Powder metallurgy warm compaction process and application

Abstract

The application discloses a powder metallurgy warm pressing process and application thereof, and relates to the field of forming technology of metallurgical parts. The powder metallurgy warm pressing process comprises the following steps: mixing alloy powder raw materials and internal lubricant to obtain a mixture; heating and treating the mixture in a reducing protective atmosphere to obtain heated mixture; feeding the heated mixture into a mold for warm pressing treatment to obtain a green body; and sintering the green body to obtain a powder metallurgy workpiece; wherein the internal lubricant comprises polytetrafluoroethylene, lithium stearate, molybdenum disulfide, copper powder, graphite powder and a dispersing agent. The application improves the powder pressing formability by heating the powder during powder mixing and heating the mold during pressing, and uses special internal lubricant and mold wall lubricant, so that the density and performance of the powder metallurgy workpiece are improved.

Description

Technical Field

[0001] This invention relates to the field of metallurgical parts forming technology, specifically to a powder metallurgy warm pressing process and its application. Background Technology

[0002] Powder metallurgy is a process that uses metal powders to form and sinter metal products or composite materials. With its advantages of high material utilization, good forming precision, and suitability for mass production, it is widely used in machinery, automotive, aerospace, and other fields. Among these processes, warm pressing, as an upgrade to room-temperature powder metallurgy, effectively improves powder formability by heating the powder and mold, using lubricants, thereby increasing the density and performance of the finished parts. It has become one of the mainstream processes for preparing medium- and high-strength powder metallurgy parts.

[0003] There are already various studies and patents related to powder metallurgy warm pressing processes in the existing technology. However, the existing warm pressing processes generally suffer from imperfect control of core technologies. Specifically, this is manifested in poor control of warm pressing process parameters, unreasonable sintering process design, and inappropriate selection of lubricant types and ratios. As a result, the high density and high performance technical advantages of warm pressing processes are not fully utilized, and the mechanical properties and fatigue properties of the parts are difficult to meet the requirements of high-end mechanical components.

[0004] Therefore, developing a powder metallurgy warm pressing process that can improve the density and mechanical properties of parts has become an urgent technical problem to be solved in this field. Summary of the Invention

[0005] This application provides a powder metallurgy warm pressing process and its application to solve the technical problems of low density and poor performance of parts prepared by existing warm pressing processes, and to achieve the effect of obtaining high-density, high-performance powder metallurgy parts at low cost.

[0006] In a first aspect, this application provides a powder metallurgy warm pressing process, which includes the following steps: The alloy powder raw material and the internal lubricant are mixed to obtain a mixture; The mixture is heated in a reducing protective atmosphere to obtain a heated mixture; The heated mixture is fed into a mold for thermo-pressing treatment to obtain a green body; The green blank is sintered to obtain a powder metallurgy part. The internal lubricant includes polytetrafluoroethylene, lithium stearate, molybdenum disulfide, copper powder, graphite powder, and dispersant.

[0007] In some embodiments, the mass ratio of the components in the internal lubricant is: polytetrafluoroethylene: lithium stearate: molybdenum disulfide: copper powder: graphite powder: dispersant = (12-16): (78-82): 3: 1: 1.5: 0.5.

[0008] In some embodiments, the amount of the internal lubricant added is 0.1-0.3% of the total mass of the alloy powder raw material.

[0009] In some embodiments, the alloy powder raw material comprises the following chemical components by mass fraction: Ni 0.8-1.2%, Mo 0.8-1.5%, Cu 1.5-2.5%, Ti 0.2-0.5%, C 0.2-1.0%, with the balance being iron powder and unavoidable impurities.

[0010] In some embodiments, the iron powder satisfies at least one of the following conditions: The iron powder is composed of 95-99% atomized iron powder and 1-5% carbonyl iron powder, wherein the particle size of the atomized iron powder is 40-150 μm and the particle size of the carbonyl iron powder is less than 10 μm. The iron powder contains less than 0.1% O2. The iron powder contains less than 0.006% carbon (C). The N2 content in the iron powder is less than 0.0013%.

[0011] In some embodiments, before the step of mixing the alloy powder raw material and the internal lubricant, a pretreatment step of the alloy powder raw material is also included: placing the iron powder in an electric furnace and heating it in an H2 atmosphere for 40-60 minutes to perform reduction annealing treatment.

[0012] In some embodiments, the temperature of the heat treatment is 130-150°C.

[0013] In some embodiments, the heat treatment time is 30-60 minutes.

