The sampling and analysis of sulphide mineral processing plants is addressed in this study. A review of the published literature has shown that the foundations of this topic were laid in the 1970's, but typically a single sampling test was performed, and its representativity accepted provided its metallurgical balance closed without excessive adjustments. There was no mention made of quality control or equivalent tests of representativity of the feed material during sampling tests. No recognition of the effect(s) of ore grade on metallurgical performance was given. / In this study, a quantitative model, called a statistical benchmark survey, is presented. Multiple surveys are completed over a limited time; the corresponding stream samples of the surveys deemed acceptable are combined to obtain high confidence composite samples. The head grade of each survey is compared to two distributions to test its acceptability, typically at a 95% confidence level. These distributions are called the Internal Reference Distribution and the External Reference Distribution. / The first test---on the Internal Reference Distribution---uses the Sichel t-estimator, a lognormal model designed for use on small data sets, on the set of six survey unit head grades. The associated confidence limits of this mean grade are equivalent to two standard errors of the distribution, but are skewed about the sample mean. The second test, this time by the External Reference Distribution, also uses a lognormal platform, designed by Krige, but uses larger data sets from 1-3 months of shift sample head grades. The associated confidence limits of this second model are also skewed, but are wider than for the Sichel model, and are equivalent to two standard deviations of the sample mean. This outlier rejection model produces ore grade estimates that are in good agreement with the more robust External Reference Distribution means. / The Raglan Mine case study is used to illustrate that ore grades in situ are highly lognormal; this lognormality is also present in the time domain in head samples (taken at the cyclone overflow), but is less pronounced (i.e. residual). / Two survey models are presented. The benchmark model describes typical operations. The campaign model specifically chooses ore types that are mined and milled in a specific week of operations for predictive or diagnostic purposes. / The multiple mineral hosting of nickel across three orders of magnitude extends this problem into that of a compound distribution. The construction and use of an External Reference Distribution to estimate the mean and associated skew confidence limits of this compound distribution is shown for both drill core and ore milled (the latter in a case of residual lognormality). A trial decomposition of the spatial External Reference Distribution is discussed. The heterogeneous nickel mineral hosting in ore, after processing, becomes an artificially controlled final concentrate, containing most of the economic nickel sulphides in a normal distribution, and most of the uneconomic nickel minerals in a final tailing with a residually bimodal lognormal distribution. / The presence of bimodal lognormality in final tailing data may have historical or predictive uses: at Raglan, flowsheet improvements and more seasoned operations contributed to the decrease in the mean of both the low-grade and high-grade modes, and increase the contribution of the low-grade mode.

Industrial experience has revealed that when used to treat multi-component metal chloride waste liquors, existing fluidized bed acid regeneration facilities are not as efficient as when employed for the pyrohydrolysis of conventional iron chloride solutions (i.e. waste pickle liquor). As a result, experimental studies and thermochemical modelling were performed to characterize the transformation of a saturated Al-Fe-Mg-Cl solution at 105°C, after it is injected into a reactor at 850°C. Efforts were geared toward defining the sequence of reactions that take place as the liquor gradually transforms into oxides.C, after it is injected into a reactor at 850°C. Efforts were geared toward defining the sequence of reactions that take place as the liquor gradually transforms into oxides.C, after it is injected into a reactor at 850°C. Efforts were geared toward defining the sequence of reactions that take place as the liquor gradually transforms into oxides.C, after it is injected into a reactor at 850°C. Efforts were geared toward defining the sequence of reactions that take place as the liquor gradually transforms into oxides. / Upon completing a comprehensive literature review, testwork was initially performed with a simplified experimental set-up to study the physical behaviour of the chloride solution as it is exposed to a static bed of oxides at 850°C, and ultimately identify the various phases of the transformation process. Subsequently, controlled evaporative crystallization experiments were conducted under pseudo-equilibrium