India, which produced nearly 67 Mt steel in 2010, aims to produce, in the near future, more than 100 Mt/year and to become, after China, the second largest steelmaker worldwide. To do this, India benefits from large iron ore reserves, especially of high-grade hematites, which presently constitute the largest amount of the local consumption as well of the exports. For the future, however, it will be necessary to beneficiate the large reserves of lower-grade iron ores, especially the magnetites. Furthermore, the question of the amount of the Indian iron ores available for export will have to be considered. India also has very large coal resources but, unhappily, mainly in non-coking coal, and often with high ash content: this is the main problem of the Indian iron and steel industry, to select the best routes and processes to make steel. The Indian iron and steel industry has to choose between: the conventional route based on the Blast Furnace and Oxygen Converter, which implies increasing the imports of high-grade coking coal, mainly from Australia; various routes based on local Indian coals, such as: (a) COREX or FINEX processes to produce liquid hot metal, or (b) direct reduction processes, either based on natural gas where it is available, or on local coals, presently mainly in rotary kilns (but with serious problems of energy efficiency and environmental pollution, in spite of the large present development), or based on coal gasification processes (such as MXCOL or ITmk3 processes). Finally, another special feature of the Indian iron and steel companies, specially of the largest private ones such as Tata, Essar and JSW (Jindal), is their development outside of India, which means the control of some 18 Mt steel/year, aiming to reach about 25 Mt/year in the near future!

L’objectif de cette étude est de proposer un critère de fatigue anisotrope pour le dimensionnement en fatigue de pièces industrielles forgées. Des résultats de différentes campagnes d’essais obtenus sur 3 nuances d’acier laminés sont tout d’abord présentés. Une attention particulière est portée à l’observation et à l’analyse des mécanismes d’amorçage à l’origine du comportement anisotrope en fatigue. Un critère de fatigue probabiliste permettant de tenir compte de la compétition possible entre différents types de mécanismes d’amorçage est ensuite développé. Ce critère permet notamment de tracer un diagramme de type Kitagawa probabiliste.

In standard diffraction experiments, ensembles of objects are characterized yielding averaged, statistical properties (meaningful only if the ensemble is monodisperse). Focused x-ray beams are used here to localize single nanostructures, identifying and probing individual objects one by one. In a scanning mode, a 2-dimensional image of the sample is recorded, which allows the reproducible alignment of a specific nanostructure for analysis. The x-ray scattered signal is analyzed and modelled, to give access to the shape, strain and composition inside the single object with sub-micron resolution. Combination of x-ray microdiffraction technique with other micro-probe experiments on the very same individual object (simultaneous coupling of x-ray diffraction measurements with atomic force microscopy (AFM)) is also shown; we prove the possibility to interact with the objects and to address elastic properties for individual nano-structures out of an ensemble.

Les aciers inoxydables austénitiques non sensibilisés peuvent subir dans l’acide nitrique un type de corrosion intergranulaire (CIG) particulier. Un modèle d’estimation de la durée de vie de ces matériaux dans ces milieux est proposé. Il reproduit de manière fiable les cinétiques de corrosion obtenues expérimentalement.

The mechanical properties of a CuCr1Zr alloy were measured with the help of a Gleeble 3500 machine at temperatures ranging from 250 °C to 1000 °C. Some tensile tests were also performed at 20 °C. The measured data were first used to determine the thermal linear coefficient at different temperatures. The measured curves were then simulated with an elasto-visco-plastic constitutive model assuming that the material behaviour was isotropic. This law requires the knowledge of temperature dependent parameters that were determined by inverse method. This work represents a part of a PhD study on hot tearing susceptibility during welding.

Les alliages biphasés α2/γ de base TiAl sont des candidats prometteurs pour des applications à hautes températures dans les domaines de l’aéronautiques. Leur développement reste limité du fait de la faible robustesse de la réponse aux traitements thermiques en particulier en présence de macroségrégation ou de la réactivité à haute température, limitant la surchauffe du métal liquide et donc la coulabilité de ces alliages. Les procédés de coulée centrifuge permettent un remplissage des moules à grande vitesse ce qui permet de pallier la faible coulabilité. La caractérisation de ce procédé passe par une meilleure compréhension de la formation des macroségrégations en présence de force centrifuge. Dans cette étude nous présentons les résultats de modélisation de macroségrégation prenant en compte la force centrifuge et le mouvement des grains pour un alliage de base Ti-Al-Nb.

PVD ZnCr coatings exhibit different metastable crystal structures δ, ζ, Γ depending on the Cr content and the deposition conditions. Here we describe the different mechanical and electrochemical properties of these phases. We show that by introducing an appropriate Cr concentration profile it is possible to produce a ZnCr coating with a thin Γ-phase interface layer optimized for substrate adhesion and a δ-phase matrix with a strong basal texture which possesses excellent cold forming properties. This alloy coating is tailored so that the application of a short low temperature annealing step after forming, such as an automotive paint bake hardening treatment, transforms the textured δ-phase into a nanocrystalline ı-phase with no marked texture. The latter microstructure provides significantly improved primary corrosion protection.

Les matériaux de fonderie, du fait de leur procédé d’obtention, présentent une population de défauts initiaux qui joue un rôle primordial sur leur comportement en fatigue. Dans ce travail, on propose de prendre en compte, dans un modèle de fatigue ad hoc, ces défauts de manière indirecte, i.e., sans les caractériser géométriquement. Cette approche est ensuite utilisée pour prévoir la tenue à la fatigue d’une structure obtenue par fonderie : une hélice marine.

A thermal fatigue test (INTHERPOL) was developed by EDF in order to study the initiation of cracks. These tests are carried out on tubular specimens under various thermal loadings and surface finish qualities in order to give an account of these parameters on crack initiation. The main topic of this study is to test the sensitivity of different fatigue criteria to surface conditions using a micro/macro modelling approach. Therefore a 304L polycrystalline aggregate, used for cyclic plasticity based FE modelling, have been considered as a Representative Volume Element located at the surface and subsurface of the test tube. This aggregate has been cyclically strained according to the results issued from FE simulation of INTHERPOL thermal fatigue experiment. Different surface parameters have been numerically simulated: effects of local microstructure and of grains orientation, effects of machining: metallurgical prehardening, residual stress gradient, and surface roughness. Three different fatigue criteria (Manson Coffin, Fatemi Socie and dissipated energy types), previously fitted at a macroscale for thermal fatigue of 304L, have been computed at a meso scale, in order to show the surface “hot spots” features and test the sensitivity of these three criteria to different surface conditions. Results show that grain orientation and neighbouring play an important role on the location of hot spots, and also that the positive effect of prestraining and the negative effect of roughness on fatigue life are not all similarly predicted by these different fatigue criteria.