High-Temperature Oxidation Behaviour of Duplex Fe-Mn-Al-Ni-C Lightweight Steel

Lightweight Fe-Mn-Al-Ni-C steels are an attractive material, due to the combination of low density, high elongation, and yield strength. However, the high Al content is also interesting from the point of view of high-temperature resistance. High-temperature resistance is important for high-temperature applications and oxidation during heat treatment. Oxidation tests at 700, 800 and 900 °C were carried out to investigate the oxidation rates. Oxidation at 700 °C resulted in slight decarburisation, which was reflected in a slight weight loss in the thermogravimetric analysis. In contrast, the weight in the thermogravimetric analysis increased at 800 and 900 °C and the kinetics followed a parabolic law. The higher the temperature, the more weight is gained and the thicker the oxide layer becomes. The oxidation layer at 800 and 900 °C consisted mainly of hematite and magnetite, with minor amounts of wüstite, alumina and hercynite. Preferential oxidation of austenite was also observed, as it has an increased Mn content. In addition, ferrite had an increased content of Al and Ni, which provide additional oxidation resistance.