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  • 1.
    Alipour, Yousef
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Machining of CoCr28Mo62011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The machining process of Cobait-Chromium medical ailoys become a veryessential topic for research due to widening range of application. They aregeneraily used because of their high wear resistance, low corrosioncharacteristics and high fatigue strength. This project describes an investigationof chip formation during the machining of Cobalt-Chromium-Molybdenum highcarbon alloy. A quick stop device has been employed to investigate mechanismof chip formation through analyzing of shear zone and shear plane. Thicknessmeasurement of segments, surface conditions after finishing, lowest valley andhighest peak with three different cutting tool inserts were studied as weil.Moreover cutting force measurement at different cutting speeds, feeds and radialnoses were performed. Microstructure and hardness of work material before andafter machining has been studied. Tool life of inserts was evaluated bymeasuring flank wear.

    The consequences obtained from the study illuminated:

    1. For the constant cutting speed and nose radius flank wear increased whenthe feed increased.
    2. For the constant feed and nose radius, increase in the cutting speedlowered flank and crater wear.
    3. Cutting force increased with the increase in feed.
    4. Increase in cutting speed to 40 m/min raised cutting force. However afterthat cutting force decreased.
    5. Insert CNMG 120408-MF1 TS2000 with cutting data v~=70 m/min, ap= 3mm and f=0.1 mm seemed fit the best in base of lower flank and craterwear, almost lower cutting force and smoother finish roughness.
  • 2. Antonsson, T.
    et al.
    Fredriksson, Hasse
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    The effect of cooling rate on the solidification of INCONEL 7182005In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 36, no 1, p. 85-96Article in journal (Refereed)
    Abstract [en]

    The superalloy INCONEL 718 (IN718) is a commonly used material in aerospace and turbine components. The advantage of this type of material with sluggish precipitation-hardening kinetics is that IN718 is readily weldable. Both wrought and cast parts are used and welded together. While the alloy has been studied previously, new production processes such as laser treatment demand better knowledge of the solidification process in IN718. especially at high cooling rates. In this investigation. the solidification process was studied over a wide range of cooling rated by three different experimental techniques: differential thermal analysis (DTA), mirror furnace (MF), and levitation casting. The solidification sequence and the reaction temperatures were identified. The microstructure and the change in growth morphology were also studied. Segregation measurements were performed, and the distribution of Nb was analyzed in detail for the different types of samples. because of its strong impact on the solidification sequence and microstructure. New observations are that the latent heat decreases and the effective partition coefficient increases with increasing cooling rate. The diffusion rate also seems to be enhanced in the first part of primary solidified dendrites. It is suggested that the new observations can be explained by an increased number of lattice defects formed in the solid as the cooling rate increases.

  • 3.
    Carlsson, Leo
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Using Multilayer Perceptrons asmeans to predict the end-pointtemperature in an Electric ArcFurnace2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 4.
    Cendekia, Bintang Bergas
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing. KTH Royal Institute of technology.
    The Effect of Electromagnetic Stirring and Flow Control Devices on Eight-Strand Tundish Performance2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The strand similarity and inclusion removal capability are two critical parameters to measure the performance of multi-strand tundish in clean steel production. In this work, the effect of two flow regulators, i.e., Flow Control Devices (FCD) and Electromagnetic Stirring (EMS) on eight-strand tundish performance have been investigated by establishing a water model and conducting numerical simulations of water model. The water model was focused on revealing the effect of stirring while the simulation was employed to investigate the effect of two FCDs, namely baffle wall and turbo-stopper. The analysis of strand similarity and inclusion removal were conducted by analyzing flow characteristics derived from Combined Model of Residence Time Distribution (RTD) curve and observing the flow movement in the tundish model. In addition, the tundish capability to remove inclusions was also studied by injecting inclusion particles using Discrete Phase Model (DPM) in ANSYS Fluent. Experiment results cause the Combined Model needs to be modified. This modification was employed when analyzing tundish configuration involving stirring. By using the modified Combined Model, the stirring can significantly increase the well-mix volume to almost 100% as it annihilates dead zone. The stirring also increases the similarity between strands and makes the RTD curve more similar to ideal mixing curve.  However, the problem of short-circuiting flow need to be solved and care should be taken into consideration regarding the selection of stirring direction as well as bath surface condition when implementing EMS in reality. The simulation results show that the addition of baffle wall and turbo-stopper are beneficial to improve mixing as well as to avoid the short-circuiting flow. Furthermore, compared to individual FCD, the combination of baffle wall and turbo-stopper results in the best performance to remove inclusions by providing surface-directed flow and generating a higher plug flow.

  • 5. Dhindaw, B. K.
    et al.
    Kumar, L.
    Alkarkhi, N. C. Amer
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Fredriksson, Hasse
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Microstructure development and solute redistribution in aluminium alloys under low and moderate shear rates during rheo processing2005In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 413, p. 156-164Article in journal (Refereed)
    Abstract [en]

    Microstructural features and microsegregational behaviour of solute are studied in shear or stir-cast aluminium alloys under low and moderate shear rates. Alloys studied are Al-6.2% Cu, Al-7.3% Si and Al-13.2% Mg. In all the cases, microstructures of the primary pre-quench solid for stir-cast samples show rosette or ellipsoidal morphologies. Volume fractions of pre-quenched solid phase show significantly higher values for stir-cast alloys as compared to calculated. Microsegregation studies by microprobe analysis along the grains of the samples solidified under different treatment conditions show that stir casting changes the segregation pattern significantly. Except for Al-13.2% Mg alloys lower values than those calculated by Scheil's microsegregation equation are observed for other systems. A model for microstructure evolution during stir casting is presented. The microsegregation patterns have been discussed in terms of interaction between the diffusing solute and the vacancies migrating from solid into liquid.

