Grey iron contains iron, silicium and carbon (3% to 4.5%). If one lets the liquid metal cool slowly, the elements (iron and carbon) dissociate and carbon disperses in the mass in the form of spangles. Its melting point is around 1200 C. Grey iron is amalgamated easily: it is fluid, forms easily the shapes of the moulds in which one runs it. Moreover, it is easy to machinable.
Applications: car cylinder blocks, gears, frameworks for machines, supports, wheels, sections of kettles.
Ductile iron is a new alloy. It combines the easily fluid and machineable properties of grey iron with the mechanical properties of steel. One of its biggest characteristics is its structure in which graphite is present in the form of sphere of nods. The magnesium allows the carbon to take a sphere form. Ductile iron tends to replace malleable cast iron and molding iron.
Applications: agricultural manufacture of rolls, pipes, agricultural machines, etc.