Fluid flow phenomena are very closely related to the casting quality and surface finish of the cast part. In addition, the good quality of the casting product can be achieved by using an optimum gating system design. In this work, a vortex well, which is one of the important components of gating system design, is utilized in order to demonstrate its effectiveness in improving the mechanical and microstructure properties of the cast part. An X-ray radiography test was performed in order to investigate the porosity distribution in castings with different vortex well dimensions. The scatter of flexure strength results was quantified by Weibull statistics. Microstructure analysis was conducted by using a scanning electron microscope (SEM) to examine the microstructure of selected casting specimens produced from the vortex well design. By optimizing the vortex well design, porosity inside the casting was significantly reduced, while the mechanical strength and reliability of aluminum casting were further enhanced.

Stainless steels are often used instead of painted carbon steels or weathering steels in architecture or construction for aesthetic reasons and/or when maintenance cost reduction is considered. With duplex stainless steels the investment cost can also be significantly reduced using their better yield and tensile stresses. Then the choice of material depends on the environment corrosivity. Usual accelerated corrosion tests as salt spray type may help to rank stainless steels but not to select a cost effective material for an outdoor location. Considering the lack of available data, Industeel launched five years ago an extensive field exposure program with the aim to collect representative data. Six locations were chosen in North America and Europe to cover a wide range of humidity, temperature, pH, chloride ions and pollutant contents. In this way more than 200 coupons with and without weld were exposed in marine, industrial, urban and rural atmospheres or combinations of them. This paper shows some of the first results obtained on duplex (lean duplex included), austenitic, martensitic and ferrito-martensitic stainless steel specimens after several years of exposure. Correlation between environmental parameters, alloy chemical composition, microstructure and localized corrosion resistance are discussed.

The Production of aluminium is one of such industrial processes that have the potential to release great quantities of dangerous toxic material into the atmosphere. To protect the environment, the Alucam Company has put in place two collection and treatment stations. The main indicator of performance of this system is the collection and treatment efficiency. All other parameters kept constant, this efficiency is proportional to the fume flow rate at the chimney. But the key parameters to control in case of variation are poorly mastered. The collection efficiency of the treatment stations can deteriorate at any moment without any successful intervention to bring back the situation to normal. This article presents the first part of a research work which intends to solve this problem of variations in the flow rate by increasing the fume flow rate and controlling the system within specified limits. We use a Continuous Improvement Methodology which involves the use of Six Sigma tools at the completion of the analysis phase of which we get the fundamental causes of the low performance.

A metallurgical route to produce S700MC/Grade100 steel on a hot strip mill has been developed at ArcelorMittal Europe, based on laboratory simulations and industrial trials. The importance of ThermoMechanically Controlled Processing (TMCP) has been illustrated, mainly to optimize the low temperature toughness. Furthermore, it has been shown that the optimum combination of strength and low temperature toughness can be found through optimization of the transformation and the precipitation. The concept developed shows a good robustness against typical industrial process variations.The steel shows a good weldability using typical MAG welding parameters, without loss in strength and a good toughness. The high cycle fatigue performance of the steel is very good.

Le comportement mécanique et la tenue en fatigue sont étudiés en fonction de l’orientation des fibres et en fonction du chargement (traction-torsion) pour un thermoplastique renforcé par des fibres de verre courtes. Les résultats présentent une forte anisotropie qui exige la mise en œuvre d’une chaîne de dimensionnement qui intègre la simulation du procédé : simulation de l’orientation des fibres par Moldflow, estimation du comportement mécanique par homogénéisation de type Mori Tanaka et enfin application d’un critère énergétique. La confrontation entre les résultats expérimentaux et cette modélisation complète est très satisfaisante.

In the present study, the formation and growth of an oxide film on a titanium alloy Ti6Al4V surface immersed in 3% NaCl solution using anodisation at various imposed potentials was investigated by two electrochemical techniques, cyclic polarisation and impedance measurements. In the cyclic polarisation studies at different scan rates, the obtained curves show a large range of passivation, due to the formation of a protective oxide film, generally TiO2. In addition, the negative hysteresis that appeared during the cyclic polarisation with the shift of the corrosion potential in the more noble direction (approximately +260 mV) may be explained by a reduction of the corrosion products. It was found that the lower the scan rates the lower the passivation current, and the scan rates did not have a significant effect on the potential or current of corrosion. The impedance measurements (Nyquist and Bode plots) at various imposed potentials show that Ti6Al4V has a capacitive behaviour in the passive field, due to the formation and growth of the oxide film.

