Comparison of Variant Selection between Lenticular and Lath Martensite Transformed from Deformed Austenite

A variant selection of ausformed lath martensite in an Fe-9Mn alloy (M-s = 602 K) and ausformed lenticular martensite in an Fe-25Ni-0.5C alloy (M-s = 220 K) are compared quantitatively using EBSD measurements combined with a method for the reconstruction of austenite orientation. Differences were found in the selected variants by ausforming between those two martensite morphologies. In ausformed lath martensite, variants with habit planes parallel to the active slip planes in austenite were preferentially selected. This variant selection in lath martensite may be attributed to the preferential nucleation on the microband structures in austenite and lack of growth inhibition from the microband boundaries. On the other hand, in ausformed lenticular martensite, variants with habit planes parallel to the compression plane were preferentially selected. The reason for this is that lenticular martensite whose habit plane is parallel to the compression plane can grow easily in austenite grains elongated along the compression plane. This means fewer disturbances for those variants to grow with a habit plane parallel to the compression plane than for other variants.