Dependency of work-hardening behavior of a metastable austenitic stainless steel on the nucleation site of deformation-induced martensite

Abstract

Effects of the nucleation site and morphology of deformation-induced martensite on the work-hardening behavior of transformation-induced plasticity (TRIP)-assisted austenitic stainless steel with different austenite grain sizes were examined. By increasing grain size from the ultrafine-grained (UFG) range to the coarse grained (CG) regime, the nucleation site of α′-martensite changed from the grain boundaries to the interior of the deformed grains (i.e., shear bands and their intersections), where the nucleation on the ε-martensite was also observed. The nucleation site was found to be responsible for the morphology of the α′-martensite, which changed from blocky shape to film-like by increasing the grain size from the UFG range to the CG regime. The strengthening effect brought by the strain-induced martensite formation was quantified based on the deviation of the work-hardening behavior from the conventional strain-hardening behavior (by the generation and interaction of dislocations, as represented by the Hollomon law). Film-like α′-martensite formed on the shear bands and their intersections led to a higher work-hardening rate compared to the blocky α′-martensite formed on grain boundaries.