Stress Relief Annealing

Annealing is a heat treatment to stabilize the structure and relieve internal stresses caused by welding or previous machining steps. The part is heated evenly in a furnace to a temperature below the transformation point and held there so the atoms can move back to their normal positions. Then you let it cool slowly, otherwise you'll introduce new stresses. If you skip this, the workpiece can warp or even crack during machining.