Case study on submerged arc strip cladding of NiCr20Mn3Nb on 20MnMoNi55: influence of strip width on weldability and microstructure for nuclear pressure vessel applications

This study examines the influence of strip width on microstructure, weldability, and cracking behavior of NiCr20Mn3Nb cladding deposited on 20MnMoNi55 pressure vessel steel using the Submerged Arc Strip Cladding (SASC) process. Two industrial strip widths, 30 mm (SAW-W30) and 60 mm (SAW-W60), were compared to evaluate differences in heat-input distribution, weld-pool geometry, solidification behavior, and elemental segregation under post-weld heat-treatment (PWHT) conditions. While both conditions satisfied mechanical property requirements, SAW-W30 exhibited higher energy density, deeper fusion, and increased susceptibility to microfissuring in cross-bead tests. Microstructural characterization using scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) revealed pronounced niobium and manganese segregation along grain boundaries in SAW-W30, particularly in regions subjected to repeated thermal cycling, which acted as the primary mechanistic cause for the observed micro-fissuring. In contrast, SAW-W60 promoted more uniform solidification and superior cladding integrity. Quantitative EDS analysis demonstrated significantly higher Nb segregation ratios at grain boundaries in the narrower strip condition, particularly in bead-overlap regions, which directly correlated with the observed tendency toward microfissuring. The results provide practical guidelines for optimizing strip width selection in nuclear pressure vessel cladding by linking fabrication-induced segregation and microfissuring behavior to the expected long-term resistance to corrosion, oxidation, and irradiation-assisted degradation.