Injection molding process of modified 17-4PH powder with high density and high polishing effect

Abstract

The invention discloses a high-density and high-polishing-effect modified 17-4PH powder injection molding process which comprises the following steps that 1, 17-4PH powder and a binding agent are weighed, and the 17-4PH powder comprises, by mass, 15%-17.5% of Cr, 3%-5% of Ni, 3%-5% of Cu, 0.15%-0.45% of Nb, 0.2%-0.3% of O, 0.15%-0.25% of C and the balance Fe; 2, putting the 17-4PH powder and a binder into an internal mixer for mixing, extruding and granulating to obtain a feed; 3, putting the feedstock into an injection stock bin, and injecting the feedstock into a mold to obtain a 17-4PH green body; 4, the 17-4PH green body is subjected to degreasing treatment, and a 17-4PH brown blank is obtained; 5, the 17-4PH brown blank is sintered, the first stage is a thermal degreasing process, the second stage is a sintering process, then cooling is conducted, and a 17-4PH sintered part is obtained; and sixthly, the 17-4PH sintered part is subjected to heat treatment. According to the injection molding process for the modified 17-4PH powder with the high density and the high polishing effect, the modified 17-4PH powder is matched with an optimized metal injection molding process, and the high density and the high polishing effect of a 17-4PH material are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of metal injection molding, and in particular to a modified 17-4PH powder injection molding process with high density and high polishing effect. Background Art

[0002] 17-4PH stainless steel is a precipitation-hardening stainless steel with excellent corrosion resistance and high strength, and is widely used in fields such as aerospace, medical devices, and consumer electronics. The metal injection molding process (MIM) is a process that combines plastic injection molding with metal powder metallurgy, breaking through the limitations of traditional metal powder die pressing forming processes in terms of product shape, and at the same time taking advantage of the characteristics of plastic injection molding technology to mass-produce and efficiently form parts with complex shapes, becoming a near-net-shape forming technology for rapidly preparing precision parts. The 17-4PH stainless steel components prepared by the metal injection molding process (MIM) can achieve high-precision forming of complex shapes, with high material utilization rate and saving secondary processing. However, currently, 3C consumer electronic products have extremely high requirements for appearance, especially the polishing effect of products. Due to the lower density of the metal injection molding process itself compared to that of plates and poor polishing effect, the low density and poor surface polishing effect of 17-4PH are the technical difficulties of the existing metal injection molding process.

[0003] Existing technical solution: CN116640978A, a preparation method of a non-magnetic 17-4PH material for mirror polishing, which makes 17-4PH become austenite by using a non-magnetic process, but has low strength (hardness about 180-240HV) and cannot meet the requirements of high strength. Summary of the Invention

[0004] The technical problem to be solved by the present invention is: to provide a new modified 17-4PH powder injection molding process with high density and high polishing effect.

[0005] To solve the above technical problem, the technical solution adopted by the present invention is: a modified 17-4PH powder injection molding process with high density and high polishing effect, comprising the following steps: Step 1, weigh a certain mass of 17-4PH powder and binder, wherein the mass percentage of Cr in the 17-4PH powder is 15-17.5%, the mass percentage of Ni is 3-5%, the mass percentage of Cu is 3-5%, the mass percentage of Nb is 0.15-0.45%, the mass percentage of O is 0.2-0.3%, the mass percentage of C is 0.15-0.25%, and the balance is Fe; Step 2, put the 17-4PH powder and the binder into a mixer for mixing, extruding and granulating to obtain a feedstock; Step 3: Put the above-mentioned feedstock into the injection agent bin and inject it into the mold to obtain a 17-4PH green compact. Step 4: Debind the 17-4PH green compact to obtain a 17-4PH brown compact. Step 5: Sinter the 17-4PH brown compact. The first stage is a thermal debinding process, followed by a second-stage sintering process, and then cooling to obtain a 17-4PH sintered part. Step 6: Heat-treat the 17-4PH sintered part.