[0014] In some embodiments, the warm pressing process includes: heating the mold to 140-180°C, spraying mold wall lubricant on the inner surface of the mold, loading the heated mixture into the mold, warm pressing at 670-860 MPa, and holding the pressure for 3-5 minutes.

[0015] In some embodiments, the mold wall lubricant is a mixture of polytetrafluoroethylene and vinyl bis-stearamide, wherein the mass ratio of the polytetrafluoroethylene to the vinyl bis-stearamide is (1-3):(3-6).

[0016] In some embodiments, the thickness of the mold wall lubricant sprayed on the inner surface of the mold is 0.02-0.1 mm.

[0017] In some embodiments, the sintering process includes: loading the green billet into the furnace once, sintering in two stages, cooling to a cooling section of 700-850°C and holding for heat after sintering, and finally naturally cooling to room temperature. In the first stage, the green billet is sintered at 450-550°C for 1-2 hours; in the second stage, the temperature is raised to 1000-1350°C and sintered for 1.5-3 hours.

[0018] In some embodiments, the powder metallurgy warm pressing process further includes a post-processing step: the sintered powder metallurgy parts are subjected to carburizing and quenching for surface strengthening, followed by machining.

[0019] Secondly, this application provides a powder metallurgy part, which is prepared by the powder metallurgy warm pressing process described above.

[0020] Compared with the prior art, the beneficial effects of this application are as follows: 1. The density of the powder metallurgy parts prepared in this application is about 7.6 g / cm³, which is far greater than the 7.2-7.4 g / cm³ of the parts prepared in the prior art. The static strength of the gear parts prepared reaches 96% of that of fully dense steel parts, and the bending fatigue strength reaches 87.5% of that of fully dense steel parts, which fully demonstrates the technical advantages of high density and high performance of the warm pressing process. 2. This application designs a composite internal lubricant with a specific ratio, in which each lubricating component forms a highly efficient synergistic effect, ensuring excellent lubrication effect and good compatibility with iron-based alloy powder, avoiding sintering defects caused by lubricant residue. At the same time, it is combined with a suitable mold wall lubricant, which solves the problems of improper use of lubricant and incompatibility with process in the prior art, and greatly improves the powder pressing formability. 3. This application pre-treats the iron powder raw material by reduction annealing and controls its impurities and particle size indicators. It optimizes the parameters such as temperature, pressure and time of powder heating, mold temperature pressing and two-stage sintering. Moreover, each process link is highly compatible with the special lubrication system, which solves the problems of poor temperature pressing process control and unreasonable sintering process in the existing technology. It ensures the uniformity of the composition and performance of the parts, greatly reduces defects such as porosity and cracks, and improves the yield of the parts. 4. While achieving a significant improvement in part density and performance, this application only brings about a 10% increase in cost. Compared with high-density preparation processes such as powder forging, the cost is lower. Compared with the existing moderately effective warm pressing process, it achieves a leapfrog improvement in performance with a slight increase in cost, making it more suitable for mass industrial production. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 A flow chart of the powder metallurgy warm pressing process provided in the embodiments of this application; Figure 2 A diagram of the powder metallurgy gear compressive strength testing equipment provided in Embodiment 1 of this application; Figure 3 This is a test curve of the compressive strength of powder metallurgy gears provided in Embodiment 1 of this application; Figure 4 A graph showing the compressive strength test results for fully dense steel components; Figure 5 This is a density detection diagram of a powder metallurgy gear provided in Embodiment 1 of this application; Figure 6 This is a hardness curve distribution diagram of the powder metallurgy gear provided in Embodiment 1 of this application. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0024] Powder metallurgy warm pressing is a technology developed from room temperature pressing. Its core is to improve the performance of the parts by adding powder heating and mold heating processes, using special internal lubricants and mold wall lubricants, and optimizing the sintering process. The difference in the formulation of the internal lubricant is the core difference between different warm pressing processes. It directly determines the heating temperature of the powder and the mold, which in turn affects the pressing and sintering process parameters, ultimately leading to differences in the density, performance and manufacturing cost of the parts.

