The effects of Mn and Nb on the microstructure and mechanical properties of Alloy 152 welds.

This study was to investigate the synergetic effects of Mn and Nb on the microstructure and mechanical properties of Ni-based welds. The dissimilar weldments of Alloy 690 and SUS 304 L were welded with a manual shielding metal arc welding (SMAW) process. The weld metals were made of a core wire of Alloy 52 coated with fluxes of various Mn and Nb additions. The results showed that an increase in Mn could induce finer grains and smaller Nb-rich phases in the welds, while the dendrites and Mn-oxides became larger. For the welds with 3.99 wt.% Mn and 1.82 wt.% Nb, Nb-rich precipitates and Mn-oxides became smaller, and dendrites grew denser concurrently. The elongation of the welds at room temperature increased with the addition of Mn, but, by contrast, their hardness decreased. High contents of Mn and Nb could improve the notch strength and ductility at 300 °C, while they had little effects on the tensile stress at room temperature. Ductile ridges were the dominant fracture feature of the welds with an addition of Mn. For the welds with 3.99 wt.% Mn and 1.82 wt.% Nb, ridges dotted with small and deep dimples became prevalent. [ABSTRACT FROM AUTHOR]