This study has been conducted to better undestand the phenomenon of graphite flotation in cast irons. It is well-known that graphite flotation occurs in sufficiently hypereutectic compositions of ductile cast iron, accompanied by the formation of exploded graphite. It has also been observed that graphite flotation in compacted graphite cast irons occurs as exploded graphite and that compacted graphite does not participate in flotation. A series of cast irons were prepared wherein the carbon equivalent was varied and the amount and type of nodularizer (magnesium and rare earths) added was varied. These irons were cast into dif ferent section size castings, or samples were taken at temperatures during the solidification process and were rapidly quenched to retain the structure. All specimens were examined using conventional microscopy and/or scanning electron microscopy. It was demonstrated that exploded graphite develops as the normal growth of a graphite spheroid is altered. Intensive supercooling (both constitutional and thermal) in front of the interface results in the development of cellular or dendritic growth of the graphite into a form recognized as exploded graphite. The morphology of the exploded graphite depends upon the composition and thermal conditions present infront of the interface. (Growth of graphite throughout this morphology change occurs in the C direction of the graphite crystal due to the presence of sufficient magnesium and/or rare earths). The formation of fan-like segments of exploded graphite and of chunky graphite has also been interpreted through these studies. Graphite flotation shown to occur as a result of the development of proeutectic spheroidal graphite which degenerated to exploded graphite during subsequent growth prior to the development of the austenite-graphite eutectic. As a result it is influenced by carbon equivalent,factors af solidification rate, andfactors af fecting the fecting the growth mode of the proeutectic graphite.
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