Effects of Filler Metal Composition on Joining Properties of Alloy 800H Weldments

摘要

The influences of filler metal composition on the microstructure, mechanical properties and corrosion resistance of Alloy 800H weldments were investigated. Three filler metals including Inconel 625 (60%Ni- 21%Cr-9%Mo), Inconel 82 (72%Ni-17%Cr-2%Nb) and Alloy 309 (62%Fe-22%Cr-15%Ni) were used. Microscopic examination of the base materials, fusion zones and interfaces was characterized by using an optical microscope (OM), scanning electron microscope (SEM) and electron probe micro-analysis (EPMA). The results revealed precipitates of TiN with cuboidal morphology in the austenitic matrix along the grain boundaries of the Alloy 800H base metals. The thickness of unmixed zone formed at the Inconel filler metal/800H interface was much thinner than that at the Alloy 309/800H interface after welding. The formation of the unmixed zone with the different concentration gradients of the Ni, Cr and Fe elements was observed at the Alloy 800H/weld metal interface owing to the diffusion of nickel and iron during the re-solidification. The weldments made with the Inconel filler materials exhibited much higher strength and better ductility than iron-base Alloy 309 weld metal at room temperature. Inconel 625 exhibited the highest corrosion resistance among all tested filler metals and offered the optimum mechanical properties for Alloy 800H weldments.