Heat Affected Zone (HAZ) is the area adjacent to weld where heat alters grain structure; the HAZ does not melt.

• A. It melts during welding
• B. It does not melt but grain structure can be altered
• C. It is unaffected by welding
• D. It only affects surface oxidation

Answer: (B)

When welding, the area next to the weld is heated by the hot metal, but not hot enough to melt the material. That region is the heat-affected zone. Its solid metal experiences changes in its grain structure due to the thermal cycle, which can alter properties like strength and hardness. This is why the correct statement says it does not melt but the grain structure can be altered.

The other ideas don’t fit because the HAZ isn’t molten metal itself, it’s heated enough to change its microstructure without melting. It is definitely affected by welding, and while surface oxidation can occur, the defining effect is the internal grain structure change, not just surface chemistry.