Ductile Iron Casting

Structure
The main difference between ductile iron and grey iron is the morphology of the graphite particles which take on a nodular or almost spherical form after suitable treatments are made to the melt.
Similar to grey iron the matrix may be ferritic, pearlitic or martensitic depending factors such as chemistry and other process variables.

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.

Applications
The wide range of properties mean that the various grades of ductile iron can be used in a variety of applications.
Ductile iron castings have production and machining cost advantages over steel fabrications, forgings and castings within the limitations of the ductility and impact properties and have strength to weight advantages over grey iron castings where breakage is a problem.
Ductile iron is specifically useful in many automotive components, where strength needs surpass that of aluminum.
 Other major industrial applications include off-highway diesel trucks, , agricultural tractors, and oil well pumps and so on .

Key Properties
As with most grades of cast iron, ductile irons display:
•         Good hardness and good wear resistance
•         Good corrosion resistance
•         Have tensile and yields strengths that vary widely across the various grades.
•         Have compressive strengths that can be utilised more widely (than tensilestrengths),  with values tending to be about twice the tensile strength.
•         Impact strengths are better than grey irons, with lower grades approaching values common for mild steel.

Acceptance at the base of Mechanical character