Below is a list of Spheroidal Graphite Cast Iron manufacturers from Grand Rapids, Michigan. Spheroidal graphite cast iron is a group of iron alloys specially formulated to create molded products with heightened elasticity, tensile strength and durability. Despite its wide use, grey iron tends to be brittle and is therefore discounted in many metallurgical applications. The creation of a spheroidal or nodular graphite microstructure, however, produces ductile cast iron that can be used more broadly.