Part powder metallurgy production process based on regenerated stainless steel powder

Abstract

The invention discloses a part powder metallurgy production process based on regenerated stainless steel powder, and relates to the technical field of part powder metallurgy production. The high-performance stainless steel part is manufactured through the steps of mixing and grinding, forming agent adding, granulating and drying, formula preparing, precise pressing forming, vacuum sintering, finished product detecting and the like. The core is that the particle size and uniformity of the powder are controlled through a unique pretreatment process, the national standard component requirement is met by adopting accurate formula regulation and control, the combination of cracking degreasing and powder metallurgy of the forming agent is synchronously realized in the vacuum sintering process, and an independent degreasing procedure is not needed; compared with a traditional process, the method has the advantages that the energy consumption is greatly reduced, the mechanical property and the corrosion resistance meet the requirements of brands such as 304 / 316, and the method has the advantages of resource recycling and environmental protection and is suitable for production of various products such as valves, fasteners and structural members.

Description

Technical Field

[0001] This invention relates to the field of powder metallurgy production technology for parts, specifically to a powder metallurgy production process for parts based on recycled stainless steel powder. Background Technology

[0002] Stainless steel parts are widely used in valves, fasteners, automotive parts, electrical structural components, and many other fields due to their excellent mechanical properties, corrosion resistance, and stability. Currently, the traditional production of stainless steel parts mainly adopts the process route of smelting-casting-forging-machining. This process requires a high-energy-consuming smelting stage, which not only consumes a lot of energy but also has a production cycle of 3-5 days, resulting in low production efficiency. At the same time, the material utilization rate in the traditional process is low, and a large amount of metal material is wasted during machining, leading to high product production costs. The market price of traditionally smelted stainless steel products is about 50,000-60,000 yuan / ton, which puts a lot of pressure on enterprises' production costs.

[0003] In addition, traditional stainless steel production processes generate a large amount of wastewater and slag during smelting and casting, and some processes also emit waste gas containing pollutants, causing certain environmental pollution. With the increasing prominence of global resource shortages and the continuous improvement of environmental protection requirements, the recycling of waste stainless steel has received widespread attention. However, existing recycling methods are mostly simple smelting and regeneration, resulting in low added value of products and failing to achieve high-value resource utilization of waste stainless steel.

