Ductile iron, sometimes referred to as nodular or spheroidal graphite iron, is a relative newcomer to the field of cast irons. Developed in the 1940's, ductile iron has seen rapid and continued growth as a viable engineering material. With mechanical properties that compete with steels, ductile iron is being used more often as a cost savings tool in fabrication to casting conversion projects.

Chemically, ductile iron is similar to grey iron, with some minor but important exceptions. By treating the molten base metal with magnesium, the excess carbon that comes out of solution during solidification can be forced into a spheroidal shape. This spheroidal formation of graphite is what gives ductile iron it's unique mechanical properties.

Smith Foundry produces ductile iron in accordance with American Society of Testing and Materials (ASTM) A536. ASTM A536 covers a general class of ductile irons not specific to any application.

Grades of ASTM A536 Ductile Iron Produced at Smith Foundry


ASTM A536 Grade (SAE) Tensile Strength Yield Strengths Elongation Brinell Hardness
60-40-18 (D4018) 60,000 p.s.i. 40,000 p.s.i. 18 % 187 Max
65-45-12 (D4512) 65,000 p.s.i 45,000 p.s.i 12 % 156-217
80-55-06 (D5506) 80,000 p.s.i. 55,000 p.s.i. 6 % 187-255
100-70-03 (D7003) 100,000 p.s.i 70,000 p.s.i. 3 % 241-302



*Tensile, Yield and Elongation values are minimums required by ASTM A536 for an independantly cast tensile test bar sample. Consult ASTM A536 or Smith Foundry for more information.

Desirable properties Common Applications
Strength comparable to some steels Shaft and drive components
Ductility Valve Bodies
Impact resistance Couplers
Toughness Lift arms and linkages
Low cost alternative to steel castings and fabrications Brackets
  Discs and digger teeth





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Ductile Iron