The reheating of a heat treated metal, such as with a welding torch

• A. Can significantly affect a metal's properties in the reheated area
• B. Improves properties everywhere
• C. Has no effect
• D. Causes cracking

Answer: (A)

When metal that has been heat treated is reheated during welding, the heat-affected zone near the weld undergoes microstructural changes. The original heat-treatment sets a specific balance of hardness, strength, and toughness. Bringing that region back up to welding temperatures alters the phases present, can dissolve or precipitate carbides, promote grain growth, or relieve residual stresses, and these changes directly change the material’s properties in that heated area. As a result, the reheated region can become softer or more ductile, or, if overheated or cooled improperly, more prone to cracking. Because this alteration occurs right where the heat is applied, it can significantly affect the properties in the reheated area, even if the rest of the metal remains as originally treated.