Study on the corrosion behavior and mechanical properties of Q690 high-strength steel in flowing seawater environment

In this study, the electrochemical corrosion behavior, corrosion morphology evolution, and mechanical property degradation of Q690 high-strength steel under different seawater flow velocities were systematically investigated. Open-circuit potential, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and mass loss measurements were employed to quantitatively evaluate the effect of flow velocity on corrosion kinetics. CT scanning, SEM, and nanoindentation were used to characterize corrosion pits and nonuniform corrosion layers, while tensile tests were conducted to assess mechanical degradation under flow-accelerated corrosion (FAC) conditions. The results show that flow velocity does not alter the fundamental electrochemical corrosion mechanism but significantly accelerates corrosion kinetics. With increasing flow velocity, the corrosion current density increases, charge transfer resistance decreases, and mass loss rate rises. The corrosion morphology evolves from uniform shallow corrosion under static conditions to deep pitting and pronounced nonuniform corrosion layers under flow conditions, accompanied by increased surface roughness and defect severity. Mechanical properties degrade progressively with increasing mass loss rate, with elongation showing the highest sensitivity, while yield strength and tensile strength decrease approximately linearly. Predictive models were established to describe the relationships between mass loss rate and the residual elastic modulus, yield strength, tensile strength, and elongation. These findings clarify the coupled corrosion–mechanical degradation mechanism of Q690 steel under FAC and provide a quantitative basis for durability evaluation and structural integrity assessment of high-strength steels in marine environments.