Effect of Mn on oxide formation by Fe-Cr and Fe-Cr-Ni alloys in dry and wet CO2 gases at 650 degrees C

摘要

Model alloys Fe-20Cr-2Mn and Fe-20Cr-20Ni-2Mn (wt.%) were exposed to Ar-20CO(2)-(20H(2)O) gases at 650 degrees C. Oxide formation was affected by alloy Mn diffusion, reaction temperature and gas composition. In dry CO2, both alloys initially formed thin scales of Mn3O4, Cr2O3 and MnCr2O4 layers. In wet CO2, Fe-20Cr(2)-Mn formed a thin, duplex scale of (MnCr2O4 + Cr2O3). The Fe-20Cr-20Ni-2Mn alloy formed a thin Cr2O3 scale. In both cases, different oxides were observed over alloy grain boundaries. Oxide development is discussed in terms of changes to diffusion paths resulting from alloy microstructural features, and the presence in oxide grain boundaries of carbon and hydrogen. (C) 2016 Elsevier Ltd. All rights reserved.