As the weld cools, residual stress is formed.[2] For thicker materials, these stresses can reach an unacceptable level and exceed design stresses. Therefore, the part is heated to a specified temperature for a given amount of time to reduce these stresses to an acceptable level.[2] In addition to residual stresses, microstructural changes occur due to the high temperatures induced by the welding process.[1] These changes can increase hardness of the material and reduce toughness and ductility.