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  • 301.
    Ekbom, Lars B.
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Antonsson, Tomas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Ekbom, M
    Computer simulation of solution and growth processes during the initial stage of liquid phase sintering of tungsten heavy metal2005Ingår i: Scandinavian journal of metallurgy, ISSN 0371-0459, E-ISSN 1600-0692, Vol. 34, nr 5, s. 312-316Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the initial stage of liquid phase sintering, particle dissolution and growth processes occur. The melting matrix penetrates the solid particle agglomerates. A fraction of the particles dissolves in the liquid matrix phase and the original powder size will initially be reduced. At the same time the agglomerates of particles are effectively separated. In a second stage larger particles grow in equilibrium with the matrix, whilst smaller, pure particles dissolve into the matrix and the mean particle size increases. When an equilibrium is reached, the solid particles start to grow in the liquid matrix phase in accordance with the ripening process. The initial stages of liquid phase sintering have been investigated by short time sintering under microgravity and are presented in a series of micrographs. Mathematical models for the 3 stages have been developed. Computer simulations of these different stages in the solution and growth processes have been used to visualise the change in particle size distribution.

  • 302. Ekengard, J.
    et al.
    Andersson, Margareta A.T.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Jönsson, Pär G.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Distribution of metal droplets in top slags during ladle treatment2008Ingår i: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 35, nr 8, s. 575-588Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The investigation focused on the mixing of the metal and slag phases during ladle refining from the point of tapping the EAF to casting. Steel droplet distributions were determined for slag samples taken at different stages in the ladle refining process at two different steel plants in Sweden. The droplet distributions were determined using light optical microscopy and classification according to the standard SS111116. Sample analysis results showed the slag samples taken before vacuum degassing to contain the greatest concentration of steel droplets. The total interfacial area between the steel droplets and slag was determined to be 3-14 times larger than the projected flat interfacial area between the steel and slag. The effects of slag viscosity and reactions between steel and slag on metal droplet formation in slag were also considered.

  • 303.
    Ekengård, Johan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Slag/Metal Metallurgy in Iron and Steel Melts2016Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    In this work, the metal and slag phase mixing in three steps of a ladle refining operation of steel melts and for an oxygen balance during cooling of cast iron melts have been studied at two Swedish steel plants and at two Swedish cast iron foundries, respectively. In order to predict the oxygen activity in the steel bulk in equilibrium with the top slag as well as in metal droplets in the top slag in equilibrium with the top slag, three slag models were used. In addition, the assumptions of a sulphur-oxygen equilibrium between steel and slag and the dilute solution model for the liquid steel phase were utilized in the calculations. Measured oxygen activities in steel bulk, which varied between 3.5-6 ppm, were compared to predicted oxygen activities. The differences between the predicted and measured oxygen activities were found to be significant (0-500%) and the reasons for the differences are discussed in the thesis. Slag samples have been evaluated to determine the distribution of the metal droplets. The results show that the relatively largest numbers of metal droplets are present in the slag samples taken before vacuum degassing. Also, the projected interfacial area between steel bulk and top slag has been compared to the interfacial area between the metal droplets and slag.

    The results show that the droplet-slag interfacial area is 3 to 14 times larger than the flat projected interfacial area between the steel and top slag. Furthermore, the effect of the reactions between top slag and steel and the slag viscosity on the metal droplet formation is discussed. The results show significant differences between the steel bulk and steel droplet compositions and the reasons for the differences are discussed in the thesis. The oxygen activity in different cast irons was studied. Plant trials were performed at three occasions for lamellar, compacted and nodular iron melts. The results show that at temperatures close to the liquidus temperature the oxygen activities were 0.03-0.1 ppm for LGI, around 0.02 ppm for CGI, and 0.001ppm for SGI. In addition, it was found that as the oxygen activities increased with time after an Mg treatment, the ability to form a compact graphite or a nodular graphite in Mg-treated iron melts was decreased. Also, extrapolated oxygen activity differences up to 0.07 ppm were found for different hypoeutectic iron compositions for lamellar graphite iron at the liquidus temperature. Overall, the observed differences in the dissolved oxygen levels were believed to influence how graphite particles are incorporated into the austenite matrix and how the graphite morphology will be in the cast product.

  • 304.
    Ekengård, Johan
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Jönsson, Pär
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Andersson, Margareta
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Slag-metal equilibrium calculations for estimation of oxygen activity in molten steel during ladle treatmentManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    In the present paper three different methods to calculate the equilibrium oxygen activity have been compared with measured oxygen activities and oxygen activities based on sulphur equilibrium between slag and steel during ladle treatment at Scana Björneborg.

    Three slag models were used to estimate the oxide component activities of Al2O3 and SiO2 in the top slag and in the equilibrium calculations the dilute solution model for the liquid steel phase was used. The results show significant discrepancies between the calculated and measured oxygen activities and the reasons for the differences are discussed.

  • 305.
    Ekengård, Johan
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Jönsson, Pär
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Dioszegi, Attila
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. Jönköping University.
    A STUDY OF OXYGEN ACTIVITIES BEFORE THE START OF SOLIDIFICATION OF CAST IRONS2016Ingår i: International Journal of metalcasting, ISSN 1939-5981, E-ISSN 2163-3193, Vol. 10, nr 4Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Focus in this work was to study dissolved oxygen content and oxygen activities in different cast irons. Plant trials were performed at three occasions for lamellar, compacted and nodular iron melts. The results show that at temperatures close to the liquidus temperature the oxygen activities ranged from 0.03-0.1 ppm for LGI, around 0.02 ppm for CGI and 0.001ppm for SGI. In addition, it was found that as oxygen activities increase with time after an Mg treatment, the ability to form compacted graphite or nodular graphite in Mg-treated iron melts was lowered. Also, oxygen activity differences up to 0.07 ppm were found for different hypoeutectic iron compositions for lamellar graphite iron at the liquidus temperature. Overall, the observed differences in the dissolved oxygen levels are believed to influence how graphite particles are incorporated into the austenite matrix and how the graphite morphology will be in the cast product.

