Nitrogen is one of the gases that can easily been solved in liquid metal ; during cooling it needs to be evacuated from the molten pool , but if it remains in the solidified metal, it causes porosity. Not talking about other effects on mechanical properties ..
If you consider that ambient air consists of 80% nitrogen and about 20% oxygen , it's very obvious why we need a "shielding" gas : preventing of nitrogen & oxygen to react with the molten metal.
Arc stability has something to do with physics. Some gases do easily form ions , others (like nitrogen) not ; resulting in stable or unstable plasma flows.
Remember : the 'i" in TIG stands for "INERT" gas : Argon, Helium ; wich means it will not react with the molten weld pool, nor with the Tungsten electrode
By jwm80
Date 01-29-2005 22:10
Tim is correct, Nitrogen is a poor choice. You have two choices, Argon or Helium. Both has their advantages and disadvantages but Argon seems to be the #1 pick.
I used nitrogen without problem, it's thrue the root appearance is not so good than using argon, but it depends the use of component to be welded.
Regarding mechanical properties, there is not any difference with other welds using argon.
Regards.
By -
Date 03-31-2005 01:41
To just add to the discussion, that high of a nitrogen content can, and usually will, cause breakdown of the tungsten. Research has shown when using over 3% nitrogen as a shielding gas "can" cause the tungsten to break down and cause tungsten inclusions. If you are welding stainless steel, there are even more reasons not to use straight nitrogen as a shielding gas. You did not say whether you were welding stainless or carbon steel.
CM