[0004] Powder metallurgy technology has been applied in the production of stainless steel parts, but there are still many shortcomings: some processes require a separate degreasing process, which increases the production process and energy consumption; the raw materials are mostly virgin stainless steel powder, which is costly, and the powder pretreatment process is not perfect, resulting in poor particle size uniformity, which affects the subsequent pressing and sintering effect; the sintering process parameters are not precisely controlled, which can easily lead to problems such as insufficient product density and unstable mechanical properties, making it difficult to meet the high performance requirements of the diversified market for different grades of stainless steel parts. Therefore, developing a low-cost, high-efficiency, green and environmentally friendly stainless steel parts production process that can realize the high-value utilization of waste stainless steel has become an urgent technical problem to be solved in this field. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a powder metallurgy production process for parts based on recycled stainless steel powder, thus solving the problems mentioned in the background section.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a powder metallurgy production process for parts based on recycled stainless steel powder, comprising the following steps: S1. Select recycled metal powder made from waste stainless steel as the core raw material. The main components of the raw material powder match the components of the stainless steel matrix and there are no obvious impurities or lumps. S2. The recycled metal powder selected in step S1 is put into a mechanical grinding and mixing equipment and mixed and ground for 5-8 hours. The Fisher particle size of the powder after grinding is controlled to be 2.8-3.2μm to ensure uniform distribution of powder components and ensure the activity of subsequent pressing and sintering. S3. Add a plastic molding agent to the powder after step S2. The mass ratio of the molding agent to the powder is 1-3:100. Stir and mix for 1-2 hours until uniform. The molding agent can enhance the compressibility of the powder and improve the strength of the pressed blank. S4. The powder after mixing the molding agent in step S3 is granulated to obtain granular powder with a particle size of 0.1-0.3mm. Then, the granular powder is placed in a drying equipment and dried at 80-120℃ for 2-3 hours to remove excess moisture and volatile components from the powder, improve the powder flowability and filling properties, and facilitate automated pressing. S5. Based on the basic composition test results of the granular powder after drying in step S4, and referring to the composition requirements of the corresponding grade of stainless steel in GB / T20878-2007, add the insufficient alloying elements. The alloying elements include one or more of chromium, nickel, and molybdenum. Put the powder and alloying elements into a homogenizing mixing device and mix for 3-4 hours to ensure that the chemical composition of the mixed powder meets the requirements of the target grade of stainless steel. S6. Fill the mixed powder prepared in step S5 into a precision parts mold, and use a hydraulic press to perform unidirectional or bidirectional pressing at room temperature. Adjust the pressing pressure to 500-800MPa according to the complexity of the product, and the holding time to 10-30s to obtain a compact with the specified shape, size and sufficient strength. Control the compact density to reach 7.5-7.6g / cm³. 3 ; S7. Place the pressed blank obtained in step S6 directly into the induction vacuum sintering furnace without a separate degreasing process, and control the vacuum degree inside the sintering furnace to ≥10. -3 Pa, according to the preset heating curve, the heating rate is 5-10℃ / min, avoiding the stage of violent volatilization of the forming agent. After heating to 1300℃, hold for 6-8h to achieve atomic diffusion and metallurgical bonding between powder particles, achieving complete densification. During the sintering process, the forming agent is effectively decomposed and discharged in a vacuum environment. S8. Perform dimensional accuracy testing, density testing, mechanical property testing, and corrosion resistance testing on the finished product after sintering in step S7, and screen out products with a density ≥ 7.5 g / cm³. 3 Finished stainless steel parts with a density of ≥98% and meeting all performance standards; S9. Clean the surface and remove burrs from the qualified finished products, and classify and package them according to product type to obtain the final product.

[0007] Optionally, the purity of the recycled metal powder in step S1 is ≥99.5%, and the moisture content is ≤0.5%.

[0008] Optionally, the target grade stainless steel mentioned in step S5 includes grades 304 and 316, and the different grades can be switched by adjusting the type and amount of alloying elements.

[0009] Optionally, the dimensional accuracy error of the precision component mold in step S6 is ≤ ±0.01mm. The mold needs to be maintained after every 500-1000 products to ensure the stability of the product dimensional accuracy.

[0010] Optionally, the temperature control accuracy of the induction vacuum sintering furnace in step S7 is ±5℃, and the furnace temperature and vacuum data are recorded in real time during the sintering process to ensure that the process parameters are traceable.

[0011] Optionally, the mechanical property tests in step S8 include tensile strength and hardness tests, and the corrosion resistance test adopts a salt spray test. The test standards meet the industry usage requirements of the corresponding grade of stainless steel.

[0012] This invention provides a powder metallurgy production process for parts based on recycled stainless steel powder, which has the following beneficial effects: This powder metallurgy production process for parts based on recycled stainless steel powder uses recycled waste stainless steel powder as the core raw material, replacing traditional virgin stainless steel powder or smelting raw materials. This not only solves the problem of low added value in the recycling of waste stainless steel, achieving high-value resource utilization, but also significantly reduces raw material procurement costs. Simultaneously, the near-net-shape forming technology achieves a material utilization rate far exceeding that of traditional machining processes, further reducing material waste and lowering production costs. During vacuum sintering, the forming agent can be simultaneously decomposed and discharged during the heating stage, eliminating the need for a separate degreasing process, greatly simplifying the production process and shortening the production cycle. Production efficiency is significantly improved, enabling rapid response to market demands. Furthermore, this process eliminates the energy-intensive smelting and casting steps of traditional processes, and the vacuum sintering process has low energy consumption; at the same time, there is no wastewater or waste residue discharge throughout the entire production process; this invention ensures the stability of subsequent processes by strictly controlling the powder particle size, uniformity and moisture content through a precise powder pretreatment process. Furthermore, this process can produce stainless steel parts of different grades such as 304 and 316 by adjusting the amount of alloying elements added, and is suitable for the production of various products such as valves, fasteners, and structural parts, meeting diversified market demands. Detailed Implementation

[0013] 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.

