Chromium vaporization of the ferritic steel Crofer22APU and ODS Cr5Fe1Y₂O₃ alloy

The chromium vaporization rate of the Crofer22APU steel as compared to Cr5Fe1Y₂O₃ alloy was studied under humidified air at 800 °C over a period of up to 1300 h by using the transpiration method. Under oxidizing atmosphere, the Crofer22APU steel forms a (Cr,Mn)₃O₄ spinel layer on the surface, which hinders chromium release at 800 °C by about a factor of 3 as compared to Cr5Fe1Y₂O₃ alloy forming a pure chromia scale. The impact of minor alloying additives in the Crofer22APU ferritic steel on the chromium vaporization was considered. The steel with the lowest amount of Al and Si in the matrix exhibits a low chromium vaporization rate over 1300 h. The microstructure and composition of the oxide scales and surfaces formed were investigated using high-resolution scanning electron microscopy, X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry. The results obtained give insight into the chromium vaporization mechanism.