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  • 1.
    Gustafsson, Emil
    Dalarna University, School of Technology and Business Studies, Materials Technology. Luleå tekniska universitet.
    Experiments on Sheet Metal Shearing2013Licentiate thesis, comprehensive summary (Other academic)
  • 2.
    Gyhlesten Back, Jessica
    Dalarna University, School of Technology and Business Studies, Materials Technology. Luleå tekniska universitet, Material- och solidmekanik.
    Modelling and Characterisation of the Martensite Formation in Low Alloyed Carbon Steels2017Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The current work contains experimental and theoretical work about the formation of martensite from the austenitic state of the steel Hardox 450. Simulation of rolling and subsequent quenching of martensitic steel plates requires a model that can account for previous deformation, current stresses and the temperature history, therefore dilatometry experiments were performed, with and without deformation. Two austenitization schedules were used and in the standard dilatometry the cooling rates varied between 5-100 °C/s, in order to find the minimum cooling rate that gives a fully martensitic microstructure. Cooling rates larger than 40°C/s gave a fully martensitic microstructure. The cooling rate of 100 °C/s was used in the deformation dilatometry tests where the uniaxial deformation varied from 5-50 %. The theoretical work involved modelling of the martensite formation and the thermal/transformation strains they cause in the steel. Characterizations were done using light optical microscopy, hardness tests and electron backscatter diffraction technique. The parent austenite grains of the martensitic structure were reconstructed using the orientation relationship between the parent austenite and the martensite. Kurdjumov-Sachs orientation relationships have previously been proven to work well for low-carbon steels and was therefore selected.

    The standard implementation of the Koistinen-Marburger equation for martensite formation and a more convenient approach were compared. The latter approach does not require the storage of initial austenite fraction at start of martensite formation. The comparison shows that the latter model works equally well for the martensite formation. The results showed that the use of martensite start and finish temperatures calibrated versus experiments for Hardox 450 works better when computing thermal expansion than use of general relations based on the chemistry of the steel.

    The results from deformation dilatometry showed that deformation by compressive uniaxial stresses impedes the martensite transformation. The simplified incremental model works well for deformation with 5 % and 10 %. However, the waviness in the experimental curve for deformation 50 % does not fit the model due vi to large barrelling effect and the large relative expansion for the material that the sample holders are made of.

    Crystallographic reconstruction of parent austenite grains were performed on a hot-rolled as-received reference sample and dilatometry samples cooled with 60 °C/s and 100 °C/s. The misorientation results showed that the samples match with the Kurdjumov-Sachs orientation relationship in both hot rolled product and dilatometry samples. When misorientation between adjacent pixels are between 15° and 48°, then the boundary between them was considered as a parent austenite grain. The austenitic grain boundaries of the sample cooled at 100 °C/s is in general identical with the hot rolled sample when considering high angle boundaries (15°-48°). The results from the hardness tests showed that the rolled product exhibits higher hardness as compared to samples cooled by 100 °C/s and 60 °C/s. This can be attributed to the formation of transition-iron-carbides in the hot rolled product due to longer exposure of coiling temperature.

  • 3.
    Gyhlesten Back, Jessica
    Dalarna University, School of Technology and Business Studies, Materials Technology. Luleå tekniska universitet.
    Simplified Implementation of the Koistinen-Marburger Model for Use in Finite Element Simulations2016In: Proceedings of the 11th international congress on thermal stresses, Severino: Edizioni Paguro , 2016, p. 107-110Conference paper (Other academic)
  • 4.
    Gyhlesten Back, Jessica
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology. Research and Development, SSAB Europe, Borlänge.
    Engberg, Göran
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Investigation of parent austenite grains from martensite structure using EBSD in a wear resistant steel2017In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 10, no 5, article id 453Article in journal (Refereed)
    Abstract [en]

    Crystallographic reconstruction of parent austenite grain boundaries from the martensitic microstructure in a wear resistant steel was carried out using electron backscattered diffraction (EBSD). The present study mainly aims to investigate the parent austenite grains from the martensitic structure in an as-rolled (reference) steel sample and samples obtained by quenching at different cooling rates with corresponding dilatometry. Subsequently, this study is to correlate the nearest cooling rate by the dilatometer which yields a similar orientation relationship and substructure as the reference sample. The Kurdjumov-Sachs orientation relationship was used to reconstruct the parent austenite grain boundaries from the martensite boundaries in both reference and dilatometric samples using EBSD crystallographic data. The parent austenite grain boundaries were successfully evaluated from the EBSD data and the corresponding grain sizes were measured. The parent austenite grain boundaries of the reference sample match the sample quenched at 100 °C/s (CR100). Also the martensite substructures and crystallographic textures are similar in these two samples. The results from hardness measurements show that the reference sample exhibits higher hardness than the CR100 sample due to the presence of carbides in the reference sample.