  • 6.
    El-Bealy, Mostafa O.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Air-Water Mist and Homogeneity Degree of Spray Cooling Zones for Improving Quality in Continuous Casting of Steel2011In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 82, no 10, p. 1187-1206Article in journal (Refereed)
    Abstract [en]

    A theoretical investigation used previous experimental works for validation of model predications and for studying the effect of different nozzle designs on the quality of continuously cast steel slabs has been undertaken. This is by optimizing the homogeneity degree of cooling pattern "HDCP'' between a pair of rolls. The idea behind this technique is to maximize the solid shell resistance against thermo-metallurgical and mechanical stresses and therefore minimizes the defects generated in different cooling zones. A 2-D mathematical model of thermal, solidification, solid shell resistance and cooling conditions has been developed. The model determines the temperature distributions, the different phases associated with the solidification and three phase peritectic reaction L + delta -> gamma of Fe-0.12%C steel alloy as well as isotherms. The effect of different cooling patterns for various spray cooling systems on the homogeneity degree and solid shell resistance are examined. In additional to traditional water and air-water (AWM) nozzles, a new design of air-water mist nozzle has been proposed to improve the homogeneity degree of spray cooling system. The results indicate generally that the increasing in the homogeneity degree of cooling conditions is proportional to the increasing in the solid shell resistance and therefore to the improving of slab quality. Model predications of different effects of different nozzle designs on the surface and inner quality levels are compared and discussed in the mold and secondary spray cooling zones.

  • 7.
    El-Bealy, Mostafa O.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Influence of direct chill casting process variables on surface quality of aluminum alloy sheet ingots2012In: Light Metals 2012, John Wiley & Sons, 2012, p. 1107-1112Conference paper (Refereed)
    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.

  • 8.
    El-Bealy, Mostafa Omar
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Advanced solute conservation equations for dendritic solidification processes: Part I: Experiments and theory2013In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 84, no 6, p. 565-583Article in journal (Refereed)
    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.

  • 9.
    El-Bealy, Mostafa Omar
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Advanced solute conservation equations for dendritic solidification processes part II: Numerical simulations and comparisons2013In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 84, no 6, p. 584-606Article in journal (Refereed)
    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.

  • 10.
    El-Bealy, Mostafa Omar
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Insulated sprayed roll technique "ISRT" and solid shell resistance of inner quality of continuously cast steel slabs2011In: Mater. Sci. Technol. Conf. Exhib., MS T, 2011, p. 743-750Conference paper (Refereed)
    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

  • 11.
    El-Bealy, Mostafa Omar
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    On the formation of interdendritic cracking phenomena in direct chill casting of aluminum alloy slabs2008In: TMS Light Met., 2008, p. 721-725Conference paper (Refereed)
    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.

  • 12.
    El-Bealy, Mostafa Omar
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    On the Formation of Interdendritic Internal Cracks During Dendritic Solidification of Continuously Cast Steel Slabs2012In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 43, no 6, p. 1488-1516Article in journal (Refereed)
    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.

  • 13.
    El-Bealy, Mostafa Omar
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    On the Formation of Macrosegregation and Interdendritic Cracks During Dendritic Solidification of Continuous Casting of Steel2014In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 45, no 3, p. 988-1017Article in journal (Refereed)
    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.

  • 14.
    El-Bealy, Mostafa Omar
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing. Department of Materials Processing and Technology, ASU, Egypt .
    On the mechanism of mechanical soft reduction and macrosegregation quality criteria of continuous casting of steel2014In: AISTech - Iron and Steel Technology Conference Proceedings, 2014, Vol. 3, p. 2959-2967Conference paper (Refereed)
    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.

  • 15.
    El-Bealy, Mostafa Omar
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Spray cooling pattern and microthermomechanical rigidity criterion for improving inner quality in continuously cast steel slabs2013In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 40, no 3, p. 167-188Article in journal (Refereed)
    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.

  • 16.
    Eliasson, Anders
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Ekbom, L.
    Fredriksson, Hasse
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Tungsten grain separation during initial stage of liquid phase sintering2008In: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 51, no 4, p. 343-349Article in journal (Refereed)
    Abstract [en]

    The initial stage, the first few seconds of liquid phase sintering has been investigated in experiments using a tungsten heavy alloy with low tungsten content. The heavy alloy has been melted in a temperature gradient for short periods, similar to 9 s in an ellipsoid mirror furnace. During the liquid phase sintering at about 1470 degrees C, a penetration followed by a remarkably rapid separation and dispersion of the tungsten grains by the molten matrix occur. The suggested explanation for this grain separation and dispersion is based on the effect of composition gradients in the liquid matrix and a theory based on interagglomerate melt swelling due to a Kirkendall effect.

  • 17.
    Eliasson, Anders
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Fredriksson, Hasse
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Interaction behaviour between alumina particles and solidification front and particle behaviour in iron based alloys at deoxidation by Kirkendall effect2007In: International Journal of Cast Metals Research, ISSN 1364-0461, E-ISSN 1743-1336, Vol. 20, no 3, p. 127-130Article in journal (Refereed)
    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.

  • 18.
    Emi, Toshihiko
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Improving steelmaking and steel properties2005In: Fundamentals of Metallurgy, Elsevier Inc. , 2005, p. 503-554Chapter in book (Other academic)
  • 19.
    Emi, Toshihiko
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Fredriksson, Hasse
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    High-speed continuous casting of peritectic carbon steels2005In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 413, p. 2-9Article in journal (Refereed)
    Abstract [en]

    Productivity of an integrated steel plant is improved by high-speed casting of hypo-peritectic steels that makes the productivity of caster meet basic oxygen furnace. In high-speed casting, however, strands of the steels tending to form cracks on the shell in the mold, require off-line conditioning that limits the plant productivity and premium yield. Hypo-peritectic transformation occurring on solidification in mold results in irregular shell-surface roughness that causes non-uniform heat transfer to the mold, causing local lifting of the shell from the mold, recalescence, and surface cracks. Influential factors are summarized on the development of the surface roughness, the non-uniform heat transfer and the decline of mechanical properties of the shell upon recalesce. Effective means are presented to reduce the non-uniformity and the cracks at high casting speeds by controlling the properties of mold flux film infiltrating into the solidifying shell/mold boundary.