  • 306.
    Ekström, Madeleine
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Mekanisk metallografi.
    Development of a ferritic ductile cast iron for improved life in exhaust applications2013Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Due to coming emission legislations, the temperature is expected to increase in heavy-duty diesel engines, specifically in the hot-end of the exhaust system affecting components, such as exhaust- and turbo manifolds. Since the current material in the turbo manifold, a ductile cast iron named SiMo51, is operating close to its limits there is a need for material development in order to maintain a high durability of these components. When designing for increased life, many material properties need to be considered, for example, creep-, corrosion- and fatigue resistance. Among these, the present work focuses on the latter two up to 800°C improving the current material by additions of Cr, for corrosion resistance, and Ni, for mechanical properties. The results show improved high-temperature corrosion resistance in air from 0.5 and 1wt% Cr additions resulting in improved barrier layer at the oxide/metal interface. However, during oxidation in exhaust-gases, which is a much more demanding environment compared to air, such improvement could not be observed. Addition of 1wt% Ni was found to increase the fatigue life up to 250°C, resulting from solution strengthening of the ferritic matrix. However, Ni was also found to increase the oxidation rates, as no continuous SiO2-barrier layers were formed in the presence of Ni. Since none of the tested alloys showed improved material properties in exhaust gases at high temperature, it is suggested that the way of improving performance of exhaust manifolds is to move towards austenitic ductile cast irons or cast stainless steels. One alloy showing good high-temperature oxidation properties in exhaust atmospheres is an austenitic cast stainless steel named HK30. This alloy formed adherent oxide scales during oxidation at 900°C in gas mixtures of 5%O2-10%H2O-85%N2 and 5%CO2-10%H2O-85%N2 and in air. In the two latter atmospheres, compact scales of (Cr, Mn)-spinel and Cr2O3 were formed whereas in the atmosphere containing 5%O2 and 10%H2O, the scales were more porous due to increased Fe-oxide formation. Despite the formation of a protective, i.e. compact and adherent, oxide scale on HK30, exposure to exhaust-gas condensate showed a detrimental effect in form of oxide spallation and metal release. Thus, proving the importance of taking exhaust-gas condensation, which may occur during cold-start or upon cooling of the engine, into account when selecting a new material for exhaust manifolds. 

  • 307.
    Ekström, Madeleine
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Mekanisk metallografi.
    Oxidation and corrosion fatigue aspects of cast exhaust manifolds2015Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Emission regulations for heavy-duty diesel engines are becoming increasingly restrictive to limit the environmental impacts of exhaust gases and particles. Increasing the specific power output of diesel engines would improve fuel efficiency and greatly reduce emissions, but these changes could lead to increased exhaust gas temperature, increasing demands on the exhaust manifold material. This is currently the ferritic ductile cast iron alloy SiMo51, containing about 4 wt% Si and ~1 wt% Mo, which operates close to its fatigue and oxidation resistance limits at peak temperature (750C). To ensure high durability at higher temperatures, three different approaches to improving the life of exhaust manifolds were developed in this thesis.

    The first approach was to modify SiMo51 by adding different combinations of Cr and Ni to improve its high-temperature strength and oxidation resistance, or by applying a thermal barrier coating (TBC) to reduce the material temperature and thereby improve fatigue life. In the second approach, new materials for engine components, e.g. austenitic ductile iron and cast stainless steel, were investigated for their high-temperature fatigue and oxidation properties. In order to identify the most suitable alloys for this application, in the third the environmental effects of the corrosive diesel exhaust gas on the fatigue life of SiMo51 were investigated.

    The high-temperature oxidation resistance of SiMo51 at 700 and 800C in air was found to be improved by adding Cr, whereas Ni showed adverse effects. The effects of solid-solution hardening from Ni and precipitation hardening from Cr were low at 700C, with improvements only at lower temperatures. Applying a TBC system, providing thermal protection from a ceramic topcoat and oxidation protection from a metallic bond coat, resulted in only small reductions in material temperature, but according to finite element calculations still effectively improved the fatigue life of a turbo manifold. Possible alternative materials to SiMo51 identified were austenitic cast ductile iron Ni-resistant D5S and austenitic cast stainless steel HK30, which provided high durability of exhaust manifolds up to 800 and 900C, respectively. Corrosion fatigue testing of SiMo51 at 700C in diesel exhaust gas demonstrated that the corrosive gas reduced fatigue life by 30-50% compared with air and by 60-75% compared with an inert environment. The reduced fatigue life was associated with a mechanism whereby the crack tip oxidized, followed by crack growth. Thus another potential benefit of TBC systems is that the bond coat may reduce oxidation interactions and further improve fatigue life.

    These results can be used for selecting materials for exhaust applications. They also reveal many new research questions for future studies. Combining the different approaches of alloy modification, new material testing and improving the performance using coatings widened the scope of how component life in exhaust manifolds can be improved. Moreover, the findings on environmental interactions on SiMo51 fatigue provide a completely new understanding of these processes in ductile irons, important knowledge when designing components exposed to corrosive environments. The novel facility developed for high-temperature corrosion fatigue testing can be useful to other researchers working in this field. 

  • 308.
    Ekström, Madeleine
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Mekanisk metallografi.
    Jonsson, Stefan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Mekanisk metallografi.
    High-temperature corrosion fatigue of a ferritic ductile cast iron in inert and corrosive environments at 700˚C2015Ingår i: International Journal of Cast Metals Research, ISSN 1364-0461, E-ISSN 1743-1336Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the present work, low-cycle fatigue testing of a ferritic ductile cast iron named SiMo51 has been carried out in three atmospheres: argon, air and a synthetic diesel exhaust-gas at 700°C. The fatigue life was reduced up to 80% in the worst case. Two crack growth mechanisms were observed and directly linked to oxidation. At weak oxidation, a nodule-to- nodule crack growth occurred. At strong oxidation, crack growth occurred through oxidized material in front of the crack tip. 

  • 309.
    Ekström, Madeleine
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Mekanisk metallografi.
    Jonsson, Stefan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Mekanisk metallografi.
    High-temperature mechanical- and fatigue properties of cast alloys intended for use in exhaust manifolds2014Ingår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 616, s. 78-87Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the present work materials for use in exhaust manifolds of heavy-duty diesel engines were tested in air from 20 to 1000 degrees C with respect to mechanical properties. Two cast irons, SiMo51 and Ni-resist D5S, four austenitic cast steels, HF, A3N, HK30 and HK-Nb, and one ferritic cast steel, 1.4509 were studied. The experimental work included thermal conductivity, thermal expansion, uniaxial stress-strain testing, low-cycle fatigue testing up to 30,000 cycles and fractography. Below 500 degrees C, SiMo51 is superior. At higher temperatures, a transition from elastic to plastic strain dominance was observed for the cast irons, reducing their performance. Carbide-forming elements increase heat conductivity and result in a dendrite-like fracture surfaces during fatigue testing. The austenitic steels are superior only at higher temperatures.

  • 310.
    Ekström, Madeleine
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Mekanisk metallografi.
    Jonsson, Stefan
    The influence of Cr and Ni on the high-temperature low-cycle fatigue behavior of a ferritic cast ductile iron2012Ingår i: Conference proceeding for 7th International Conference on Low Cycle Fatigue, 2012Konferensbidrag (Refereegranskat)
    Abstract [en]

     The current material in exhaust manifolds for heavy-duty diesel engines: a Si- and Mo-alloyed, ferritic ductile cast iron, named SiMo51, is operating close to its limits and improvements are needed. Thus, in the present study, the effects on mechanical properties of adding Cr and Ni to SiMo51 has been investigated with focus on low-cycle fatigue behavior in air, at temperatures up to 700°C. Both additions improve fatigue life but reduce elongation. Adding 1wt% Ni improves fatigue life up to 250°C whereas adding 0.5wt% Cr improves fatigue life at room temperature, only.

