What additional requirement is usually necessary for welding when using low carbon steel?

When welding low carbon steel, preheating is often necessary to reduce the likelihood of cracking, particularly in thicker sections or when welding common joint configurations. Low carbon steel has a lower carbon content, which means it has good weldability; however, it can still be susceptible to certain types of cracking, especially when welded under rapid cooling conditions.

By preheating the material, the risk of thermal shock is minimized. Heating the steel beforehand allows for a more gradual temperature transition, which helps to mitigate the stresses that can occur during the cooling phase of the weld. This preheating also aids in minimizing the hardness of the heat-affected zone (HAZ) that can lead to cracking in some alloy compositions if cooled too quickly after welding.

While other factors such as amperage settings, waiting times, and filler metal may influence the welding process, they do not specifically address the risk of cracking associated with the rapid cooling of lower carbon steels. Thus, preheating is the most relevant requirement to ensure a quality weld and to prevent issues related to cracking.