SPHEREOIDAL GRAPHITE IRON
Cast iron in which the graphite is in the form of nodules (spheroids). This particular microstructure is obtained by the addition of magnesium in the cast iron shortly before molding (if the melt is kept in fusion, it loses the specificities of the GS fonts after about ten minutes). Magnesium evaporates but causes a rapid crystallization of graphite in the form of nodules. This micro-structure gives it mechanical characteristics close to steel.