Powder metallurgy stainless steel gasket and process for making

Abstract

The present application relates to the technical field of powder metallurgy, and discloses a powder metallurgy stainless steel gasket and a preparation process, the preparation process comprises the following steps: mixing superfine stainless steel powder with an appropriate oxygen content, boron powder and silicon powder; after compression molding, two-step sintering is carried out, that is, low-temperature pre-sintering and high-temperature densification; finally, the gasket is obtained through post-processing; the present application provides reaction raw materials through appropriate oxygen content, utilizes the synergistic effect of the preferential segregation of boron at the grain boundary to reduce and remove the continuous Cr oxide network and the generation of nano-SiO2 strengthening phase in the grain, and combines the two-step sintering timing control, so that the work hardening ability of the material is repaired while the ultrafine grain structure is retained, the problem that the ultrafine grain powder metallurgy stainless steel has high strength but poor plasticity is solved, and the synchronous improvement of strength and plasticity is realized.

Description

Technical Field

[0001] This invention relates to the field of powder metallurgy technology, and in particular to a powder metallurgy stainless steel gasket and its preparation process. Background Technology

[0002] Because carbon ceramic brake discs have an extremely low coefficient of thermal expansion, while metal wheel hubs have a high coefficient of thermal expansion, up to 80% of the interfacial thermal stress between the two needs to be buffered by gasket materials. In traditional technology, carbon steel is not corrosion resistant enough as a gasket, making it difficult to meet the dual requirements of corrosion resistance and strength under complex working conditions. Moreover, due to the limitations of sheet metal properties, it is difficult to form complex-shaped parts, and additional processing is required to improve performance, making the process quite complicated.

[0003] To address the limitations of carbon steel, the industry has attempted to use powder metallurgy to prepare stainless steel gaskets in order to improve corrosion resistance and material utilization. Using ultrafine-grained powders can achieve high strength through grain refinement, which offers the possibility of improving gasket performance. However, research has found that when the grain size is refined to the submicron scale, the work hardening capacity of the material decreases sharply, leading to early plastic instability during deformation. At the same time, ultrafine powders have a large specific surface area, and the oxygen adsorbed on the surface reacts with alloying elements such as chromium during sintering, forming a continuous chromium oxide network at the boundaries of the original powder particles. This intergranular oxide network becomes a preferential crack propagation channel, further exacerbating the loss of work hardening capacity. These two factors result in existing ultrafine-grained powder metallurgy stainless steels generally exhibiting the characteristics of high strength but poor plasticity.

[0004] To address the aforementioned issues, existing technologies have made various attempts. For example, Chinese patent application CN117020216A discloses a method for purifying grain boundaries in boron-doped molybdenum-tungsten refractory metals, achieving densification by adding boron and lowering the sintering temperature. Chinese patent application CN120715217A discloses a stainless steel part and its hot isostatic pressing preparation method and application, which addresses the common problem of original particle boundary precipitate defects in powder metallurgy stainless steel parts through a synergistic process of plasma activation combined with segmented hot isostatic pressing. The original particle boundary precipitates include various types such as carbides and oxides, among which grain boundary oxides are the main factor leading to intergranular brittle fracture. However, although the above technical solutions can improve density or improve the original particle boundary precipitation, they fail to effectively eliminate the intergranular oxide network from the perspective of restoring work hardening ability. While the prepared materials achieve high strength, the elongation is still not ideal. Summary of the Invention

[0005] The technical problem to be solved by this invention is: how to solve the problem of the imbalance between strength and plasticity of ultrafine-grained powder metallurgy stainless steel by repairing work hardening ability and eliminating grain boundary oxides while maintaining the fine-grain strengthening effect. To this end, we propose a powder metallurgy stainless steel gasket and its preparation process.

[0006] To achieve the above objectives, this application adopts the following technical solution: a powder metallurgy stainless steel gasket and its preparation process, characterized by the following steps: mixing ultrafine stainless steel powder with boron powder and silicon powder to obtain a mixed powder, wherein the oxygen content of the ultrafine stainless steel powder is 800-1500 ppm to provide an oxygen source for subsequent reactions; loading the obtained mixed powder into a gasket forming mold and pressing it on a powder press to obtain a pressed blank; placing the obtained pressed blank in a controlled atmosphere sintering furnace, firstly sintering at low temperature to preferentially agglomerate boron to the grain boundaries, and then reducing it with chromium oxides on the grain boundaries to eliminate the intergranular oxide network; secondly, densifying at high temperature to allow silicon to combine with oxygen inside the grains to generate a nano-SiO2 strengthening phase, while simultaneously achieving densification through liquid phase sintering; finally, cooling to obtain a sintered blank; and then deburring and dimensionally finishing the obtained sintered blank.

