We studied, in steady and in unsteady state, the gas-solid reaction of gas nitriding (NH3-H2) of steel, in order to control the atomic nitrogen transfer in α-iron as a function of the inlet flow rates. We obtained the simultaneous simulation of the gas phase variations, and the nitrogen transfer in the sample. The evolution of the nitrogen concentration at the surface and inside of the α-iron, as a function of the time, is presented. The results are in good agreement with the experiment and with previous work. We also established a correlation between the gas composition around the sample and the inlet conditions, in order to obtain an optimal nitrogen transfer at the sample’s surface, and thus control the nitride layer growth.

Dans le cadre de l’étude de la fatigue thermique de tuyauteries du parc de centrales nucléaires, des essais de fatigue multiaxiale à grand nombre de cycles sont effectués pour tenter de quantifier l’effet de la multiaxialité et de contrainte moyenne sur la durée de vie du matériau et alimenter un modèle d’endommagement à deux échelles. Des outils de mesures de champs cinématiques ainsi que d’observations micrographiques sont mis en place afin de tirer le maximum d’information de chaque essai : comportement cyclique, déformation plastique progressive, scénario d’apparition des fissures. Des résultats d’essais proportionnels et non-proportionnels sont présentés.

This article presents the work carried out to define quality criteria of a new scrap source for the steel industry: steel wires generated by grinding end-of-life tires. The definition of this promising new secondary raw material source is perfectly in agreement with the European Directives 75/442/CEE and 2000/53/EC, dealing with waste and recycling of end-of-life vehicles, thus answering the environmental needs of our society.

Grinding tires generates an interesting secondary raw material (rubber granulates) but also two wastes, steel wires and textile fibers. We estimate that steel wires represent in Europe 180 kt of steel every year which is not, or badly, valorized. This study showed that the recycling of these steel wires in steel mills was possible and viable, one necessary condition being the determination of the non-metallic content remaining on the wires and keeping it lower than 4%.

Tenova started a research program in 2002 for strongly lowering NOx emissions. After the excellent results achieved in the reheating furnaces, the Tenova FlexyTech® burner family was enlarged with the TLX burner whose first application was in the furnace for austenitizing treatment of seamless tubes at TenarisDalmine (2006). The main goals of the revamping were strongly decreasing NOx emissions and increasing the productivity. The results after one year of operation are presented.

The effect of superheating and substrate morphology on heat exchange at the melt-solid interface was studied. An experimental device was set up to yield a unidirectional heat flow from the Sn-Pb bath to the lubricated steel substrate and the heat transfer resistance was evaluated from the thickness of the solidified material at a fixed time. A higher solidification efficiency was obtained with moderate superheating, and also with a proper choice of surface topography and lubricant.

The role of the tundish in the continuous casting process has evolved from that of a buffer between the ladle and mold to being a grade separator, an inclusion removal device and a metallurgical reactor. For both grade separation and inclusion removal, the flow patterns inside the tundish play an important role. The separation of non-metallic inclusions at the interface between the steel and the slag in the tundish is to a great extent controlled by interfacial phenomena in the steel-slag-inclusion system. One constant in the world of high-purity, low-residual and clean steels is the continual drive to reduce and control the frequency of the inclusions. For example, there are high-purity, low-residual clean steels such as IF- steel sheets for automobiles which require the absence of oxide inclusions with diameters larger than 100 micrometers. Great efforts have been made to optimize the flow and turbulence in the tundish through weirs, dams or other systems. Furthermore, a new system, the porous annular well block for injecting argon, has been developed to optimize the bubble size and distribution and hence to achieve a high efficiency in trapping inclusions and in decreasing the hydrogen content in steel. Consequently, the steel quality is further improved in the tundish. Tested with success in a seamless steel shop, the new system gives results in agreement with the water models.

The cracking behaviour of the oxide layer formed during hot rolling was studied together with different combinations of process parameters in order to find their single influence on the surface quality and formation of oxide defects. Several trials were performed on the CRM pilot line to study in detail the impact of strip reduction, strip temperature, entry scale thickness, roll degradation, lubrication, skin cooling, chemical composition and humidity on the scale behaviour. In general, the degree of deformation, entry scale thickness and rolling temperatures are the most important parameters and the importance decreases in that order.

Les phénomènes de fatigue thermique ou mécanique de matériaux conduisent à l’altération des structures, allant jusqu’à la création de fissures. L’objectif du contrôle non destructif (CND) est de détecter ces fissures et déterminer leurs dimensions, données permettant de statuer sur leurs nocivités et l’endommagement de la structure. Parmi les différentes méthodes de CND, les ultrasons offrent en outre un examen volumique de l’ensemble de la structure, avec une mise en œuvre relativement aisée et non contraignante en termes de sécurité et règlementation. L’interaction entre les ondes ultrasonores et les discontinuités ou fissures présentes au sein de la structure conduit à des échos observés en réception, lesquels après interprétation permettent de dimensionner voire caractériser les défauts à l’origine de ces échos. Selon la nature de l’endommagement (fissure isolée ou réseau de défauts, par exemple dans le cas d’un faïençage thermique, fissure ouverte ou partiellement fermée) et la technique de contrôle utilisée, des phénomènes plus ou moins complexes sont mis en jeu : interaction entre une fissure et un réseau de faïençage proche, contacts partiels entre les faces de la fissure sous l’effet de contraintes … Ces phénomènes peuvent limiter les capacités de dimensionnement, voire même de détection des fissures. Dans cet article, différentes applications menées par le CEA LIST, dans le domaine nucléaire, sont discutées. Ces techniques reposent sur l’utilisation de capteurs multi-éléments ultrasonres, permettant de maîtriser l’orientation et la focalisation du faisceau ultrasonore rayonné dans la pièce, de façon à optimiser la détection et le dimensionnement de défauts. Différents défauts ont été étudiés : fissure de fatigue mécanique inspectée par ultrasons sous contrainte ou hors contrainte, fissure de fatigue thermique, en présence ou non d’un réseau de faïençage. Ces techniques sont optimisées à partir des outils de simulation disponibles au sein de laplateforme logicielle multi-techniques (ultrasons, courants de Foucault, radiographie) CIVA, permettant de prédire les résultats des inspections et ainsi de concevoir et/ou optimiser des techniques de contrôle. Les performances de ces différentes techniques sont évaluées expérimentalement et confrontées aux simulations.

