What is the common shielding gas for GMAW mild steel?

The common shielding gas for Gas Metal Arc Welding (GMAW) of mild steel is typically a mixture of 75% Argon and 25% carbon dioxide (CO2). This combination is favored because it helps achieve a stable arc and produces good weld quality. Argon acts as a primary shielding gas that provides an inert atmosphere to protect the weld pool from contamination, while CO2 enhances the stability of the arc and improves penetration and weld characteristics.

Using a pure argon shielding gas can lead to difficulties in achieving a stable arc when welding mild steel since argon on its own lacks the reactive properties needed for optimal penetration. Conversely, a mixture of 50% nitrogen and 50% argon is not standard for mild steel welding, as nitrogen can negatively affect the weld properties and lead to issues such as reduced ductility. Pure helium might be used in specialized applications but is not typically the choice for mild steel due to its higher heat dissipation and challenges in maintaining a stable arc.

Therefore, 75% Argon and 25% CO2 effectively balances the need for arc stability, weld penetration, and overall weld quality for mild steel in GMAW processes.