Corrosion behavior of 9Cr-ODS steel in stagnant liquid lithium and lead-lithium at 873 K

摘要

Corrosion experiments of 9Cr-ODS steel were carried out in static Li at 873 K for 250 h and compared with those of 9Cr-ODS in Pb-Li at the same exposure conditions. After exposure to liquid Li, 9Cr-ODS showed slight weight loss and decrease in hardness near surface. The tensile property exhibited a negligible change at 973 K and the creep property degraded at 973 K. By metallurgical analyses, 9Cr-ODS demonstrated a non-uniform corrosion behavior by preferential grain boundary attack and pronounced nodule-like morphology. The slight depletion of Cr was detected to about 15 μm in depth by chemical composition analyses. According to the calculation of free energy of formation, the nano-scale oxide particles of TiO_2 in 9Cr-ODS were thermodynamically less stable while Y_2O_3 were more stable compared with those of Li_2O in Li environment. However, Y_2O_3 may be reacted with Li to form YLiO_2. The mechanism of corrosion was proposed as the slight dissolution of Cr and Fe in matrix into liquid Li, chemical interaction of nano-scale oxide particles with Li, preferential grain boundary attack and penetration of Li, and finally development of extreme nodule-like structure during cleaning of Li. On the contrary, 9Cr-ODS showed much larger weight loss and depletion of Cr near surface but less marked corroded morphology in Pb-Li than in Li, which may be derived from higher solubility of Cr and Fe and lower activity of Li in Pb-Li than in Li.