Structural and compositional transformations in the near-surface layers of Fe–Cr based steels exposed to lithium – Effect of alloying and corrosion-assisted substructure coarsening

The corrosion behaviour of RAF/M RUSFER-EK-181 and F/M (EP-823, SUS410) steels was investigated in static “pure” (0.004 wt.% N) and N-added Li (0.5 wt.% N) at 600 °C up to 750 h. The weight losses of samples increased with time and nitrogen content in Li. The corrosion-assisted coarsening was observed in the near-surface layers of RAF/M steels. It is caused by the dissolution of Cr and decomposition of carbides during exposure to both melts. The coarsening mechanism and the influence of alloying on the structural and compositional transformations in steels exposed to Li are discussed.

Research highlights
► RAF/M steels corroded in Li qualitatively similar to the convectional F/M steels.
► Selective dissolution of Cr and decomposition of carbides took place.
► Corrosion intensified substantially in the N-added Li compared to the pure melt.
► Corrosion resulted in the phase transformation from martensite to ferrite.
► Corrosion-assisted coarsening of sub-structure occurred in the corroded layers.