Hilarie Hurlbut

The basic gas for MIG/MAG welding is argon (Ar). Helium (He) can be added to increase penetration and fluidity of the weld pool. Argon or argon/helium mixtures can be used for welding all grades. However, small additions of oxygen (O2) or carbon dioxide (CO2) are usually needed to stabilize the arc, improve the fluidity and improve the quality of the weld deposit. For stainless steels there are also gases available containing small amounts of hydrogen (H2).

The table indicates the appropriate choice of shielding gas for MIG/MAG welding, taking account of different types of stainless steel and arc types.

a) Preferably in pulsed MIG welding.b) Higher fluidity of the molten pool than with CO2 addition.c) Not to be used in spray-arc welding where extra low carbon is required.d) Better short-arc welding and positional welding properties than with Ar + (1-2)% O2.e) Higher fluidity of the molten pool than with Ar. Better short-arc welding properties than with Ar + (1-2)% CO2.f) For nitrogen-alloyed grades.

The normal gas for TIG welding is argon (Ar). Helium (He) can be added to increase penetration and fluidity of the weld pool. Argon or argon/helium mixtures can be used for welding all grades. In some cases, nitrogen (N2) and/or hydrogen (H2) can be added to achieve special properties. For instance, the addition of hydrogen gives a similar, but much stronger, effect as adding helium. However, hydrogen additions should not be used for welding martensitic, ferritic or duplex grades.

Alternatively, if nitrogen is added, the weld deposit properties of nitrogen alloyed grades can be improved. Oxidizing additions are not used because these 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 mostly used as plasma gas, and pure argon as shielding gas.

a) Improves flow compared with pure Ar. b) Preferably for automatic welding. High welding speed. Risk of porosity in multi-run welds.

A perfect welding result, without impairment of corrosion resistance and mechanical properties, can only be obtained when using a backing gas with very low oxygen content. For best results, a maximum of 20 ppm O2 at the root side can be tolerated.

listen) pew-AL-əp or /pjuːˈɔːləp/ pew-AWL-əp) is a city in Pierce County, Washington , United States, located about 10 miles (16 km) southeast of Tacoma and 35