Analysis of Solidification Path of Fe-Cr-Ni Ternary Alloy

The solidification path of an Fe-Cr-Ni ternary alloy was calculated numerically on the basis of thermodynamic analysis. In order to evaluate the effect of back diffusion in the solid, three models are used for the analysis. That is, 1) a equilibrium model with perfect diffusion in the solid, 2) the Scheil model with no diffusion, 3) a limited back diffusion model, and obtained results were compared. In the calculations, the equilibrium tie line at the solid-liquid interface, which varies depending on both temperature and composition, was determined for each step of numerical computation. The solidification path with back diffusion was calculated by a new technique combining thermodynamic calculation and diffusion analysis. In this model, δ-γ transformation, which occurs during solidification of the Fe-Cr-Ni ternary system, was dealt with under the assumption that the transformation is diffusion controlled. The relationship between temperature and the fraction solid of the ternary alloy for different cooling rates obtained from the limited back diffusion model was located between those obtained from the equilibrium and Scheil models, demonstrating the validity of the analysis.