We recently ran some WPQRs with Dual Shield 71 Ultra using 100% CO2 and "25% CO2/ 75% Argon(C25). Interesting to note that the C25 did in fact increase tensile strength over the CO2 using the same wire. I'm relying on memory here but I think the tensile and yield strengths increased by about 5 - 6 KSI, percentage of elongation was practically the same but on the low side of acceptable, CVN impact strength averaged lower but still acceptable. Please note that our results may differ from others because of things like heat input (ours is on the high side),product formulas, lot chemistry, and other variables.

You can also request the yearly test results from the various wire manufacturers to see what they ran for parameters and the results

It was interesting to note that many engineers I have dealt with, have reservations in authorizing FCAW for their projects because of reports of brittle welds. In evaluating our AWMT results one could think they have good reason. Some tensile readings were only 5 KSI (93) above the yield. However, my personal, unverified opinion is that most production welds, in our situation, are single pass welds and have good admixture with the base metal. That would "dilute" the higher strengths and increase the ductility somewhat. I think the electrode manufacturers formulate their wire knowing they can't control base metal chemistry and want to make sure the base metal fails before the weld does. So a WPQR, which is conducted to reduce/eliminate base metal contamination in the AWMT will show higher than normal results. Again, this is only my opinion. If I'm incorrect I'd appreciate knowing.

One more thing. If your wire is 71M Outershield, then you have a Lincoln product. Both ESAB and Lincoln have websites that can give further product info.

Hope this helps,
CHGuilford

When welding C/Steel, the general rule is that the more CO2 you have, the more carbon is lost during welding. This translates to lower tensile strengths.

Typically, you should use the gas recommended by your filler metal supplier. They know for which gas they formulated their wire. Having said this, 75/25 gas is often used for FCAW of CS.

You must also realise that tensile strengths (& impact properties) can be severely affected by the heat input. If this is too high, it will result in large grain structures and consequent low properties.

Hope this helps

Regards
Niekie Jooste

Trying to keep this as short as possible, here goes....wire manufacturers design flux core wires with certain amounts of de-oxidizers, based on a recommended shielding gas mixture of Argon and Carbon Dioxide...when the arc is established and the heat hits around 20,000 degrees, the CO2 dissassociates in to Carbon Monoxide and Free Oxygen, and float around in the weld pool....the deoxidizers attach to the free oxygen, and remove them from the molten weld puddle in the form of slag. If you use the wrong mixture of CO2 and Ar, (like maybe 10-15%), there are these de-oxidizers floating around looking for the oxygen molecules, and since there aren't any left over, they combine with the weld puddle to become part of the weldment. (I am not sure but I think the free oxygen content is around 12% of the Co2 content of the mixture-i.e. 12% of 25% in C-25)..When this happens, the deoxidizers increase the tensile strength of the weld...problem with increased tensile strength is ductility goes down.. I hope this helps to ensure that if the wire manufacturer suggests C-25 for a shielding gas, then that is what is used.
On a side note: Argon is introduced in the mixture for a couple of reasons...to lower the amount of fume generated, easier arc establishment due to electrical conductivity of argon, puddle control, and I am sure a thousand other reasons.
Have a great day