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Theses

Etude des mécanismes de la transformation de phase bainitique dans les aciers bas carbone

Abstract : The aim of this thesis is to understand and to model the mechanisms of phase transformation from austenite to bainite in a low carbon low alloy steel and especially to investigate a possible variant selection phenomenon at local scale. A series of torsion tests enabled to determine the mechanical behaviour of the austenite and bainite phases at high temperature in order to improve an already developed micromechanical model of variant selection and to obtain samples having different microstructures of austenite before transformation. Then, samples obtained from isothermal bainitic transformations were realised in order to study the influence of the phase transformation temperature and of the austenite grain size on the variant selection at local scale. The investigation of microtextures was carried out thanks to the EBSD technique. It allowed us confirming the existence of a non-random distribution of neighbour variants within a former austenite grain. The micromechanical model of variant selection deals with a self-accommodation criterion of the transformation strains between specific variants, which leads to a reduction of the total energy of a system composed of the austenite and at least two variants of bainite. The transformation strains are determined thanks to the PTMC, and then the interactions between variants are obtained by solving an Eshelby inclusion problem. Comparison between experimental results and model predictions leads to a better understanding of the microstructures of martensite and bainite formed at low temperature by the self-accommodation criterion of the transformation strains than of the bainitic microstructures formed at high temperature.
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https://pastel.archives-ouvertes.fr/tel-00422924
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Submitted on : Thursday, October 8, 2009 - 3:53:36 PM
Last modification on : Thursday, September 24, 2020 - 6:30:04 PM
Long-term archiving on: : Tuesday, June 15, 2010 - 10:35:11 PM

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  • HAL Id : tel-00422924, version 1

Citation

Sophie Lubin. Etude des mécanismes de la transformation de phase bainitique dans les aciers bas carbone. Mécanique [physics.med-ph]. École Nationale Supérieure des Mines de Paris, 2009. Français. ⟨NNT : 2009ENMP1634⟩. ⟨tel-00422924⟩

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