On the Duplex Structure of Graphite Spheroids of an Fe–Ce–C Alloy

Abstract Nearly 80 years after the discovery of spheroidal graphite cast irons, the mechanism by which the addition of magnesium or cerium spheroidizes the graphite in cast irons and Fe–C (and Ni–C, Co–C) alloys is still not fully understood. Spheroids are characterized by a stack of graphite layers whose c -axis is parallel to the spheroid radius at any point. However, while transmission electron microscopy has shown that in many cases well-defined sectors begin to radiate directly from the nucleus, in other cases a disturbed inner zone develops first, followed by a better-organized outer zone. The latter type of duplex structure was observed and investigated in the present study in a Fe–C–Ce sample. The results strongly suggest that this phenomenon is linked to the use of a high cerium content in the spheroidizer, and this conclusion is corroborated by an analysis of data from the literature highlighting the effect of the ratio between rare earths and magnesium used for spheroidization.