Stress relief heat treatment
The aim of the stress relief heat treatment, witch can basically be applied to all metallic materials, is the reduction of internal stresses in components without significant alteration of structure and the material characteristics.
Stresses can as a result of cold forming (e.g. metal forming processes, straightening), after welding, after cutting operations (e.g. milling, turning), after irregular cooling (e.g. strinkage resistance during the casting) occur or result from structural transformations. The superposition of internal stress with the strain stresses occurring in use can lead to unwanted shape changes (warping) or in the worst case even to component failure by fracture. A complete elimination of internal stresses is demonstrably not possible, however, a stress releasing well above 90% when properly executed the rule.
The stress relief heat treatment usually carried out at steel in a temperature range of 550 to 650°C (1022 to 1202°F), the material begins to flow plastically, the stresses accordingly. As a result, the unwanted warping is decreased at the final mechanical finishing.