The most widely used process to reduce iron ore and to produce pig iron is the blast furnace. The blast furnace is a large source of CO2 emissions since it is a coal based process and due to that the main energy source and reducing agent is coke, it is difficult to reduce these further. IRONARC is a new method used to produce pig iron by reducing iron ore and all the energy used for heating comes from electricity, which gives the opportunity to use renewable resources. The process uses plasma generators that inject gas at high temperature and velocity into a slag that consists of iron oxides. The iron oxides are reduced in two steps that appear by using gas as reduction agent in the first step and carbon in the second step.   It exists in a smaller pilot plant scale and this project was the first step in the future upscaling of the IRONARC process. Computational Fluid Dynamics (CFD) modelling was used and the goal was to determine the penetration depth of the IRONARC pilot plant process by numerical simulation in the software ANSYS FLUENT. The penetration depth is of importance because to be able to scale up the process it is important to know the flow pattern and the structure of the flow in the process, which is dependent on how far into the slag the gas reaches. Two numerical models were made. First an air-water model that described the initial penetration of air injected into water. The air-water simulation was made with parameters and data from an experiment found in literature. This was done to build an accurate CFD model for the penetration depth in FLUENT and validate the model with the results of the penetration depth from the experiment. The air-water simulation gave good and promising results and yielded the same result regarding the penetration depth as the experiment.  The model for the penetration depth was then used with the IRONARC geometry and parameters. After simulation the penetration depth of the IRONARC process was determined. For the future, the penetration depth of the pilot plant needs to be measured and compared with the simulated result for the penetration depth.

The process optimization of continuous annealing furnace, RHF 125, for recrystallization annealing of two steel grades, Sandvik 13C26 and Sandvik 20C has been carried out. To recreate the continuous annealing process carried out in the roller hearth furnace in the industry, samples with different cold reduction rates were chosen from ongoing production lines. An experimental heat treatment model was chosen by the ‘Design of Experiments’ approach from MODDE (from U-Metrics). The annealing temperature was chosen below the austenitization temperature for both steel grades and soaking time of 30 seconds to 240 seconds were chosen. Microscopic estimation of fraction recrystallized was performed with the help of Electron Back Scattered Diffraction, accompanied by mechanical testing methods to measure the hardness and yield strength of the steel strips. The experimental output was used to create a model to correlate between the different cold reduction rates and annealing parameters to achieve a higher degree of recrystallization along with desirable mechanical properties. Also, a modified Johnson-Mehl-Avrami-Kolomogrov model, based on hardness values, to determine the transformation kinetics by tracking the progress of recrystallization was developed. The model was verified with EBSD measurements for Sandvik 13C26 strip steels. For 20C, inhomogeneous recrystallization was observed, thus limiting the model’s adaptability to steels which exhibit homogeneous recrystallization behavior and negligible change in precipitation and/or coarsening of secondary phases. / Processoptimering av en kontinuerlig glödgningsugn, RHF 125, för rekristallisationsglödgning av två Sandvik-stål, Sandvik 13C26 och Sandvik 20C, har genomförts. För att återskapa den kontinuerliga glödgningsprocessen som utförs den verkilga processen i valdes prover och olika kallreduktionshastigheter från pågående produktionslinjer. En experimentell värmebehandlingsmodell valdes med metoden 'Design of Experiments' med MODDE (från U-Metrics). Glödgningstemperaturen valdes till en temperatur under austeniseringstemperaturen för båda stålen och hålltider varierade från 30 s till 240 s. Mikroskopisk uppskattning av fraktionen rekristalliserat material utfördes med hjälp av Electron Back Scatter Diffraktion (EBSD), åtföljd av mekaniska testmetoder för att mäta hårdheten och sträckgränsen för stålproverna. De experimentella resultaten användes för att skapa en modell för att korrelera mellan de olika reduktionshastigheterna och glödgningsparametrarna för att uppnå högre grad av rekristallisation tillsammans med önskvärda mekaniska egenskaper. Dessutom utvecklades en modifierad Johnson-Mehl-Avrami-Kolomogrov-modell, baserad på hårdhetsvärden, för att bestämma transformationskinetiken genom att spåra evolutionen för rekristallisation. Modellen verifierades genom jämförelse med EBSD-mätningarna för Sandvik 13C26 bandstål. För 20 °C observerades inhomogen rekristallisation, vilket begränsade modellens användbarhet till stål som uppvisade homogent rekristallisationsbeteende och försumbar förändring i utskiljning och/eller förgrovning av sekundära faser.

