Effect of Manganese Sulfides and Nitriding on the Corrosion Resistance of Laser Marked Medical Martensitic Stainless Steel

The medical device industry is required to apply unique device identification tags on multi-use equipment. In the industry, this is most commonly done via oxidative laser marking, which has been shown to decrease corrosion resistance of stainless steels locally in the laser marking. Two martensitic stainless steels, EN 1.4197 and 1.4028, commonly used in the medical industry, were subjected to high temperature solution nitriding, in an attempt to mitigate the loss of corrosion resistance associated with a subsequent laser marking. A nanosecond pulsed fibre laser was utilized to investigate different laser parameter sets on nitrided specimens. The key difference between the steels is that 1.4197 has been re-sulfurized to form MnS, while 1.4028 only contains MnS as impurities. An analysis of the microstructure and electrochemical properties was carried out to map the influence of nitrogen and different laser parameters. A positive effect of increased nitrogen content was not found, but instead nitriding resulted in a more severe laser oxidation. A large effect from the presence of abundant MnS and the laser energy input was identified.