Ductile Iron Casting
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In ductile iron the free graphite is in the form of discrete nodules or spheroids. The matrix may be ferritic, pearlitic or a mixture of the two. Other bainitic and martensitic structures may be formed by heat treatment processes such as quenching and tempering and ‘austempering’.
Properties:
The discrete form of the graphite nodules in comparison to the planes of weakness of the graphite flakes in grey iron means that the properties of ductile iron are determined more by the matrix of the material than the form of the graphite. Thus ductile iron has higher strengths, greater elongation and better resistance to impact than grey iron.
In the as cast condition a range of properties from high ductility to comparatively high strengths can be produced by control of the composition and production process. This range of properties may be extended by alloy adjustments and subsequent heat treatment including surface hardening and through hardening by quench and tempering.
Whilst the production of ductile iron is more involved than grey iron, it is still possible to produce complex shapes which are more easily machined than steel.
Application
Ductile iron casting as found wide acceptance and competes favourably with steel such that its use in engineering has increased in recent times as while grey cast iron and malleable cast iron has fallen in popularity as other materials such as plastics have found favour.
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