Pretreatments of gray cast iron with different inoculants

Steel scraps were used as the main raw materials (including 70% steel scraps and 30% pig iron) to prepare the gray cast iron HT250 in a medium-frequency induction melting furnace. A new inoculant X, which mainly contains SiC, and a conventional one (FeSi75) were added into the molten iron, respectively. The effects of the inoculants were investigated through metallurgical analysis of the matrix microstructure and the mechanical properties of the cast test bar, and scanning electron microscope (SEM) observation of the tensile fractured surfaces. The properties of the graphite morphology, matrix structure, mechanical properties and fracture characteristics of the cast iron were examined. The results show that both the new inoculant X and the conventional inoculant FeSi75 resulted in improved properties of the molten iron over the original uninoculated molten iron. The inoculants produced smaller graphite particles, reduced tendency to form shrinkage cavities and porosities during the solidification of the molten iron, decreased supercooling degree, reduced formation of non-metal inclusions, and enhanced mechanical properties (of the cast irons). Most important, the new inoculants X displayed more significant effects than the conventional one because SiC had a high melting point and did not dissolve immediately after being added into the molten iron, which helped to form a large number of micro-zones with high carbon and silicon concentrations and induced heterogeneous nucleation of graphite.