What is an effect of heat on the heat-affected zone (HAZ) during welding?

The heat-affected zone (HAZ) refers to the area of the material that experiences changes due to the heat generated during welding but does not melt like the weld pool does. When welding occurs, the base material is subjected to high temperatures, which can cause alterations in its microstructure.

One significant effect of this heat is the potential reduction of strength and toughness in the HAZ. As the temperature increases, certain phases of the material, particularly in steel, can transform from their original structures to forms that may not possess the same mechanical properties. For instance, areas in the HAZ can experience a transformation from a hard, high-strength phase (like martensite) to softer phases (like ferrite or pearlite) as they cool down. This transformation can lead to decreased hardness and potentially increased brittleness, resulting in a reduction of both strength and toughness in that specific zone.

Understanding this behavior is crucial for welders and fabricators, as it emphasizes the need for proper heat control and post-weld treatments to mitigate these adverse effects on the material properties surrounding the weld.