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Compréhension et modélisation de l'influence du taux de renforts et de la texture de déformation sur la recristallisation des aciers ODS ferritiques

Abstract : Oxide dispersion strengthened steels are considered as cladding materials for Sodium Fast Reactor. Due to the nano-precipitates incorporated within the microstructure, their mechanical properties are very high, especially under creep loading. Moreover, the ferritic-martensitic lattice gives ODS steels a remarkable swelling resistance under radiation. The manufacturing route of ferritic ODS steels is complex and induces a strong morphologic and crystallographic texture. The microstructure needs to be recrystallized but this recrystallization is often heterogeneous and difficult to control. In this framework, this investigation aims at achieving a better understanding of the recrystallization mechanisms in ODS steels that strongly rely both on the nano-oxydes concentration and the applied deformation. Thereby, several model grades with various concentrations of oxydes were elaborated and characterized at different scales (EBSD, SANS, DSC). It appears that the chemical composition of the nano-oxydes strongly influence the microstructure stability and its ability to recover after consolidation. Throughout this study, the strong relationship between the cold-deformation path, the stored energy distribution and the recrystallized microstructure has been highlighted. When the thermo-mechanical treatment is optimal, homogeneous recrystallized microstructures weakly textured can be achieved. Experiments also showed that decreasing the nano-oxydes concentration does not clearly favor recrystallization. Monte Carlo modelling was performed to simulate grain growth and recrystallization in the presence of second phase particles and the simulations helped to identify the mechanisms that occur experimentally. Furthermore, the tensile properties of different metallurgical states were investigated and it came out that the recrystallization notably increases the ductility at high temperature without significantly affecting the yield strength. The results obtained on model materials allowed to achieve a better understanding of the mechanisms implied in the recrystallization process of ODS steels. Several possible optimizations to the current manufacturing route are discussed from the conclusions of this study.
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https://tel.archives-ouvertes.fr/tel-01968026
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Submitted on : Wednesday, January 2, 2019 - 1:10:22 AM
Last modification on : Friday, October 7, 2022 - 3:57:01 AM
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  • HAL Id : tel-01968026, version 1

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Benjamin Hary. Compréhension et modélisation de l'influence du taux de renforts et de la texture de déformation sur la recristallisation des aciers ODS ferritiques. Chimie inorganique. Université Paris Saclay (COmUE), 2017. Français. ⟨NNT : 2017SACLS339⟩. ⟨tel-01968026⟩

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