Optimisation de la gamme de fabrication de tubes en acier renforcés par une dispersion nanométrique d'oxydes (ODS) : compréhension des relations microstructures / propriétés mécaniques

Abstract : Oxide dispersion strengthened steels, elaborated by powder metallurgy, are considered as reference materials for high burn up cladding tubes for future Sodium Cooled Fast reactors. They present superior radiation resistance compared with austenitic steels and high creep strength due to reinforcement by the homogeneous dispersion of hard nano-sized particles. After mechanical alloying of the matrix powder and the yttrium oxides, ODS steels are consolidated by hot extrusion and manufactured by using cold pilgerin process. ODS steels are usually characterized by a low ductility and a high hardness at room temperature. The cold-rolling passes have to be punctuated by intermediate heat treatments in order to soften the raw tube and avoid any damage in the course of manufacturing.The aim of this study is to identify the key points for the control of the manufacturing of two grades: a Fe-14Cr-1W ferritic grade and a Fe-9Cr-1W martensitic grade. The relationship between thermomechanical treatments and microstructure is studied by multi-scale characterizations. The understanding of the microstructure evolution permits the determination of robust fabrication routes for both grades. The deformability of the ODS Fe-14Cr-1W ferritic grade is ensured by grain growth at high temperature following a Strain Induced Boundary Migration (SIBM) mechanism. Optimizations through primary recrystallization are proposed. Fabrication route of ODS Fe-9Cr-1W martensitic grade permits to obtain a material characterized by deformability and high temperature mechanical properties similar or even better than those of literature grades. Fabrication routes evolutions and chemical composition optimization are proposed to improve the corrosion and thermal creep resistance.
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Louise Toualbi. Optimisation de la gamme de fabrication de tubes en acier renforcés par une dispersion nanométrique d'oxydes (ODS) : compréhension des relations microstructures / propriétés mécaniques. Autre. Ecole Nationale Supérieure des Mines de Paris, 2012. Français. ⟨NNT : 2012ENMP0052⟩. ⟨tel-01609775⟩

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