In the heat-affected zone, which region has the highest hardenability?

In the heat-affected zone, which region has the highest hardenability?

• A. Fine grain region
• B. Partial transformation region
• C. Coarse grained region
• D. Base metal region

Answer: (C)

Hardening tendency in the heat-affected zone follows how the microstructure forms during welding. The region that experiences the highest peak temperature and allows grains to grow the most—the coarse-grained HAZ—develops very large austenite grains. When this region cools, there are fewer grain boundaries to nucleate softer products like pearlite or bainite, so the remaining austenite tends to transform into harder phases such as martensite more readily. That makes this region the most prone to hardening. In contrast, the fine-grained zone has smaller grains with more nucleation sites for softer transformations, the base metal remains unchanged by the weld, and the partial transformation region falls between these extremes.

Hardening tendency in the heat-affected zone follows how the microstructure forms during welding. The region that experiences the highest peak temperature and allows grains to grow the most—the coarse-grained HAZ—develops very large austenite grains. When this region cools, there are fewer grain boundaries to nucleate softer products like pearlite or bainite, so the remaining austenite tends to transform into harder phases such as martensite more readily. That makes this region the most prone to hardening. In contrast, the fine-grained zone has smaller grains with more nucleation sites for softer transformations, the base metal remains unchanged by the weld, and the partial transformation region falls between these extremes.