Cyclic Oxidation Behavior of the Super Austenitic Stainless Steel 904L in Air at 500–650 °C

Cyclic oxidation behavior of the super austenitic stainless steel 904L was studied for 100 h over the intermediate temperature range from 500 to 650 °C in air. The oxidized surfaces and cross sections of the oxidized samples were examined by scanning electron microscope (SEM–EDS), X-ray diffractometer and electron probe micro analyzer. The weight gain was found to follow nearly parabolic rate law. At 500 and 550 °C, there was rapid weight gain up to the initial 5 h of exposure, whereas the rapid weight gain at 600 and 650 °C was up to 10 and 25 h of exposure, respectively. The weight gain was drastically reduced during the later stage of exposure. Since the formed scales were thin, strong peaks of austenite (γ)-matrix were observed in all the exposed samples. There was formation of thin layer of Cr2O3 on the specimens exposed at 500 and 550 °C. Also, there was heterogeneous formation of iron oxides in some regions. The exposure at higher temperatures of 600 and 650 °C led to the formation of different spinels of oxides such as FeCr2O4, NiCr2O4, FeNi2O4 and others, along with Cr2O3 and Fe2O3 oxides.