[0025] Several patents related to warm pressing processes in powder metallurgy have been published, but existing technologies generally suffer from imperfect process control. Specifically, this manifests as poor control of the warm pressing process, unreasonable sintering process design, and inappropriate selection and proportioning of lubricants. Some patents even avoid the core design of internal lubricants, fail to define the alloy powder composition, or use overly general sintering processes, resulting in low density and poor overall performance of the prepared powder metallurgical parts, failing to fully leverage the high density and high performance advantages of warm pressing. For example, patent CN109434093A does not specify the internal lubricant and has a simple sintering process, resulting in a part density of only 7.2-7.4 g / cm³; patent CN102896320A has a vague process description lacking practical guidance; and patent CN1319680A has a vague description of the internal lubricant, resulting in a part density of only 7.26-7.29 g / cm³. Furthermore, none of these patents specify the mechanical performance indicators of the products. Overall, existing warm pressing processes are only capable of basic forming with limited application effects.

[0026] The applicant discovered, through extensive experimental research, that by designing a specific ratio of composite powdered internal lubricant, combined with precisely controlled powder heating, warm pressing, and a two-stage sintering process, the formability and sintering bonding of metal powders can be effectively improved. Under the premise of increasing the process cost by only about 10%, the density of the prepared powder metallurgy parts can be increased to over 7.6 g / cm³, and their static strength and bending fatigue performance are also significantly better than those of existing warm pressing process parts, approaching the level of fully dense steel parts.

[0027] In view of this, this application provides a powder metallurgy warm pressing process and its application to solve the technical problems of low density and poor performance of parts prepared by existing warm pressing processes, and to achieve the effect of obtaining high-density, high-performance powder metallurgy parts at low cost.

[0028] Firstly, this application provides a powder metallurgy warm pressing process. According to embodiments of this application, such as... Figure 1 As shown, the powder metallurgy warm pressing process includes the following steps: S100: The alloy powder raw material and the internal lubricant are mixed to obtain a mixture; S200: The mixture is heated in a reducing protective atmosphere to obtain a heated mixture; S300: The heated mixture is fed into a mold for thermo-pressing treatment to obtain a green body; S400: The green blank is sintered to obtain a powder metallurgy part; The internal lubricant includes polytetrafluoroethylene, lithium stearate, molybdenum disulfide, copper powder, graphite powder, and dispersant.

[0029] The powder metallurgy warm pressing process of this application employs a composite powdered internal lubricant composed of polytetrafluoroethylene (PTFE), lithium stearate, molybdenum disulfide, copper powder, graphite powder, and a dispersant. Lithium stearate serves as the main lubricating component, providing fundamental core lubrication and effectively reducing frictional resistance between powder particles. PTFE and molybdenum disulfide, as auxiliary lubricating components, complement and enhance the overall lubrication performance. Copper powder and graphite powder not only further improve the lubrication effect but also exhibit good compatibility with iron-based alloy powder raw materials, preventing defects such as porosity and impurities caused by lubricant residue during subsequent sintering. The dispersant ensures that the various lubricating and compatible components are evenly dispersed and tightly coated on the surface of the metal powder, allowing the lubricant to exert its effect uniformly throughout the mixing, heating, and pressing processes, synergistically enhancing the advantages of each component.

[0030] Furthermore, the special internal lubricant, in conjunction with the powder heating under a reducing protective atmosphere, the mold warm pressing, and the subsequent sintering process, effectively improves the formability during powder pressing and significantly increases the density of powder-molded parts, achieving a density of over 7.6 g / cm³. Simultaneously, it enhances the mechanical and fatigue properties of the parts. The static strength of the prepared gear parts reaches 96% of that of fully dense steel parts, and the bending fatigue strength reaches 87.5% of that of fully dense steel parts, far exceeding the performance indicators of parts produced by conventional warm pressing processes. Moreover, this process only increases costs by about 10%, achieving high density and high performance in powder-molded parts at a low cost, fully leveraging the technical advantages of warm pressing.

[0031] In some embodiments of this application, the mass ratio of the components in the internal lubricant is: polytetrafluoroethylene: lithium stearate: molybdenum disulfide: copper powder: graphite powder: dispersant = (12-16): (78-82): 3: 1: 1.5: 0.5. By limiting the mass fraction ratio of each component in the internal lubricant within the above range, lithium stearate, as the main lubricating component, provides the basic core lubrication effect, effectively reducing the frictional resistance between powder particles. Polytetrafluoroethylene and molybdenum disulfide, as auxiliary lubricating components, complement and enhance each other, further improving the overall lubrication performance.

[0032] In some embodiments of this application, the amount of internal lubricant added is 0.1-0.3% of the total mass of the alloy powder raw material. Limiting the amount of internal lubricant added within the above range can improve the overall lubrication performance.

