Hot Working Characteristic of Superaustenitic Stainless Steel 254SMO

Hot deformation characteristic of superaustenitic stainless steel 254SMO has been studied by isothermal compression testing in the temperature range of 950–1,200 °C and strain rate range of 0.01–10 s^-1. The activation energy of 496 kJ/mol was calculated by a hyperbolic-sine type equation over the entire range of strain rates and temperatures. In order to obtain optimum hot working conditions, processing maps consisting of power dissipation map and instability map were constructed at different strains. The power dissipation map exhibits two domains with relatively high efficiencies of power dissipation. The first domain occurs in the temperature range of 990–1,070 °C and the strain rate range of 0.01–0.1 s^-1. Microstructure observation in this domain indicates the partial dynamic recrystallization (DRX) accompanied with precipitation of tetragonal sigma phase. The second domain occurs in the temperature range of 1,140–1,200 °C and the strain rate range of 0.01–1 s^-1 with a peak efficiency of power dissipation of 39%, and in this domain, the microstructure observation reveals the full DRX. The instability map shows that flow instability occurs at the temperatures below 1,140 °C and the strain rates above 0.1 s^-1.