Low Cycle Fatigue Behaviour of Nitrided Layer of 42CrMo4 Steel

Abstract

Abstract:Steel 42CrMo4, used in the manufacturing of transmission systems (gears), poses problems in service under specific cyclic stress conditions of the operating mode of its bodies. The treatment of ion nitriding during 20 hours with 520°C applied to 42CrMo4 steel in an untreated state (quenched and tempered) led to the formation of a compound layer (mixture of nitrides γ' and carbonitrides ε with irregular thickness evaluated at 5µm and a diffusion layer of depth equal to 295µm). In the diffusion layer, the presence of inserted nitrogen leads to the increase in hardness (3 times that of basic material) and to the creation of a compressive residual stress field (-400MPa). This superficial hardening does not modify the tensile mechanical characteristics of 42CrMo4 steel but renders it more sensitive to overload in fatigue. As a result, a 0.7% total deformation imposed corresponding to a loading level of 850MPa, constitutes the limit of gain in fatigue obtained by the ion nitriding considered.

Study of the Effect of Gas Nitriding Time on Microstructure and Wear Resistance of 42CrMo4 Steel

“…Nitriding process is a chemical-heat treatment consists in introducing nitrogen into metallic materials to improve their surface hardness, fatigue life, wear and corrosion resistance [1] [2] [3]. In engineering the depth of nitriding is generally about 0.3 -0.4 mm; this thin harder surface layer may cause surface layer spall from matrix because of high-applied load or great stress gradient in surface layer [3] [4] [5] [6].…”