Investment casting with ductile iron offers an array of benefits, from wear, impact and fatigue resistance to far greater strength than cast iron – up to double the tensile strength. The biggest difference between ductile and cast iron is the form of graphite that exists within the alloy. Graphite is a crystalline form of carbon with its atoms in a hexagonal structure. Ductile iron has spherical graphite structure in the metal, while weaker cast iron has graphite flakes. The typical composition of ductile iron is approximately 94% iron (atomic number 26), a few percent each of carbon and silicon and small percentages of copper and other elements. Ductile iron can be used in an extensive list of applications, but it is more expensive than cast iron, so cast iron is often used when possible.