On the deformation mechanism of austenitic stainless steel at elevated temperatures: A critical analysis of fine-grained versus coarse-grained structure

Abstract The novel concept of phase reversion involving severe cold deformation of austenite to martensite, followed by annealing when martensite reverts to austenite was used to obtain fine-grained (FG) 18Cr–8Ni austenitic stainless steel with high strength-high elongation combination. Through the application of the concept, the objective of the study is to study the deformation behavior and mechanism of austenitic stainless steel at elevated temperatures in the range of 25 °C–800 °C and compare with the as-received coarse-grained (CG) 18Cr–8Ni steel counterpart. The study clearly underscored that with the increase of temperature from 25 °C to 800 °C, the deformation mechanism in CG steel varied from TRIP at 25 °C, TWIP at 200 °C, dislocation slip at 600 °C to dynamic recrystallization + grain boundary sliding at 800 °C. Whereas, the deformation mechanisms in FG steel varied from primary TRIP + minor TWIP at 25 °C, primary TWIP + minor TRIP at 200 °C, primary grain boundary sliding + minor dislocation slip + TWIP at 600 °C to grain boundary sliding + dynamic recrystallization at 800 °C. The difference in deformation mechanism between CG and FG steels is a grain size effect and is related to the increase grain boundary density and stability of austenite with decrease in grain size.