  • 20. Formenti, A.
    et al.
    Eliasson, Anders
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Mitchell, A.
    Fredriksson, Hasse
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Solidification sequence and carbide precipitation in Ni-base superalloys IN718, IN625 AND IN9392005In: High Temperature Materials and Processes, ISSN 0334-6455, E-ISSN 2191-0324, Vol. 24, no 4, p. 239-258Article in journal (Refereed)
    Abstract [en]

    Differential Thermal Analysis (DTA) and Directional Solidification and Quenching (DSQ) were used to evaluate the solidification and precipitation sequence for the Ni-base superalloys IN718, IN625 and IN939. They all showed a similar precipitation sequence, with an initial precipitation of gamma dendrites, followed by an intermediate non-invariant divorced eutectic reaction of type L -> gamma + MC, and a final eutectic precipitation of Laves phase for alloy IN718 and IN625 and of eta-phase for alloy IN939. The reaction temperatures and the amounts of carbides and of final precipitates were evaluated. Precipitated nitrides were found to act as nucleation sites for the precipitation of blocky carbides/carbonitrides, at low interdendritic supersaturation, while in interdendritic regions with high supersaturation, a 'script-like' carbide formation was found instead.

  • 21.
    Formenti, Angelo
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Eliasson, Anders
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Ceramics.
    Fredriksson, Hasse
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    On the dendritic growth and microsegregation in Ni-base superalloys IN718, IN625 and IN9392005In: High Temperature Materials and Processes, ISSN 0334-6455, E-ISSN 2191-0324, Vol. 24, no 4, p. 221-238Article in journal (Refereed)
    Abstract [en]

    Directional Solidification and Quenching (DSQ) has been used to analyse the solidification, segregation and precipitation behaviour of the Ni-base alloys IN718, IN625 and IN939. The microsegregation in the primary solidified gamma-phase was analysed by Energy Dispersive Spectroscopy (EDS) and were mainly found to be Nb for alloy IN718 and Ti for alloy IN939. The microsegregation behaviour were analysed by numerical back diffusion models and it was found that the diffusion rate in the samples was higher than expected from the theory. A suggested explanation was that this was an effect of the formation of lattice defects during the solidification process. The coarsening process that occurs during the further cooling of the samples is proved to be by the mechanism of back diffusion i.e. the smaller secondary dendrite arms grow together with the thicker ones into a plate.

  • 22.
    Fredriksson, Hasse
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Fredriksson, E.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    A model of liquid metals and its relation to the solidification process2005In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 413, p. 455-459Article in journal (Refereed)
    Abstract [en]

    X-ray analysis shows that a liquid is build up of clusters of atoms with a certain number of nearest neighbours. The X-ray analysis shows that 8-11 nearest neighbours surround each atom. Each cluster has a crystal-like structure. Between the clusters there are some free atoms and free electrons. The enthalpy of fusion is according to Richard's rule around the gas constant times the temperature of melting and the heat capacity in the liquid state is normally constant and for some metals lower than that in the solid state. For metals with low melting points it will decrease further with increasing temperature. This behaviour of the metals can be explained by the use of statistical mechanics and by assuming that the clusters, observed by X-ray analysis are rotating around a centre of its mass. The cluster model is applied to explain the diffusion rate in liquid metals. The effect of the experimental set upon measurements of diffusion constants is discussed as well as its effect on crystal growth.

  • 23.
    Fredriksson, Hasse
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Haddad-Sabzevar, M.
    Hansson, K.
    Kron, J.
    Theory of hot crack formation2005In: Materials Science and Technology, ISSN 0267-0836, E-ISSN 1743-2847, Vol. 21, no 5, p. 521-529Article in journal (Refereed)
    Abstract [en]

    The hot crack sensitivity in metals is suggested to be caused by the supersaturation of vacancies created during the solidification process. Equations have been derived to predict the nucleation and growth of cracks by the condensation of vacancies. The transition temperature from brittle to ductile fracture was found to be related to the decrease in the supersaturation of vacancies due to an annealing process. The hot crack sensitivity was observed to be related to the supersaturation of vacancies, the diffusion rate, and the structure coarseness. The effect of surface active elements such as phosphorous and sulphur in steel alloys is discussed.

  • 24.
    Fredriksson, Hasse
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Stjerndahl, J.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Tinoco, J.
    On the solidification of nodular cast iron and its relation to the expansion and contraction2005In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 413, p. 363-372Article in journal (Refereed)
    Abstract [en]

    Directional solidification and quench-out thermal analysis experiments have been performed in Mg-treated cast iron alloys. The volume fraction of liquid, allstenite and graphite was evaluated. It was observed that the volume fraction of austenite is much larger than expected from the equilibrium phase diagram at the beginning of the solidification process. It was also been observed that the last melt solidifies far below the equilibrium eutectic temperature. The solidification process was analyzed by non-equilibrium thermodynamic models. The theoretical treatment was supported by the observation that the latent heat decreases during the solidification process. The formation of small pores was observed at the very end of the solidification. An explanation for the formation of the small pores is given in terms of a vacancies creep model. The formation of macropores was related to the large fraction of austenite formed during the first part of the solidification process.

  • 25.
    Gharehbaghi, Ali
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Precipitation Study in a High Temperature Austenitic Stainless Steel using Low Voltage Energy Dispersive X-ray Spectroscopy2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Precipitation of second phase particles is a key factor dominating the mechanical properties of high temperature alloys. In order to control and optimize the precipitation effect it is of great importance to study the role of alloying elements in the formation and stability of precipitates. As a favored family of corrosion and creep resistant austenitic stainless steels the 20Cr-25Ni alloy was modified by addition of copper, molybdenum, nitrogen, niobium and vanadium. A set of alloys with similar matrix but varying contents of niobium, vanadium and nitrogen were prepared. Sample preparation process included melting, hot forging, solution annealing and finally aging for 500 h at 700, 800 and 850 ºC.Light optical and scanning electron microscopy revealed micron-scale precipitates on grain and twin boundaries as well as sub-micron intragranular precipitates in all samples. Characterization of precipitates was carried out by means of energy dispersive X-ray spectroscopy (EDS). Among micron-scale precipitates M23C6 carbide was the dominant phase at 700 ºC aging temperature; whereas silicon-rich eta phase (M5SiC) was the main precipitate in samples aged at 800 and 850 ºC. A few sigma phase particles were found in one of the niobium containing samples aged at 700 and 800 ºC. Sub-micron intragranular precipitates were analyzed using low voltage EDS. The spatial resolution of EDS microanalysis at 5 kV accelerating voltage was estimated as almost 100 nm which was at least eight times better than that using the ordinary 20 kV voltage. Also, low voltage EDS revealed the presence of light elements (carbon, nitrogen and boron) in the composition of sub-micron particles thanks to the less matrix effect in absorption of low energy X-rays of light elements. In samples aged at 700 ºC niobium-rich and vanadium-rich carbonitrides were found as the dominant precipitates; whereas they contained much less carbon in samples aged at 800 ºC and mostly became carbon-free nitrides with well-defined cuboidal shapes at 850 ºC aging temperature. This showed that niobium/vanadium-rich nitride phases are stable precipitates at aging temperatures above 700 ºC.The drawbacks of low voltage EDS were indicated as high detection limit (no detection of low- content elements), poor accuracy of quantitative analysis and high sensitivity to surface contamination. Some possible ways to improve the accuracy of low voltage EDS, e.g. longer acquisition time were examined and some other suggestions are proposed for future works.

