It is usual to characterize quantitatively a pearlitic structure by three parameters; (1) the ferrite and pearlite percentage, (2) the interlamellar spacing of the pearlite, and (3) nodule diameter of the pearlite. These parameters vary as a function of the transformation temperature. The conditions necessary for obtaining a fully pearlitic structure by continuous cooling have been determined for plain carbon steels containing from 0.2% to 0.8%C. When the carbon content is below 0.6%, pearlite is always degenerate, with low yield strength but good reduction in area. Pearl ites containing more than 0.6%C always present normal cementite lamellae with high yield strength but small reduction in area. For 0.6%C steel, fragmented or continuous lamellar structures can be obtained, leading to high yield strength and reduction in area values.

No abstract

is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. AbstractGaseous nitriding of steels is a well-established thermochemical surface treatments that increases the fatigue resistance of treated parts. The present work proposes a modelling of the fatigue life as a function of the applied stress. It takes into account the hardness and compressive residual stresses that developed during nitriding. The model is suitable to help optimizing nitriding parameters by reverse modelling.

Abstract. The objective of this work is to propose a model abled to optimize the mechanical properties from gaseous nitriding of steels (hardness, residual stresses) for a given loading and fatigue lifetime. Multiaxial fatigue criteria are used and the present study focuses on the influence of residual stresses. Starting from a surface loading profile, the theoretical residual stress in-depth profile can be calculated aiming infinite fatigue lifetime. The model allows then optimization of the nitriding parameters.

No abstract