Automatic TIG welding of austenitic stainless steels in nitrogen and nitrogen-based gas mixtures

The paper treats studies of TIG gas-shielded arc welding using pure nitrogen, N2+ 5-20 % Ar gas mixtures and N2 + 2-10%H2 gas mixtures. A weld root shielding was provided by nitrogen gas.Welding in N2 requires by 40%lower welding current than welding in argon. The study showed that porosity was an issue due to over alloying of N2 in the weld pool; it can, however, be avoided with adequate welding parameters, particularly sufficiently high welding speed and controlled low heat input. The microstructure of all-weld metal is fully austenitic (γ). Hydrogen reduces nitrogen solubility in the weld pool and produces an austenitic-ferritic (γ+δ) microstructure. Titanium increases nitrogen solubility in the weld pool and strongly reacts with nitrogen. Consequently, there is a high fraction of TiN inclusions in the weld metal. (Author) 25 refs.