Processing properties
Spheroidal graphite cast irons - Processing properties

The relative ease with which cast irons can be machined, which is one of their main advantages, is due to the presence of graphite. The shape and quantity of graphite determine surface quality, while the nature of the matrix determines cutting conditions (tool life, speed, feed).

Brinell hardness measurement is an index of machinability, since it depends primarily on the structure. However, hardness alone cannot be a sufficient criterion of machinability, as machinability is affected more by the presence of hard constituents (e.g. traces of free carbides, which have a very detrimental effect on tool life) than by the variation in hardness resulting from these microstructural modifications.