Les pièces de forge sont universellement reconnues pour leurs bonnes propriétés mécaniques, notamment en fatigue. L’approche proposée ici consiste à intégrer la simulation du forgeage dans le dimensionnement en fatigue des pièces forgées. Le fibrage et le taux de corroyage sont deux caractéristiques principales du forgeage. À l’aide du logiciel FORGE®, le fibrage est calculé tout au long des opérations de mise en forme. Ce fibrage, ainsi que les contraintes résiduelles, sont ensuite introduits dans des outils de dimensionnement pour améliorer la prédiction du calcul de durée de vie en fatigue. Les critères de fatigue actuels, basés sur des modèles isotropes, ne permettent pas de valoriser le sens long de ce fibrage, et par là les pièces de forge, car c’est en général dans ce sens que ces pièces sont le plus sollicitées. Une extension anisotrope du modèle de Papadopoulos est proposée sur la base d’une campagne expérimentale effectuée sur des éprouvettes prélevées à 0°, 45° et 90° par rapport à la direction de fibrage. Une modélisation à l’échelle micro (DIGIMICRO) permet également de mieux comprendre le rôle des inclusions sur les sollicitations en fatigue. La mise en place d’une chaîne de simulation virtuelle globale à l’échelle d’un composant industriel, associée à des modélisations microstructurales, permet de mieux comprendre et de quantifier le rôle du fibrage sur les propriétés en fatigue à grand nombre de cycles des pièces forgées.

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!

Experimental rolling trials were performed at different temperatures on EN 1.4462 duplex steel imposing also different reduction ratios and a possible solution quenching. A clear and significant relation between the applied thermo-mechanical process and the microstructural evolution was shown, and it is useful for designing the steel microstructure. The mechanical properties, the micro-structural features and the texture characteristics were defined for each condition in order to point out the operative parameters (i.e. thermal level, imposed strains and application of solution quenching) that permit to maximize the formability of the final hot-rolled products.

The aim of this study is the control of the growth of the γ’-iron nitride layer during gas nitriding. We simultaneously simulated both the gaseous and solid phases as well as the development of the γ’-iron nitride layer on the α-iron nitride layer. The theoretical atomic nitrogen flux at constant superficial concentration was used as the boundary limit at the sample’s surface. Only using the input data, we obtained, as a function of the time, the atomic nitrogen profiles in the sample and the evolution of the γ’-iron nitride layer thickness. The numerical results favorably compare with the experimental ones.

A new micromechanical modelling is proposed to correlate some microstructural parameters and dissipation in ferritic steels under cyclic loading. We assumed the occurrence of two dissipative mechanisms associated with anelastic and inelastic deformations, respectively. We showed that the modelling provides good qualitative prediction of the heating curves when changing the volume fraction of precipitates in ferritic steels. We highlighted the key role of the dispersion of the grain size on the local and global dissipation.

The Hollomon-Jaffe parameter is commonly used to characterize thermal cycles and define time-temperature equivalences during tempering, but it can only be computed for simple thermal cycles defined by a couple of values [temperature; time]. Its use is not adapted for complex thermal cycles. Three tempering parameters which integrate the full thermal cycles were investigated: the Hollomon-Jaffe derivative parameter, and the Tsuchiyama and Arrhenius laws. Simple and complex thermal cycles were performed on a water-quenched carbon steel (i.e. different heating and cooling rates or two-step cycles, with temperature varying between 450 °C and 750 °C and times from 30 s to 3 days). All three tempering parameters show good correlation with the tensile properties of the material, even when complex cycles were performed, provided that the material constant is optimized. The sensitivity to the determination of this constant is low for the Tsuchiyama and Arrhenius laws: they can be considered as robust and reliable. On the contrary, the Hollomon-Jaffe derivative parameter proved unstable.

A new technology for lubricating the work rolls during hot rolling has been successfully tested in the finishing mill of ArcelorMittal Dunkirk. This new technology allows spraying very low quantities of pure oil on the work rolls to reduce the rolling forces by up to 20% and with an increased efficiency of 50% compared with emulsions. The lubricant was a pure natural oil without any additives.

The Australian Pilbara blend lump ore, which entered the Chinese market in 2007, is a special blending ore. To master its behavior and effect in a BF adequately, the metallurgical properties and high temperature reactivity of the Pilbara blend lump ore and six other kinds of lump ore were researched. The reasonable proportion and mixing pattern of the Pilbara blend lump ore was studied by carrying out softening and dropping property tests, and this provides technological support for practical production.

Un modèle thermique a été développé afin d’identifier les sources de chaleur accompagnant les déformations micro-plastiques intervenant au cours d’un essai de fatigue cyclique. Dans la première minute de chaque palier, un modèle de barre infinie permet de différer la prise en compte des pertes conductives par les mors. Les sources sont identifiées au fil des paliers de chargement croissant, tout en évitant d’entrer dans le domaine de plasticité macroscopique.