Weld Shrinkage Stress
Residual stresses caused by the restriction of thermal contraction during the cooling of the welded structure. They can lead to cracks or unacceptable component deformations.
When welding, the material heats up locally. When the weld and the surrounding area then cool down, the metal contracts. But because the part doesn't do this uniformly everywhere, stresses remain – that's called shrinkage stress. These can cause the workpiece to distort or the weld to crack. To get this under control, you need to make sure the part doesn't cool too quickly or too unevenly. The slower and more uniform the cooling, the less stress builds up. So if you don't force-cool the weld with water or compressed air, but just let it cool down calmly, you're already doing a lot right. For thick parts, it also helps to let the weld cool down slowly after welding with a thermal blanket or in an oven.