Influence of solute drag on the growth of proeutectoid ferrite in Fe-C-Mn alloy

The diffusion-controlled growth of proeutectoid ferrite (alpha) from austenite (gamma) in an Fe-C-Mn alloy was simulated incorporating the possible drag effect of Mn on the migration of alpha:gamma interphase boundaries. The magnitude of drag force or the dissipation of free energy by drag was evaluated by means of Cahn and Purdy-Brechet models. The growth rate of ferrite was calculated from the flux balance equation for carbon taking into account the fact that the carbon concentration at the boundary in austenite varied with time. Whereas the time exponent of growth deviated from one-half at each moment, the overall time dependence was dictated by carbon volume diffusion in austenite. The reported differences of experimental growth rates from those calculated assuming paraequilibrium were reduced considerably by incorporating the drag of Mn, although simulation results may largely depend on the shape and depth of solute interaction potential with alpha:gamma boundaries and Mn diffusivity within the boundary, etc. (C) 1999 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.