Stress relieving:
The process is employed for relieving the internal stresses. No structural changes take place in this process. Internal stresses are those stresses, which can exist within the body in the absence of external forces. These are also known as residual stresses or locked-in stresses. Internal stresses can be developed while solidification of castings, welding, machining, shot peening, surface hammering, electro plating, cold working etc… internal stresses in certain conditions result in adverse effects. The presence of residual stresses enhances the tendency of steel towards warpage and dimensional instability.
The process consists of heating the steel to a predetermined temperature below the lower critical temperature and holding at this temperature for sufficient time and then cooling uniformly. Uniform cooling is utmost important since non-uniform cooling itself will result in formation of residual stresses. For plain carbon steels the maximum temperature is about 600° C. for high alloy steels higher temperatures are employed. For hardened and tempered steels, a temperature 25-30° C below the tempering temperature is employed.
COMMENTS