Abstract: Structural integrity of nuclear power plants under extreme conditions imposes stringent demands on the dissimilar pipe connection. Herein, a cumulative strain-induced gradient heterostructure strengthening strategy based on surface mechanical rolling (SMR) was proposed to synchronously enhance the mechanical properties and corrosion resistance of IN690/316LN dissimilar joints. A pre-engineered gradient dislocation network was implemented, significantly mitigating the initiation and propagation of cracks through suppressing strain localization. The gradient dislocation prefabricated by cumulative strain facilitates the formation of gradient-distributed domains, which are characterized by severe strain gradients and high-density geometrically necessary dislocations along the depth direction, further promoting a hetero-deformation-induced (HDI) hardening effect, and the effective depth exceeds 360 μm. The back stress during tensile deformation increases significantly following SMR, with a maximum enhancement of 56.1 MPa, thereby facilitating the strength-ductility synergy. The severe plastic deformation induced by SMR triggers martensitic transformation, introducing deformed twins and high-density stacking faults, synergistically enhancing mechanical properties through defect interaction and HDI hardening. Compared with as-welded joints, the surface hardness and elastic modulus increased by 35.15% and 91.4%, and the wear resistance improved by 105.3%, while the tensile strength and elongation rose by 39.71 MPa and 5.2%. Additionally, the corrosion resistance was substantially enhanced, with passivation film thickness increasing by 84.2%. The findings provide a technical foundation for high-performance manufacturing in nuclear power.

Key words: Inertial friction welding, Surface mechanical rolling, Gradient heterostructure, Mechanical properties, Corrosion resistance