Characterization of weld metal microstructure in a Ni-30Cr alloy with additions of niobium and molybdenum

Additions of niobium (Nb) and molybdenum (Mo) were made to an Alloy 690 base alloy in order to investigate the formation of a eutectic constituent at the end of solidification and to evaluate the effect of the eutectic liquid on backfilling (or healing) of solidification cracks. Solidification cracking was induced using the cast pin tear test (CPTT) and regions of backfilling were located and characterized via optical and electron microscopy. Computational predictions of fraction eutectic and composition of the eutectic constituent were compared to experimental findings and were found to correlate well in both cases. The extent of crack backfilling increased significantly with increasing Nb content, but the addition of Mo did not seem to influence the amount of eutectic constituent or the degree of backfilling. SEM/EDS analysis confirmed that the eutectic composition is constant and that increasing Nb above 4wt% has little effect on expanding the solidification temperature range, but has a beneficial effect on mitigating solidification cracking by a crack healing effect. •Increasing fraction eutectic as a function of Nb, as predicted by ThermoCalc™, is consistent with image analysis results.•Nb, unlike Mo, had a significant effect on the fraction eutectic formed.•Both influence the composition of the eutectic.•Thermocalc™ predictions regarding Nb content in eutectic are consistent with EDS results, but are high for the Mo content.•Increased levels of niobium resulted in a higher degree of crack backfilling and leads to a lower cracking susceptibility.•Mo may influence the eutectic liquid along solidification grain boundaries, improving backfill and thus cracking resistance.