AbstractThe corrosion behavior or commercial Fe ana Co base alloys and Fe‐Cr model alloys with different contents of Co and/or Mn was investigated by continuous exposure tests in the presence of a thin carbonate film. All alloys studied form multi‐layered corrosion scales consisting of outer Li containing oxides and inner Cr rich oxides, i.e. spinels or LiCrO2. The LiCrO2 is formed on alloys with high Cr contents (≤ 20 wt.%), whereas mixed (Fe,M)3‐x CrxO4 spinels (M = Co, Mn, Ni) were found on alloys with lower Cr content (15–20 wt.%). Insoluble Cr containing oxides occur only in the inner layers of the corrosion scale, whereas on the surface of corroded specimens soluble chromates were detected. Alloys with Mn contents greater than 15 wt.% form Mn2O3 in the initial stages of the experiments, this oxide reacts with the melt and formation of Li2MnO3 takes place. In exposure tests up to 500 h Fe‐Cr alloys with low contents of Mn and Co (10 wt.% Co or Mn) form iron rich oxides (LiFeO2 and LiFe5O8) with varying amounts of dissolved Mn or Co. In the later corrosion stages outward diffusion of Mn and/or Co takes place and LiCoO, and Li2MnO3 are formed on top of LiFeO2, whereby the concentration of Mn and/or Co in the inner layers (LiFeO2 and spinel) decreases. The outer Li containing oxides LiFeO2, LiCoO2 and Li2MnO3 are nearly insoluble in the melt and when present at the surface protect the metallic material from further corrosive attack. Fe‐Cr model alloys containing Co and Mn form multi‐layered corrosion layers after 2000 h of exposure. These layers consist of four oxides in the following sequence from the metal‐scale to the scale‐melt interface: (Fe,Cr,Co,Mn)3O4 spinel, LiFeO2, Li2MnO3 and LiCoO2.