Effect of Transverse Auxiliary Magnetic Field Strength on the Microstructure, Mechanical Properties, and Ductility‐Dip Cracking Susceptibility of ERNiCrFe‐7A GTAW Overlays

ERNiCrFe‐7A is widely used for welding critical nuclear‐island components because of its excellent corrosion resistance and high‐temperature performance. However, it remains susceptible to ductility‐dip cracking (DDC) during thick‐section welding. In this study, transverse magnetic‐field‐assisted gas tungsten arc welding was utilized to fabricate ERNiCrFe‐7A overlays. The effects of magnetic field strength on weld microstructure and mechanical properties were systematically investigated. Applying the magnetic field transformed coarse, elongated (Nb and Ti)C precipitates into fine, dispersed particles and converted Cr 23 C 6 precipitates at grain‐boundary triple junctions from thick, continuous lamellae to discontinuous granular particles. With increasing magnetic field strength, grain size and kernel average misorientation first decreased and then increased, whereas the fractions of low‐angle grain boundaries (LAGBs) and low‐Σ coincidence‐site lattice (CSL) boundaries first increased and then decreased. At 10 mT, the overlay exhibited the highest hardness of 188.7 HV and the best tensile properties, with tensile and yield strengths of 567.5 and 387.6 MPa, respectively, at 350°C. The critical strain for crack initiation at 950°C also increased and then decreased with increasing magnetic field. The critical strain for crack initiation increased to about 6% at 10 mT. The improved strength–ductility balance and reduced DDC susceptibility are attributed to mechanical interlocking induced by grain‐boundary serration, enhanced precipitate dispersion, Cr 23 C 6 granulation, and increased fractions of LAGBs and low‐Σ CSL boundaries.