[0006] The beneficial effects of the present invention are as follows: The modified 17-4PH powder injection molding process with high density and high polishing effect realizes the high density and high polishing effect of 17-4PH materials through the modified 17-4PH powder (with a C content of 0.15-0.25%, different from the 0.02-0.07% C content of conventional 17-4PH powder) in combination with the optimized metal injection molding process, meeting the market demand of products. Description of the Drawings

[0007] Figure 1 It is the polished metallographic diagram of the 17-4PH sintered part in the first embodiment of the present invention; Figure 2 It is the polished metallographic diagram of the 17-4PH sintered part in the first comparative example; Figure 3 It is the polished metallographic diagram of the 17-4PH sintered part in the second comparative example; Figure 4 It is the polished metallographic diagram of the 17-4PH sintered part in the third comparative example; Figure 5 It is the polished metallographic diagram of the 17-4PH sintered part in the fourth comparative example. Detailed Embodiments

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

[0009] A modified 17-4PH powder injection molding process with high density and high polishing effect includes the following steps: Step 1: Weigh a certain mass of 17-4PH powder and binder. In the 17-4PH powder, the mass percentage of Cr is 15-17.5%, the mass percentage of Ni is 3-5%, the mass percentage of Cu is 3-5%, the mass percentage of Nb is 0.15-0.45%, the mass percentage of O is 0.2-0.3%, the mass percentage of C is 0.15-0.25%, and the balance is Fe; Step 2: Put the 17-4PH powder and the binder into a mixer for mixing, extrude and granulate to obtain a feedstock. Step 3: Place the feedstock into the injection cartridge and inject it into the mold to obtain a 17-4PH green compact. Step 4: Debind the 17-4PH green compact to obtain a 17-4PH brown compact. Step 5: Sinter the 17-4PH brown compact. The first stage is a thermal debinding process, followed by a second-stage sintering process, and then cooling to obtain a 17-4PH sintered part. Step 6: Heat-treat the 17-4PH sintered part.

[0010] As can be seen from the above description, the beneficial effects of the present invention are as follows: This modified 17-4PH powder injection molding process with high density and high polishing effect uses modified 17-4PH powder (with a C content of 0.15 - 0.25%, different from the 0.02 - 0.07% C content of conventional 17-4PH powder) in combination with an optimized metal injection molding process, achieving high density and high polishing effect of 17-4PH materials, meeting the market demand for products.

[0011] Further, the particle size specifications of the 17-4PH powder are: D90 < 25 μm, D50 is 6 - 9 μm, and D10 < 3 μm.

[0012] Further, the volume ratio of the 17-4PH powder is 55% - 70%; the binder includes the following raw materials in percentages: 85% - 89% POM, 4% - 6% PE, 2% - 4% EVA, 2% - 4% SA, and 1% - 2% PW.

[0013] Further, the kneading temperature in Step 2 is 150 - 200 °C, and the kneading time is 2 hours.

[0014] Further, the injection temperature of the injection machine in Step 3 is 160 - 200 °C, the screw speed is 60 r / min, the injection pressure is 100 - 200 MPa, and the temperature of the mold is 90 - 120 °C.

[0015] Further, in Step 4, catalytic debinding is carried out using nitric acid, and the debinding rate > 95%.

[0016] Further, the thermal debinding process in Step 5 is as follows: Heat up at a heating rate of 2 - 8 °C / min to 350 - 380 °C and hold for 0.5 - 2 h; heat up at a heating rate of 1 - 4 °C / min to 450 - 500 °C and hold for 0.5 - 2 h; heat up at a heating rate of 1 - 4 °C / min to 580 - 620 °C and hold for 0.5 - 2 h.

[0017] Further, the sintering process in Step Five is as follows: heating at a heating rate of 1 - 4 °C / min to 800 - 900 °C and holding for 0.5 - 4 h; heating in an Ar atmosphere at a heating rate of 0.5 - 2 °C / min to 1000 - 1200 °C and holding for 0.5 - 4 h; heating in an Ar atmosphere at a heating rate of 0.5 - 2 °C / min to 1260 - 1300 °C and holding for 0.5 - 4 h; cooling in an Ar atmosphere at a cooling rate of 3 - 6 °C / min to 850 - 1000 °C, and then cooling by forced cooling.

[0018] Further, the heat treatment process in Step Six is as follows: holding at a temperature of 1000 - 1100 °C for 0.5 - 3 hours and then rapidly cooling, and performing aging treatment at a temperature of 480 - 530 °C for 3 - 5 hours.

