Effect of the High-Temperature Deformation on the M _s Temperature in a Low C Martensitic Stainless Steel

The effects of cooling rate and plastic deformation at 1100 °C on the start of the austenite-to-martensite transformation in a low carbon Fe-12Cr stainless steel were investigated by dilatometry and thermal analysis of pre-strained samples. The experimental M _s was found constant (397.2 °C) for cooling rates between 15 and 30 °C/min. Outside this range, the M _s apparently decreases as the cooling rate decreases below 15 °C/min or increases above 30 °C/min. An overall average value of 380.9 ± 11.8 °C was observed within the complete range of cooling rates investigated (8-40 °C/min). This value is 50 °C higher than that predicted from the chemical composition of the steel and Andrews’ equation for M _s. Prior plastic deformation of austenite at 1100 °C increases the M _s temperature and broadens the martensitic domain (M _f-M _s). This effect increases as the magnitude of the applied pre-strain increases.