Corrosion behavior and surface analysis of 690 MPa-grade offshore steels in chloride media

High-strength low-alloy steels have been used prevalently in marine engineering and the defense industry because of their superior yield strength, toughness, and weldability. Although these materials have excellent mechanical properties, the corrosion resistance of high-strength low-alloy steels is a crucial problem, particularly when they are used in a marine environment. In this study, the corrosion behavior of a newly designed NiCu-containing low-carbon steel (NiCu steel) and conventional S690Q alloy steel (S690Q steel) was investigated and compared. Potentiodynamic polarization results indicated that for NiCu steel, current densities are apparently reduced in the anodic region. Surface analyses indicated that NiCu steel created a thick and uniform inner rust layer after it was immersed in NaCl solution for 7 days. Furthermore, a high-density Cr-rich region was observed in the NiCu inner rust layer after an immersion test. Electrochemical impedance spectroscopy results suggested that NiCu steel exhibits higher corrosion resistance than S690Q steel in NaCl solution. Keywords: High-strength low-alloy steel, Corrosion resistance, Polarization curve, Rust, X-ray photoelectron spectroscopy, Electron probe microanalyze