Characterization and corrosion studies of laser-melted carbon steel surfaces

We have observed by conversion electron Mössbauer spectroscopy (CEMS) that the irradiation of carbon steel surfaces with an industrial CO 2 laser, under different experimental conditions, brings about the formation of α-Fe 2O 3, Fe 3O 4 and Fe 1− x O. The larger beam-surface interaction times favour the formation of greater amounts of Fe 3+ oxides (mainly α-Fe 2O 3) within the depth that can be probed by CEMS (≈300 nm). A model based on the numerical solution of the heat-diffusion equation gives evidence that the oxidation processes are mainly dictated by the time at which the metal remains at temperatures higher than the melting point. In addition, the samples have been subjected to wet–dry corrosion cycles in SO 2-polluted atmospheres and monitored by CEMS and weight gain. The oxide layer reduces noticeably the corrosion rate of steel against corrosion. This protection is related to the composition of the oxidation layer.