Hydrogen Embrittlement Behavior of SMAW Nickel-Based Weld Metal in 13%Ni Steel: Dual Role of NbC in Hydrogen Trapping and Localized Damage

The hydrogen embrittlement behavior of Shielded Metal Arc Welding (SMAW) nickel-based weld metal (WM) in 13%Ni steel was systematically investigated. Microstructural characterization revealed that the WM mainly consists of columnar solidification grains with an average grain size of ~98.25 μm. Precipitates were identified primarily as dispersed (Nb, Mo, Ti)C carbides, with minor amounts of Al 2 O 3 inclusions and only very weak XRD signals consistent with Laves phase observed. Hydrogen distribution was analyzed using silver decoration and Nano-scale secondary ion mass spectrometry (NanoSIMS), both of which indicated preferential hydrogen accumulation at NbC precipitates. Slow strain rate testing (SSRT) conducted in 10 MPa hydrogen gas at room temperature revealed measurable hydrogen-induced ductility loss, with the reduction of area decreasing from 42.2% to 32.8%, while no complete transition to brittle fracture was observed. Fractographic analysis indicated that ductile dimples remain dominant, although localized cleavage cracks and increased microcrack density were observed under hydrogen exposure. Electron backscatter diffraction (EBSD) analysis revealed no appreciable difference in the average geometrically necessary dislocation (GND) density between air and hydrogen environments. Crack initiation was predominantly observed within NbC precipitates. The degree of crack initiation and propagation were strengthened by hydrogen. These results suggest that NbC precipitates may play a dual role in the hydrogen embrittlement behavior of the weld metal. The combined effects of hydrogen trapping and localized damage are proposed to contribute to the observed hydrogen-assisted degradation behavior of the SMAW Ni-based weld metal.