[0019] Example 1 of the present invention is: a modified 17 - 4PH powder injection molding process with high density and high polishing effect, including the following steps: Step One, weighing a certain mass of plastic - based binder and modified gas - atomized 17 - 4PH powder; in the 17 - 4PH powder, the mass percentage of Cr is 15 - 17.5%, the mass percentage of Ni is 3 - 5%, the mass percentage of Cu is 3 - 5%, the mass percentage of Nb is 0.15 - 0.45%, the mass percentage of O is 0.2 - 0.3%, the mass percentage of C is 0.15 - 0.25%, and the balance is Fe; the particle size specifications of the 17 - 4PH powder are: D 90 <25 μm, D 50 is 6 - 9 μm, D 10 <3 μm; the volume ratio of the 17 - 4PH powder is 55% - 70%; the plastic - based binder includes the following raw materials by percentage: 85% - 89% POM, 4 - 6% PE, 2 - 4% EVA, 2 - 4% SA, 1 - 2% PW. By adjusting the specific formula of the binder, the shrinkage ratio of the green body and the product is adjusted to obtain a product that meets the dimensional requirements.

[0020] Step Two, putting the 17 - 4PH powder and the binder into a mixer and mixing at a temperature of 150 - 200 °C for 2 hours. After forming a uniform paste, extruding and granulating to obtain the feedstock.

[0021] Step 3: Put the feedstock into the hopper of the injection molding machine. After the feedstock is plasticized by the screw of the injection molding machine, it is extruded into the mold cavity through extrusion and filled completely. After cooling for 5 - 15 seconds, the mold is opened, and the green compact is ejected by the ejection mechanism to obtain a 17 - 4PH green compact. The injection temperature of the injection molding machine is 160 - 200 °C, the screw speed is 60 r / min, the injection pressure is 100 - 200 MPa, and the temperature of the mold is 90 - 120 °C. The specific process parameters are based on ensuring uniform and full injection of the 17 - 4PH green compact without defects, reaching more than 94% of the theoretical green compact density.

[0022] Step 4: Catalytic debinding is carried out using nitric acid. Specifically: Put the 17 - 4PH green compact into a nitric acid debinding furnace, decompose the binder in the 17 - 4PH green compact into small - molecule organic substances and then burn them out to obtain a porous 17 - 4PH brown embryo. Debinding must ensure that most of the binder can be removed. The main component removed in this stage is POM in the binder, and the debinding rate > 95% to avoid unstable performance caused by excessive residual carbon content.

[0023] Step 5: Sinter the 17 - 4PH brown embryo. The first stage is the thermal debinding process. The specific thermal debinding process is as follows: Heat up at a heating rate of 2 - 8 °C / min to 350 - 380 °C (negative - pressure debinding), hold for 0.5 - 2 h (negative - pressure debinding); heat up at a heating rate of 1 - 4 °C / min to 450 - 500 °C (negative - pressure debinding), hold for 0.5 - 2 h (negative - pressure debinding); heat up at a heating rate of 1 - 4 °C / min to 580 - 620 °C (negative - pressure debinding), hold for 0.5 - 2 h (negative - pressure debinding). Then carry out the second - stage sintering process. The specific sintering process is as follows: Heat up at a heating rate of 1 - 4 °C / min to 800 - 900 °C (negative - pressure debinding or vacuum internal sintering), hold for 0.5 - 4 h (vacuum internal sintering); heat up at a heating rate of 0.5 - 2 °C / min in an Ar atmosphere to 1000 - 1200 °C (partial - pressure sintering), hold for 0.5 - 4 h (vacuum internal sintering); heat up at a heating rate of 0.5 - 2 °C / min in an Ar atmosphere to 1260 - 1300 °C (partial - pressure sintering), hold for 0.5 - 4 h (partial - pressure sintering). Subsequently, cool down at a cooling rate of 3 - 6 °C / min in an Ar atmosphere to 850 - 1000 °C, and then cool down to room temperature by forced cooling to obtain a 17 - 4PH sintered part; Step 6: Heat - treat the 17 - 4PH sintered part. Specifically: Hold at a temperature of 1000 - 1100 °C for 0.5 - 3 hours and then cool quickly, and carry out aging treatment at a temperature of 480 - 530 °C for 3 - 5 hours. The heat - treatment process is adjusted according to different performance requirements of the product.

[0024] Polish the heat - treated 17 - 4PH product to obtain a 17 - 4PH product with a polished effect.

[0025] Figure 1 This is the polished metallographic diagram of the 17-4PH product in the first embodiment.

