Microstructural, mechanical, and corrosion characterization of nitrogen-implanted plastic injection mould steel

Abstract

Nitrogen-ion implantation can be used to improve the wear and corrosion behaviour of moulds for plastic injection by modifying the near-surface layers of these materials. In this study, an FeCr ferritic stainless steel (X36CrMo17, similar to AISI-420F) was ion implanted with 85 keV nitrogen ions to low and high doses of 2×1017 and 1×1018 ions/cm2 at a substrate temperature <200 °C in an industrial implantation facility. The N-implanted layer microstructures, thicknesses, and hardnesses were studied by a combination of symmetric and grazing incidence X-ray diffraction (XRD and GIXRD), conversion electron Mössbauer spectroscopy (CEMS), cross-sectional scanning electron microscopy (SEM), and nanohardness measurements. The friction, wear, and corrosion behaviour were investigated by a pin-on-disc tribo tester and a salt spray corrosion analysis method. The XRD, CEMS, and SEM analyses indicate that the N-implanted layers are ∼0.05-0.08 μm thick and are composed of ε-(Fe,Cr,Mn)2+xN with paramagnetic and magnetic characteristics. The treated layer shows nearly two times better corrosion resistance than does the substrate. The wear and nanohardness measurements indicate that the wear behaviour and the N-implanted layer hardness are dose dependent and the latter is increased by more than a factor of 1.6 for the high-dose implanted specimen in comparison with that of the substrate material.