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 ledimensionnement en fatigue de pièces industrielles forgées. Des résultats de différentescampagnes d’essais obtenus sur 3 nuances d’acier laminés sont tout d’abord présentés. Uneattention particulière est portée à l’observation et à l’analyse des mécanismes d’amorçageà l’origine du comportement anisotrope en fatigue. Un critère de fatigue probabilistepermettant de tenir compte de la compétition possible entre différents types de mécanismesd’amorçage est ensuite développé. Ce critère permet notamment de tracer un diagramme detype Kitagawa probabiliste.

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

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 Gleeble3500 machine at temperatures ranging from 250 °C to 1000 °C. Some tensile tests were alsoperformed at 20 °C. The measured data were first used to determine the thermal linearcoefficient at different temperatures. The measured curves were then simulated with anelasto-visco-plastic constitutive model assuming that the material behaviour wasisotropic. This law requires the knowledge of temperature dependent parameters that weredetermined by inverse method. This work represents a part of a PhD study on hot tearingsusceptibility during welding.

Les alliages biphasés α2/γ de base TiAl sont des candidatsprometteurs pour des applications à hautes températures dans les domaines del’aéronautiques. Leur développement reste limité du fait de la faible robustesse de laréponse aux traitements thermiques en particulier en présence de macroségrégation ou de laréactivité à haute température, limitant la surchauffe du métal liquide et donc lacoulabilité de ces alliages. Les procédés de coulée centrifuge permettent un remplissagedes moules à grande vitesse ce qui permet de pallier la faible coulabilité. Lacaractérisation de ce procédé passe par une meilleure compréhension de la formation desmacroségrégations en présence de force centrifuge. Dans cette étude nous présentons lesrésultats de modélisation de macroségrégation prenant en compte la force centrifuge et lemouvement des grains pour un alliage de base Ti-Al-Nb.

PVD ZnCr coatings exhibit different metastable crystal structures δ, ζ, Γ depending onthe Cr content and the deposition conditions. Here we describe the different mechanicaland electrochemical properties of these phases. We show that by introducing an appropriateCr concentration profile it is possible to produce a ZnCr coating with a thin Γ-phaseinterface layer optimized for substrate adhesion and a δ-phase matrix with a strongbasal texture which possesses excellent cold forming properties. This alloy coating istailored 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-phaseinto a nanocrystalline ı-phase with no marked texture. The latter microstructure providessignificantly 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 initiationof cracks. These tests are carried out on tubular specimens under various thermal loadingsand surface finish qualities in order to give an account of these parameters on crackinitiation. The main topic of this study is to test the sensitivity of different fatiguecriteria to surface conditions using a micro/macro modelling approach. Therefore a 304Lpolycrystalline aggregate, used for cyclic plasticity based FE modelling, have beenconsidered as a Representative Volume Element located at the surface and subsurface of thetest tube. This aggregate has been cyclically strained according to the results issuedfrom FE simulation of INTHERPOL thermal fatigue experiment. Different surface parametershave been numerically simulated: effects of local microstructure and of grainsorientation, effects of machining: metallurgical prehardening, residual stress gradient,and surface roughness. Three different fatigue criteria (Manson Coffin, Fatemi Socie anddissipated 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 andtest the sensitivity of these three criteria to different surface conditions. Results showthat grain orientation and neighbouring play an important role on the location of hotspots, and also that the positive effect of prestraining and the negative effect ofroughness on fatigue life are not all similarly predicted by these different fatiguecriteria.