The collection efficiency is the major indicator for the evaluation of the pollution rate and the environmental performance of the aluminium electrolysis process. This efficiency is proportional to the flow rate of the released gases at the chimney. Since December 2009, the normal flow rate has being decreasing and fluctuating in the Alucam smelting factory. At the Analysis step of the DMAIC methodology, the fundamental causes of the variations and the decrease in the gas normal fume flow rate were identified in a previous study. We intend here to stabilize the flow rate, to Improve the efficiency and to put into place a reliable mechanism of Control in order to maintain target variables within Six Sigma limits. Therefore, we propose an appropriate model of the pipeline network which permits us to identify the causes of the process low capability by excluding the interpretation controversy of the relation between the stopping of pots and the decrease in the fume collection and treatment installation. Then, we choose to achieve the modulation of the suction fan to adapt to changes in system load, and the replacement of the fan impeller to reach the continuous regulation of the flow rate. Benefits cannot be over emphasized because the company may improve on its collection and treatment efficiency, hence an effective reduction of dangerous gaseous fluoride emissions.

The use of stainless steels as concrete reinforcement is becoming increasingly popular in coastal and marine constructions in order to prevent corrosion induced by chloride ions penetrating into the concrete. In these highly aggressive situations, the lean duplex stainless steels have been extensively employed due to their high mechanical and corrosion resistances. However, the influence of Mo addition on pitting corrosion resistance of these steels is not clearly understood in alkaline chloride conditions even if this element is widely associated to an increasing corrosion resistance in acidic and neutral environments. Therefore, understanding Mo mechanism on corrosion resistance in alkaline media is hence of major importance to the setting of optimized alloy composition. The present work aims to study the effect of Mo addition on pitting corrosion properties of lean duplex stainless steels in alkaline environments (concrete). The results are discussed with respect to the influence of Mo addition on pitting potential for two industrial duplex alloys (1.4362 and 1.4462) in several aggressive media mainly in synthetic, chlorinated and carbonated solution simulating concrete pore environments (pH10 solution with carbonates and chlorides ions). In order to establish the real role of Mo addition on lean duplex corrosion and passivation properties, the corrosion behaviors of two specific laboratory lean duplex alloys, which the only difference between then is the amount of Mo (0 and 3% wt. Mo), are also studied. Furthermore, scanning electronic microscopy (SEM) was used to verify which phase of duplex microstructure (ferritic or austenitic) is mostly susceptible to the pit nucleation in these corrosion conditions as the role of Mo is probably different to each simple phase.

Les alliages ferritiques Fe-8 %Al possèdent des propriétés physiques et mécaniques prometteuses pour le développement et la conception de nouveaux types d’aciers allégés. Ces alliages présentent cependant des défauts de surface appelés « roping », apparaissant après l’étape d’emboutissage à froid. La formation de ces défauts est principalement attribuée à la distribution hétérogène des orientations des grains. Dans cette étude, les effets de la quantité de déformation, de la vitesse de déformation et de la température ont été examinés en utilisant la torsion à chaud. Les essais ont été réalisés à des températures comprises entre 900 °C et 1100 °C et des vitesses de déformation comprises entre 0,1 s-1 et 10 s-1. Il a été montré que deux types de recristallisation dynamique pouvaient intervenir durant la déformation à chaud : la recristallisation dynamique continue et la recristallisation dynamique discontinue.

Les aciers inoxydables ferritiques connaissent un développement régulier depuis de nombreuses années, en partie grâce aux variations importantes du coût des éléments d’alliage et notamment du nickel qui impactent fortement le prix des nuances austénitiques classiques. Toutefois, il ne faut pas négliger les avantages techniques que présentent les nuances ferritiques. Cet article présente une série d’exemples illustrant les performances des aciers inoxydables ferritiques dans des domaines d’applications variés et souligne la large gamme de propriétés qui peuvent être obtenues.

Nowadays, finding ceramic materials with good physical-chemistry characteristics to make ceramic cups is no longer a big difficulty. However, the stability of the construction, the anti-penetration ability and the adaptability of the working profile of the hat face of the ceramic cup are of critical importance to prolong the campaign life of the ceramic cup itself and thus the BF hearth. In a lot of cases, the so-called “ceramic cup” is formed just by one, two or more rings of the standard-shaped ceramic bricks which are installed closely against the carbon hot face. In these linings, there are many penetrating linear joints from the hot face to the cold face through the ceramic lining. Both the overall stability of the construction and the anti-penetration ability of the lining are very poor. Therefore, the goal of installing a ceramic cup, to protect the carbon lining from the erosion of hot metal, would be difficult to achieve and the lifetime of the ceramic cup would not be long no matter what excellent materials were being used. However, an “Integrated Ceramic Cup” structure for the BF hearth is composed of special-shaped ceramic blocks which are all interlocked with each other. In such a construction, there is no linear breakthrough joint from the hot face to the cold face of the ceramic lining. A ceramic lining with this structure can effectively avoid hot metal and gases penetrating into and then through the joints of the ceramic lining to attack the carbon lining behind. As a result, the campaign life of the BF hearth, and also the campaign life of the blast furnace, would be prolonged. Nowadays the “Integrated Ceramic Cup” structure has been used in many modern blast furnaces and its significant performance has been proved.