[0014] Example: A powder metallurgy process for producing 304 stainless steel ball valve cores based on recycled stainless steel powder includes the following specific steps: S1. Select recycled metal powder made from waste 304 stainless steel through processing. The powder purity is 99.6% and the moisture content is 0.3%. S2. Add the recycled metal powder to a mechanical grinding and mixing equipment, grind and mix for 6 hours, and control the powder Fisher particle size to be 3.0μm; S3. Add plastic molding agent to the ground powder. The mass ratio of molding agent to powder is 2:100. Stir and mix for 1.5 hours until uniform. S4. Granulate the powder of the mixed molding agent to obtain granular powder with a particle size of about 0.2 mm, and then dry it at 100°C for 2.5 h to remove moisture and volatile components. S5. Test the composition of the dried powder. According to the requirements of GB / T20878-2007 for the composition of 304 stainless steel, add appropriate amounts of chromium and nickel alloy elements, and mix in a homogenizing mixer for 3.5 hours to ensure that the chemical composition fully meets the standard. S6. Fill the prepared powder into a special mold for ball valve cores, and use a hydraulic press for bidirectional pressing at a pressure of 650 MPa for 20 seconds to obtain a compact with a density of 7.55 g / cm³. 3 ; S7. Place the pressed billet into an induction vacuum sintering furnace and control the vacuum level inside the furnace to ≥10. -3 Pa, heating at a rate of 8℃ / min to avoid the stage of violent volatilization of the molding agent, heating to 1300℃ and holding for 7h, the molding agent decomposes and is discharged during the sintering process; S8. Inspect the sintered ball valve core; the dimensional accuracy error is ±0.008mm, and the density is 7.6g / cm³. 3 The density is 98.6%, the tensile strength is ≥520MPa, the hardness is HB≥180, and there is no rust after 72h salt spray test. All properties meet the standards. S9. Clean the surface and remove burrs from qualified finished products, classify and package them to obtain the final product.

[0015] Comparative Example: The traditional smelting process for producing 304 stainless steel ball valve cores of the same specifications includes the following specific steps: S1. The raw material is virgin stainless steel ingot with a purity of 99.5%; S2. Put the stainless steel ingot into the electric arc furnace, heat it to 1500℃ for melting, remove impurities and adjust the composition. S3. Pour the molten steel into the mold and cool it to form a billet. The cooling time is 12 hours. S4. Heat the billet to 1100℃ for forging to improve its microstructure and properties; S5. Through multiple machining processes such as turning, milling, and grinding, the material is processed to the target size; S6. Product dimensional accuracy error ±0.015mm, density 7.7g / cm³, density 97.5%, tensile strength ≥500MPa, hardness HB≥170, no obvious corrosion in 72h salt spray test; S7. Production data statistics show a production cycle of 4 days, a material utilization rate of 65%, energy consumption that is 3.2 times that of the example, and a production cost of 55,000 yuan / ton.

[0016] Comparison results of the examples and comparative examples project Example (Process of the Invention) Comparative example (traditional smelting process) Production cycle 2.5 days 4 days Material utilization rate 95.8% 65% Energy consumption (relative value) 1.0 3.2 Production cost (ten thousand yuan / ton) 3.8 5.5 Dimensional accuracy error ±0.008mm ±0.015mm Density 98.6% 97.5% Tensile strength (MPa) ≥520 ≥500 Environmental emissions No wastewater or waste residue, and very little exhaust gas. Wastewater, waste residue, and exhaust gas emissions are generated. The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A powder metallurgy production process for parts based on recycled stainless steel powder, characterized in that, Includes the following steps: S1. Select recycled metal powder made from waste stainless steel as the core raw material. The main components of the raw material powder match the components of the stainless steel matrix and there are no obvious impurities or lumps. S2. The recycled metal powder selected in step S1 is put into a mechanical grinding and mixing equipment and mixed and ground for 5-8 hours. The Fisher particle size of the powder after grinding is controlled to be 2.8-3.2μm to ensure uniform distribution of powder components and ensure the activity of subsequent pressing and sintering. S3. Add a plastic molding agent to the powder after step S2. The mass ratio of the molding agent to the powder is 1-3:

