Influence of Nb Microalloying on the Microstructure and Toughness of 1000 MPa-Grade Deposited Weld Metals

The effect of Nb content on the microstructure and properties of deposited weld metal was investigated using experimental methods such as scanning electron microscopy, electron backscatter diffraction, and transmission electron microscopy. The results show that the deposited weld metal mainly consists of a mixed lath martensite and bainite microstructure. The addition of 0.068 wt.% Nb resulted in the precipitation of a small number of spherical and cubic Nb-rich carbides inside and on the boundaries of the laths of the deposited weld metal, and the presence of a small number of spherical NbC particles with sizes in the range of 100-200 nm. After the addition of Nb, the dislocation and precipitation strengthening is enhanced, the strength of the deposited weld metal increased by about 6.1%, and the impact toughness is reduced. In addition, changes in low-temperature toughness were explored by methods such as oscillometric impact and fracture analysis, which support the development and application of 1000 MPa-class high-strength steel welding consumables.