[0007] Preferably, the amount of boron powder added is 0.05-0.3 wt.%, and the amount of silicon powder added is 0.1-0.5 wt.%.

[0008] Preferably, the amount of boron powder added is 0.05-0.3 wt.%, and the average particle size is 2-5 μm.

[0009] Preferably, the amount of silicon powder added is 0.1-0.5 wt.%, and the average particle size is 3-8 μm.

[0010] Preferably, the temperature of the low-temperature sintering stage is 900-1000℃, and the temperature of the high-temperature densification stage is 1150-1200℃.

[0011] Preferably, the temperature in the low-temperature sintering stage is increased from room temperature to 950°C at a rate of 8°C / min.

[0012] Preferably, the temperature during the high-temperature densification stage is increased from room temperature to 1180°C at a rate of 15°C / min.

[0013] Preferably, the gasket has an ultrafine crystalline structure, with nanoscale oxide particles discontinuously distributed at the grain boundaries and nano-SiO2 reinforcing phases dispersed within the grains.

[0014] Preferably, the average grain size of the gasket is less than 1 μm, and the proportion of low-energy grain boundaries is not less than 32%.

[0015] Preferably, the strength-ductility product of the gasket is not less than 10000 MPa.

[0016] The technical effects and advantages of this invention are as follows:

[0017] In this invention, by controlling the oxygen content of the raw material powder within a suitable range, the necessary oxygen source for subsequent reactions is provided, while avoiding the problems of insufficient oxygen for borosilicates when the oxygen content is too low and oxide residue when it is too high. The synergistic effect is achieved by utilizing the differentiated behaviors of boron and silicon during sintering. Boron, with its small atomic radius and rapid diffusion, preferentially segregates to the grain boundaries during the low-temperature pre-sintering stage, disintegrating and volatilizing the continuously distributed intergranular Cr oxide network through an in-situ reduction reaction, thus cutting the channels for fracture propagation along the grain. Silicon, on the other hand, combines with oxygen within the grains to generate a nano-SiO2 dispersed strengthening phase, further enhancing strength reserves and achieving a unified approach to grain boundary purification and intragranular strengthening. A sintering process of first low-temperature purification and then high-temperature densification is employed, allowing boron to thoroughly clean the grain boundaries before rapidly increasing the temperature to achieve densification. This timing control ensures sufficient boron segregation and reaction at the grain boundaries while avoiding grain coarsening at high temperatures, thus simultaneously completing grain boundary purification and densification while preserving the ultrafine grain structure. Attached Figure Description

[0018] The disclosure of this invention is illustrated with reference to the accompanying drawings. It should be understood that the drawings are for illustrative purposes only and are not intended to limit the scope of protection of this invention. In the drawings, the same reference numerals are used to refer to the same parts:

[0019] Figure 1 This is a schematic diagram of the powder metallurgy stainless steel gasket and its preparation process according to the present invention. Detailed Implementation

[0020] It is readily understood that, based on the technical solution of this invention, those skilled in the art can propose various interchangeable structural methods and implementations without altering the essential spirit of the invention. Therefore, the following detailed embodiments and accompanying drawings are merely illustrative examples of the technical solution of this invention and should not be considered as the entirety of the invention or as limitations or restrictions on the technical solution of this invention.

[0021] Unless otherwise specified, the raw materials and equipment used in this invention are all commercially available products in the field. The following describes the raw materials involved in the specific embodiments of this invention.

[0022] The stainless steel powder is gas-atomized 304L austenitic stainless steel powder. The oxygen content of the powder is controlled by adjusting the atomization process parameters, and the powder particle size D50 is controlled at 8-12μm to ensure the foundation of ultrafine grain strengthening.

[0023] To control the oxygen content, the oxygen partial pressure of the atomizing medium was changed during the atomization process to obtain powder raw materials with different oxygen contents. The oxygen content was determined by the inert gas melting method, in accordance with the GB / T 11261-2006 standard "Determination of Oxygen Content in Steel - Pulse Heating Inert Gas Melting-Infrared Absorption Method".

