2205 Duplex Question

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Hi all, quick question here on autogenous welds with 2205 SST @ 0.020 thickness.  I know that in general ER2209 is highly recommended due to it's ferrite minimizing quality, but for a number of reasons I would really rather not use a filler.Does anyone have experience with blending Nitrogen balanced with Argon to encourage the formation of Austenite in the HAZ?  This would in effect limit or combat the formation of Ferrite due to the lack of the benefits of the ER2209.I was thinking of starting with a 5%N 95%Ar blend to start with.Any thoughts or experience would be appreciated.Thanks
Reply:Makes perfect sense to me.  I think you're looking for a 50/50 austenite/ferrite balance, right?  From your avatar photo, looks like your doing mechanized TIG.  Do you a ferrite meter to measure the completed weld?  Could you take the percentages you get without added nitrogen, and then use the WRC formula to help estimate how much nitrogen pickup is needed, just to get in the ball park.  It would be interesting to run a statistical series of welds at a few various N2 levels, just mixing with two flow meters, then measure the ferrite and plot the regression curve.  Since the welding parameters/cooling rate also affect ferrite, the results would only apply directly to similar welds.Look forward to hearing what you come up with.
Reply:Thanks for the reply Pulser.  This is an auto TIG application, and I did decide to go with a mixer.  50/50 austenite/ferrite balance is the target.  This is a consultation so I think your idea of picking up a ferrite meter(damn $$) is the right way to go.  Developing some tables would be a nice future project.  The duplexes are getting more and more popular and there doesn't seam to be a large published knowledge base yet.