  • 311.
    Ekström, Madeleine
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Mekanisk metallografi.
    Szakalos, Peter
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Jonsson, Stefan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Mekanisk metallografi.
    Influence of Cr and Ni on High-Temperature Corrosion Behavior of Ferritic Ductile Cast Iron in Air and Exhaust Gases2013Ingår i: Oxidation of Metals, ISSN 0030-770X, E-ISSN 1573-4889, Vol. 80, nr 5-6, s. 455-466Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Due to an expected temperature increase of the exhaust gases in heavy-duty engines in order to meet future emission regulations, there is a need to develop materials that can operate at higher temperatures. The exhaust manifold in the hot end of the exhaust system is specifically affected since the most common material today, SiMo51, is already operating close to its limits. Accordingly, the effects of Cr and Ni-additions on the high-temperature corrosion resistance of this material in air and exhaust gases were examined. It was found that the addition of 0.5 and 1 wt% Cr improved the oxidation resistance in air at 700 and 800 A degrees C by the formation of an SiO2 barrier layer as well as a Cr-oxide at the oxide/metal interface. However, no Cr-oxide was detected after exposure to exhaust gases, probably due to a water vapor-assisted evaporation of Cr from the oxide. The addition of 1 wt% Ni resulted in a deteriorated SiO2 barrier layer and reduced oxidation resistance.

  • 312.
    Ekström, Madeleine
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialteknologi.
    Thibblin, A.
    Tjernberg, A.
    Blomqvist, C.
    Jonsson, Stefan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Mekanisk metallografi.
    Evaluation of internal thermal barrier coatings for exhaust manifolds2015Ingår i: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 272, s. 198-212Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Seven different thermal barrier coatings (TBC) intended for coating the inside of an exhaust manifold to reduce its material temperature were studied. They comprised five plasma-sprayed (mullite, forsterite, La2Zr2O7, 8YSZ, and nanostructured 8YSZ) and two sol-gel composite (one sprayed and one dipped) coatings, which were examined for their thermal insulation properties and oxidation and spallation resistance. Thermal cyclic tests in air and in exhaust gas in a diesel test engine showed that thermal expansion mismatch between substrate and TBC was most crucial for TBC lifetime. Moreover, thermal modeling indicated that it is possible to reduce the material temperature by 50 °C, which is important for improving the fatigue life of exhaust manifolds. This reduction can be obtained with a 0.2 mm thick TBC with thermal conductivity close to 0.1 W/m K, or a 3–6 mm thick TBC with thermal conductivity 1.5–3 W/m K. 

  • 313.
    Ekström, Madeleine
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Mekanisk metallografi.
    Zhu, B.
    Szakalos, P.
    Jonsson, Stefan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Mekanisk metallografi.
    High-temperature corrosion of materials for cast exhaust components2014Ingår i: 7th European Corrosion Congress, 2014Konferensbidrag (Övrigt vetenskapligt)
  • 314.
    Ekström, Madeleine
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Mekanisk metallografi.
    Zhu, B.
    Scania.
    Szakalos, Peter
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Jonsson, Stefan
    An electrochemical impedance spectroscopy study on the effect of condensate on oxides formed on a 25Cr/20Ni cast stainless steel in exhaust environmentsManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

     Condensation of diesel exhaust gases inside an exhaust- or turbo manifold may occur during cold-start and cooling of an engine, resulting in acidic liquid covering the oxide surfaces inside the manifolds. In the present study, the interaction between a chloride-containing exhaust-gas condensate of pH 2.4 and oxide scales formed on a 25Cr/20Ni cast stainless steel in air and in two different exhaust environments, 10%H2O-5%O2-85%N2 and 10%H2O-5%CO2-85%N2, at 900°C has been examined by means of electrochemical impedance spectroscopy, EIS. Interpretation of impedance spectra was coupled to oxide scale structures, revealed by SEM, EDX, XRD and GDOES, and to metal release studies using ICP. It was observed that the acidic condensate caused oxide spallation, followed by corrosion of the underlying metal surface for all test samples. The metal release rate of the oxide scale and underlying alloy was found to decrease at longer immersion times (>1h), most likely due to precipitation of corrosion products on the surfaces. EIS combined with equivalent circuit fitting showed to be a useful technique in describing the electric properties of the oxide scales, suggesting oxidation in H2O/O2 to result in formation of oxide scales being more resistive compared to the other environments. This was coupled to higher thickness and higher defect density, which correlated well with oxide scale analysis.

  • 315.
    El-Bealy, Mostafa O.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processteknologi.
    Influence of direct chill casting process variables on surface quality of aluminum alloy sheet ingots2012Ingår i: Light Metals 2012, John Wiley & Sons, 2012, s. 1107-1112Konferensbidrag (Refereegranskat)
    Abstract [en]

    Surface defects formation and their effects on the surface quality of aluminum direct-chill cast sheet ingots have been investigated by metallographic examinations and mathematical modeling. The influence of process variables such as alloy composition, casting speed and lubricant on the surface defects especially extruded surface segregation layer has been determined. The metallographic study for collected samples of plant trials involved visual, micro-examinations and macrosegregation analysis. A 2-D mathematical model has been developed to characterize the thermal, solidification, interdendritic strain and macrosegregation distributions. Also, the model contained a new approach to evaluate qualitatively the macrosegregation formed during dendritic solidification. The model predications were compared to measurements from collected samples to verify the model, where a good agreement was obtained. The model predications illustrate that all the process variables tested have an observed effect on the surface quality by different levels. The mathematical analysis of strain fields as well as metallographic study has been used to explain and discuss the effects of different process variables on the surface quality.

  • 316.
    El-Bealy, Mostafa Omar
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processteknologi.
    Advanced solute conservation equations for dendritic solidification processes: Part I: Experiments and theory2013Ingår i: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 84, nr 6, s. 565-583Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The macrosegregation formed in dendritic equiaxed structure during early stages of solidification of Al-4.5%Cu alloy has been studied by experimental work and by metallurgical study of cast samples taken from the experimental work. An experimental work was conducted to study the coupled effect of natural convection streams, interdendritic strain and mushy permeability of Al-4.5%Cu aluminum alloy solidified in horizontal rectangular parallelepiped cavity at different superheats. The metallurgical study includes macro-microstructure evaluation, measurements of grain size of equiaxed crystals and macrosegregation analysis. This study shows that the level of surface segregation exhibiting as positive segregation varies with superheat whereas the rest of inner ingot areas show the light fluctuation in segregation values. In addition to experimental work, there is a mathematical study which contains a complete derivation of local solute redistribution equations based on Fleming's approach under different solute diffusion mechanisms in the dendritic solid. This derivation includes also the effects of interdendritic strain and mushy permeability on the local solute redistribution distribution. Owing to the length of the study, it is presented in two parts. The first part describes the experimental work and its results as well as a detail derivation of solute conservation equations. This part also involves comparison and discussion between existing and proposed solute conservation equations. The second part contains the mathematical analyses of a two dimensional mathematical model of fluid flow, heat flow, solidification, interdendritic strain and macrosegregation. Also, this part also contains the numerical simulations by using finite difference technique "FDT" to create convection patterns, heat transfer, interdendritic strain, and macrosegregation distributions. This part also includes comparisons between the available measurements and model predications as well as full discussion of different model simulations. The mechanism of interdendritic strain generation and macrosegregation formation during solidification of dendritic equiaxed structure under different diffusion mechanisms in dendritic solid has also been explained and discussed. Macrosegregation in dendritic equiaxed structure during the early stages of solidification of Al-4.5%Cu alloy has been studied experimentally. The metallurgical study includes macro-microstructure evaluation, measurements of grain size of equiaxed crystals, and macrosegregation analysis. In addition to the experimental work, there is a mathematical study which contains a complete derivation of local solute redistribution equations based on Fleming's approach under different solute diffusion mechanisms in the dendritic solid.

