Corrosion behavior of aluminum-containing austenitic steels exposed to high-temperature molten chloride salt

Solar salts have a high energy storage density, and using solar thermal power generation technology can provide humanity with long-term, stable, and low-cost electricity. However, severe corrosion of structural materials when in contact with molten chloride salts is one of the main challenges limiting their long-term service at high temperatures. In this study, two types of aluminium-containing austenitic (AFA) stainless steels: 18Ni and 25Ni AFA steels, were prepared and their corrosion behavior in molten chloride salt (NaCl-MgCl₂-KCl with 30.2–47.1–22.7 mol.%) at 700 °C over different durations (200, 400, 600, and 800 h) was investigated. The corrosion products, thickness of the corrosion layer, and microstructure were characterized in detail. The effects of alloying elements on enhancing resistance to molten chloride salt corrosion were studied. Both types of AFA steels exhibited significant dissolution and oxidation behavior during the corrosion process, and the aggregation of Laves phases was observed. The corrosion depth after 800 h was found to reach a maximum of 131.3 μm, significantly lower than conventional 304 stainless steels under similar conditions. Why AFA steels exhibit resistance to chloride salt corrosion is discussed. The findings provide valuable guidance for the development of structural materials suitable for high-temperature molten chloride salt applications.