Stress Relieving Annealing

Stress Relieving Annealing:

As the name suggests, this process is employed to relieve internal stresses. No micro-structural changes occurs during the process.
Internal stresses are those stresses which can exist within a body in the presence of external forces. These are also known as residual stresses are locked in stresses.
These cracking also enhance the tendency of steels towards warpage and dimensional instability.
Fatigue strength is reduced considerably when residual tensile stresses are present in steel.
The problems associated with internal stresses are more difficult in brittle materials than in ductile materials.
The process of stress relieving consists of heating materials uniformly to a temperature below the lower critical temperature, holding at this temperature for sufficient time, followed by uniform cooling.
Uniform cooling is of utmost importance as non-uniform cooling will itself result in the development of internal stresses. Thus the very purpose of stress relieving will be lost.
Plain carbon steels and low alloy steels generally temperature is limited to 600⁰C . Higher temperature is used for high alloy steels.
The extent of the stresses relieved depends upon the temperature employed and holding time.