Effects of nitrogen implantation on lifetime of cutting tools made of SK5M tool steel

Nearly 100 cutting tools made of SK5M tool steel (DIN S 6-5-2-5) were implanted with 80 keV nitrogen ions at fluences ranging from 1 to 5×1017 cm−2. The tool lifetimes were examined during routine shaping of roller-bearing rings made of LH15 bearing steel on the production line of an industrial roller-bearing manufacturer. It was found that the lifetime-dose dependence could be described by a quadratic expression and for an optimum nitrogen ion dose, lifetime was found to increase by a factor of 1.6. Measurements were made of nitrogen profiles samples of SK5M steel by glow discharge optical spectroscopy (GDOES). The phase composition of the implanted layer was studied by conversion electron Mössbauer spectroscopy (CEMS) and micro- and nano-hardness measurements were also performed. Good agreement was found between the experimental results and the theoretically predicted profiles of implanted nitrogen with sputtering taken into account. Hardness increments associated with implantation were moderate. It has been concluded that the increased wear resistance can be correlated with the content of Fe3−xN (x=0.33 and 0.5) phases in the implanted layer.