To avoid residual stresses after welding, what must be done with alloy steels?

To mitigate residual stresses in alloy steels after welding, it is essential to employ preheating, interpass heating, and post-weld heat treatment techniques. These processes work to manage the thermal gradient within the material, as welding introduces significant localized heating followed by rapid cooling. This can lead to undesirable residual stresses, which might compromise the integrity and performance of the welded joint.

Heating the alloy steel before welding helps to reduce temperature differences between the weld zone and the surrounding material, thereby decreasing the thermal shock and the tendency for cracking. Similarly, maintaining a consistent temperature during the welding process (interpass heating) ensures that the material does not cool too quickly between passes, allowing the heat to dissipate more uniformly. After welding, post-weld heat treatment can further relieve internal stresses by allowing the material to undergo a controlled cooling process, which helps to relax residual stresses and can also restore toughness.

In contrast, rapidly cooling or quenching the material after welding tends to exacerbate residual stresses, as the quick temperature drop can cause differential contraction and lead to thermal stresses. Additionally, welding in phases may be a strategy used for managing heat input, but it does not specifically address the reduction of residual stresses as effectively as a comprehensive heating strategy does.