It is the heat treatment carried out to reduce the internal stresses in the parts to a level that does not cause problems or to completely eliminate them. Internal stresses may occur due to rapid cooling due to the temperature difference between the surface and the core, plastic forming such as straightening-bending, welding or after machining in thin surface layers for many different reasons. Stress relieving is normally done after roughing, before final machining, for example before polishing or grinding.
Parts with narrow dimensional tolerances and subsequent processing should be stress relieving, such as nitro-carburizing.
Welded structures can be made stress-free by stress relieving.
Stress relieving does not change the structure of the material and does not greatly affect its hardness.
Stress relieving should be done at a temperature approximately 50°C below the tempering temperature so that the hardness of the hardened and tempered parts does not change.
Before nitro-carburization, stress relieving should be performed at temperatures above 600°C.
Stress relieving can also be applied to copper and brass alloys. High temperature thawing is normally required for stainless steels.