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  • 1. Avazkonandeh-Gharavol, M. H.
    et al.
    Haddad-Sabzevar, M.
    Fredriksson, Hasse
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Analysis of phase diagram and diffusion coefficient for modeling of microsegregation2017Inngår i: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 52, nr 3, s. 1446-1460Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Thermodynamic description of phase diagram and diffusion data are required to model microsegregation during solidification of metallic alloys. Knowledge about non-equilibrium phase diagrams is essential for modeling of microsegregation in practical situations. Therefore, the aim of this study is to theoretically analyze phase diagram and diffusion data for calculation of microsegregation. For this purpose, aluminum-rich part of the Al-Cu phase diagram was recalculated under non-equilibrium conditions. Effect of excess vacancies formed during solidification was considered on both the phase diagram and diffusion coefficient. The results show that by modifying the phase diagram, the calculated results have better consistency with the experimental results, but there is still room for improvement. When the effect of excess vacancies on diffusion coefficient is considered, the modeling results show a much better correlation with the experimental results. The origin of discrepancies between the calculations and experiments are deeply discussed using current theories in solidification.

  • 2. Avazkonandeh-Gharavol, M. H.
    et al.
    Haddad-Sabzevar, M.
    Fredriksson, Hasse
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Experimental analysis of partition coefficient in Al-Mg alloys2016Inngår i: Iranian Journal of Materials Science and Engineering, ISSN 1735-0808, Vol. 13, nr 2, s. 62-72Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Because the partition coefficient is one of the most important parameters affecting microsegregation, the aim of this research is to experimentally analyse the partition coefficient in Al-Mg alloys. In order to experimentally measure the partition coefficient, a series of quenching experiments during solidification were carried out. For this purpose binary Al-Mg alloys containing 6.7 and 10.2 wt-% Mg were melted and solidified in a DTA furnace capable of quenching samples during solidification. Cooling rates of 0.5 and 5 KJmin were used and samples were quenched from predetermined temperatures during solidification. The fractions and compositions of the phases were measured by quantitative metallography and SEM/EDX analyses, respectively. These results were used to measure the experimental partition coefficients. The resultant partition coefficients were used to model the concentration profile in the primary phase and the results were compared with equilibrium calculations and experimental profiles. The results of calculations based on the experimental partition coefficients show better consistency with experimental concentration profiles than the equilibrium calculations.

  • 3.
    Muhmond, Haji Muhammad
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Fredriksson, Hasse
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Effect of the cooling rate on the graphite nodule count and size distribution in nodular cast iron2018Inngår i: 11th International Symposium on the Science and Processing of Cast Iron, SPCI-XI 2017, Trans Tech Publications, 2018, Vol. 925, s. 45-53Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The graphite nodule count, size distribution and homogenization of the nodules distribution are the factors which are of more significance for the properties of the material. By just increasing the inoculants or Mg will not help to get rid of problems like the un-even size distribution and or increasing the nodule count. The cooling conditions of the melt prior to solidification and during solidification can control these two parameters to a large extent. In this research, it is more emphasized on the nucleation sequence of MgO particles and on the cooling rates. The nucleation of MgO at different temperatures and at different cooling rates was found to have a great influence on the nodule size distribution and the homogenization of the microstructure. A mathematical model was derived to relate the Mg concentration in the liquid to the cooling rate, prior to solidification. The MgO particles count was calculated as a function of cooling rate. It was found that at higher cooling rates, MgO can be nucleated in multi steps during cooling process, which can increase the nodule count tremendously.

  • 4.
    Saleem, Saud
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Metallernas gjutning.
    Fredriksson, Hasse ()
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Metallernas gjutning.
    The influence of peritectic reaction/transformation on crack susceptibility in the continuous casting of steelsInngår i: Metallurgical and Materials Transactions B, ISSN 1073-5615Artikkel i tidsskrift (Annet vitenskapelig)
  • 5.
    Saleem, Saud
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Metallernas gjutning.
    Vynnycky, Michael
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Metallernas gjutning.
    Fredriksson, Hasse
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Metallernas gjutning.
    A Study of the Oscillation Marks’ Characteristics of Continuously Cast Incoloy Alloy 825 Blooms2016Inngår i: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 47, nr 8, s. 4068-4079Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A comprehensive experimental study of oscillation mark (OM) formation and its characteristics during the solidification of Incoloy alloy 825 in the continuous casting of blooms is investigated by plant trials and metallographic study. The experiments involved two heats with the same casting and mold conditions and sampling at different locations across the strand. The metallographic study combined macro/micro-examinations of OMs and segregation analysis of Cr, Mn, Mo, Ni, and Si by microprobe analysis. The results show that OMs have widely different characteristics, such as mark type, depth, segregation, and accompanying microstructure. Furthermore, the mark pitch can vary considerably even for the similar casting conditions, leading to different conditions for the marks’ formation in relation to the mold’s cyclic movement. Finally, a mechanism for the OM formation is discussed and proposed. Possible solutions for minimizing the observed defects by optimizing the mold conditions are suggested.

