Nitrogen as a backing gas for welding stainless steel

[aclarke]

Does anyone have any experience of using Nitrogen as a backing gas for the welding of stainless steel - in particular duplex grade 1.4362 to EN10088 (ASTM S32304)?

The torch shielding gas will remain as Argon/2% Nitrogen. The steel is in sheet form 1.0mm thick butt welded using ASTM S32205 filler wire.

 

[Jeffro]

Hi aclarke
Although I haven't used it for welding duplex grades of SS I have used it on a number of occasions for back purging of 304 & 316 grades of SS with great success. I would even go so far as to say that the finished appearance of the welds looks better than when using Argon purging.

 

[kenvlach]

For reference, nitrogen is permitted for use as a backing gas (only) in the welding of CRES steels per Paragraph 5.3.5.6 of MIL-STD-2219 FUSION WELDING FOR AEROSPACE APPLICATIONS. The nitrogen should meet Federal spec. BB-N-411.
[Note: this document was cancelled as of 10 Sept. 1999]

 

[nousakmj]

I've used it successfully as a backing gas for both austenitic and duplex stainless materials, but you should be aware that the austenite - ferrite percentages may change since nitrogen will increase the amount of the austenite phase. If you have limits on on the pahse percentages, you'll have to do a metallographic evaluation of the weld deposit from your PQR to tell whether or not it works for you.

Matt Nousak, P.E.
Senior Staff Engineer
Middough Associates Inc.
nousakmj@middough.com

 

[MOB1]

We have had experience of pipe fabrication companies getting their ferrite/austenite ratio correct in the root pass when welding duplex stainless by modifying the amount of nitrogen in the purge gas.
MOB1