Working with steel is a challenging and often complex operation. Working with steel in cutting, welding or machining of any type causes stress or internal structural changes in the grain of the metal. When this happens, there can be different types of stress found in the metal.
The most common types of stress are residual, thermal and structural. Residual stress occurs with machining and working with the metal and can impact how fast a part will corrode. It will also reduce the ability of the metal to withstand fatigue and also decrease the breaking strength.
Thermal stress occurs with welding or other heating processes. It is caused by contraction and expansion during heating and cooling. Structural stress will decrease the tensile strength of the part or component and make it less able to stand up to applied forces.
Relieving the Stress
There are practical and effective options for stress relieving steel as well as other non-ferrous alloys. This is a relatively simple process, but it has to be done correctly and at the correct temperatures and cooling times and conditions.
In stress relieving steel, the steel is exposed to heat at a given temperature and then cooled. The length of time the steel is held at the required temperature is a factor of the thickness of the piece. It is essential to avoid exceeding the maximum temperature during the process. The cooling has to be carefully controlled rate and temperature drop. This is perhaps the most essential part of the process, with incorrect cooling having the potential to reintroduce stress into the part or component.
At the specific temperature for the application of heat, the stress in the grain of the metal is relieved. In some cases, if the part has distortion, the distortion can be smoothed and removed, leaving the correct surface without the twisting or irregularities.