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 nitrogentransfer in α-iron as a function of the inlet flow rates. We obtained the simultaneoussimulation of the gas phase variations, and the nitrogen transfer in the sample. Theevolution of the nitrogen concentration at the surface and inside of the α-iron, as afunction of the time, is presented. The results are in good agreement with the experimentand with previous work. We also established a correlation between the gas compositionaround the sample and the inlet conditions, in order to obtain an optimal nitrogentransfer 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 centralesnucléaires, des essais de fatigue multiaxiale à grand nombre de cycles sont effectués pourtenter de quantifier l’effet de la multiaxialité et de contrainte moyenne sur la durée devie du matériau et alimenter un modèle d’endommagement à deux échelles. Des outils demesures de champs cinématiques ainsi que d’observations micrographiques sont mis en placeafin de tirer le maximum d’information de chaque essai : comportement cyclique,déformation plastique progressive, scénario d’apparition des fissures. Des résultatsd’essais proportionnels et non-proportionnels sont présentés.

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

Grindingtires generates an interesting secondary raw material (rubber granulates) but also twowastes, steel wires and textile fibers. We estimate that steel wires represent in Europe180 kt of steel every year which is not, or badly, valorized. This study showed that therecycling of these steel wires in steel mills was possible and viable, one necessarycondition being the determination of the non-metallic content remaining on the wires andkeeping 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 cracking behaviour of the oxide layer formed during hot rolling was studied togetherwith different combinations of process parameters in order to find their single influenceon the surface quality and formation of oxide defects. Several trials were performed onthe CRM pilot line to study in detail the impact of strip reduction, strip temperature,entry scale thickness, roll degradation, lubrication, skin cooling, chemical compositionand humidity on the scale behaviour. In general, the degree of deformation, entry scalethickness and rolling temperatures are the most important parameters and the importancedecreases in that order.

The role of the tundish in the continuous casting process has evolved from that of abuffer between the ladle and mold to being a grade separator, an inclusion removal deviceand a metallurgical reactor. For both grade separation and inclusion removal, the flowpatterns inside the tundish play an important role. The separation of non-metallicinclusions at the interface between the steel and the slag in the tundish is to a greatextent controlled by interfacial phenomena in the steel-slag-inclusion system. Oneconstant in the world of high-purity, low-residual and clean steels is the continual driveto 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 theabsence of oxide inclusions with diameters larger than 100 micrometers. Great efforts havebeen made to optimize the flow and turbulence in the tundish through weirs, dams or othersystems. Furthermore, a new system, the porous annular well block for injecting argon, hasbeen developed to optimize the bubble size and distribution and hence to achieve a highefficiency in trapping inclusions and in decreasing the hydrogen content in steel.Consequently, the steel quality is further improved in the tundish. Tested with success ina seamless steel shop, the new system gives results in agreement with the water models.

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!

Les phénomènes de fatigue thermique ou mécanique de matériaux conduisent à l’altérationdes structures, allant jusqu’à la création de fissures. L’objectif du contrôle nondestructif (CND) est de détecter ces fissures et déterminer leurs dimensions, donnéespermettant de statuer sur leurs nocivités et l’endommagement de la structure. Parmi lesdifférentes méthodes de CND, les ultrasons offrent en outre un examen volumique del’ensemble de la structure, avec une mise en œuvre relativement aisée et non contraignanteen termes de sécurité et règlementation. L’interaction entre les ondes ultrasonores et lesdiscontinuités ou fissures présentes au sein de la structure conduit à des échos observésen réception, lesquels après interprétation permettent de dimensionner voire caractériserles défauts à l’origine de ces échos. Selon la nature de l’endommagement (fissure isoléeou réseau de défauts, par exemple dans le cas d’un faïençage thermique, fissure ouverte oupartiellement fermée) et la technique de contrôle utilisée, des phénomènes plus ou moinscomplexes sont mis en jeu : interaction entre une fissure et un réseau de faïençageproche, contacts partiels entre les faces de la fissure sous l’effet de contraintes … Cesphénomènes peuvent limiter les capacités de dimensionnement, voire même de détection desfissures. Dans cet article, différentes applications menées par le CEA LIST, dans ledomaine nucléaire, sont discutées. Ces techniques reposent sur l’utilisation de capteursmulti-éléments ultrasonres, permettant de maîtriser l’orientation et la focalisation dufaisceau ultrasonore rayonné dans la pièce, de façon à optimiser la détection et ledimensionnement de défauts. Différents défauts ont été étudiés : fissure de fatiguemécanique inspectée par ultrasons sous contrainte ou hors contrainte, fissure de fatiguethermique, en présence ou non d’un réseau de faïençage. Ces techniques sont optimisées àpartir des outils de simulation disponibles au sein de laplateforme logiciellemulti-techniques (ultrasons, courants de Foucault, radiographie) CIVA, permettant deprédire les résultats des inspections et ainsi de concevoir et/ou optimiser des techniquesde contrôle. Les performances de ces différentes techniques sont évaluéesexpérimentalement et confrontées aux simulations.

