Corrosion kinetics of Steel T91 in flowing oxygen-containing lead–bismuth eutectic at 450 °C

Specimens cut from two different sample materials of T91 ferritic/martensitic steel were exposed for up to 8000 h to flowing oxygen-containing lead–bismuth eutectic (LBE) at 450 °C, 2 m/s flow velocity and oxygen concentration averaging 1.1 × 10−6 mass%. Under these conditions, T91 forms an essentially bi-layer corrosion scale consisting of magnetite and iron–chromium spinel, whose thickness as a function of exposure time was measured in the light-optical microscope. The accompanying metal recession was assessed independently by a metallographic method as well. The quantitative data was analysed using different kinetic laws, in consideration of the results of electron-microscopic investigations and energy-dispersive X-ray micro-analyses of the scale. The implications of the data with respect to a solid-state transformation at the magnetite/spinel interface and extrapolation of the data to times relevant for operation of LBE-cooled nuclear systems is discussed.