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Konkurrensen inom stålbranschen blir allt hårdare och för att stanna i toppsegmentet krävs innovation och ständiga förbättringar. Då höglegerade stål såsom rostfria stål kyls till rumstemperatur passeras inte temperaturen för fullständig martensitbildning. Genom att använda flytande kväve kan temperaturen sänkas så lågt som till -196°C. Således kan andelen martensit i provet ökas samtidigt som andelen austenit minskar. I detta examensarbete undersöks hur djupkylning med flytande kväve påverkar stålsorterna Flap-X och SS716 gentemot kylning till rumstemperatur. Målet med arbetet är att genom ett antal olika testmetoder kartlägga djupkylningens inverkan på stålens mekaniska egenskaper och ge underlag till en eventuell investering. Temperaturer och tider för värmebehandling är hämtade ur voestalpine precision strips tillverkning i Munkfors för att kunna simuleras med fullgott resultat. De olika tester som utfördes var hårdhetsmätning med Vickersmetoden, dragprov, utvärdering av mikrostruktur i laserkonfokalmikroskop samt restaustenitmätning med röntgendiffraktometer. Testerna har utförts vid voestalpine i Munkfors, Bergsskolan i Filipstad samt vid Uddeholm i Hagfors. Testresultaten visar en trend till att materialen uppnår en högre hårdhet och lägre halter av restaustenit vid djupkylning. Flap-X uppvisar även viss ökning av sträckgräns samt brottgräns vid djupkylning. SS716 visar ingen ökning av vare sig sträckgräns eller brottgräns. I den mikrostrukturanalys som utfördes av de båda stålen kunde inga större skillnader påvisas mellan djupkylda prov respektive ej djupkylda. Testresultaten ska beaktas som en trend på grund utav statistiskt osäkra värden och omständigheter vid provning såsom inverkan av textur på restaustenitmängden vid röntgenundersökning.

Developing the third generation of Calphad databases with more physical basis valid within a wider temperature range is the aim of the present work. Atomistic scale (ab-initio) methods, particularly techniques based on DFT theory, are used for modelling dierent phenomena, so as to gauge the capacity for use in Calphad modelling. Several systems are investigated in this work for studying dierent phenomena, such as magnetism and vibration of atoms. In the case of pure elements (unaries), thermodynamic properties of Mn, Al and C are optimized in the whole temperature range by the help of new models. In addition, DFT results and specic characteristics of these elements are also used to develop models for describing magnetic properties and atomic vibrations. With regards to coupling between DFT and Calphad, the EMTO technique is used for determining the magnetic ground state of the metastable hcp phase in Fe and Mn, and the TU-TILD technique is used for modelling solid phases above the melting point. TU-TILD is also used for calculating thermodynamic properties of bcc Mn at nite temperatures. The same phenomena are investigated in higher-order systems, i.e. the binaries Fe-Mn and Mn-C. Thermodynamic properties and phase diagrams of these systems are assessed against experimental data. Moreover, the revised magnetic model is used for modelling magnetic properties in these systems. It is shown through this investigation that although the DFT methods are powerful tools for model development and for resolving discrepancies between dierent experimental datasets, they should not be overly-trusted. Caution must be taken when using DFT results, since the approximations and assumptions for computational implementations may cause some errors in the results. Moreover, implementing them into Calphad software as a connected methodology is not currently accessible due to the computational limitations. It is concluded that coupling between the DFT and Calphad approaches can currently be achieved by using DFT results as an input in Calphad modelling. This will help to improve them until they can be integrated into the Calphad approach by the progress of computational possibilities. One of the advantages of developing the third generation Calphad databases is the possibility of using the 0 K DFT results in Calphad modelling, since the new databases are valid down to 0 K. This has not been possible in the past, and such potential opens a new door to bring more physics into the Calphad approach. / <p>QC 20171006</p>

