Nucleation and solidification of thin walled ductile iron-Experiments and numerical simulation

Investigation of solidification of thin walled ductile cast iron has been performed based on experiments and numerical simulation. The experiments were based on temperature measurement and microstructure examination. Both hyper- and near-eutectic alloys have been investigated with plate thicknesses of 2.8, 4.3 and 8 mm. Temperature measurement revealed that eutectic solidification in the thinner plates (≤4.3 mm) was divided into two stages. The first stage was relatively short with little or no recalescence. The second stage was the main stage with a larger recalescence. In 8 mm plates the eutectic solidification had only one main stage. Color etching revealed the presence of austenite dendrites. Results of the experiments have been compared with a 1-D numerical solidification model that takes into account the precipitation of off-eutectic austenite during the eutectic stage. Simulations reveal that the first stage of eutectic solidification in the thin plates can be explained by growth of off-eutectic austenite.