Retransformation (α′→γ) kinetics of strain induced martensite in 304 stainless steel

Coupons of austenitic 304 stainless steel (γ) were transformed to approximately 90% martensite (α′) and 10% austenite by rolling at 77 K. Subsequently the reverse α′→γ transformation was instigated by heating the coupons to 680°C. The retransformation was monitored, in situ, by dilatometry and neutron Bragg edge diffraction (BED). Results from the two techniques show good agreement and suggest that the transformation kinetics are best described by two Avrami exponents, n=2.5 and n=0.2 respectively. A limited discussion of the lattice parameter evolution during the transformation is included. Possible mechanisms for growth dynamics and stress relaxation are discussed.