This bachelor degree project is about determining the impact that additional bottom stirring may have on the desulphurization process at SSAB Luleå. During one week of field work steel samples were collected from 39 different heats. 31 of the heats were samples with the bottom stirring function enabled and the remaining 8 heats without the bottom blowing function, which is the standard method today at SSAB Luleå and they can be referred as references. Data from 15 old reference heats were also used for analysis.Two different behaviors of bottom stirring appeared and they were therefore separated to type 1 and type 2 bottom stirring. Type 1 bottom stirring turned out to have highest possibility of all methods to reach dissolved sulfur content of maximum 0.001%. If the ingoing dissolved sulfur content is around 0.03% has type 1 bottom stirring 33% chance to reach 0.001% dissolved sulfur content already after 13.3 minutes of injection and that can save sulfur reagents. The method with highest reagent efficiency showed type 1 bottom stirring to have, on second place came type 2 bottom stirring and the references showed to have lowest reagent efficiency.

It is well known that REMs are strong oxide and sulphide formers that can easily form large clusters which have harmful effect on the casting process as well as the quality of the final steel product. By adding these elements right before casting, the number of narrow transfer parts are eliminated (compared to if added in ladle) Also, the REM inclusions has less time to sinter together to form large clusters, preventing clogging. The general idea behind this alloying method in the continuous casting machine is to feed a wire of FeSiRE powder blend, coated with a metal strip, into the melt in the chilled Cu mold (CC mold) Adding REMs to the steel, in particular Ce, can increase the resistance to oxidation at high temperatures by improving the properties of the chromia layer. This is of big interest for SANDVIK as it can improve their corrosion resistant grades and may also, in the future, enable alloying in with other volatile elements such as Zr. This master thesis has the objective to find out the dissolution time of the wire, coated with three different metal strips; Steel, Cu and Al. The experiments were performed with steel grade 316L, provided by SMT, in a 2kg melt in a lab scaled induction furnace at 1500oC, 1510oC and 1530oC. The operations were performed both with and without FeSiRE powder inside. The results obtained with powder inside at 1500oC showed that the Al wire experienced the shortest dissolution time ( 0,5 to 1s) followed by Cu (≤10s) and Steel (18 to 20s). In addition to this, sampling procedures was implemented ( 1, 1, 3, 5 10 and 29mins after wire addition) in a depth of 40mm for each wire. Here, the yield of Ce 1 minute after wire addition was highest for the Steel wire (41.9%) followed by Cu wire (25%) and Al wire (<14.8%). From samples taken 1 and 5mins after wire addition in the Al wire experiment, inclusions were extracted and collected on a film filter after electrolytic extraction and filtration. The film filter was observed in SEM. The morphology and compositions were analysed and compared. It was found that Ce and La was present as Ce La oxy sulfides both individually and on Al Mg O clusters.

The inclusions have a different chemical composition and give the steel different mechanical properties. These inclusions affect several properties of steel. In order to understand how the inclusions will affect the steel properties, the electrolytic extraction of 3D investigate method is applied on the steel grade of 42CrMo4. Then follow with Scanning Electron Microscope (SEM) observation. Steel samples from both ingot and rolling with and without heat treatment are observed and compared with different ratios. The result shown that, heat treatment can be applied for removing carbides successfully. And most inclusions are belonging to Type RS which is rod like MnS. The percentage of broken particles can be up to 80%, which means that the reason for the inclusions broken should be find. And heat treatment can affect the characteristics of elongated MnS.

