Graphite Spheroids: The Place Where they are Born

Abstract

In the same way that a building needs a solid foundation to remain firm and stable, graphite requires proper nucleation sites to precipitate and grow in the right way. Phenomena that occur during solidification process will determine the nature of the nuclei (non-metallic inclusions), as the topology of the land will establish the quality of a construction. Their presence will define the nucleation potential of the melt, being highly influenced by a multitude of variables such as the base metal composition, the graphite spheroidization treatment, or the inoculation process. A good knowledge of the formation of these particles will help an excellent control of the formation of graphite. Silicates, oxides, sulfides, carbides, and nitrides were found acting as nuclei for graphite depending on the solidification conditions. The objective of this paper is to improve the understanding of the mechanisms that govern nucleation, verifying some theories already described by other researchers, but also developing some new ones. The direct relation between the type of nuclei and the processes that occur during the liquid–solid transformation was also demonstrated.