I have to agree with your assessment. Nitrogen is not good as a shielding gas, because you will form a great deal of nitrates in the weld, rendering it very brittle. For TIG, using nitrogen will result in the tungsten degrading very rapidly.

Nitrogen is sometimes used as a backing gas when welding stainless steels where it is difficult or impractical to purge with Ar. While this is a relatively common practice, I am not greatly in favour of it because I have my doubts about the quality of the internal weld surface.

Regards
Niekie Jooste

Tolga,

I have posted a similar question here that deals with using N2 as a backing gas on this site and on ENG Tips.com. A lot of good responses came up. search by my id "apiguy"... As for the quality of the root, none have passed x-ray with medium to large cracks being found. The material we are welding is super-austenitic though.

Nitrogen is never used as a welding shielding gas. In the heat of the welding arc it disassociates into atomic nitrogen and then can then combine with the metals to make nitrides as posted previously. Porosity is another problem associated with using nitrogen in shielding. A good reference on the topic is at Praxair. Their shielding gas selection manual talks about this.
Another note, if nitrogen is used as a backing gas, it should not be getting into the arc and therfore behaves inertly. N2 backing gas should only to be used with 300 series stainless steel (304, 316...), not other grades. It can cause real problems with other materials

For the shielding gas selection manual go to:
http://www.praxair.com/praxair.nsf/d63afe71c771b0d785256519006c5ea1/3a5665b9858c53d085256a08005e1cff?OpenDocument

Regards.