Correlation between impact angle and corrosion-erosion damage behavior of ferritic/martensitic steel exposed to flowing oxygen-saturated lead-bismuth eutectic

Impact angle is considered to be one of the main factors that influence the damage behavior of materials exposed to flowing lead-bismuth eutectic (LBE) conditions in Gen IV LBE-cooled fast reactors, especially in the areas where the flow changes its direction sharply, such as sudden expansions or elbows. In the current study, the corrosion-erosion damage behaviors of T91 ferritic/martensitic steel under different impact angles were investigated in flowing (∼3 m/s) oxygen-saturated LBE at 500 °C. The results show that the damage behaviors of T91 steel are closely related to the impact angles. When the flowing direction is parallel to the specimen surface, i.e., 0° impact angle, the oxide scales show partially damaged features in the form of local buckling and exfoliation after exposure for 300 h. With continued exposure for 600 h and 1000 h, the specimen surface seems to be covered completely by the undamaged oxide scales again. In sharp contrast, when the flowing direction is perpendicular to the specimen surface, i.e., 90° impact angle, the oxide scales are almost totally delaminated after exposure for 600 h and 1000 h. As a consequence, the liquid LBE permeates into the T91 steel substrate along the boundaries of prior austenite to induce intergranular corrosion. Correspondingly, the possible reasons behind such phenomena are discussed. Meanwhile, the damage process models of oxide scales associated with 0° and 90° impact angles are established, respectively.