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  • 51.
    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.

     

     

  • 52.
    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.

  • 53.
    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.

  • 54. 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)
  • 55.
    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.

  • 56.
    Ratnasari, Devy Kartika
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Yang, Weihong
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology. KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Jönsson, Pär
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Two-stage ex-situ catalytic pyrolysis of lignocellulose for the production of gasoline-range chemicals2018In: Journal of Analytical and Applied Pyrolysis, ISSN 0165-2370, E-ISSN 1873-250X, Vol. 134, p. 454-464Article in journal (Refereed)
    Abstract [en]

    The appropriate system is needed to produce a scalable and economically viable renewable energy from biomass. The objective of this study is to improve the quality of bio-oil, in terms of Organic Liquid Product (OLP), water content, acidity, favourable fractions, as well as gasoline-range chemicals. The influence of a staged layered catalyst system consists of a mesoporous catalyst, Al-MCM-41, and a microporous catalyst, HZSM-5, on the bio-oil quality was investigated. Additionally, the effect of reaction temperatures in the range of 400-600 degrees C with the optimum staged catalyst system on the catalytic pyrolysis product was analysed. The experiments of lignocellulosic biomass pyrolysis and catalytic pyrolysis were performed using a fixed bed reactor equipped with oil condensers and a gas collection sample bag. The quality of bio-oil produced from the thermal pyrolysis of lignocellulosic biomass, catalytic pyrolysis with single catalysts, catalytic pyrolysis with the staged catalyst system, as well as catalytic pyrolysis with mixed catalyst system was studied. The results show that Al-MCM-41 with HZSM-5 in the staged catalyst system enhanced the production of favourable compounds: hydrocarbons, phenols, furans, and alcohols. The favourable compounds yield that boosted 5.25-6.43% of that with single HZSM-5 catalyst was produced with HZSM-5:Al-MCM-41 mass ratio of 3:1 and 7:1. The pyrolysis and catalysis temperature of 500 degrees C with HZSM-5:Al-MCM-41 ratio of 3:1 obtained the optimum quality of bio-oil with 11.08 wt.% of OLP, 76.20% of favourable fractions, 41.97 wt.% of water content, low TAN of 43.01 mg-KOH/g, high deoxygenation, as well as high gasoline-range production of 97.89%.

  • 57.
    Sanet, Jan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Nassar, Hani
    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.
    Hot Working Behaviour of Cast Metal Samples2009Report (Other academic)
  • 58. Tinoco, J.
    et al.
    Widell, Björn
    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.
    Metal spray deposition of cylindrical preforms2005In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 413, p. 56-65Article in journal (Refereed)
    Abstract [en]

    A number of deposition experiments were carried out in a metal spray deposition facility for cylindrical preforms, at Sandvik Steel AB. Thick layers of modified Inconel 625 were sprayed over steel bars 170 mm in diameter and 8 m long. The rods were at room temperature during the deposition process. The effect of rotational velocity and fraction solidified in the spray was studied. Measurements of grain length intercept and porosity content were performed, as well as estimations of the shape of the actual deposition profile. Microprobe analysis was accomplished in different locations on the samples. A computational fluid dynamic model is implemented together with a continuum heat transfer model in order to facilitate the analysis. The range of the rotational velocity studied did not show any large effect on the formation of the base porosity. Three main zones were identified in the microstructure, i.e. porous-dendritic, transition and equiaxed. The segregation patterns suggested that a chemical homogenization occurred during the process. This was supported by the results of the numerical calculations.

  • 59. Zhang, H.
    et al.
    Nakajima, Keiji
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Su, M.
    Shibata, H.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Wang, W.
    Lei, H.
    Wang, Q.
    Jönsson, Pär
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    He, J.
    Prediction of Influences of Co, Ni, and W Elements on Carbide Precipitation Behavior in Fe–C–V–Cr–Mo Based High Speed Steels2018In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 89, no 10, article id 1800172Article in journal (Refereed)
    Abstract [en]

    The effects of Co, Ni together with W addition on the precipitation sequence, amount, and composition of carbides and FCC matrix in Fe–C–V–Cr–Mo based alloys are investigated with the help of Partial Equilibrium (PE) approximation and thermodynamic calculations as well as differential scanning calorimetry (DSC) and electron backscatter diffraction (EBSD) - energy dispersive spectrometer (EDS) analyses. Results show that, individually, Co and Ni elements strengthen the matrix by their great solubility in FCC matrix; W element enlarges the hardness of the alloy through benefiting the formation of M6C carbide. Mutually, the addition of Co and Ni together with W increases the precipitation temperature of the eutectic carbides, although the addition of Co and Ni itself exerts little influence on the nature (type, amount, and composition) of the carbides. These predictions combined with the experimental verifications provide potentials for the alloy design and the property control in high speed steels.

  • 60. Åberg, J.
    et al.
    Vynnycky, M.
    Fredriksson, Hasse
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Heat-flux measurements of industrial on-site continuous copper casting and their use as boundary conditions for numerical simulations2009In: Transactions of the Indian Institute of Metals, ISSN 0019-493X, Vol. 62, no 4-5, p. 443-446Article in journal (Refereed)
    Abstract [en]

    An embedded sensor, designed for rapid and accurate response times and using wireless data transmission, has been developed for the on-site measurement of temperatures in industrial continuous casting moulds. The sensor has been used to measure the temperature at several points in the mould during production in a Southwire copper casting process. The measured data has been used to calculate the temperature gradient in the mould to estimate the heat flux through it; this is then used as a boundary condition for numerical simulations of solidification. For these, we employ a method that tracks the solidification front explicitly; this has an advantage over fixed-grid methods in simulations for materials having a short solidification interval, since the release of latent heat at the solidification front can be resolved without resorting to a very fine mesh. The special considerations required for setting the initial condition for the numerical scheme and the time taken for the superheated melt to form a solid shell are also discussed.

  • 61.
    Åberg, Jonas
    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.
    An On-site Industrial Experimental Heat Flux Study during Solidification of Pure Copper in the Southwire Process2007In: T INDIAN I METALS, ISSN 0972-2815, Vol. 60, no 2-3, p. 191-196Article in journal (Refereed)
    Abstract [en]

    To study the production of pure copper and copper alloys in the Southwire process the temperature in the mould has been measured on-site in the production process in a number of positions. To increase the accuracy and robustness of measurements a new type of thermocouple based temperature sensor has been developed and tested. The test system includes wireless transmission of measured data from the moving mould. The results from the measurements are then used to calculate the energy transfer rate from the solidifying shell as a function of time. An initial in-situ measurement campaign has been performed and the results are very promising.

  • 62.
    Åberg, Jonas
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Vynnycky, Michael
    KTH, School of Engineering Sciences (SCI), Centres, Faxén Laboratory.
    Widell, Björn
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Development of a finite element model for study of the developing stress and strain in a solidifying shell2006Report (Other academic)
  • 63.
    Åberg, Jonas
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Widell, Björn
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Fredriksson, Hasse
    Intrinsic Material Damping in Mg, Al and Fe Alloys and a Discussion of its Dependence on the Internal Structure of the Material2006Report (Other academic)
  • 64.
    Åberg, Jonas
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Widell, Björn
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Larsson, Petra
    Investigation of the Damping in Twelve Metallic Plates Using Frequency Response2006Report (Other academic)
12 51 - 64 of 64
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