Experiments were carried out on the solidification of iron-manganese alloys containing sulphur and carbon. The alloys were solidified under controlled conditions in a travelling furnace constructed especially for the investigation. Qualitative and quantitative metallography and electron-probe microanalysis were used to determine the solidification structure, dendrite arm spacings, solute concentration profiles and inclusion compositions. The results were interpreted in the light of existing knowledge and concepts especially developed for the purpose of this investigation. / Thesis / Doctor of Philosophy (PhD)

<p> The advantages of Thin-Slab Cast Direct-Rolling (TSCDR) process include reduced capital, energy, labour and inventory costs, as well as the ability to roll thinner strip compared to the conventional process of thick slab casting, reheating and hot rolling. There is great interest in utilizing this technology to produce microalloyed steels which can meet American Petroleum Institute (API) standards. However, whereas the conventional approach can produce APIX80, APIXlOO, and even APIX120 steels; the TSCDR process can only produce APIX70 and APIX80. The main obstacles in the way of achieving high API grades are the non-uniform initial as-cast microstructure and the large grains that result from grain growth at high temperature. The production of APIX80 and higher grade steels can only be achieved through a comprehensive research initiative that combines careful control of solidification, homogenization, thermomechanical-processing, cooling and coiling. </p> <p> This contribution examines the solid state microstructure evolution of microalloyed steels under simulated TSCDR conditions. The grain growth kinetics in delta-ferrite and austenite were studied separately using two model alloys. At high temperatures and in the absence of precipitation, the growth kinetics in both delta-ferrite and austenite appeared to follow a simple parabolic growth law. The measured grain growth kinetics was then applied to the problem of grain-size control during the process of TSCDR. Several strategies of controlling and refining the grain size were examined. The kinetics of delta-ferrite to austenite phase transformation was investigated using a quenching dilatometer; the results showed that the austenite phase formed along the original delta grain boundaries, and that the precipitation of austenite at the delta-ferrite grain boundaries effectively pins delta grain growth. The kinetics of the phase transformation was modeled using a local equilibrium model that captures the partitioning of the substitutional elements during the transformation. </p> <p> A novel delta-ferrite/austenite duplex microstructure is proposed to achieve fine and uniform high-temperature microstructure. The grain growth of the matrix phase (delta-ferrite) is controlled by the coarsening mechanism of pinning phase (austenite). The effectiveness of this delta/austenite duplex microstructure was validated experimentally and analyzed in details using a physically-based model. </p> / Thesis / Doctor of Philosophy (PhD)

Powder bed fusion (PBF) is a metal additive manufacturing process that is increasingly used in the aerospace and medical industry to build complex parts directly from computer-aided design. Due to the presence of large temperature gradients and rapid cooling rates during the processing, the PBF process is assumed to follow a rapid solidification processing route. However, the extent of deviation of the solid-liquid interface from equilibrium as a function of processing conditions has not been studied in detail for the PBF process. In this thesis, a numerical model is developed to study the interfacial characteristics as a function of processing conditions to characterize if the PBF process exhibits rapid solidification or not. The model is based on the work of Hunt et al. [1, 2, 3] and is capable of simulating cellular and dendritic growth at both low and high interface velocities. The developed model accounts for the various undercooling such as constitutional and curvature undercooling, the variation of the liquidus temperature with composition, and the partition coefficient and diffusion coefficient with temperature. Moreover, the variation of the partition coefficient and the liquidus slope with the growth velocity has also been considered in the developed model. The model is used to predict the range of primary cellular/dendritic spacing for a given set of input parameters. In addition to this, the tip undercooling, tip Péclet number and spacing Péclet numbers have also been estimated using the model to quantify the extent of deviation of the solid-liquid interface from equilibrium. A good qualitative agreement between the predicted values from the numerical model and the analytical KGT model is achieved. This new model can be used to understand the relationship between the processing conditions, material system and interfacial characteristics during the PBF process, and thus improve microstructural development during PBF processing. / Thesis / Master of Science in Materials Science and Engineering (MSMSE)

No description available.

No description available.

Aluminum alloys are presently used extensively as a conductor material for overhead transmission wires. Their lack of strength must be compensated by using a reinforcing agent, namely steel. The aim of this thesis was to investigate the possibility of deforming Al-Fe and Al-Ni alloys in order to produce high strength, high conductivity wire product. The main goal was to produce a two phase Al alloy wire with adequate strength so that the wire would be self supporting as an overhead electrical power transmission line. The Al-Fe and Al-Ni two phase alloy rods were Ohno cast to provide directional solidification. In both alloys, wire drawing was unsuccessful due to fiber fracture and damage accumulation during drawing. The Al-Fe alloy was subjected to hydrostatic extrusion in an attempt to induce co-deformation of the matrix material and the brittle intermetallic second phase, Al6Fe. Hydrostatic extrusion proved to be successful in inducing some deformation of the Al6Fe and provided valuable initial insight into the investigation of the deformation of Al6Fe. The final stage in the development of an aluminum alloy for use as a self supporting overhead transmission wire was the development of a “macrocomposite”. This macrocomposite was a combination of an Fe rod 4 mm in diameter and a tube of aluminum 8 mm in diameter. This macrocomposite was successfully cold worked to achieve an overall yield strength of 395 MPa. / Thesis / Master of Engineering (MEngr)

