What are primary causes of weld cracking as per AWS D1.1?

Weld cracking can significantly impact the integrity of a welded joint, and understanding its primary causes is essential for ensuring quality in welding practices. According to AWS D1.1, improper preheating combined with rapid cooling is recognized as a major contributor to weld cracking.

Preheating the base metal is a crucial step before welding because it helps to reduce thermal gradients and the risk of stress concentrations that lead to cracking. When welding is performed on a cold base material, the heat input from the weld can lead to quick changes in temperature, resulting in high residual stresses. These stresses can cause the weld metal to crack if the preheating temperature is inadequate.

Rapid cooling, often caused by ambient temperatures or inadequate control over cooling rates, can also exacerbate the situation. If the cooling rate is too fast, it can lead to the formation of brittle microstructures in the weld and heat-affected zone, increasing the susceptibility to cracking.

The other factors mentioned, such as excessive welding speed, moisture, low-quality filler metals, paint on the base metal, and low ambient temperatures, can contribute to welding issues, but they do not specifically address the critical combination of preheating and cooling rates, which are essential elements in minimizing the risk of weld cracking