Corrosion behavior of FBR candidate materials in stagnant Pb-Bi at elevated temperature

Three materials proposed for use in fast breeder reactors - FBR grade type 316ss, high chromium type martensitic steel and oxide dispersion strengthened martensitic type steel - were subjected to corrosion tests in stagnant lead-bismuth eutectic (LBE) containing 10-6 wt% of oxygen at 500-650degC for up to 5,000h. After each test, the specimens were analyzed metallurgically using a scanning electron microscopy with energy dispersive X-ray analyzer and an X-ray diffractometer. It proved that, at temperature not higher than 550 degC, martensitic steels containing chromium to more than 9wt% presented good resistance against corrosion by the formation of spinel layer on the base metals, though outer porous oxide formed on the steels was detached and/or dissolved into LBE. At temperatures above 600degC, the oxide layer thickness diminished. This alteration in corrosion behavior seems to be ascribable to a change taking place at 570degC in the stable form of iron oxide from magnetic to wustite. At the temperatures, dissolution attack was observed at some portions. It was estimated that the oxide became to lose its adhesion to the base metal. (author)