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

At cryogenic temperatures, 316L austenitic stainless steels (ASSs) exhibit remarkable strength while retaining high ductility, defying conventional stress-strain trade-off. Despite extensive studies documenting the cryo-tensile properties of ASSs, the underlying mechanisms behind this phenomenon remain largely unexplored. This study systematically re-examines the tensile properties of 316L 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 (~ 80% GPa) are discussed through electron backscatter diffraction (EBSD) microstructure characteristics. The results undoubtedly suggested that the transformation mechanisms, specifically the shift from deformation twinning to martensitic transformation (γ → ε → α; γ → α), play a crucial role in enhancing elongation at cryogenic temperatures. At these temperatures, the Gibbs free energy difference between ε-martensite and γ-austenite approaching zero, resulting in slow martensite growth. The stress-strain curves at low temperatures satisfy the Considère criterion, indicating delayed necking under these conditions. This behavior is ascribed to presence of various hierarchical microstructures, including ε, α, γ-twins, ε-twins and their intersections, which act as sources of work hardening. This study provides new insights into deformation behavior of ASSs under cryogenic conditions.