[0024] Boron powder has a purity of >99.5% and an average particle size of 2-5μm, while silicon powder has a purity of >99% and an average particle size of 3-8μm. They are mixed with stainless steel powder using a V-type mixer for 4 hours at a speed of 25 rpm / min to ensure uniform distribution.

[0025] Example 1

[0026] The present invention provides a powder metallurgy stainless steel gasket and its preparation process, which includes the following steps.

[0027] S1: Powder ingredients

[0028] Take 100 kg of 304L ultrafine austenitic stainless steel powder with an oxygen content of 1050 ppm and a D50 of 9.5 μm, add 0.15 kg of boron powder (0.15 wt.%) and 0.3 kg of silicon powder (0.3 wt.%), and mix in a V-type mixer for 4 hours at a speed of 25 r / min.

[0029] S2: Compression molding

[0030] The mixed powder was loaded into a gasket molding die and pressed on a 100-ton powder press at a pressure of 65 MPa for 15 seconds, yielding a density of approximately 6.2 g / cm³. 3 The pressed blank.

[0031] S3: Two-step sintering

[0032] The compact was placed in a controlled atmosphere sintering furnace and sintered using high-purity argon gas at a flow rate of 20 L / min, following the process described below:

[0033] The first stage involves heating to 950℃ at a rate of 8℃ / min and holding for 45 minutes.

[0034] The second step involves rapidly increasing the temperature to 1180℃ at a rate of 15℃ / min and holding it at that temperature for 90 minutes.

[0035] In the third stage, the temperature is reduced to below 200℃ at a rate of 10℃ / min, and then cooled with the furnace.

[0036] S4: Post-processing

[0037] After sintering, the gaskets are deburred and dimensionally adjusted.

[0038] Example 2

[0039] This embodiment provides a powder metallurgy stainless steel gasket and its preparation process. Compared with Embodiment 1, the difference is as follows:

[0040] 304L powder with an oxygen content of 800ppm was used, and other parameters were the same.

[0041] Example 3

[0042] This embodiment provides a powder metallurgy stainless steel gasket and its preparation process. Compared with Embodiment 1, the difference is as follows:

[0043] 304L powder with an oxygen content of 1500ppm was used, and other parameters were the same.

[0044] Example 4

[0045] This embodiment provides a powder metallurgy stainless steel gasket and its preparation process. Compared with Embodiment 1, the difference is as follows:

[0046] The amount of boron powder added was 0.05 wt.%, and the amount of silicon powder added remained unchanged at 0.3 wt.%.

[0047] Example 5

[0048] This embodiment provides a powder metallurgy stainless steel gasket and its preparation process. Compared with Embodiment 1, the difference is as follows:

[0049] The amount of boron powder added is 0.3 wt.%, and the amount of silicon powder added remains unchanged at 0.3 wt.%.

[0050] Example 6

[0051] This embodiment provides a powder metallurgy stainless steel gasket and its preparation process. Compared with Embodiment 1, the difference is as follows:

[0052] The amount of silicon powder added is 0.1 wt.%, and the amount of boron powder added remains unchanged at 0.15 wt.%.

[0053] Example 7

[0054] This embodiment provides a powder metallurgy stainless steel gasket and its preparation process. Compared with Embodiment 1, the difference is as follows:

[0055] The amount of silicon powder added is 0.5 wt.%, and the amount of boron powder added remains unchanged at 0.15 wt.%.

[0056] Example 8

[0057] This embodiment provides a powder metallurgy stainless steel gasket and its preparation process. Compared with Embodiment 1, the difference is as follows:

[0058] The temperature was increased to 1200℃ at a rate of 15℃ / min and held for 90 minutes, while other parameters remained unchanged.

[0059] Example 9

[0060] This embodiment provides a powder metallurgy stainless steel gasket and its preparation process. Compared with Embodiment 1, the difference is as follows:

[0061] The temperature was increased to 1150℃ at a rate of 15℃ / min and held for 90 minutes, while other parameters remained unchanged.

[0062] Example 10

[0063] This embodiment provides a powder metallurgy stainless steel gasket and its preparation process. Compared with Embodiment 1, the difference is as follows:

[0064] The temperature was increased to 900℃ at a rate of 8℃ / min and held for 45 minutes, while other parameters remained unchanged.

