Effets d'hétérogénéités de teneur en carbone sur les cinétiques de transformations de phase et sur la genèse des contraintes internes lors du refroidissement d'aciers

Abstract : Heat treatment is a process that needs the control of both final microstructures and residual stresses and deformations. Numerical simulation is a useful tool for a better optimization of this process. The aim of our work was to contribute to the development of a numerical tool for the prediction of microstructures, stresses and strains during cooling of pieces that may contain chemical heterogeneities, particularly carbon content heterogeneities. Firstly, an existing model for the prediction of transformation kinetics in steels has been further developped in order to take into account the effects of the carbon content enrichment of austenite due to a partial ferritic transformation on the subsequent transformations. Coupled thermal, metallurgical, mechanical calculations have then been performed to study the effects of carbon content gradients on the microstructural evolutions and on the residual stresses development during cooling. Particularly, the possible effects of solidification macro and mesosegregations have been quantified in massive cylinders with sizes close to the size of an ingot. Secondly, experimental validations have been performed for homogeneous cylindrical specimen (40CrMnMo8 steel) and for a chemically heterogeneous specimen specifically designed for our study. The complete set of input data necessary for the simulations has been established from experimental characterizations of the steel. The role of chemical heterogeneity has been analysed through the experimental and calculated results. Finally, a good correlation has been obtained between measurements and calculation of the deformation during cooling of a 3D "croissant" shaped specimen.
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Theses
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http://docnum.univ-lorraine.fr/prive/INPL_T_2003_LOUIN_J_C.pdf
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Submitted on : Thursday, March 29, 2018 - 12:39:53 PM
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Jean-Charles Louin. Effets d'hétérogénéités de teneur en carbone sur les cinétiques de transformations de phase et sur la genèse des contraintes internes lors du refroidissement d'aciers. Autre [cond-mat.other]. Institut National Polytechnique de Lorraine, 2003. Français. ⟨NNT : 2003INPL077N⟩. ⟨tel-01750167⟩

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