The automotive industry of today faces ever harder requirements from regulatory bodies to increase the fuel efficiency, reduce the carbon footprint and increase the safety of their vehicles. The problem is being tackled in different ways; one of them being the use of innovative materials to reduce the overall weight while improving the crash safety of the vehicle. One such material is 22MnB5, an ultra-high strength (UHS) boron-alloyed steel, capable of reaching tensile strength of 1900 MPa. The weldability is a vital factor for applying boron steel in an efficient way into a vehicle construction. Resistance spot welding (RSW) is, among the different welding methods, the primary joining methods used within the automotive industry. The main challenges with RSW of UHS boron steel is the narrow welding window and increased risk of expulsion compared to conventional automotive steel. The aim of this thesis was evaluating how the weldability of three-sheet UHS boron steel combinations could be improved by applying different innovative welding methods. The methods investigated where; three-pulsed welding, two-pulsed welding with force profile and using hollow-cone electrodes instead of regular electrodes. The different methods where evaluated with welding experiments and analysis of the nugget diameter, vicker hardness comparison and tensile strength test of welding nugget. The results from this thesis shows that the current window of three-sheet combinations with UHS boron steel can be significantly improved by using hollow-cone electrodes in RSW. The results also showed that the width of the current window varied depending on the depth of the hole in the electrode, a deeper hole improved the current window but also increased the oxide build-up. Applying a force profile with lowered electrode force during the welding sequence provided an improved process window compared to the constant electrode force when welding a three-sheet combination containing AlSi-coated boron steel. A three-pulse welding sequence performed better than the reference two-pulse welding schedule but still not good enough to meet VCC acceptance criteria. / Bilindustrin står idag inför allt hårdare krav från tillsynsmyndigheter förbättra bränsleeffektiviteten, minska koldioxidavtrycket och öka säkerheten på deras fordon. Problemet angrips från ett flertal olika vinklar. varav en ökad användning av innovativa material för att minska den totala vikten samtidigt som fordonets kraschsäkerhet bibehålls eller ens förbättras. Ett sådant material är 22MnB5, ett höghållfast (UHS) borstål, kapabelt att uppnå brottgränser på 1900 MPa.  Svetsbarheten är en vital faktor för att kunna applicera borstål på ett effektivt sätt i en fordonskonstruktion. Inom bilindustrin är motståndspunksvetsning (RSW) den dominanta svetsmetoden. De största utmaningarna med att punktsvetsa höghållfast AlSi-belagt borstål är det har ett generellt smalare svetsfönstren, samt den ökade risken för sprut under svetsprocessen, jämfört med konventionella stål. Målet med denna avhandling var att utvärdera hur svetsbarheten av tre-plåtskombinationer med höghållfast AlSi-belagt borstål kunde förbättras genom att applicera innovativa svetsmetoder. De utvärderade metoderna var; tre-pulsad svetsning, två-pulsad svetsning med applicerad kraftprofil, samt användning av ihåliga elektroder istället för vanliga elektroder. Metoderna utvärderades genom svetsexperiment och analys av svetslobens storlek, vicker hårdhets mätning samt brottgränsmätning av svetsloben. Resultaten från denna avhandling visar att svetsbarheten för tre-plåts kombinationer med UHS borstål kan förbättras avsevärt genom att använda ihåliga elektroder för punktsvetsning. Resultaten pekar också på att förbättringen beroende på hålets djup i elektroden. Ett djupare hål gav större förbättringar men ökade också uppbyggnaden av oxid och restmetall i elektroden.  Genom att applicera en kraftprofil, där elektrodkraften sänktes under svetsprocessen kunde svetsbarheten förbättras för två-puls svetsning, jämfört med att ha konstant elektrodkraft, vid svetsning av en tre-plåtskombination innehållande höghållfast AlSi-belagt borstål. En tre-puls svetssekvens utförde bättre än referenspulssvetsschemat men fortfarande inte tillräckligt bra för att uppfylla VCC-acceptkriterierna.