Les pièces de forge sont universellement reconnues pour leurs bonnes propriétésmécaniques, notamment en fatigue. L’approche proposée ici consiste à intégrer lasimulation du forgeage dans le dimensionnement en fatigue des pièces forgées. Le fibrageet le taux de corroyage sont deux caractéristiques principales du forgeage. À l’aide dulogiciel FORGE®, le fibrage est calculé tout au long desopérations de mise en forme. Ce fibrage, ainsi que les contraintes résiduelles, sontensuite introduits dans des outils de dimensionnement pour améliorer la prédiction ducalcul de durée de vie en fatigue. Les critères de fatigue actuels, basés sur des modèlesisotropes, ne permettent pas de valoriser le sens long de ce fibrage, et par là les piècesde forge, car c’est en général dans ce sens que ces pièces sont le plus sollicitées. Uneextension anisotrope du modèle de Papadopoulos est proposée sur la base d’une campagneexpérimentale effectuée sur des éprouvettes prélevées à 0°, 45° et90° par rapport à la direction de fibrage. Une modélisation à l’échelle micro(DIGIMICRO) permet également de mieux comprendre le rôle des inclusions sur lessollicitations en fatigue. La mise en place d’une chaîne de simulation virtuelle globale àl’échelle d’un composant industriel, associée à des modélisations microstructurales,permet de mieux comprendre et de quantifier le rôle du fibrage sur les propriétés enfatigue à grand nombre de cycles des pièces forgées.

Experimental rolling trials were performed at different temperatures on EN 1.4462 duplexsteel imposing also different reduction ratios and a possible solution quenching. A clearand significant relation between the applied thermo-mechanical process and themicrostructural evolution was shown, and it is useful for designing the steelmicrostructure. The mechanical properties, the micro-structural features and the texturecharacteristics were defined for each condition in order to point out the operativeparameters (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’-ironnitride layer during gas nitriding. We simultaneously simulated both the gaseous and solidphases as well as the development of the γ’-iron nitride layer on theα-iron nitride layer. The theoretical atomic nitrogen flux at constantsuperficial concentration was used as the boundary limit at the sample’s surface. Onlyusing the input data, we obtained, as a function of the time, the atomic nitrogen profilesin 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 parametersand dissipation in ferritic steels under cyclic loading. We assumed the occurrence of twodissipative mechanisms associated with anelastic and inelastic deformations, respectively.We showed that the modelling provides good qualitative prediction of the heating curveswhen changing the volume fraction of precipitates in ferritic steels. We highlighted thekey 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 definetime-temperature equivalences during tempering, but it can only be computed for simplethermal cycles defined by a couple of values [temperature; time]. Its use is not adaptedfor complex thermal cycles. Three tempering parameters which integrate the full thermalcycles were investigated: the Hollomon-Jaffe derivative parameter, and the Tsuchiyama andArrhenius laws. Simple and complex thermal cycles were performed on a water-quenchedcarbon steel (i.e. different heating and cooling rates or two-step cycles, withtemperature varying between 450 °C and 750 °C and times from 30 s to 3 days). All threetempering 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 andArrhenius laws: they can be considered as robust and reliable. On the contrary, theHollomon-Jaffe derivative parameter proved unstable.

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

A new technology for lubricating the work rolls during hot rolling has been successfullytested in the finishing mill of ArcelorMittal Dunkirk. This new technology allows sprayingvery low quantities of pure oil on the work rolls to reduce the rolling forces by up to20% and with an increased efficiency of 50% compared with emulsions. The lubricant was apure natural oil without any additives.

Un modèle de comportement élastoplastique cyclique cristallin est proposé pour les métauxet alliages cubiques à face centrée, et en particulier pour le nickel. Il est utilisé lorsde simulations par éléments finis de la déformation cyclique uniaxiale d’un polycristalnon-texturé, représenté par l’assemblage de grains à géométrie cubique et à orientationcristalline aléatoire. Ce modèle distingue les grains pour lesquels l’axe de chargement sesitue dans la partie centrale du triangle stéréographique standard (auxquels un mode dedéformation en glissement planaire est imposé) et les grains pour lesquels il est situéprès des bords du triangle standard (auxquels un comportement en glissement multiple estattribué). Les résultats des simulations obtenus sont en accord avec les donnéesexpérimentales disponibles, autant au niveau de la courbe d’écrouissage cyclique, qu’auniveau des boucles d’hystérésis décrivant le comportement stabilisé. Ce modèle seraensuite employé pour l’étude de la localisation de la déformation sous forme de bandes deglissement persistantes, comme observé lors du chargement cyclique de polycristaux denickel.