conditions to define the McClx·yH 2O precipitation path that takes place during the H2O evaporation phase and to determine whether the chlorides precipitate independently or as complex compounds. Further experiments were performed in a fully instrumented tube furnace to elaborate on the nature of the reactions (dehydration and/or pyrohydrolysis) that take place after all of the water in the starting solution has evaporated (i.e. T=300°C+). / In an effort to assist with the interpretation of the experimental results, thermochemical modelling was performed to predict the equilibrium phase assemblages that could occur during the transformation of the saturated Al-Fe-Mg-Cl solution, at reaction temperatures of 200°C+. / The research study at hand has shown that when the saturated Al-Fe-Mg-Cl solution at 105°C is exposed to fluidized bed pyrohydrolyzer operating conditions at 850°C, the following sequence of events take place: (1) rapid solvent H2O evaporation (i.e. vigorous boiling) and onset of solid metal chloride precipitation. (2) slurry densification due to a gradual increase in crystal content (i.e. AlCl·6H2O, FeCl2 ·xH2O, and MgCl2·xH2O, where x = 2 or 4). (3) hydrated crystal drying and onset of pyrohydrolysis (i.e. thermal decomposition of McClx·yH2O). The same holds true for the high temperature hydrolysis of typical waste pickle liquors (i.e. primarily FeCl2 solution). / The crystallization studies revealed that when the Al-Fe-Mg-Cl solution is allowed to gradually evaporate at 105°C,.AlCl3·6H 2O precipitates when 15% of the solvent water evolves from the liquor, followed by FeCl2·xH2O and MgCl2·xH 2O (where x = 2 or 4) at 26 and 41% evaporation, respectively. Ferric chloride remains in solution even after 54% of the water has been driven from the liquor. The latter result suggests that higher ferric concentrations in the reactor feed are more than likely to favour an increase in the quantity of liquor entrainment by the fluidizing gases and therefore lead to lower process efficiencies. Dedicated pyrohydrolysis experiments, with a simulated reactor atmosphere (gaseous, not dynamic), have shown that excluding kinetic effects, the transformation of the Al-Fe-Mg-Cl solution occurs primarily over the 300 to 600°C temperature range. / Thermochemical modelling revealed that with the exception of AlCl 3·6H2O hydrolysis, the majority of the reactions taking place as the saturated Al-Fe-Mg-Cl liquor is introduced into and eventually reaches 850°C are governed by either reaction kinetics or diffusion. Furthermore, the resulting phase assemblage at any given temperature was predicted to vary significantly with oxygen potential. A liquid chloride phase (including molten salt), other than the feed liquor, was not predicted to form at any temperature (i.e. 200°C or above) under the range of oxidizing or reducing conditions considered. / The findings of this research were quite useful in identifying the means for improving the performance of a commercial fluidized bed pyrohydrolyzer for a spent chloride liquor containing the said species.

Joining of superalloy Inconel 617 using a foil interlayer with transient liquid phase bonding (TLP) was studied. Inconel 617 is a solid solution, Ni-Cr-Co-Mo alloy with an exceptional combination of high temperature strength, oxidation and carburization resistance and thermal stability. / Two types of interlayer compositions for the TLP bonding process were selected. Specifically, boron containing (AWS BNi-3) and phosphorus rich (AWS BNi-6) were employed as melting point depressant (MPD) elements. Process parameters such as bonding temperature, holding time, composition and thickness of interlayer were selected for study. Two bonding temperatures, 1065°C and 1150°C, and two interlayer thicknesses with various holding times ranging from 5 minutes to 24 hours were selected. / Joints were fabricated using Inconel 617 specimens measuring 25 mm long, 5 mm wide and 1 mm thick. A tube furnace under vacuum (1 x 10-5 mbar) was used to carry out the experiments. The specimens were fixed with stainless steel fixture and held at the bonding temperature for the selected times. / Optical microscopy, SEM, FEG-SEM, VP-SEM were used to follow microstructure evolution and identify its constituents. The microstructure of the joint area, formation and dissolution of precipitates and the evolution of the base metal grain size with holding time for the two bonding temperatures and interlayer thickness were also characterized using the above techniques. TEM, EBSD and XRD techniques were employed to identify the phases such as borides, carbides, phosphides and other precipitates in the joint area. Microhardness tests of the joint were performed to investigate relationships between microstructure and mechanical properties of the joint. A critical review of the existing theoretical models for isothermal solidification of the TLP bonding was carried out and their application to the obtained results for Inconel 617 was assessed.

