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. AbstractPhase transformations during nitriding of a ternary carbon iron-based alloy Fe-3%Cr-0.345%C were studied, aiming for a better understanding of residual stresses generation and evolution. The relationship between the precipitation of Cr 7 C 3 carbides and CrN nitrides, the induced volume change and the mechanical properties were investigated at three distinct depths of the diffusion zone. The relaxation of residual stresses arose through phase transformations according to the diffusion of nitrogen but also of carbon.

A methodology is proposed combining the scattering vector method with energy dispersive diffraction for the non-destructive determination of stress- and composition-depth profiles. The advantage of the present method is a relatively short measurement time and avoidance of tedious sublayer removal; the disadvantage as compared to destructive methods is that depth profiles can only be obtained for depth shallower than half the layer thickness. The proposed method is applied to an expanded austenite layer on stainless steel and al- lows the separation of stress, composition and stacking fault density gradients.International audienceA methodology is proposed combining the scattering vector method with energy dispersive diffraction for the non-destructive determination of stress- and composition-depth profiles. The advantage of the present method is a relatively short measurement time and avoidance of tedious sublayer removal; the disadvantage as compared to destructive methods is that depth profiles can only be obtained for depth shallower than half the layer thickness. The proposed method is applied to an expanded austenite layer on stainless steel and al- lows the separation of stress, composition and stacking fault density gradients

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. To cite this version :Sébastien JEGOU, Laurent BARRALLIER, Régis KUBLER, Marcel SOMERS -Evolution of residual stress in the diffusion zone of a model Fe-Cr-C alloy during nitriding

Abstract.The GFAC (French Association for residual stress analysis) has been working for several years on external reference samples in relation with the EN 15305-2009 standard. The purpose of this campaign is to provide an external reference sample to each laboratory involved in the round-robin to allow a good calibration, a good quality control of their X-ray diffraction system and an easiest way to compare results between laboratories. All the procedures to qualify external reference materials will be described in the paper.

Abstract. This work deals with the development of residual stresses during nitriding of steels. The main features of a chemico-thermo-mechanical model of nitriding are presented. A micro-macro approach is applied based on volume change computation in agreements with thermochemical modifications. Results are correlated with the characterization of a ternary Fe-C-3w.%Cr alloy nitrided at 550¡C for various time. Residual stress-depth analyses are carried out by X-rays diffraction. Residual stress generation is deeply dependant on chemical and thermodynamical evolutions during the treatment, taking advantage on microstructural effects.

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.This is an author-deposited version published in: https://sam.ensam.eu Handle

Nitriding of steels is an important treatment in duplex hardening methods. This treatment is known in the art but some advances still need to be done in terms of residual stress understanding. Although they originate from volume micro-loading accompanying the precipitation of nitrides, questions about their in-depth distribution of a nitrided layer during the treatment are still a challenge. A chemico-thermo-micromechanical model has been developed on the volume change computation of secondary phase transformation. Supported by some experimental observations (TEM, X-ray analysis, Electron Probe Micro Analysis (EPMA), ...), this model gives some better understanding about nitriding. Residual stresses are mainly due to the precipitation of semi-coherent MN nitrides (M=Cr,V,Mo,.. .). Moreover carbon, often not enough considered in the literature, is of importance in the treatment as it involves a second kind of precipitation that is the transformation of carbides M 23 C 6 and M 7 C 3 into incoherent nitrides. The volume change of this transformation is a critical entry data of the mechanical modelling.

Nitriding of low-alloy steels is widely used for gears and bearings in aerospace industry. Some highly stressed surfaces require high nitrided depth, which involves long time/high temperature nitriding treatment. This study focused on identifying process parameter effects on hardness and residual stress profiles in a large range of nitriding time and temperature. We demonstrate that core and case can be considered as two materials, softening of which can be predicted by two tempering laws. In addition, a basic relationship was derived from the nitriding depth and a pseudo-diffusion coefficient, allowing prediction of the hardness profile. Residual stress results show that the diffusion controlled effect can also be used to predict residual stress profile affected depth. Likewise, the tempering controlled effect can be used to predict surface and maximum values of the residual stress profile.