A first-order solute-drag theory for effects of alloying elements on the growth of proeutectoid ferrite in steels

A simple model is developed to describe the effects of alloying elements on the proeutectoid ferrite transformation in steels, for cases where the interfacial velocity is comparable to D2i/δ, the quotient of the substitutional interfacial diffusion coefficient and the interfacial thickness. The model allows for the loss of local equilibrium for the substitutional alloying element with increasing interface velocity. Local equilibrium is maintained for the interstitial solute, carbon. The treatment allows for a transition from local equilibrium to “paraequilibrium” conditions, and for a “solute drag” effect under certain conditions. The shape stability of the transformation front is considered.