The reason for the metallurgical heat-treatment process of stress relieving is primarily to remove residual, induced stresses from the steel. These stresses will occur as a result of rolling, forging, machining, welding, etc.
The only effective method or removing residual stresses is by the application of heat to the steel. When the heat-treatment cycle is started and the steel is being raised to the austenitizing temperature, for instance, the stress relieving will begin in the steel unless it has been previously reduced by the process of stress relieving.
The stress relieving process is generally accomplished by raising the steel to a temperature between 800°F and 1200°F. The higher the temperature chosen, the faster the stress relieving occurs. However, more surface oxidation (scale) results with higher temperatures. If the steel surface condition is critical, keep the stress relief temperature around 800-900°F. The steel will still oxidize on the surface, but it will discolor only and will not form heavy scale.
