Corrosion Fatigue Mechanisms of Marine High-Strength Steel Investigated Through Accelerated Laboratory Testing

The effect of applied loads (0.7σs, 0.8σs, and 0.9σs) on the corrosion fatigue behavior of a marine high-strength steel in natural seawater was investigated. Fatigue life decreased by 80.1% as the load increased to 0.9σs. Conversely, pit dimensions decreased with increasing load due to shorter pre-failure exposure times. The applied load governed the competitive growth of cracks: 0.9σs led to rapid dominant crack formation, 0.8σs allowed extensive secondary crack growth, and 0.7σs resulted in shallow pit-induced cracks. Fractography revealed transgranular cracking and accelerated growth under higher cyclic load. The corrosion fatigue mechanism is governed by pit-induced stress concentration, cyclic loading-induced dislocation accumulation, passive film rupture, and anodic dissolution, further accelerated by a local “large cathode, small anode” effect. These findings provide a theoretical basis for the integrity assessment of marine structures under variable loads.