Excellent strength-toughness synergy in metastable austenitic stainless steel due to gradient structure formation

The effect of cold swaging and subsequent annealing on the structure mechanical properties a 321-type metastable austenitic stainless steel was studied. Cold to strain 90% produced gradient with gradual decrease in α-phase content from edge center bar. Globular lamellar regions both strain-induced martensite retained austenite were found center, meanwhile, completely globular austenite–martensite dual-phase formed at edge. After 500 °C, (~30° below reverse martensite-to-austenite phase transformation temperature) microstructure refinement due simultaneous development recrystallization observed. Both ultimate tensile strength yield increased noticeably after annealing. Besides, notch toughness annealed specimen doubled comparison that cold-swaged condition almost reached level coarse-grained condition.