Three-Dimensional Numerical Simulation of Mechano-Electrochemical Coupling Behavior of Q420NS Steel with Different Corrosion Pit Morphologies Under Simulated South China Sea Environment

The mechano-electrochemical coupling behavior of Q420NS steel containing pits in the South China Sea environment was investigated. A three-dimensional numerical model incorporating elastoplastic deformation and corrosion kinetics was developed using COMSOL Multiphysics. The effects of axial tensile displacement and five typical pit morphologies on the local corrosion behavior were systematically examined, and the threshold displacement at which plastic deformation initiates was determined for each pit morphology. The results indicate that increasing tensile displacement elevates the stress, equivalent plastic strain, and corrosion rate at the pit bottom. Among the five morphologies, conical pits exhibited the earliest plastic yielding, the highest corrosion rate, and the strongest coupling effect, whereas semi-ellipsoidal pits demonstrated the best corrosion resistance. A coupling intensity coefficient K is originally proposed to quantify the intensity of the mechano-electrochemical coupling for different pit morphologies. This coefficient reveals the underlying mechanism by which pit morphology regulates the coupled corrosion process through stress concentration, thereby providing a scientific basis for the defect-tolerant design of marine steel structures.