Creep and tensile behaviour of austenitic Fe–Cr–Ni stainless steels

The control of creep behaviour during service of reformer tubes made of HP-40 austenitic stainless steels is still limited by the knowledge of creep mechanisms in these alloys. Two different HP-40 alloys modified with a low-level addition ofNbwere studied. Creep testswere carried out at 980 and 1050 ◦C with different stress levels, in the range of 20–50MPa, and their resultswere plotted in a Norton-type diagram. Also, low strain rate tensile tests were performed at temperature of 950, 980 or 1000 ◦C. As low strain rate tensile tests showed a plateau at nearly constant stress for a given strain rate, they could be somehow linked with creep tests. Accordingly, tensile and creep results were plotted together on a Larson–Miller (LMP) diagram. The fracture modes of tensile and creep samples were investigated and the effect of different parameters such as sample dimensions, temperature and atmosphere, was also studied

Microstructure evolution of HP40-Nb alloys during aging under air at 1000 °C

Two as-cast HP 40 alloys provided by different manufacturers were aged at 1000 °C under laboratory air. They had the same as-cast microstructure consisting of austenite dendrites delineated by a network of eutectic Nb-rich MC and Cr-rich M7C3 carbides. After aging for several months, they showed similar microstructures in the bulk materials, though M7C3 carbides have been replaced by M23C6 carbides. As expected, a sub-surface zone depleted in chromium has appeared where a tetragonal CrNbC could be identified in both materials. However, the composition of the transition zones between the surface and the bulk materials differed, mainly because one of the materials underwent significant nitrogen pick-up with associated precipitation of M6(C,N) and M2(C,N) phases. On the contrary, the other alloy did show only one intermediate zone with a mix of CrNbC, M23C6 and MC carbides. A full account of the microstructures observed in the aged materials is given

Les gardes rouges : des rebelles sous influence

La révolution culturelle a précipité la Chine dans des désordres et des affrontements dont le principal acteur fut la jeunesse scolarisée des villes, qui se laissa embrigader dans le mouvement des Gardes rouges. Ceux-ci se mobilisèrent en réponse à des incitations et des manipulations venues de Mao et de son entourage. Pourtant, même s’ils bénéficièrent plus d’une fois du soutien de l’armée et de la police politique, ils jouirent d’une véritable autonomie. Mais cette autonomie, ils aliénèrent totalement, en s’en servant pour imiter le modèle « révolutionnaire » qui leur avait été inculqué par l’école et la propagande, au cours de violences et d’actes barbares qui visaient les autorités établies en tant que telles. Dans un contexte où les pères biologiques avaient été infantilisés et marginalisés par le régime totalitaire, ils briguaient ainsi la reconnaissance d’une figure de super-père, Mao

Effect of external stress on the Fe–Cr phase separation in 15-5 PH and Fe–15Cr–5Ni alloys

The effect on Fe–Cr phase separation of a uniaxial stress during thermal ageing at 4251C is investigated on a Fe–15Cr–5Ni steel, a model alloy of commercial 15-5 PH steel. The applied stress is shown to accelerate the ageing kinetics, and influence the morphology of Cr rich domains. A dependence of the phase separation decomposition kinetics on the relative orientations of the load and the crystal local orientation has also been observed

Corrosion Behavior of 6101 Aluminum Alloy Strands for Automotive Wires

Microstructural states produced by each step of the manufacturing process leading to the production of automotive strand arms in 6101 aluminum alloy (AA6101) for wiring harnesses were investigated in relation to their corrosion behavior in NaCl solution. The observed corrosion morphology,i.e., pitting corrosion or intergranular corrosion, was strongly dependent on the precipitation state, i.e., mainly the presence of intergranular Mg2Si precipitates. A ‘grain size – corrosion resistance’ relationship was also evidenced with an ennoblement of the corrosion potential for wires heavily cold drawn, which were characterized by a nanometric grain size. Dislocation density as well as the homogeneity of alloying element distribution were also found to be relevant parameters for explaining the electrochemical behavior of each microstructural state. Plastic deformation and recrystallization phenomena occurring during the manufacturing process were found to be associated with redistribution of alloying elements, which impeded the formation of intergranular Mg2Si precipitates. Therefore, in the present study, the cold drawing process was found to increase the intergranular corrosion resistance of AA6101

The catastrophic flash-flood event of 8–9 September 2002 in the Gard region, France: a first case study for the Cévennes–Vivarais Mediterranean Hydrometeorological Observatory

The Cévennes–Vivarais Mediterranean Hydrometeorological Observatory (OHM-CV) is a research initiative aimed at improving the understanding and modeling of the Mediterranean intense rain events that frequently result in devastating flash floods in southern France. A primary objective is to bring together the skills of meteorologists and hydrologists, modelers and instrumentalists, researchers and practitioners, to cope with these rather unpredictable events. In line with previously published flash-flood monographs, the present paper aims at documenting the 8–9 September 2002 catastrophic event, which resulted in 24 casualties and an economic damage evaluated at 1.2 billion euros (i.e., about 1 billion U.S. dollars) in the Gard region, France. A description of the synoptic meteorological situation is first given and shows that no particular precursor indicated the imminence of such an extreme event. Then, radar and rain gauge analyses are used to assess the magnitude of the rain event, which was particularly remarkable for its spatial extent with rain amounts greater than 200 mm in 24 h over 5500 km2. The maximum values of 600–700 mm observed locally are among the highest daily records in the region. The preliminary results of the postevent hydrological investigation show that the hydrologic response of the upstream watersheds of the Gard and Vidourle Rivers is consistent with the marked space–time structure of the rain event. It is noteworthy that peak specific discharges were very high over most of the affected areas (5–10 m3 s−1 km−2) and reached locally extraordinary values of more than 20 m3 s−1 km−2. A preliminary analysis indicates contrasting hydrological behaviors that seem to be related to geomorphological factors, notably the influence of karst in part of the region. An overview of the ongoing meteorological and hydrological research projects devoted to this case study within the OHM-CV is finally presented

The AVuPUR project (Assessing the Vulnerabiliy of Peri-Urbans Rivers): experimental set up, modelling strategy and first results

International audienceLe projet AVuPUR a pour objectif de progresser sur la compréhension et la modélisation des flux d'eau dans les bassins versants péri-urbains. Il s'agit plus particulièrement de fournir des outils permettant de quantifier l'impact d'objets anthropiques tels que zones urbaines, routes, fossés sur les régimes hydrologiques des cours d'eau dans ces bassins. Cet article présente la stratégie expérimentale et de collecte de données mise en ½uvre dans le projet et les pistes proposées pour l'amélioration des outils de modélisation existants et le développement d'outils novateurs. Enfin, nous présentons comment ces outils seront utilisés pour simuler et quantifier l'impact des modifications d'occupation des sols et/ou du climat sur les régimes hydrologiques des bassins étudiés. / The aim of the AVuPUR project is to enhance our understanding and modelling capacity of water fluxes within suburban watersheds. In particular, the objective is to deliver tools allowing to quantify the impact of anthropogenic elements such as urban areas, roads, ditches on the hydrological regime of suburban rivers. This paper presents the observation and data collection strategy set up by the project, and the directions for improving existing modelling tools or proposing innovative ones. Finally, we present how these tools will be used to simulate and quantify the impact of land use and climate changes on the hydrological regimes of the studied catchments