Lubricating oil pump gears made of grey cast iron, SL 20 (Grade 14- BS 1452) intended for use in highspeeddiesel engine have been parallelly nitrided (550oC, 25 h) in plasma N2/H2/CH4 gaseous mixture and in NH3 gas usingconventional procedure.The process of plasma nitriding has been performed so as to enable obtaining of compound layer type e (bonding zonewith a mono-phase) which was confirmed by x-ray and microstructure testing.Nitriding in NH3, however, gives compound layer type bonding zone with duplex phase (g` +e) which is less resistantto wear than the mono-phase because it is brittle and porous and often prone to cracking and scaling.In addition, plasma nitriding affects dimensions to a lesser degree and offers better surface quality if compared withconventional nitriding which results in separation of rough graphite clusters - ``pimply``of surface.
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