Annealing softening
Heat treatment of cast iron

In most cases, the desired structure and properties of lamellar graphite cast irons are obtained in the as-cast state, i.e. without heat treatment. This is practically the same for spheroidal graphite cast irons, for obvious reasons of simplification and economy. However, some foundries continue to anneal as a matter of course. Moreover, when the metallurgical process accidentally results in parts containing carbides, for example, or even more pearlite than necessary, treatment is indeed necessary, not only to lower hardness but also to improve ductility.

Softening by graphitizing or pearlitizing annealing can therefore be either corrective (to hard spots on defective parts) or systematic. It is generally recommended, if not always necessary, after a welding operation