Sébastien JégouEcole Nationale Supérieure d'Arts et Métiers | ENSAM · Laboratoire Mécanique, Surfaces, Matériaux et Procédés (MSMP)
Sébastien Jégou
Associate Professor
About
30
Publications
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157
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Introduction
Additional affiliations
September 2011 - May 2016
June 2010 - July 2011
Publications
Publications (30)
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 a...
Gaseous 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...
The gaseous nitriding behaviour of 33CrMoV12-9 steel was investigated. The co-diffusion of nitrogen and carbon, precipitation at grain boundaries and mechanical properties evolutions (microhardness, residual stresses) are compared for several nitriding potentials, nitriding time and temperatures. While hardening unequivocally depends on the precipi...
Anomalous small angle scattering (ASAXS) is a powerful non-destructive technique that can provide characteristic features of nanoscale precipitates such as the volume fraction, and chemical composition. In this paper, the technique is used for the first time to explore nanoscale MN nitrides (M = Cr,Fe) after nitriding of a model iron alloy (Fe-0.35...
The aim of this study is to adapt and use a procedure to investigate the influence of the microstructure on the local mechanical behavior of a tempered and nitrided low-alloyed steel. A well-known technique is employed, consisting in Digital Images Correlation (DIC) of SEM field images acquired during In-situ loads. To avoid heterogeneous macroscop...
Uniaxial cyclic loadings of homogeneously nitrided steel plates were carried out to charac-terize the crack initiation mechanisms with respect to the microstructure. S-N (Stress - Num-ber of cycles to failure) curves corresponding to the nitrided layer of a 33CrMoV12-9 steel grade were created in order to estimate the number of cycles for interrupt...
Le traitement thermochimique de nitruration est un traitement de surfaces permettant d'améliorer la durée de vie en fatigue des pièces traitées. Les dernières avancées dans ce domaine permettent de relier les paramètres technologiques du procédé (temps, température, potentiel azote, composition de l'acier) aux caractéristiques mécaniques des couche...
The present work focuses on the industrial inhibition of gaseous nitrided parts and on the industrial in-situ pre-treatment that can be used to avoid these inhibitions. The first objective is to obtain a repeatable defective nitriding process on carbon iron-based alloys, while the second is to determine the ability of determined in-situ pre-treatme...
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 t...
The present study aims to develop an algorithm able to predict the fatigue lifetime of nitrided steels. Linear multi-axial fatigue criteria are used to take into account the gradients of mechanical properties provided by the nitriding process. Simulations on rotating bending fatigue specimens are made in order to test the nitrided surfaces. The fat...
Le but de cette étude est de mettre en place un modèle de calcul en fatigue prenant en compte les caractéristiques mécaniques d’un matériau nitruré. Le travail est réalisé sur acier de nuance 32CrMoV13 utilisé dans la conception de pignon de transmission de puissance par Hispano-Suiza.
The GFAC (French Association for residual stress analysis) decided in 2007 to work on external reference samples for residual stress analysis by X-ray diffraction as defined in the XPA 09-285 and EN 15305-2009 standards. Seven materials are studied: ferritic steel, martensitic steel, aluminium alloy, titanium alloy, 2 types of Nickel-Chromium alloy...
The evolution of residual stresses during short time gas nitriding of 33CrMoV12-9 steel grade is studied. It aims understanding the influence of nitriding parameters (temperature T and nitriding potential Kn) on the generation and evolution of residual stresses in the very first stage of nitriding. The samples are gas nitrided using a thermobalance...
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...
In a previous study, the capability of X-ray diffraction technique to qualify damage occurring during friction had been proven [1]. The purpose of this study is to complete this research in order to develop a method to quantify the damage induced by the friction loading.
Development and evolution of compressive residual stress during nitriding treatment are studied. A model carbon iron-based alloy Fe-3wt.%Cr-0.35wt.%C was nitrided in gas at 550 °C for different times. Microstructural investigation indicated an influence of the transformation and the associated carbon diffusion on the in-situ relaxation of residual...
Nitriding is a well-established thermochemical surface treatment of carbon micro-alloyed steels aiming enhancing surface properties such as fatigue, wear and corrosion resistances. The idea is taking benefits from the high hardening level due to a fine nitride precipitation and also the compressive residual stress state. Due to some complex interac...
Cette étude présente les capacités d’une modélisation de la nitruration, procédé thermochimique destiné à améliorer la tenue en service des pièces mécaniques. La formation d’un gradient de microstructure accompagné d’une variation de volume génère un gradient de contraintes résiduelles. Le modèle se base sur une étape de diffusion / précipitation d...
Phase 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 Cr7C3 carbides and CrN nitrides, the induced volume change and the mechanical properties were investigated at three d...
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 F...
Nitriding is a well-established thermo-chemical surface treatment of carbon micro-alloyed steels aiming better surface properties such as fatigue, wear and corrosion resistances. The idea is taking benefits from the high hardening level due to the fine nitride precipitation and also the compressive residual stress state. Relaxation of residual stre...
Residual stresses of nitrided steels find origins through volumetric misfit accompanying the precipitation during the treatment. A residual stress gradient is generated from the primary gradient of chemical composition and the resulting gradient of microstructure. It is also the consequence of macroscopic strain incompatibilities. Volumetric strain...
Les contraintes résiduelles de nitruration ont pour origine les incompatibilités de déformations volumiques issues de la précipitation au cours du traitement. Le gradient de contraintes résiduelles résulte des gradients de composition chimique et de microstructure, ainsi que des incompatibilités de déformations macroscopiques. L'évolution du gradie...
Projects
Projects (2)
Design of high-performance and lighter mechanical systems needs a
perpetual work on materials used. In the power transmission field, gaseous nitriding
thermochemical treatment enhances significantly the life-cycle of the parts which are
higher stressed on the surface. While the contribution of the mechanical property
gradients due to the treatment on the fatigue life is well-known, the microstructure effects
on the (micro-)plasticity mechanisms remains undetermined. This work concerns
exclusively the nitrided 33CrMoV12-9 graded steel, used for gears and bearings in the
naval and aeronautical industry. It aims particularly at defining mechanical properties
linked to crack initiation mechanisms during high-cycle fatigue. Properties such as Young
modulus, hardness, yield stress and fatigue limits are looked at several scales, from
microstructural ones to hardened case one. In-situ and post-mortem investigation on
loaded and damaged nitrided layers leads to estimating the microstructural influence on
local deformations, microplasticity and damage but no particular mechanisms were
found. Special fully-nitrided parts were designed to perform the experiments. This tool
helps to carry out simple loadings and measure the strain-hardening curve and fatigue
limits. Finally, it as been attested that measured properties depend on scales, means and
methodology.
Nitriding of carbon steels from technological parameters to fatigue life of treated parts, simulation and experimental approaches
