Corrosion behavior of different stainless steels in Pb-Bi eutectic at high temperatures

Accelerator driven subcritical (ADS) system requires the structural materials to be in contact with the molten lead bismuth eutectic at 400 degC and at higher temperatures. One of the primary concerns in using the molten lead-bismuth eutectic (LBE) as the coolant in the primary circuit of these systems is the degradation of structural materials in contact with LBE. An experimental setup has been fabricated to expose the materials in the molten LBE at high temperatures in the stagnant condition under inert atmosphere. Samples from five different stainless steels (304L, 316L, SS 403, SS SAF 2205 and SS 2RK65) were exposed in this setup at 450 degC for 200h and at 500 degC for 600 and 2100 h. SEM results showed dissolution of materials at the surface in 2RK65 and preferential dissolution of austenite phase in duplex SS. The other stainless steel samples did not show any localized or selective corrosion but formation of oxide on their surfaces. The thickness and compositional profiles of these oxides analyzed by EPMA confirmed the formation of a double layer oxide. The oxide thickness was highest on SS 403, while it was lowest on 304L and 316L. The composition of LBE before and after the tests was analyzed by XRF technique. The result showed the presence of Fe,Cr and Ni in the used LBE but these elements were not present in the virgin Pb-Bi alloy. This shows that the corrosion of stainless steels in LBE at temperatures up to 500 degC is due to oxidation and dissolution of alloying elements through the oxide on stainless steels in the molten LBE. (author)