Remarkable cryogenic tensile property of the 304L stainless steel with a lamellar bimodal heterostructure

Designing a 304L stainless steel (SS) with high strength and ductility was always desired. This was because it can effectively guarantee the service safety and realize the lightweightness of the 304L structural parts. In the current work, the 304L SS with a novel lamellar bimodal heterostructure (LBHS) was fabricated by a synthetical processing method of cold rolling (CR, thickness reduction of ~ 90%) and subsequent annealing (695 °C for 0–60 min). The LBHS was consisted of lamellar micro-recrystallization grains (MRGs) uniformly distributed in an ultrafine-grained matrix. Compared to homogeneous 304L SSs with coarse grains (CGs) or fine grains (FGs), the present LBHS 304L SS exhibited a superior combination of cryogenic tensile strength and ductility. The cryogenic yield strength was ~ 1530 MPa, which was ~ 263% higher than that of the CG 304L SS. Meanwhile, the cryogenic uniform elongation was also excellent with value of ~ 34.7%. Its higher yield strength was mainly resulted from the low-temperature strengthening and heterodeformation-induced (HDI) strengthening, while its good ductility was because of the remarkable Lüders deformation, transformation-induced plasticity (TRIP) effect, and dislocation slipping/accumulation toughening effect. This study will provide a theoretical basis and technical guidance for the industrial application of a high-strength–ductility LBHS 304L SS.