Air-Assisted Solvent Extraction (AASX) is a novel concept that uses a solvent-coated bubble to contact the organic and aqueous phases. The advantages over conventional solvent extraction (SX) are high solvent to aqueous contact area with reduced solvent volume and ease of phase separation due to the buoyancy imparted by the air core. This opens the way to treat dilute solutions (<1 g/L), such as effluents. / The novel contribution in this thesis is the production of solvent-coated bubbles by exploiting foaming properties of kerosene-based solvents. / The basic set-up is a chamber to generate foam which is injected through a capillary (orifice diameter 2.5 mm) to produce solvent-coated bubbles (ca. 4.4 mm) which release into the aqueous phase. This generates a solvent specific surface area of ca. 3000 cm-1, equivalent to solvent droplets of ca. 20 mum. Demonstrating the process on dilute Cu solutions (down to 25 mg/L), high aqueous/organic ratios (ca. 75:1) and extractions are achieved. The solvent readily disengages to accumulate at the surface of the aqueous solution. / The LIX family of extractants imparts some foaming to kerosene based solvents but D2EHPA does not. An extensive experimental program determined that 1.5 ppm silicone oil provided the necessary foaming action without affecting extraction or stripping efficiency, greatly expanding the range of solvents that can be used in AASX. / To complement the foam study, films on bubbles blown in solvent were examined by interferometry (film thickness) and infra-red spectroscopy (film composition). A "bound" solvent layer was identified with an initial thickness of ca. 2 - 4 mum, comparable to that determined indirectly (by counting bubbles in an AASX trial and measuring solvent consumption). The film composition appeared to be independent of film thickness as it decreased with time. / As a start to scaling up, the single bubble generation system was adapted by installing up to 8 horizontal capillaries. The bubbles generated were ca. 3.4 mm. Trials showed the multi-bubble set up was a simple replication of the individual bubble case. Preliminary analysis of kinetic data shows a fit to a first-order model.

Rare-Earth elements by virtue of its typical magnetic, electronic and chemical properties are gaining importance in power, electronics, telecommunications and sustainable green technology related industries. The Magnets from RE-alloys are more powerful than conventional magnets which have more longevity and high temperature workability. The dis-equilibrium in the Rare-Earth element supply and demand has increased the importance of recycling and extraction of REE's from used permanent Magnets. However, lack of the thermodynamic data on RE alloys has made it difficult to design an effective extraction and recycling process. In this regard, Computational Thermodynamic calculations can serve as a cost effective and less time consuming tool to design a waste magnet recycling process. The most common RE permanent magnet is Nd magnet (Nd2Fe14B). Various elements such as Dy, Tb, Pr, Cu, Co, Ni, etc. are also added to increase its magnetic and mechanical properties. In order to perform reliable thermodynamic calculations for the RE recycling process, accurate thermodynamic database for RE and related alloys are required. The thermodynamic database can be developed using the so-called CALPHAD method. The database development based on the CALPHAD method is essentially the critical evaluation and optimization of all available thermodynamic and phase diagram data. As a results, one set of self-consistent thermodynamic functions for all phases in the given system can be obtained, which can reproduce all reliable thermodynamic and phase diagram data. The database containing the optimized Gibbs energy functions can be used to calculate complex chemical reactions for any high temperature processes. Typically a Gibbs energy minimization routine, such as in FactSage software, can be used to obtain the accurate thermodynamic equilibrium