Abstract: The erosion-corrosion behavior of three low-alloy martensitic steels with varying carbon contents under two typical flow conditions encountered by dredging metal components of high-velocity normal sand impingement and low-velocity low-angle sand impingement was investigated. The synergistic contributions of corrosion-enhanced erosion and erosion-enhanced corrosion were quantitatively distinguished using electrochemical and gravimetric measurements. The local damage mechanism was further elucidated through surface and cross sectional morphology characterization. Results revealed that the increased hardness and strength associated with higher carbon content significantly enhance the erosion resistance of these steels under both conditions. However, the resistance to erosion-corrosion displayed varying patterns depending on the carbon content. In high-velocity normal sand impingement conditions, total erosion-corrosion loss of the steels stemmed primarily from erosion. The elevated carbon content markedly reduces the fracture of extruded lips on the steel surface, thereby mitigating erosion damage and ultimately improving erosion-corrosion resistance. Conversely, under low-velocity low-angle sand impingement conditions, the synergistic interaction between corrosion and erosion dominated the mass loss mechanism. The formation of erosion-corrosion pits altered the local erosion mechanism from micro-cutting to detachment of the cliff-like substrate at the pit edges. Increasing carbon content shifted the detachment mode at pit edges from ductile fracture to brittle fracture, leading to more severe erosion. Consequently, the erosion-corrosion resistance decreased with the increasing carbon content. Based on these findings, a material selection strategy for low-alloy martensitic steels applicable to different dredging conditions was proposed.