The focus of this thesis work is to optimize rare earth metal (REM) addition in Therma 253MA, an austenitic stainless-steel grade in order to get a good trade-off between oxidation resistance property and the amount of big REM inclusions formed. Big REM inclusions are detrimental to material properties and REM is required to be dissolved in the matrix for improving the oxidation resistance. REM optimization can also lead to economical savings for Outokumpu. The distribution of REM between matrix and inclusion is affected by factors such as REM addition, initial oxygen and sulphur contents and time to casting of the melt. The re-oxidation of melt in the tundish also affects the REM distribution. Hence, the effect of these factors on the inclusion characteristics is investigated by analysing samples with different REM additions, using light optical microscope (LOM) and scanning electron microscope (SEM). LOM analysis focussed on stringer inclusion characteristics. SEM+EDS analysis is done using automated "INCA Feature" software with focus on overall inclusion characteristics. Oxidation and creep tests are also performed to study the effect of different REM additions on oxidation and creep behaviour. The results from inclusion analysis show that increasing REM addition and time to casting has a bad effect on stringer and overall inclusion characteristics. The re-oxidation in the tundish influences the inclusion formation, but does not affect the stringer characteristics. The resistance to oxidation of the samples is also compared and is observed to increase within increasing REM addition. Finally, this works suggests an optimal REM addition for Therma 253MA to get a good balance between oxidation resistance and amount of big inclusions. / Fokus för detta avhandlingsarbete är att optimera tillsats av sällsynt jordartsmetall (REM) i Therma 253MA, en austenitisk rostfritt stålkvalitet för att få en bra avvägning mellan oxidationsbeständighetsegenskap och mängden stora REM-inneslutningar som bildas. Stora REM-inneslutningar är skadliga för materialegenskaperna och REM måste lösas i matrisen för att förbättra oxidationsbeständigheten. REM-optimering kan också leda till ekonomiska besparingar för Outokumpu. Fördelningen av REM mellan matris och inkludering påverkas av faktorer såsom REM-tillsats, initialt syre- och svavelinnehåll och tid till gjutning av smältan. Re-oxidation av smälta i tunden påverkar också REM-fördelningen. Följaktligen undersöks effekten av dessa faktorer på inkluderingsegenskaperna genom att analysera prover med olika REM-tillsatser, med användning av ljusoptiskt mikroskop (LOM) och avsökning av elektronmikroskop (SEM). LOM-analys fokuserade på stringer-inkluderingsegenskaper. SEM + EDS-analys görs med hjälp av automatiserad "INCA Feature" -programvara med fokus på övergripande inkluderingsegenskaper. Oxidations- och krypningstest utförs också för att studera effekten av olika REM-tillsatser på oxidation och krypbeteende. Resultaten från inkluderingsanalys visar att ökande REM-tillsats och tid till gjutning har en dålig effekt på stringer och totala inkluderingsegenskaper. Återoxidationen i tunden påverkar inkluderingsbildningen, men påverkar inte stringeregenskaperna. Motståndet mot oxidation av proverna jämförs också och observeras öka inom ökande REM-tillsats. Slutligen föreslår detta ett optimalt REM-tillägg för Therma 253MA för att få en bra balans mellan oxidationsmotstånd och mängd stora inneslutningar.

Sandvik Materials Technology tillverkar varje år cirka 230 000 ton stål varav en stor del är rostfritt stål. För att sänka kolhalten i stålet används en AOD-konverter där en kombination av syrgas och inertgas blåses in stålet för att avlägsna kol som kolmonoxid. Vissa duplexa rostfria stålsorter är trögfärskade vilket lätt leder till att konvertern blir flaskhalsen i stålverket. Syftet med arbetet är att undersöka och kartlägga parametrar som påverkar färskningstiden för trögfärskade duplexa stålsorter. Tiden i konvertern kan variera kraftigt mellan olika charger och det finns därför en ekonomisk drivkraft i att förkorta färskningstiden. Kolfärskningen i AOD-konvertern bygger på drivkraften hos kol att reagera med syre. Genom att använda blåssteg med ökande andel inertgas kan partialtrycket av CO-gas i stålet sänkas vilket gynnar oxidationen av kol. Vid färskning av rostfria stål som innehåller höga halter krom oxideras både kol och krom på grund av hög affinitet för syre. En liten slaggvolym kan anses som gynnsamt för färskningen då en mindre mängd kromspineller kan bindas till slaggen. Parametrarna har undersökts genom statistik från historiska charger samt genom ytterligare provtagningar under färskningsförloppet. De parametrar som undersökts är ståltemperatur, tid i överföringsskänk, mängd justeringar, antal dysor och gasflöde, operatör, stålsammansättning och slaggens inverkan. Det är ett stort antal parametrar som påverkar färskningen och det är svårt att avgöra vilken eller vilka som påverkar mest. Utifrån resultatet kan det ses att de undersökta parametrarna påverkar resultatet på olika sätt; en hög temperatur in i konvertern är gynnsam lika som en kort tid i överföringsskänken och en stålsammansättning nära riktvärdet. Många av parametrarna är dessutom beroende av varandra så som att stålsammansättningen påverkas av justeringarna och temperaturen påverkas av tiden i överföringsskänken. Slaggens inverkan på färskningen studerades utifrån typen och mängden slaggbildare. Resultaten visar att kromspineller bildas i slaggen oberoende av vilken slaggbildare som används. För chargen med slaggbildare 1 var det tydligt att det fanns fri kalciumoxid i slaggen vilket tyder på att slaggen är mättad på kalciumoxid. En mättad slagg kan leda till bildandet av en större mängd spineller vilket kan leda till en längre färskningstid. När slaggbildartillsatsen förändrades och tillsattes under steg 2 visar resultatet att 5/10 charger når en kolhalt under riktvärdet vid prov 54. Slutsatser som kan dras är att det är viktigt att fokusera på de parametrar som har en stor påverkan på färskningstiden men samtidigt är möjliga att påverka. Det kan vara att använda fler dysor och på så sätt öka gasflödet, minska slaggvolymen eller undvika att stålet förvaras långa tider i överföringsskänken.

