Effect of pre-strain and reheating on isothermal α′ martensite formation in Fe–25.5Ni–4Cr austenitic steel

The effect of pre-strain on α′ martensitic transformation was examined for Fe–25.5Ni–4Cr austenitic steel. α′ martensitic transformation was gradually suppressed with pre-strain up to about 10%, but was contrarily enhanced with pre-strain over about 10%. Specimens pre-strained to 10% and 30% were reheated to clarify the mechanism of suppression and enhancement on α′ martensite formation. The diffusion activation energy of component atoms in this steel was obtained from the relation between the amount of α′ martensite and the reheating time. In specimens pre-strained to 10%, the apparent activation energy is fairly close to the diffusion activation energy of C in austenitic steels. In specimens pre-strained to 30%, the apparent activation energy is close to the diffusion activation energy of Ni and Cr in austenitic steels. The suppression and enhancement of α′ martensitic transformation is attributed to diffusion of C, Ni and Cr in Fe–25.5Ni–4Cr.