The Ideal of cast iron with ductility, long sought by metallurgists, was realized with the introduction of ductile iron in 1948. Acclaimed to be one of the most significant metallurgical developments in this century, ductile iron has had an increasing impact in many industries. Ductile iron has ductility – as the name implies – and in addition, it has strength and impact resistance far greater than that of gray iron; yet it retains the proven corrosion resistance of gray iron, thus making it an ideal piping material.
Ductile iron is produced by treating molten low sulfur base iron with magnesium under closely controlled conditions. The startling change in the metal is characterized by the free graphite in ductile iron being deposited in spheroidal or nodular form instead of flake form as in gray iron. With the free graphite in nodular form, the continuity of the metal matrix is at a maximum, accounting for the formation of a far stronger, tougher ductile material greatly exceeding gray iron in strength, in ductility, and in impact characteristics.
Photomicrograph Showing Graphite Form in Ductile IronPhotomicrograph Showing Graphite Form in Gray Iron