AbstractThe fatigue properties of a high‐strength steel, a structural steel, and a duplex stainless steel in artificial seawater were investigated. Consequently, a test chamber for the existing ultrasonic test stand was implemented. The experiments were performed with smooth specimens at a loading with R = −1 up to 2 · 109 cycles. The specimens were fully submerged in artificial seawater. The fatigue data were statistically evaluated using the pearl string method and compared to different SN curves from the literature in air. The results show continuously decreasing SN curves under seawater conditions for all materials, with no detectable fatigue limit. Fracture surface investigations reveal large corrosion areas for the structural steel with, generally, no clear crack initiation location. The duplex stainless steel shows less corrosion pits but a high degree of scatter of the SN data. For the high‐strength steel, multiple crack initiation locations were observed from the surface.