During the casting process of thin-wall parts, due to fast cooling rate or chemical composition of the ductile iron, cementite may exist in the microstructure that retards the mechanical properties of the iron greatly. This research studied the variation of cooling rates of metal and green sand molds, silicon content of the iron, as well as the thickness of the casting plates, namely 3mm or 6mm, on the extend of iron carbide (cementite) formation of spheroidal graphite cast iron. The effects on various mechanical properties also evaluated. The results showed that if the carbide content was limited to 5-10%, the hardness and strength of the ductile iron will be increased significantly without losing too much of the ductility. The elongation would still conform to requirement of ASTM A536-84 grade 65-45-12 specification.
Cementite Iron carbide Ductile iron