Cast Irons

Cast iron is a material with a long history and tradition. According to the binary iron-carbon diagram, cast irons are alloys with more than 2.0% carbon, thus solidifying in the eutectic range with a low melting point. Cast irons usually solidify following the stable iron-carbon diagram, thereby forming graphite during solidification. In technical alloys, the additions of carbon and silicon are combined in the “carbon equivalent” (CE = %C + 1/3%Si). A CE of 4.3 represents a eutectic alloy, while those with a lower CE are called hypo-eutectic and those with a higher CE are called hyper-eutectic.

The family of cast irons comprises six classes of materials according to the characteristics of their graphite and matrix microstructure:

• Grey irons with lamellar graphite - GJL (DIN EN 1561)
• Ductile or nodular irons with spheroidal graphite - GJS (DIN EN 1563)
• Vermicular irons with compacted graphite - GJV (ISO 16112)
• White cast irons - GJN (DIN EN 126113)
• Malleable irons - GJMB/GJMW (DIN EN 1562)
• Austenitic irons - GJLA-X/GJSA-X (DIN EN 13835)

Definition of cast iron and steel types

In special cases, cast irons can be subjected to heat treatment after solidification for property improvement. The initial ferritic-pearlitic microstructure of the matrix is modified by “austempering” to become bainitic with a high fraction of metastable retained austenite. These irons are known as:

• Austempered ductile irons - ADI (DIN EN 1564)
• Austempered grey irons - AGI

Cast steels are defined as alloys where the combined addition of carbon and silicon (%C + 1/6%Si) is below 2%.