Comprehensive Effect of Mn Content on Marine Atmospheric Corrosion and Mechanical Properties of Medium Manganese Steel For Marine Infrastructure Applications

Abstract

The role of Mn on the corrosion resistance in simulated marine atmosphere and mechanical property of medium manganese steel was investigated. The microstructure of the medium manganese steels was examined by electron backscatter diffraction (EBSD), and transmission electron microscope (TEM). The mechanical properties of test steels were evaluated through impact testing and tensile testing. The corrosion resistance of medium-manganese steels was investigated through dry-wet cyclic corrosion tests, electrochemical techniques, and compositional analysis. The results indicate that reducing Mn content is beneficial for corrosion resistance of medium-Mn steels. Lowering Mn content can effectively reduce the initial corrosion rate. The decrease of Mn content enhances the α/γ* ratio in corrosion products, thereby improving the protective quality of the rust layer. In the rust layer, Mn exists as MnO2, which not only accelerates the formation of iron oxides but also alters the relative proportions of iron oxide species, resulting in a decreased α/γ* ratio and enhanced corrosion resistance. Nevertheless, upon establishment of protective oxide layers, the investigated steel specimens demonstrated comparable corrosion kinetics. Notably, manganese content exerts negligible effects on the strength-ductility synergy in the experimental steels. However, reducing Mn content induces marked deterioration in impact toughness, primarily attributed to diminished stability of retained austenite.

Keywords: Marine atmosphere corrosion, Rust Layer, Retained austenite, Medium manganese steel, TRIP effect, Impact toughness