The aim of the present work was to get an overview of the steel cleanness in tool steel. Plant trial studies of three steel grades were done with different focuses. Firstly the change of the inclusion characteristics during the vacuum degassing in the ladle was looked upon. The top slag composition was altered and sampling was made before and after vacuum degassing and the results showed that the top slag composition has an effect on the inclusion composition. Thermodynamic calculations indicated that the oxygen activity for the steel/inclusion was twice as large as that of the steel/top slag before vacuum degassing. However, after vacuum degassing the oxygen activity values were close. In order to study the inclusion characteristics during vacuum degassing the process was interrupted at five pre-determined time points for sampling. During vacuum the number of the smaller inclusions was decreased. However, for the larger inclusions (&gt;11.2µm) the number of inclusions had increased. Throughout the degassing process the inclusion composition was found to approach the top slag composition and at the end of the process only one type of inclusion composition was found. The removal of hydrogen, nitrogen and sulphur was studied. Samples were taken before and after vacuum degassing. It was found that the removal kinetics of hydrogen and nitrogen can be described with first-order reactions. When 10 minutes of vacuum degassing have passed, the removal of hydrogen and nitrogen is more or less finished for the studied steel grades. Two steel grades with similar process route and with only a few differences in steel composition were studied. The sum of FeO and MnO was found to be a clear indicator for when reoxidation had taken place. The results from oxygen activity calculations indicate that calculations of oxygen activities with multivalence slag species such as Fe and Cr requires measurements for validations to ensure that reliable results are obtained. / Syftet med denna studie var att få en överblick av verktygsståls renhet. Studier på tre olika stålsorter utfördes. Inneslutningsbilden under vakuumbehandling undersöktes. Resultaten är baserade på industriförsök likväl som termodynamiska beräkningar. Försöken gjordes på två olika stålsorter där toppslaggens sammansättning varierades och stål- och slaggprover tog ut före och efter vakuumbehandling. Proverna analyserades för att bestämma den kemiska sammansättningen på stål och slagg, men inneslutningsbilden undersöktes också. Med hjälp av termodynamiska beräkningar beräknades syreaktiviteten för jämvikterna stål/inneslutning och stål/toppslag. Beräkningarna jämfördes sinsemellan samt med uppmätt syreaktivitet från stålsmältan. Resultaten visar att toppslaggens sammansättning har en påverkan på inneslutningarnas sammansättning. Specifikt så fanns att när CaO-halten i toppslaggen ökar syns en ökning av CaO i inneslutningssammansättningen. De termodynamiska beräkningarna visar att syreaktiviten för jämvikten stål/inneslutning är dubbelt så stor som den för jämvikten stål/topplagg före vakuumbehandling. Dock är syreaktiviteterna för de olika jämvikterna lika efter vakuumbehandlingen. För att studera hur inneslutningsbilden utvecklas under vakuumbehandling avbröts vakuumbehandlingen vid fem förutbestämda tidpunkter. Vid varje avbrott av vakuumbehandlingen togs stål- och slaggprover som analyserades för att bestämma totalsyre, inneslutningsmängd och inneslutningssammansättning. Före vakuumbehandlingen var antalet inneslutningar stort, medan antalet små inneslutningar minskade under vakuumbehandlingen. Däremot konstaterades att antalet stora inneslutningarna (&gt;11.2μm) ökade under avgasningen. Vad beträffar inneslutningssammansättningen syntes en variation i analys före vakuumbehandlingen som sedan förändrades till att likna toppslaggens sammansättning under vakuumbehandlingstiden. I slutet av processen märktes endast en typ av inneslutningssammansättning i stålsmältan. Vad som också noterades var att efter ungefär 10 minuter av vakuumbehandling så hade inneslutningsantalet nått sitt minimumvärde. För att erhålla rent stål är väte-, kväve- och svavelreningen också av stor vikt under vakuumbehandlingen. Dessa tre element studerades genom att prover togs vid olika tillfällen i processen; före, under (vid fem olika förutbestämda tidpunkter) och efter vakuumbehandling. De kemiska sammansättningarna för stål- och slaggproverna användes för att beräkna väte-, kväve- och svavelreningarna. Beräkningarna visade att för väte och kväve så kan kinetiken beskrivas med en förstagradsekvation. Specifikt så gäller detta för stålsorten i studien, samt under förutsättningen att svavelhalten är lägre än 0,003 vikts-%. Dessutom så visade resultaten att väte- och kvävereningen är i stort sett klar för den studerade stålsorten efter 10 minuters vakuumbehandling. När det gäller svavel så kan en förstagradsekvation inte användas vid beräkningarna Istället uppvisar svavel en tendens att följa jämviktshalten av svavel genom hela avgasningsprocessen. Genom att kontrollera processen finns stora möjligheter att erhålla en bra renhet på stålet. Två stålsorter studerades i denna specifika studie, där de hade en liknande processväg samt endast ix några små skillnader i stålanalysen. Stål- och slaggprover samlades in och analyserades. Summan av FeO och MnO visade sig vara en klar indikation på när reoxidation har skett, men mängden "carry-over" slagg från ljusbågsugnen kunde inte predikteras med hjälp av någon specifik indikator. Dessutom så beräknades syreaktiviten och beräkningarna jämfördes sedan med uppmätt syre i stålet. Resultaten indikerar att beräkningar av syreaktivitet med toppslagger som innehåller multivalenselement, såsom Fe och Cr, kräver valideringar med mätningar för att trovärdiga predikteringar ska erhållas. / <p>QC 20160523</p>