In the present study, magnetite pellets with the additives olivine, calcite and quartzite were isothermally reduced in a tubular furnace to study the interaction between iron oxides and the additives. Exaggerated amounts of additives were used in order to enable analyses of phases that do not otherwise occur in sufficient amounts for X-ray diffraction and EDS-analyses. The reduction was set to yield either magnetite or wüstite in the temperature range 500-1300ºC. For olivine, reduction tests were also performed to allow metallization in the range 1000-1300ºC. The mineralogical phases which had formed were studied after oxidation as well as after reduction. The results showed that it was possible to identify, by X-ray diffraction, the main phases formed by the additives in all samples, after oxidation as well as reduction.In the olivine sample, the forsteritic olivine particles react partly during the oxidation pre-treatment to form magnesioferrite and vitreous silica along the particle corona. This breakdown of the olivine particles during oxidation liberates magnesium from the particles, which do not react until temperatures of above 1150°C in reducing atmosphere. When the hematite in the sample is reduced, and when temperature is high enough to allow solid-state diffusion at ~800ºC, the magnesium of the magnesioferrite redistributes so that the magnesium concentration approaches the same level throughout the structure. For magnetite, this does not occur below 800°C. At 1000°C, this magnesium reacts further with the silica in the glassy slag phase, which crystallizes into fayalitic olivine. At this temperature the magnesium diffuses over distances more than 600µm from the olivine particles. From this point the binding media to resist the swelling tensions in the pellet is mainly solid fayalite. The metallization front concentrates the MgO in the remaining wustite which can lead to MgO levels of up to 10% locally. The melting point of the fayalite is raised from 1145ºC to a melting range of 1238-1264ºC due to the MgO-increase, as estimated based on the phase diagram tuned to the pellets tested. Much of the olivine which remained unaltered in the oxidation process will be encapsulated by iron before the magnesium begin to dissolve in reducing conditions, and therefore play no role in the reduction before final melting of the particles occur.The quartzite particles are not affected by the oxidation pre-treatment. The binding strength of quartzite pellets therefore comes from the sintering of quartzite particles to neighboring hematite as well as the glassy slag resulting from the acid gangue and the bentonite. Substantial reaction of the quartzite particles during reduction did not occur before 1000ºC even though the process has occurred to a very low extent already at 900ºC. Also the glassy slag crystallizes into fayalite in the presence of quartzite. From this point fayalite represents the binding media in the pellet. Pure fayalite melts already at 1177ºC and can at this temperature dissolve up to 76wt% FeO. This leads to early softening, which is one of the main concerns for the softening/melting properties of the pellet. In the pellets with calcite, CaO reacts with Fe2O3 during induration to form a low-melting calcium ferrite slag in the pellet that melts to react with silica in the pellets. If more calcium is added than what is required to react with the silica, calciumferrites becomes part of the binding mass together with the dicalciumsilicate. The calciumferrites forming in pellets with larger additions of calcite are weak to resist the tensions arising due to the low-temperature reduction of hematite and are associated with low temperature disintegration. As the reduction proceeds to wustite, the calcium from the ferrite dissolves in the wustite so that porous calciumwustite forms. The dicalciumsilicate remain stable during the entire reduction until reaction and melting of the phase begin at 1283ºC. / Godkänd; 2013; 20130411 (parsem); Tillkännagivande disputation 2013-05-20 Nedanstående person kommer att disputera för avläggande av teknologie doktorsexamen. Namn: Pär Semberg Ämne: Processmetallurgi/Process Metallurgy Avhandling: Interactions Between Iron Oxides and the Additives Olivine, Quartzite and Calcite in Magnetite Pellets Opponent: Professor Abdel-Hady Abdel-Hady El-Geassy, CMRDI, Cairo, Egypt Ordförande: Professor Bo Björkman, Institutionen för samhällsbyggnad och naturresurser, Luleå tekniska universitet Tid: Måndag den 10 juni 2013, kl 10.00 Plats: F531, Luleå tekniska universitet

Coal is the single largest fossil fuel used world-wide and accounts for more than 60% of the total commercial energy consumed. Between 60 to 80% of this coal is used for electric power generation and most of which through a system of pulverised coal combustion. Major portion of the coal used for such power generation is not clean enough to maintain environmental standards. This problem is attributed to high sulphur content in coal used in most of the western countries or ash as is the case in countries like India. In India at present nearly 200 million tonnes per year of coal is used for power generation and the average ash in coals used is invariably above 40%. A substantial portion of ash is liberated as it enters the boiler from the mill. It is crucial to reduce the amount of ash going from the mill to the boilers not only to improve the performance of power generation and increase the life of the boilers but also became mandatory due to environmental regulations. Thus the