Spheroidal graphite cast irons - Processing properties

As with all cast irons, the presence of free carbon greatly facilitates the machining of spheroidal graphite cast irons, as the carbon acts as a lubricant and promotes chip breakage. In addition, considerable progress has been made in the weldability of these cast irons, particularly ferritic cast irons, which are less prone to crystalline transformations due to heating of the weld zone, a zone which is thermally affected. The wear-resistance properties of spheroidal graphite cast irons can also be improved by surface heat treatment or coating.

Last but not least, major advances have now made it possible to produce spheroidal graphite cast irons with a bainitic structure, resulting from a special heat treatment known as isothermal quenching, which transforms the austenite into a structure with much higher tensile strength and toughness characteristics.

Standard NF EN 1564 of October 1997 specifies minimum values for tensile strength, 0.2% yield strength and elongation for four grades (table 1 ).