The influence of Nb and Mo on the microstructure and mechanical properties of Ni-Cr-Fe GTAW welds

This paper was intended to investigate the influence of Nb and Mo on the microstructure and mechanical properties of Ni-Cr-Fe welds. Alloy 52, Alloy 52M and two variants of customized weld metals with higher contents of Nb and Mo were used as the test weld metals. Welding was conducted with a machine gas tungsten arc welding (GTAW) process. The results showed that the welds were dominant with dendrites and interdendritic phases. In Alloy 52 weld, large TiCs/TiNs were the main interdendritic phases. Tiny TiCs/TiNs and Cr-carbides were found in the matrix and along the grain boundaries, respectively. With an increase of Nb/Mo content, large precipitates transformed from NbC/(Nb,Ti)C into Laves phases and their sizes increased. Tiny precipitates NbC/(Nb,Ti)C in the matrix turned into (Nb,Mo)/C when Mo was added. The precipitation of Cr-carbides along grain boundaries was reduced with the addition of Nb/Mo. The hardness measurements of the fusion zone increased proportionally with the contents of Nb and Mo. Tensile tests showed that Nb and Mo increased the tensile strength. Ductile dimples were the fracture feature observed with the weld specimens with lower Nb contents.