Quantitative analysis of the effect of inoculation and magnesium content on compacted graphite irons – Experimental approach

In many industrial domains, compact graphite cast irons are developing rapidly at the expense of lamellar graphite irons. The formation of the microstructure, especially graphite shape, during the solidification stage of these alloys is however still not clearly understood, showing characteristics similar to both lamellar and spheroidal graphite irons. The aim of this work was to provide quantitative information on the solidification of compact graphite cast irons, whether inoculated or not, by thermal analysis in the foundry shop. This includes the effect of the amount of nodularizer on the undercooling before solidification starts and the amount of recalescence when bulk eutectic solidification sets up. Comparing quantitative analysis of the as-cast microstructure with the characteristics of the cooling curves gives hints to a better understanding of the microstructure formation in compact graphite irons. This work thus provides a set of quantitative data necessary to verify the relevance of any solidification modelling approach for compact graphite cast iron. On a practical point of view, it suggests that thermal analysis could certainly be a useful means for control of melt preparation for CGI casting by adding very low level of inoculant in the standard thermal analysis cups.