Influence of tempering treatment on microstructure and pitting corrosion of 13 wt.% Cr martensitic stainless steel

Tempering of 13 wt.% Cr martensitic stainless steel resulted in nano-sized M3C carbides at 300 °C, nano-sized Cr-rich M23C6 carbides at 550 °C and sub-micron sized Cr-rich M23C6 carbides at 700 °C. Austenitization resulted in lath martensite with undissolved M23C6 carbides. Pitting resistance for tempered condition was lower than the austenitized condition with least resistance at 550 °C. The observation was attributed to the presence of a Fe-rich surface film and massive carbide precipitation with a Cr depletion zone of 7-9 nm at carbide interface for 550 °C tempered condition as opposed to a Cr-enriched passive film for the austenitized condition.