This work has had the purpose to examine defects and the cause of crack growth during long term storage in rolled bars. The bars in question are rolled and stored at Ovako in Hofors. The problem is approached by theoretically examining the possibilities of hydrogen damage, room temperature creep and naturally occurring porosity. Seven bars of three steel type groups and with different rolling dates were selected and examined for defects with ultrasonic testing. Four of the bars show defects. Specimens containing the defects are cut out and grinded so that the defects can be examined in the scanning electron microscope and analyzed with energy dispersive x-ray spectroscopy. One of the specimens shows some form of cavity containing iron carbide. One of the others shows a surface with inclusions. The remaining two both shows inclusions and cracks that seem to originate from inclusions. The theoretical studies show that there are two types of hydrogen damage that could be in effect in the studied case and also that room temperature creep could facilitate but not cause crack growth and that porosity could serve as crack initiation points. Steps should be taken to minimize the problems mentioned above when they are suspected causes. Further examination of inclusions in different steel types should be made if considered a problem. / Detta arbete har haft syftet att undersöka defekter och orsaken till spricktillväxt under långtidsförvaring av spårvalsade stänger. Stängerna i undersökningen är valsade och lagrade hos Ovako i Hofors. Problemet är angripet genom att teoretiskt undersöka risken för väteskador, kryp i rumstemperatur och naturligt förekommande porositet. Sju stänger indelade i tre stålsortsgrupper och med olika valsningsdatum valdes ut och undersöktes med ultraljud. Fyra av stängerna visade på defekter. Prov innehållande dessa defekter blev utkapade och slipade så att defekterna kan bli undersökta i svepelektronmikroskop och analyserade med energidispersiv röntgenanalys. Ett av proverna visar på ett hålrum innehållande en järnkarbid. Ett av de andra proverna visar på en yta med inneslutningar. De två återstående proverna visar på inneslutningar och sprickor som verkar utgå från inneslutningar. De teoretiska studierna visar att det finns två typer av väteskador som är aktuella i det studerade fallet och även att kryp vid rumstemperatur kan underlätta spricktillväxt men inte orsaka den och att porositet kan tjäna som sprickinitieringsställen. Åtgärder för att minimera de nämnda problemen bör tas i fall där de är misstänkta orsaker. Ytterligare undersökningar av inneslutningsbilden bör göras om inneslutningar anses vara ett problem.

We are living in a world of steel. Although there are a lot of other material in use, our most used material is steel. From building industry to transportation and even mother industries like mining, we use steel in different grades and amounts. There is always need for different grades of steel, and there is always interest in better properties and lower costs. Fe-Mn-Al-C steel group is one of the grades of steel is from the TWIP family. Beside its interesting mechanical properties, its corrosion resistance and cryogenic properties makes it very desirable to substitute more expensive current classes of the steel used in the industry. The automobile industry is also looking forward to implement this family of the steel in their products. This group of steel based on their chemical content can created a carbide ordered phase called κ which is one of the reasons of its interesting mechanical properties beside the TWIP properties. While κ may give more hardness due to precipitation hardening, it will make the steel brittle. Thus we need an understanding of the phase diagram of this group of the steels in order to choose our material and process accordingly. Phase diagrams are material engineers’ road maps for the processes and material choice as the initial steps, since we can predict the processes results and stable phases based on the equilibrium state from the diagrams. As the number of components gets more than three the phase diagram calculations and determination gets harder. For the ternary alloying systems we can only show sections of the phase diagrams as isothermal sections, or consider an element constant and depict the diagram as a “binary” system for the other two alloying elements at the other element concentration. In this work, we tried to experiment on the experimental data for equilibrium phases of Fe-Mn-Al-C alloying system based on the Equilibrated Alloys for alloys containing 20, 30 and 40 weight percent Manganese. The results were compared to the current database of the Thermo-Calc software for this family and we found some inconsistencies between the experimental data and the calculations which shows that the calculated results for this alloying system with its high Mn-content, is not reliable and that the thermodynamic descriptions must be adjusted. / PrecHiMn (RFSR-CT-2010-00018)

A large number of Li-ion batteries used today will reach their End-Of-Life (EOL) in a few years. After their EOL, the recovery of their precious elements is required. By applying physical separation, a fraction with fine particle size is left behind which is known as Black Mass (BM). BM is rich in LIB precious materials, including Li metal oxides and graphite. In this study, pyrometallurgical recycling of BM is investigated. In the first step, the BM high-temperature transformations are being studied, focusing on reducing Li metal oxides, Li evaporation, and F removal. In the second step, Fe and Cu oxides are added to the BM to investigate how the graphite remaining in the BM can be used as a reducing agent and form alloys with Co and Ni. The use of mechanical activation as a mean to improve the kinetics of the reactions and the efficiency of the reduction reaction was also studied. To model the experiments in this study, thermodynamic softwares (FactSage and HSC) were also employed.