It is important to optimize glass compositions for their specific purpose but also for the efficiency of the production process, the manufacturing of glass. This will be beneficial economically and environmentally. Today many processes and glass compositions are already optimized, but due to more strict legislation on toxic elements and substances there must be changes in many glass compositions. One of these elements is antimony; the oxide is used as fining agent to obtain a bubble free glass within a reasonable process time. One aim with this thesis is to obtain a deeper understanding of the fining mechanism in 20R2O-10MO-70SiO2 (R=Na and/or K, M = Ca and/or Ba, Mg, Sr) glasses in order to minimise the amount of Sb2O3. Another intention is to study the structure of 20R2O-10CaO-70SiO2 (R = Na, K) with Cu2+ as probe ion and thus get a deeper knowledge of the surrounding glass matrix.  The optical basicity scale is used to determine the acid/base character of the different glass compositions.   Fining efficiency results showed a remarkable increase of the number of remaining bubbles when the glass contains either approximately equal amounts of Na and K or Ca and Ba, Mg or Sr. The much higher number of bubbles in the potassium containing glasses compared to the sodium containing is explained by the increase in viscosity, the increase in optical basicity and thus lower oxygen activity. The differences in the fining efficiency when altering alkaline earth ions cannot be explained by the optical basicity values, it seems to be a more complicated situation.   This thesis also reports maximum in Vickers hardness and packing density as well as minimum in glass transition temperature for the mixed alkali glasses. The mixed alkaline earth glasses do not exhibit any clear nonlinear behaviour. Raman spectroscopy measurements showed a variation in the network connectivity which has a clear relation to the optical basicity of the different glass compositions. The combination of UV-Vis-NIR and X-ray absorption spectroscopy measurements showed that the coordination sphere for Cu(II) is a tetragonal distorted octahedron with two elongated Cu-O bonds along the z axis. There were no trends in the degree of tetragonal distortion, thus it was about the same for all the investigated glass compositions. Cu(I) is found to be coordinated by two oxygen ligands in mainly linear coordination sphere, evidenced from X-ray absorption spectroscopy.

No description available.

QC 20101221

This work is about development and methodology verification of data collection which will be used in the research of the reoxidation in steel castings. To examine reoxidation rate will be measured oxygen activity in the furnace, in the ladle and in the mould. Next it will be evaluated the chemical structure of mould slag, the chemical changes of steel and measured the volume and the area of the casting defects. Each technique is briefly described by the principle of measurement and each method has the results which are analysed. In the conclusion the experiment is summarized and there are mentioned the observations from this experiment.