[0026] Comparative Example 1: A method for preparing 17-4PH material, comprising the following steps: Step 1, weigh a certain mass of a plastic-based binder and modified gas-atomized 17-4PH powder; the mass percentage of Cr in the 17-4PH powder is 15-17.5%, the mass percentage of Ni is 3-5%, the mass percentage of Cu is 3-5%, the mass percentage of Nb is 0.15-0.45%, the mass percentage of O is 0.2-0.3%, the mass percentage of C is 0.02-0.07%, and the balance is Fe; the particle size specification of the 17-4PH powder is: D 90 <25μm, D 50 is 6-9μm, D 10 <3μm; the volume ratio of the 17-4PH powder to the total is 55%-70%; the plastic-based binder includes the following raw materials in percentage: 85%-89% POM, 4-6% PE, 2-4% EVA, 2-4% SA, 1-2% PW. By adjusting the specific formula of the binder, the shrinkage ratio of the green body and the product is adjusted to obtain a product that meets the dimensional requirements.

[0027] Step 2, put the 17-4PH powder and the binder into a mixer and mix them at a temperature of 150-200°C for 2 hours. After forming a uniform paste, extrude and granulate to obtain a feedstock.

[0028] Step 3, put the feedstock into the hopper of an injection molding machine. After the feedstock is plasticized by the screw of the injection molding machine, it is extruded into the mold cavity through extrusion to complete the filling. After cooling for 5-15 seconds, open the mold and eject the green body through the ejection mechanism to obtain a 17-4PH green body. The injection temperature of the injection molding machine is 160-200°C, the screw speed is 60 r / min, the injection pressure is 100-200 MPa, and the temperature of the mold is 90-120°C. The specific process parameters are based on ensuring that the 17-4PH green body is injected evenly and fully without defects, reaching more than 94% of the theoretical green body density.

[0029] Step 4, perform catalytic debinding with nitric acid. Specifically: put the 17-4PH green body into a nitric acid debinding furnace, decompose the binder in the 17-4PH green body into small molecule organic substances and then burn them out to obtain a porous 17-4PH brown embryo. Debinding must ensure that most of the binder can be removed. In this stage, the main component removed from the binder is POM, and the debinding rate > 95% to avoid unstable performance caused by excessive residual carbon content.

[0030] Step 5: Sinter the 17-4PH green body. The first stage is the thermal debinding process, and the specific thermal debinding process is as follows: Heat up at a heating rate of 2-8 °C / min to 350-380 °C (negative pressure debinding), and hold for 0.5-2 h (negative pressure debinding); heat up at a heating rate of 1-4 °C / min to 450-500 °C (negative pressure debinding), and hold for 0.5-2 h (negative pressure debinding); heat up at a heating rate of 1-4 °C / min to 580-620 °C (negative pressure debinding), and hold for 0.5-2 h (negative pressure debinding). Then carry out the second-stage sintering process. The specific sintering process is as follows: Heat up at a heating rate of 1-4 °C / min to 800-900 °C (negative pressure debinding or vacuum internal sintering), and hold for 0.5-4 h (vacuum internal sintering); heat up in an Ar atmosphere at a heating rate of 0.5-2 °C / min to 1000-1200 °C (partial pressure sintering), and hold for 0.5-4 h (vacuum internal sintering); heat up in an Ar atmosphere at a heating rate of 0.5-2 °C / min to 1260-1300 °C (partial pressure sintering), and hold for 0.5-4 h (partial pressure sintering). Subsequently, cool down in an Ar atmosphere at a cooling rate of 3-6 °C / min to 850-1000 °C, and then cool down to room temperature by forced cooling to obtain the 17-4PH sintered part; Step 6: Heat-treat the 17-4PH sintered part. Specifically, hold at a temperature of 1000-1100 °C for 0.5-3 hours and then rapidly cool, and carry out aging treatment at a temperature of 480-530 °C for 3-5 hours. The heat treatment process is adjusted according to different performance requirements of the product.

[0031] Polish the heat-treated 17-4PH product to obtain the 17-4PH product with a polished effect.

[0032] Figure 2 The polished metallographic diagram of the 17-4PH product of Comparative Example 1.

[0033] Comparative Example 2: A preparation method of a 17-4PH material, including the following steps: Step 1: Weigh a certain mass of plastic-based binder and modified gas-atomized 17-4PH powder; in the 17-4PH powder, the mass percentage of Cr is 15-17.5%, the mass percentage of Ni is 3-5%, the mass percentage of Cu is 3-5%, the mass percentage of Nb is 0.15-0.45%, the mass percentage of O is 0.2-0.3%, the mass percentage of C is 0.07-0.15%, and the balance is Fe; the particle size specifications of the 17-4PH powder are: D 90 <25 μm, D 50 is 6-9 μm, D 10<3μm; The volume ratio of 17-4PH powder to the total volume is 55%-70%; The plastic-based binder includes the following raw materials in percentages: 85%-89% POM, 4-6% PE, 2-4% EVA, 2-4% SA, 1-2% PW. The shrinkage ratios of the green body and the product are adjusted by adjusting the specific formula of the binder to obtain a product that meets the dimensional requirements.

