Abstract
In order to clarify the mechanism of the formation of spheroidal graphite in cast iron, the interfacial energies between molten irons, which were solidified with different graphite structures, and specific planes of graphite crystal were measured using the sessile drop technique. The interfacial free energy ratio was calculated from the measured interfacial energy and used as a parameter of the stability of various geometrical arrangements.
In the Mg-treated molten iron with no addition of any anti-spheroidizing element, the interfacial free energy ratio of polycrystalline graphite was lower than that of single crystal graphite. The solidified iron had mostly the spheroidal graphite. In the Mg-untreated molten iron with Pb addition, this ratio of single crystal graphite was lower than that of polycrystalline graphite. This iron solidified with flaky graphite. When the Mg-treated molten iron was held at high temperature and fading occurred, these two ratios were intermediate and the spheroidal and vermicular graphites grew in the cast iron. When the molten iron treated with Mg after Pb addition, this ratio of polycrystalline graphite was lower than that of single crystal graphite at the early stage of measurement. But the ratios were reversed later. This fact can explain the “fading” phenomenon.
The interfacial free energy ratio is, therefore, regarded as a deciding parameter of graphite-spheroidization in cast iron.
