What is the effect of stress relief on the hardness of weld metal?

Stress relief is a heat treatment process that aims to reduce residual stresses in welded components. These residual stresses can arise from temperature gradients during welding, leading to potential cracking or distortions. When a welded structure undergoes stress relief, it typically involves heating the weld metal to a temperature that is below its melting point and then allowing it to cool gradually.

The effect of stress relief on the hardness of weld metal is that it generally decreases hardness. This reduction in hardness occurs because the heat treatment allows for the redistribution of dislocations and the relaxation of internal stresses within the weld metal. As the material is heated, it softens, leading to improved ductility while reducing hardness. This softening effect can help enhance the material's overall toughness and reduce its susceptibility to cracking.

Therefore, stating that stress relief decreases the hardness of the weld metal aligns with the understanding of how heat treatment processes affect the microstructure and mechanical properties of welded joints.