Influence of surface preparation and ion flux on the nitriding efficiency of austenitic stainless steel

Ion beam nitriding of an austenitic stainless steel (ASS) at moderate temperatures (∼400 °C) produces a supersaturated nitrogen solid solution that has beneficial effects on the mechanical properties. The nitriding efficiency cannot be improved by increasing the treatment temperature in order to preserve the stainless character contrary to other parameters such as surface pretreatment, ion flux, etc. The effect of flux and pretreatment with argon is investigated in ion beam nitriding of 304L ASS. The ion energy and temperature were 1.2 keV and 400 °C, respectively, the ion current densities were 0.5, 0.67, and 0.83 mA·cm−2. The obtained results show that nitrogen uptake increases with increasing the ion flux. The pretreatment with argon beam for 1 min at RT increases nitrogen uptake at early stages of nitriding and longer pretreatment times do not provide any improvement. The results are discussed in relation with surface effects and atomic transport mechanism.