Stress relieving is a process to remove the intern stress or changes in molecular structure in steel as well as other types of alloys. As steel is machined, bent, formed, cold rolled or even welded, the molecular structure within the steel itself changes. This can also happen with quenching so that it may be completed at different times and stages in the component production process.
As this structure changes, it creates tension in the steel. This will result in distortions in the steel that can potentially increase the risk of stress cracking. At the very least this type of internal stress
The Process Of Stress Relieving Steel
This is a complex process that requires specific heat. The temperature will typically be at 1100 to 1200 degrees, which will be at just below the critical temperature for the steel.
At this temperature, which is just below the austenitic transformation level, will be held for a specific amount of time. The time and the temperature will be determined by the specific steel alloy. This temperature needs to be held consistently without cycling through heating and cooling.
This temperature, it is important to note, is below the temperatures used for annealing or for normalizing. Unlike these two processes, the goal behind stress relieving of steel is not to change the internal molecular structure; rather it is simply to remove the stress.
After heating, the second step of stress relieving of steel occurs. This involves a slower cooling period in air, without any quenching. By allowing the steel to cool slowly, there is no hardening or change in the surface layer of the piece.
In applications where steel is welded and then machined, stress relieving is often completed before the machining. This prevents warping of the stressed steel during the machining process, allowing for higher levels of precision manufacturing.
