Nodular Graphite Dissolution and Nucleus Observation: High-Temperature Dynamics of Ductile Iron Recycling

Abstract

This investigation examines the dynamic behavior of the nodular graphite structure in ductile cast iron at elevated temperatures during the recycling process. It comprises a systematic analysis of the impact of high temperature on the change in chemical composition, followed by a set of examinations of the nodular graphite structure dissolution mechanism at the early phase of the remelting process. The results indicate that prolonged holding at higher temperatures affects the carbon or silicon concentration due to oxidation, which correlates with the operating temperature and the dynamic concentration proportion of those two main alloying elements. It is also substantiated that the dissolution of nodular graphite, the only carbon source during the ductile cast iron remelting process, does not occur primarily in the liquid state but has already started during the solid phase because of austenitization. This dissolution is governed mainly by a surface reaction, as indicated by the residual graphite structure with preserved nonmetallic nuclei. Hence, this approach also provides an alternative method for observing the nodular graphite core by intentionally partially dissolving the graphite structure.