Post-weld heat treatment (PWHT) is applied to steel assemblies primarily to reduce the likelihood of brittle fracture by reducing the level of tensile welding residual stresses and by tempering hard, potentially brittle, micro structural regions.

Conventional welding processes, which rely upon the local melting and fusion of material, generate significant residual stress distributions in the weldment. The magnitude of these stresses can, under conditions of high restraint, approach the yield strength of either the parent or weld materials. Post-weld heat treatment is applied to welded steel assemblies, primarily to reduce the likelihood of brittle fracture. The benefits of PWHT include a significant reduction of tensile residual stresses in the weld joint and, to a lesser extent, tempering of the heat-affected zone and the weld metal microstructures. PWHT is required where there is a risk of environmentally-assisted cracking.