Breaking the strength-ductility trade-off in austenitic stainless steel at cryogenic temperatures: Mechanistic insights

At cryogenic temperatures, 316L austenitic stainless steel (ASS) exhibits remarkable strength while retaining high ductility, defying the conventional stress-strain trade-off. Despite extensive studies documenting the cryotensile properties of ASSs, the underlying mechanisms behind this phenomenon remain largely unexplored. This study systematically re-examines the tensile properties of 316L stainless steel and the associated mechanisms across a range of low temperatures (293 K, 223 K, 123 K, and 77 K). The reasons for the superior stress-strain balance (similar to 80 % GPa) are discussed using results from electron backscatter diffraction (EBSD) microstructure characteristics. The results undoubtedly suggest that the transformation mechanisms, specifically the shift from deformation twinning to martensitic transformation (gamma -> epsilon -> alpha '), play a crucial role in enhancing elongation at cryogenic temperatures. At these temperatures, the Gibbs free energy difference between epsilon-martensite and gamma-austenite approaches zero, resulting in slow martensite growth. The stress-strain curves at low temperatures satisfy the Considere criterion, indicating delayed necking under these conditions. This behavior is ascribed to the presence of various hierarchical microstructures, including epsilon, alpha ', gamma-twins, epsilon-twins and their intersections, which act as sources of work hardening. This study provides new insights into deformation behavior of ASSs under cryogenic conditions.