In this work, the austenite-ferrite transformation in Fe-0.23C-1.86Mn alloy is studied by a 2-D model based on Gibbs-Energy-Balance considerations at the moving interface. Plate-lengthening, plate-thickening and isotropic growth are calculated. Growth with a plate-like morphology leads to the fastest reduction in Gibbs energy when the transformation takes place at 500°C and 600°C On the contrary, isotropic (i.e. spherical) growth is preferential at 650°C. The concept, stasis for thickening of single plate, is put forward. The conditions for the single bainitic sheaf stasis correspond nicely to the conditions for macroscopic stasis.