Metallurgical study on corrosion of RAFM steel JLF-1 in Pb-Li alloys with various Li concentrations

Highlights: • Nitrogen concentrations in Pb-Li alloys with various Li contents were measured by an ammonia extraction method. • The Fe dissolution from RAFM steel in liquid Pb-Li alloys was larger when the Pb concentration in the alloys was higher. • The effect of nitrogen dissolved in liquid Pb-Li alloys on the Cr depletion of the steel in the alloys was discussed. - Abstract: The corrosion behaviors of the RAFM steel JLF-1 in liquid Pb-Li alloys with various Li concentrations were investigated by means of the corrosion tests in a liquid Pb, a liquid Pb-5Li alloy, a liquid Pb-17Li alloy and a liquid Pb-45Li alloy at 873 K for 750 h. The multiple oxide layer, which consisted of the porous outer layer by Fe₃O₄ and the compact inner layer by Cr-rich Fe-Cr-O, was formed on the steel surface during the immersion to the liquid Pb. Any oxide layer was not detected on the steel surface after the immersion to the liquid Pb-Li alloys, since the oxygen potential in the liquid alloy was lower than that for the formation of the oxide layer. Then, the dissolution type corrosion was caused on the steel surface. The Pb diffusion was detected along the boundaries of grains and subgarins in a martensitic structure of the steel. The corroded surface revealed a pebble-like microstructure by the immersion to the liquid Pb-45Li alloy. This surface microstructure was formed by the phase transformation and the preferential dissolution along the boundaries. The dissolution type corrosion could become larger when the Pb concentration in the alloy was larger, since the liquid Pb had larger solubility for Fe and Cr than the liquid Li. The corrosion in the Li rich Pb-Li alloy might be influenced by the concentration of dissolved impurities (i.e., carbon, oxygen and nitrogen) in the alloy.