Influence of various gaseous environments on SiO2 formation on the 330Cb (Fe-35Ni-18Cr-1Nb-2.15Si) alloy at 900 °C

The influence of various gaseous environments on the 330Cb (Fe-35Ni-18Cr-1Nb-2.15Si) oxidation during 144 h, at 900 °C, has been studied. In air, a non-adherent Mn1.5Cr1.5O4 and Cr2O3 containing scale is formed and no continuous silica scale is observed at the alloy/oxide interface. In nitrogen, the chromia scale is adherent and a continuous cristobalite subscale is detected at the alloy/oxide interface. In Ar-5 vol.% H2, the oxide scale is mainly composed of chromia and manganese chromite. A thick cristobalite scale is also present at the alloy/oxide interface. On this austenitic alloy the protective silica scale formation is promoted by low oxygen containing gaseous environments and the high silicon content.

► In air the Mn1.5Cr1.5O4 and Cr2O3 scale does not show a good adherence.
► In air no silica scale formation is observed at the internal interface.
► The low oxygen containing gases (N2 or Ar-5% H2) improve the oxide scale adherence.
► Low oxygen gaseous environments promote a cristobalite external scale formation.