a b s t r a c tEvolution of spinodal decomposition and G-phase precipitation in ferrite of a thermally aged Mo-free duplex stainless steel was studied by Atom Probe Tomography (APT). Kinetics was compared to kinetics observed in ferrite of some Mo-bearing steels aged in similar conditions. This paper shows that formation of the G-phase particles proceeds via at least a two-step mechanism: enrichment of a/a 0 interdomains by G-former elements followed by formation of G-phase particles. As expected, G-phase precipitation is much less intense in the Mo-free steel than in Mo-bearing steels. The kinetic synergy observed in Mo-bearing steels between spinodal decomposition and G-phase precipitation is shown to also exist in Mo-free steel. Spinodal decomposition is less developed in the ferrite of the Mo-free steel investigated than in Mo-bearing steels: both the amplitude of the decomposition and the effective time exponent of the wavelength (0.06 versus 0.16) are much lower for the Mo-free steel. Neither the temperature of homogenisation nor quench effects or Ni and Mo contents could successfully explain the low time exponent of the spinodal decomposition observed in the Mo-free steel. The diffusion mechanisms could be at the origin of the different time exponents (diffusion along a/a 0 interfaces or diffusion of small clusters).
h i g h l i g h t s Link of microstructural characterization to microhardness of the ferrite for a wide variety of duplex steels. Quantification of G-phase and spinodal contributions to ferrite hardening. G-phase can be the main contributor to hardening.
In October 1991 the CHOOZ A PWR plant, operated by the French and Belgian company SENA, was shut down after 24 years. It was the first PWR shutdown in France. According to the EDF life duration project it was decided to perform an examination program on samples taken from the wall of the vessel in order to complete the feedback.
The results obtained show the following: • The embrittlement measured by the pressure vessel surveillance program is representative of that of the Shell determined at different axial and angular locations for the 1/4 of the internal thickness. This observation is consistent with the relative homogeneity of the embrittling elements (Cu, P, Ni) throughout the entire Shell, • The mechanical properties evolution through the wall thickness of the Shell measured after irradiation is interpreted in relation with fluence variation and unirradiated mechanical properties profile through the thickness, • The comparison of direct toughness measurement with the French code RCCM evaluation confirms the safety nature of the conventional approach. For the weld, after an irradiation damage of 2 1019 n.cm-2 (E>1MeV), a margin of the order of the irradiation effect seems to exist.
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