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

Abstract

An accurate prediction of ductile cast iron 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 ductile cast iron using synchrotron X-ray tomography in combination with a high temperature environmental cell. In the present investigation, a new sphere of influence 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 sphere of 2 influence model successfully predicts both growth of individual nodules as well as the size distribution of a large nodule population during solidification.

Recent trends in X‐ray‐based characterization of nodular cast iron

“…Overall, it can be concluded that the time‐resolved 3D X‐ray tomography studies conducted so far have captured the dynamic processes of the nucleation, growth, and floating of GPs and highlighted how the degenerate features develop from spheroidal GPs. These findings are crucial for the development of advanced models where some of the simplifying assumptions associated with the traditional solidification models are relaxed 24 …”

In situ synchrotron investigation of degenerate graphite nodule evolution in ductile cast iron

“…It is equally important to understand the effect of thermal fluctuations on the local microstructure. Several numerical models have been proposed to describe nodule growth ranging from a 1D spherical coordinate model [37] (based on a uni-nodular approach [38]) to a 3D Phase Field simulation [39]. These models assume uniform spherical nodule growth, degenerate morphologies are not taken into consideration.…”