[0065] Example 11

[0066] This embodiment provides a powder metallurgy stainless steel gasket and its preparation process. Compared with Embodiment 1, the difference is as follows:

[0067] The temperature was increased to 1000℃ at a rate of 8℃ / min and held for 45 minutes, while other parameters remained unchanged.

[0068] Comparative Example 1

[0069] This comparative example provides a powder metallurgy stainless steel gasket and its preparation process. The difference between this example and Example 1 is that:

[0070] The gaskets are made of Q235-A carbon steel stamped sheets purchased from the market, with a thickness of 3mm, and have not undergone subsequent heat treatment.

[0071] Comparative Example 2

[0072] This comparative example provides a powder metallurgy stainless steel gasket and its preparation process. The difference between this example and Example 1 is that:

[0073] 304L stainless steel gaskets were prepared using conventional powder metallurgy processes. The 304L powder had an oxygen content of 350 ppm and a D50 of 25 μm. No boron powder or silicon powder was added. The gaskets were pressed at a pressure of 600 MPa and sintered at 1200℃ for 90 minutes in an atmosphere of decomposed ammonia, with the main components being 75% hydrogen and 25% nitrogen. No pressure assistance was used.

[0074] Comparative Example 3

[0075] This comparative example provides a powder metallurgy stainless steel gasket and its preparation process. The difference between this example and Example 1 is that:

[0076] No boron powder or silicon powder is added, but all other parameters remain the same.

[0077] Comparative Example 4

[0078] This comparative example provides a powder metallurgy stainless steel gasket and its preparation process. The difference between this example and Example 1 is that:

[0079] Add 0.02 wt.% boron powder, do not add silicon powder, and keep other parameters the same.

[0080] Comparative Example 5

[0081] This comparative example provides a powder metallurgy stainless steel gasket and its preparation process. The difference between this example and Example 1 is that:

[0082] Add 0.05 wt.% silicon powder, do not add boron powder, and keep other parameters the same.

[0083] Comparative Example 6

[0084] This comparative example provides a powder metallurgy stainless steel gasket and its preparation process. The difference between this example and Example 1 is that:

[0085] 316L powder with a D50 of 10 μm and 430 powder with a D50 of 12 μm were mixed at a mass ratio of 65:35 without adding boron powder or silicon powder. The mixture was then cold isostatically pressed at 200 MPa and sintered at 1350 °C for 60 minutes to obtain a bimodal stainless steel.

[0086] The gasket samples prepared in Examples 1-8 and Comparative Examples 1-6 were subjected to systematic performance tests to verify the effectiveness of the technical solution of the present invention and the impact of each process feature on product performance.

[0087] The microstructure characteristics of each embodiment and comparative example were detected as follows, and the results are shown in Table 1.

[0088] Density was determined according to GB / T 5163-2006 "Determination of Density, Oil Content and Porosity of Sintered Metallic Materials" using the Archimedes' water displacement method. Five samples were tested per group, and the average value was taken as the actual density. The percentage of the actual density to the theoretical density of the material was calculated, which is the compacted density. The formula is as follows:

[0089]

[0090] Where ρ is the packing density; ρ 理论 ρ is the theoretical density of stainless steel. 实际 This represents the actual density of the sample.

[0091] Crystal size was determined in accordance with GB / T 6394-2017 "Method for determination of average grain size of metals" and GB / T 13298-2015 "Method for examination of microstructure of metals".

[0092] The proportion of low-energy grain boundaries was determined in accordance with GB / T 36165-2018 "Determination of Average Grain Size of Metals by Electron Backscatter Diffraction" and GB / T 30705-2014 "Guidelines for Determination of Experimental Parameters of Microbeam Analysis Electron Probe Microscopic Analysis Spectroscopy", with reference to ASTM E2627-2019 "Quantitative Analysis Standard of Electron Backscatter Diffraction".

[0093] Table 1. Microstructural characteristics of each embodiment and comparative example.

[0094]

[0095] Note: Comparative Example 1 was not characterized at the microstructure level.

[0096] As can be seen from Table 1, the microstructure of Example 1 shows an average grain size of 0.95 μm and a low-energy grain boundary ratio of 32.5%. Comparative Example 3, without the addition of boron and silicon, also obtained an ultrafine grain structure, but the low-energy grain boundary ratio was only 16.5%. The low-energy grain boundary ratios of Comparative Examples 4 and 5 were 23.5% and 19%, respectively, both lower than that of Example 1. This indicates that the synergistic addition of boron and silicon has a positive effect on increasing the low-energy grain boundary ratio. Even under lower pressing pressure and pressureless sintering conditions, the grain boundary segregation and reduction reaction of boron can still occur effectively.

