Welder Red Seal · Question
What is the primary metallurgical reason for performing Post-Weld Heat Treatment (PWHT) on a welded P91 (Cr-Mo) steel component?
Welding Cr-Mo steels like P91 creates a hard, brittle martensitic structure in the heat-affected zone (HAZ) and introduces high residual stresses. PWHT tempers
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Question: What is the primary metallurgical reason for performing Post-Weld Heat Treatment (PWHT) on a welded P91 (Cr-Mo) steel component?
Answer options:
- To increase the ultimate tensile strength of the weld
- To remove surface oxides and spatter for inspection ✅ To temper the brittle martensitic structure and relieve residual stresses
- To solution anneal the austenitic grains for corrosion resistance
Correct answer: To temper the brittle martensitic structure and relieve residual stresses
Explanation: Welding Cr-Mo steels like P91 creates a hard, brittle martensitic structure in the heat-affected zone (HAZ) and introduces high residual stresses. PWHT tempers this martensite, restoring toughness and ductility, while also relieving the internal stresses that could lead to cracking.
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