EFFECTS OF CARBON AND MANGANESE IMPURITIES ON CERIUM INCORPORATION INIRON-OXIDES SCALES

Comparison of oxidation results (T=700 degrees C - pO(2)=0.04 Pa) obta ined on ceria-coated Fe-Mn, Fe-C and Fe-Mn-C steels, shows that it is the Mn-C combination which hinders the cerium incorporation in iron ox ide scales. Carbon and manganese alone have no detrimental effect on t he cerium incorporation into an iron oxide scale as a CeFeO3 compound. The CeFeO3 formation is attributed to an oxidation-reduction process between the CeO2 coating and the FeO nuclei at the beginning of the ox idation test. On ceria-coated Fe-Mn-C steel, carbon and manganese impu rities, together, have a strong influence on the oxidation rate and on the rare-earth element location. After the coated steel oxidation, ce rium is located at the scale-gas interface as a CeO2 phase. Cerium is not incorporated inside the iron oxide scale. This is due to the iron- manganese carbides presence inside the steel grain boundaries. The car bide oxidation prevents the formation of CeFeO3 due to the manganese a nd carbon oxide evaporation at the beginning of the reaction. After th e coating spallation, no contact between the reducing FeO nuclei and t he oxidant CeO2 phase is then permitted any more to produce the CeFeO3 phase.