Effects of nitrogen and hydrogen in argon shielding gas on bead profile, delta-ferrite and nitrogen contents of the pulsed GTAW welds of AISI 316L stainless steel

Abstract

The general effects of 1, 2, 3 and 4 vol.-% nitrogen and 1, 5 and 10 vol.-% hydrogen in argon shielding gas on weld bead profile (depth/width ratio: D/W) and the δ-ferrite content of AISI 316L pulsed GTAW welds were investigated. The limits for imperfections for the quality levels of welds were based on ISO 5817 B. The plates with a thickness of 6 mm were welded at the flat position and the bead on plate. Increasing hydrogen content in argon shielding gas increases the D/W ratio. Excessive hydrogen addition to argon shielding gas will result in incompletely filled groove and excessive penetration of weld. Increasing welding speed decreases the weld-metal volume and the D/W ratios. Nitrogen addition to argon shielding gas has no effect on the D/W ratio. The addition of a mixture of nitrogen and hydrogen to argon shielding gas on the D/W ratio does not show any interaction between them. An effect on the D/W ratio can be exclusively observed as a function of hydrogen content. Increasing hydrogen content in argon shielding gas increases the δ-ferrite content of weld metal. Increasing either nitrogen content in shielding gas or welding speed decreases the δ-ferrite content of weld metal. The nitrogen addition increases the weld metal nitrogen content, however, the hydrogen addition leads to a decrease of weld metal nitrogen content.

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“…All gas lines correctly purge to the chamber. V. Decrease of air/oxygen partial pressure in furnace atmosphere by feeding the Ar+N 2 shielding gas into the chamber at 0.3 bar at the flow rate of 5 L/min [23]. Check the operating pressure at the pressure gauge.…”

“…Duplex stainless steels (DSSs) typically consist of 50:50 ratio in amounts of phase balance between -ferrite (BCC, body centred cubic crystallographic structure) and -austenite (FCC, face centred cubic crystallographic structure) [1,20,22]. The delta phase renders the high strength property and stress corrosion cracking (SCC) resistance while the gamma phase provides the toughness and general corrosion resistance [23]. Note that, DSSs have been chosen as an alternative stainless steels selection not only expecting the excellent mechanical property but also the acceptable corrosion susceptibility [24].…”