Superior Pitting Corrosion Resistance of Ultra-high Strength Low Alloy Steel Via Co-alloying Al and Cu

Advanced high-strength low alloy (HSLA) steels with outstanding corrosion resistance are extensively applied in marine engineering. However, corrosion sensitivity increases with steel strength. In this study, we developed a yield strength of 890 MPa ultra-high-strength offshore steel with superior corrosion resistance by regulating co-precipitation nanoparticles through co-alloying Al and Cu. Dispersed nanoparticles reduce lattice mismatch with the matrix and decrease pitting sensitivity, promoting the formation of a more homogeneous and dense passive film in the early corrosion stage. Al in EH890 steel is more prone to react with oxygen, resulting in the formation of Al2O3, which increases the protection of the passivation film. As a result, the corrosion potential of EH890 steel is higher, and its corrosion current density is five times lower than that of EH690 steel in 3.5 wt.% NaCl solution. As the corrosion progresses, Cu and Al can also encourage the formation of & alpha;-FeOOH in the rust layer, providing better protection to the substrate material. The EH890 steel has improved pitting resistance and electrochemical durability. This strategy may be informative for the development of advanced HSLA steels with superior corrosion resistance.