Abstract: The influence of hot deformation process on austenite-ferrite transformation was investigated to predict the starting temperature of ferrite precipitation of low carbon steels during deformation (Ar3d) and the starting transition temperature of Nb-V microalloyed steels during continuous cooling (Ar3). The results indicate that the lower the C or Mn content, the higher the Ar3d temperature under the same deformation conditions, and Ar3d increases with the increase of strain amount or the decrease of strain rate for the same steel grade. On the other hand, Ar3 decreases with the increase of cooling rate and increases due to deformation. The simulated results were found in agreement with experimental ones, which implied that such a theoretical approach can be used to model the transformation process above mentioned.