Graphite in Cast Iron – From Carbon Atom to Graphite Spheroid

The momentous research efforts directed to the understanding of nucleation and subsequent crystallization of graphite, and related solidification phenomena was driven in part by the growing interest in the use of spheroidal graphite cast iron in the manufacture of large castings such as wind turbine parts that require exceedingly long solidification times. The goal of this paper is to provide an update on the advances achieved in understanding the mechanisms that govern the nucleation and crystallization of spheroidal graphite and of the related imperfect morphologies from iron-carbon-silicon melts. In this analysis, we examine the crystallization of graphite not only in cast iron, but also that of metamorphic graphite (natural graphite formed through transformation by heat, pressure, or other natural actions), and of other materials with similar lattice structure and crystallization morphologies. The reader will be taken on a trip that starts with formation of the graphene sheets and turbostratic graphite on heterogeneous nuclei, followed up by crystallization through different mechanisms, to finally produce graphite spheroids, known mostly as graphite nodules to the foundryman.