Influence of heat treatments on microstructure, mechanical properties and corrosion resistance of Inconel 625 overlay cladded using PTIG

Abstract

The influence of post-weld heat treatment (PWHT) temperatures on the microstructure, mechanical properties and corrosion resistance of Inconel 625 overlay cladded using pulsed tungsten insert gas (PTIG) was studied. The microstructure observation shows that as welded Inconel 625 overlay exhibits notable difference in grains morphology and size, and some precipitates, such as laves phase and MC phase, are distributed in the interdendritic zone. With an increase in PWHT temperature, equiaxed dendrites transform to columnar dendrites, and the overall difference in the microstructure decreases gradually. Compared with the as welded overlay, the size and number of the precipitates for the overlay heat treated at 650 °C shows very slight change. When the PWHT temperature increases to 750 °C, δ phase precipitates with the dissolving of laves phase. The number of δ phase increases clearly, and its size coarsens obviously with a further increasing PWHT temperature. Tensile tests indicate that there is a slight increase in the yield strength (YS) and ultimate tensile strength (UTS), but a decrease in elongation with the raise of PWHT temperature, which is no greater than 750 °C. Conversely, when the PWHT temperature beyond 750 °C, the YS and UTS decrease, the elongation increases slightly. Corrosion tests in the environment containing H2S and CO2 reveal that the Inconel 625 overlay heat treated at 650 °C exhibits superior corrosion resistance than that of other temperatures. Whereas, with an increase in PWHT temperature, the corrosion resistance degenerates seriously for the formation of δ phase.