Safe disposal of contaminated dredged material has become a significant issue especially as public environmental awareness and concerns increase. Solidification/ stabilization technology potentially may provide for a safer, more effective and more economical means of disposal. This research investigated the technical feasibility of applying solidification/stabilization technology to contaminated sediment from Indiana Harbor Canal, Indiana. Specifically, physical strength and reduction of chemical leachability resulting from solidification/stabilization A with various cement based, pozzolanic, and proprietary additives were analyzed. Also investigated was the immobilization capability of a proprietary polymer for selected organic contaminants when used in conjunction with solidification/stabilization processes. Physical strength is an important parameter in determining the ultimate bearing capacity, stability of embankments and pressure against retaining walls. Physical stabilization of contaminated dredged material is a viable treatment option. Application of cement-based and pozzolanic—based processes uses the sediment moisture to form hydration products, therefore dewaterimg is not required. All process formulations produced a solidified sediment. / Master of Science

Cette thèse est le volet expérimental d’un projet de recherche qui vise à développer un code de calcul qui prédit finement la micro ségrégation des aciers présentant une réaction péritectique. La caractérisation expérimentale de la micro ségrégation a été menée grâce à des essais de solidification dirigée et des essais de trempe en cours de solidification dirigée ainsi que sur des échantillons de lingots industriels. Les alliages sélectionnés font partie des systèmes Fe-C-Ni et Fe-C-Cr. Nous avons d’abord étudié sur des aciers solidifiés l’effet de la composition chimique et l’effet du premier solide ferrite / austénite sur la micro ségrégation. Par la suite nous avons caractérisé la formation de la micro ségrégation avec et sans réaction péritectique. On a montré aussi les effets de la taille de la structure, de la microstructure (dendritique / cellulaire)et de la texture du grain sur la micro ségrégation (colonnaire / équiaxe) sur la micro ségrégation. Enfin, nous avons comparé les résultats expérimentaux avec les résultats de la modélisation. / This PhD work is an experimental part of a global R&D project witech aim to study the microsegregation in peritectic steels. The experimental investigations were made by a Directional Solidification device (DS), Quenched Directional Solidification (QDS) and from parts of industrials ingots. The alloys selected were taken from the Fe-C-Ni and Fe-C-Cr systems. On the solidified steels we investigate the effect of the chemical composition and the first solid (ferrite/austenite) on the microsegregation. The next step was the characterization of the microsegregation during the solidification with and without a peritectic reaction. Afterwards we study the effects of the length of the structure, the microstructure (dendritic/cellular) and the texture of the grains (columnar/equiaxed) on the microsegregation. At the end we have do a comparison bethween the experimental results and those from the numerical simulations

L'objectif de ce travail de thèse, est de développer un matériau d'apport et un mode opératoire de soudage associé permettant d'assembler des tôles d'acier K44X pour la fabrication de collecteurs d'échappement automobiles. Les propriétés de l'acier K44X ayant été optimisées pour répondre au mieux aux contraintes de l'application, les conditions de soudage recherchées devront, dans la mesure du possible, éviter de dégrader les caractéristiques de l'acier, en particulier en termes de tenue mécanique à haute température et de résistance à l'oxydation et à la fatigue thermique. Ce mémoire est divisé en quatre chapitres. Le premier chapitre est consacré à une présentation synthétique des évolutions dans le domaine de la fabrication des collecteurs d'échappement automobiles, et des connaissances actuelles dans les domaines des aciers inoxydables ferritiques et sa soudabilité, des procédés de soudage à l'arc. Le second chapitre présente les caractéristiques de l'acier K44X et la problématique de l'étude, puis décrit le travail d'élaboration des matériaux d'apport de différentes compositions. Ainsi que les résultats d'une caractérisation préliminaire des soudures obtenues avec les différents matériaux. Le chapitre 3 traite de la caractérisation de la tenue en service de l'assemblage retenu à l'issu du chapitre précédent. Les tests d'oxydation, de traction à chaud sur zone fondue des soudures ou sur assemblages complets, et de fatigue thermique, utilisés pour réaliser cette caractérisation sont décrits, et les résultats sont discutés. La fin de ce chapitre est consacrée à la caractérisation des précipités formés dans les zones fondues. Enfin, le dernier chapitre est consacré à la modélisation thermique du soudage et à la modélisation de la solidification, dans le but de tenter de prédire le type de microstructure de zone fondue formée lors d'une opération de soudage, en fonction des paramètres procédés. Cette modélisation, qui s'appuie sur les résultats d'un essai de soudage instrumenté, doit notamment permettre de prédire si les conditions de soudage, pour une composition d'acier donnée, permettent ou non de former une structure de grains équiaxe en zone fondue des soudures. / The objective of this work is to develop a filler metal and an associated welding procedure allowing to join sheets of steels K44X for the manufacturing of exhaust manifolds for automotive. The properties of the steel K44X having been optimized to answer at best the constraints of the application, the welding conditions will have to, as possible, avoid degrading the characteristics of the steel, in particular in terms of mechanical strength with high temperature, oxidation resistance and in thermal fatigue.This report is divided into four chapters.The first chapter is dedicated to a synthetic presentation of the evolutions in the field of the manufacturing of the automotive exhaust manifolds, and current knowledge in the domains of ferritic stainless steels and its weldability, and in arc welding processes.The second chapter presents the characteristics of the steel K44X and the problem of the study, then described the work of elaboration of the filler metals with various compositions. As well as the results of a preliminary characterization of the welds obtained with the various materials.The chapter 3 is about the characterization of the in-service behavior of the assembly stemming from the previous chapter. The tests of oxidation, hot traction on molten zone of the welds or on complete assemblies, and of thermal fatigue, used to realize this characterization are described, and the associated results are discussed. The end of this chapter is dedicated to the characterization of precipitates formed in the molten zones.Finally, the last chapter is dedicated to the thermal modelling of the welding and to the modelling of the solidification, with the aim of trying to predict the type of microstructure of molten zone formed during a welding operation, according to the process parameters. This modelling, based on the results of a instrumented experimental test of welding, has to allow in particular to predict if the welding conditions, for a given composition of steel, allow or not to form a structure of grains equiaxed in molten zone of the welds.

