A transverse crack is usually caused by:

A transverse crack is typically caused by rapid cooling of the material after welding. When the weld cools too quickly, it can create a thermal gradient that induces stresses within the weld and the surrounding base metal. These stresses can exceed the material's tensile strength, resulting in the formation of transverse cracks. This phenomenon is especially common in materials that are susceptible to such thermal stresses, as the quick contraction can lead to brittle failure across the weld seam.

In contrast, while improper wire manipulation, root gap, or incorrect amperage settings can lead to various welding defects, they do not directly result in transverse cracking. Improper wire manipulation can cause issues with bead shape or fusion, an improper root gap might lead to poor penetration or incomplete fusion, and the wrong amperage setting can lead to underheating or overheating of the weld. However, none of these factors are as directly linked to the phenomenon of transverse cracking as rapid cooling is.