Microstructural evolution and corrosion behaviour of thermally aged dissimilar metal welds of low-alloy steel and nickel-based alloy

Abstract

The influences of thermal aging on the microstructure, mechanical properties, and corrosion resistance of two different Ni-based weld metal/low-alloy steel dissimilar metal weld fusion boundaries were analysed. Cr23C6 precipitated at the fusion boundary immediately after welding. Additional precipitates were formed in 15 years of thermal aging and coarsened after 30 years of thermal aging. Changing precipitate morphology induced changes in other properties; the highest hardness and corrosion rate were observed at 15 years of thermal aging. The potential difference was bigger in welds with Alloy 152 than those with Alloy 182, yielding higher rates of galvanic corrosion.