Influence of gas nitriding on the fatigue bending strength of the 42CrMo4 steel

Fatigue behaviour of gas nitrided steel. The role of the compound layer to resistance fatigue fracture of a 42CrMo4 steel was established through the study of the relation between the micro-structure and tensile and fatigue properties of the gaseous nitriding layer in comparison with the basic material. Results show a clear dependence of the fatigue life on the fracture resistance of the nitrided layer. This resistance was seen to depend on the hardening and the stress (applied and residual) and the states, which change with the cyclic loading. It results in, 20% fatigue limit improvement in the high cycle fatigue domain. The high over-load sensitivity of the compound-layer constitutes a serious limitation of the nitriding treatment in the low cycle fatigue domain.