Abstract The evolution of passivity in air exposure of air-formed films on as-polished bare irons and electrochemically reduced bare irons was investigated by electrochemical methods. Passivity and surface structure were characterized by the recovery duration against open-circuit breakdown and the spontaneous potential, respectively. A new factor, pre-exposure duration ( t pre , exposure duration prior to electrochemical treatments), was found to affect both surface structure and passivity of air-formed films. At t pre t pre t pre > 6 h, in agreement with that (20.7 min) of the passive film. These results are explained by the dependence of the passivity on the crystal structure.