[0033] In some embodiments of this application, the alloy powder raw material comprises the following chemical composition by mass fraction: Ni 0.8-1.2%, Mo 0.8-1.5%, Cu 1.5-2.5%, Ti 0.2-0.5%, C 0.2-1.0%, with the balance being iron powder and unavoidable impurities. This low-alloy composition design balances the strength, hardness, and toughness of the part. Ni and Mo elements can improve the hardenability and mechanical strength of the part, Cu element can achieve a sintering self-lubricating effect, Ti element can refine the grains and improve the high-temperature performance of the part, and C element provides hardness support for the part. The synergistic effect of each element lays the compositional foundation for the high performance of the part.

[0034] It should be noted that "unavoidable impurities" refers to trace impurities that are naturally present in the raw materials and cannot be completely removed by conventional processes, with a total mass fraction not exceeding 0.1%.

[0035] In some embodiments of this application, the iron powder satisfies at least one of the following conditions: The iron powder is composed of 95-99% atomized iron powder and 1-5% carbonyl iron powder, wherein the particle size of the atomized iron powder is 40-150 μm and the particle size of the carbonyl iron powder is less than 10 μm. The iron powder contains less than 0.1% O2. The iron powder contains less than 0.006% carbon (C). The N2 content in the iron powder is less than 0.0013%.

[0036] Atomized iron powder, as the main iron powder raw material, has the advantages of good fluidity and excellent formability, making it suitable for mass warm pressing. A small amount of ultrafine carbonyl iron powder can fill the gaps between the atomized iron powder particles, effectively increasing the bulk density of the powder and thus improving the final density of the molded parts. Simultaneously, strictly controlling the oxygen, carbon, and nitrogen impurities in the iron powder can avoid the adverse effects of oxide and nitride inclusions and carbon content fluctuations on the sintering performance and mechanical properties of the molded parts, ensuring the stability of the composition and performance of the molded parts. Preferably, the iron powder simultaneously meets all the above conditions to achieve optimal basic raw material properties.

[0037] In some embodiments of this application, the copper powder is electrolytic copper powder with a particle size of 20-50 μm. Electrolytic copper powder has high purity and regular particle morphology. The 20-50 μm particle size can not only help improve the lubrication effect, but also has good compatibility with iron-based powder, avoiding uneven mixing caused by excessively large particles or agglomeration caused by excessively small particles.

[0038] In some embodiments of this application, the graphite powder particle size is required to be below 20 μm. Graphite powder with a particle size of no more than 20 μm is finer and can be uniformly dispersed in the lubricant system, further optimizing the lubrication effect while better bonding with metal powder.

[0039] In some embodiments of this application, the dispersant is a compound of fatty acids, oligomeric paraffins and higher fatty acid metal salts, which has a small contact area and can effectively promote the uniform coating of the internal lubricant on the surface of the metal powder during the mixing process.

[0040] In some embodiments of this application, before mixing the alloy powder raw material and the internal lubricant, a pretreatment step for the alloy powder raw material is included: placing the iron powder in an electric furnace and heating it in a H2 atmosphere for 40-60 minutes for reduction annealing. Reduction annealing in a hydrogen atmosphere reduces trace oxides on the surface of the iron powder, further reducing the oxygen content of the iron powder, while simultaneously eliminating internal stress generated during iron powder preparation, improving the plasticity and formability of the iron powder, and providing higher-quality raw materials for subsequent mixing and warm pressing. Preferably, the heating temperature for reduction annealing is 860°C, at which the reduction reaction is sufficient and does not lead to excessive grain growth in the iron powder.

[0041] In some embodiments of this application, the mixing time of the alloy powder raw material and the internal lubricant is 60-90 minutes. Limiting the mixing time within the above range ensures that the materials are fully and uniformly mixed, guaranteeing that the internal lubricant is evenly coated on the surface of the alloy powder raw material, making the lubrication performance of each part of the mixture consistent, and avoiding the problem of uneven density and performance fluctuations of the green blank after warm pressing due to uneven mixing.

[0042] In some embodiments of this application, the reducing protective atmosphere is a mixture of 20% hydrogen and 80% helium. Hydrogen has reducing properties, which can prevent the powder from oxidizing during heating. Helium is an inert gas, which can dilute the hydrogen and ensure the stability of the protective atmosphere. The protective effect of this mixed atmosphere is better than that of single hydrogen or other inert gases, and it is safer, avoiding the explosion risk of pure hydrogen.

