What is the minimum preheat temperature for ASTM A572 grade 42 steel that is 1 3/4" thick welded with SMAW E7018?

For ASTM A572 grade 42 steel, the preheat temperature is a critical factor in ensuring sound welds, especially when using the Shielded Metal Arc Welding (SMAW) process with E7018 electrodes. The AWS D1.1 code specifies minimum preheat requirements based on the thickness of the steel and the carbon equivalent (CE) of the material.

In the case of 1 3/4" thick ASTM A572 grade 42 steel, the code indicates that a minimum preheat temperature of 150°F is required. This temperature is specified to help prevent the formation of brittle microstructures that can lead to cracking in the heat-affected zone during welding. It's particularly important for thicker sections as the cooling rate after welding can be much higher, increasing the risk of stress and cracking if proper preheating is not applied.

Choosing a preheat of 150°F not only aligns with code requirements but also provides an adequate margin to ensure the welds are of good quality and possess the necessary mechanical properties.