La macroségrégation est un défaut connu dans les procédés de coulées industrielles. La genèse de ce défaut est la conséquence de l'interaction complexe entre la microségrégation ou la distribution des espèces chimiques à l'échelle de la microstructure et les mouvements des phases liquide et solides. Les hétérogéneités de concentration en solutés à l'échelle de la pièce peuvent être rédhibitoires vis-à-vis de la qualité du produit.Dans ce travail, on propose un modèle numérique pour simuler et prédire la formation des macroségrégations en coeur des pièces d'alliages multi-constitués, induites par des variations thermiques et solutales dans la phase liquide. Dans un premier temps, on considère que le métal solidifie à volume constant. Dans ce contexte, la convection thermosolutale est étudiée ainsi que son influence sur la formation des canaux ségrégées à différentes échelles de modélisation. Dans un deuxième temps, le modèle vise à prédire les macroségrégations en présence de changement de volume du métal, dont la cause principale est le retrait à la solidification, pouvant être à l'origine du phénomène de ségrégation inverse. La surface entre le métal et le gaz environnant au cours du retrait évolue pendant le retrait en fonction du chemin de solidification qui varie avec la macroségrégation. Cette évolution d'interface est suivi par la méthode level set. Des prédictions de concentration moyenne, couplées aux bases de données thermodynamiques pour mieux prédire les chemins de solidification des alliages multi-constitués, sont analysées et comparées avec des résultats expérimentaux. Finalement, des calculs de solidification en microgravité sont présentées, simulant un essai expérimental dans le contexte du projet CCEMLCC lancé par l'Agence Spatiale Européenne. Les résultats en fin de solidification montrent un accord acceptable quant à la forme et l'élongation des échantillons solidifiés. Ces calculs sont faits avec des approximations binaire, ternaire et quaternaire d'une même nuance d'acier utilisée dans les essais en microgravité. / Macrosegregation is key defect in industrial casting processes. During solidification, solute redistribution at the scale of microstructure, also known as microsegregation, take place with complex interactions, in order to form one or more solid phases. These interactions between microsegregation and movements of liquid and solid phases may lead to macrosegregations. These solute heterogeneities spanning on a larger scale, may result in a bad casting quality. In this thesis, we propose a numerical model to simulate and predict macrosegregations occurring in the centre of multicomponent alloys, caused by thermal and solutal variations in the liquid phase. First, we assume that the metallic alloy solidifies with a constant volume. In this context, we study the influence of thermosolutal convection on the formation of channel segregations, at different modelling scales. The second part of this modelling work consider solidification while the metallic alloy's volume is decreasing, mainly due to overall density variation, also known as solidification shrinkage, possibly leading to the so-called inverse segregation phenomenon, appearing on the alloy's skin. In the context of solidification shrinkage, the shape of the metal's boundary with surrounding gases varies according to a constantly changing solidification path due to macrosegregation. The level set method is therefore used to track its evolution with time. Composition predictions, coupled with thermodynamic database mappings for more accurate multicomponent solidification paths, are analysed and compared to existing experimental setups. Finally, simulations of a reduced-gravity solidification cases are performed, mocking an experimental benchmark from the CCEMLCC project launched by the European Space Agency. The results after complete solidification show acceptable agreement for the final shape, compared to experimental results. These computations were performed with binary, ternary and quaternary approximations of the same steel grade which was used in reduced-gravity experiments.