AbstractThe iron oxide which predominates inferritic stainless steel conversion coatings for photothermal conversion is a chromium substituted magnetite (Fe2+Fe3+2−xCr3+x)O2−4: the chromium content of this magnetite could be at least that of the stainless steel substrate (x≥0·5). This substituted magnetite coexists with a partially oxidised magnetite. The thermal treatment of these coatings induces theformation of the corundum type phaseαFe2O3by oxidation of the substituted magnetitefrom 175°C. At higher temperatures, FeCr2O4andαFe6−yCryO9appear.MST/1216