Relation between martensite morphology and volume change accompanying fcc to bcc martensitic transformation in Fe–Ni–Co alloys

The change in morphology and substructure of α′ martensite with a volume change accompanying austenite (fcc) to martensite (bcc) transformation was studied using various Fe–Ni–Co alloys. The volume change accompanying martensitic transformation was decreased by the Invar effect of austenite with Co addition to the Fe–Ni binary alloys. In Fe–28Ni–20Co and Fe–24Ni–30Co (mass%) alloys, small and negative volume changes were established (−0.30% and −0.39%, respectively). With a decrease in volume change, the transition temperature of martensite morphology from lenticular to lath increases. The dislocation densities in martensite and austenite decrease as the volume change approaches zero.