How to improve the density of stainless steel powder metallurgy?

In the production process of stainless steel powder metallurgy, it is easy to produce porosity, which seriously affects the use of stainless steel powder metallurgy and makes its mechanical properties, corrosion resistance and wear resistance decrease, which seriously limits its application in stainless steel powder metallurgy.

A, super solid-phase line sintering

1, the traditional stainless steel sintering generally uses solid-phase sintering, but solid-phase sintering will produce a large number of residual pores in stainless steel. Super solid-phase line liquid-phase sintering makes stainless steel pre-alloy powder in the sintering process to form a liquid phase. The liquid phase fills the pores through flow to improve the density and properties of the sintered body.

2, 1400 ℃ super solid-phase line liquid-phase sintering of stainless steel density, hardness, wear resistance and corrosion resistance are higher than 1200 ℃ solid-phase sintering should be careful to avoid excessive grain growth and excessive combustion due to high sintering temperature.

B, the use of appropriate additives

1, add some low melting point alloying elements in the powder, through the liquid phase formed during the sintering process to reduce the porosity, so that stainless steel can meet the higher performance requirements. For example, the commonly used 304 stainless steel with 2%-8% copper-based alloy. Due to the low melting point of copper, the liquid phase can be formed at 960°C, and all the liquid phase can be formed at 1000°C. When the temperature is higher than the melting point of copper, the liquid phase flows so that the surface porosity is continuously terraformed and contracted, and can be uniformly distributed due to the good wettability of copper. On the stainless steel substrate, the sintered body is made. With the reduction of the pores, the microhardness also increases.

2, in order to improve the performance of stainless steel powder metallurgy, you can add the appropriate strengthening phase, especially mechanical properties. Take 316L stainless steel as an example, add 1.5%-3% silicon carbide to the stainless steel. Due to the interaction between silicon carbide and stainless steel, a low melting point phase is formed, which increases the density of the sintered body and improves the hardness and wear resistance of the sintered body.

Powder premixing process, due to the different specific gravity of different components of the particles, will lead to the mixing process of powder segregation phenomenon, the binder effectively improve the segregation, the powder due to different particle size, uneven distribution of easy to cause porosity, the binder can make a reasonable distribution of particles, fill the pores, improve the strength of the press billet.

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