Effect of grain boundaries on microstructure formation during the early stage of martensitic transformation in Fe-0.15C–18Ni steel by three-dimensional observation

The influence of prior austenite grain boundaries (PAGBs) on block formation during the early stage of martensitic transformation was investigated in three dimensions using serial sectioning and electron backscatter diffraction (EBSD). During the early stage, blocks predominantly formed in contact with PAGB edges, and their longitudinal directions aligned along the PAGB plane. Variants whose close-packed direction (CD) is nearly parallel to the PAGB and that satisfying the Kurdjumov–Sachs orientation relationship (K–S OR) with the adjacent prior austenite grain (PAG) are preferentially selected. Among the multiple PAGBs within a single austenite grain, blocks preferentially formed along the PAGB that met a greater number of variant selection rules among the 24 possible crystallographic variants.