METALLURGICAL STUDY OF LOW-TEMPERATURE PLASMA CARBON DIFFUSION TREATMENTS FOR STAINLESS-STEELS

We recently reported a novel low-temperature carbon diffusion techniqu e for surface hardening of stainless steels. The treatment was shown t o provide benefits in terms of abrasive wear resistance. There is also evidence to suggest that by performing diffusion treatments at low te mperatures (i.e. below 400-degrees-C), these benefits can be achieved without compromising corrosion resistance. Here a variety of surface a nalysis and depth profiling techniques have been used to determine the physical and mechanical properties of carbon-rich layers produced on a range of stainless steel substrate materials. X-ray diffraction (XRD ) was employed to determine the crystallographic structure, whilst wav elength dispersive X-ray analysis (WDX) and glow discharge optical spe ctroscopy (GDOS) gave information on the concentration and distributio n of the diffused species within the treated layers. A variety of carb ide-based structures was detected, including the expected M23C6 and, m ore surprisinglY, M3C. Optical and electron microscopy techniques were used to provide information on layer morphology. The surfaces produce d by the low-temperature carbon-diffusion process generally exhibit a distinct diffusion layer of between 1 and 20 mum depending on the mate rial and the treatment conditions. Austenitic stainless steels appear to give the best response to treatment, however other types of stainle ss steel can be treated, particularly if the microstructure contains a bove 5% retained austenite. Here we discuss the changes in mechanical and metallurgical properties provided by this technique and its potent ial value for treatment of both austenitic and other stainless steel s ubstrate materials.