There are three types of annealing treatment available for ductile cast iron: ferritizing annealing, full annealing and graphitizing annealing.
While both steel and ductile iron have almost the same composition, the higher percentage of carbon and silicon levels in ductile iron imparts different mechanical properties to it than steel. The higher carbon level in ductile cast iron makes it susceptible to quench cracking. Additionally, the higher level of silicon also lowers the solubility of carbon in austentite, which precipitates as graphite during slow cooling to form a ferritic matrix. Heat treatment of ductile cast iron is therefore a critical task.
Ductile cast iron can be hardened by quenching process as well. This involves austenitization at higher temperatures, followed by quenching to form matensite.
One other form of heat treatment for ductile cast iron is surface hardening treatment. This involves induction and flame hardening to increase the surface hardness and wear resistance of cast iron components.
Here are the benefits of heat treatment in brief. Do note that not all of these may be applicable to ductile cast iron.
It relieves internal stresses
Refines the grain size
Increases hardness or tensile strength
Improved machinability of the ductile castings
Modification in electrical conductivity, etc.
The most important parameters in the heat treatment process include the treatment temperature, holding time, and the rate of heating and cooling.
heat treatment ductile iron castings
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