Corrosion behavior of 316L austenitic steel in liquid lithium lead alloy under stress loading conditions

The material compatibility is one of the important issues for the development of liquid LiPb blanket of fusion reactors. The corrosion characteristics of 316L austenitic steel under tensile stress loadings were investigated by means of the immersion of C-ring specimens into liquid LiPb at 573 K and 773 K for 1000 h. The corrosion of 316L austenitic steel was negligibly small in liquid LiPb at 573 K regardless of the tensile stress loadings. The corrosion was caused by the dissolution of alloying elements (i.e., Fe, Cr and Ni) on the surface of specimens exposed to liquid LiPb at 773 K without the tensile stress loadings. The phase transformation from fcc structure of austenite to bcc structure of ferrite was induced on the surface according to the depletion of Ni in the corrosion procedure, which was austenite-stabilizing element. The dissolution corrosion was mitigated on the area around the apex of the C-ring specimens where the tensile stresses of 100 MPa and 200 MPa were applied. Cr- and C- rich regions were detected on the tensile-strained area of the specimens which could function as an anti-corrosion layer in liquid LiPb. The enrichment of Cr was induced by the depletion of Fe and Ni on the surface since the solubility of Cr was smaller than that of Fe and Ni in liquid LiPb. The dissolution of Cr could be mitigated by the carburization on the surface. The stress-induced martensitic transformation and the introduction of dislocations could contribute the formation of Cr- and C- rich regions.