Why do heavy forgings need heat treatment after forging?

The purpose of heat treatment for large forgings after forging is to refine the coarse grains caused in the forging process, eliminate work hardening and residual stress, reduce hardness, improve cutting performance, prevent white spots from forming inside the forgings, ensure the required metal structure and mechanical properties, and prepare for the final heat treatment. The following 6 types are commonly used.

Complete annealing -- eliminate the coarse uneven structure and widmanstatten structure caused in the forging process, refine the grain, eliminate the residual stress of the forging and reduce the hardness.

Spheroidizing annealing - to obtain spheroidal cementite and ferrite structure, which not only has lower hardness, but also is easy to obtain smooth machining surface during cutting, and is not easy to produce deformation cracks during subsequent quenching.

Isothermal annealing --- It can not only shorten the annealing time, but also obtain uniform structure and reduce hardness. In important large forgings, it can also be used to diffuse hydrogen to prevent white spots. The post forging heat treatment of aluminum alloy and copper alloy generally adopts annealing process. The purpose is to eliminate work hardening, stress and improve plasticity.

Normalizing --- fine pearlite can be obtained, which can improve the mechanical properties of forgings and is suitable for machining.

Normalizing and tempering at high temperature --- eliminate the stress generated during normalizing and cooling, and improve plasticity and toughness.

Quenching and tempering --- make heavy forgings have good comprehensive mechanical properties.