Graphite has important applications in several key industries, which has been listed as a “criticalraw material” considered to be supply-risk by European since 2020. Purification of engineered graphite is one of the essential processes for the manufacturing of high-quality graphite. In this work, the production process and the existing methods to purify the three major types of graphite are evaluated and compared. Then purification method focusing on acid washing to remove iron from bio-graphite is investigated. The results showed that the impurity removalefficiency of acid washing increases with the increase of temperature, but efficiency decreased because of HCl volatilization when the temperature reaches 100 ℃. High concentrations of hydrochloric acid and other strong acids can improve the ability of acid washing. The smaller the graphite particle size, the more iron impurities are removed. Finally, through multi-steps acid washing with hydrochloric acid and aqua regia at 80 °C, bio-graphite with a purity of 99.67 % was obtained. This meets the requirements of metallurgical electrodes and other applications. The acquisition of ultra-high-purity graphite still needs more further work. / Grafit har viktiga tillämpningar i flera nyckelindustrier, som har listats som en "kritisk råvara" som anses vara en försörjningsrisk av Europa sedan 2020. Rening av teknisk grafit är en av de väsentliga processerna för tillverkning av högkvalitativ grafit. I detta arbete utvärderas och jämförs produktionsprocessen och de befintliga metoderna för att rena de tre huvudtyperna av grafit. Därefter undersöks reningsmetod med fokus på syratvätt för att avlägsna järn från biografit. Resultaten visade att effektiviteten för avlägsnande av föroreningar vid syratvätt ökar med ökningen av temperaturen, men effektiviteten minskade på grund av HCl-förångning när temperaturen når 100 ℃. Höga koncentrationer av saltsyra och andra starka syror kan förbättra förmågan till syratvätt. Ju mindre grafitpartikelstorlek, desto mer järnföroreningar avlägsnas. Slutligen erhölls biografit med en renhet på 99,67 % genom syratvätt i flera steg med saltsyra och aqua regia vid 80 °C. Detta uppfyller kraven för metallurgiska elektroder och andra applikationer. Förvärvet av grafit med ultrahög renhet kräver fortfarande mer arbete.

Automated image recognition software has earlier been used for various analyses in the steel making industry. In this study, the possibility to apply such software to classify Scanning Electron Microscope (SEM) images of two steel samples was investigated. The two steel samples were of the same steel grade but with the difference that they had been treated with calcium for a different length of time.  To enable automated image recognition, a Convolutional Neural Network (CNN) was built. The construction of the software was performed with open source code provided by Keras Documentation, thus ensuring an easily reproducible program. The network was trained, validated and tested, first for non-binarized images and then with binarized images. Binarized images were used to ensure that the network's prediction only considers the inclusion information and not the substrate. The non-binarized images gave a classification accuracy of 99.99 %. For the binarized images, the classification accuracy obtained was 67.9%.  The results show that it is possible to classify steel samples using CNNs. One interesting aspect of the success in classifying steel samples is that further studies on CNNs could enable automated classification of inclusions. / Automatiserad bildigenkänning har tidigare använts inom ståltillverkning för olika sorters analyser. Den här studiens syfte är att undersöka om bildigenkänningsprogram applicerat på Svepelektronmikroskopi (SEM) bilder kan klassificera två stålprover. Stålproven var av samma sort, med skillnaden att de behandlats med kalcium olika lång tid. För att möjliggöra den automatiserade bildigenkänningen byggdes ett Convolutional Neural Network (CNN). Nätverket byggdes med hjälp av öppen kod från Keras Documentation. Detta för att programmet enkelt skall kunna reproduceras. Nätverket tränades, validerades och testades, först för vanliga bilder och sedan för binariserade bilder. Binariserade bilder användes för att tvinga programmet att bara klassificera med avseende på inneslutningar och inte på grundmatrisen. Resultaten på klassificeringen för vanliga bilder gav en träffsäkerhet på 99.99%. För binariserade bilder blev träffsäkerheten för klassificeringen 67.9%. Resultaten visar att det är möjligt att använda CNNs för att klassificera stålprover. En intressant möjlighet som vidare studier på CNNs kan leda till är att automatisk klassificering av inneslutningar kan möjliggöras.

