Cold-worked metals are heated at temperatures lower than recrystallization temperatures to remove internal stresses, but remain cold-hardening. This is called stress relief annealing, also known as low-temperature annealing. The change of metal structure and properties during stress relief annealing corresponds to the recovery stage of temperature distribution. In practical production, the application of stress relief annealing process is much broader than the above definition. Hot forging, casting, all kinds of cold deformation processing, cutting or cutting, welding, heat treatment, even after machine parts are assembled, do not change the structure state, keep cold working, hot working or surface hardening, which parts of steel or machine processing are heated at lower temperatures to remove internal stress and reduce the tendency of deformation and cracking can be called elimination. Stress relief annealing.


Internal stresses may occur during pressure processing, casting, welding, heat treatment, cutting and other processes. In most cases, part of the residual stress will be retained in the metal at the end of the process. Residual stress can lead to cracking, deformation or size change of the workpiece. Residual stress also increases the chemical activity of metals. Intergranular corrosion cracking is particularly prone to occur under residual tensile stress. Therefore, the residual stress will affect the performance of the material or lead to premature failure of the workpiece.


During stress relief annealing, the metal undergoes local plastic deformation (when the stress exceeds the yield strength of the material at this temperature) or local relaxation (when the stress is less than the yield strength of the material at this temperature) at a certain temperature. Relax the residual stress in order to eliminate it. During stress relief annealing, the workpiece is usually slowly heated to a lower temperature (for gray cast iron, 500-550 degrees C, for steel, 500-650 degrees C, and less than the recrystallization start temperature of non-ferrous metal alloy stampings). Cooling to prevent new residual stresses.


Stress relief annealing can not completely eliminate the residual stress in the workpiece, but can only eliminate it to a large extent. In order to completely eliminate the residual stress, it is necessary to heat the workpiece to a higher temperature. In these cases, other organizational changes may occur, endangering the performance of the material.