  • 317.
    El-Bealy, Mostafa Omar
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processteknologi.
    Advanced solute conservation equations for dendritic solidification processes part II: Numerical simulations and comparisons2013Ingår i: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 84, nr 6, s. 584-606Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The mathematical model of derived solute equations in part I for equiaxed dendritic solidification with melt convection streams and interdendritic thermo-metallurgical strain is applied numerically to predict macrosegregation distributions with different diffusing mechanisms in dendritic solid. Numerical and experimental results are present for solidification of a Al-4.5% Cu alloy inside horizontal rectangular cavity at different superheats. The numerical simulations were performed by using simpler method developed by Patanker. The experiments were conducted to measure the cooling curves via thermocouples and the metallurgical examinations to measure the grain size and macrosegregation distributions in Part I. Preliminary validity of the model is demonstrated by the qualitative and quantitative agreements between the measurements and predications of cooling curves and predicted macrosegregation distributions including mushy permeability and interdendritic strain. In addition, several important features of macrosegregation in equiaxed dendritic solidification are identified through this combined experimental and numerical study. Also, quantitative agreements between the numerical simulations and experiments reveal several areas for future research work. The differences and errors between predicted macrosegregation results under different diffusing mechanisms have been discussed. The mathematical model of derived solute equations in Part I for equiaxed dendritic solidification with melt convection streams and thermal is applied numerically to predict macrosegregation distributions with different diffusing mechanisms in dendritic solid. Numerical and experimental results are present for solidification of a Al-4.5% Cu alloy inside horizontal rectangular cavity at different superheats.

  • 318.
    El-Bealy, Mostafa Omar
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Metallernas gjutning.
    Initial development of micro-shrinkage crack during early stages of direct chill casting of Al-4.5% Cu Alloy2016Ingår i: TMS Light Metals, The Minerals, Metals, and Materials Society, 2016, s. 657-662Konferensbidrag (Refereegranskat)
    Abstract [en]

    An investigation has been carried out under controlled laboratory conditions designed to approximate the conditions encountered during the early stages of direct chill of Al-4:5% Cu aluminum alloy ingots to study the formation of micro- shrinkage crack. Also, a couple models have been established at the author's organization to compute convection patterns, thermal fields, interdendritic thermo-metallurgical strain and macrosegregation distributions. Comparisons between the available microstructure taken from the samples and model predictions of convection streams to verify the mechanism of the random sedimentation of free crystals and therefore the micro-shrinkage crack formation were performed where good agreements were obtained. The effects of convection streams of various melt superheats at different locations in the aluminum ingots on the formation micro-shrinkage crack have been studied and analyzed. The mechanism of micro-shrinkage crack formation with different convection streams patterns and superheats were also discussed.

  • 319.
    El-Bealy, Mostafa Omar
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processteknologi.
    Insulated sprayed roll technique "ISRT" and solid shell resistance of inner quality of continuously cast steel slabs2011Ingår i: Mater. Sci. Technol. Conf. Exhib., MS T, 2011, s. 743-750Konferensbidrag (Refereegranskat)
    Abstract [en]

    In order to get a better inner quality of continuously cast steel slabs, insulated sprayed roll technique by using a ceramic material has been developed to increase the slab thermo-mechanical rigidity against the thermo-mechanical stresses. The idea behind this technique is to increase the slab solid shell resistance "Ic" by optimizing the homogeneity of cooling conditions between a pair of rolls. This is by minimizing a rapid fluctuation in the surface temperature between rolls especially at roll contact area. The mathematical model of thermal, solidification, solid shell resistance and cooling conditions has been developed. The model predications indicate that the increasing in the thickness of this layer "δC" or decreasing its thermal conductivity "κC" is proportional to decreasing the surface temperature peak at roll contact area. The predications also point out that the improving of the solid shell resistance depends on the optimum selection of δC and κC with cooling conditions between rolls. Also, the predications were used to explain and discussed the mechanism of characteristics of insulated layer with Ic and thermo-mechanical rigidity of steel slab. Copyright

  • 320.
    El-Bealy, Mostafa Omar
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Modeling of Heat Transfer and Interdendritic Strain for Exuded Surface Segregation Layer in the Direct Chill Casting of Aluminum Alloys2016Ingår i: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 47, nr 1, s. 630-648Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This investigation on the formation of exuded surface segregation layer "ESSL" is intended to provide experimental and simulated comparison to verify the model developed previously by El-Bealy. Preliminary verification and calibration of the previous 2D mathematical model are demonstrated by quantitative errors between the previous measurements and predictions of temperature and macrosegregation. Also, the results from these comparisons reveal that the errors are in the reasonable and within allowable limits. These comparisons lead to the fact that the exuded surface segregation layer mostly forms on the middle slice of broad sheet ingot face and in the early stages of mold zone. The model predictions point out also that the different interdendritic strain hypotheses associated with fluctuations of mold cooling conditions. This affects the interdendritic liquid flow between the equiaxed crystals which influences the severity of ESSL formation and its macrosegregation level. The mechanism of ESSL with heat flow and interdendritic strain generation has been analyzed and discussed. The quantitative comparisons between the pervious experimental results and numerical simulation in this investigation reveal also several solutions to prevent this defect for future work.

  • 321. El-Bealy, Mostafa Omar
    Modelling of heat flow and interdendritic crack formation in twin-roll strip casting of aluminium alloys2016Ingår i: Canadian metallurgical quarterly, ISSN 0008-4433, E-ISSN 1879-1395, Vol. 55, nr 1, s. 23-44Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Preliminary mathematical analyses of different interdendritic cracks associated with variation of heat transfer and generation of interdendritic strain in horizontal twin-roll strip casting have been investigated. A 1-D transient finite difference model of heat flow, dendritic solidification and interdendritic thermo-metallurgical strain has been developed. The model contains two cracking criteria to predict qualitatively and quantitatively the tendency of interdendritic crack formation during dendritic solidification of pure aluminium and 6022 aluminium alloy. The model predictions are compared to available analytical methods and previous measurements. This is to verify and calibrate the model where good and reasonable agreements are obtained, respectively. The variations of heat transfer modes during different contact cooling zones and their effects on the generation of interdendritic thermo-metallurgical strain at the surface and central strip locations have been analysed. The model predictions point out that the different contact cooling zones of strip surface and surroundings control the stages of interdendritic crack formation in different mushy regions. The mechanism of interdendritic crack formation in twin-roll strip casting process with previous and present cracking criteria have been explained and discussed. These discussions show the importance of selection of mathematical treatment to predict the stages of interdendritic crack formation. 