[0034] Step 2: Put 17-4PH powder and the binder into a mixer and mix them. Knead at a temperature of 150-200°C for 2 hours. After forming a uniform paste, extrude and granulate to obtain the feedstock.

[0035] Step 3: Put the feedstock into the hopper of an injection molding machine. After the feedstock is plasticized by the screw of the injection molding machine, extrude the feedstock into the mold cavity through extrusion until it is filled. After cooling for 5-15 seconds, open the mold and eject the green body through the ejection mechanism to obtain the 17-4PH green body. The injection temperature of the injection molding machine is 160-200°C, the screw speed is 60 r / min, the injection pressure is 100-200 MPa, and the temperature of the mold is 90-120°C. The specific process parameters are based on ensuring that the 17-4PH green body is injected evenly and fully without defects, reaching more than 94% of the theoretical green body density.

[0036] Step 4: Catalytic debinding is carried out using nitric acid. Specifically: Put the 17-4PH green body into a nitric acid debinding furnace, decompose the binder in the 17-4PH green body into small molecule organic substances and then burn and discharge them to obtain a porous 17-4PH brown embryo. Debinding must ensure that most of the binder can be removed. In this stage, the main component removed from the binder is POM, and the debinding rate > 95% to avoid unstable performance caused by excessive residual carbon content.

[0037] Step 5: Sinter the 17-4PH green body. The first stage is the thermal debinding process, and the specific thermal debinding process is as follows: Heat at a heating rate of 2-8 °C / min to 350-380 °C (negative pressure debinding), and hold for 0.5-2 h (negative pressure debinding); heat at a heating rate of 1-4 °C / min to 450-500 °C (negative pressure debinding), and hold for 0.5-2 h (negative pressure debinding); heat at a heating rate of 1-4 °C / min to 580-620 °C (negative pressure debinding), and hold for 0.5-2 h (negative pressure debinding). Then carry out the second stage sintering process. The specific sintering process is as follows: Heat at a heating rate of 1-4 °C / min to 800-900 °C (negative pressure debinding or vacuum internal sintering), and hold for 0.5-4 h (vacuum internal sintering); in an Ar atmosphere, heat at a heating rate of 0.5-2 °C / min to 1000-1200 °C (partial pressure sintering), and hold for 0.5-4 h (vacuum internal sintering); in an Ar atmosphere, heat at a heating rate of 0.5-2 °C / min to 1260-1300 °C (partial pressure sintering), and hold for 0.5-4 h (partial pressure sintering). Subsequently, cool in an Ar atmosphere at a cooling rate of 3-6 °C / min to 850-1000 °C, and then cool down to room temperature by forced cooling to obtain a 17-4PH sintered part; Step 6: Heat-treat the 17-4PH sintered part, specifically: Hold at a temperature of 1000-1100 °C for 0.5-3 hours and then rapidly cool, and carry out aging treatment at a temperature of 480-530 °C for 3-5 hours.

[0038] Polish the heat-treated 17-4PH product to obtain a 17-4PH product with a polished effect.

[0039] Figure 3 It is the polished metallographic diagram of the 17-4PH product of Comparative Example 2.

[0040] Comparative Example 3: A method for preparing a 17-4PH material, comprising the following steps: Step 1: Weigh a certain mass of a plastic-based binder and modified gas-atomized 17-4PH powder; in the 17-4PH powder, the mass percentage of Cr is 15-17.5%, the mass percentage of Ni is 3-5%, the mass percentage of Cu is 3-5%, the mass percentage of Nb is 0.15-0.45%, the mass percentage of O is 0.2-0.3%, the mass percentage of C is 0.25-0.35%, and the balance is Fe; the particle size specification of the 17-4PH powder is: D 90 <25 μm, D 50 is 6-9 μm, D 10<3μm; The ratio of 17-4PH powder to the total volume is 55%-70%; The plastic-based binder includes the following raw materials in percentages: 85%-89% POM, 4-6% PE, 2-4% EVA, 2-4% SA, 1-2% PW. Adjust the shrinkage ratio of the green body and the product by adjusting the specific formula of the binder to obtain a product that meets the dimensional requirements.

