Abstract
• Improved depth of penetration with the use of activated, nano-oxide flux welding for Incoloy 925. • The yield and tensile strengths of the weld joints were considerably increased when subjected to direct ageing. • The occurrence of γ′, M 7 C 3 , η, and σ phases were noticed along the grain boundaries in the direct aged condition. • High angle grain boundaries (HAGBs) were dominated in the jointed regions after subjecting to ageing. Precipitation strengthened Ni based alloy, Incoloy 925 is widely used in the H 2 S-containing hot sour environments because of its excellent properties. Metallurgical properties, which is known to affect the performace of this alloy greatly depends on the welding technique adopted, ageing condition, formation of inter-metallic phases and hardness. Hence, in this research work, the joints of Incoloy 925 are accomplished in a single pass with the use of nano-SiO 2 activtated flux tungsten inert gas (A-TIG) welding process. Further, the A-TIG welded joints were subjected to direct ageing for 4 h and 8 h at 732 °C and air-cooled. Recrystallized grains were observed in the fusion region in the as-welded (AW) condition. The grain boundaries of the weld seams were precipitated with M 7 C 3 carbides, discrete amounts of η (Eta) and σ (Sigma) phases after subjecting to DA. The tensile strength of the weld seams was increased to ∼ 41 % and 31 % after having exposed to DA for 4 and 8 h respectively. The failures due to tension occurred in the fusion zone of Incoloy 925 irrespective of the DA conditions. The formation of η phase and high angle grain boundaries (HAGBs) resulted in a lower percentage of elongation and impact toughness when aged for 8 h.
Published Version
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