Modelling volume change during solidification of SG cast iron with eutectic composition

Background/aims: Due to the special solidification characteristics of S.G. iron, the shrinkage and feeding behaviour presents a very complex situation and sound castings are obtained only by rather empirical methods. Some experimental results have been reported, estimating and measuring the expansion and shrinkage during eutectic solidification. Since the measured value includes the solid and liquid parts of volume change, the behaviour of eutectic expansion in the mushy zone is not completely understood up till now. The aim of this work is to construct a theoretical model of volume change in the mushy zone and the casting during eutectic reaction. Further, it is an aim to discuss the influence of kinetic parameters on the volume change in the mushy zone and casting during the solidification of S.G. cast iron. Methods: A microscopic model of eutectic solidification based on the kinetics of nucleation and growth is coupled to a simple description of heat transfer to calculate the temperature field of casting. A method of coupling the volume change model to the Rappaz growth model and correcting the solid fraction following eutectic reaction is developed. Results and conclusions: A computer program is developed to calculate the temperature field, compositions of carbon and silicon, solid fraction and the volume changes. The initial results show that it is feasible to employ the growth kinetics to simulate the volume change during solidification of S.G. cast iron. The volume changes of casting during solidification consist of those occurring in the mushy zone and the solid zone. The calculation result is compared with the experiment and early theoretical prediction which shows good agreement.