in multicomponent systems. As part of a large thermodynamic database development for permanent magnet recycling and Mg alloy design, all thermodynamic and phase diagram data in the literature for the fourteen Fe-RE binary systems: Fe-La, Fe-Ce, Fe-Pr, Fe-Nd, Fe-Sm, Fe-Gd, Fe-Tb, Fe-Dy, Fe-Ho, Fe-Er, Fe-Tm, Fe-Lu, Fe-Sc and Fe-Y are critically evaluated and optimized to obtain thermodynamic model parameters. The model parameters can be used to calculate phase diagrams and Gibbs energies of all phases as functions of temperature and composition. This database can be incorporated with the present thermodynamic database in FactSage software to perform complex chemical reactions and phase diagram calculations for RE magnet recycling process. / Les terres rares, en vertu de leurs propriétés magnétiques, électroniques et chimiques uniques, gagnent en importance dans les industries électroniques, des centrales, des télécommunications et des technologies vertes. Les aimants de terres rares possèdent des propriétés très supérieures par rapport aux aimants traditionnels. Ils disposent d'une puissance et d'une longévité plus élevées, et d'une meilleure usinabilité à haute température. Le déséquilibre entre la demande et l'approvisionnement en terres rares a accru l'importance du recyclage et de l'extraction des terres rares à partir des aimants permanents usagés. Cependant, le manque de données thermodynamiques sur les systèmes de terre rare a rendu difficile la conception de procédés efficaces de recyclage et d'extraction. À cet égard, les calculs thermodynamiques peuvent servir d'outil rentable en termes de temps et d'argent afin de concevoir un procédé de recyclage des aimants permanents usagés. L'aimant permanent de terre rare le plus commun est l'aimant au néodyme (Nd2Fe14B). Divers éléments tels que Dy, Tb, Pr, Cu, Co, Ni, etc. sont également ajoutés pour améliorer ses propriétés magnétiques et mécaniques.Afin d'effectuer des calculs thermodynamiques fiables pour le procédé de recyclage des terres rares, des bases de données thermodynamiques précises pour les terres rares et leurs alliages sont requises. Les bases de données thermodynamiques peuvent être développées en utilisant la méthode dite CALPHAD. Le développement de bases de données basé sur la méthode CALPHAD consiste essentiellement en l'évaluation critique et en l'optimisation de toutes les données thermodynamiques et de diagramme de phase disponibles. En conséquence, un ensemble de fonctions thermodynamiques cohérentes pouvant reproduire tous les données thermodynamiques et de diagramme de phase fiables est obtenu pour toutes les phases dans un système donné. La base de données contenant les fonctions optimisées d'énergie libre de Gibbs peut être utilisée pour calculer des réactions chimiques complexes pour n'importe quels procédés à haute température. Typiquement, une routine de minimisation de l'énergie libre de Gibbs, telle que présente dans le logiciel FactSage, peut être utilisée pour obtenir l'équilibre thermodynamique précis dans un système comprenant de multiples composants.Dans le cadre du développement d'une base de données thermodynamiques pour le recyclage des aimants permanents et la conception d'alliages de magnésium, toutes les données thermodynamiques et de diagramme de phase dans la littérature pour les quatorze systèmes binaires Fe-terre rare incluant Fe-La, Fe-Ce, Fe-Pr, Fe-Nd, Fe-Sm, Fe-Gd, Fe-Tb, Fe-Dy, Fe-Ho, Fe-Er, Fe-Tm, Fe-Lu, Fe-Sc et Fe-Y sont évaluées de manière critique et optimisées pour obtenir les paramètres du modèle thermodynamique. Les paramètres du modèle peuvent ensuite être utilisés pour calculer les diagrammes de phases et les énergies libres de Gibbs de toutes les phases en fonction de la température et de la composition. Cette base de données peut être incorporée à la base de données thermodynamiques présente dans le logiciel FactSage afin de calculer des réactions chimiques complexes et des diagrammes de phase pour le procédé de recyclage des aimants de terres rares.

