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 approximate to 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 approximate to 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. This work constructs a heterogeneous lamellar structure by phase-reversion annealing of deformation-induced martensite in 304ss. The resultant HSLed 304ss demonstrates a combination of high yield strength in excess of 1.2 GPa and large ductility with uniform elongation of approximate to 28%.image (c) 2024 WILEY-VCH GmbH