Microstructure transition from lamellar to compacted graphite using different modification agents

The graphite morphology present in compacted graphite irons can vary between a spheroidal and lamellar range of shapes. These graphite shapes have been studied by scanning electron microscopy (SEM). Samples used were treated either with magnesium, cerium or lanthanum to investigate differences in the modification of the graphite structure between each of these elements. To facilitate the SEM study the samples were deep etched to reveal the graphite structure in three dimensions. Results showed that there was little difference between the morphologies displayed in the well-formed compacted graphite. However, the lamellar graphite formed varied considerably with each of the three modification agents. The transition from compacted to lamellar shape was continuous for Mg treatment, whereas there was a sharp transition when treated with rare earth elements. Furthermore, several degenerated graphite structures in the La-treated sample were observed.