Ultrahigh strength nano/ultrafine-grained 304 stainless steel through three-stage cold rolling and annealing treatment

An approach involving grain refinement through three-stages of cold rolling and annealing was explored with 304 austenitic stainless steel to obtain ultrahigh strength. Equiaxed nano/ultrafine austenite grains of average grain size of ~150nm (the smallest grain size was ~80nm) was obtained with desirable combination of strength and moderate ductility (yield strength −1120MPa, tensile strength −1440MPa, and elongation −12%). The mechanism of transformation of martensite to austenite was diffusional reversion, when the specimens were annealed in the temperature range of 550–650°C. [Display omitted] •Equiaxed austenite with the smallest grain size ~80nm was formed via three-stage cold rolling and annealing treatment.•The nano/ultrafine-grained 304 stainless steel exhibited a combination of superior strength and good ductility.•The yield strength, ultimate tensile strength, and elongation were 1120MPa, 1440MPa, and 12%, respectively.•We confirmed that the mechanism of martensite reversion was diffusional type when samples were annealed at 550–650°C.