Plasma immersion ion implantation of cold-work steel

Plasma immersion ion implantation can be used to modify the near surface region of steels at temperatures lower than 400°C. Hence even the surface properties of heat-sensitive steels like cold-work steels, which are not accessible for conventional nitriding, can be enhanced by reducing the friction coefficient and improving wear behaviour. Subsequent implantation of nitrogen and carbon into X155CrVMo12.1 steel using voltage pulses of −30 kV with combined doses up to 2.7×1018 cm−2 was performed at different temperatures between 300 and 400°C. Layers of ε-Fe2+x(C,N) of several micrometers were detected using X-ray diffraction and glow discharge optical spectroscopy. Wear tests were performed with an oscillating ball-on-disc tribometer using a stainless steel ball and contact pressures between 0.7 and 1.4 GPa. For the lower contact pressure, a reduction of the abrasive wear by one order of magnitude was observed while the friction coefficient was reduced by 75%. At the higher contact pressures the wear mechanism changed from adhesive wear to slightly abrasive wear after nitrogen/carbon implantation, eliminating the cold welding between a stainless steel ball and the untreated sample completely. An optimum treatment temperature of 350°C was found.