Comparison of Various Nitriding Process of M 50 NiL Steel

M 50 NiL steel is a variety of tool steel having high toughness. This steel is potential materials for several bearings of aero-engine. This steel is used in carburized condition. However, nitriding has several advantages over carburizing. The main goal of this work is to compare and contrast the microstructural features, mechanical properties and tribolgical performances of this steel nitrided by gas, liquid and plasma nitriding processes. In view of the above, M 50 NiL steel was nitrided by the processes mentioned above. Microstructural characteristics, mechanical properties, sliding wear response in unidirectional and reciprocation mode were evaluated. The results reveal formation of compound layer in gas and plasma nitrided samples. Surface hardness was comparable for all three nitrided layers. Liquid nitrided specimen indicates best wear resistance in unidirectional and reciprocating sliding conditions. The friction coefficient is lower and wear rate is higher under reciprocating sliding than under unidirectional sliding. While delamination cracks are the main features of unidirectional sliding, cracks perpendicular to the surface were noted under reciprocating sliding.