Effets d'environnement sur la fatigue de l'acier inoxydable 304L en milieu primaire REP sous chargement cyclique

Abstract : The present study was undertaken in order to get further insights on cracking mechanisms in a304L stainless steel.More precisely, a first objective of this study was to evaluate the effect of various coldworking conditions on the cyclic stress-strain behavior and the fatigue life in air and in PWR primaryenvironment. In air a prior hardening was found to reduce the fatigue life in the LCF regime but not inprimary environment. In both environments, the fatigue limit of the hardened materials was increasedafter cold working.The second objective addresses the effect of the air and the PWR primary environments onthe cracking mechanisms (initiation and propagation) in the annealed material in the LCF regime.More precisely, the kinetics of crack initiation and micro crack propagation were evaluated with amulti scale microscopic approach in air and in primary environment.In PWR primary environment, during the first cycles, preferential oxidation occurs alongemerging dissociated dislocation and each cycle generates a new C-rich/Fe-rich oxide layer. Then,during cycling, the microstructure evolves from stacking fault into micro twinning and preferentialoxidation occurs by continuous shearing and dissolution of the passive film. Beyond a certain crackdepth (<3μm), the crack starts to propagate with a direction close to a 90° angle from the surface. Thecrack continues its propagation by successive generation of shear bands and fatigue striations at eachcycle up to failure.The role of corrosion hydrogen on these processes is finally discussed.
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Nicolas Huin. Effets d'environnement sur la fatigue de l'acier inoxydable 304L en milieu primaire REP sous chargement cyclique. Autre. ISAE-ENSMA Ecole Nationale Supérieure de Mécanique et d'Aérotechique - Poitiers, 2013. Français. ⟨NNT : 2013ESMA0009⟩. ⟨tel-00835093⟩

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