[0097] The mechanical properties and corrosion resistance of each embodiment and comparative example were tested as follows, and the results are shown in Table 2.

[0098] The Rockwell hardness tester was used to perform HRB scale tests according to GB / T 230.1-2018 "Metallic materials Rockwell hardness test - Part 1: Test method". The sample surface was ground and polished. Five different points were tested on each sample, and the arithmetic mean was taken as the final hardness value.

[0099] The tensile strength, yield strength and elongation were determined in accordance with GB / T 228.1-2021 "Metallic materials - Tensile testing - Part 1: Test method at room temperature" and GB / T7964-2020 "Sintered metallic materials - Tensile testing at room temperature". A universal testing machine was used, and the specimens were standard dog bone tensile specimens. The tensile rate was 1 mm / min. Three specimens were tested for each formulation, and the average value was taken to obtain the tensile strength, yield strength and elongation.

[0100] The test was conducted according to ASTM B895-16, "Standard Test Method for Evaluating the Corrosion Resistance of Stainless Steel Powder Metallurgy Components / Specimens by Immersion in Sodium Chloride Solution". The specimens were completely immersed in a 5% NaCl solution and removed for observation every 24 hours. The time when the first rust or staining appeared on the specimen surface was recorded. At the same time, a neutral salt spray test (NSS) was performed according to GB / T10125-2021, "Artificial Atmosphere Corrosion Test - Salt Spray Test". After 48 hours of continuous spraying, the corrosion status of the specimen surface was observed.

[0101] Table 2 Mechanical properties and corrosion resistance of each embodiment and comparative example

[0102]

[0103] As shown in Table 2, the yield strength of Example 1 was 452 MPa and the elongation was 26.5%. Although the yield strength of Comparative Example 3 reached 380 MPa, the elongation was only 6.5%. Although the elongation of Comparative Example 6 reached 32.5%, the yield strength was only 285 MPa. The elongation of Comparative Example 4 was 12.8%, and the elongation of Comparative Example 5 was 11.5%, all of which were significantly lower than that of Example 1, verifying the effect of borosilicate synergy in suppressing intergranular brittle fracture.

[0104] The yield strength and elongation of Example 1 are higher than those of Examples 2 and 3, indicating that the oxygen effect of borosilicate is limited when the oxygen content is too low, and the purification capacity is insufficient when it is too high. 800-1500 ppm is the suitable range.

[0105] Comparing the low-temperature pre-sintering temperatures, the elongation of Examples 10 and 11 was lower than that of Example 1, indicating that 950℃ is a better low-temperature pre-sintering temperature. Comparing the high-temperature densification temperatures, the elongation of Examples 8 and 9 was lower than that of Example 1, indicating that 1180℃ is a better high-temperature densification temperature. Comparing two-step sintering with one-step sintering, the average grain size of Example 8 was larger than that of Example 1, the proportion of low-energy grain boundaries was lower than that of Example 1, and the yield strength and elongation were both lower than those of Example 1, confirming the key role of the low-temperature pre-sintering stage in grain boundary purification.

[0106] The correlation analysis between grain boundary characteristics and mechanical properties of some comparative examples and embodiments was conducted, and the results are shown in Table 3.

[0107] The continuous oxide at grain boundaries shall be determined in accordance with YB / T 6121-2023 "Method for Determination of Intergranular Oxidation Depth in Steel" and GB / T30705-2014 "Guidelines for Determination of Experimental Parameters of Electron Probe Microscopy for Microscopic Analysis".

[0108] The intracrystalline nanophase was determined in accordance with GB / T 30544.5-2014 "Nanotechnology Terminology Part 5: Nano / Bio Interfaces", GB / T 30705-2014 "Guidelines for Determination of Experimental Parameters of Electron Probe Microscopy for Microscopic Analysis", and ISO / TS10798:2011 "Characteristics of Single-Wall Carbon Nanotubes for Transmission Electron Microscopy in Nanotechnology".