  • 26.
    Gharehbaghi, Ali
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Precipitation Study in a High Temperature Austenitic Stainless Steel using Low Voltage Energy Dispersive X-ray Spectroscopy2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Precipitation of second phase particles is a key factor dominating the mechanical properties of high temperature alloys. In order to control and optimize the precipitation effect it is of great importance to study the role of alloying elements in the formation and stability of precipitates. As a favored family of corrosion and creep resistant austenitic stainless steels the 20Cr-25Ni alloy was modified by addition of copper, molybdenum, nitrogen, niobium and vanadium. A set of alloys with similar matrix but varying contents of niobium, vanadium and nitrogen were prepared. Sample preparation process included melting, hot forging, solution annealing and finally aging for 500 h at 700, 800 and 850 ºC.

    Light optical and scanning electron microscopy revealed micron-scale precipitates on grain and twin boundaries as well as sub-micron intragranular precipitates in all samples. Characterization of precipitates was carried out by means of energy dispersive X-ray spectroscopy (EDS). Among micron-scale precipitates M23C6 carbide was the dominant phase at 700 ºC aging temperature; whereas silicon-rich eta phase (M5SiC) was the main precipitate in samples aged at 800 and 850 ºC. A few sigma phase particles were found in one of the niobium containing samples aged at 700 and 800 ºC. Sub-micron intragranular precipitates were analyzed using low voltage EDS. The spatial resolution of EDS microanalysis at 5 kV accelerating voltage was estimated as almost 100 nm which was at least eight times better than that using the ordinary 20 kV voltage. Also, low voltage EDS revealed the presence of light elements (carbon, nitrogen and boron) in the composition of sub-micron particles thanks to the less matrix effect in absorption of low energy X-rays of light elements. In samples aged at 700 ºC niobium-rich and vanadium-rich carbonitrides were found as the dominant precipitates; whereas they contained much less carbon in samples aged at 800 ºC and mostly became carbon-free nitrides with well-defined cuboidal shapes at 850 ºC aging temperature. This showed that niobium/vanadium-rich nitride phases are stable precipitates at aging temperatures above 700 ºC.

    The drawbacks of low voltage EDS were indicated as high detection limit (no detection of low- content elements), poor accuracy of quantitative analysis and high sensitivity to surface contamination. Some possible ways to improve the accuracy of low voltage EDS, e.g. longer acquisition time were examined and some other suggestions are proposed for future works.

  • 27.
    Hailom Yosef, Futsum
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Fredriksson, Hasse
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    On the peritectic reaction of iron based binary alloys2005Report (Other academic)
  • 28.
    Hulme-Smith, Christopher
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing. University Of Cambridge.
    Pickering, Ed
    University of Cambridge.
    Steeling the Show2012In: The Naked Scientists: Science Articles and FeaturesArticle, review/survey (Other (popular science, discussion, etc.))
  • 29.
    Jaradeh, Majed
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Carlberg, Torbjörn
    Analysis of solidification in a Bridgman furnace as a simulation of DC casting of aluminium alloy slabs2007In: Materials Science and Technology, ISSN 0267-0836, Vol. 23, no 4, p. 475-482Article in journal (Refereed)
    Abstract [en]

    The vertical Bridgman directional solidification equipment has been used in several investigations to simulate direct chill casting of wrought aluminium alloys. As a basis for such investigations and alloy developments, it is important to have an understanding of the performance of the furnace used during simulation of the casting conditions. In this investigation the thermal conditions in the furnace have been analysed in detail, both by measurements and by mathematical modelling. The growth characteristics of the furnace, such as gradient, growth rates and cooling rates have been compared to conditions in large ingots. The direct chill casting conditions, which the simulations have been compared to, are casting of slabs of 330 and 600 mm thickness of an aluminium AA3003 type alloy. The results show that the experiments are able to simulate the cooling conditions in the ingots except from the surface zone. Comparisons of the microstructures have been made and a good agreement has been obtained for structure parameters such as grain size and DAS.

  • 30.
    Jonnalagadda, Krishna Praveen
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Influence of Graphite type on copper diffusion in P/M copper steels2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    One main reason for the use of Fe-Cu-C system in PM industry is the presence of liquid phase (copper) at the start of sintering (1120oC). The diffusion of liquid copper into iron causes swelling in the structure. This in turn can cause high dimensional change and, if not controlled properly, may cause distortion. So it is of paramount importance to control the copper diffusion. Carbon, added as graphite, reduces the swelling of copper by changing the dihedral angle. The affect of graphite on copper diffusion depends on the graphite type, particle size of graphite and heating rate. The aim of this work was to find the influence of graphite type and particle size of graphite on copper diffusion. Water Atomized iron (ASC100.29) produced in Höganäs AB was taken as the base powder.  Two types of graphite were used each with two different particle sizes. Two different graphite quantities (0.2% & 0.8%) for each type was taken. Natural fine graphite (UF4), Natural coarse graphite (PG44), Synthetic fine graphite (F10) and  Synthetic coarse graphite (KS44) were the graphites used in this work. Powders were compacted at 600 Mpa and the sintering was done at 1120oC for 30 minutes in 90/10 N2/H2. Dilatometry and metallographic investigation of the samples sintered in the production furnace were used to understand the graphite influence.

