In situ and ex situ Raman microspectroscopy and electrochemical measurements on rotating disc electrodes have been used to identify surface films formed on iron and its alloys with carbon in 0.5 M Na2CO3 + 0.5 M NaHCO3 at 75-degrees-C and potentials where susceptibility and resistance to SCC occur. A good quantitative correlation between data of in situ Raman spectroscopy, galvanostatic surface film reduction, and SCC tests was found. At active dissolution potentials, where transgranular SCC was observed, the iron-carbon alloys’ surfaces were blocked by FeCO3 or FeCO3 . H2O salt films. At potentials of the active-passive transitions, where intergranular SCC was noticed, in situ Raman spectroscopy revealed the formation of Fe3O4 for both decarbonized iron and iron-carbon alloys. The magnetite film, formed on iron-0.7% C at potentials of the maximum SCC susceptibility, in contrast to films formed on decarbonized iron, was found to be strongly heterogeneous and often incorporated FeCO3. At more positive potentials, ie - 0.6 V (sce) at which the resistance to SCC was observed, galvanostatic reduction and in situ Raman spectroscopy revealed formation of FeOOH. At this potential Raman signals from Fe3O4 were not detectable. It is suggested that intergranular SCC is favoured by the electrochemical conditions for which ferric oxides or oxyhydroxides are in equilibrium with Fe3O4 and/or Fe(II) species.