100. Stir and mix for 1-2 hours until uniform. The molding agent can enhance the compressibility of the powder and improve the strength of the pressed blank. S4. The powder after mixing the molding agent in step S3 is granulated to obtain granular powder with a particle size of 0.1-0.3mm. Then, the granular powder is placed in a drying equipment and dried at 80-120℃ for 2-3 hours to remove excess moisture and volatile components from the powder, improve the powder flowability and filling properties, and facilitate automated pressing. S5. Based on the basic composition test results of the granular powder after drying in step S4, and referring to the composition requirements of the corresponding grade of stainless steel in GB / T20878-2007, add the insufficient alloying elements. The alloying elements include one or more of chromium, nickel, and molybdenum. Put the powder and alloying elements into a homogenizing mixing device and mix for 3-4 hours to ensure that the chemical composition of the mixed powder meets the requirements of the target grade of stainless steel. S6. Fill the mixed powder prepared in step S5 into a precision parts mold, and use a hydraulic press to perform unidirectional or bidirectional pressing at room temperature. Adjust the pressing pressure to 500-800MPa according to the complexity of the product, and the holding time to 10-30s to obtain a compact with the specified shape, size and sufficient strength. Control the compact density to reach 7.5-7.6g / cm³. 3 ; S7. Place the pressed blank obtained in step S6 directly into the induction vacuum sintering furnace without a separate degreasing process, and control the vacuum degree inside the sintering furnace to ≥10. -3 Pa, according to the preset heating curve, the heating rate is 5-10℃ / min, avoiding the stage of violent volatilization of the forming agent. After heating to 1300℃, hold for 6-8h to achieve atomic diffusion and metallurgical bonding between powder particles, achieving complete densification. During the sintering process, the forming agent is effectively decomposed and discharged in a vacuum environment. S8. Perform dimensional accuracy testing, density testing, mechanical property testing, and corrosion resistance testing on the finished product after sintering in step S7, and screen out products with a density ≥ 7.5 g / cm³. 3 Finished stainless steel parts with a density of ≥98% and meeting all performance standards; S9. Clean the surface and remove burrs from the qualified finished products, and classify and package them according to product type to obtain the final product.

2. The powder metallurgy production process for parts based on recycled stainless steel powder according to claim 1, characterized in that, The purity of the recycled metal powder in step S1 is ≥99.5%, and the moisture content is ≤0.5%.

3. The powder metallurgy production process for parts based on recycled stainless steel powder according to claim 1, characterized in that, The target stainless steel grades mentioned in step S5 include 304 and 316 grades. The different grades can be switched by adjusting the types and amounts of alloying elements.

4. The powder metallurgy production process for parts based on recycled stainless steel powder according to claim 1, characterized in that, The dimensional accuracy error of the precision component mold mentioned in step S6 is ≤ ±0.01mm. The mold needs to be maintained after every 500-1000 products to ensure the stability of the product dimensional accuracy.

5. The powder metallurgy production process for parts based on recycled stainless steel powder according to claim 1, characterized in that, The temperature control accuracy of the induction vacuum sintering furnace described in step S7 is ±5℃. During the sintering process, the temperature and vacuum data inside the furnace are recorded in real time to ensure that the process parameters are traceable.

6. The powder metallurgy production process for parts based on recycled stainless steel powder according to claim 1, characterized in that, The mechanical property tests mentioned in step S8 include tensile strength and hardness tests. The corrosion resistance test adopts a salt spray test, and the test standards meet the industry usage requirements of the corresponding grade of stainless steel.