We know that both ductile iron and steel have almost similar composition; the high percentage of silicon and carbon levels present in ductile iron lends a different set of mechanical properties to it compared to steel. Because of the higher carbon level, ductile cast iron is prone to quench cracking. In addition to this, the higher percentage of silicon reduces carbon solubility in austenite, which precipitates in the form of graphite in the slow cooling process to produce a ferritic matrix.  This, therefore, makes heat treatment of ductile iron a crucial task. In India, only few manufacturers of ductile cast iron do it at the precision level.

The following are the different annealing treatment employed for ductile cast iron: full annealing, graphitizing annealing and ferritizing annealing.
The quenching process is useful for the hardening of ductile cast iron. This means austenitization is performed at higher temperature levels, after which quenching is done to produce martensite. Surface hardening treatment is an alternate heat treatment method. This involves flame hardening and induction to enhance the hardness of the surface as well as the wear resistance of different cast iron components.

The following are some of the benefits of heat treatment, though not in detail. Remember not all of these benefits may hold true for ductile cast iron:

• It frees internal stress
• Affects ductility by refining the grain size
• Increases tensile strength or hardness
• Improves ductile casting’s machinability
• Modifies electrical conductivity, etc.

The key parameters in the process of heat treatment include holding time, treatment temperature and rate of cooling and heating.