Effect of the Type of Inoculant on the Shrinkage Porosity of High-Silicon SG Iron

High-Si spheroidal graphite (SG) iron is a relatively new addition to the family of SG irons. While the industry has been successful in producing class 500-14 and 600-10 irons there is a paucity of published research data on the efficiency of inoculation on shrinkage and porosity reduction. The critical phase is the end of solidification when, as the amount of eutectic graphite generated decreases, graphite expansion may become insufficient to compensate the solidification shrinkage, increasing the risk of micro-shrinkage (microporosity) formation. The goal of this industrial research was to assess the efficiency of eight commercial inoculants in minimizing porosity occurrence in a 3.45%C, 3.75%Si SG iron. Metallographic analysis was conducted on the TA cups to evaluate the nodule count and size distribution. SEM analysis was used to study the type of nuclei, and tomography to quantify the amount of porosity in each TA cup. An attempt was made to correlate the graphite formation rate during eutectic solidification with the porosity level. Inoculants rich in Zr seem to produce the best results.