     

    The investigation showed that at low graphite levels (0.2%), the affect of graphite type or graphite size was not significant on copper diffusion. At high graphite levels (0.8%),  synthetic graphites were more effective in reducing the swelling of copper. Influence of  particle size of synthetic graphites on Cu diffusion was not significant compared to the influence of particle size of natural graphite. There was also a considerable affect of heating rate on graphite dissolution and copper swelling.

     

     

  • 31.
    Khan, Fareed Ashraf
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Casting of Metals. KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Melt stirring nodular cast iron2017In: 11th International Symposium on the Science and Processing of Cast Iron, (SPCI-XI), Jönköping, 2017 / [ed] Attila Diószegi, Vasile Lucian Diaconu and Anders E W Jarfors, Switzerland, 2017Conference paper (Refereed)
    Abstract [en]

    In this work the effects of stirring/vigorous shearing on matrix and graphite phase in nodular cast iron melt during solidification were studied. Several experiments were conducted for different cooling and stirring times. Samples were prepared and examinations of the microstructure were conducted and compared using Leica Optical Microscope and Scanning Electron Microscope (SEM). In addition, a chemical analysis of the graphite precipitate was performed using EDX equipment mounted on SEM. Oxidation of the melt and formation of oxide nuclei during stirring were observed and analysed. The influence of melt shearing on the structure, nodule count, distribution, area fraction and on overall graphite precipitation was observed and examined with the help of respective computer programs and soft wares. Stirring resulted in increasing the nucleation sites for graphite precipitation thereby increasing the nodule count and area fraction of carbide and transforming the structure from pearlitic matrix to ferritic matrix

  • 32.
    Khan, Fareed Ashraf
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Casting of Metals. KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Some aspects of convection as well as graphite and carbide formations during casting.2018Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    It is an established fact that segregation during casting affects the physical properties of carbon-based ferro alloys; this motivates the study of the segregation behaviour of carbon and carbide-forming solute elements. In this context, this thesis investigates two different situations: the effects of cooling rate and turbulence on the precipitation behaviour of the graphite nodules in nodular cast iron; the nature of carbide precipitation in a bearing steel grade and the effects of subsequent soaking on these carbides.

    The structures of boiling water reactor inserts cast by the uphill and downhill casting of nodular cast iron were examined. The samples were taken from representative locations in the top, middle and bottom cross sections of the castings. It was observed that in uphill-cast inserts the nodules were larger but fewer in number the bottom section, whereas in downhill-cast inserts the nodules in the bottom section were smaller, but greater in number. Variation in volume fraction of the graphite nodules across the inserts was also observed. The probable cause of this variation was the difference in cooling rate in different sections of the insert. Between the steel tubes located at the central part of the casting, the fraction of graphite was lower, which could be the result of carburization of the steel tubes.

    To study the effects of melt stirring during the solidification of nodular cast iron, several experiments were conducted at variable cooling rates and for different stirring times. Examination of the microstructure was conducted using Light Optical Microscope (LOM) and Scanning Electron Microscope (SEM). It was observed that during stirring the melt oxidized and oxide nuclei were formed. The number of nucleation sites for the precipitation of graphite nodules increased, which raised the nodule count and the fraction of the graphite precipitated. The matrix transformed from pearlite to ferrite, which could be due to the fact that more carbon had diffused out of the matrix.

    The segregation behaviour in hypereutectoid bearing steel produced by ingot casting was also studied. The effects of soaking on micro and macro segregation was investigated in samples taken from as cast and soaked ingots; emphasis was laid on the bulk matrix and A-segregation channels. Samples were also taken from ingots which were soaked and then hot worked. The micro and macro examination of the microstructure was conducted using LOM and SEM. Quantitative and qualitative composition analysis was performed using Energy-dispersive X-ray spectroscopy (EDX) and an electron micro probe analyzer (EMPA). It was observed that M3C, M2C and M6C had precipitated. The carbide morphology in the bulk matrix was different to that in the A-segregation channels. All the primary carbides in the bulk matrix were found to have dissolved after 4 hours of soaking at 1200oC.

  • 33.
    Khan, Fareed Ashraf
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Casting of Metals. KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Structure investigation of downhill and uphill casted inserts.In: Svensk kärnbränslehantering, ISSN 1651-4416Article in journal (Refereed)
    Abstract [en]

    The cast structure has been analyzed in one downhill and one uphill casted insert. Samples on different positions in cross sections of the inserts have been investigated on three different positions form bottom to top of the inserts. The fraction, the size and the number of graphite nodules have been measured. The fraction of porosities as well as the pore size was evaluated. It was found that the size of the nodules was larger and the numbers were fewer in the bottom of the uphill casted insert. The opposite was observed for the downhill casted one. The volume fraction and the size of the porosities followed the numbers and the size of the nodules. The larger the nodules were the larger was the pores and its fraction.

     

    The volume fraction and the numbers of graphite nodules also varied across the insert. These variations were close to independent of the height. This was explained as a difference in cooling rates in different parts of the cross section, depending on the cooling of the melt from the steel tubes in the central part of the inserts. The volume fraction of graphite nodules was lower between the steel tubes probably as a result of carburizing the steel tubes.

    A large fraction of oxide inclusions was observed in both the inserts. Those are formed during the casting operation due to a strong convection during the mold filling operation.

  • 34.
    Khan, Fareed Ashraf
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Casting of Metals. KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    The effect of soaking on segregation and primary-carbide dissolution in an ingot-cast bearing steel.In: Article in journal (Refereed)
    Abstract [en]

    In this work the segregation in the cast- and hot worked structure, as well as the effects of soaking on macro and micro segregation, in hypereutectoid bearing steel produced by ingot casting were studied. Samples were selected from ingots that where either as cast or soaked for twenty hours. Two similar bearing steel grades were used for this investigation. For the as cast ingot, samples were selected from both A-segregation channel regions and the matrix region. Samples were also selected from hot-worked bars originating from ingots that had been soaked for four hours or twenty hours.

    Both micro and macro examinations of the microstructures were conducted and compared. In addition, a segregation analysis of the substitutional solute elements was performed using EDX equipment mounted on a Scanning Electron Microscope (SEM). EMPA mapping of the composition pattern in the bulk, as well as the carbides, was conducted. Precipitation of M3C, M2C and M6C was observed. The carbides at A-segregation channels were found to have a different morphology to those precipitated in the bulk matrix. After soaking at 1200oC for 4 hours, all the primary carbides are dissolved.

