Effect of annealing treatment at 550 °C on ferrite of thermally aged cast austenitic stainless steels and ageing kinetics of reverted cast austenitic stainless steels

Abstract Ageing of Cast Austenitic Stainless Steels (CASS) was attributed to the decomposition of the ferrite by spinodal decomposition and precipitation of G-phase particles. This leads to an increase in hardness and a decrease in Charpy-impact energy. It is possible to restore the mechanical properties of these steels by annealing treatment above the Fe-Cr miscibility gap in order to dissolve α’ phase. In this work, an annealing treatment for 2 h at 550 °C followed by water quenching was applied to various Mo-free and Mo-bearing steels. This treatment allowed to restore almost completely the mechanical properties of Mo-free steels and partly Mo-bearing steels regardless of the initial ageing time. The mechanical property changes were attributed to the complete dissolution of spinodal decomposition and complete or partial dissolution of G-phase particles. After annealing, a re-ageing kinetics was studied. The preexisting G-phase particles have minor influence on the kinetic of spinodal decomposition until 2,400 h at 400 °C.