[0043] In some embodiments of this application, the heat treatment temperature is 130-150°C; and / or the heat treatment time is 30-60 minutes. This heating temperature and time are matched with the composite internal lubricant system of this application, which can soften the internal lubricant and improve the lubrication effect without causing the internal lubricant to decompose and fail. If the heating temperature is too high or the time is too long, the internal lubricant is easily decomposed, loses its lubricating effect, and will also produce harmful gases. If the heating temperature is too low or the time is too short, the powder is not heated sufficiently, the internal lubricant softening effect is poor, and the powder formability cannot be effectively improved.

[0044] In some embodiments of this application, the warm pressing process includes: heating the mold to 140-180°C, spraying a mold wall lubricant onto the inner surface of the mold, loading the heated mixture into the mold, and warm pressing at a pressure of 670-860 MPa for 3-5 minutes. Heating the mold to a temperature slightly higher than that of the powder avoids rapid cooling of the heated mixture after it is loaded into the mold, ensuring the formability of the powder during warm pressing. The warm pressing pressure of 670-860 MPa and the holding time of 3-5 minutes allow the powder to be fully compacted, increasing the green density, while avoiding the problems of excessive pressure leading to accelerated mold wear or insufficient pressure leading to insufficient green density.

[0045] In some embodiments of this application, the mold is heated by machining a groove in the annular die retaining ring, installing a built-in heating element, and setting a temperature measuring point on the back of the die. The mold temperature control accuracy is ±5℃. This heating method can achieve uniform heating of the mold. Combined with precise temperature control at the measuring point, it ensures that the temperature of all parts of the mold is consistent, avoiding the problem of uneven green density and performance caused by uneven mold temperature.

[0046] In some embodiments of this application, the mold wall lubricant is a mixture of polytetrafluoroethylene (PTFE) and vinyl bis-stearamide (VDI), wherein the mass ratio of PTFE to VDI is (1-3):(3-6); further, the coating thickness of the mold wall lubricant on the inner surface of the mold is 0.02-0.1 mm. This ratio of mold wall lubricant works synergistically with the internal lubricant system of this application to further reduce the friction between the powder and the inner surface of the mold, improving the demolding effect and surface quality of the green body; the coating thickness of 0.02-0.1 mm ensures lubrication without causing a decrease in the dimensional accuracy of the part due to excessive coating thickness.

[0047] In some embodiments of this application, the sintering process includes: loading the green billet into the furnace once, sintering in two stages, cooling to a cooling section of 700-850°C and holding for heat after sintering, and finally naturally cooling to room temperature. In the first stage, the green billet is sintered at 450-550°C for 1-2 hours; in the second stage, the temperature is raised to 1000-1350°C and sintering continues for 1.5-3 hours.

[0048] This application employs a two-stage sintering process. The low-temperature pre-sintering stage (450-550℃) gradually removes lubricants and volatiles from the green blank, avoiding the rapid decomposition of lubricants and the generation of large amounts of gas caused by direct high-temperature sintering, which could lead to defects such as porosity and cracks in the parts. The high-temperature sintering stage (1000-1350℃) promotes atomic diffusion and metallurgical bonding between metal powder particles, improving the density and mechanical properties of the parts. The cooling section after sintering effectively eliminates internal stress in the parts, improving their dimensional stability and toughness.

[0049] In some embodiments of this application, the sintering process is carried out in a vacuum sintering furnace. The vacuum environment can further prevent oxidation of the parts during the sintering process, while promoting the discharge of gases during the sintering process and improving the density of the parts.

[0050] In some embodiments of this application, the powder metallurgy warm pressing process further includes a post-processing step: surface strengthening by carburizing and quenching the sintered powder metallurgy parts, followed by machining. Carburizing and quenching can improve the surface hardness and wear resistance of the parts, while ensuring the toughness of the core, meeting the usage requirements of transmission components such as gears; subsequent machining can ensure that the dimensional accuracy and surface roughness of the parts meet the usage standards. Preferably, the surface hardness of the parts after carburizing and quenching can reach 700HV0.2 or higher.

[0051] Secondly, this application provides a powder metallurgy part, which is prepared by the powder metallurgy warm pressing process described in the first aspect above.

