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

Abstract

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, c O, of 10 −6 mass%, corresponding to a lead oxide (PbO) activity of approximately 10 −3. Owing to initial problems controlling c O, some of the exposed specimens experienced varying conditions, which allowed for investigating the influence of temporarily low c O (down to ∼10 −9 mass%), in addition to constantly high c O (averaging 1.6 × 10 −6 mass%). Maximum exposure times at constantly high c O 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 c O ≈ 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 c O proved to be beneficial for the performance of both steels, while, in the case of the ODS steel, excursions to higher c O should be prevented in order to achieve optimum oxidation resistance.