Wear resistance after low-energy high-flux nitrogen implantation of AISI 304L stainless steel

Nitrogen implantation into 304L austenitic stainless steel has been carried out at 400 and 500 °C using a Kaufman-type ion source with an accelerating voltage of 1.2 kV and a current density of 1 mA/cm2. For a processing time of 1 h (fluence ∼3.5×1019 ions/cm2) at 400 °C, a nitrided layer of f.c.c. expanded austenite of approximately 3.5 μm was formed. Thicker layers of approximately 6 μm were produced at 500 °C, but the formation of chromium nitride precipitates embedded in a b.c.c. ferritic matrix was observed. The hardness increased from 2.8 GPa for the untreated steel to approximately 15 GPa for implantation at 400 °C and to 18 GPa for implantation at 500 °C; in addition, a considerable reduction in the wear rate was observed. The durability of the wear improvement can be associated with the high hardness and significant thickness of the nitrided layers, as well as with the hardening mechanisms, which are different at both temperatures: a solid solution effect at 400 °C and a precipitation effect of chromium nitride at 500 °C.