[0052] The powder metallurgy parts provided in this application, through the use of a specific ratio of composite internal lubricant and precisely controlled temperature pressing and sintering processes, achieve a density of over 7.6 g / cm³ and a static strength reaching 96% of that of fully dense steel gears of the same specification, significantly superior to the 85%~95% of conventional temperature pressing processes. The bending fatigue strength reaches 28KN, exceeding 87.5% of that of fully dense steel parts (32KN), far surpassing the 60%~80% of conventional temperature pressing processes. These performance indicators demonstrate that the parts produced in this application have mechanical properties approaching the level of fully dense materials, and their overall performance is significantly superior to similar products prepared using existing temperature pressing processes. Simultaneously, this process only increases costs by approximately 10%, maintaining good economic efficiency while achieving a performance leap, possessing outstanding cost-effectiveness advantages, and is suitable for large-scale industrial applications.

[0053] In some embodiments of this application, the powder metallurgy part is a gear, particularly suitable for engine gears. For example... Figure 2-4 As shown, the gear prepared in this embodiment underwent a static strength test, and its tooth strength reached 6314.4 kgf, which is 98.9% of the tooth strength of a fully dense steel gear of the same specification (6560.2 kgf). This result indicates that the powder metallurgy gear prepared by the warm pressing process of this application has a static strength close to that of a fully dense steel gear, exhibiting excellent structural load-bearing capacity and meeting the usage requirements of high-strength applications such as engine gears.

[0054] It should be noted that "gear resistance" refers to the compressive static strength of the gear, or simply gear static strength.

[0055] The technical solutions provided in this application will be described in detail below with reference to the embodiments.

[0056] The raw materials used in the embodiments and comparative examples of this application are all conventional industrial finished powders in the field of powder metallurgy, and their specific specifications are as follows: Atomized iron powder: particle size 40-150μm, O2 content <0.1%, C content <0.006%, N2 content <0.0013%; Carbonyl iron powder: particle size ≤10μm, O2 content <0.1%; Ni powder: purity ≥ 99.5%, particle size < 80μm; Mo powder: purity ≥ 99.5%, particle size < 80μm; Cu powder: Electrolytic copper powder, particle size 20-50μm; Ti powder: purity ≥ 99.5%, particle size < 80μm; C powder: Particle size < 80μm; Graphite powder: particle size ≤20μm; Internal lubricant components: polytetrafluoroethylene micro powder, lithium stearate micro powder, molybdenum disulfide micro powder, electrolytic copper powder, graphite powder, and the dispersant is a compound of fatty acids, oligomeric paraffins and higher fatty acid metal salts. Mold wall lubricant components: polytetrafluoroethylene powder, vinyl bis-stearamide (EBS) powder.

[0057] Example 1 This embodiment 1 provides a powder metallurgy warm pressing process for manufacturing engine gears, and the specific steps are as follows: 1. Powder Selection and Pretreatment: Alloy powder raw materials were selected, with the following chemical composition by mass fraction: Ni 1.2%, Mo 1.0%, Cu 1.8%, Ti 0.3%, C 0.5%, with the balance being iron powder and unavoidable impurities; the iron powder consisted of 95% atomized iron powder and 5% carbonyl iron powder. The iron powder was placed in an electric furnace at 860℃ and heated for 40 minutes in a H2 atmosphere for reduction annealing.

[0058] 2. Mixing: Add internal lubricant at 0.2% of the total mass of the alloy powder raw materials. The mass fraction ratio of the components of the internal lubricant is: polytetrafluoroethylene: lithium stearate: molybdenum disulfide: copper powder: graphite powder: dispersant = 14:80:3:1:1.5:0.5. Place the pretreated iron powder, other alloy powder raw materials, and internal lubricant together in a powder mixer and stir for 90 minutes to ensure that the internal lubricant evenly coats the surface of the alloy powder raw materials, thus obtaining the mixture.

[0059] 3. Powder heating: Place the mixture in a barrel and heat it to 145℃ in a reducing protective atmosphere of 20% hydrogen + 80% helium and keep it at that temperature for 50 minutes to obtain the heated mixture.

[0060] 4. Warm pressing: A groove is machined in the annular die retaining ring, and a built-in heating element (heating wire) heats the die. A temperature measuring point is set on the back of the die to control the die temperature at 160℃ with a control accuracy of ±5℃. A die wall lubricant is sprayed onto the inner surface of the die using a high-pressure spray gun, with a spray thickness of 0.02-0.1mm. The die wall lubricant is a powder mixture of polytetrafluoroethylene and vinyl bis-stearamide in a ratio of 1.5:5. The heated mixture is loaded into the die through a powder feeder and pressed under a pressure of 820MPa for 5 minutes to obtain the green blank.

