Effect of Nb on the Corrosion Resistance of Ni-Cr-Fe-Based Weld Metals

The localized corrosion behaviors (intergranular corrosion, pitting, and interdendritic corrosion) of Ni-Cr-Fe-based weld metals with different niobium concentrations were investigated both in the as-welded and heat-treated conditions using the modified Huey test (ASTM A262-2010). Results indicated that Nb could reduce the intergranular corrosion susceptibility of Ni-Cr-Fe-based weld metals by preventing Cr carbides from precipitating at grain boundaries. However, the degree of pitting corrosion became more severe with the increase of Nb. The Laves phase could be corroded easily in the oxidizing environment, which increased the pitting corrosion sensitivity of weld metals. Interdendritic corrosion became the main corrosion type of weld metals that were heat treated at 620°C for 29 h. The depletions of elements Cr and Ni occurred in the interdendritic region, which resulted in the interdendritic corrosion of the heat-treated weld metals. With increasing Nb, the degree of Cr and Ni depletions became higher and the interdendritic corrosion sensitivity of the heat-treated weld metals increased.