• martensitic stainless steel;
  • cryo treatment;
  • aging

In the present investigation, 15Cr-5Ni-1Mo-1W martensitic stainless steel was studied for the microstructure and mechanical properties after heat treatment (solution treatment, cryo treatment, and aging). A combination of high strength and ductility was obtained by cryo treatment (−70°C for 2 h), and aging (500°C for 2 h). Transmission electron microscopy (TEM) and X-ray diffraction (XRD) were employed to identify the phases in the steel. TEM studies have shown the presence of retained austenite and large (Nb,V)C carbides in the martensite matrix after solution treatment. Aging at 500°C for 2 h has shown precipitation of fine Mo2C precipitates in the martensite matrix. The increase in strength after cryo treatment and aging is attributed to transformation of retained austenite and precipitation of fine Mo2C precipitates, respectively. The yield strength of the steel in aged condition calculated based on the Orowan strengthening is in good agreement with the experimental value considering the softening induced by reversed austenite. The present steel showed yield strength and ultimate tensile strength of 1050 and 1235 MPa, respectively with a ductility of 20.4%. This paper brings out the details of the investigation results and a correlation between microstructure and strength.