The heat-affected zone (HAZ) is the area of a metal workpiece that structurally and property-wise changes because of the thermal heat from welding, cutting, or other heat processes, but does not melt.

Key Features:

• Thermal Impact: The high temperature changes the microstructure of the metal in this zone, which may influence its hardness, strength, and toughness relative to unaffected base metal and the weld metal.
• Possible Weak Points: Since the HAZ could become harder, softer, more brittle, or more corrosion-prone, it is usually an area of crucial inspection to check the integrity and performance of the welded joint.
• Broad Applicability: The principle of the HAZ is significant in techniques such as arc welding, laser cutting, flame cutting, and brazing, where heat input control is important to reduce unwanted metal alteration.

The importance of knowing the heat-affected zone is to preserve the intended mechanical properties of welded structures. For instance, high heat input can develop a large HAZ, resulting in residual stresses, cracking, or a decrease in toughness. Experienced welders and engineers implement preheating, post-weld heat treatment, and accurate heat control to control the HAZ and form robust, dependable joints. In safety-critical sectors like ship construction, pipelines, and steel structures, HAZ control is crucial to safety and longevity.