main objective of the work is to develop a dry tribo-electrostatic process for the separation of ash forming inorganic matter from coal material with a thorough understanding of the response and behaviour of coal and non-coal matters to contact electrification and in electric field. This work is financially supported by the Department for Research Cooperation of the Swedish International Development Cooperation Agency (SIDA). The literature on dry coal preparation processes has been reviewed and the advantages of triboelectric process compared to other processes have been highlighted and further research needs to make it a viable industrial technology are outlined. Three Indian coal samples from three different major coal fields, i.e., Ramagundam, Ib-valley and Talcher, have been collected and characterised for macerals and mineral composition by microscopic and XRD analyses. The beneficiation potential at different size fractions of the coal samples is judged by the washability studies. The charge polarity and magnitude of pure quartz, kaolinite, illite and carbon after contact electrification with different tribo-charging media have been measured by Faraday cup method using Keithley electrometer. The predicted work functions of the tribo charging material and mineral phases agree closely with the reported values. The electron accepting and donating (acid-base) property of mineral phases determined by Krüss Tensiometer through polar and non-polar liquid contact angles on solids also corroborated the acquired charge polarity in contact electrification with copper, aluminium and brass materials underlying their work functions. This methodology is being applied for the choice of organic acidic/basic solvents treatment of coal material to enlarge the difference in work functions between the tribo-charger and mineral phases, and to achieve greater separation efficiency of inorganic matter from coal. The coal samples have been tested for the separation between coal and non-coal matters in a laboratory in-house built tribo electric separator and the influence of equipment and process variables have been evaluated. The results showed that the ash content was reduced from 45% to about 18%, and a clean coal product as judged by the washability studies can be obtained. / Godkänd; 2006; 20070110 (haneit)

Slag is a vital part of metal production since it removes impurities from the metal. As slag is continuously produced, the options are either to dispose slag in landfill or acknowledge slag as a product. Slag can be used in many different applications, ranging from fertilizer to construction material; in some cases, the properties of slag make it a superior alternative to virgin stone materials. The properties and thereby the field of application is determined by the mineralogical composition of the slag. Slag is considered an environmentally friendly material as long as the leaching of certain elements stay below specified thresholds, for leaching of chromium the limit is at 0.5 mg/kg for slag to be considered inert material. The most common leaching approach is to compare leaching analyses from slag samples to deduce which elements and/or phases contribute or prevent leaching of specific elements. With this method each slag need to be investigated separately and the result may only apply for that specific slag type. In this thesis the approach is different: individual minerals are synthesized and dissolved separately at various pH to accurately assess their dissolution capabilities. By studying the dissolution of individual minerals the leaching of any type of slag with known mineralogical composition can be anticipated. Slag leaching can then be tailored, for example, chromium leaching can be eliminated if all chromium containing phases are removed or not capable of dissolving. In this thesis the dissolution of akermanite, β- and γ-dicalciumsilicate, merwinte, monticellite, pseudowollastonite and magnesiowüstite with varying FeO/MgO ratios are studied. Leaching tests of magnesiowüstite with 4 wt% Cr2O3 were also included. The dissolution of each mineral is calculated by the acid addition required to maintain a constant pH with 50 mg of mineral in 100 ml water. As expected, the dissolution decreases as pH increases, with exception of the dicalcium silicates which dissolved completely at pH 4 to 10. The dissolution of the minerals is largely connected to the elemental composition. In the silica based minerals a high Ca ratio promotes dissolution while a high Si ratio impedes the dissolution rate. Both dissolution and chromium leaching of magnesiowüstite depends on the FeO content, with increasing FeO content the dissolution and leaching decreases, magnesiowüstite with at least 60 wt% FeO does not dissolve at pH 10. None of the magnesiowüstite compositions were close to the chromium leaching limit of inert material, 0.5 mg/kg, as the highest leaching sample, with 52 wt% FeO, leached 0.069 mg/kg.

