Effects of Substitutional Solute Accumulation at α/γ Boundaries on the Growth of Ferrite in Low Carbon Steels

The growth of proeutectoid ferrite in Fe-C-X alloys containing ∼3 at. pct X, where X is Mn, Ni, Cr, and Si, is re-examined in terms of solute drag using the Hillert–Sundman theory. The differences of measured growth rates from those calculated under paraequilibrium (PE) reported previously were accounted for taking into account not only the binding energy of substitutional solute with the boundary, but also the transformation temperature of the alloy. The ferrite growth in quaternary Fe-C-Mn-Si alloys was modeled using the stationary-interface approximation for the matrix of finite grain size. The principal features of growth in these alloys, i.e., initial fast unpartitioned growth and subsequent slow partitioned growth with a high level of carbon supersaturation in austenite, were reproduced incorporating cosegregation of Mn and Si at the boundary. Thus, a strong Mn-Si interaction is likely to enhance accumulation of these elements at the boundary and yield the growth behavior that resembles the growth stasis in Fe-C-Mo alloys.