Single-phase solid solution alloys, Mg-2.9Y and Mg-2.9Zn (in wt%), and two-phase (α-Mg solid solution + intermetallic) Mg-Zn-Y alloys were selected using the CALPHAD (Calculation of Phase Diagram) method to investigate texture weakening mechanisms in the presence of Y. Microstructure and texture evolution during deformation and subsequent isothermal annealing were studied using optical and electron microscopy, X-ray texture measurements and EBSD (electron backscatter diffraction) techniques.It was found that at large strain levels (i.e. the steady state region of hot compression flow curves), a strong basal texture with similar maximum intensity of basal pole figures developed in all the alloys, indicating that the hot deformation texture at large strains is independent of alloy composition, initial microstructure and the volume fraction of dynamic recrystallization (DRX). The progress of DRX during deformation did not lead to texture weakening, regardless of the presence of Y. Although recrystallization of new grains at intermetallics was observed in the ternary alloys, the bulk texture remained strongly basal during and after hot deformation.Y in solid solution, unlike Zn, suppressed DRX; however, a strong basal texture with the same maximum intensity of basal pole figures developed in the Mg-2.9Y and Mg-2.9Zn alloys after hot deformation (compression and rolling at 350 °C). When the two hot-rolled binary alloys were isothermally annealed (at 400 °C between 15 min and 30 min), static recrystallization (SRX) occurred in Mg-2.9Y and grain coarsening took place in Mg-2.9Zn. The texture was weakened only in the Mg-2.9Y alloy during annealing, which resulted in higher ductility and lower in plane anisotropy in the tensile flow curve and r value when compared to Mg-2.9Zn.It was shown that, even in the absence of Y, texture weakening can be attained in Mg when there is no DRX, and SRX occurs during annealing. When DRX was absent in the Mg-2.9Y and Mg-2.9Zn alloys, i.e. by rolling of the latter alloy at room temperature, deformation was partly accommodated by compression and double twinning in basal parent grains, leading to the formation of bands. In the two binary alloys, compression and double twinning during deformation generated orientations that mostly lay within the orientation spread of basal parent grains, and did not therefore participate in the weakening of the basal texture, but rather to basal texture formation. The orientation of statically recrystallized grains at bands/twins (TSRX grains) was close to that of double and compression twins. However, the orientation of such recrystallized grains was much more evenly distributed and slightly wider than that of the basal parent grains and twins, which resulted in a weaker basal texture. In both Mg-2.9Zn and Mg-2.9Y alloys, a continuous texture weakening occurred during SRX, which resulted in a bimodal microstructure consisting of small TSRX grains and larger ones which mainly formed by recrystallization of basal parent grains. During grain coarsening following the completion of SRX in the two binary alloys, the value of maximum intensity vs. grain size rose linearly, with the slope of the lines being nearly identical. This texture strengthening was ascribed to the consumption of small TSRX grains by larger ones. / Les alliages binaires et monophasés de solution solide, Mg-2.9Y et Mg-2.9Zn (en pourcentage massique) et les alliages ternaires (Mg-Zn-Y) et biphasés (solution solide α-Mg + intermétallique) ont été sélectionnés par la méthode CALPHAD (Calculation of Phase Diagram) afin d'étudier les mécanismes d'affaiblissement de la texture en présence de l'yttrium (Y). L'effet de la déformation et des traitements thermiques sur la microstructure et la texture de ces alliages a été étudié par microscopie optique et électronique ainsi que par la méthode de diffraction des rayons-X (XRD) et des électrons rétrodiffusés (EBSD).À des niveaux élevés de contrainte (à l'état d'équilibre des courbes de déformation à chaud), une texture fortement basale avec une intensité similaire a été développée dans tous les alliages, indiquant que la texture de déformation à chaud est indépendante de la composition chimique, la microstructure initiale et la fraction volumique de la recristallisation dynamique (RXD).L'augmentation de la fraction volumique de la RXD lors de la déformation n'a pas conduit à l'affaiblissement de la texture, indépendamment de la présence de l'yttrium. Même si la recristallisation des nouveaux grains aux composés intermétalliques a été observée dans les alliages ternaires, dans l'ensemble, leur texture est demeurée fortement basale pendant et après la déformation à chaud.L'yttrium en solution solide, contrairement au Zn, a empêché la RXD de se produire; cependant, une forte texture basale avec la même intensité maximale des figures de pôles basales s'est développée