Mechanism of surface corrosion resistance of 304 stainless steel processed by nanosecond laser pulses

A nanosecond pulsed fiber laser was used to modify the surface of 304 stainless steel. The compactness, microstructure, chemical composition, and corrosion resistance of the stainless steel passive film were observed by the blue dot detection method, scanning electron microscopy, x-ray photoelectron spectroscopy, and electrochemical methods. The influence of different laser fluences on the stability and corrosion resistance of the stainless steel passive film was studied. The results show that with increasing laser fluence, the discoloration reaction time of the stainless steel surface increases first and then decreases, while the surface roughness decreases first and then increases. When the laser fluence is lower than 11.19 J/cm(2), a compact and uniform passive film is formed. When the laser fluence is larger than this value, the stainless steel substrate is prone to secondary corrosion. Chromium oxides are enriched in the passive film, and the anodic dissolution rate decreases, which promotes a positive shift in the corrosion potential of the stainless steel, decreases the corrosion current density and increases the polarization resistance and the corrosion resistance. The surface corrosion resistance is thus significantly improved.