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Rôle du carbone lors de la nitruration d’aciers de construction et influence sur les propriétés mécaniques

Abstract : During the nitriding treatment, the diffusion of nitrogen in the steels causes the transformation of initial carbides into nitrides. During this transformation, carbon is released into the ferritic matrix. The experimental study has highlighted that the decarburization of the nitride layer occurs regardless of the type of nitriding and could reach 20% when the nitriding surface is not composed of compound layer This decarburization is induced by the reaction of the carbon released during the transformation of the cementite, with the hydrogen produced by the decomposition of ammonia to give a carburized species ?, this reaction occurs as long as any compound layer exists at the surface of the sample. This carbon redistribution has an influence on the microstructure and the residual stresses of the nitride layers. Based on experimental results, this phenomenon has been implemented in the nitriding simulation model developed in the laboratory. This implementation focuses on initial and boundary conditions obtained by complementing the experimental results with a thermodynamic simulation, to simulate nitrogen and carbon profiles close to those obtained experimentally. The model also calculates the volume change due to ? the precipitation and calculates the fields of residual stresses generated at the nitriding temperature and their evolution during cooling.. The multiphase character of the material is taken into account; the simulation allowing knowing the residual stresses in the ferrite, the precipitates and macroscopic residual stresses through a micromechanical model of scale transition like self-consistent. This multiphysics approach is applicable to all alloy carbon steels (Cr, Mo, V). This model has specifically been applied to industrial grade 33CrMoV12-9. The entire study allows understanding the influence of carbon on the mechanical properties of nitrided layers and the development of an industrial nitriding cycle based on experimental results and simulation
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Submitted on : Wednesday, July 20, 2016 - 3:49:07 PM
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  • HAL Id : tel-01347211, version 1


Guillaume Fallot. Rôle du carbone lors de la nitruration d’aciers de construction et influence sur les propriétés mécaniques. Mécanique des matériaux [physics.class-ph]. Ecole nationale supérieure d'arts et métiers - ENSAM, 2015. Français. ⟨NNT : 2015ENAM0029⟩. ⟨tel-01347211⟩



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