  • 322.
    El-Bealy, Mostafa Omar
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processteknologi.
    On the formation of interdendritic cracking phenomena in direct chill casting of aluminum alloy slabs2008Ingår i: TMS Light Met., 2008, s. 721-725Konferensbidrag (Refereegranskat)
    Abstract [en]

    The formation of interdendritic crack of continuously cast aluminum alloy slabs has been studied by macrosegegation analysis of cast samples and by performing a set of mathematical analyses of heat flow, solidification, interdendritic strain and interdendritic cracking criteria. The study has revealed that the interdendritic cracking phenomena depends mainly on the interdendritic coherernt region width and the accumulated interdendritic strain generated due to various cooling conditions during dendritic solidification process. Interdendritic crack is expected in the positive segregation areas where the tensile strain is present. The morphology of this crack depends mainly on the kind, degree and pattern of macrosegregation.

  • 323.
    El-Bealy, Mostafa Omar
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processteknologi.
    On the Formation of Interdendritic Internal Cracks During Dendritic Solidification of Continuously Cast Steel Slabs2012Ingår i: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 43, nr 6, s. 1488-1516Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this study of solidification during the continuous casting of steel slabs, the effect of the different spray cooling conditions on the interdendritic internal cracks formed between the columnar dendrites has been examined by a metallographic study of the slab samples and by performing a set of mathematical analyses. The metallographic study involved plant trials to measure the slab surface temperature within different secondary spray cooling conditions. Also, macro/microexaminations of the collected samples from plant trials, measurements of dendrite arm spacing, and interdendritic distance between the columnar dendrites, as well as a segment length of interdendritic crack, have been performed. The experimental results show that the morphology of the interdendritic cracks described by the segment width and length fluctuate with the distance from the slab surface based on the secondary spray cooling conditions. A one-dimensional mathematical model of the heat transfer, solidification, structure evolution, interdendritic strain, and elementary interdendritic area (EIA) has been developed. This model takes into account also calculating the width of interdendritic crack. The model predictions are in a good agreement with the measurements. The results pointed out also that this criterion can be considered as the most important tool to measure the inner quality of the continuously cast steel slabs. Therefore, it helps also to define the required mechanism and reduction level of hot working deformation to close these interdendritic internal cracks. The formation mechanism of these cracks during the dendritic solidification of continuously cast steel slabs has been discussed and the available solutions have been proposed.

  • 324.
    El-Bealy, Mostafa Omar
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processteknologi.
    On the Formation of Macrosegregation and Interdendritic Cracks During Dendritic Solidification of Continuous Casting of Steel2014Ingår i: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 45, nr 3, s. 988-1017Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The aim of the current article is to elucidate the significant effects of macrosegregation distribution and its level on the different stages of interdendritic crack formation during dendritic solidification in continuously cast steel slabs. Couple formations of macrosegregation and interdendritic crack phenomena during dendritic solidification of peritectic carbon steels have been investigated by metallographic study of collected slab samples and by performing a set of mathematical analyses. The metallographic study involved plant trails to measure slab surface temperature of different secondary spray cooling conditions. Also, macro-microexaminations, measurements of dendrite arm spacing, macrosegregation analysis, and interdendritic distance between the dendrites of collected samples from plant trials have been performed. The experimental results show a fluctuation of carbon segregation with respect to distance from slab surface. These results also reveal that the interdendritic cracks vary with this fluctuation in various nano, macro, and microscales based on the cooling conditions. A mathematical model of heat transfer, solidification, structure evolution, interdendritic strain, macrosegregation, and elementary interdendritic area "EIA" has been developed. This model takes also into account the calculating of interdendritic distance between the dendrites "IDD" to evaluate the interdendritic crack width. The model predictions of different thermal and solidification phenomena show a good agreement with measurements. The results pointed out also that the coupled effect of interdendritic strain and macrosegregation phenomena and their distributions can be considered as the most important tools to evaluate the surface and internal interdendritic cracks in continuously cast steel slabs. The formation mechanisms of different types of interdendritic crack with interdendritic strain patterns and fluctuation of macrosegregation levels during various cooling zones have been explained, and the possible solutions to these problems have been discussed.

  • 325.
    El-Bealy, Mostafa Omar
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processteknologi. Department of Materials Processing and Technology, ASU, Egypt .
    On the mechanism of mechanical soft reduction and macrosegregation quality criteria of continuous casting of steel2014Ingår i: AISTech - Iron and Steel Technology Conference Proceedings, 2014, Vol. 3, s. 2959-2967Konferensbidrag (Refereegranskat)
    Abstract [en]

    In order to study the central quality of continuously cast tool steel slabs, the mathematical model has been developed to simulate the quality criteria. The model calculates different quality criteria such as average macrosegregation level criterion "ASL", its average fluctuation level "FSV and its average segregation quality number "SQN" of different segregated elements. These criteria were calculated based on the previous measurements in central areas of lower and upper slab sides. These measurements of carbon and sulfur concentrations were performed by chemical analysis technique. The effect of mechanical soft reduction technique "MSR" on the central quality of slab was also examined and studied. The model predications illustrated that this technique affects the centerline quality significantly by different ways based on the casting speed. These predications pointed out also that the macro-segregation quality criteria and their distributions can be considered as the most simple and important tools of steel industries men to explain preventive techniques and formation mechanisms of different defects in slab central area.

  • 326.
    El-Bealy, Mostafa Omar
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processteknologi.
    Spray cooling pattern and microthermomechanical rigidity criterion for improving inner quality in continuously cast steel slabs2013Ingår i: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 40, nr 3, s. 167-188Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A new concept has been developed to assess, and a new technique developed to improve, the microthermomechanical rigidity of the solidifying shell in the secondary cooling zones during continuous casting of steel. This is to maximise the coherent solid shell resistance 'I-c' against thermometallurgical and mechanical stresses at different levels from meniscus. The idea behind this concept is to optimise the degree of homogeneity of the cooling pattern between a pair of rolls. The effect of the degree of homogeneity of the cooling pattern between a pair of rolls 'HDCP', in different spray cooling zones on the different types of centreline segregates has been investigated. A number of plant trials with two different water cooling patterns between a pair of rolls have been performed. The metallographic investigation contains examinations and measurements of the level of centreline segregates of collected samples. A one dimensional (1D) transient finite difference mathematical model of thermal, solidification, solid shell resistance and cooling conditions has been developed to test the different effects of spray patterns on the microthermomechanical rigidity concept and therefore on the mechanism of centreline macrosegregation level. The results indicate that the increase in the degree of homogeneity of the cooling conditions is proportional to the increase in slab internal microquality. The results show that the degree of homogeneity of the cooling pattern affects centreline macrosegregation significantly. This depends significantly on the degree of homogeneity of cooling pattern between a pair of rolls, its location from the meniscus and, generally, on the increase microthermomechanical rigidity concept.

