Wear behaviour of nitrogen-implanted AISI 420 martensitic stainless steel

In the present work the effects of nitrogen implantation on AISI 420 steel have been investigated. Implantation has been carried out at 90 keV and doses above 10¹⁷ ions cm^-2. Wear and friction behaviour was studied by means of a Falex wear test at 900 N load using lubricated conditions, and with a dry pin-on-disc procedure at loads of about 10 N. Implantation reduced significantly the wear by 5.5 times and also the friction coefficient during the running-in period. Scuffing was also notably reduced on the surface of the implanted test pieces. X-ray photoelectron spectroscopy showed that the implanted nitrogen was almost entirely bound to chromium, forming nitrides; this explains the increases in wear resistance and surface hardness obtained. The bombardment during ion implantation modified the initial oxide layer on the surface of the steel; the observed change in the wear mechanism is analysed in view of this result.