Effect of Nitrogen Addition to Shielding Gas on Cooling Rates and in the Microstructure of Thin Sheets of Duplex Stainless Steel Welded by Pulsed Gas Tungsten Arc Welding Process

Abstract

The effect of the nitrogen content in the shielding gas and its effect on temperature distributions at the welded zone of thin sheets of duplex stainless steel have been evaluated. The duplex stainless steels have many features due to unique microstructural combination of austenite and ferrite grains. The phase balance can be easily shifted depending on the welding parameters. Two sheets were welded using pure argon and pure argon plus 2% of nitrogen as shielding gas. The thermal profile had shown that N 2-supplemented shielding gas lead to higher peaks of temperature using similar welding parameters. Microstructural examination showed that the austenite phase in the weld increased with the presence of nitrogen in the shielding gas. The added nitrogen promoted primary austenite formation and slightly increases the microhardness at the solidified zone. Microhardness mapping and metallographic imaging presented information about microstructures, confirming the formation of secondary phases during thermal cycle in the temperature range 850 °C and 950 °C. Control of ferrite amounts in the welds is essential mainly to improve mechanical properties and corrosion resistance of welding zones.

Effect of the Addition of Nitrogen through Shielding Gas on TIG Welds Made Homogenously and Heterogeneously on 300 Series Austenitic Stainless Steels

“…The addition of N 2 is known to increase the temperature of the weld pool as reported by [18][19][20]. The surface tension-driven Marangoni convection depends on the maximum temperature reached in the molten state.…”

Reduction of the Backing Gas Sequence as a Facile Method to Improve Corrosion Resistance in Duplex Stainless Steel (DSS) Weldment

“…The effect of mixing 2% nitrogen added 98% argon as backing gas for greater than 10 mm thickness, improving the corrosion resistance (Sales et al, 2016). Furthermore, several authors reported utilising nitrogen in the shielding and backing gas, leading to an increase of the austenite formation and lower chromium nitrides in the weld metal microstructure (Baghdadchi et al, 2020;Betini et al, 2019;Gozarganji et al, 2021;Liu et al, 2020;Matsunaga et al, 2013;Muthupandi et al, 2005). In contrast, the unbalance A/F transformation still occurred even with mixing a small percentage of nitrogen in argon for shielding gas or backing gas because the solubility and diffusion kinetics of atomic nitrogen in the solid-state is not in the liquid phase.…”

“…Although many studies on the detrimental phases such as chromium nitride and austenite precipitation in DSS while welding process has been reported (Baghdadchi et al, 2020;Betini et al, 2019;Gozarganji et al, 2021;Karlsson et al, 1995;Lippold & Kotecki, 2005;Liu et al, 2020;Matsunaga et al, 2013;Muthupandi et al, 2005;Ramirez et al, 2003), not much work has been done to simplify the DSS's welding method by reducing backing gas consumption. In this research, the authors simplified its method by varying sequences of backing gas.…”

Strain Rate Sensitivity Analysis of Duplex and Superduplex Steels in Tensile Tests

“…Many studies have been performed about microstructural and metalurgical aspects of these alloys (weldability, aging, heat treatments, phases, etc. for instance see [2][3][4][5][6][7][8][9][10][11][12] , but only a few about the phenomenological aspects of the macrossopic mechanical behavior, mainly concerned with Finite Element simulations 9,10 . It is not the goal of the present paper to perform an extensive review of these studies, but the previously mentioned references give a reasonable idea of the research in thie area.…”