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

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 degrees C-800 degrees 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 degrees C to 800 degrees C, the deformation mechanism in CG steel varied from TRIP at 25 degrees C, TWIP at 200 degrees C, dislocation slip at 600 degrees C to dynamic recrystallization + grain boundary sliding at 800 degrees C. Whereas, the deformation mechanisms in FG steel varied from primary TRIP + minor TWIP at 25 degrees C, primary TWIP + minor TRIP at 200 degrees C, primary grain boundary sliding + minor dislocation slip + TWIP at 600 degrees C to grain boundary sliding + dynamic recrystallization at 800 degrees 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.