A graphite nodule growth model validated by in situ synchrotron x-ray tomography

An accurate prediction of ductile cast iron (DCI) microstructures is crucial for a science-based optimisation of cast component design. The number density and distribution of graphite nodules critically influence the mechanical performance of a component in service. Although models predicting nodule growth have been researched for many years, recent improvements have been impeded by lack of detailed experimental data on nodule growth kinetics for validation. This data has now been made available through in situ observations of the solidification of DCI using synchrotron x-ray tomography in combination with a high temperature environmental cell. In the present investigation, a new sphere of influence (SoI) model for spheroidal graphite growth is proposed. It inherently incorporates the competition for carbon between neighbouring nodules and the depletion of carbon in the matrix. Comparing simulation results to the in situ observations of graphite growth, the SoI model successfully predicts both growth of individual nodules as well as the size distribution of a large nodule population during solidification.