Thesis (M.Sc.) - Cairo University - Faculty of Engineering - Department of Metallurgical Engineering

This research was aimed at investigating the effect of shielding and backing gases composition by supplementing nitrogen compared to usage of pure argon on: (i) microstructure of hyper duplex stainless steel root weld and phase balance within the weld regions; (ii) mechanical properties of the root weld zone in terms of amount of impact toughness and Vicker{u2019}s hardness; (iii) ferrite Content measurement ); (iv) susceptibility to pitting corrosion in terms of mass losses It was found that adding 2% nitrogen to argon in the composition of the shielding/backing gases in welding the root passes by gas tungsten arc welding process significantly improves the weld mechanical characteristics, phase balancing and noticeably enhances the corrosion resistance of the weldment. This is related to nitrogen which is a strong austenite stabilizer which leads to increase the austenite content in the weld zone during welding. And it was found that inferior mechanical properties, imbalanced microstructure which leads to poor corrosion resistance in the root weld zone were obtained in case of using pure argon gas as a shielding/backing gas

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