Strength‐Ductility Synergy in 304 Austenitic Steel with a Phase‐Reversion‐Induced Heterogeneous Lamellar Microstructure

A thermomechanical processing route involving severe cold‐rolling deformation of austenite to generate strain‐induced martensite, followed by short‐time annealing when martensite reverts to austenite, is used to introduce the heterogeneous lamellar structures (HLS) into 304 stainless steel (304ss). First, a nanolamellar structure consisting of mostly martensite with retained austenite grains is formed in the severe cold‐rolled 304ss, which results in an ultra‐high strength of ≈1.9 GPa but poor ductility. After short‐time annealing, an HLS, comprised of soft recrystallized austenite lamellae with micro/sub‐micron grains embedded inside a hard matrix of reversed ultrafine/nanoaustenite grains containing high‐density dislocations, is introduced into the 304ss through phase reversion and partial recrystallization. The resultant HSLed 304ss exhibits a high yield strength in excess of 1.2 GPa with a large uniform elongation of ≈28%. Strong heterodeformation‐induced hardening associated with the joint activation of twin‐induced plasticity and transformation‐induced plasticity effect is responsible for the excellent strength–ductility combination. The thermomechanical processing route used here can be easily scaled up for industrial production and can be generalized to other materials.