Reversible movement of the austenite-martensite interface and dislocation structures in reverse-transformed austenite in Fe-Ni-C alloys

The movement of the austenite-martensite interface and the formation of dislocations during the reverse martensitic transformation in Fe-Ni-C alloys with high nickel contents have been studied by optical and electron microscopy. It was found that the interface moves backwards, leaving hairpin-shaped dislocations in austenite. The interface which moves backwards on heating can move forwards again on recooling. The dislocations formed in reversed-transformed austenite are considered to lie on the (101) plane, which corresponds to the (112)α′ twinning plane of transformation twins in the original martensite plate. The formation of these dislocations are well explained by the mechanism proposed previously for Cu-Zn alloys. A necessary and sufficient condition for the reversible movement of the austenite-martensite interface is given, and the mobility of the interface is discussed in relation to the dislocation formation.