Cast iron is subjected to a process known as ductile iron casting in which magnesium and cerium are added as an alloy. Cast iron is subjected to a process known as ductile iron casting in which magnesium and cerium are added as an alloy. It alters the formation of graphite by reacting with the sulfur & oxygen in the liquid metal. Checkout here: https://www.bd-machinery.com/ductile-iron-casting/ for more info.