  • 6.
    Saleem, Saud
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Metallernas gjutning.
    Vynnycky, Michael
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Metallernas gjutning.
    Fredriksson, Hasse
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Metallernas gjutning.
    Effect of casting parameters on the formation of oscillation marks during continuous castingManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    In the present investigation, oscillations marks formed at the surfaces of two different steel grades are studied; this includes metallographic investigation. The characteristics of the marks are examined rigorously, and the analysis is performed serially. The statistical data is compared withanalytical relations and possible reasons for the deviations from the average values are discussed.From the ongoing analysis, it can be seen that the formation of the primary shell is an important parameter which can affect the depth of the depression. Moreover, the results show that theformation of the oscillation marks is a complex phenomenon and that there could be more than one explanation for their formation.

  • 7.
    Saleem, Saud
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Metallernas gjutning.
    Vynnycky, Michael
    KTH, Skolan för teknikvetenskap (SCI), Centra, FaxénLaboratoriet. KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Metallernas gjutning.
    Fredriksson, Hasse
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Metallernas gjutning.
    The Influence of Peritectic Reaction/Transformation on Crack Susceptibility in the Continuous Casting of Steels2017Inngår i: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 48, nr 3, s. 1625-1635Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The work presented here examines the surface cracks that can form during the continuous casting of near peritectic steels due to the volume changes during the peritectic reaction/transformation. The investigated samples were collected during plant trials from two different steel grades. The role and mode of the peritectic reaction/transformation are found to depend on the composition of the alloy, resulting in different types of surface cracks. The effect of the local variation in the cooling rate on the formation of the different types of cracks present in each steel grade, which can be due, for example, to the formation of oscillation marks, is demonstrated. The enhanced severity of the surface and internal oxidation, both of which depend on the alloy composition and consequent peritectic reaction, is highlighted. Experimental and theoretical studies show that different types of surface cracks can occur in peritectic steels depending upon the alloy composition and cooling rate, both of which define the fraction of the remaining liquid upon completion of the peritectic reaction/transformation.

  • 8.
    Tadesse, Abel
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Fredriksson, Hasse
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Metallernas gjutning.
    On the Solidification and Structure Formation during Casting of Large Inserts in Ferritic Nodular Cast Iron2018Inngår i: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 49, nr 3, s. 1223-1235Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The graphite nodule count and size distributions for boiling water reactor (BWR) and pressurized water reactor (PWR) inserts were investigated by taking samples at heights of 2160 and 1150 mm, respectively. In each cross section, two locations were taken into consideration for both the microstructural and solidification modeling. The numerical solidification modeling was performed in a two-dimensional model by considering the nucleation and growth in eutectic ductile cast iron. The microstructural results reveal that the nodule size and count distribution along the cross sections are different in each location for both inserts. Finer graphite nodules appear in the thinner sections and close to the mold walls. The coarser nodules are distributed mostly in the last solidified location. The simulation result indicates that the finer nodules are related to a higher cooling rate and a lower degree of microsegregation, whereas the coarser nodules are related to a lower cooling rate and a higher degree of microsegregation. The solidification time interval and the last solidifying locations in the BWR and PWR are also different.

  • 9.
    Tadesse, Abel
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Fredriksson, Hasse
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    The effects of carbon on the solidification of nodular cast iron- its study with the help of linear variable differential transformer and microstructural analysis2018Inngår i: International Journal of Cast Metals Research, ISSN 1364-0461, E-ISSN 1743-1336, Vol. 31, nr 2, s. 108-117Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The effect of carbon on the solidification of ductile cast iron (DCI) was studied using linear variable differential transducers (LVDT) and microstructural analysis. Thermal expansion during the eutectic solidification was investigated by using LVDT and temperature measurements. The eutectic volume change was compared with the theoretical calculation. Furthermore, the primary austenite during solidification was evaluated by using differential thermal analysis and the samples undergo a dilatometer experimentation to assess the effect of cooling rates. It was found that the samples show no expansion in the transversal direction due to higher micro-shrinkages in the centre whereas in the longitudinal direction the samples shows expansion until solidification completed. The theoretical and measured volume changes agree with each other. The austenite fraction and micro-shrinkage pores decrease with increase in carbon content. The nodule count and distribution changes with carbon content. The thermal contraction of DCI is not influenced by carbon content variation at lower cooling rate.

