Strain hardening behavior of phase reversion-induced nanograined/ultrafine-grained (NG/UFG) austenitic stainless steel and relationship with grain size and deformation mechanism

The concept of phase reversion involving severe cold deformation of metastable austenite to generate strain-induced martensite, followed by temperature–time annealing sequence, was used to obtain varying grain size from nanograined/ultrafine-grained (NG/UFG) to coarse-grained (CG) regime with the objective to elucidate the interplay between strain hardening behavior and deformation mechanisms in conjunction with the mechanical properties. The study underscores that irrespective of the grain structure and operating deformation mechanisms (twinning versus strain-induced martensite), the generic nature of strain hardening is unaltered. However, there were subtle differences in the three-stage strain hardening ability that were governed by noticeably different deformation mechanisms. There was transition in deformation mechanism from essentially nanoscale twinning in NG/UFG and sub-micron grained (SMG) structures to strain-induced martensite transformation in the fine-grained (FG) and CG structures, a behavior related to the increase in the stability of austenite with decrease in grain size.