What is meant by "post-weld heat treatment" (PWHT)?

Post-weld heat treatment (PWHT) refers specifically to a process used primarily to relieve residual stresses that remain in the weld area following the welding operation. During the welding process, the rapid heating and cooling cycles can create significant thermal stresses in the material. If left untreated, these stresses may lead to warping, cracking, or compromised mechanical properties of the weld and the base material.

By carefully heating the welded component to a specific temperature for a predetermined period and then allowing it to cool slowly, PWHT helps to redistribute and reduce these stresses. This treatment can also enhance the toughness of the weld and the heat-affected zone, making the components more resistant to failure.

The other options, while related to welding processes, do not accurately capture the primary purpose of PWHT. For example, strengthening the weld or improving its appearance may involve different processes altogether, and corrosion protection is typically addressed through other means such as coatings or material selection.