The effect of high content of nitrogen in shielding gas and filler metal on microstructures and ferrite content of tungsten inert gas multilayer welding duplex 31803

Abstract

Alloy of duplex stainless steel UNS S31803 (2205) has a combination of mechanical properties with good pitting corrosion resistance. This is due to the chemical composition and the equilibrium phase of the microstructure (40- 60%) in duplex. Comparison of the volume fraction of the ferrite-austenite phase which is balanced can change due to the influence of heat due to repeated welding processes. Nitrogen is one of the austenite former element besides nickel. The equilibrium of the ferrite-austenite phase can change due to nitrogen. The loss of nitrogen results in a higher ferrite content. The phenomenon of nitrogen loss, both by using high and low heat inputs, is an important factor that can have a detrimental effect in the welding of duplex stainless steel. Duplex stainless steel can be joint using Tungsten Inert Gas (TIG) welding process. Uncontrolled welding duplex can result in the formation of detrimental phases (nitrides and sigma phases). Adding nitrogen to the shielding gas welded duplex stainless steel using the TIG process can facilitate the formation of austenite and reduce the amount of nitride precipitation and sigma phase, resulting in increased toughness. Corrosion resistance will also increase with the addition of nitrogen. The use of fillers metal with austenite-forming elements that exceed base metal can also help austenite formation. The aim of this study was to investigate the effect of adding nitrogen as shielding gas and filler metal to the equilibrium volume fraction phase of ferrite-austenite and microstructure evolution. In this study using a variable of 2% nitrogen, 4% nitrogen, 6% nitrogen, 8% nitrogen, and 10% nitrogen mixed with argon gas. The result is N2 in shielding gas more than 2% has porosity defect and nitrides. 2% N2 has wider austenite area than pure Ar and good phase balance. ER2594 also made lower ferrite content.