Ductile Iron is not a single material, but a family of materials offering a wide range of properties obtained through microstructure control. The common feature that all Ductile Irons share is the roughly spherical shape of the graphite nodules. These nodules act as "crack-arresters" and make Ductile Iron "ductile". This feature is essential to the quality and consistency of Ductile Iron, and is measured and controlled with a high degree of assurance by competent Ductile Iron foundries.

Ferritic Ductile Iron

Graphite spheroids in a matrix of ferrite provides an iron with good ductility and impact resistance and with a tensile and yield strength equivalent to a low carbon steel. Ferritic Ductile Iron can be produced "as-cast" but may be given an annealing heat treatment to assure maximum ductility and low temperature toughness.

Ferritic Pearlitic Ductile Iron

These are the most common grade of Ductile Iron and are normally produced in the "as-cast" condition. The graphite spheroids are in a matrix containing both ferrite and pearlite. Properties are intermediate between ferritic and pearlitic grades, with good machinability and low production costs.

Pearlitic Ductile Iron

Graphite spheroids in a matrix of pearlite result in an iron with high strength, good wear resistance, and moderate ductility and impact resistance. Machinability is also superior to steels of comparable physical properties.The preceding three types of Ductile Iron are the most common and are usually used in the as-cast condition, but Ductile Iron can be also be alloyed and/or heat treated to provide the following grades for a wide variety of additional applications.

Martensitic Ductile Iron

Using sufficient alloy additions to prevent pearlite formation, and a quench-and-temper heat treatment produces this type of Ductile Iron. The resultant tempered martensite matrix develops very high strength and wear resistance but with lower levels of ductility and toughness.

Bainitic Ductile Iron

This grade can be obtained through alloying and/or by heat treatment to produce a hard, wear resistant material.

Austenitic Ductile Iron

Alloyed to produce an austenitic matrix, this Ductile Iron offers good corrosion and oxidation resistance, good magnetic properties, and good strength and dimensional stability at elevated temperatures. The unique properties of Austenitic Ductile Irons are treated.

Austempered Ductile Iron (ADI)

ADI, the most recent addition to the Ductile Iron family, is a sub-group of Ductile Irons produced by giving conventional Ductile Iron a special austempering heat treatment. Nearly twice as strong as pearlitic Ductile Iron, ADI still retains high elongation and toughness. This combination provides a material with superior wear resistance and fatigue strength.