An Experimental Methodology Based on Solidification Curves for Controlling the Manufacture of Compacted Graphite Irons

Two models for the prediction of the nodularity level in compacted or vermicular cast irons (CGI) have been developed. The experimental CGI irons were produced with either FeSiMg alloy or a combination of FeTi and FeSiMg. The models development was based on the data provided by the cooling curves recorded from standard inoculated samples and their associated microstructures. A first model included the definition of a nodularity index (NIst) that can be determined rapidly for a given metal batch. Inoculation was also shown to be essential in guaranteeing optimal formation of graphite particles. A second model considered the effect of the cooling conditions on the graphite particles. The cooling curves and the metallographic features of a number of test-castings with different cooling moduli (M) were studied so as to improve the predictive model, previously developed. A nodularity index that includes the effect of the modulus, NIM, was defined for this goal. A good correlation between the experimental and the calculated NIM values was found in the range of 5-90% nodularity. Finally, validation experiments were performed using real castings in order to evaluate the application of both predictive models in industrial conditions.