Gas-shielded, flux-cored arc welding (FCAW-G) is a very popular and versatile welding process. It is used with mild steel, low-alloy steel and other alloy materials in a variety of applications, such as heavy fabrication, structural, shipbuilding and offshore. The two most common (but not exclusive) shielding gases used with the FCAW-G process are carbon dioxide (CO2) and a binary blend of 75% argon (Ar) / 25% CO2. Other blends, such as 80% Ar / 20% CO2, can also be used.
So which shielding gas, 100% CO2 vs. an Ar/CO2 blend, should you choose for your flux-cored welding? Each type offers some advantages and disadvantages. The factors of cost, quality and productivity should be considered when manufacturing decisions are made. The choice of shielding gas affects each of these factors, sometimes in a conflicting way. The merits of the two basic gas options for FCAW on steel applications will be the focus of this article.
Choosing a Shielding Gas for Flux-Cored Welding
Figure 1: Gas-shielded, Flux-Cored Arc Welding
Before getting into the particular advantages of the gas options, it is appropriate to review some basics. It should also be noted that this article only focuses on a few types of gases. As a more comprehensive reference, ANSI/AWS A5.32/A5.32M [Specification for Welding Shielding Gases," prescribes the requirements for shielding gases, defining requirements for testing, packaging, identification and certification. Additionally, it contains helpful information on ventilation during welding as well as general safety considerations.
How Shielding Gas Works
The primary function of all shielding gases is to protect the molten weld puddle and electrode from the oxygen, nitrogen and moisture in air. Shielding gases flow through the welding gun and exit the nozzle surrounding the electrode, displacing the air and forming a temporary protective pocket of gas over the weld puddle and around the arc. Both CO2 and Ar/CO2 blends shielding gases accomplish this purpose.
Some shielding gases make it easier to create the arc plasma, providing a current path for the welding arc. The choice of shielding gas also affects the transfer of thermal energy in the arc and forces on the puddle. For these issues, CO2 and Ar/CO2 blends will behave differently.