  • 35.
    Korojy, Bahman
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Ekbom, Lars
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Fredriksson, Hasse
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    On solidification shrinkage of copper-lead and copper-tin-lead alloys2009In: International Journal of Cast Metals Research, ISSN 1364-0461, E-ISSN 1743-1336, Vol. 22, no 1-4, p. 179-182Article in journal (Refereed)
    Abstract [en]

    Solidification shrinkage is an important concept in achieving sound castings. In the present work solidification shrinkage was studied in copper-lead and copper-lead-tin alloys. A series of solidification experiments was performed under different cooling rates using a dilatometer which was developed for melting and solidification purposes. The volume change was measured during primary solidification and the monotectic reaction. In order to explain the volume-changing results, the sample macrostructures were studied to evaluate gas and shrinkage cavities which were formed during the solidification. Furthermore, the volume fraction of the primary phase during solidification was evaluated in the samples that were quenched from different temperatures below the liquidus temperature. A shrinkage model was used to explain the volume changes during solidification.

  • 36.
    Korojy, Bahman
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Fredriksson, Hasse
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    On solidification and shrinkage of brass alloys2009In: International Journal of Cast Metals Research, ISSN 1364-0461, E-ISSN 1743-1336, Vol. 22, no 1-4, p. 183-186Article in journal (Refereed)
    Abstract [en]

    The solidification process was investigated in brass alloys containing a wide range of zinc, between 32.5 and 47.1 wt-%. A series of solidification experiments was performed under different cooling rates using differential thermal analysis (DTA) and a confocal mirror furnace. The cooling rate and the solidification under cooling temperature were evaluated from cooling curves. Furthermore, the peritectic reaction was studied in view of the starting and the ending temperatures and shrinkage behaviour. The volume change was measured in the peritectic alloys using a dilatometer which was developed to investigate the melting and solidification processes. A theoretical analysis was developed to evaluate the volume change effect on the peritectic reaction.

  • 37.
    Korojy, Bahman
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Fredriksson, Hasse
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    On solidification of hypereutectic Al-Si alloys2009In: Transactions of the Indian Institute of Metals, ISSN 0019-493X, Vol. 62, no 4-5, p. 361-365Article in journal (Refereed)
    Abstract [en]

    Precipitation of primary silicon was studied in Al-Si hypereutectic alloys with 15, 18, and 25 wt. % silicon content. The alloys were solidified with different cooling rates from different super heat temperatures. The liquidus and eutectic temperature were evaluated from the cooling curves. The liquidus temperature was found to decrease with cooling rate. The evaluation of microstructure showed that the fraction of primary silicon decreased with increasing the cooling rate and super heat temperature. Furthermore, the morphology of the primary silicon changed as an effect of cooling rate and super heat temperature.

  • 38. Kron, J.
    et al.
    Fredriksson, Hasse
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Measurements and modelling of air gap formation in Cu-based alloys2005In: International Journal of Cast Metals Research, ISSN 1364-0461, E-ISSN 1743-1336, Vol. 18, no 1, p. 21-28Article in journal (Refereed)
    Abstract [en]

    The formation of an air gap has been experimentally studied during solidification of pure Cu, Cu-Te and Cu-6%Sn in a cylindrical mould. The displacements of the casting and the mould causing an air gap have been measured during solidification and cooling of the casting. The temperature distribution was measured simultaneously. Mathematical modelling has been performed to increase the understanding of the solidification process and the shrinkage of the casting leading to air gap formation. A model, which has been tested in earlier work showing good results for aluminium based alloys, has been applied here to describe air gap formation during solidification of copper based alloys. The model includes the effect of the formation and condensation of vacancies on the solidification process as well as on the material shrinkage resulting in air gap formation. The results from the modelling show a reasonable agreement with the experimental measurements.

  • 39. Kron, J.
    et al.
    Lagerstedt, A.
    Fredriksson, Hasse
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Measurements and modelling of air gap formation in aluminium based alloys2005In: International Journal of Cast Metals Research, ISSN 1364-0461, E-ISSN 1743-1336, Vol. 18, no 1, p. 29-40Article in journal (Refereed)
    Abstract [en]

    The formation of an air gap has been experimentally studied during solidification of several aluminium based alloys. Air gap widths and temperature distribution have been measured during solidification in a cylindrical mould. The effect of grain refinement on heat transfer and air gap formation has been studied. Mathematical modelling has been performed to increase the understanding of the solidification process and air gap formation. A model was developed for description of air gap formation in alloys solidifying with varying solidification intervals. The model includes the effect of formation and condensation of lattice defects on the solidification process and air gap formation. The calculated shrinkage using this model shows good agreement with the experimental data.

  • 40.
    Kron, Jenny
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Lagerstedt, Anders
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Fredriksson, Hasse
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Modelling of air gap formation in solidification processing2005In: Transactions of the Indian Institute of Metals, ISSN 0019-493X, Vol. 58, no 4, p. 531-538Article in journal (Refereed)
    Abstract [en]

    Different models are used today to model air gap formation during a solidification process. In this work air gap modelling is discussed with reference to experimental work with air gap measurements during casting. Thermal and thermomechanical modelling were done with thermal boundary conditions found experimentally. The measured displacements of the mould and the solidifying metal were used in order to check the validity of the simulation results and compare it with reality. The description of the thermal shrinkage and its connection to air gap formation is especially discussed. Al- and Fe-based alloys investigated elsewhere have been used in this work.

  • 41.
    Lagerstedt, Anders
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Fredriksson, Hasse
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    A model for prediction of cracks in a solidifying shell2005In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 413, p. 37-43Article in journal (Refereed)
    Abstract [en]

    A model coupling temperature and stress calculations with cracking criteria has been developed in order to predict crack positions in a solidifying shell. The model is based on a one-dimensional FDM approach suitable for continuous casting of slabs. The strain/stress model is based on a purely elastic analysis of a solidifying shell giving a straightforward comparison between stresses and crack criteria. This approach makes the model easy to use. The model is numerically evaluated using available material data for Fe-2%Ni with primary ferrite solidification and Fe-10%Ni with primary austenitic solidification. The results of the calculations are discussed and the impact of material behavior as well as process parameters is evaluated. Evaluation of the influence of changes in the heat transfer coefficient shows that the rapid changes introduce stresses large enough to induce crack formation in the solidifying shell.

