Effect of Al Addition on Corrosion Behavior of High Mn Steels in a Cl^–-Containing Environment

The high Mn steels are expected to become a novel steel for liquefied natural gas (LNG) tank building because of their low cost, high strength, and excellent low-temperature impact toughness. Up until now, it is still limited for studies on corrosion behavior of high Mn steel in a Cl^–-containing environment. We found that strong Mn enrichment layers always exist in the outer rust layer, whereas strong Al enrichment layers always exist in the inner rust layer. However, the Al and Cl simultaneously enrich in the same area. Although the corrosion resistance can be further improved by increasing Al content from 5.0 mass% to 8.0 mass%, the improvement degree becomes weak and the pitting corrosion becomes serious due to the formation of δ-ferrite. There are two aspects to explain why Al improves corrosion resistance. (1) More Al addition can enhance the resistance of passive oxide. (2) The α-FeOOH content can be increased and the compactness of the rust layer can be also enhanced by increasing Al content.