What is the minimum preheat and inter-pass temperature when welding ASTM A572 grade 50 steel plate using E9018 electrodes?

The minimum preheat and inter-pass temperature requirement for welding ASTM A572 Grade 50 steel using E9018 electrodes is set at 50°F. Maintaining this temperature is crucial because it helps to reduce the risk of cracking in high-strength steel during the welding process.

Preheating serves several purposes: it helps in lowering the cooling rate of the weld metal, which minimizes the formation of hard brittle microstructures within the weld and heat-affected zone that could lead to cracking. Additionally, a proper preheat can reduce the stresses that build up during the cooling phase after welding, ensuring that the integrity of the weld and the base material is preserved.

The choice of 50°F is also in line with the guidelines provided in the AWS D1.1 code, ensuring that welders and engineers adhere to best practices when working with materials that exhibit certain characteristics prone to weld cracking. Other temperatures listed would either not provide sufficient protection against these risks or may be unnecessarily high for the materials involved.