Although Iron and steel industry is essential for the development of society, the industry is responsible for a large portion of CO2 emissions. The industry also produces by-products like metallurgical slag in orders of million tons. The slag is alkaline in nature and rich in Ca and Mg oxides. Upon use the oxide interact with atmospheric CO2 and form carbonates, making them unstable. Storing CO2 in the slag would make it more stable, enhances its life cycle and promotes further usage in various applications. CO2 sequestration can be done through carbonation of steel slag. Carbonation of slag can be achieved through direct and indirect carbonation. Direct carbonation is performed either in a gaseous or an aqueous state in a single step. Indirect carbonation involves multiple steps as it activates the Ca/Mg ions in the slag before they interact with CO2. For an industrial process the direct route would be more viable as it involves lesser steps, easier to scale up. Since there are no solvents to activate the Ca/ Mg the cost involved is also less. This thesis focuses on developing an industrial process to sequester CO2 in metallurgical slag. Sequestration through a combination of gaseous and aqueous has been attempted while studying the effect of carbonation time, carbonation temperature and shape of slag used. Carbonation of the slag is performed using CO2 and steam. The results show that carbonation yield increases with carbonation time and decreases with increase in temperature. The effect of the shape of slag used for carbonation was studied by performing carbonation test in a slag pellet. Diffusion plays a significant role in carbonation process. Powdered slag showed higher carbonation yield compared to the pellet. CO2 uptake as high as 53g of CO2/kg of slag at 200 oC for 6 hr has been achieved. The results indicate the possibility for an industrial carbonation process. / Även om järn- och stålindustrin är avgörande för samhällets utveckling, är industrin ansvarigför en stor del av koldioxidutsläppen. Industrin producerar också biprodukter som metallurgisk slagg i order på miljoner ton. Slaggen är alkalisk till sin natur och rik på Ca- och Mg-oxider. Vid användning interagerar oxiden med atmosfärisk CO2 och bildar karbonater, vilket gör dem instabila. Att lagra koldioxid i slaggen skulle göra den mer stabil, förbättra livscykeln och främja ytterligare användning i olika applikationer. CO2-bindning kan göras genom kolsyrning av stålslagg. Kolsyrning av slagg kan uppnås genom direkt och indirekt karbonatisering. Direkt karbonatisering utförs antingen i ett gasformigt eller vattenhaltigt tillstånd i ett enda steg. Indirekt kolsyrning involverar flera steg eftersom den aktiverar Ca/Mg-jonerna i slaggen innan de interagerar med CO2. För en industriell process skulle den direkta vägen vara mer livskraftig eftersom den innebär mindre steg, lättare att skala upp. Eftersom det inte finns några lösningsmedel för att aktivera Ca/Mg är kostnaden också mindre. Denna avhandling fokuserar på att utveckla en industriell process för att binda koldioxid i metallurgisk slagg. Sekvestrering genom en kombination av gasformig och vattenhaltig har försökt under undersökning av effekten av kolsyratid, kolsyratemperatur och form av den använda slaggen. Kolsyringen av slaggen utförs med CO2 och ånga. Resultaten visar att karbonatiseringsutbytet ökar med kolsyratiden och minskar med temperaturökningen. Effekten av formen på slagg som användes för karbonatisering studerades genom att utföra karbonatiseringstest i en slaggpellet. Diffusion spelar en viktig roll i karbonatiseringsprocessen. Pulveriserad slagg visade högre karbonatiseringsutbyte jämfört med pelleten. CO2-upptag så högt som 53 g CO2/kg slagg vid 200 oC under 6 timmar har uppnåtts. Resultaten indikerar möjligheten för en industriell karbonatiseringsprocess.

