Electron microscopic studies of martensitic transformations in iron alloys and steels

Abstract

It has been demonstrated by electron microscopy of Fe3Pt and Fe3Al(-C) martensites that the Bain distortion is unambiguously realized upon the fee to bec or bet martensite transformation in iron alloys and steels. Secondly, internal inhomogeneities in ferrous martensites are summarized, and discussed with regard to the uniqueness of the (112) twinning plane, the deviation of the martensite twin interface plane from (112), the nature of (Oil) twins in bct martensite, distribution of (112) twins and the nature of the midrib, dependency of the habit plane on internal inhomogeneities, and internal structures in thin martensite platelets. Accordingly, it is emphasized that in order to discuss consistently the correlation between the internal inhomogeneities and other crystallographic properties, all crystallographic properties should be measured for a given martensite plate. Finally, a recent study of an Fe-16.5 wt pet Mn-0.25 wt pct C alloy subjected to cyclic heating and cooling (400°C ⇌-l96°C) is introduced to show the existence of long period stacking order structures [15R(3•2)3 and 18R(5•1)3] in some ferrous alloys.