Metallurgical, impact and fatigue performance of electron beam welded duplex stainless steel joints

Fusion zones of electron beam welded (EBW) 2205 duplex stainless steel (DSS) joints pertaining to two different levels of heat input, exhibited variable microstructural morphology as well as ferrite-to-austenite (alpha/gamma) ratio. Both the weld zones showed phase imbalance with ferrite being the dominating phase over austenite. However, as governed by the associated thermal cycles experienced by these welds, low heat input weld metal exhibited a relatively higher proportion of austenite as compared to the high heat input weld. Thermal aging at 850 degrees C/0.5 h promoted the formation of Cr and Mo-rich intermetallic sigma-phase and carbides in the welds, whereas welding resulted into Cr2N precipitation, which consequentially influenced their impact toughness and fatigue crack growth behavior. The aged joints showed a severe degradation in their impact toughness, the extent of which was more in the base metal than in the weld metal. The role played by the prevalence of secondary phases, unlike impact toughness degradation, was not detrimental but rather beneficial, as aged weld metals exhibited significantly superior fatigue crack growth resistance as compared to their unaged counterparts, which probably could be attributed to dispersion strengthening that occurred due to intermetallic precipitation.