[0061] 5. Sintering treatment: The green blank is loaded into the vacuum sintering furnace at one time and sintered in two stages: the first stage is sintering at 510℃ for 1.5h; the second stage is to raise the temperature to 1250℃ and continue sintering for 2h; after sintering, the temperature is lowered to 780℃ and held for 30min in the cooling section, and finally naturally cooled to room temperature to obtain the sintered part.

[0062] 6. Post-processing: The sintered parts are subjected to carburizing and quenching surface strengthening treatment to achieve a surface hardness of 800HV0.2. Then, they are machined to obtain engine gear parts.

[0063] Example 2 This embodiment 2 provides a powder metallurgy warm pressing process, which differs from embodiment 1 in that: 1. The iron powder consists of 99% atomized iron powder and 1% carbonyl iron powder; 2. The reduction annealing time for iron powder is 60 minutes; 3. The amount of internal lubricant added is 0.1% of the total mass of the alloy powder raw material, and the internal lubricant ratio is polytetrafluoroethylene: lithium stearate: molybdenum disulfide: copper powder: graphite powder: dispersant = 12:82:3:1:1.5:0.5; 4. The powder heating temperature is 130℃, and the holding time is 60 minutes; 5. The mold heating temperature is 140℃, the temperature and pressure is 670MPa, and the holding time is 3min; the mold wall lubricant ratio is polytetrafluoroethylene: vinyl bis-stearamide = 1:6; 6. Sintering process: First stage: sintering at 450℃ for 2 hours; second stage: sintering at 1000℃ for 3 hours; cooling section: holding at 700℃ for 30 minutes.

[0064] Example 3 This embodiment 3 provides a powder metallurgy warm pressing process, which differs from embodiment 1 in that: 1. The iron powder consists of 97% atomized iron powder and 3% carbonyl iron powder; 2. The internal lubricant formulation is polytetrafluoroethylene: lithium stearate: molybdenum disulfide: copper powder: graphite powder: dispersant = 16:78:3:1:1.5:0.5, and the addition amount is 0.2% of the total mass of the alloy powder raw materials; 3. The powder heating temperature is 150℃, and the holding time is 30 minutes; 4. The mold heating temperature is 180℃, the thermostatic pressure is 860MPa, and the holding time is 4min; the mold wall lubricant ratio is polytetrafluoroethylene: vinyl bis-stearamide = 1:5; 5. Sintering process: First stage sintering at 550℃ for 1 hour, second stage sintering at 1350℃ for 1.5 hours, cooling section holding at 850℃ for 30 minutes.

[0065] Comparative Example 1 Comparative Example 1 provides a powder metallurgy warm pressing process, which differs from Example 1 in that the internal lubricant is a single lithium stearate powder, while the other process parameters are the same as in Example 1.

[0066] Comparative Example 2 This comparative example provides a powder metallurgy warm pressing process, which differs from Example 1 in that the sintering process is direct sintering at 1250℃ for 3.5h, without low-temperature pre-firing and cooling section heat preservation, while the other process parameters are the same as in Example 1.

[0067] Performance testing The powder metallurgical parts prepared in Examples 1-3 and Comparative Examples 1-2 were subjected to density, static strength, flexural fatigue strength, and surface hardness tests, respectively. All performance tests were performed using conventional standard methods in the art. Furthermore, the specific method for estimating the incremental process cost was as follows: Example 1 was used as the standard cost reference, and Examples 2 and 3, and Comparative Examples 1 and 2 were expressed based on this.

[0068] The test results are shown in Table 1.

[0069] Table 1 Test Results

[0070] Table 1 shows that the test data from Examples 1-3 and Comparative Examples 1-2 indicate that the embodiments of this application outperform the other embodiments in terms of key properties such as density, static strength, flexural fatigue strength, and surface hardness. Among them, the performance indicators of Example 1 are particularly outstanding, while the increase in process cost is at a moderate level. Considering the overall performance and the economics of industrial production, this solution can achieve excellent overall performance at a reasonable cost and is more suitable for the needs of industrial mass production. Therefore, Example 1 is the preferred solution of this invention.

[0071] Figure 5 The paper shows that the core porosity of the powder metallurgy gear in Example 1 of this application is 3.2% and the density is 7.6 g / cm³.

[0072] Figure 6 The Vickers hardness curves of the powder metallurgy gear of Embodiment 1 of this application are shown at different locations from the surface to the core. Combined with the hardness test report shown in Table 2, it can be seen that the surface hardness of the part reaches approximately 842 HV (0.1 mm from the surface), the effective hardened layer depth (based on a criterion of 550 HV) is approximately 1.09 mm, and the core hardness is approximately 547 HV (1.1 mm from the surface), demonstrating the performance characteristics of "high surface hardness and strong core toughness" after carburizing and quenching.

