Hot-deformation behavior of super-cooled austenite within the austenite-ferrite (gamma-alpha) phase field was studied in low carbon steels (0.15 wt.%) at various strain rates. Flow softening was observed during the hot-deformation at temperatures lower than critical temperature. The critical temperature was observed to be significantly higher than To temperature. This was due to large shift of gamma-alpha phase-equilibrium to a higher temperature during hot-deformation. A thermodynamic model to account the effect of non-uniform deformation-induced stress on the gamma-alpha phase-equilibrium during hot-deformation was proposed and its prediction was in good agreement with the experimentally measured critical temperature. (C) 2010 Elsevier B.V. All rights reserved.