Abstract
The nucleation and growth behaviour of chunky graphite in heavy section ductile cast irons were studied. The microstructure in quenched samples during solidification was observed using optical microscopy and EPMA. Only spheroidal graphite was observed as the initial form of graphite at the early stage of the solidification. When the growth of the graphite nodules stopped during solidification, chunky graphite began to nucleate at the interfacial sites around the solidification front of the austenite and grow at the thin liquid channel in austenite. During this growth, the advancing end came into contact with the residual liquid iron through the thin liquid channel. Spheroidal graphite is not directly related to the nucleation and growth of chunky graphite. In this study, the Site Theory was used as one explanation of the nucleation and growth mechanism.