Le développement des réacteurs nucléaires de génération IV et des réacteurs à fusion nucléaire requiert l’utilisation de matériaux possédant de bonnes propriétés mécaniques au-delà de 550 °C. En service, ces matériaux seront soumis à du fluage à haute température couplé à des sollicitations cycliques de fatigue. Les aciers martensitiques à 9–12 % Cr sont pressentis pour ces applications; cependant leur comportement en fatigue et fatigue-fluage à haute température est encore insuffisant : la microstructure martensitique grossit et l’acier s’adoucit rapidement. Afin de stabiliser sa microstructure, l’acier commercial P91 a subi un traitement thermo-mécanique incluant du laminage à 600 °C suivi d’un revenu d’une heure à 700 °C. Les observations microstructurales confirment que le traitement thermo-mécanique a conduit à une martensite plus fine, émaillée de nombreux et fins précipités de type MX. Les divers essais mécaniques réalisés prouvent que ces changements ont un effet positif sur les propriétés de l’acier : sa dureté est plus élevée de 100 Hv par rapport à l’acier P91 à réception, et sa limite d’élasticité conventionnelle est supérieure de 430 MPa à 20 °C et de 220 MPa à 550 °C. La durée de vie du P91 optimisé en fluage à 650 °C sous 120 MPa est plus de 14 fois supérieure à celle du P91; et l’essai de fatigue à 650 °C et 0,7 % de déformation totale montre un adoucissement légèrement moins rapide.

Les verres métalliques présentent des caractéristiques très intéressantes, en particulier leurs propriétés élastiques, combinées avec une relative facilité de mise en œuvre à température pas trop élevée. C’est ce qui conduit à leur utilisation comme matériau pour des composants en micro-mécanique, des matériels sportifs, des boitiers pour la téléphonie ou l’informatique. Mais pour de nombreuses applications une autre caractéristique mécanique peut être essentielle : leur coefficient d’amortissement. Si par exemple pour certaines pièces mécaniques un rendu optimal de l’énergie est requis (cas par exemple d’une raquette de tennis de haute performance), une forte capacité d’amortissement peut en revanche être indispensable pour d’autres composants mécaniques. Le coefficient d’amortissement dépend pour un matériau donné, notamment de la fréquence de sollicitation et de la température. Pour les verres métalliques, il apparaît schématiquement deux domaines : – À basse température, c’est-à-dire par exemple à la température ambiante pour les verres métalliques massifs base zirconium, palladium ou cuivre, le coefficient d’amortissement est très faible, de l’ordre de quelques 10-6, une valeur proche de celle observée dans la silice de très haute pureté. Combinée au caractère conducteur du matériau, ceci permet d’envisager l’application de ces matériaux pour la réalisation d’éléments de résonateurs. Un exemple, celui d’un résonateur hémisphérique pour application gyroscopique est présenté en détail. Il est montré dans ce cas que des traitements thermiques appropriés peuvent conduire à l’amélioration des caractéristiques recherchées. – À haute température, c’est-à-dire au voisinage de la température de transition vitreuse. Celle-ci se situe pour les matériaux considérés (base Zr, base Pd ou base Cu) aux alentours de 400 °C. À l’instar de tous les autres matériaux amorphes, le coefficient d’amortissement devient alors très grand et des valeurs du facteur de perte supérieures à 1 sont fréquemment observées. Ceci résulte de la mobilité atomique ou moléculaire qui devient alors très importante, entrainant une dissipation d’énergie importante lors de toute sollicitation mécanique. Dans ces conditions l’effet de la fréquence devient très net. Ces différents résultats, obtenus lors d’essais mécaniques dynamiques, sont corroborés par des essais de caractérisation de la microstructure du matériau, notamment par diffraction des rayons X in-situ. Différents modèles physiques permettant de comprendre le comportement mécanique en lien avec la nature du matériau sont présentés.

The developments of plates are strongly driven by demands from high-sophisticated pipeline and structural applications. Such needs reflect in plates with higher thickness, larger width, higher toughness also at lower temperatures, higher strength and/or better resistance to sour environments. The requirement profiles are, in some cases, exceptional and have become achievable, in an extreme combination of alloying and processing technologies, only as a result of comprehensive development work and plant investments. A broad potential for innovation derives by the utilization of the key-technology TMCP (Thermo-Mechanical Controlled Process). The status of present-day heavy plate production will be presented. An outline of the production facilities, routes and process variants will be given. As a central element to achieve high-class requirements, aspects and parameters of the metallurgical design will be explained. The utilization will be explained and illustrated with selected recent applications.

