Nitriding of AISI 304 stainless steel in a 85% H2/15% N2 mixture with an inductively coupled plasma source

We present some results obtained from nitriding of AISI 304 stainless steel substrates. The process take place in an inductively coupled plasma discharge supplied by a ∼300 W source at 13.56 MHz in a 85% hydrogen and 15% nitrogen gas mixture. The samples, placed into a pyrex glass discharge chamber (3.5 cm diameter and 60 cm long) were biased by DC power from 0 to −300 V with respect to ground. The resulting hardness is a function of the increasing nitrogen concentration in the substrate and this, in turn, of the temperature which varied from 200 to 470 °C. After nitriding at −300 V, hardness values of 1790 HV under 10 g loads and of 632 HV for 300 g were measured. X-ray diffraction indicates that the expanded phase amplitude (γN) depends on the substrate temperature.