Internal stress can arise in steel due to welding activities or even during the production process. This stress can lead to cracks and tears. By the application of the stress relieving process, this material stress can be reduced.

Stress relieving after welding is also known as Post Weld Heat Treatment (PWHT). Welding involves heating the area around the weld to extreme temperatures. When the material cools down, it will want to contract, but the surrounding cold steel will not allow it to. This causes tensile tension in and around the weld, leading to minuscule cracks that condensation will settle in, thereby causing corrosion (rust) in the long term. This stress corrosion will cause further cracking and thus result in a vicious cycle. This, of course, is unacceptable, especially if the welds are to be approved and certified.

 

 

Homogeneity and dimensional stability

Internal stresses are not caused by welding alone – they can result from deforming, bending, setting, or casting the steel. These stresses will have to be relieved before the material can be properly machined, as they may cause undesirable deviations and deformations. The solution? Stress relieving! This process makes the material’s structure more homogeneous, thereby making it easier to machine. In addition, a greater homogeneity of the steel will also result in less wear and tear on the machines and tools used to process the steel, increasing their service life.

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Heating and cooling slowly

Stress relieving entails heating the material in question to a temperature between 500 and 700°C. A vital prerequisite for the success of this heat treatment is that both heating and cooling are done very slowly in order to avoid creating new stresses due to temperature gradients within the workpiece. Cooling the material with calm air or in a sealed oven should take about twice as long as heating it.

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