How to improve the sealing performance of powder metallurgy parts

How to improve the sealing performance of powder metallurgy stainless steel seals? Ningbo City Haixin Xin Bang Powder Metallurgy Co., Ltd. powder metallurgy stainless steel seals production and processing.
Stainless steel is usually produced by smelting process. Because of its difficulty in cutting and machining, there are insufficient dimensions and roughness in the parts made, so there are still many technical problems in the manufacturing of stainless steel. Compared with the stainless steel produced by traditional smelting process, PM stainless steel has the advantages of close to net forming, high precision, high material utilization and uniform structure, and has been widely used in machinery, chemical industry, ship, automobile, instrument and instrument and other industries.
However, because of the pores in the powder metallurgy stainless steel, the mechanical properties, wear resistance, corrosion resistance and sealing properties of the stainless steel are greatly reduced, which seriously restricts its application. The results show that almost all properties of powder metallurgy stainless steel increase with the increase of density. Therefore, how to improve the density and reduce porosity of powder metallurgy stainless steel is the key to improve the properties of powder metallurgy stainless steel.
1. The sintering of the super solid phase line.
Conventional stainless steel sintering generally uses solid-phase sintering. However, during solid phase sintering, a large amount of pores will be left inside the stainless steel, resulting in a decrease in its density and properties. In recent years, the liquid-phase sintering of super solid phase lines has been used to make the stainless steel pre alloyed powder form liquid phase, and the liquid phase fills the pores through the flow to improve the density and properties of the sintered body. Different from ordinary liquid phase sintering, the liquid phase sintering of the super solid phase line is the sintering of the pre alloy powder, and it is always a single phase during the sintering process. The sintering temperature is between the solid phase and the liquidus. At that temperature, the grain, grain boundary and particle surface of the pre alloyed powder particles are formed into liquid phase, and the particles are realized under the action of liquid capillary force.  Rearrangement, the place where the surface curvature change is larger will be dissolved first, through the liquid phase flow mass transfer, precipitation in the large particle sags or pores, to achieve the purpose of rapid transfer of material, thus making the sintered body to be compact. It is reported that the density, hardness, wear resistance and corrosion resistance of 316L stainless steel obtained at 1400 C by supersolid phase liquid phase sintering are higher than that of solid phase sintered products at 1200 C. However, due to the high sintering temperature, excessive grain growth and overburning should be avoided.
Two. Use the appropriate additives.
Adding some low melting point alloy elements to the powder can greatly reduce the porosity by the liquid phase formed during the sintering, thus making the stainless steel meet the higher performance requirements. For example, adding 2% to 8% copper based alloys in 304 stainless steel powder, because the melting point of copper is low, the liquid phase is formed at 960 C, and the liquid phase is formed at 1000 C. When the temperature is higher than the melting point of copper, the flow of liquid makes the surface pores continuously spheroidizing and narrowing; because copper has a good wettability to the stainless steel matrix, it can be evenly distributed. On the stainless steel substrate, the porosity of the sintered body decreased significantly and the microhardness increased. When the addition amount is 8%, the density increases after sintering at 1350 7.05g/cm3.
The properties of the powder metallurgy stainless steel can be improved by adding appropriate hardening phase, especially the mechanical properties. For example, adding 1.5%~3% (volume fraction) SiC to 316L stainless steel has formed a Fe-SiC phase with low melting point due to the interaction between SiC and stainless steel matrix, which improves the density of the sintered body, and increases the hardness, wear resistance and sealing properties of the sintered body.