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The first objective of the thesis was to reveal the characteristic magnetic behaviour of natural weakly magnetic minerals (such as hematite and chromite), and the size limits of the particles recoverable by the existing modem high intensity and high gradient magnetic separators. The second objective was to enhance the particle aggregation andlor the magnetic response for wet magnetic concentration of the ultrafines which escaped from the separators. It was observed that weakly magnetic natural minerals (hematite and chromite) exhibited variations in the magnetic behaviour with respect to magnetizing field, temperature and even particle size, It was indicated that high gradient magnetic separation with industrial matrices was efficient for weakly magnetic minerals as small as 10 um, but below this size, poor separation efficiency was obtained. In this thesis, modifications to the existing magnetic technology or alternative methods were investigated for the efficient recovery of particles below 10 gm. The technology or methods included "carrier" or "piggy-back" method, aggregation with magnetic bonding (with permanent or fieldinduced magnetic moment), and hydrophobic magnetite seeding. The thesis discusses the theoretical aspects of the problem and the experimental work. It was clearly demonstrated that wet magnetic concentration was more efficient for the ultrafine fractions whereas other methods could be used to increase the effective particle size dimensions andlor the magnetic susceptibilities. / Godkänd; 1993; 20070426 (ysko)

A comparative study on bioleaching of a pyrite concentrate using ten different industrial oxidic by-products as neutralising agent has been performed with a commercial grade slaked lime chemical serving as reference material. The acid produced during oxidation of pyrite was neutralised by regular additions of neutralising agent whenever needed to maintain a pH of 1.5. Bioleaching was conducted as batch experiments in 1-L scale reactors, with a mixed mesophilic culture at a temperature of 35º C. The different industrial oxidic by-products used were steel slag, ashes, dust and lime sludge. The aim of the study was to investigate the possibility to replace normally used lime or limestone with oxidic by-products, considering their neutralising capacities and possible negative impact on the bacterial activity. The bioleaching efficiency was found to be equally good or better, when by-products were used for neutralisation instead of slaked lime, and the bioleaching yields of pyrite were in the range 69-80%, except the Waste ash, which had a leaching yield of 59%. Some of the by-products used contained potentially toxic elements for the bacteria, like fluoride, chromium and vanadium, but no negative effect of these elements could be observed on the bacterial activity. The Waste ash contained a large number potentially toxic elements and a high chloride concentration of 11%, which had a negative effect as observed on the lower redox potential and leaching yield. Slags originating from stainless steel production should be avoided for environmental reasons, due to the presence of chromium. The electric arc furnace (EAF) dust has a good potential to be used as neutralising agent in bioleaching processes for zinc recovery from zinc sulphides, due to the high content of zinc, however the chlorides present should be removed prior to its use. The neutralising capacity, as determined by the amount needed for neutralisation during bioleaching, were rather high for all the steel slags, EAF dust, Bioash and Mesalime with a range of 16-37 g as compared with 22 g needed for slaked lime. However, Waste ash and Coal & Tyres ash had lower neutralising capacities with 81 g and 57 g needed, respectively. Hence, it is concluded that considerable savings in operational costs can be obtained by replacement of lime or limestone with steel slag, ash, dust or sludge without negative impact on bioleaching efficiency. Use of industrial oxidic by-products would provide opportunities to recycle elements present in them as for example zinc rendering an eco-friendly process and a means for sustainable use of natural resources. / Godkänd; 2008; 20080519 (ysko)