Carbon in the form of graphite is often used as an additive in the production of cast iron, amounting to 2 to 4 percent by weight or 6 to 10 percent by volume in typical castings. The microstructure of graphite within cast iron significantly affects the mechanical properties of the casting. When graphite takes the form of thin flakes the result is flake cast iron, which is hard and brittle. When graphite arranges itself as spherical nodules the result is ductile cast iron, which is softer and more malleable than flake cast iron. The relative high strength and toughness of ductile cast iron provides advantages in many structural applications including automotive crankshafts, pistons and cylinder heads.