Fitting corrosion of 304 stainless steel after laser surface melting in argon and nitrogen atmospheres

This paper studies the efficiency of high-power laser methods for modifying the AISI 304 steel surface in order to increase its corrosion resistance. The surface of SS 304 was melted in argon and nitrogen atmospheres using different laser beam scan rates and gas flows. The results obtained show that in both cases the laser surface melting (LSM) induced improvements in pitting resistance with respect to the base steel. Electrochemical studies showed that the improvements are greater when the LSM is carried out in a nitrogen environment because of the incorporation of nitrogen into solid solution. As a result, the corrosion and pitting potential shift to more noble values while the passive current density decreases by nearly two orders of magnitude. The presence of chromium oxides and nitrogen compounds on the surface of the specimens seem to indicate that nitrogen may help the reconstruction of the passive layer as well as act as a barrier for the electrolyte. (C) 2001 Elsevier Science Ltd, All rights reserved.