically as follows: The solution parts are held at 570 °C for 240 min under vacuum conditions and then rapidly cooled to room temperature. The cooling medium is nitrogen at 200 KPa to obtain ultra-high strength maraging steel.

[0046] The maraging steel obtained in Step 7 is subjected to a tensile test to test its mechanical properties. The tensile test method refers to the national standard GB / T228.1-2021. After the tensile test, the yield strength of the maraging steel sample obtained by the powder injection molding method of maraging steel in Comparative Example 1 reaches 1515 MPa, and the elongation reaches 6%.

[0047] Comparative Example 2: A powder injection molding method for maraging steel, comprising the following steps: Step 1: Knead the maraging steel powder with a binder to obtain a feedstock. Specifically, in the maraging steel powder, the weight percentage of Co is 15.2%, the weight percentage of Cr is 7.95%, the weight percentage of Ni is 6.56%, the weight percentage of Mo is 6.36%, the weight percentage of Nb is 0.34%, and the balance is Fe; the particle size of the maraging steel powder is < 30 μm; the components of the binder are 84% polyoxymethylene, 8% polyethylene, 3% paraffin wax, 3% ethylene-vinyl acetate copolymer, and the balance stearic acid.

[0048] Step 2: Crush and granulate the prepared feedstock. Specifically, in Step 2: Add the metal powder and the binder into a mixer at a mass ratio of 10:1, knead evenly to obtain a feedstock, and then granulate it.

[0049] Step 3: Inject mold the feedstock after crushing and granulating to obtain a green body. Specifically, inject mold the granulated feedstock in an injection molding machine and a mold. The injection temperature is 195 °C, the injection pressure is 200 MPa, the holding pressure is 120 MPa, and the mold temperature is 100 °C.

[0050] Step 4: Catalytically debind the obtained green body. Specifically, use nitric acid for catalytic debinding. The acid feeding rate is 4 g / min, the debinding temperature is 100 °C, the debinding time is 8.5 h; the relative debinding rate > 96%.

[0051] Step 5: Subject the sample after catalytic debinding to negative pressure debinding, vacuum internal sintering, and sintering in sequence to obtain a sintered part. Specifically, in Step 5: Place the sample after debinding in a sintering furnace for negative pressure debinding. Argon is introduced into the furnace, and the argon flow rate is 40 L / min. Raise the furnace temperature to 260 °C at a heating rate of 4 °C / min, hold for 60 min, then raise the furnace temperature to 450 °C at a heating rate of 2 °C / min, hold for 90 min, then raise the furnace temperature to 600 °C at a heating rate of 5 °C / min, hold for 120 min, and finally raise the furnace temperature to 800 °C at a heating rate of 3 °C / min, hold for 60 min to complete the negative pressure debinding process, ensuring that all the remaining binder after catalytic debinding is thermally decomposed; keep the furnace pressure < 10 Pa, raise the furnace temperature to 1050 °C at a heating rate of 4 °C / min, hold for 80 min to complete the vacuum internal sintering process; keep the argon flow rate in the furnace at 30 L / min, raise the furnace temperature to 1300 °C at a heating rate of 2 °C / min, hold for 60 min, then raise the furnace temperature to 1340 °C at a heating rate of 1 °C / min, hold for 300 min, and then cool the furnace to room temperature to complete the sintering process.

[0052] Step Six: Subject the obtained sintered parts to solution treatment followed by quenching to obtain solution-treated parts with a fully martensitic structure. The specific solution treatment process in Step Six is as follows: Place the sintered parts in a vacuum and hold at 1050°C for 60 minutes, then rapidly cool to room temperature. The cooling medium is nitrogen at 800 KPa, and the cooling rate is ≥50°C / min.

[0053] Step Seven: Subject the solution-treated parts to aging treatment to obtain maraging steel. Step Seven is specifically as follows: Place the solution-treated parts in a vacuum and hold at 570°C for 240 minutes, then rapidly cool to room temperature. The cooling medium is nitrogen at 200 KPa to obtain ultra-high-strength maraging steel.

[0054] Conduct a tensile test on the maraging steel obtained in Step Seven to test its mechanical properties. The tensile test method refers to the national standard GB / T228.1 - 2021. Through the tensile test, the yield strength of the maraging steel sample obtained by the powder injection molding method of the maraging steel in Comparative Example 2 reaches 1950 MPa, and the elongation rate reaches 4.5%.