dans les alliages Mg-2.9Y et Mg-2.9Zn après la déformation (compression et laminage à 350 °C). Lorsque les deux alliages binaires laminés à chaud ont été recuits (400 °C durant 15-30 min), la recristallisation statique (RXS) s'est produite dans Mg-2.9Y et le grossissement des grains a eu lieu dans Mg-2.9Zn. La texture a été uniquement affaiblie dans Mg-2.9Y pendant le recuit, ce qui a permis d'obtenir une meilleure ductilité et une faible anisotropie planaire par rapport au Mg-2.9Zn.Les résultats de cette étude démontrent que même en l'absence de l'yttrium l'affaiblissement de la texture peut être atteint dans le Mg lorsque la RXD est empêchée de se produire, et la RXS se développe au cours du recuit. L'absence de RXD durant la déformation des alliages Mg-2.9Y et Mg-2.9Zn, par laminage de l'alliage Mg-2.9Zn à la température ambiante, a mené à la formation de macles de contractions et secondaires dans les grains parents basals, conduisant à la formation des bandes. Dans les deux alliages binaires, le maclage a généré des orientations proches de celle de texture basale, et n'a donc pas participé à l'affaiblissement de la texture basale, mais plutôt à sa formation. L'orientation des grains statiquement recristallisés dans les bandes/macles (nommés MRXS) a été proche de celle des macles. Toutefois, l'orientation de ces grains recristallisés est beaucoup mieux répartie et légèrement plus large que celle des grains parents basals et des macles, donnant naissance ainsi à une plus faible texture basale. Dans le Mg-2.9Y et Mg-2.9Zn, un affaiblissement de la texture dans le temps s'est produit lors de la RXS, produisant une microstructure bimodale constituée de petits grains MRXS et de gros grains qui ont été formés par la recristallisation des grains déformés. Pendant la croissance des grains (après la fin de la RXS) dans les deux alliages binaires, l'intensité de la texture en fonction de la taille des grains a augmenté de façon linéaire avec une pente similaire. L'intensification de la texture a été attribuée à la croissance des gros grains de forte texture aux dépends des grains MRXS.

The quality of steel may be seriously affected by the surface defects that appear on slab surfaces after hot rolling. These defects are related to iron oxidation and, in order to reduce the occurrence of these defects, it is necessary to better understand the formation of iron oxides during high temperature oxidation and the oxide descaling mechanisms. However, systematic research tools and experimental strategies for addressing these issues have not yet been developed. In addition, the mechanisms of oxide cracking and failure have not been understood. In this thesis, research tools and strategies are proposed for studying the high temperature oxidation of low carbon steels. These tools allow the presentation of new data on the phase composition of iron oxides at elevated temperature, characteristics of iron oxide formation, oxide microstructure and texture, oxide defects, and stress distributions in different oxide layers, as well as residual stresses. The microscopic model that was proposed for description of oxide failure allows better understanding of the mechanism for surface defect formation during hot rolling. To describe the dynamics of phase composition changes in textured oxides at elevated temperature, a new phase analysis method is proposed. This x-ray diffraction phase analysis is based on the Rietveld and Dickson's methods, and is used for investigating the effect of alloying elements on the oxidation process. This method was also adopted to track in-situ phase composition changes during high temperature oxidation of commercial low carbon steels. The structure of oxides on low carbon steels, pure iron, and Si-steels was systematically examined by orientation imaging microscopy (OIM). It is demonstrated that OIM can be an invaluable tool for visualizing the oxide microstructure texture and studies of oxide defects. In order to simulate industrial hot rolling of oxidized steel sheet, high temperature oxidations tests were made in the tube furnace up to 950°C, in air. The oxidation process and microstructure development were described using OIM maps including image quality (IQ) and inverse pole figure (IPF) maps. The three different iron oxides phases could be distinguished and the characteristics of oxides with different oxidation histories were compared. Iron oxides developed during high temperature oxidation consisted of wustite (FeO), magnetite (Fe304), and hematite (Fe20s) structures with varying texture, grain shape and size. In order to understand the mechanical properties of iron oxides, residual stresses in the three iron oxides phases were assessed using a specially designed x-ray stress measurement system. The stress distributions in the oxide layers were also simulated using finite element simulation of the hot rolling process.