  • 327.
    El-Bealy, Mostafa Omar
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. MTC, Egypt.
    Transient Simulation of Mold Heat Transfer and Solidification Phenomena of Continuous Casting of Steel2016Ingår i: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 47, nr 5, s. 3013-3038Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A comprehensive model of heat transfer and solidification phenomena has been developed including microstructure evolution and fluctuation macrosegregation in continuously cast steel slabs with an objective of evaluation of various mold cooling conditions. The study contains plant trials, metallographic examinations, and formulation of mathematical modeling. The plant trials involved sample collection from three slab casters in use at two different steel plants. The metallographic study combined measurements of dendrite arm spacings and macrosegregation analysis of collected samples. A one-dimensional mathematical model has been developed to characterize the thermal, solidification phases, microstructure evolution, interdendritic strain, and therefore, the macrosegregation distributions. Two cooling approaches were proposed in this study to evaluate the Newtonian heat transfer coefficient in various mold regions. The first approach is a direct estimation approach (DEA), whereas the second one is a coupled approach of the interfacial resistor model and direct estimation approach (CIR/DEA). The model predictions and standard analytical models as well as the previous measurements were compared to verify and to calibrate the model where good agreements were obtained. The comparison between the model predictions and the measurements of dendrite arm spacings and fluctuated carbon concentration profiles were performed to determine the model accuracy level with different cooling approaches. Good agreements were obtained by different accuracy levels with different cooling approaches. The model predictions of thermal parameters and isotherms were analyzed and discussed.

  • 328.
    Elfsberg, Jessica
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processvetenskap.
    Influence of Mould Flux Properties on Early Solidification in Continuous Casting2010Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
  • 329.
    Elfsberg, Jessica
    et al.
    KTH, Tidigare Institutioner                               , Metallernas gjutning.
    Fredriksson, Hasse
    KTH, Tidigare Institutioner                               , Metallernas gjutning.
    Oscillation Mark Formation on Continuously Cast Copper2003Rapport (Övrigt vetenskapligt)
  • 330.
    Elfsberg, Jessica
    et al.
    KTH, Tidigare Institutioner                               , Materialvetenskap.
    Fredriksson, Hasse
    KTH, Tidigare Institutioner                               , Materialens processteknologi.
    Oscillation Mark Formation on Continuously Cast Stainless Steel and Carbon Steel Slabs2003Rapport (Övrigt vetenskapligt)
  • 331.
    Elfsberg, Jessica
    et al.
    KTH, Tidigare Institutioner                               , Metallernas gjutning.
    Fredriksson, Hasse
    KTH, Tidigare Institutioner                               , Metallernas gjutning.
    Theoretical Study of Oscillation Mark Formation in Continuous Casting Processes2003Rapport (Övrigt vetenskapligt)
  • 332.
    Elfsberg, Jessica
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processvetenskap.
    Matsushita, Taishi
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processvetenskap.
    Determination of the interfacial tension between commercial steel grades and mould flux slags by experiments and by empirical modelsIngår i: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344XArtikel i tidskrift (Övrigt vetenskapligt)
  • 333.
    Elfsberg, Jessica
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processvetenskap.
    Seetharaman, Seshadri
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processvetenskap.
    Matsushita, Taishi
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processvetenskap.
    Experimental study of interfacial phenomena between commercial steel and mould flux slag: influence of oxide additions to the mould fluxIngår i: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460Artikel i tidskrift (Övrigt vetenskapligt)
  • 334.
    Elfsberg, Jessica
    et al.
    KTH, Tidigare Institutioner                               , Metallernas gjutning.
    Widell, Björn
    KTH, Tidigare Institutioner                               , Metallernas gjutning.
    Fredriksson, Hasse
    KTH, Tidigare Institutioner                               , Metallernas gjutning.
    Experimental Study of the Formation of Oscillation Marks in Continuous Casting of Steel Billets2002Ingår i: 4th European Continuous Casting Conference, Oct 14-15 2002, Birmingham,England, 2002Konferensbidrag (Övrigt vetenskapligt)
  • 335. El-Geassy, A. A.
    et al.
    Nassir, Nassier Abdul
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processvetenskap.
    Ahmed, H. M.
    Seetharaman, Seshadri
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processvetenskap.
    Simultaneous reduction nitridation for the synthesis of tungsten nitrides from Ni-W-O precursors2013Ingår i: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 56, nr 5, s. 411-419Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Tungsten nitrides were synthesised from NiO-WO3 and NiWO 4 precursors at 973-1273 K in a flow of H2-N2 gas mixture. The reduction-nitridation reactions were carried out isothermally in fluidised bed reactor, and the off-gas from the reactions was continuously analysed by gas chromatography. The effect of reaction temperature and precursor composition on the rate of formation of Ni-W nitrides was studied. The different phases developed during the reduction-nitridation reactions were identified by X-ray diffraction analysis technique. The morphology and the grain structure of the precursors were examined by SEM, and the elemental composition in the structure was analysed by electron dispersive spectrometry. The results showed that the reduction of Ni-W-O precursors proceeded in a stepwise manner (NiWO4→Ni-WO3→Ni-WO2→Ni-W). Tungsten nitrides (WN and WN2) were formed from the reaction of the freshly reduced W metal with N2 gas and WN was the predominant phase detected at higher temperatures. The reaction mechanisms were elucidated from the apparent activation energy values and the application of different formulations derived from the gas-solid reaction model at early and later stages of reactions. It was concluded that the interfacial chemical reaction is the rate determining step at initial stages, while a combined effect of gaseous diffusion and interfacial chemical reaction controlled the reaction at later stages. At final stages, the nitridation reactions contributed to the reaction mechanism leading to produce tungsten nitrides.

