For stainless steel powder metallurgy, in recent years has been valued by everyone. But the stainless steel powder metallurgy in the manufacturing process is easy to produce air gap, seriously affect the use, make the mechanical properties, corrosion resistance and wear resistance decreased, which limits its application in stainless steel in powder metallurgy. Therefore, in the development of stainless steel powder metallurgy, it is imperative to improve the density. Then, how to improve the density of stainless steel powder metallurgy?
Sintering by over solidus
1, the conventional sintering of stainless steel is usually solid phase sintering, however, solid sintering will result in a large number of pores remaining in the stainless steel. In addition, the liquid phase of stainless steel pre alloyed powder is sintered during the over phase liquid sintering, and the liquid phase fills the pores through flow to improve the density and performance of the sintered body.
2. The stainless steel obtained by over phase liquid phase sintering at 1400 C has higher density, hardness, wear resistance and corrosion resistance than that of solid phase sintering at 1200 C. Attention should be paid to avoiding the excessive growth and over burning of the grain due to the excessive sintering temperature.
Two, the use of suitable additives
1. Add some low melting point alloy elements to the powder to reduce porosity by sintering the liquid phase formed during sintering so that the stainless steel meets the higher performance requirements. For example, we used the 304 stainless steel, the copper alloy containing 2% - 8% which, due to the low melting point of copper, 960 DEG C to start forming a liquid phase, the formation of the liquid to 1000 degrees, when the temperature is higher than the melting point of copper, the liquid flow makes the surface pore ball and reduce continuously due to copper; have a good wettability, can be evenly distributed on the stainless steel substrate, the porosity of sintered body was significantly reduced, the hardness will be significantly improved.
2, to improve the performance of stainless steel powder metallurgy, can also be achieved by adding appropriate strengthening phase, especially mechanical properties. We used 316L stainless steel as an example, adding 1.5% ~ 3% of silicon carbide in stainless steel, because of the interaction between silicon carbide and stainless steel, the formation of low melting phase, improve sinter density, the hardness and wear resistance were improved.
The two methods described above are the longest used methods for increasing the metallurgical density of stainless steel powders. Compared with stainless steel produced by traditional smelting process, stainless steel powder metallurgy has the characteristics of close to net forming, high dimensional precision, high material utilization ratio and homogeneous structure. If the problem of the density of stainless steel powder metallurgy is solved, then this material will be widely used in production and life.