  • 10.
    Tadesse, Abel
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Fredriksson, Hasse
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    The experimental study of nodular cast iron volume changes during solidification2018Inngår i: 11th International Symposium on the Science and Processing of Cast Iron, SPCI-XI 2017, Trans Tech Publications Inc., 2018, Vol. 925, s. 140-146Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The volume changes during solidification of Nodular Cast Iron (NCI) in the sand mold studied using Linear Variable Differential Transformer (LVDT). Both hypo- and hyper-eutectic compositions are considered by adjusting the carbon fraction in the composition during the experimental studies. The microstructural analysis and measurements are taken from the samples to evaluate the different phases present, the nodule count and size distributions. At the beginning of solidification, the experimental result shows the volume change is negligible. During the eutectic growth, the samples expand until the end of solidification. The displacement measurement shows the expansion continued when solidification finished. The volume change studies during solidification indicate that as the carbon fraction increases the volume expansion decreases. On the other hand, it is found that the pore fraction decreases as the volume expansion decreases. The fraction of primary austenite decreases as the fraction of carbon increases, and that leads to having a lower pore fraction.

  • 11.
    Vynnycky, Michael
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Saleem, Saud
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Metallernas gjutning.
    Fredriksson, Hasse
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Metallernas gjutning.
    An asymptotic approach to solidification shrinkage-induced macrosegregation in the continuous casting of binary alloys2018Inngår i: Applied Mathematical Modelling, ISSN 0307-904X, E-ISSN 1872-8480, Vol. 54, s. 605-626Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The modelling of macrosegregation in the continuous casting of alloys normally requires resource-intensive computational fluid dynamics (CFD). By contrast, here we develop an asymptotic framework for the case when macrosegregation is driven by solidification shrinkage; as a first step, a binary alloy is considered. Systematic asymptotic analysis of the steady-state two-dimensional mass, momentum, heat and solute conservation equations in terms of the shrinkage parameter indicates that the overall problem can be reduced to a hierarchy of decoupled problems: a leading-order problem that is non-linear, and a sequence of linear problems, with the actual macrosegregation of the solute then being determined by means of one-dimensional quadrature. A numerical method that solves this sequence is then developed and implemented, and yields realistic macrosegregation profiles at low computational cost.

  • 12.
    Vynnycky, Michael
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Metallernas gjutning.
    Saleem, Saud
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Metallernas gjutning.
    Fredriksson, Hasse
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Metallernas gjutning.
    Towards an asymptotic framework for solidification shrinkage-induced macrosegregation in the continuous casting of binary alloysManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    The modelling of macrosegregation in the continuous casting of alloysnormally requires resource-intensive computational fluid dynamics(CFD). By contrast, here we develop an asymptotic framework for thecase when macrosegregation is driven by solidification shrinkage; as a firststep, a binary alloy is considered. Systematic asymptotic analysis of thesteady-state two-dimensional mass, momentum, heat and solute conservationequations in terms of the shrinkage parameter indicates that theoverall problem can be reduced to a hierarchy of decoupled problems: aleading-order problem that is non-linear, and a sequence of linear problems,with the actual macrosegregation of the solute then being determinedby means of one-dimensional quadrature.

  • 13. Yang, Wenchao
    et al.
    Fredriksson, Hasse
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Metallernas gjutning.
    Ji, Shouxun
    Halo formation of Zn-Al alloys under conventional solidification and intensive convection solidification2017Inngår i: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 696, s. 460-469Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A halo occurred usually as an envelope of one phase around a primary phase in many alloys after solidification. Its formation mechanism was investigated for hypoeutectic, eutectic and hypereutectic compositions of Zn-Al alloys under conventional solidification and under intensive convection solidification. It was found that the Zn-rich halos occurred in the surroundings of the Al-rich primary phase for the hypereutectic Zn-Al alloys at Al> 5 wt% and no halos occurred for the hypoeutectic and eutectic Zn-Al alloys at Al <= 5 wt% under conventional solidification. However, the Zn-rich halos were completely absent from the Al-rich phase because of the uniform temperature distribution and enhanced mass transport under intensive convection solidification. Once the intensive convection was interrupted during solidification for the solid-liquid co-existing melt, a halo was formed on the surface of the existing Al-rich phase created either during the primary solidification or the eutectic solidification. Therefore, it was concluded that the halo formation should be a growth-dominant phenomenon not a nucleationdominant phenomenon. And, the interaction among the solid phases and the liquid phase was responsible for the halo formation, in which the difference in the elasticity modulus and the density of the different phases resulted in the variation of strain energy in the individual phase.

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