What does the term "heat-affected zone" (HAZ) refer to in welding?

The term "heat-affected zone" (HAZ) specifically refers to the region of the base metal that experiences changes in its microstructure due to the heat generated during the welding process. When welding occurs, the area immediately adjacent to the molten weld pool is subjected to temperatures that can alter the crystalline structure of the metal, leading to variations in its mechanical properties. This zone does not melt but is affected by the high temperatures and ultimately may become softer, harder, or experience other changes depending on the material and welding conditions.

Understanding the significance of the HAZ is crucial for welders because these alterations can influence the strength, ductility, and overall integrity of the weld joint. Identifying and managing the HAZ is essential to ensure that the welded structure meets the required specifications and will perform safely under its intended load conditions.