A. Aiello, M. Azzati, G. Benamati, A. Gessi, B. Long, and G. Scaddozzo, Corrosion behaviour of stainless steels in flowing LBE at low and high oxygen concentration, J. Nucl. Mat. 335, 169-173 (2004).
Two steels were examined: martinsitic T91 (stabilized with vanadium and niobium, and 9Cr-1 Mo) and the austenitic steel 316L. They were exposed to flowing LBE under two conditions: high (10-6 to 10-5 wt%) and low (10-10 to 10-8 wt %) oxygen concentration. Exposure was for 1500, 3000, and 4500 hr at 400 C. At low oxygen concentrations, both samples lost weight. In the austenitic 316L sample, the corroded layer was depleted in Cr and Ni, as shown by EDX. In the martensitic T91 sample, the sample was uniformly corroded after 4500 hr, with the LBE penetrating into the matrix of the steel, and no preferential dissolution for any element. At high oxygen concentrations, the two samples gained weight. The martensitic T91 gained much more than the austenitic 316L sample (i.e, 316L was considerably more corrosion-resistant). The 316L sample developed a thin (< 1 micron thick) oxide layer (of unknown composition), while the T91 developed a 6 micron thick oxide layer, consisting of an inner layer (a compact spinel (Fe,Cr)3O4 and an outer layer, porous magnetite. The basic physical picture: there is an initial oxide layer that is present before exposure to LBE. At low oxygen concentrations, the oxide layer has to be removed before corrosion can occur. The removal occurs more easily on the T91 than on the 316L. At high oxygen concentrations, a protective oxide layer is detected. The protective oxide layer forms more easily the surface of 316L than T91.