This project mainly investigated how the niobium(Nb) content influences the microstructure and mechanical properties of grey cast iron. Considering the mechanism, the study also analyzes the relationship between microstructure and mechanical properties. Generally, the work is based on 127 test bars/samples from two cylinder heads and three batches of plates, which were studied by measuring tensile strength, microhardness, graphite size, carbide amount and chemistry. The result data has been evaluated with statistical methods. The experiments mainly included the preparation of the samples for test and analysis. The mechanical properties in this study are evaluated by the tensile strength of the grey cast iron. Meanwhile, various microscopies were applied to observe how niobium and cooling rate influence the microstructure. Finally, from the analysis results, it tells that the niobium does affect the tensile strength of grey cast iron. Higher the niobium content is, higher the tensile strength is. The computed result based on the data also shows niobium’s strong effect. The faster cooling rate will increase the tensile strength and pearlite microhardness of grey cast iron as well. The carbide amount of grey cast iron can be increased by the addition of niobium content. Furthermore, some future work needs to be done to explain the unsolved problem in this result. The reasons of why a specific position A-2-d of plates has high values of tensile strength demand more microstructure investigation. For the niobium influence, more experiments and data containing a larger range of niobium content also need to be done to prove the mathematics results in this report. / Detta projekt undersökte huvudsakligen hur innehållet av niob (Nb) påverkar gråstålens mikrostruktur och mekaniska egenskaper. Med tanke på mekanismen analyserar undersökningen även förhållandet mellan mikrostruktur och mekaniska egenskaper. Arbetet baseras i allmänhet på 127 provstänger / prover från två cylinderhuvuden och tre satser av plattor, vilka studerades genom mätning av draghållfasthet, mikrohårdhet, grafitstorlek, karbidmängd och kemi. Resultatdata har utvärderats med statistiska metoder. Experimenten inbegriper huvudsakligen beredningen av proven för test och analys. De mekaniska egenskaperna i denna studie utvärderas av gråstålets draghållfasthet. Under tiden applicerades olika mikroskopier för att observera hur niob- och kylhastigheten påverkar mikrostrukturen. Slutligen, från analysresultaten, berättar den att niobet påverkar draghållfastheten hos grågjutjärn. Ju högre niobinnehållet är, desto högre är draghållfastheten. Det beräknade resultatet baserat på data visar också niobins starka effekt. Den snabbare kylhastigheten ökar också draghållfastheten och pearliten-mikrohårdheten hos grågjutjärn. Karbidmängden av grågjutjärn kan ökas genom tillsats av niobhalt. Vidare måste vissa framtida arbeten göras för att förklara det olösta problemet i detta resultat. Skälen till varför en specifik position A-2-d av plattor har höga dragkrafter kräver mer mikrostrukturundersökning. För niobinpåverkan måste fler experiment och data som innehåller ett större antal niobinnehåll också göras för att bevisa matematikresultaten i denna rapport.

The crater wear of alumina coated WC-Co cutting tools is thought to be influenced by the chemical reactions between the coating and the workpiece material. Three different crystal orientations ((001), (012), and (100) of alpha alumina CVD coatings are examined in combination with four workpiece materials of steel to establish what reactions are present, and the extent of diffusion. The alumina coatings and workpiece materials were pressed together as diffusion couples and heat treated at 1250- 1300°C for 10-20hours. It was fond that the types of inclusions present in the workpiece were more impactful on the chemical wear of the coating than the crystal orientation of the coating. EDS measurements show significant amounts of W and Co on the surface of the coatings and on the steel surfaces after heat treatment. This is thought to be connected to the migration of Co through the coating in cooling cracks and other impurities. In the surface of the coating, areas of solidified Co-rich structure have been found, implying that Co has formed an alloy with Fe, C, Al, and W with sufficiently low melting temperature to partially melt during the heat treatment. This has been confirmed as possible by simulations in Thermo-calc. Turning tests and scratch tests were made with the same combinations of coatings and workpiece material and show differences in adhesion of workpiece material on the different coating orientations. The 100-orientation has been found to have the most adhered workpiece material, the reason for this being its higher surface roughness. Ultimately no noticeable differences in chemical reactivity between the coating crystal orientations was found. The Co diffusion though the coating occurred for all the coating orientations and further experiments in turning with the different workpiece materials are required to determine the effect of Ca-rich inclusions on the magnitude of chemical wear. / <p>Handledare på företag:</p><p>Susanne Norgren </p><p>Doc.  Ph.D,  Group Expert Materials Design</p>