  • 42.
    Lagerstedt, Anders
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Kron, Jenny
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Hailom Yosef, Futsum
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Fredriksson, Hasse
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Measurements and modeling of air gap formation in iron-base alloys2005In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 413, p. 44-51Article in journal (Refereed)
    Abstract [en]

    The formation of an air gap has been experimentally studied during solidification of several iron-based alloys. Air gap widths and temperature distribution have been measured during solidification in a cylindrical water-cooled Cu-mold. Mathematical modeling has been performed to increase the understanding of the solidification process and the air gap formation. A model, developed earlier for Al- and Cu-based alloys, for description of air gap formation in alloys solidifying with varying solidification intervals was tested for Fe-base alloys. The model includes the effect of formation and condensation of lattice defects on the solidification process and the air gap formation. The calculated shrinkage using this model shows good agreement with the experimental data.

  • 43. Lee, J.
    et al.
    Shin, M.
    Park, J. H.
    Seetharaman, Seshadri
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Studies of wetting characteristics of liquid Fe-Cr alloys on oxide substrates by sessile drop technique2010In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 37, no 7, p. 512-515Article in journal (Refereed)
    Abstract [en]

    The purpose of this study was to investigate the wetting characteristics of three different oxide substrates (alumina, magnesia and dolomite) in order to examine the work of adhesion of Fe-Cr alloys on these substrates. The contact angle of a liquid drop (Fe-Cr alloy) on the oxide substrates was investigated at 1823 K under a H-2 atmosphere by the sessile drop technique. The contact angle slightly decreased on the alumina and dolomite substrates with increasing chromium concentration, but did not change as much on the magnesia substrate. Among the tested substrates, alumina exhibited the highest contact angle and dolomite exhibited the lowest one. Accordingly, dolomite had the strongest work of adhesion, which was in agreement with the observations in the practical process.

  • 44. Li, Peng
    et al.
    Zhang, Mei
    Wang, Lijun
    Seetharaman, Seetharaman
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Thermal Conductivity of Al–Salt Composites2015In: International journal of thermophysics, ISSN 0195-928X, E-ISSN 1572-9567, Vol. 36, no 10-11Article in journal (Refereed)
    Abstract [en]

    With a view to examine the possibility of estimating the content of entrapped metallic aluminium in the salt cake from aluminium remelting, the thermal diffusivity of reference composites of KCl–NaCl–Al was measured as a function of aluminium metal content at room temperature. The thermal conductivity of the reference composites was found to increase with the metallic Al content. The lumped parameter model approach was carried out to discuss the influence of different geometry arrangements of each phase, viz. air, salts and metallic aluminium on the thermal conductivity. Application of the present results to industrial samples indicates that factors such as the interfacial condition of metallic Al particles have to be considered in order to estimate the amount of entrapped Al in the salt cake.

  • 45.
    Muhmond, Haji Muhammad
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    On the Inoculation and Graphite Morphologies of Cast Iron2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Research was conducted to understand the nucleation mechanism of graphite flakes and nodules and the effect of various elements on the growth morphology of graphite. Investigations were started on flake graphite cast iron. The effect of S on the graphite morphology and MnS was experimentally analysed. The influence of various type of oxides on the growth morphology of MnS and their relation with the graphite growth morphology was studied carefully through series of experiments, and results were related to the thermodynamic calculations, performed to predict the nucleation of oxides and sulfides at any temperature. The calculations were supported by EDX analysis on particles in the samples, showing sequential nucleation of flake graphite. The austenite volume fraction and the dendrite growth orientations were affected by the addition of Al to the melt. The effect of aluminium oxide and sulfur was studied on the austenite growth morphology with the help of colour etching technique. Thermal analyses were performed to study the effect of sulfur content on austenite volume fraction and growth morphology using DSC. The latent heat of solidification and the rate of austenite formation was studied and related to the sulfur content in the alloy.

    To study the effect of O and S on the graphite morphology, pure Fe-C alloy was prepared and strong de-oxidizers and de-sulfurizer (Mg, Ca and Sr) were tested. With the help of ion etching and polishing, we were able to reveal the graphite growth morphology. The morphological changes in the graphite were explained by relating it to the composition of the melt in regard of dissolved S and O in the melt. The effect of other trace elements such as S, F, O, N, P, B and Se, was also investigated by testing them on an ultra-pure Fe-C alloy. The possibility of substituting a foreign atom in the basal plane of graphite was analysed based on the bonding energy between C and the foreign atoms. The resulting change in the structure of the basal plane was studied using Avogadro software and the resulting model were compared with the experimental results. The basal plane of nodular, flake and undercooled graphite was studied with the help of HRTEM, which showed differences in the lattice spacing between different graphite morphologies. The latent heat measurement showed that flake graphite have higher energy than the undercooled or vermicular graphite. This research made us enabled to tell about the growth along c-plane in graphite and the reason behind the transition of graphite morphology.

    The effect of inoculation temperature and inoculation sequence on the nodularity was studied. EDX analysis were performed and the results were compared to the thermodynamic calculations.  It was found that, the melt composition is controlling the graphite growth morphologies. Strong de-oxidizers and de-sulfurizer are necessary to reduce O and S to a level where it does not influence the graphite growth morphology. The effect of various elements on the activity of oxygen in the melt is calculated. High Al cast iron was also studied. The major problem associated with this type of alloy was that, the Mg was not effective in producing nodular graphite. Experiments showed that de-oxidizers stronger than Mg are required to increase the nodularity. Thermodynamic calculations showed that the activity of oxygen in the melt was changing strongly by increasing the Al content in the alloy. This was increasing the required oxygen level to nucleate MgO.