This study was regarding the waterjets in the water atomization process. This is because the understanding of the waterjets is not complete and with a greater understanding the production of metal powder could be improved. The waterjets were going to be categorized according to their wave function, size and distribution of the droplets and the three regimes that Höganäs had divided up the jets into was also analyzed. The three regimes depend on the jets characteristics and the regimes are the transparent, milky and the droplet jet. The purpose was to get a better understanding of the correlation between velocity, temperature, waves, size and distribution of the droplets in a 50 cm long waterjet. The method to enhance the understanding of this project was to first do theoretical solution with the help of fluid dynamics. Weber, Reynolds and Ohnesorge number were calculated and evaluated to get a better understanding of the waterjet. Secondly, experiments were conducted where a waterjet with different nozzles and temperatures was filmed with a highspeed camera and the videos were analyzed with the help of a software package called ImageJ. The results show the correlation between increasing temperature and decreasing droplet size and a less cohesive waterjet core. The conclusion from the study was that with the help of temperature one can help control the droplet size. / Denna studie angår vattenstrålar i en vattenatomiserings process vid tillverkning av metallpulver och en bättre förståelse skulle förbättra tillverkningen av metallpulver. Vattenstrålen skulle kartläggas enligt dess vågfunktion, storlek och spridning av dropparna och de tre regionerna som Höganäs har delat upp vattenstrålen i skulle analyseras. Regionerna är beroende av strålens karaktäristiska utseenden vid olika delare av vattenstrålen och är genomskinlig, mjölkig och dropp stråle. Syftet med studien var att få en bättre förståelse av sambandet mellan hastighet, temperatur, vågor, storlek och spridning av dropparna i en 50 cm lång vattenstråle. Metoden som användes för att öka förståelsen av vattenstrålen var först en teoretisk del med hjälp av fluidmekanik. Weber, Reynolds och Ohnesorge tal beräknades och utvärderades för att ge en teoretisk förståelse för vattenstrålen. Sedan utfördes vattenflödesexperiment, där vattenstrålen filmades med olika munstycken och temperaturer med en höghastighetskamera och videon analyserades med hjälp av mjukvaran kallad ImageJ. Resultaten visar ett samband mellan ökad temperatur och minskad droppstorlek och en mer uppbruten kärna av vattenstrålen. Slutsatsen från studien var att man med hjälp av temperaturen kan reglera droppstorleken.

The steel industry is aiming to reduce CO2 emissions by different means; in the short-term, by replacing fossil coal with highly reactive carbonaceous material like bio-coal (pretreated biomass) and, in the longer term, by using hydrogen. The use of bio-coal as part of top charged briquettes also containing iron oxide has the potential to lower the thermal reserve zone temperature of the Blast furnace (BF) and, due to improved gas efficiency, thereby give a high replacement ratio to coke. In order to select a suitable bio-coal to be contained in agglomerates with iron oxide, the current study aims at investigating the devolatilization behavior and related kinetics of different types of bio-coals. In addition, the aim is to investigate the self-reduction behavior of bio-coal-containing iron ore composite under inert condition and simulated blast furnace thermal profile. In the BF the temperature of the top-charged material will increase rather quickly during the descent in the upper part. Ideally, all the carbon and hydrogen contained in the top-charged bio-coal should contribute to the reduction. The devolatilization of bio-coal is thus important to understand and to compare between different types of bio-coal. To explore the devolatilization behavior for different materials, a thermogravimetric analyzer equipped with a quadrupole mass spectrometer was used to monitor the weight loss and off-gases during non-isothermal tests for bio-coals having different contents of volatile matter. The samples were heated in an inert atmosphere up to 1200°C at three different heating rates: 5, 10 and 15°C/min. The thermogravimetric data were evaluated by using the Kissinger–Akahira–Sonuse (KAS) iso-conversational model and the activation energy was determined as a function of the conversion degree. Bio-coals with both low and high content of volatile matter can produce reducing gases that can contribute to the reduction of iron oxide in bio-agglomerates. Bio-coals containing a higher content of catalyzing components such as CaO and K2O will enhance the devolatilization and release of volatile matter at a lower temperature.  The self–reduction of composites was investigated by thermogravimetric analyses in argon atmosphere up to 1100°C and evolved gases were monitored by means of quadrupole mass spectroscopy. Composites with and without 10% bio-coal and sufficient coke breeze to keep the C/O molar ratio equal to one were mixed and Portland cement was used as a binder. To explore the effect of added bio-coals, interrupted vertical tube furnace tests were conducted in a nitrogen atmosphere at temperatures selected based on thermogravimetric results, using a similar thermal profile as for the thermogravimetric analyzer. The variation between fixed carbon, volatile matter contents and ash composition for different types of bio-coal influences the reduction of iron oxide. The results showed that the self-reduction proceeds more rapidly in the bio-coal-containing composite and that the volatile matter could have contributed to the reduction. The self-reduction of bio-coal-containing composites started at 500°C, while it started at 740°C with coke as the only carbon source. The hematite was successfully reduced to metallic iron at 850°C with bio-coal present as a reducing agent, but not until 1100°C when using coke. Use of bio-coal with high content of volatile matter but low content of catalyzing elements as potassium, sodium and calcium in bio-agglomerates for the BF can be recommended because it enhances the self-reduction of iron oxide, e.g., wustite was detected by XRD analysis in samples treated up to 680°C. Bio-coal with low content of volatile matter, low alkalis, low phosphorous and high content of fixed carbon will also be suitable to use in the BF.

