Solidification macrostructure of spheroidal graphite cast iron

Methods to reveal the macrostructure of spheroidal graphite cast iron (SGI) are not available. This has caused a number of controversies involving the soldification mechanism of this metallic alloy. The objective of the prese nt work is to examine the use of a novel technique (DAAS) reported recently , to reveal the solidification macrostructure of SGI made using conventiona l melting and pouring practices, and cast in sand moulds. The results show that the DAAS technique successfully reveals the macrostructure. The basic features of the solidification macrostructure of SGI are similar to those o f most metallic alloys. Nevertheless, some particular features have become evident. The grain size of SGI is considerably larger than previously estim ated. The grain size of hypereutectic SGI is consistently smaller than that of hypo and eutectic irons cast in similar conditions. The observation of the actual solidification macrostructure of SGI led the authors to propose a description of the solidification mechanism that takes into account the a ctual size and morphology of the solidification units. The new DAAS techniq ue is a very valuable tool which can be used to investigate a number of iss ues about SGI solidification still under discussion.