Abstract
The effects on the microstructure and room temperature mechanical properties of the nickel-based filler metal ERNiCrFe-7 due to a post weld heat treatment (PWHT) at 610 °C have been studied. It was shown that PWHT caused an increase in yield strength and ultimate tensile strength, but at the cost of reduced ductility and impact toughness. Crack tip opening displacement (CTOD) fracture toughness tests revealed an initial increase in maximum CTOD when a short PWHT was given, but declined with prolonged PWHT. The PWHT also caused a transition in fracture mechanism from microvoid coalescence to quasi-cleavage in room temperature air. Chromium-rich M23C6 type grain boundary carbides were present already in the as-welded weld metal, and were observed to coarsen during the PWHT. Intragranular M23C6 carbides were not observed in the as-welded state, but were precipitated during the 610 °C PWHT. Precipitation of these intragranular carbides is believed to be the main reason for the changes in mechanical properties.
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