Post-Weld Heat Treatment
A targeted thermal process such as stress relieving performed after welding to reduce residual stresses and homogenize the microstructure. It increases resistance to cracking and failure.
After welding, stresses and an uneven structure remain in the workpiece. Heat treatment anneals the material evenly, relieves the stresses, and calms the structure. This prevents cracks and makes the weld tougher.
Without annealing, the weld can remain hard and stressed, which quickly leads to cracks, especially in stiffer materials. If you do the heat treatment wrong, for example by heating or cooling too fast, you'll ruin the part rather than save it.
In practice, this means: heat the weld cleanly and evenly, not too hot, and above all, let it cool slowly. For sensitive or high-alloy steels, stress-relief annealing is mandatory; just letting it cool is not enough.