What is the heat-affected zone (HAZ)?

What is the heat-affected zone (HAZ)?

• A. The portion of base metal whose microstructure and properties are altered by welding heat but not melted.
• B. The area of molten weld pool
• C. The outer surface of the weld bead
• D. The region of the plate unaffected by heat

Answer: (A)

When welding, the heat affects surrounding base metal enough to change its microstructure and properties, but not enough to melt it. That region is the heat-affected zone, and it sits between the completely melted weld metal and the untouched base metal. The HAZ is important because the metallurgical changes can change hardness, strength, or toughness, depending on the material and cooling rate. It’s distinct from the molten weld pool (which actually melts), the weld bead surface (which is just the outside of the weld), and the regions of base metal that were not heated at all.

When welding, the heat affects surrounding base metal enough to change its microstructure and properties, but not enough to melt it. That region is the heat-affected zone, and it sits between the completely melted weld metal and the untouched base metal. The HAZ is important because the metallurgical changes can change hardness, strength, or toughness, depending on the material and cooling rate. It’s distinct from the molten weld pool (which actually melts), the weld bead surface (which is just the outside of the weld), and the regions of base metal that were not heated at all.