Tempering reactions and elemental redistribution during tempering of martensitic stainless steels

Tempering reactions in the martensite phase of Fe-13Cr-0.47C (mass pct) stainless steel and its Si- and Mn-added modifications were studied by correlative dilatometry and magnetic measurements. Tempering for 5 minutes was performed at sequentially higher temperatures up to 923 K (650 °C). Classical tempering reactions including the segregation of C atoms at defects, precipitation of M3C and Cr-rich carbides, and austenite decomposition were clearly identified. The formation of M3C carbides was partially and entirely suppressed by Mn and Si additions, respectively. Compared to low-alloy steels, the decomposition of retained austenite in stainless steels was delayed to temperatures above 823 K (550 °C). The latter occurred concurrently with the formation of Cr-rich carbides in the martensite. In addition, non-classical tempering reactions such as the partial dissolution of C clusters at temperatures above 573 K (300 °C) and the short-range diffusion of substitutional elements including Cr and Mn to C clusters and M3C carbides in the temperature range of 673 K to 823 K (400 °C to 550 °C) were identified based on the associated increase in the magnetization.