What is residual stress and stress relief?
Residual Stress is an internal pressure that is retained by metal after mechanical or thermal straining once the source has been removed. The source of residual stress in metal can be mechanical (forcibly changing the shape of grains), or thermal (sharp temperature drop). Stress, in particular, heat-induced stress, causes three types of problems – distortion following machining or grinding, delayed distortion, and premature fatigue failures. Stress relief neutralizes thermally induced stress, thereby eliminating subsequent problems. Changing mechanical properties or grain structure is not necessary to accomplish stress relief of thermally induced residual stress.