HETEROGENEOUS NUCLEI AND GRAPHITE CHEMISTRY IN FLAKE AND NODULAR CAST IRONS

Nodular and flake graphite have been extracted from commercial cast irons and studied by a variety of techniques, including high voltage transmission electron microscopy. For nodular graphite the nuclei are (in these cast irons at least) 2 to 5 μm diam spherical particles of primarily CeCO2, MgO, and Fe2C3. In addition the nuclei contain variously Ca, Al, P, S, and Si. The composition of the nuclei is highly variable, presumably due to the highly nonequilibrium conditions under which they are formed. For flake graphite the nuclei are apparently sulfide particles, again of variable composition. They are spherical and approximately the same diameter as the nodular nuclei. Moreover, chemical analysis of flake and nodular graphites shows that there is a relatively high concentration of oxygen in solution in flake graphite but not in nodular graphite, which suggests oxygen is a growth modifier. © 1979 American Society for Metals and the Metallurgical Society of AIME.