The heat-affected zone is the portion of the

• A. The Metal That Is Added To Produce The Weld Joint.
• B. Base Metal That Has Been Melted And Solidified.
• C. Base Metal That Has Not Been Melted But Where Properties Have Been Altered By The Welding Heat.
• D. Original Metal That Is Welded.

Answer: (C)

The heat-affected zone is the portion of base metal that has not melted but has had its properties altered by the welding heat. When welding, the heat travels into the surrounding metal, changing its microstructure near the joint without actually melting it. This region sits between the weld bead (where the metal has melted and then solidified) and the untouched base metal farther away. Because the metal in this zone experiences different cooling rates and thermal cycles, its hardness, strength, and toughness can change, which is why the HAZ is a distinct and important part of welded joints. The other areas are not the HAZ: the weld metal is the material that actually melted and re-solidified, and metal farther from the weld may remain in its original, unaltered state.