Characterization and corrosion studies of laser-melted carbon steel surfaces

We have observed by conversion electron Mossbauer spectroscopy (CEMS) that the irradiation of carbon steel surfaces with an industrial CO2 laser, under different experimental conditions, brings about the formation of alpha-Fe2O3, Fe2O4 and Fe1-xO. The larger beam-surface interaction times favour die formation, of greater amounts of Fe3+ oxides (mainly alpha-Fe2O3) within the depth that can be probed by CEMS (approximate to 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 SO2-polluted atmospheres and monitored by GEMS 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. (C) 1999 Elsevier Science B.V. All rights reserved.