Casting of test castings from low – carbon steel with different deoxidation degrees. Oxygen activity measurement in castings – from the temperatures over liquidus to solidification of metal. Analysis of chemical composition of inclusions. Calculation of thermodynamic equilibrium between oxygen activity and aluminium, silicon and manganese activities in unalloyed steel. Estimation of conditions for the course of carbon reactions in studied casting.

Two industrial studies and one set of lab scale trials have been done. In addition, a theoretical study has been done. The main focus has been on non metallic inclusion composition during the ladle refining operation in industrial steel production. Sampling has been done together with careful inclusion determination. The inclusion composition is related to different variables. In the industrial trials samples have been taken at different steps during the ladle refining period. Steel and slag composition as well as temperature and oxygen activity have been determined. The thesis is based on five supplements with different major objectives, all related to the inclusion composition. The equilibrium top slag-steel bulk and inclusions-steel bulk were investigated by comparison between calculated and measured oxygen activity values. The oxygen activity and relation to temperature has also been discussed as well as oxygen activity and temperature gradients. The effect of vacuum pressure on inclusion composition has been evaluated in a theoretical study as well as lab scale trials. The inclusion composition has been studied during the industrial ladle treatment process. The inclusion composition was related to top slag composition and other parameters during ladle treatment. The major findings in the thesis are the lack of equilibrium conditions with respect to top-slag and steel bulk before vacuum treatment. The inclusions have been found to be closer to equilibrium with the steel bulk. Al/Al2O3 equilibrium has been found to control the oxygen activity after Al-deoxidation. Evaluation of inclusion composition during the ladle refining has revealed that the majority of the inclusions showed a continuous composition change throughout the ladle refining process, from high Al2O3, via MgO-spinel to finally complex types rich in CaO and Al2O3. The final inclusion composition after vacuum treatment was found to be close to the top slag composition. Vacuum pressure has been found to have a theoretical effect on inclusion composition at very low pressures. / QC 20100712

ABSTRACT AN INVESTIGATION OF COMPACTED GRAPHITE IRON PRODUCTION BY MEANS OF THERMAL ANALYSIS TECHNIQUE AND OTHER PROCESS CONTROL WINDOWS El-mabrouk, Omar PhD, Metallurgical and Material Engineering Department Supervisor: Prof. Dr. Ali Kalkanli January 2007, 123 pages Compacted graphite irons have been proved valuable in many applications such as exhaust manifolds, hydraulic valves, and diesel engine blocks, the process of producing compacted graphite irons is not a straight forward process because of its narrow processing windows and its high sensitivity to the section thickness, treatment reaction time, pouring temperatures and charge composition. In this thesis, compacted graphite was produced with minimum variations through all section thickness and the effect of Mg/S ratio, section thickness, and treatment agents on the graphite morphology, electrical resistivity property and fracture strength at high temperatures was investigated. The range of Mg/S ratio and the section thickness was from 2/3 to 7/1 and 5 mm to 40 mm respectively. FeSiMg and FeSiMg cermish metal were used as a treatment agent. Optical metallographic method was implemented to investigate the graphite morphology change. For being a distinguishable characteristic for compacted graphite iron over ductile iron, thermal conductivity changes at high temperatures ranging from room temperature to 500 0C was examined by a suitable electrical setup in the manner of electrical conductivity changes by measuring the electrical resistance. On the other hand, due to the higher values of mechanical properties of compacted graphite iron over those of gray iron, tensile strength was also examined by means of tensile test. The relation between the compacted graphite shape and the alloy properties such as fracture strength and thermal conductivity was investigated. The most important controlling parameters to produce compacted graphite are Mg/S ratio and oxygen activity. The relation between these parameters with both fracture strength and thermal conductivity was established by means of multiple regression analysis technique.

Diploma thesis deal with definnig the casuses of stell castings defects in the DSB EURO s.r.o Foundry. The main target is to optimise technological parameters for avoiding the surface casting defects. The first stage is the identification of the defects, describing of the main reasons and mechanic. Defect quantification is make from measuring of area and volume of the mended defects. In association with surface defects, the number of the crackings was observed. Finally there are suggested correction actions based on the previous investigation.