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What is Ductile Iron ?

May 10, 2017

Ductile iron, also known as ductile cast iron,  SG iron,spheroidal graphite iron, spheroidal graphite cast iron and nodular cast iron, is a type of graphite-rich cast iron discovered in 1943 by Keith Millis. While most varieties of cast iron are brittle, ductile iron has much more impact and fatigue resistance, due to its nodular graphite inclusions.


A typical chemical analysis of this material:

Manganese 0.1 to 0.2% Sulfur 0.005 to 0.02%
Carbon 3.2 to 3.60% Copper <0.40%
Silicon 2.2 to 2.8% Phosphorus 0.005 to 0.04%
Magnesium 0.03 to 0.04% Iron balance











Ductile iron microstructure at 100×. Note carbon is landing effect around nodules.


Ductile iron is a part of a group of materials which can be produced with a wide range of properties through control of their microstructure. In ductile irons, graphite is in the form of nodules rather than flakes as in grey iron. Whereas sharp graphite flakes create stress concentration points within the metal matrix, rounded nodules inhibit the creation of cracks, thus providing the enhanced ductility that gives the name of alloy.


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