Nitrogen Alloying Additive in Shielding Gas

Nitrogen in the shielding gas isn't an additive that 'blows off' something; it dissolves in the weld metal and acts as an alloying element there. For austenitic steels, it ensures the structure stays fully austenitic and doesn't flip to martensite. That's important because if you lose the structure, toughness and corrosion resistance suffer. In practice, this means: when welding austenitic steel, use a shielding gas with a nitrogen content if the base material itself is nitrogen-alloyed. You don't want to pull nitrogen out of the melt, but keep the balance. Just watch that you don't add too much nitrogen to the gas, or you'll get porosity. And the gas flow must be constant, otherwise the melt pulls in air, and that really causes trouble with pores and scaling.