Why flux cored welding wire is protected by CO2 gas?

The reasons for using CO₂ gas shielding in flux-cored welding wire can be analyzed from multiple perspectives, including welding performance, cost-effectiveness, and process adaptability. The following are the key points:

1. Weld Quality and Penetration Advantages
Deep Penetration: CO₂ decomposes into CO and oxygen atoms at the high arc temperature. The oxygen reacts with deoxidizing elements (such as silicon and manganese) in the welding wire to form slag, while simultaneously releasing a large amount of heat, significantly increasing penetration and making it suitable for welding medium and thick plates.
Arc Stability: CO₂ gas has a high degree of ionization, maintaining a stable arc, making it particularly suitable for high-speed welding and reducing spatter (this can be further optimized by using arc stabilizers in flux-cored wire).
2. Economical and Availability
Low Cost: CO₂ is a byproduct of industry (such as fermentation or petrochemical production) and is significantly less expensive than inert gases like argon, making it suitable for large-scale applications.
No Gas Mixing Required: Pure CO₂ can meet most welding requirements, eliminating the complexity and cost of preparing mixed gases (such as Ar + CO₂). 3. Synergistic Effects of Flux-Cored Wire
Self-Shielding Replenishment: The flux inside the flux-cored wire contains a deoxidizer and slag-forming agent, which offsets the negative effects of CO₂ oxidation (such as porosity) while simultaneously generating a protective slag covering the weld and improving mechanical properties.
Flexible Alloying: The flux-cored wire adds alloying elements (such as nickel and chromium) to compensate for alloy burnout under CO₂ protection, meeting high-strength or corrosion-resistant requirements.
4. Wide Process Adaptability
Suitable for Various Welding Positions: CO₂-shielded flux-cored wire performs well in flat, vertical, and overhead welding, and is particularly suitable for outdoor or ventilated environments (its wind resistance is superior to that of pure inert gas).
Efficient Deposition Rate: The concentrated heat of the CO₂ arc, combined with the high deposition efficiency of the flux-cored wire, makes it suitable for rapid weld filling. 5. Disadvantages Compared to Other Gases
Limitations of Inert Gases (such as Ar): While pure Ar shielding produces less spatter, it also results in shallow penetration and high cost, making it primarily used for stainless steel and aluminum. CO₂, on the other hand, offers a more cost-effective solution for carbon steel and low-alloy steels.
A Compromise Gas Mixture (Ar + CO₂): While it can balance spatter and penetration, flux-cored wire is already optimized for performance through flux, and pure CO₂ can achieve similar results.
Additional Notes: Spatter Issue: CO₂ shielding can produce significant spatter, but the flux powder of flux-cored wire contains arc-stabilizing components (such as potassium and sodium compounds) that effectively mitigate this issue.
Environmental Benefits: CO₂ shielding is non-toxic, but proper ventilation of welding fumes is essential.
In summary, the combination of CO₂ gas and flux-cored wire offers both economical efficiency and process flexibility while ensuring weld quality, making it particularly suitable for industrial welding of carbon steel and low-alloy steel.