Modeling of in situ heat treatment in austempered ductile iron

The material properties of cast irons depend mainly on the structure of the matrix in as-cast condition or after of heat treatment. A simulation model has been developed to predict the microstructural evolution during solidification of spheroidal graphite (SG) cast iron in gravity die casting and the subsequent solid state transformations during in situ heat treatment. The fraction of solid, the nodule sizes, the nodule counts and the fraction of solid state phases which form during austempering were calculated in this model. The temperature distribution during the solidification in a permanent mould and during the subsequent austempering heat treatment was determined. The bainitic transformation occurring during the austempering was simulated by the Avrami equation. The simulation was verified with experimental results.