Deformation-Induced Austenite-to-Ferrite Massive Transformation in Medium Carbon Steel

Austenite-to-ferrite transformation behavior during hot deformation within the two-phase field was studied in a medium carbon (0.25 wt pct) steel containing 1.1 wt pct Mn-0.25 wt pct Si. Flow softening was observed during hot deformation at temperatures lower than a critical temperature within a two-phase field under the slow strain rate condition. This was because the austenite-to-ferrite transformation during deformation occurred by the deformation-induced massive transformation. The critical temperature was observed to be significantly higher than the T ₀ temperature, suggesting that the γ-α equilibrium temperature was largely shifted toward higher temperature during hot deformation. The T ₀ shift was believed to be possible because a nonuniform deformation-induced stress can develop between austenite and ferrite phases during hot deformation due to the presence of a significant yield stress difference between two phases.