EBSD investigation of the crystallographic features of deformation-induced martensite in stainless steel

Abstract

Variant selection during the martensitic transformation in steels may play an important role in determining the transformation kinetics and the resulting mechanical properties. In this study, the variant selection and crystallographic features of deformation-induced martensite were investigated by quasi in situ electron backscatter diffraction (EBSD) in grade SUS321 during tensile deformation. Significant differences in variant selection between austenite (γ)→hcp-martensite (ε)→bcc-martensite (α’) and γ→α’ transformation routes were observed and reported in detail, which demonstrated that ε-martensite plays an important role in the variant selection of α’. Variant selection at different deformation stages was also analysed and revealed that α’ variants with the highest priority and variant pairs were preferred at the initial and last deformation stages in the γ→ε→α’ sequence, respectively. Meanwhile, the single α’ variant nucleated at the thin slip band keeps its crystallography feature upon further deformation in the γ→α’ sequence. In addition, the strain work of the martensitic transformation for applied loads was quantitatively estimated to explain the variant selection and associated mechanism. When these calculations are compared to the experimental results it is found that they are not able to predict which α’ variant is forming preferentially during either during the γ→α’ or the ε→α’ sequences, while only accurate predictions are obtained for the γ→ε transformation which indicates that the γ→α’ variant selection is more complex.