[0055] Summarize the material properties of the maraging steel obtained in Examples 1 and 2 and Comparative Examples 1 and 2 in Table 1:

[0056] Table 1 As can be seen from the above, on the basis of Comparative Example 1, Example 1 added a pre-tensile treatment. After adding the pre-tensile treatment, its yield strength increased by about 100 MPa, and the elongation rate remained unchanged; On the basis of Comparative Example 2, Example 2 added a pre-tensile treatment. After adding the pre-tensile treatment, its yield strength increased by about 150 MPa, and the elongation rate decreased slightly.

[0057] In summary, the powder injection molding method for improving the properties of maraging steel provided by the present invention can introduce high-density and uniform dislocations inside the material through appropriate pre-tensile treatment of the material. These dislocations are beneficial to the precipitation of strengthening phases, thereby improving the comprehensive properties of the material. At the same time, due to the high dislocation density introduced by pre-tensile treatment, the addition of precious metals such as Co and Mo can also be appropriately reduced, which helps to reduce costs.

[0058] The above are only the embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent transformation made by using the content of the specification and drawings of the present invention, or directly or indirectly applied in the relevant technical fields, shall be included in the patent protection scope of the present invention by the same token.

Claims

1. A powder injection molding method for improving the properties of maraging steel, characterized in that, It includes the following steps: Step 1: Knead the maraging steel powder with a binder to prepare a feedstock; Step 2: Crush and granulate the prepared feedstock; Step 3: Inject mold the feedstock after crushing and granulating to obtain a green body; Step 4: Catalytic debind the obtained green body; Step 5: Subject the sample after catalytic debinding to negative pressure debinding, vacuum internal sintering, and sintering in sequence to obtain a sintered part; Step 6: Subject the obtained sintered part to solution treatment and quenching to obtain a solution-treated part with a fully martensitic structure; Step 7: Perform pre-stretching treatment on the obtained solution-treated part; Step 8: Perform aging treatment on the pre-stretched sample to obtain maraging steel.

2. The powder injection molding method for improving the properties of maraging steel according to claim 1, characterized in that: In the maraging steel powder, the weight percentage of Co is 7 - 16%, the weight percentage of Cr is 6 - 8.5%, the weight percentage of Ni is 6.5 - 8.5%, the weight percentage of Mo is 6 - 7.5%, and the weight percentage of Nb is 0 - 0.5%.

3. A powder injection molding method for improving the properties of maraging steel according to claim 1, characterized in that: The particle size of the maraging steel powder is less than or equal to 50 μm.

4. A powder injection molding method for improving the properties of maraging steel according to claim 1, characterized in that: In Step 3, for injection molding, the injection temperature of the injection molding machine is 170 - 200 °C, the injection pressure is 100 - 200 MPa, the holding pressure is 80 - 160 MPa, and the mold temperature for injection molding is 90 - 120 °C.

5. A powder injection molding method for improving the properties of maraging steel according to claim 1, characterized in that, The specific steps of the negative pressure debinding process in Step 5 are as follows: Raise the ambient temperature from room temperature to 250 - 350 °C at a heating rate of 0.1 - 10 °C / min, hold for 0 - 180 min, continue to raise the temperature to 400 - 500 °C at a heating rate of 0.1 - 10 °C / min, hold for 0 - 180 min, and continue to raise the temperature to 550 - 800 °C at a heating rate of 0.1 - 10 °C / min, hold for 0 - 180 min; the atmosphere in the furnace during the negative pressure debinding stage is an inert atmosphere.

6. A powder injection molding method for improving the properties of maraging steel according to claim 1, characterized in that, The specific steps of the vacuum internal sintering process in Step 5 are as follows: Raise the temperature to 900 - 1200 °C at a heating rate of 0.1 - 10 °C / min, and keep the furnace pressure less than 10 Pa, hold for 30 - 240 min.

7. A powder injection molding method for improving the properties of maraging steel according to claim 1, characterized in that, The specific steps of the sintering process in Step 5 are as follows: The sintering temperature is 1300 - 1400 °C, the holding time is 60 - 360 min, and then it is cooled to room temperature.

8. A powder injection molding method for improving the properties of maraging steel according to claim 1, characterized in that The solution treatment in Step 6 specifically includes: The solution temperature is 1000 - 1100 °C, the holding time is 60 - 180 min, then it is cooled to room temperature, the cooling medium is nitrogen and / or argon, and the cooling rate ≥ 50 °C / min.

9. A powder injection molding method for improving the properties of maraging steel according to claim 1, characterized in that: For the pre-stretching treatment in Step 7, a universal material testing machine is used, and the pre-strain is 0.3 - 1.2%.

10. A powder injection molding method for improving the properties of maraging steel according to claim 1, characterized in that: The aging temperature for the aging treatment in Step 8 is 480 - 610 °C, and the holding time is 180 - 360 min.

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