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In this investigation, a precipitation hardenable martensitic stainless steel (12Cr-10Ni-0.25Ti-0.7Mo) was subjected to different heat treatment cycles to study their influence on the microstructure and mechanical properties. The heat treatment cycles include solution treatment (S), cryogenic treatment (C), and aging (A). Two solution treatment temperatures, 750 and 1000°C, and two aging temperatures, 250 and 500°C, were selected. Solution treatment was followed by a cryogenic treatment at-70°C for 2 h and an aging treatment at the aforementioned temperatures. Transmission electron microscopy of the solution-treated samples showed four phases: martensite matrix, M 23 C 6 carbide, Ti(C, N), and retained austenite. On aging at 500°C, an additional phase (Ni 3 Ti precipitates) was observed in the martensite matrix. Mechanical properties were evaluated at room temperature for all the heat-treated samples. A reasonable increase in yield strength (YS) was observed after cryogenic treatment possibly due to transformation of retained austenite to martensite. After aging at 500°C, a significant increase in the YS was observed over solution-treated condition. This increase in YS after aging is attributed to precipitation of fine Ni 3 Ti precipitates. Solution treatment temperature had an insignificant effect on the mechanical properties of the stainless steel.

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