Shielding gases for TIG and plasma-arc welding
The normal gas for TIG welding is argon or helium, or a mixture. In some cases nitrogen (N2) and/or hydrogen (H2) is added in order to achieve special properties. For instance, an addition of hydrogen can be used for many conventional stainless steels to increase productivity.
Alternatively, if nitrogen is added, the weld deposit properties can be improved. Oxidizing additions are not used because they destroy the tungsten electrode.
Recommendations for shielding gases used in TIG welding of different stainless steels are given in the table. For plasma-arc welding, the gas types with hydrogen additions in the table are most ly used as plasma gas, and pure argon as shielding gas.
|Parent metal (type of material)|
|High-alloy austenitic stainless steel||Nickel alloys|
|Ar + He||●||●||●||●||●||●a|
|Ar + (2-5)% H2||●b||-||-||-||●b||●b|
|Ar + (1-2)% N2||-||●||●||-||-||-|
|Ar + 30% He + (1-2)% N2||-||●||●||-||-||-|
a) Ar + 30% He improves flow compared with Ar.
b) Preferably for automatic welding. High welding speed. Risk of porosity in multi-run welds.