Annealing is an umbrella term used in heat treating, which refers to the process of raising the temperature and controlled cooling of a material to make it more ductile, reduce its hardness and generally make it more amenable to machine. The annealing technique is applied to castings primarily to improve machinability by softening the material. This heat-treating process is used to turn pearlite into ferrite. Whereas the annealing of steel only coalesces lamellar pearlite into granular pearlite, the annealing of cast iron results in a completely ferrite base structure without any eutectic iron carbide content. The annealing temperature in this case is just below the eutectoid interval at around 700°C.
Annealing heat treatment is carried out for the following grades.