· The Martensitic transformation occurs when the austenite is cooled rapidly to below the M_S- start temperature and results from a displacive distortion of the crystal lattice caused by a supersaturation of interstitial carbon. In the transformation the high temperature FCC lattice transforms to a body-centered-tetragonal (BCT) or a BCC lattice.
· The photographs show Martensite formed in an Fe - 1.8 wt% C alloy after quenching to (a) 24 C, (b) -60 C, and (c) -100 C . (dT/dt) is about 200 C/s