When making a weld comprised of two dissimilar base metals for which there is a code required minimum preheat temperature, which of the following statements is correct?

When welding dissimilar metals, it is critical to adhere to the code-required minimum preheat temperatures for both base metals involved. The governing factor is generally the higher of the two preheat temperatures. This is because the metal that requires a higher preheat temperature is typically more susceptible to issues such as cracking or other weld-related defects. Implementing the higher preheat temperature helps mitigate these risks by ensuring that the weld area, as well as the surrounding base metal, maintain adequate thermal conditions throughout the welding process.

By using the higher preheat temperature, the weld can achieve the necessary ductility and toughness, particularly in the heat-affected zone, and thus enhance the overall integrity of the weld joint. This approach helps to align the thermal properties during the welding process, reducing the potential for thermal stresses that could arise from the welding of two dissimilar materials with differing thermal expansion and contraction rates.

Thus, it is essential to follow this guideline in order to achieve a sound weld when dealing with dissimilar metals, making it the correct choice regarding preheat requirements in such applications.