Heat-Affected Zone (HAZ) Welding

The heat-affected zone experiences peak temperatures insufficient to melt the material yet high enough to initiate recrystallization, grain growth, and phase transformations that alter hardness and toughness. In low-carbon steels, the HAZ typically softens slightly; in high-strength steels, it often hardens and becomes brittle, introducing a vulnerability to stress-concentration cracking.

Stainless steels suffer sensitization in the 400-900°C temperature window where chromium carbides precipitate at grain boundaries, causing intergranular corrosion if the material is not stabilized or solution-annealed post-weld. Minimizing HAZ severity through controlled heat input, rapid cooling strategies, and post-weld heat treatment are fundamental to achieving sound, corrosion-resistant structural weldments in demanding chemical and aerospace applications.