Make a weld on the steel and then cut and etch with 5 cc nitric acid HNO3 & 100 cc ethyl alcohol C2H5OH. Compare with a mixture of 96% Argon 4% CO2. The CO2 mixture will give a more rounded weld bead profile. Check out/measure & compare the total fumes generated between the two mixes. And perform the mechanical tests to determine strengths required. A good test is always better than a thousand opinions.