Carbon dioxide is used either alone or as an additive to argon in shielding gases used with the gas metal arc welding (GMAW) process when fabricating steels.
Solid Wire GMAW
When C02 is used alone for shielding with solid filler wires, the arc tends to produce excessive spatter unless it is kept very short. To avoid porosity, the filler wires must be specially deoxidized. However, when the arc length is properly controlled, the gas offers many advantages, such as high welding speeds, deep penetration and low cost. For these reasons, it is often the gas of choice, particularly for mechanized applications. Its use is restricted to mild steels, because both carbon and oxygen pick-up in the welds can be problems with stainless steels or low-alloy steels when toughness or control of weld composition are requirements.
Carbon dioxide is also used as an additive to argon. A mixture of 25% C02 and 75% argon is used to improve the arc stability and weld quality for the short circuiting modification of the GMAW process. Lower amounts, 6% to 8% C02, are used with argon to stabilize the spray transfer mode when welding carbon steels and low-alloy steels. Still lower concentrations of 1% or 2% C02 are used to stabilize the spray arc mode when welding stainless steels.
Flux-Cored Arc Welding
The effects of C02 on the welding arc and control of weld deposit composition are completely different when C02 is used to shield flux-cored wires. Because of arc stabilizers in the wire cores, the arcs can be very stable and free of spatter. Also, carbon pick-up can be controlled, allowing the gas to be used alone to deposit acceptable welds in stainless steels. However, since
better control of the arc and carbon is obtained by using a mixture of 25% C02 and 75% argon, this mixture is frequently used for shielding cored wires.