High temperature nitriding of grey cast iron substrates in arc plasma heated furnace

Abstract

Grey cast iron substrates were case nitrided at 1000-1100 degrees C by varying several process parameters such as nitriding time, flowrate of N(2) and nitriding gas configuration. Ar and N(2) were mixed with N(2) to change the configuration and to observe their influence on the nitrided case. Nitriding was carried out in a specially designed arc plasma heated reactor with water cooled steel casing. X-ray diffraction studies show that the nitride peaks arise due to growth of iron nitride phases such as gamma' (Fe(4)N: 5.7-6.1% N), epsilon (Fe(3)N: 8-11.2% N) and carbon nitride (C(3)N(4)). Typical surface morphologies of the 10-30 mu m nitride layer were studied by SEM. Microhardness studies exhibited twofold improvement of surface hardness. Nanoindentation test indicated poor plastic behaviour of the surface. Micro-Raman spectra of the nitided case established the presence of beta-C(3)N(4), a superhard phase. Nitrided grey cast iron may find use in wear and corrosion resistant dies, machine components and parts in various industrial applications.