Corrosion fatigue damage and mechanism evolution of Q420B steel in simulated dry/wet cyclic coastal atmosphere

Q420B low-alloy high-strength steel is the primary material used in China's ultra-high voltage (UHV) transmission towers. In coastal regions, the interaction of wind-induced fatigue and atmospheric corrosion makes it vulnerable to corrosion fatigue (CF), endangering grid safety. This study investigates the CF behavior and underlying mechanisms of Q420B steel, utilizing a specially designed dry/wet cyclic CF device. The results indicate that Q420B steel exhibits high sensitivity to CF, with the failure mechanism being controlled by anodic dissolution and hydrogen embrittlement. The crack initiation process unfolds in three stages: the formation of surface corrosion products, pitting corrosion beneath the rust layer, and nucleation of corrosion fatigue cracks (CFCs). Under low peak stress, anodic dissolution, hydrogen diffusion, and plastic deformation at the crack tip collectively hasten the propagation of CFCs. Under high peak stress, the mechanical effect at the crack tip dominates CFCs propagation. These insights are vital for optimizing the design and maintenance of UHV transmission towers.