The formation kinetics of deformation twin and deformation induced ϵ-martensite in an austenitic Fe-C-Mn steel

Abstract

Inelastic deformation is generally known to aid the kinetics process of solid-state phase transformations either by an increased strain energy or generating new catalyzing defect sites for transformation. The deformation induced martensitic transformation can thus be divided into two categories, viz. stress-assisted and strain-induced transformation. In the present study, the transformation kinetics of {epsilon}-martensite as well as the formation kinetics of deformation twin during inelastic deformation has been investigated experimentally by conducting a series of tensile tests using an austenitic Fe-25Mn-0.2C steel at the various temperatures ranging from 7.5 C to 277 C. When this steel was plastically deformed, both the {epsilon}-martensite and deformation twin were observed at the temperatures ranging from 7.5 to 57 C, while only the deformation twins were observed at the higher temperatures between 127 C and 177 C. The volume fractions of transformed {epsilon}-martensite and deformation twin were measured by using the usual X-ray diffraction method and the point counting method, respectively. The transformation behavior for both the deformation twin and {epsilon}-martensite formation was then analyzed using the recently proposed kinetics relation, in which the deformation induced phase transformation is viewed as an effective relaxation process to relieve the internal strain energy accumulating during inelasticmore » deformation.« less