Characterization of carbides in nickel-base weld metals of 13 %Ni steel and first-principles study of their hydrogen solubility

The precipitation behavior and hydrogen-related properties of carbides in Ni-based weld metals fabricated by shielded metal arc welding (SMAW), gas tungsten arc welding (GTAW), and submerged arc welding (SAW) were systematically investigated. Microstructural characterization using SEM, EBSD, and TEM revealed that NbC is the dominant carbide in SMAW weld metals, while Mo₂C and M₆C prevail in GTAW and SAW weld metals, primarily located in inter-dendritic Nb- or Mo-rich segregation zones. Most carbide–matrix interfaces were found to be incoherent, and high dislocation densities were frequently observed around the precipitates, suggesting a potential for local hydrogen enrichment. First-principles calculations of hydrogen solution energies indicated that all carbide bulk phases exhibit significantly higher hydrogen solution energies than the Ni matrix, implying that they cannot act as effective hydrogen traps. However, non-coherent interfaces and surrounding dislocations may still serve as local hydrogen trapping sites. These findings provide critical insights into the precipitation characteristics and hydrogen–microstructure interactions in Ni-based alloy weld metals, which are relevant to the design and performance optimization of welded structures for hydrogen environment applications. • NbC precipitates dominate in SMAW weld metals; Mo₂C and M₆C dominate in GTAW/SAW. • Carbides primarily form in interdendritic Nb- and Mo-rich segregation regions. • Carbide–matrix interfaces are incoherent and surrounded by high dislocation densities. • First-principles calculations show carbide bulk phases cannot act as hydrogen traps. • Non-coherent interfaces and dislocations may still promote local hydrogen enrichment.