[0041] Step 2: Put 17-4PH powder and the binder into a mixer and mix them. Knead at a temperature of 150-200°C for 2 hours. After forming a uniform paste, extrude and granulate to obtain the feedstock.

[0042] Step 3: Put the feedstock into the hopper of an injection molding machine. After the feedstock is plasticized by the screw of the injection molding machine, extrude the feedstock into the mold cavity through extrusion to complete the filling. After cooling for 5-15 seconds, open the mold and eject the green body through the ejection mechanism to obtain the 17-4PH green body. The injection temperature of the injection molding machine is 160-200°C, the screw speed is 60 r / min, the injection pressure is 100-200 MPa, and the temperature of the mold is 90-120°C. The specific process parameters are based on ensuring that the 17-4PH green body is injected evenly and fully without defects, reaching more than 94% of the theoretical green body density.

[0043] Step 4: Catalytic debinding is carried out using nitric acid. Specifically: Put the 17-4PH green body into a nitric acid debinding furnace, decompose the binder in the 17-4PH green body into small molecule organic substances and then burn and discharge them to obtain a porous 17-4PH brown embryo. Debinding must ensure that most of the binder can be removed. In this stage, the main component removed from the binder is POM, and the debinding rate > 95% to avoid unstable performance caused by excessive residual carbon content.

[0044] Step 5: Sinter the 17-4PH green body. The first stage is the thermal debinding process, and the specific thermal debinding process is as follows: Heat up at a heating rate of 2-8 °C / min to 350-380 °C (negative pressure debinding), and hold for 0.5-2 h (negative pressure debinding); heat up at a heating rate of 1-4 °C / min to 450-500 °C (negative pressure debinding), and hold for 0.5-2 h (negative pressure debinding); heat up at a heating rate of 1-4 °C / min to 580-620 °C (negative pressure debinding), and hold for 0.5-2 h (negative pressure debinding). Then carry out the second-stage sintering process. The specific sintering process is as follows: Heat up at a heating rate of 1-4 °C / min to 800-900 °C (negative pressure debinding or vacuum internal sintering), and hold for 0.5-4 h (vacuum internal sintering); heat up in an Ar atmosphere at a heating rate of 0.5-2 °C / min to 1000-1200 °C (partial pressure sintering), and hold for 0.5-4 h (vacuum internal sintering); heat up in an Ar atmosphere at a heating rate of 0.5-2 °C / min to 1260-1300 °C (partial pressure sintering), and hold for 0.5-4 h (partial pressure sintering). Subsequently, cool down in an Ar atmosphere at a cooling rate of 3-6 °C / min to 850-1000 °C, and then cool down to room temperature by forced cooling to obtain the 17-4PH sintered part; Step 6: Heat-treat the 17-4PH sintered part. Specifically, hold at a temperature of 1000-1100 °C for 0.5-3 hours and then quickly cool, and carry out aging treatment at a temperature of 480-530 °C for 3-5 hours. The heat treatment process is adjusted according to different performance requirements of the product.

[0045] Polish the heat-treated 17-4PH product to obtain the 17-4PH product with a polished effect.

[0046] Figure 4 It is the polished metallographic diagram of the 17-4PH product of Comparative Example 3.

[0047] Comparative Example 4: A preparation method of a 17-4PH material, including the following steps: Step 1: Weigh a certain mass of plastic-based binder and modified gas-atomized 17-4PH powder; in the 17-4PH powder, the mass percentage of Cr is 15-17.5%, the mass percentage of Ni is 3-5%, the mass percentage of Cu is 3-5%, the mass percentage of Nb is 0.15-0.45%, the mass percentage of O is 0.2-0.3%, the mass percentage of C is 0.15-0.25%, and the balance is Fe; the particle size specification of the 17-4PH powder is: D 90 <25 μm, D 50 is 6-9 μm, D 10<3μm; The volume ratio of 17-4PH powder to the total volume is 55%-70%; The plastic-based binder includes the following raw materials in percentages: 85%-89% POM, 4-6% PE, 2-4% EVA, 2-4% SA, 1-2% PW. By adjusting the specific formula of the binder, the shrinkage ratios of the green body and the product are adjusted to obtain a product that meets the dimensional requirements.

[0048] Step 2: Put the 17-4PH powder and the binder into a mixer and mix them. Knead at a temperature of 150-200 °C for 2 hours. After forming a uniform paste, extrude and granulate to obtain the feedstock.