Embrittlement of duplex stainless steels after aging below 500 °C is a well documented phenomenon, usually attributed to the unmixing of the ferritic Fe-Cr solid solution, either by spinodal decomposition or by nucleation and growth of Cr-rich α′ phase, depending on aging temperature. Additional precipitation taking place during aging, like NiSiMo-rich G phase or Cu-ε, are also known to participate to embrittlement, making the composition dependence of embrittlement kinetics even more intricate. In this study, long term aging treatments, up to 2 years at intermediate temperature (250–400 °C), have been performed for various duplex stainless steels grades containing different alloying contents in Cr, Mo, Si, Ni and N. Impact toughness has been measured after each aging condition, and an apparent activation energy could be deduced for the various grades. This quantity is a good indicator of embrittlement resistance. Fine microstructural characterizations have been performed in the ferrite: composition before aging was determined by EPMA, and precipitation state before and after aging was observed on TEM. The influence of alloying elements on the embrittlement phenomenon is analyzed on the basis of these results and of driving force calculations performed on Thermo-Calc®.

On-line quality assessment has become one of the most critical requirements for improving the efficiency and the autonomy of automatic resistance spot welding (RSW) processes. An accurate and efficient model to perform non-destructive quality estimation is an essential part of the assessment process. This paper presents a structured and systematic approach developed to design an effective ANN-based model for on-line quality assessment in RSW. The proposed approach examines welding parameters and conditions known to have an influence on weld quality, and builds a quality estimation model step by step. The modeling procedure begins by examining, through a structured experimental design, the effect of welding parameters (welding time, welding current, electrode force and sheet metal thickness) and welding conditions represented by typical characteristics of the dynamic resistance curves on multiple welding quality indicators (indentation depth, nugget diameter and nugget penetration) and by analyzing their interactions and their sensitivity to the variation of the dynamic process conditions. Using these results and by combining an efficient modeling planning method, neural network paradigm, multi-criteria optimization and various statistical tools, the identification of the model form and the variables to be included in the model is achieved by executing a systematic model optimization procedure. The results demonstrate that the proposed approach can lead to a general ANN-based model able to accurately and reliably provide an appropriate assessment of the weld quality under diverse and variable welding conditions.

One of the key issues in the development of the modern duplex stainless steels was the introduction of nitrogen as an alloying element. This was made possible by e.g. the AOD process and has meant that the problems with earlier grades regarding weldability could be solved. The prime reason for the lower weldability, namely a coarse-grained heat affected zone with inferior properties was then removed. Further beneficial effects of nitrogen increases in the new generation of duplex grades were pointed out: localized corrosion resistance particularly in chloride containing solutions, enhancement of fatigue properties, improved creep properties particularly when considering heat treatment...The paper will outline the influence of nitrogen additions in duplex grades by means of thermodynamic calculations including phase diagrams, TTT phase precipitation diagrams from metallographic investigations, mechanical and corrosion properties. Metallographic investigations, corrosion resistance properties and mechanical properties will be presented. The specific links between welded joints microstructures and properties with different nitrogen contents will be discussed.

Le comportement en fatigue sous différentes charges d’un alliage d’aluminium issu de la technologie AIRWARETM a été caractérisé sur métal brut et après traitement de surface. Plusieurs traitements sont étudiés et en particulier un traitement n’utilisant pas de Cr lors de la phase de décapage est comparé aux traitements conventionnels. Les résultats montrent que, sur métal brut, la résistance à la fatigue des alliages AIRWARETM est supérieure à celle d’alliages aéronautiques conventionnels des familles 2xxx et 7xxx, comme par exemple l’alliage 2024. Après traitement de surface, cette différence est réduite mais les alliages AIRWARETM demeurent systématiquement plus résistants. L’utilisation d’un modèle de mécanique de la rupture élastique linéaire permet d’expliquer ce bon comportement par une taille moyenne de piqûres générées lors du traitement de surface réduite.

The influence of long-term ageing in NaCl on the passivity and electrochemical behaviour of UNS S32304 was studied. The passive film thickness, the Cr/Fe ratio and the chloride content were significantly increased after ageing. The chloride distribution depends on residual stresses, the sample microstructure and surface preparation. Local electrochemical measurements revealed that pitting potentials are between 250 and 550 mV vs. SCE after electropolishing. The higher the chloride content, the lower the local pitting potential. It was also shown that the presence of chloride was balanced by the enrichment in chromium after ageing. Then no pitting potential could be measured.