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Influence d’additions de titane/tungstène et de vanadium sur la précipitation de carbures secondaires au sein d’alliages modèles de type HP

Abstract : HP alloys are typically used as steam methane reforming tubes in the petrochemical industry. During service, they are exposed to temperatures between 700°C and 1000°C under gaz pressure of several MPa. Their as-cast microstructure, together with fine in-situ secondary precipitation, provide these alloys with an excellent resistance to creep deformation. Nevertheless, after long-time ageing, coarsening of secondary carbides leads to the weakening of the tubes and therefore to an accelerated damaging.The effects of some alloying elements (V, Ti/W) on secondary precipitation of M23C6 and NbC carbides were investigated through numerical simulations performed with TC-PRISMA software. On the basis of encouraging results in terms of precipitation optimization, two model HP-type alloys were cast at the laboratory and aged in the range of temperatures corresponding to service conditions. As-cast microstructures were first compared with an industrial "standard" alloy. Then, secondary precipitation were characterized for all the alloys and all ageing temperatures. Microstructural investigation highlighted the beneficial effect of vanadium and titanium/tungsten additions on secondary precipitation characteristics.
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Submitted on : Friday, December 15, 2017 - 3:38:17 PM
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Robin Guiz. Influence d’additions de titane/tungstène et de vanadium sur la précipitation de carbures secondaires au sein d’alliages modèles de type HP. Autre. Université de Lyon, 2016. Français. ⟨NNT : 2016LYSEM011⟩. ⟨tel-01665146⟩

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