In thin film solar cells there is a front contact layer called TCO, transparent conducting oxide. This layer requires high conductivity and high transmittance. Different materials such as Tin doped indium oxide (ITO) and Aluminum doped zinc oxide (AZO) are current good alternatives but several other materials are investigated to find even better materials. One of them is tungsten doped indium oxide (IOW). This project was about investigating the deposition process for IOW and characterize the properties of IOW thin film to investigate the possibilities for implementing this material as a contact layer in thin film solar cells. The results from the two batches of depositions varied a lot. Some samples came out dark, but some were transparent and had a high transmittance, suitable for a TCO. The highest transmittance reached through this process was around 95 % in the infrared (IR) range and around 90 % in the visible range. When it comes to the resistivity, no IOW-samples reaches desired levels for a TCO. The lowest resistivity reached was 6.36 * 10-4 W cm. The results showed that the sample with the lowest resistivity was the undoped material, which is contradicting the current theory on the subject. The lowest resistivity for the IOW film was 6.50 * 10-3 W cm.

Compressors that are used in refrigerators and air conditioners usually have flapper vales made of martensitic stainless steel to control the flow of the refrigerant in the system. During service the flapper valves are affected by both bending and impact fatigue in the very high cycle fatigue (VHCF) range with billions of cycles until failure. Due to the VHCF, it is time consuming and expensive to test the performance of the flapper valves. One approach to improve the valve testing could be to combine traditional sample testing with the finite element method (FEM). In this paper, FEM was used to calculate the velocity and stress between a flapper valve and the seat during impact. Three different valve tongue shapes were investigated: a circular and two elliptically shaped tongues with a width to length ratio of 3:2 and 2:1. Furthermore, two different load cases were used to make the valve move: a backpressure case that was adapted from a compressor manufacturer and a springback case that was adapted from a flapper valve testing platform. A study of the wear mark evolution was also made on the surface of flapper valves that impacts with the seat. The valves had been in use for a different amount of cycles, were supplied by a compressor manufacturer and were made of Sandvik Hiflex steel. Stereo microscopy, scanning electron microscopy (SEM) and surface measurements were used at three different areas on the valves. It was shown with the FEM that the maximum compressive stress, at a specific point in the material, does not occur at the impact for that point. Rather, that constructive interference between stress waves in the material is the probable cause for the stress peaks that are formed. In what way the valve impacts with the seat will affect the maximum compressive stress distribution in the valve tongue. If an area close to the root of the valve impacts first with the seat, a whiplash effect will cause a higher impact velocity and impact stress in the free end of the valve. The wear mark study showed an initially high growth rate for the wear mark. However, with an increasing amount of cycles, the wear mark growth rate will decrease. Areas at the edge of the valve tongue consistently had the lowest wear mark depth, while areas close to the root and the free end of the valve had similar wear mark depth in the longest tested valve. FEM and wear mark results indicate that the impact velocity and maximum compressive stress are important factors for wear mark growth.