Achieving Excellent Strength–Ductility Synergy by Tailoring the Grain Size Distribution in a Metastable Austenitic Stainless Steel

Ultrafine/fine-grained austenitic stainless steel (ASS) is prepared through severe cold rolling (CR) and subsequent annealing. The microstructure evolution and tensile deformation behavior is investigated, focusing on the influence of grain size distribution on the mechanical properties and strain-hardening behavior of the ASS. In the results, it is revealed that obvious ultrafine/fine-grained hierarchical microstructure forms after annealing at 650 °C for 80 and 110 min, respectively. And, the CR-80 sample with more ultrafine grains (UFGs) (86%) exhibits good combination of strength and ductility. The yield strength (YS), ultimate tensile strength, and total elongation are 954 MPa, 1030 MPa, and 43.4%, respectively. The high YS mainly originates from the retained martensite and grain refinement strengthening, while the ductility enhancement can be attributed to the postponed transformation-induced plasticity (TRIP) effect, which is a consequence of the significant number fraction of UFGs in the hierarchical microstructure. In this study, a new strategy is provided to solve the strength–ductility tradeoff in TRIP-assisted metallic materials by tailoring the grain size distribution.