Growth mechanisms of vermicular graphite in cast iron

To steadily produce high-quality vermicular graphite cast iron (VGI), it is essential to have a deep understanding of the growth mechanism of vermicular graphite. The morphology and microstructure of graphite in VGI were studied using various techniques, including both experimental and theoretical methods. An abnormal graphite structure with an anomalous layer distance of 6.60 angstrom was observed by transmission electron microscopy (TEM) imaging, which is approximately two times larger than the normal structure (3.40 angstrom). The theoretical simulations of possible trace elements added (approximately 34 different elements) to the graphite basal planes were studied and analyzed individually to understand the observed phenomenon and their effects on graphite growth. The theoretical calculations (6.56 angstrom) show good agreement with the experimental results (6.60 angstrom), which proves that the lattice anomaly is caused by Mg. The abnormal graphite was believed to be the remains of the transition state during the growth of graphite. Based on the investigation, a mechanism is proposed to describe the influence of Mg during the growth process of vermicular graphite.