When is a Cast Iron Eutectic?

The literature often mentions that cast irons that appear eutectic by thermal analysis are hypereutectic if one refers to the equilibrium phase diagram. This is a source of ambiguity and confusion. The analysis of experimental results on hypereutectic cast irons has previously shown that taking into account the solidification path during the primary precipitation of graphite makes it possible to differentiate slightly hypereutectic cast irons from very hypereutectic cast irons. This approach is applied here to a cast iron which appears eutectic when inoculated and hypoeutectic when not. Thus, it is confirmed that graphite growth only becomes effective when a minimal undercooling is reached, independently of inoculation. However, only an alloy with a carbon equivalent at the boundary between mildly and strongly hypereutectic alloys and which is inoculated can appear eutectic by thermal analysis.