The effect of prior deformation on the strength and annealing of reverted austenite

The strength, annealing behavior, and microstructure of reverted austenite has been measured in an Fe-31 pct Ni-0.03 pct C alloy that was plastically deformed in the martensitic state prior to the reversion to austenite. Mechanical properties of reverted austenite (e.g., austenite formed by the reverse martensite shear transformation) were measured as a function of the amount of prior deformation, heating and cooling rates to the reversion temperature, austenitizing temperature and time, repetitive cycling from martensite to reverted austenite, and prereversion heat treatments. The results showed that 80 pet prior deformation increases the yield strength of reverted austenite about 30 pct. Along with this strengthening, the dislocation configuration changes from a plate-like fine structure with a random array of tangled dislocations in reverted samples without prior deformation to a equiaxed fine structure with a high density of tangled dislocations within the fine structure in samples with 80 pct deformation prior to reversion. Although smaller amounts of prior deformation (20 pct) have only a small effect on the strength of the reverted austenite, this amount of prior deformation significantly increases the driving force for recrystallization. The results are explained on the basis that the prior deformation and the reversion process produce separate components to the strength and annealing behavior. E. GOLD, formerly with the Aeronutronic Division, Philco-Ford Corporation, Newport Beach, Calif.