Plasma immersion ion implantation of cold-work steel

Plasma immersion ion implantation can be used to modify the near surface re gion of steels at temperatures lower than 400 degrees C. Hence even the sur face properties of heat-sensitive steels like cold-work steels, which an no t accessible for conventional nitriding, can be enhanced by reducing the fr iction coefficient and improving wear behaviour. Subsequent implantation of nitrogen and carbon into X155CrVMo12.1 steel using voltage pulses of -30 k V with combined doses up to 2.7 x 10(18) cm(-2) was performed at different temperatures between 300 and 400 degrees C. Layers of epsilon-Fe2+x(C,N) of several micrometers were detected using X-ray diffraction and glow dischar ge optical spectroscopy. Wear tests were performed with an oscillating ball -on-disc tribometer using a stainless steel ball and contact pressures betw een 0.7 and 1.4 GPa. For the lower contact pressure, a reduction of the abr asive wear by one order of magnitude was observed while the friction coeffi cient was reduced by 75%. At the higher contact pressures the wear mechanis m changed from adhesive wear to slightly abrasive wear after nitrogen/carbo n implantation, eliminating the cold welding between a stainless steel ball and the untreated sample completely. An optimum treatment temperature of 3 50 degrees C was found. (C) 2000 Elsevier Science S.A. All rights reserved.