What alteration occurs in the heat-affected zone during welding?

In the heat-affected zone (HAZ) during welding, the microstructure of the material is altered due to exposure to high temperatures, although the material does not fully melt. The HAZ is the area adjacent to the weld bead where the heat from the welding process affects the material's characteristics. The raised temperatures can lead to changes in the grain structure, phase transformations, and other metallurgical changes that influence the mechanical properties of the steel.

This alteration can affect hardness, toughness, ductility, and strength in the HAZ compared to the base metal. Understanding the microstructural changes that occur in the HAZ is crucial for ensuring the performance and longevity of welded joints, as these properties can significantly affect how a structure will respond to various stresses and environmental factors.

Other options, while related to welding, do not accurately describe the key alteration that occurs specifically within the heat-affected zone.