Contribution of deformation-induced martensite to fracture appearance of austenitic stainless steel

Fracture surface commonly carries the evidence of high-energy (ductile/tough) and low-energy (brittle) regions involved in fracture history, the macroscopic appearance of a fracture surface has often been utilised to qualitatively evaluate toughness of materials. For metastable austenitic stainless steels (AISI 304LN), the degree of martensitic transformation affects the fracture appearance and thus depends critically on the strain rate. The two dimensional ductile tearing ridge pattern quantified from many tensile fractographs are observed to predict the nature of disparity in deformation and fracture responses with systematic variation in strain rate of the steel under ambient atmosphere. The spatial distribution of deformation-induced martensite under tension at various stress/strains and strain rates strongly influences void nucleation, growth, coalescence and hence, keeps the impression on the ductile tearing ridge morphologies and dimple geometries on the fracture surface, where the initial inclusion content was constant.