Thermodynamic and Kinetic Analysis of Austenite Homogenization on Carbidic Ductile Iron

The austenite homogenization of carbidic austempered ductile iron is studied from both thermodynamics and dynamics by calculation and experimentation, and a mathematical model of carbide dissolution is established to predict the dissolved quantity of carbides. The results indicate that the mass fraction of carbon in austenite (austenite-graphite stable equilibrium) calculated by the Thermo-Calc software is similar to the results quantitatively analyzed by electron probe. Based on Fick's second law, the elemental diffusion kinetics is analyzed by MATLAB software. Because the diffusion rate of chromium in austenite is lower than carbon, the carbon content is significantly decreased around undissolved carbides, but the chromium content is still high. Two equations of undissolved carbides' area are obtained by linear fitting.