Post-sintering thermal treatment of nitrogen containing pressed and sintered and PIM stainless steels

Abstract

It is known that nitrogen in the sintering atmosphere impairs the corrosion resistance but enhances the strength and hardness of sintered stainless steels. In this study, an additional post-sintering thermal treatment was applied on parts that were sintered in N₂ containing atmospheres and its effects on the mechanical properties and corrosion resistance were evaluated. Both pressed and sintered (P/S) 304L and powder injection moulded (PIM) 316L stainless steel compacts were examined. The results show that the Cr₂N compound was formed throughout the low density 304L compact, causing poor corrosion resistance when there was nitrogen in the sintering atmosphere. However, the high density PIM 316L compact only contained Cr₂N at the surfaces owing to the high sintering temperature and the lack of interconnected pores. This Cr₂N compound can be suppressed when the compact is reheated to 1100°C in argon and then cooled at a moderate rate of 57°C min⁻¹. With this post-sintering treatment, even the compact sintered in pure nitrogen showed satisfactory corrosion resistance results, similar to those of hydrogen sintered compacts.