  • 336. El-Geassy, A. A.
    et al.
    Seetharaman, Seshadri
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Synthesis and characterization of nano-structured molybdenum-iron intermetallics by gas-solid reaction technique2016Ingår i: IOP Conference Series: Materials Science and Engineering, Institute of Physics Publishing (IOPP), 2016, Vol. 119, nr 1, artikel-id 012012Konferensbidrag (Refereegranskat)
    Abstract [en]

    Ammonium molybdate and ferrous oxalate were used for the synthesis of nano-structured Mo-Fe intermetallics. Co-precipitation technique was applied to produce Mo/Fe precursors containing 58/42, 72/28 and 30/70 mass% respectively. The different phases formed were identified by XRD. The macro- and microstructures were microscopically examined by Reflected Light Microscope (RLM) and Scanning Electron Microscope (SEM) coupled with Electron Dispersion Spectroscopy (EDS). TG-DTA-DSC technique was applied to follow up the behavior of precursors up to 900oC (10K/min.). Endothermic peaks were detected at 97.8, 196.9 and 392.7oC due to the decomposition reactions to produce MoO3 and Fe2O3. The exothermic peak resulted at 427.8oC is due to the solid state reaction between these oxides to form Fe2(MoO4)3. Precursors were isothermally reduced at 600-850oC in a flow of purified H2 and the O2-weight loss from the reduction reactions was continuously recorded as a function of time. The isothermal reduction behavior of precursors was investigated. The structures of reduced products and the different phases formed were investigated and correlated with the reduction conditions. At >60% reduction extents, Fe2(MoO4)3] phase was first reduced to Fe2MoO3O8 before the formation of FeMo, while FeMoO4 and MoO2 were reduced to FeMo and Mo. In precursors containing higher content of Fe2O3, FeMo, Fe3Mo and Fe phases were produced. The visual observation of reduced samples showed that the volume was gradually shrinking with rise in temperature up to 800oC and beyond which a measurable swelling was observed reaching about 170% at 900oC.

  • 337.
    Elger, Ragna
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap. Swerea KIMAB.
    High temperature corrosion in biomass-fired energy applications: Alloying effects and test environment comparisons2016Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    To reduce the greenhouse effect, the use of renewable fuel has to be increased. As renewable fuel has different characteristics compared to fossil fuel regarding content of trace metals, alkali, chlorine and sulphur, the corrosion characteristics in high temperature energy processes have to be evaluated. This thesis concerns high temperature corrosion in the superheater region of a boiler and the syngas cooler area of a gasifier.

    For the superheater region, laboratory exposures were performed. The methods included a salt dip exposure, where samples were dipped in an equimolar solution of ZnCl2 and KCl, and two salt bed exposures with different chlorine concentrations, 10 and 20 wt%. Ranking of the materials showed that a Ni content above 10 wt% and Cr above 20 wt% reduced corrosion rates in the salt dip and in the 10% Cl salt bed exposure. For exposure in the 20% Cl bed, even higher alloying was needed. An alumina forming austenitic steel showed future potential in sulphidising-chlorinating environments.

    For the gasifier region, the effect of HCl in a simulated gasifier atmosphere was studied and also samples exposed in the syngas section of a biomass gasifier were investigated. Metal loss was low for all exposures and it was observed that chlorine had minor influence. For the plant exposed samples, a difference compared to that reported for coal gasifiers was the absence of FeS for the lowest alloyed steel. Instead, a deposit with pronounced content of Zn, Ca, S and O was present on the surface. Zinc was suggested to mitigate corrosion.

    Thermodynamic modelling was used to explain phases present and to predict the nitridation behaviour of an alumina forming austenitic steel. Equilibrium and kinetic modelling of the nitridation showed good coherence with the observed microstructures. However, the kinetic modelling resulted in larger nitridation depths than observed experimentally which was attributed to the presence of a thin oxide layer on the surface of the samples.

  • 338.
    Elger, Ragna
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap. Swerea KIMAB.
    Lindberg, Fredrik
    Swerea KIMAB AB.
    Norling, Rikard
    Swerea KIMAB.
    Pettersson, Rachel
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap. Jernkontoret.
    Exposure of 304L and 310S in chlorinating gasification environments2015Ingår i: Materials at High Temperature, ISSN 0960-3409, E-ISSN 1878-6413, Vol. 32, nr 1-2, s. 36-43Artikel i tidskrift (Refereegranskat)
  • 339.
    Elger, Ragna
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap. Swerea KIMAB.
    Magnusson, Hans
    Swerea KIMAB AB.
    Frisk, Karin
    Swerea KIMAB AB.
    Modelling internal nitridation in an alumina-forming austenitic stainless steel2016Ingår i: Materials and corrosion - Werkstoffe und Korrosion, ISSN 0947-5117, E-ISSN 1521-4176Artikel i tidskrift (Refereegranskat)
  • 340.
    Elger, Ragna
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap. Swerea KIMAB.
    Norling, Rikard
    Swerea KIMAB.
    Pettersson, Rachel
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap. Jernkontoret.
    Corrosion and deposit formation on four steels exposed in the syngas section after a biomass gasifier2016Ingår i: Materials and corrosion - Werkstoffe und Korrosion, ISSN 0947-5117, E-ISSN 1521-4176Artikel i tidskrift (Refereegranskat)
  • 341.
    Elger, Ragna
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap. Swerea KIMAB.
    Pettersson, Rachel
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap. Jernkontoret.
    Effect of Addition of 4% Al on the High Temperature Oxidation and Nitridation of a 20Cr-25Ni Austenitic Stainless Steel2014Ingår i: Oxidation of Metals, ISSN 0030-770X, E-ISSN 1573-4889, Vol. 82, s. 469-490Artikel i tidskrift (Refereegranskat)
  • 342.
    Elger, Ragna
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap. Swerea KIMAB.
    Viklund, Peter
    DEKRA Industrial AB.
    Pettersson, Rachel
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap. Jernkontoret.
    Laboratory testing to evaluate candidate alloys for superheaters in waste-fired boilersIngår i: Materials at High Temperature, ISSN 0960-3409, E-ISSN 1878-6413Artikel i tidskrift (Refereegranskat)
  • 343.
    Eliasson, Anders
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Keramteknologi.
    Interaction behaviour between solid inclusions and solidification front and inclusion behaviour in iron base alloys during teeming and at deoxidation by the Kirkendall Effect2006Rapport (Övrigt vetenskapligt)
  • 344.
    Eliasson, Anders
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Keramteknologi.
    Liquid phase sintering of W-Ni-Fe composites: liquid penetration, agglomerate separation and tungsten particle growth2006Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The initial stage of liquid phase sintering, involving liquid penetration, agglomerate separation, particle spreading and growth has been investigated in experiments using tungsten heavy alloys. The particle composites used were produced by hot isostatic pressing (HIP) of pure powder mixtures of W-Ni-Fe-(Co). By using different HIP temperatures, volume fractions of tungsten, alloying elements like Cobalt and Sulphur or excluding Iron from the matrix, liquid penetration, agglomerate separation and particle growth conditions were affected. The investigations were performed mainly under microgravity (sounding rockets or parabolic trajectories by airplanes) but at high tungsten particle fractions, short sintering times or at infiltration of solid pure tungsten, they were performed at normal gravity. The liquid penetration of the tungsten agglomerates is explained by initial wetting under non-equilibrium conditions, due to the reaction between the liquid matrix and the particles, and a decrease of interfacial energy. The dissolving of tungsten gives a pressure drop in the penetrating liquid and a driving force for the liquid movement by a suggested parabolic penetration model. For cold worked tungsten, a penetration theory was proposed, where an internal stress release in the penetrated tungsten grains creates space for the advancing liquid.

