Here's another article...
Shielding and Backing Gas Pure argon (Ar) shielding and backing gases can create weldments with sufficient corrosion resistance.
However, N loss is not uncommon to a depth of 0.5mm from the surface of the weld. To correct the phase balance and improve corrosion resistance of the weld, it is beneficial to have additions of 1-2% N in the Ar shielding and 90% N and 10% hydrogen(H) in the backing gas. Nitrogen contents above 2% in the shielding gas can cause degradation of the tungsten electrode for GTAW processes.
The addition of H to the shielding gas is not recommended as it may cause H absorption in the weld.
Back purging should be maintained on the joint until at least 6mm of weld metal thickness has been deposited.
The oxygen content of the back purged volume should not exceed 0.25 (2500ppm).
Since DSS have relatively high chromium contents and relatively low thermal expansion, an oxide scale appearing as an oxide tint is produced during welding that is typically thin and difficult to remove. The appearance and amount of heat-tint produced during welding can be minimized with low levels of oxygen (below0.25%) in the shielding and backing gases, with minimal moisture in the backing gas, and with limiting contaminants on the surface prior to welding. Hydrogen in the Ar backing gas can adversely affect the appearance of heat tint, and the base metal’s surface finish. Shielding gases suitable for the various gas shielded processes are listed in Table 5.
Table 5. Shielding gas general recommendations.
GTAW 99.996%Ar, Ar+2%N 2, Ar+5%N2
GMAW Ar+1%O2, Ar+30%He+1%O2, Ar+2%CO2, Ar+15%He+2%CO2
FCAW Ar+1%O2, Ar+20%CO2, Ar+2%CO2
PAW 99.996% Argon
There's another Table 6. which covers DSS and SDSS consumable specifications.
I'm not going to add the filler metal recommendations because they can be found in the very same article as a .pdf here:
http://stainless-steel-world.net/pdf/SSW_DEC07_fluor_LR.pdfWell, that's it for now.
Respectfully,
Henry
