Solute drag(-like) effects on the growth of ferrite in Fe-C-X alloys

The diffusion-controlled growth of proeutectoid ferrite(alpha) from austenite (gamma) in Fe-C-X alloys, where X is a substitutional alloying element, was simulated incorporating the possible drag effect of alloying elements on the migration of alpha : gamma boundaries. The interaction between carbon and an alloying element in the boundary was incorporated into Purdy-Brechet model. The flux balance equation of carbon was written using Green function to deal with the situation in which the carbon concentration at the boundary in austenite varied with the boundary velocity. The magnitude of drag may depend on a number of parameters which include the depth and shape of solute interaction potential with boundaries, the boundary diffusivity of an alloying element in relative to the rate-controlling diffusivity (carbon volume diffusion in austenite) and the nature of C-X interaction etc.. Comparing the simulation results with reported experimental growth rates of ferrite allotriomorph, the characteristics of drag exerted by respective alloying elements are discussed.