    The spreading of the tungsten agglomerates is explained by an interagglomerate melt swelling due to a Kirkendall effect. The liquid matrix undergoes a volume increase since the diffusion rates of Ni-Fe are higher than for W and initial concentration gradients of W and Ni, Fe exists. The suggested model by Kirkendall are also used for an analysis of the interaction behaviour between solid particles and a solidification front and inclusion behaviour in iron base alloys during teeming and deoxidation.

    The average tungsten particles size decrease initially since part of the tungsten particles is dissolved when the non-equilibrium matrix phase is melting. When equilibrium is reached, the tungsten particles grow in accordance with the Ostwald ripening process by an approximately 1/3 power law. Larger particle fraction of particles showed a higher growth rate, due to shorter diffusion distances between the particles. Cobalt, Sulphur and absence of iron in the matrix were found to increase the growth rate of the tungsten particles due to a higher surface tension between the solid tungsten particles and the matrix melt.

  • 345.
    Eliasson, Anders
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processteknologi.
    Fredriksson, Hasse
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processteknologi.
    Interaction behaviour between alumina particles and solidification front and particle behaviour in iron based alloys at deoxidation by Kirkendall effect2007Ingår i: International Journal of Cast Metals Research, ISSN 1364-0461, E-ISSN 1743-1336, Vol. 20, nr 3, s. 127-130Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The present paper deals with interaction phenomena by particles in liquid metals. The interpretation is to make an initial analysis how the model by Kirkendall, for diffusion phenomena in solids, can be used for the analysis of particle behaviour in liquids. Whenever there is an unequal solutal field, insoluble particles may 'move' due to concentration gradients in the liquid and a difference of diffusion rates of the solute atoms. The analysis deals with the following melt/particles interactions: one is the interaction behaviour between the solidification front and the formed slag oxide particles of Al2O3 and the critical velocity for pushing/engulfment at the interface and the other is the movement and clustering of precipitated alumina inclusions around SiO2 or FeO inclusions formed in a steel melt before deoxidation. Despite the uncertainty of the used material constants and the assumed concentration profiles, the results of the present study are in accordance with some shown experimental particle movements.

  • 346.
    Eliasson, Anders
    et al.
    KTH, Tidigare Institutioner                               , Metallernas gjutning.
    Hailom Yosef, Futsum
    KTH, Tidigare Institutioner                               , Metallernas gjutning.
    Fredriksson, Hasse
    KTH, Tidigare Institutioner                               , Metallernas gjutning.
    Dynamic temperature measurements and solidification structures in centrfugally casted IN718.2003Konferensbidrag (Övrigt vetenskapligt)
  • 347. Eloirdi, R.
    et al.
    Gouder, T.
    Korzhavyi, Pavel A.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Wastin, F.
    Rebizant, J.
    Dilution effect on the U-5f states: U in an Ag matrix2005Ingår i: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 386, nr 1-2, s. 70-74Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The electronic structure of U-diluted in an Ag matrix has been studied in situ by ultraviolet and X-ray photoelectron spectroscopy (UPS and XPS, respectively). UxAg100-x thin films (x = 0-100 at.%) were produced by sputter co-deposition in an Ar atmosphere. UPS spectra of the Ag-4d line indicate formation of a homogeneous mixture despite the fact that U and Ag do not form stable alloys. A major goal of this work was to find out whether the dilution of U atoms in an inert matrix with no bonding states induces the localisation of the U-5f states. Both U-4f core level spectra and the U-5f spectra indicate U-5f delocalisation, down to 5 at.% of uranium in UxAg100-x films.

  • 348.
    Emi, Toshihiko
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processteknologi.
    Improving steelmaking and steel properties2005Ingår i: Fundamentals of Metallurgy, Elsevier Inc. , 2005, s. 503-554Kapitel i bok, del av antologi (Övrigt vetenskapligt)
  • 349.
    Eneborg, Alexander
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Cronqvist, Pontus
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    A Study in Viking Age Brooches using Modern Technology: Simulating the Casting of a Baroque Bronze Brooch in Magma5 5.3.0.42016Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Det är mycket som inte är känt om tillverkningen av vikingatida broscher. Att försöka återskapa dem på samma sätt som vikingarna antagligen skapat dem för att öka kunskapen kring broscherna är ett tidsödande jobb.

     

    Denna studie har gjorts för att ta reda på om den tiden kan reduceras och samtidigt öka kunskapen kring broscherna med hjälp av modern teknik som 3D skanning och datorsimuleringar. Gjutsimuleringar av ett äkta vikingatida spänne har skett i Magma5, ett kraftfullt simuleringsprogram.

     

    Simuleringar utfördes med hjälp av flera olika gjutsystem, stor variation i smältans och formens initiala temperaturer, och både med och utan broschens distal figuriner.

     

    Studien har funnit att smältans och formens temperaturer har påverkan på broschens slutresultat, men legeringen som används och gjutsystemet har betydligt större påverkan på slutresultatet. Gjutsystemet som gav bäst slutresultat har ett inlopp som är placerat direkt över mitten på den mediala delen, och sedan förgrenar sig i två delar och ansluter till den norra och södra delen av formkaviteten.

  • 350.
    Engblom, Eyvind
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Effect of oxygen concentration in build chamber during laser metal deposition of Ti-64 wire2018Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Additive manufacturing of titanium and other metals is a rapidly growing field that could potentially improve component manufacturing through optimization of geometries, less material waste and fewer process steps. Although powder-based additive manufacturing processes have so far been predominant, methods using a wire as feedstock has gained popularity due to faster deposition rates and lower porosity in deposited material. The titanium alloy Ti-6Al-4V accounts for the majority of aerospace titanium alloy consumption and as titanium is a precious and expensive resource, reducing material waste is an important factor.  Laser metal deposition with wire (LMD-w) is currently used in production at GKN Aerospace in Trolhättan. One important process parameter is the oxygen level in the chamber during deposition as titanium is highly reactive with oxygen at process temperatures. Oxygen enrichment of titanium can cause embrittlement and reduced fatigue life due to formation of alpha-case, an oxygen enriched region directly beneath the surface. The oxygen level in the chamber is controlled through extensive use of protective inert gas which is a costly and time-consuming practice. The objective of this thesis was to study how elevated oxygen levels in the chamber would affect surface oxidation, chemical composition, tensile properties and microstructure.  Two different sample geometries were built with Ti-6Al-4V wire at an oxygen level of 100, 500 and 850 ppm. The subsequent analysis was based around microstructural features, alpha-case formation, chemical composition in surface layers, and tensile tests. Results showed that elevated oxygen levels in the build chamber did not degrade the chemical composition or tensile properties with regard to aerospace specifications. However, significant layers of alpha-case were found in all samples indicating that subsequent processing such as machining or etching is needed.

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