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Influence des éléments d'alliage sur la genèse des contraintes résiduelles d'aciers nitrurés

Abstract : 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 strains versus the depth of nitriding are linked to thermodynamical modifications during the treatment of carbon iron-based alloys. Decarburization relaxes close surface residual stresses. The global decrease of residual stresses during nitriding is the consequence of the transformation of initial carbides into nitrides and the resulting diffusion of carbon toward the core material. A model of nitriding is proposed based on the diffusion of nitrogen and carbon, and on precipitation calculus using Thermo-Calc software. A volumetric strain calculation is proposed in agreements with thermodynamical and mechanical assumptions. Macroscopic residual stresses as well as the stresses over the ferritic matrix are computed using a scale transition model based on a self-consistent scheme. The transformation kinetic of carbides into nitrides coupled with the diffusion kinetic of nitrogen is showed to be the main feature of stress relaxation during nitriding. The model is applied successfully on a Fe-3%Cr-O,354%C laboratory steel grade and on the 33CrMoV12-9 grade. A better description of nitriding is finally proposed with some resulting conclusions on the role played by alloying elements.
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Submitted on : Thursday, January 28, 2010 - 8:00:00 AM
Last modification on : Wednesday, November 29, 2017 - 9:42:53 AM
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  • HAL Id : pastel-00005632, version 1



Sébastien Jegou. Influence des éléments d'alliage sur la genèse des contraintes résiduelles d'aciers nitrurés. Sciences de l'ingénieur [physics]. Arts et Métiers ParisTech, 2009. Français. ⟨NNT : 2009ENAM0032⟩. ⟨pastel-00005632⟩



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