Abstract: On the basis of solidification kinetics, the mathematical model of microstructure formation of spheroidal graphite cast iron is established, improved and verified with the sample castings. In addition, nodular counts and diameters, contents of pearlite and ferrite, and hardness of practical automotive spheroidal graphite iron castings are simulated with the model and compared with results of quantitative experiment analysis. The comparison indicates that both simulated results and experimental results agree well with each other and the model of eutectoid transformation should be improved to predict contents of pearlite and ferrite more accurately. Besides, it is concluded that the nucleation and growth of graphite spheres are mainly determined by cooling rate during eutectic transformation while the contents of ferrite and pearlite are governed by both the super-cooling of eutectoid period and nodular counts of eutectic solidification.

Key words: Microstructure, Modeling, Numerical simulation, Spheroidal graphite iron castings