Effect of chemical potential of carbon on phase transformation and corrosion of JLF-1 steel in a static lithium

The corrosion and the phase transformation of RAFM (Reduced Activation Ferritic/Martensitic) steel, JLF-1(Fe–9Cr–2W–0.1C), in static lithium (Li) were investigated. The specimens were exposed to static Li at 600 °C for 250 h. The carbon potential in Li was controlled by the carbide formation on inner surface of the crucible, which was made of Mo and Nb. These materials were expected to form stable carbide, and worked as carbon trap in Li, which resulted in the decrease in the carbon potential of Li. The effect of low carbon potential on the corrosion and the phase transformation was characterized by comparison with the test performed in the crucible made of Fe–9Cr and SUS316L (18Cr–12Ni), which has no effect as carbon traps. The low carbon potential caused by Nb and Mo caused the dissolution of carbon from the surface of JLF-1 specimen to Li. The depth of the phase transformation observed after the test in Nb crucible was deeper than that tested in Mo crucible. This was because the stability of the Nb carbide was larger than that of Mo carbide causing larger driving force for the dissolution of carbides from the surface.