Heat Affected Zone (HAZ)

A zone or region of metal adjacent to the weld bead, but in the bade metal. During welding, the temperature in the heat affected zone will quickly increase and then again decrease as a result of the production of the weld bead. The heat affect on the base metal microstructure and local properties, such as strength and hardness, is more dramatic near the weld bead and diminishes at distances into the base metal, away from the weld bead.