A study of the influence of Mn and Ni on the kinetics of the proeutectoid ferrite reaction in steels

Abstract

The kinetic transition between partitioned and unpartitioned growth of proeutectoid ferrite has been studied for high-purity Fe–C–Mn and Fe–C–Ni alloys, and for temperatures just above the eutectoid. These results (and certain results of previous investigations) are compared with computed paraequilibrium and equilibrium ternary phase diagrams, and it is shown that the transition occurs well within the paraequilibrium two-phase regions, but significantly outside the limit predicted by the local equilibrium analysis of the ternary precipitation reaction. These observations are interpreted in terms of solute drag theory. It is inferred that both Mn and Ni exert a drag on the moving ferrite/austenite interfaces, and that this drag force is due to substitutional solute diffusion within the moving interface. The equilibrium binding energies of each of the substitutional solutes to the boundary are expected to be of order RT.