Simulating solidification of spheroidal graphite cast iron of Fe-C-Si system

A model to predict the solidification of spheroidal graphite (SG) cast iron during cooling process was developed. The model treated the problem of the ternary Fe-C-Si system and aimed at simulating the evolution of the solidifying microstructure. When the eutectic temperature is reached, eutectic grains are formed. The rate of nucleation depends on the melt characteristics and supercooling. The nucleation rate was assumed to be presented by power law function of undercooling. The growth of the austenite grain was controlled by carbon diffusion through austenite. Carbon and silicon concentrations at different interfaces are calculated from the Fe-C-Si equilibrium ternary phase diagram and Shell equation was applied to calculate the silicon content in the bulk liquid and the concentration of carbon in the liquid was determined to keep the eutectic reaction. The model was applied to a four-step cylindrical sand casting which has a different diameter. The simulated results were compared with the experimental ones using a post processing program which was also developed to simulate the microstructural evolution graphically. The results showed relatively good agreement and the usefulness of the proposed model was confirmed.