The Influence of Temperature on the Oxidation Mechanism in Air of HR3C and Aluminum-Containing 22Cr-25Ni Austenitic Stainless Steels

To evaluate the suitability of HR3C and 22Cr-25Ni-2.5Al AFA steels as the heat-resistant alloys, the oxidation behavior of them was investigated in air at 700, 800, 900 and 1000 degrees C. The evolution of oxide layer on the surface and subsurface was investigated using a combination of compositional/elemental (SEM, EDS) and structural (XRD, GDOES) techniques. A dense and continuous Cr2O3 healing layer on the HR3C was formed at the temperature of 700 or 800 degrees C, but the Cr2O3 oxide film on HR3C was unstable and partly converted into a less protective MnCr2O4 with the increase in temperature to 900 or 1000 degrees C. The composition and structure of oxide film of 22Cr-25Ni-2.5Al AFA steels are significantly different to the HR3C alloys. The outer layer oxides transformed from Cr2O3 to Al-containing oxides, leading to a better oxidation resistance at 700 or 800 degrees C compared to HR3C. Further, the oxide films consist of internal Al2O3 and AlN underneath the outer loose layer after 22Cr-25Ni-2.5Al AFA oxidized at 900 or 1000 degrees C. It can be proved that the internal oxidation and nitrogen would make 22Cr-25Ni-2.5Al AFA steels have worse oxidation resistance than HR3C alloys at 900 or 1000 degrees C.