A repair shop is restoring a vintage steel bridge component made of an unknown, possibly high-carbon, steel. After welding, metallurgical testing indicates a very hard and brittle heat-affected zone (HAZ). What post-weld treatment would be most effective in making the HAZ tougher and more ductile, reducing the risk of brittle fracture?

Question: A repair shop is restoring a vintage steel bridge component made of an unknown, possibly high-carbon, steel. After welding, metallurgical testing indicates a very hard and brittle heat-affected zone (HAZ). What post-weld treatment would be most effective in making the HAZ tougher and more ductile, reducing the risk of brittle fracture?

Answer options:

• Stress relieving at a low temperature to remove surface stresses only
• Normalizing to refine the grain structure throughout the component ✅ Tempering at an appropriate temperature to reduce hardness and increase ductility
• Annealing to achieve the softest possible condition for machining

Correct answer: Tempering at an appropriate temperature to reduce hardness and increase ductility

Explanation: Temperings is the most effective post-weld heat treatment for reducing hardness and increasing the ductility and toughness of hardened zones in steel. It involves heating to a specific temperature below the critical range, holding, and then cooling. Normalizing and annealing are typically performed on the entire component and aim for different microstructures than specifically improving a hardened HAZ, while low-temperature stress relieving would not sufficiently alter HAZ microstructure.