[0049] Step 3: Put the feedstock into the hopper of an injection molding machine. After the feedstock is plasticized by the screw of the injection molding machine, it is extruded into the mold cavity through extrusion to complete the filling. After cooling for 5-15 seconds, open the mold and eject the green body through the ejection mechanism to obtain the 17-4PH green body. The injection temperature of the injection molding machine is 160-200 °C, the screw speed is 60 r / min, the injection pressure is 100-200 MPa, and the temperature of the mold is 90-120 °C. The specific process parameters are based on ensuring that the 17-4PH green body is injected evenly and fully without defects, reaching more than 94% of the theoretical green body density.

[0050] Step 4: Catalytic debinding is carried out using nitric acid. Specifically: Put the 17-4PH green body into a nitric acid debinding furnace, decompose the binder in the 17-4PH green body into small molecule organic substances and then burn and discharge them to obtain a porous 17-4PH brown embryo. Debinding must ensure that most of the binder can be removed. In this stage, the main component removed from the binder is POM, and the debinding rate > 95% to avoid unstable performance caused by excessive residual carbon content.

[0051] Step 5: Sinter the 17-4PH brown embryo. The first stage is the thermal debinding process. The thermal debinding process is specifically as follows: Heat up at a heating rate of 2-8 °C / min to 350-380 °C (negative pressure debinding), and keep warm for 0.5-2 h (negative pressure debinding); Heat up at a heating rate of 1-4 °C / min to 450-500 °C (negative pressure debinding), and keep warm for 0.5-2 h (negative pressure debinding); Heat up at a heating rate of 1-4 °C / min to 580-620 °C (negative pressure debinding), and keep warm for 0.5-2 h (negative pressure debinding). Then carry out the second stage of the sintering process. The sintering process is specifically as follows: Heat up in an Ar atmosphere at a heating rate of 0.5-2 °C / min to 1000-1200 °C (partial pressure sintering), and keep warm for 0.5-4 h (vacuum internal sintering); Heat up in an Ar atmosphere at a heating rate of 0.5-2 °C / min to 1260-1300 °C (partial pressure sintering), and keep warm for 0.5-4 h (partial pressure sintering). Subsequently, cool down in an Ar atmosphere at a cooling rate of 3-6 °C / min to 850-1000 °C, and then cool down to room temperature by forced cooling to obtain the 17-4PH sintered part; Step 6: Heat-treat the 17-4PH sintered parts, specifically: keep them at a temperature of 1000 - 1100 °C for 0.5 - 3 hours and then rapidly cool, and perform aging treatment at a temperature of 480 - 530 °C for 3 - 5 hours. The heat treatment process is adjusted according to different performance requirements of the products.

[0052] Polish the heat-treated 17-4PH products to obtain 17-4PH products with a polished effect.

[0053] Figure 5 It is the polished metallographic diagram of the 17-4PH product of Comparative Example 4.

[0054] Perform performance tests on the 17-4PH sintered parts and 17-4PH products of Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4, and the test results are shown in Table 1 below:

[0055] Table 1 As can be seen from the above, the difference between Example 1 and Comparative Example 1, Comparative Example 2, and Comparative Example 3 is that the C content in the 17-4PH powder is different, and the difference between Example 1 and Comparative Example 4 is the sintering process difference.

[0056] Comparing Example 1 with Comparative Example 1 (conventional 17-4PH powder with a C content of 0.02 - 0.07%), it can be seen that the 17-4PH sintered parts made of conventional 17-4PH powder in Comparative Example 1 have a high O content and a low sintering density, and the polishing effect of the 17-4PH product in Comparative Example 1 is lower than that of the 17-4PH product in Example 1.

[0057] Comparing Example 1 with Comparative Example 2 (C content of 0.07 - 0.15%), it can be seen that the C content can be controlled within a certain range, but the O content is still high, and the polishing effect of the 17-4PH product in Comparative Example 2 is lower than that of the 17-4PH product in Example 1.

[0058] Comparing Example 1 with Comparative Example 3 (C content of 0.25 - 0.35%), it can be seen that the O content can be controlled relatively low, but the C content is on the high side, the structure of the sintered part is austenite structure, the hardness is low, and the hardness cannot be improved even by subsequent heat treatment. The polishing effect of the 17-4PH product in Comparative Example 3 is close to that of the 17-4PH product in Example 1, but the hardness is low.

