In addition:
O2 in a carbon steel weld can combine with the carbon in the steel, which can contribute to weld porosity. It provides an increase in weld energy (heat; deeper penetration) over Ar alone and stabilizes the arc.
Ar/CO2 mixes provide more weld energy than Ar/O2 mixes because of a phenomenon known as dissociation... molecular nature of the CO2 causes release of chemical energy, in addition to the arc energy, as it breaks down into CO and recombines back to CO2. Ar/CO2 beyond 1.5 percent will cause problems welding nickel based steels, but at 1.5% or less it's supposed to improve wetting, fusion, and help stabilize the arc compared to Ar. Such small amounts of CO2 require precautions in mixing/filling to assure proper results.
I recall that 10% CO2 is roughly equivalent to 1% O2 in an Ar mix, but I believe there is a subtle difference in the penetration profile... too much fog to swear to accuracy or provide detail, though. (I am thinking O2 has ten times the oxidation potential of CO2)
What anti-oxidents do you mean? I believe you will tend to find more liquidity and slag residuals with an xxxx-s6 than an xxxx-s3 wire. With the duty of my simple work, this has never been an issue for me. None of the local supply houses admit to stocking ER70-s3. That must tell you something. That established I would prefer a wire with less Si and clean the metal of rust, slag, etc before welding. I would never think of welding over scale, smut, or rust anyway.
I guess the short answer is that it depends on the metal, and it's reaction to the chemistry and heat.
Regards,
D
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