Reheating of a heat treated metal with a welding torch is most likely to:

• A. Have little or no effect on the metal's heat treated characteristics
• B. Cumulatively enhance the original heat treatment
• C. Significantly alter properties in the reheated area
• D. Be impossible to alter any properties

Answer: (C)

Reheating a metal that has already been heat treated changes its microstructure in the heated region, so the mechanical properties in that area are significantly altered. When the flame from a welding torch heats the material, the heat-affected zone experiences new phase changes and possible grain growth, which can soften the metal (loss of hardness and sometimes strength) or, if overheated, cause problematic microstructural changes. The cooling rate after heating also matters, influencing whether the material becomes softer, more ductile, or embrittled in that zone. In short, the area exposed to the torch will not stay as originally heat-treated; its properties are likely to change considerably.