[0109] The grain boundary type was analyzed using electron backscatter diffraction (EBSD). The sample was vibratory polished to eliminate the surface stress layer. Data was acquired using an EBSD probe on a scanning electron microscope with a step size of 0.1 μm. Data analysis was performed according to GB / T 18876.1-2024 "Standard Test Method for Determination of Metallographic Structure, Inclusion Content and Grade in Steel and Other Metals by Automated Image Analysis". The proportion of Σ3 twin boundaries and Σ9 grain boundaries was statistically analyzed.

[0110] The strength-ductility product characterizes a material's ability to absorb energy before fracture. A higher strength-ductility product indicates better overall performance, combining high strength and high ductility. It is commonly used as an important reference indicator for evaluating the strength-ductility balance of advanced high-strength steels and powder metallurgy materials, and is calculated using the following formula:

[0111]

[0112] Where P is the strength-plasticity product, in MPa·%; R m A represents tensile strength, in MPa; A represents elongation after fracture, in %.

[0113] Table 3 Correlation analysis between grain boundary characteristics and mechanical properties

[0114]

[0115] Table 3 further reveals the relationship between microstructure and performance. Example 1 achieved the highest strength-plasticity product due to its clean grain boundaries, the presence of a large number of nano-reinforcing phases within the grains, and the high proportion of low-energy grain boundaries. This is much higher than that of Comparative Example 3 and Comparative Example 6. This shows that the present invention achieves a good balance between strength and plasticity by purifying grain boundaries and optimizing grain boundary characteristics while maintaining ultrafine grain reinforcement.

[0116] The technical scope of this invention is not limited to the content described above. Those skilled in the art can make various modifications and variations to the above embodiments without departing from the technical concept of this invention, and all such modifications and variations should fall within the protection scope of this invention.

Claims

1. A process for preparing powder metallurgy stainless steel gaskets, characterized in that: Includes the following steps: S1: Mix ultrafine stainless steel powder with boron powder and silicon powder to obtain a mixed powder, wherein the oxygen content of the ultrafine stainless steel powder is 800-1500ppm, providing an oxygen source for subsequent reactions; S2: The mixed powder obtained in S1 is loaded into a gasket forming mold and pressed on a powder press to obtain a pressed blank; S3: The compact obtained in S2 is placed in a controlled atmosphere sintering furnace. The first step is to sinter at low temperature to allow boron to preferentially agglomerate to the grain boundaries and undergo a reduction reaction with the chromium oxide on the grain boundaries to eliminate the intergranular oxide network. The second step is to densify at high temperature to allow silicon to combine with oxygen inside the grains to generate nano-SiO2 strengthening phase. At the same time, densification is achieved through liquid phase sintering. Finally, the compact is cooled to obtain the sintered compact. S4: The sintered blank obtained in S4 is deburred and dimensionally finished.

2. The preparation process of the powder metallurgy stainless steel gasket according to claim 1, characterized in that: The amount of boron powder added is 0.05-0.3 wt.%, and the average particle size is 2-5 μm.

3. The preparation process of the powder metallurgy stainless steel gasket according to claim 1, characterized in that: The amount of silicon powder added is 0.1-0.5 wt.%, and the average particle size is 3-8 μm.

4. The preparation process of the powder metallurgy stainless steel gasket according to claim 1, characterized in that: The temperature of the low-temperature sintering stage is 900-1000℃, and the temperature of the high-temperature densification stage is 1150-1200℃.

5. The preparation process of the powder metallurgy stainless steel gasket according to claim 4, characterized in that: The temperature during the low-temperature sintering stage is increased from room temperature to 950°C at a rate of 8°C / min.

6. The preparation process of the powder metallurgy stainless steel gasket according to claim 4, characterized in that: The temperature during the high-temperature densification stage is increased from room temperature to 1180°C at a rate of 15°C / min.

7. The preparation process of the powder metallurgy stainless steel gasket according to claim 1, characterized in that: The average particle size D50 of the ultrafine stainless steel powder is 8-12 μm.

8. A powder metallurgy stainless steel gasket prepared by the preparation method according to any one of claims 1-7, characterized in that, The gasket has an ultrafine crystalline structure with nanoscale oxide particles discontinuously distributed at the grain boundaries and nano-SiO2 reinforcing phases dispersed within the grains.

9. The powder metallurgy stainless steel gasket according to claim 8, characterized in that: The average grain size of the gasket is less than 1 μm, and the proportion of low-energy grain boundaries is not less than 32%.

10. The powder metallurgy stainless steel gasket according to claim 8, characterized in that: The strength-ductility product of the gasket is not less than 10000 MPa.

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