Heat Treatment of Casting

Heat Treatment of Casting

The castings may be heat treated to improve their grain structure and to relieve them of the external stresses that get developed during the solidification. Steel castings can be hardened, tempered or annealed in usual way. For the heat treatment of cast iron, only closed-grained iron with small graphite flakes are more suitably heat-treated In comparison to a cast iron with open-grained structure. Cast iron can be hardened by preheating the casting to 600°C and then raising its temperature to 900°C rapidly. Quench it in oil or water. Take out the casting from quenching tank lest its temperature may not fall below 150°C. To temper, reheat in oil at 190°C for say half-on-hour.

Cast iron can be hardened by nitrogen-hardening process also. Shorter flame-hardening process and induction hardening process have been successfully tried to harden the cast iron. For annealing, heat the casting to 870°C, soak it until carbides are broken down and then cool slowly in the furnace.