Classification of degenerate graphite and its formation processes in heavy section ductile iron

The presence of degenerate graphite in heavy section ductile iron causes a significant decrease in its mechanical properties. In this paper, two types of degenerate graphite are classified: large non-spheroidal graphite and small chunky graphite. The formation processes of degenerate graphite have been investigated by means of simulation quench experiments. With samples quenched in water, it was observed that the large non-spheroidal graphite forms directly from the degeneration of spheroidal graphite in an austenite shell. Some liquid channels were found in the austenite shell and at certain graphite/austenite interfaces. These channels link the graphite with the bulk liquid metal during the slow eutectic solidification process. The liquid channels form as a result of the temperature fluctuations and the segregation of certain elements. The existence of these liquid channels is an important factor in the formation of non-spheroidal graphite. Chunky graphite grows from the remains of molten iron in the middle or by the end of the eutectic reaction. This chunky graphite is actually an intercrystalline eutectic graphite.MST/970