Deformation-induced martensitic transformation under various deformation modes

Abstract

Deformation induced martensitic transformation phenomenon in an austenitic stainless steel has been investigated in relation to the inelastic deformation theory. A new kinetics equation for the deformation induced martensitic transformation, formulated based on the inelastic deformation theory as f/f(s) = 1 - exp[-beta(epsilon-epsilon(0))(n)] with beta characterizing the stability of retained austenite, n denoting a deformation mode parameter, f(s) the saturation value of transformed martensite, and epsilon(0) the minimum inelastic strain to induce the martensitic transformation during the plastic deformation has been used in this study. It has been experimentally verified that this kinetics equation can effectively describe the relationship between the inelastic strain and the volume fraction of transformed martensite under various loading routes. The deformation mode parameter n defined as the nucleation site formation rate depends on phase compositions, loading route, viz. tensile and compressive loading, and the kind of transformed phase., It was found that the value of n is 2.2 under uniaxial tensile deformation, 1.25 under uniaxial compression and for the case of pure shear deformation imposed by the equal channel angular pressing. Shear deformation has been shown to be the most effective method to induce martensitic transformation.