Welding Inspection & Metallurgy API ICP Self Study Notes

An important factor in selecting shielding gases is the type or mixture. A
reactive gas such as carbon dioxide can break down at arc temperatures into
carbon and oxygen. This is not a problem on carbon and low-alloy steels.
However, on high-alloy and reactive metals, this can cause an increase in
carbon content and the formation of oxides that can lower the corrosion
resistant properties of the weld. High-alloy materials welded with gas-shielded
processes usually employ inert shielding gases or mixtures with only slight
additions of reactive gases to promote arc stability.