Martensite morphology and habit plane transitions during tensile tests for FeNiC alloys

Abstract

The morphology and habit plane of deformation-induced martensite formed in FeNiC and FeNiCrC alloys were investigated using optical and transmission electron microscopy. A morphologic transition from butterfly martensite to lath-like martensite caused by applied tensile stress was shown and studied in detail. It was found that deformation-induced martensites have two growth directions; one is along austenite {252} f plane, the other one is along austenite {111} f slip plane. With the increase of stress, the growth direction along {111} f plane is favoured and leads to the formation of lath-like martensite which was characterized by both sides of α'−γ interfaces parallel to {111} f plane with a high density of dislocations without {112} b transformation twins. The habit plane was changed simultaneously from {252} f original habit plane to a {111} f plane as the martensite plate grows. The morphologic and habit plane transitions were related to a modification in transformation strains accommodation mechanisms.