Abstract
The paper treats studies of TIG gas-shielded arc welding using pure nitrogen, N 2 + 5-20 % Ar gas mixtures and N 2 + 2-10 % H 2 gas mixtures. A weld root shielding was provided by nitrogen gas. Welding in N 2 requires by 40 % lower welding current than welding in argon. The study showed that porosity was an issue due to overalloying of N 2 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.
Highlights
TIG welding is the most widely used process for joining austenitic stainless steel sheets
Shielding gases used with this process are argon and various gas mixtures of argon with hydrogen, and argon with helium, which is more rarely
Root shielding is provided by argon, nitrogen and gas mixtures of argon with hydrogen or of nitrogen with hydrogen
Summary
TIG welding is the most widely used process for joining austenitic stainless steel sheets. In austenitic and duplex stainless steels nitrogen is an alloying element. Nitrogen hardens steel in two ways, i.e. with interstitial alloying of solid solution and with precipitation hardening by forming tiny nitrides[2, 3 and 24] In this way yield strength and tensile strength in the range from cryogenic to high temperatures are improved[1-5, 11, 20, 23 and 24]. Nitrogen decreases susceptibility to cold cracking of welds in duplex stainless steels by control of ferrite content[19]. A weakness of nitrogen in welding shows in arc instability due to reactions with a tungsten electrode[3, 13, 16 and 25] The latter will inflate and peel off due to an increased volume due to the formation of tungsten nitride. The favourable influences on austenitic alloys, favourable features of the arc, and a low price of nitrogen present a challenge for studying welding in nitrogen, which would be the cheapest TIG process variant
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