[0059] As can be seen from Example 1 and Comparative Example 4, the difference between Example 1 and Comparative Example 4 lies in the sintering process. The C and O contents in Comparative Example 4 are both relatively high. The structure of the sintered part is austenite structure, with low hardness, and the hardness cannot be improved even by subsequent heat treatment. The polishing effect of the 17-4PH product in Comparative Example 4 is lower than that of the 17-4PH product in Example 1.

[0060] In summary, the modified 17-4PH powder injection molding process with high density and high polishing effect provided by the present invention realizes the high density and high polishing effect of 17-4PH materials through the modified 17-4PH powder (with a C content of 0.15-0.25%, different from the 0.02-0.07% C content of conventional 17-4PH powder) in combination with the optimized metal injection molding process, meeting the market demand of the products.

[0061] 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 modified 17-4PH powder injection molding process with high density and high polishing effect, characterized in that, It includes the following steps: Step 1: Weigh a certain mass of 17-4PH powder and binder. In the 17-4PH powder, the mass percentage of Cr is 15-17.5%, the mass percentage of Ni is 3-5%, the mass percentage of Cu is 3-5%, the mass percentage of Nb is 0.15-0.45%, the mass percentage of O is 0.2-0.3%, the mass percentage of C is 0.15-0.25%, and the balance is Fe. Step 2: Put the 17-4PH powder and the binder into a mixer for mixing, extrude and granulate to obtain a feedstock. Step 3: Put the feedstock into an injection hopper and inject it into a mold to obtain a 17-4PH green compact. Step 4: Carry out degreasing treatment on the 17-4PH green compact to obtain a 17-4PH brown compact. Step 5: Sinter the 17-4PH brown compact. The first stage is a thermal degreasing process, then carry out the second-stage sintering process, and then cool down to obtain a 17-4PH sintered part. Step 6: Carry out heat treatment on the 17-4PH sintered part.

2. A modified 17-4PH powder injection molding process with high density and high polishing effect according to claim 1, characterized in that, The particle size specification of the 17-4PH powder is: D 90 <25 μm, D 50 is 6-9 μm, D 10 <3 μm.

3. A modified 17-4PH powder injection molding process with high density and high polishing effect according to claim 1, characterized in that, The volume ratio of the 17-4PH powder is 55%-70%; the binder includes the following raw materials in percentage: 85%-89% POM, 4-6% PE, 2-4% EVA, 2-4% SA, 1-2% PW.

4. A modified 17-4PH powder injection molding process with high density and high polishing effect according to claim 1, characterized in that: The mixing temperature in Step 2 is 150-200°C, and the mixing time is 2 hours.

5. A modified 17-4PH powder injection molding process with high density and high polishing effect according to claim 1, characterized in that: In Step 3, the injection temperature of the injection machine is 160~200°C, the screw speed is 60 r / min, the injection pressure is 100~200 MPa, and the temperature of the mold is 90-120°C.

6. A modified 17-4PH powder injection molding process with high density and high polishing effect according to claim 1, characterized in that: In Step 4, nitric acid is used for catalytic degreasing, and the degreasing rate > 95%.

7. A modified 17-4PH powder injection molding process with high density and high polishing effect according to claim 1, characterized in that, The thermal degreasing process in Step 5 is: heat up at a heating rate of 2-8°C / min to 350-380°C, hold for 0.5-2 h; heat up at a heating rate of 1-4°C / min to 450-500°C, hold for 0.5-2 h; heat up at a heating rate of 1-4°C / min to 580-620°C, hold for 0.5-2 h.

8. A modified 17-4PH powder injection molding process with high density and high polishing effect according to claim 1, characterized in that, The sintering process in Step 5 is: heat up at a heating rate of 1-4°C / min to 800-900°C, hold for 0.5-4 h; in an Ar atmosphere, heat up at a heating rate of 0.5-2°C / min to 1000-1200°C, hold for 0.5-4 h; in an Ar atmosphere, heat up at a heating rate of 0.5-2°C / min to 1260-1300°C, hold for 0.5-4 h; in an Ar atmosphere, cool down at a cooling rate of 3-6°C / min to 850-1000°C, and then cool down to room temperature by forced cooling.

9. A modified 17-4PH powder injection molding process with high density and high polishing effect according to claim 1, characterized in that, The heat treatment process in Step 6 is: hold at a temperature of 1000-1100°C for 0.5-3 hours and then rapidly cool, and carry out aging treatment at a temperature of 480-530°C for 3-5 hours.

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