  • 5.
    Hall, Josefin
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Beglund, Tomas
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Influence of microstructure and hard phase content on the mechanisms of deformation and wear of HIP:ed Stellite® 190 composites2015Conference paper (Refereed)
  • 6.
    Hall, Josefin
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Fletcher, J. S.
    Canovic, S.
    Malmberg, Per
    Comparing depth profiling of oxide scale on SOFC interconnect-materials using ToF-SIMS with 69Ga+, Bi3+/Cs+ and C60+/C602+ as primary and sputter ions2015In: Materials at High Temperatures, ISSN 0960-3409, Vol. 32, no 1-2, p. 133-141Article in journal (Refereed)
    Abstract [en]

    Oxide scale cross-sections of CeO2 coated FeCr based solid oxide fuel cell interconnect materials were examined using secondary ion mass spectrometry (SIMS) depth profiling. A duplex spinel∶chromia scale was formed after 1 h at 850°C. Ti and ceria were observed between these layers. Additionally, minor concentrations of Mn, Si and Nb were observed at the oxide/metal interface. Furthermore, Al and Ti were concentrated primarily in the metal surface close to the oxide/metal interface. Secondary ion mass spectrometry sputter depth profiles using different ion sources; 69Ga+, Bi3+/Cs+ and C60+/C602+ were compared with TEM oxide scale cross-section and field emission gun–Auger electron spectroscopy depth profiling. Secondary ion mass spectrometry depth profiling with 69Ga+, Bi3+/Cs+ showed decreased secondary ion yields in the metallic matrix. This decrease could be avoided using oxygen flooding. The C60cluster ion depth profiles were less sensitive to type of matrix and gave the best correspondence to the TEM cross-section. However, the impact energy has to be high enough to avoid carbon deposition.

  • 7.
    Keränen, Elias
    Dalarna University, School of Technology and Business Studies, Material Science.
    Experimental and modelling ofmachining behavior of stainlesssteel in interrupted cutting withcoated cemented carbide2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Understanding the chip formation process and the loads that the tools are subjected to in intermittent cutting operations of stainless steel are of importance in order to increase the span of the tool life. Examples of improvements that would follow an increased tool life are reduced use of materials, decreased energy consumption, increased productivities and increased quality of the finished product.A study has been carried out to increase the understanding of chip formation process and what conditions the cutting tool is exposed to in metal cutting in the stainless steel 316L under intermittent conditions. Wear and wear rates of the cutting tools used in these conditions are determined by mechanical and thermal fatigue caused by the stress and temperature cycles. A number of different substrates with varying carbide grain size and cobalt content were included to find the beneficial properties of the cemented carbide. The study includes both practical cutting tests and simulations done in AdvantEdge with varying feed and cutting speed.A preliminary version of a power law based temperature dependent model including damage evolution has been proposed. The model was able to predict chip segmentation but failed to capture the non-linear relation between segmentation parameters and cutting speed.Simulations showed that the tool exit generates tensile stresses in the rake face of the tool which may result in fracture of the cutting edge. These stresses are caused by the footing phenomena that alter the chip formation momentarily during the tool exit.Tests also showed that it is difficult to predict tool life in milling operations of the stainless steel 316L. Chipping proved to be a dominant wear mechanism of the cemented carbide. Tough substrates with a coarse grain size and high cobalt content proved to be beneficial in terms of wear rates and tool life.

  • 8.
    Stenström, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    Deposited copper as lubrication when drawing of titanium wire; a study of method.2016Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    This work performed at Sandvik Materials Technology has studied the possibility of using copper as lubrication during Ti-wire drawing. A PVD-method was used to deposit Cu on Ti-wires. The PVD coated copper samples were compared to a reference material of solid Cu which first had to be recrystallized. Different reduction combinations were investigated in the wire drawing and the Cu-coated wires were drawn both without and with MoS2 lubrication. Values, including drawing forces, HV and tensile testing, from already drawn Ti-wires without Cu were included in the matrix and the drawing forces were then compared. Significant contributions of friction were present in the first draw of all unlubricated Cu-coated Ti-wires. The forces decreased considerably after the first draw. After four drawings, done on one of these wires, the forces then were in the same region as the lubricated wires at the same reductions. No clear tendencies of uneven hardening were observed regardless of friction or used reduction. Tensile testing after wire drawing could not be performed as the wires broke at the wrong places. Measurements of residual stress on worked and unworked Cu-layers showed no residual stress, surprisingly. This study shows that Cu can be used as lubrication if the process is optimized with respect to Cu layer thickness, drawing tool-angles and reduced tungsten carbide grain size in drawing tools. A smoothening draw is needed before reduction of the Ti-wire to help lower the friction.

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