[0073] Table 2 Hardness Test Report

[0074] In the description of this specification, the references to terms such as "one embodiment / mode," "some embodiments / modes," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment / mode or example is included in at least one embodiment / mode or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment / mode or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments / modes or examples. Furthermore, without contradiction, those skilled in the art can combine and integrate the different embodiments / modes or examples described in this specification, as well as the features of different embodiments / modes or examples.

[0075] It should be noted that in this application, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. In this application, "a plurality of" means at least two, such as two, three, etc., unless otherwise expressly specified.

[0076] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A powder metallurgy warm pressing process, characterized in that, Includes the following steps: The alloy powder raw material and the internal lubricant are mixed to obtain a mixture; The mixture is heated in a reducing protective atmosphere to obtain a heated mixture; The heated mixture is fed into a mold for thermo-pressing treatment to obtain a green body; The green blank is sintered to obtain a powder metallurgy part. The internal lubricant includes polytetrafluoroethylene, lithium stearate, molybdenum disulfide, copper powder, graphite powder, and dispersant.

2. The powder metallurgy warm pressing process as described in claim 1, characterized in that, The mass ratio of the components in the internal lubricant is: polytetrafluoroethylene: lithium stearate: molybdenum disulfide: copper powder: graphite powder: dispersant = (12-16):(78-82):3:1:1.5:0.5; and / or, The amount of the internal lubricant added is 0.1-0.3% of the total mass of the alloy powder raw material; and / or, The alloy powder raw material comprises the following chemical components by mass fraction: Ni 0.8-1.2%, Mo 0.8-1.5%, Cu 1.5-2.5%, Ti 0.2-0.5%, C 0.2-1.0%, with the balance being iron powder and unavoidable impurities.

3. The powder metallurgy warm pressing process as described in claim 2, characterized in that, The iron powder satisfies at least one of the following conditions: The iron powder is composed of 95-99% atomized iron powder and 1-5% carbonyl iron powder, wherein the particle size of the atomized iron powder is 40-150 μm and the particle size of the carbonyl iron powder is not greater than 10 μm. The iron powder contains less than 0.1% O2. The iron powder contains less than 0.006% carbon (C). The N2 content in the iron powder is less than 0.0013%.

4. The powder metallurgy warm pressing process as described in claim 1, characterized in that, Before the mixing step of alloy powder raw materials and internal lubricant, the alloy powder raw material pretreatment step is also included: iron powder is placed in an electric furnace and heated for 40-60 min in H2 atmosphere to carry out reduction annealing treatment.

5. The powder metallurgy warm pressing process as described in claim 1, characterized in that, The heat treatment temperature is 130-150℃; and / or, The heat treatment time is 30-60 minutes.

6. The powder metallurgy warm pressing process as described in claim 1, characterized in that, The warm pressing process includes: heating the mold to 140-180℃, spraying mold wall lubricant on the inner surface of the mold, loading the heated mixture into the mold, warm pressing and molding under a pressure of 670-860MPa, and holding the pressure for 3-5 minutes.

7. The powder metallurgy warm pressing process as described in claim 6, characterized in that, The mold wall lubricant is a powder mixture of polytetrafluoroethylene and vinyl bis-stearamide, wherein the mass ratio of polytetrafluoroethylene to vinyl bis-stearamide is (1-3):(3-6); and / or, The thickness of the mold wall lubricant sprayed on the inner surface of the mold is 0.02-0.1 mm.

8. The powder metallurgy warm pressing process as described in claim 1, characterized in that, The sintering process includes: loading the green billet into the furnace once, sintering in two stages, cooling the temperature to 700-850℃ after sintering and holding it at that temperature, and finally cooling it naturally to room temperature. The first stage is sintering at 450-550℃ for 1-2 hours; the second stage is heating up to 1000-1350℃ and continuing to sinter for 1.5-3 hours.

9. The powder metallurgy warm pressing process according to any one of claims 1-8, characterized in that, It also includes post-processing steps: carburizing and quenching the sintered powder metallurgy parts to strengthen their surface, followed by machining.

10. A powder metallurgy part, characterized in that, The powder metallurgy part is prepared by any one of the powder metallurgy warm pressing process according to any one of claims 1-9.

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