What is the minimum pre-heat temperature for welding carbon steel according to AWS D1.1?

The minimum preheat temperature for welding carbon steel according to AWS D1.1 is established to help prevent issues like hydrogen-induced cracking and to ensure proper fusion during the welding process. The correct answer reflects the stand-alone criteria outlined in Table 3.2 of the AWS D1.1 code, which indicates that a minimum preheat of 100°F is necessary for certain conditions.

This preheat temperature serves multiple purposes, including increasing the material's temperature to facilitate better welding conditions and reducing the cooling rate after welding, which aids in minimizing stress and potential cracking. Different materials and thicknesses may have specific preheat requirements, but 100°F is a common benchmark that aligns with standard practices in carbon steel welding to ensure integrity and quality in welds.

Other choices do not meet the safety and quality assurances prescribed by the code for welding carbon steel, as they are either below or insufficient for effective welding under typical conditions encountered in structural steel applications. By adhering to the minimum preheat requirement, welders can improve the mechanical properties and lifespan of the welded joint.