Which term describes the region of base metal that has experienced heat but has not melted?

• A. Heat Affected Zone
• B. Weld Pool
• C. Fusion Zone
• D. Heat Sink

Answer: (A)

In welding, the heat-affected zone is the part of the base metal that has been heated by the weld enough to change its microstructure and properties, but not hot enough to melt. This area sits adjacent to the weld pool and undergoes changes during heating and subsequent cooling—its hardness or brittleness can increase or decrease depending on the material and cooling rate. It’s distinct from the weld pool, which is the molten metal, and from the fusion zone, which consists of material that actually melted and then solidified. A heat sink, by contrast, is something that absorbs heat to keep temperatures down, not a region that forms during welding.