Stress Relief Annealing
A thermal treatment below the transformation temperature where thermally assisted recovery processes and localized plastic yielding eliminate up to 90 percent of existing residual stresses. This serves to ensure dimensional stability prior to final machining.
You do stress relief annealing after welding to remove the internal stresses caused by rapid cooling. The workpiece is heated in a controlled manner to a temperature below the transformation temperature and held there so that the structure remains stable and the stresses can relax. The correct temperature and holding time depend on the material; if you're too sloppy with it, it won't do any good, and too much heat can ruin the structure. It's important to heat the part slowly and evenly and, after holding, let it cool down slowly again so that no new stresses build up.