Ductile (Nodular) Iron Ductile iron is alloyed with magnesium, which causes
the excess carbon to precipitate in the form of small spheres or nodules. These nodules
disrupt the structure less than do the graphite flakes of gray iron, thereby giving
substantial ductility along with improved tensile strength, stiffness, and impact resistance.
Ductile iron is specified by three numbers, as 60-40–18, which denote tensile
strength (60 ksi), yield strength (40 ksi), and elongation (18 percent).
Typical applications include engine crankshafts, heavy-duty gears, and hardware
items such as automobile door hinges.