The need for new refractories for copper converters is addressed in this thesis. Penetration resistance is viewed as the first property that must be evaluated for the selection of new refractories since it is known that melt penetration can promote or enhance the main wear mechanisms in copper converters: dissolution, erosion and spalling. Thus, a penetration test was designed where it is possible to control the oxygen potential and the "in-situ" formation of converter melts by injecting a mixture of inert gas and oxygen according to thermodynamic calculations. Initially, the effects of oxygen potential and matte grade on three different refractories (burned magnesite chrome brick, burned spinel bonded magnesite brick and spinel direct bonded) were studied using the operating conditions of copper converters. This allowed the selection of a potential candidate, the spinel direct bonded brick. Subsequently, the effect of time, temperature and melt composition on the penetration resistance of this candidate was studied and compared with the current refractory used in copper converter, namely burned magnesitechrome brick. The reactions occurring at the refractory pill-interface, the mechanisms and kinetics of penetration and the differences in performance were determined. In addition the mechanism of dissolution and penetration of magnetite coatings applied into basic refractories were elucidated since it is considered important when proposing new solutions and alternative refractories to avoid or reduce wear in copper converters.

Modification of the eutectic silicon in Al-Si alloys is traditionally performed by sodium and strontium addition. Although not traditionally used as a modifier, calcium also has the potential to modify the eutectic silicon in Al-Si alloys. Metallographic observation and thermal analysis studies in A357 alloy indicate that. when the cooling rate is quite low. Ca modifies the eutectic silicon. but the effect of Ca as a modifier is not as strong as is Na or Sr. When the cooling rate is high, a fully modified structure can be obtained with calcium. Recovery of Ca in the melt is high and certain. It does not fade with long holding times. Moreover, a premodified ingot can be used, and even when such all ingot is remelted repeatedly there is no calcium loss. / Calcium does increase porosity in castings. In general modification treatment with Ca improves mechanical properties, especially elongation. / Calcium adversely interacts with strontium and reduces the ability of strontium as a modifier. Microstructural and thermal analysis studies show that Ca has a deleterious effect on Sr-modified castings and vice versa. (Abstract shortened by UMI.)

One of the major quality problems encountered in continuous casting is the formation of transverse cracks, which is partly due to the poor hot ductility of the cast steel. In this work, high temperature tensile testing is used to determine the hot ductility of a Nb-Ti and Ti-B microllayed steels. The influence of reheat treatment on hot ductility of the alloys is studied. In order to accomplish this task, steel specimens were reheated near the incipient melting temperature, and subsequently tensile tested to fracture at a strain rate typical of the unbending operation over a range of temperatures, in order to obtain hot ductility data. The results are compared to those obtained after melting and solidification prior to high temperature tensile testing. / As well, tensile specimens were subjected to thermal histories typical of continuously cast billet surface up to the unbending operation, and then subjected to a tensile test to fracture. In other words, physical simulations of the continuous casting procedure were performed. (Abstract shortened by UMI.)