Interface Corrosion Characteristics of T91 Steel in Static Lead-bismuth Eutectic with 0.01 ppm Oxygen

The interface corrosion characteristics of T91 steel, one of the candidate structural materials of lead-based reactor, were studied in static lead-bismuth eutectic (LBE) with an oxygen concentration of 0.01 ppm at 500 ℃ for 500, 1000 and 2000 h, respectively. The morphology at corrosion interface was examined by SEM. In addition, the product composition and element diffusion behavior were analyzed by EDX. The results show that the oxidation of T91 steel occurs and a three-layered oxidation film forms on the surface. The outermost layer is magnetite (Fe₃O₄) which has a porous structure penetrated by LBE, the middle layer is (Fe,Cr)₃O₄ that is more compact and protective, and the innermost layer is an internal oxidation zone (IOZ) consisting of Cr-rich oxides. With the increasing of corrosion time, the thicknesses of Fe₃O₄ and (Fe,Cr)₃O₄ increase rapidly at first, which reach 6.5 μm and 7.4 μm at 1000 h, respectively. Subsequently, the thickness of Fe₃O₄ slightly decreases while the thickness of (Fe,Cr)₃O₄ slightly increases, but the thickness of IOZ always increases slowly with time and the growth kinetics follows a linear law approximately.