Oxidation behaviour of P122 and a 9Cr–2W ODS steel at 550 °C in oxygen-containing flowing lead–bismuth eutectic

The long-term performance of 12Cr–2W ferritic/martensitic steel P122 and a 9Cr–2W ODS steel was tested in oxygen-containing flowing lead–bismuth eutectic (LBE) at 550 °C and a flow velocity of 2 m/s by means of exposure experiments in the CORRIDA loop. The target for the enrichment of dissolved oxygen was a concentration, cO, of 10−6 mass%, corresponding to a lead oxide (PbO) activity of approximately 10−3. Owing to initial problems controlling cO, some of the exposed specimens experienced varying conditions, which allowed for investigating the influence of temporarily low cO (down to ∼10−9 mass%), in addition to constantly high cO (averaging 1.6 × 10−6 mass%). Maximum exposure times at constantly high cO were 10,000 and 20,000 h for P122 and the ODS steel, respectively. Under the testing conditions, both steels were affected by moderate oxidation resulting in the formation of a compact layer of a spinel-type oxide on the surface and a more or less pronounced internal oxidation zone. The thickness of the oxide scale was quantified and used for determining the material loss (metal recession). For cO ≈ 10−6 mass%, logarithmic and power rate laws were fitted to the obtained data as a basis for predicting the metal recession at times exceeding the experimental exposure times. Temporarily lower cO proved to be beneficial for the performance of both steels, while, in the case of the ODS steel, excursions to higher cO should be prevented in order to achieve optimum oxidation resistance.