Microstructural analysis of thermally induced and deformation induced martensitic transformations in Fe–12.5 wt.% Mn–5.5 wt.% Si–9 wt.% Cr–3.5 wt.% Ni alloy

Martensitic transformations induced by thermally and compression deformation at room temperature in Fe–12.5 wt.% Mn–5.5 wt.% Si–9 wt.% Cr–3.5 wt.% Ni alloy were studied in detail by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). From microstructural observations, it was seen that heat treated samples exhibited regular overlapping of stacking faults and ɛ martensite plates were formed parallel to each other. Also, TEM investigations showed that the orientation relationship between γ (fcc) and ɛ (hcp) phases corresponds to Shoji–Nishiyama type. With applied low plastic deformation rate, only ɛ martensite occurred in austenite grain. As a consequence, 4 and 25% plastic deformation at room temperature caused ɛ martensite formation in austenite phase and the new ɛ (hcp) and α′ (bcc) martensite formation in martensite phases, respectively. Orientation relationship between ɛ and α′ phases was found by the electron diffraction analysis.