Effect of shielding gas composition and activating flux on the weld bead morphology of the P91 ferritic/martensitic steel

In the current work, efforts have been made to study the effects of the activating flux and the shielding gas composition on the Tungsten Inert Gas (TIG) welding of SA 387 Gr 91 CL.2 steel (P91 steel). Multicomponent flux comprising of TiO2, SiO2, NiO, CuO, and CeO2 was used as an activating flux. Pure argon (Ar) and argon with nitrogen (Ar + N-2) were used as shielding gases. The relation between weld bead morphology and the welding conditions were emphasized with the help of welding arc column profile and arc voltage. Stereomicroscope, Optical microscope and Field emission scanning electron microscope (FE-SEM) equipped with energy dispersive spectroscopy (EDS) were used for macrostructure and microstructure analysis of the P91 weldments. The results suggested that the depth of penetration increases and bead width decreases in presence of the activating flux under Ar shielding. However, depth of penetration and bead width both increased by under Ar + N-2 shielding. Activating flux was found insignificant to reduce the bead width during welding under Ar + N-2 shielding. The welding arc inconstancy was found responsible for weld bead characteristics obtained during welding under Ar + N-2 shielding.