Nucleation, coarsening and deformation accommodation mechanisms of ε-martensite in a high manganese steel

The nucleation, coarsening and deformation accommodation mechanisms of epsilon-martensite in an Fe-17Mn-3A1-2Si-1Ni-0.06C wt.% high manganese steel subjected to plane strain compression and cold-rolling up to 88% thickness reduction was studied using a combination of electron microscopy techniques. Intrinsic stacking faults in gamma-austenite led to the nucleation of fine deformation-induced epsilon-martensite laths. In accordance with previous observations, the lateral coarsening of deformation-induced epsilon-martensite laths occurred via their coalescence with neighbouring epsilon-martensite plates/laths. Electron back-scattering diffraction and high-angle annular dark-field observations showed that epsilon-martensite accommodates deformation via a combination of perfect and partial basal slip, pyramidal slip and {10<(1)overbar>2} & LANG;<(1)overbar>011 & RANG;(epsilon) extension twinning. The operation of partial basal slip; generating I-1 and I-2-type basal stacking faults at smaller thickness reductions and thereafter, only I-1-type stacking faults at larger thickness reductions was observed in epsilon-martensite. Consequently, a mechanism that enables a transition from epsilon-martensite I-2 to I-1-type stacking faults is proposed.