Short-term corrosion behavior of Indian RAFM steel in liquid Pb-Li: Corrosion mechanism and effect of alloying elements

Abstract

The compatibility of RAFM steels in liquid lead-lithium (Pb-Li) is a major area of concern for the development of Pb-Li cooled fusion reactor blankets. In order to establish the corrosion mechanism during the short term exposure (i.e. Incubation Period) when the protective oxide layers are present over the RAFM surface, the dissolution behavior of Indian RAFM steel (IN RAFMS) has been studied in liquid Pb-Li under static conditions at 773 K for 1, 000 h of exposure. Pure chromium and plain carbon steel (as a substitute for pure iron) have also been exposed along with IN RAFMS under similar conditions for understanding the effect of alloying elements over the corrosion process. The dissolution rate of pure chromium in Pb-Li was found to be the highest among all materials although iron dissolution was the rate controlling step for IN RAFMS corrosion. It was established that Pb-Li attack over RAFM steels during exposures up to 1, 000 h was associated with non-uniform dissolution of oxide scales and grain boundary penetration which can also dislodge the grain boundary carbides. The dissolution of constituent elements into the grain boundary channels of Pb-Li governed the depth of elemental depletion from the exposed surface. However, dissolution of oxide scales was found to be the major factor behind weight loss during short term exposures. An attempt has been made to theoretically model the depletion of chromium from IN RAFMS surface which was a result of its slower diffusivity in the steel matrix.