  • 46.
    Nassar, Hani
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    On Peritectic Reactions and Transformations and Hot Forming of Cast Structures2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis deals with peritectic reactions and transformations that occur during the solidification of many alloys. Peritectics are believed to be a major cause of crack-formation in many steels, thus, good knowledge of the mechanisms by which these phenomena occur is essential for preventing such defects. The thesis also handles the behaviour of metals, in particular cast structures, during hot forming. Grain size and microstructure are of most importance in determining the strength, toughness and performance of a steel. For achieving enhanced mechanical and microstructural properties, good understanding of the phenomena occurring during hot forming is required.

    Peritectic reactions and transformations were studied in Fe-base and steel alloys through differential thermal analysis (DTA) experiments and micrographic investigation of quenched DTA samples. The effect of the ferrite/austenite interface strain during the peritectic reaction on equilibrium conditions was thermodynamically analysed, and the results were related to temperature observations from DTA experiments conducted on Fe-base alloys and low-alloy steels. Massive transformations from ferrite to austenite were observed in the micrographs of a number of quenched low-alloy steel samples and it was proposed that these transformations are uncontrolled by diffusion, and occur in the solid state as a visco-plastic stress relief process. DTA study of an austenitic stainless steel indicated that the alloy can exhibit primary precipitations to either ferrite or austenite. A continuously-cast breakout shell of the steel was analyzed and it was suggested that the observed irregularities in growth were due to alternating precipitations of ferrite and austenite; parts of the shell with higher ratios of primary-precipitated ferrite shrink in volume at the peritectic temperature and experience reduced growths.

    An experimental method for studying the behaviour of metals during hot forming developed, and hot compression tests were conducted on cast copper and ball-bearing steel samples. Flow stress curves were obtained at varying temperatures and strain rates, and the results showed good agreement with earlier observations reported in literature. Micrographic analysis of quenched samples revealed variations in grain size and a model was fitted to describe the grain size as a function of deformation temperature and strain.

    Solidification growth during continuous casting of stainless steel and copper was numerically modelled. A varying heat transfer coefficient was proposed to approximate the experimentally measured growth irregularities in the continuously-cast stainless steel breakout shell. Solidification growth of pure copper was also modelled in the Southwire continuous casting process. Temperature measurements from the chill mould were used to approximate the temperature gradient and the heat extraction from the solidifying strand, and the results were used in a two-dimensional model of solidification.

     

     

  • 47.
    Nassar, Hani
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Fredriksson, Hasse
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    On the effect of strain on peritectic reactions and transformations in Fe-Ni and Fe-Cu binary alloys2009In: International Journal of Cast Metals Research, ISSN 1364-0461, E-ISSN 1743-1336, Vol. 22, no 1-4, p. 232-235Article in journal (Refereed)
    Abstract [en]

    Differential thermal analysis (DTA) experiments conducted on Fe-Ni and Fe-Cu alloys showed undercooling below the equilibrium peritectic temperatures, T-P. The intervals between the observed liquidus and peritectic temperatures were on average 11 degrees C and 8 degrees C larger than the intervals obtained from equilibrium phase diagrams of Fe-Ni and Fe-Cu respectively. The transformation from delta-Fe to gamma-Fe during the peritectic reaction is associated with density change and strain build up at the delta-Fe/gamma-Fe interface. Thermodynamic calculations showed that by introducing the strain energy at the delta-Fe/gamma-Fe interface, T-P dropped 9 K below its equilibrium value and the increase in the liquidus-to-peritectic temperature interval was in reasonable agreement with the experimental observations. The growth rate of gamma-Fe during a peritectic transformation was calculated based on the strain-induced undercooling in T-P and the results showed partial agreement with observations obtained from CSLM directional solidification experiments conducted earlier on Fe-Ni alloys.

  • 48.
    Nassar, Hani
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Korojy, Bahman
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Fredriksson, Hasse
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    A study of shell growth irregularities in continuously cast 310S stainless steel2009In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 36, no 7, p. 521-528Article in journal (Refereed)
    Abstract [en]

    Growth irregularities in continuous casting are believed to be associated with crack formation and breakouts. Differential thermal analysis on 310S stainless steel samples indicated primary precipitations of both austenite and ferrite during solidification. In tensile tests on solidifying samples, abrupt shrinkages in volume were detected in the peritectic range of temperatures. Micrographic and microsegregation analysis on samples extracted from a breakout shell revealed high ratios of primary-precipitated austenite in the thick sections of the shell, and high ratios of primary-precipitated ferrite in the thin sections. Alternating precipitations of austenite and ferrite are proposed to occur during solidification. Regions of the shell with high ratios of primary austenite remain in contact with the mould and exhibit high growth rates, whereas regions with high ratios of primary ferrite shrink in volume due to the ferrite to austenite transformation, which results in the formation of air gaps between the shell and the mould and reductions in growth rate.

  • 49. Peet, Mathew James
    et al.
    Hulme-Smith, Christopher
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing. University Of Cambridge.
    Stone, H. J.
    Partitioning and supersaturation of carbon in low-temperature bainite2015In: PTM 2015 - Proceedings of the International Conference on Solid-Solid Phase Transformations in Inorganic Materials 2015, 2015Conference paper (Refereed)
  • 50.
    Ranganathan, Sathees
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Makaya, Advenit
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Fredriksson, Hasse
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Influence of Mo in the structure of rapidly solidified Fe-Mo-Cr-Mn-Si-C alloy2009In: International Journal of Cast Metals Research, ISSN 1364-0461, E-ISSN 1743-1336, Vol. 22, no 1-4, p. 264-267Article in journal (Refereed)
    Abstract [en]

    An Fe-Mo-Cr-Mn-Si-C alloy was prepared in an induction furnace and was cast into cylindrical rod in a copper mould in castmatic equipment (low pressure casting). A single phase non-equilibrium featureless (no visible microstructures after deep etching) phase was observed over a certain range of thickness of the rod. In this present work, the extent of the featureless phase was studied with different concentrations of Mo (5-25 wt-%) for 5.5 mm diameter of cylindrical rod at a cooling rate of 1100 K s(-1). Light optical microscopy, scanning electron Microscopy and Vickers hardness tests were used to analyse the samples. The amount of the featureless area varies as the Mo content changes and the maximum featureless area was obtained for 7 wt-% of Mo. This single phase featureless structure exhibits very high hardness (>1350 HV) which can be used in many interesting applications with or without suitable heat treatments.

12 1 - 50 of 57
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