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  • 1.
    Adegoke, Olutayo
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Homogenization of Precipitation Hardening Nickel Based Superalloys2012Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Allvac 718 Plus and Haynes 282 are relatively new precipitation hardening nickel based superalloys with good high temperature mechanical properties. In addition, the weldability of these superalloys enhances easy fabrication. The combination of high temperature capabilities and superior weldability is unmatched by other precipitation hardening superalloys and linked to the amount of the γ’ hardening precipitates in the materials. Hence, it is these properties that make Allvac 718 Plus and Haynes 282 desirable in the manufacture of hot sections of aero engine components.

    Studies show that cast products are less weldable than wrought products. Segregation of elements in the cast results in inhomogeneous composition which consequently diminishes weldability. Segregation during solidification of the cast products results in dendritic microstructure with the segregating elements occupying interdendritic regions. These segregating elements are trapped in secondary phases present alongside γ matrix. Studies show that in Allvac 718Plus, the segregating phase is Laves while in Haynes 282 the segregating phase is not yet fully determined.

    Thus, the present study investigated the effects of homogenization heat treatments in eliminating segregation in cast Allvac 718 Plus and Haynes 282. Paramount to the study was the effect of different homogenization temperatures and dwell time in the removal of the segregating phases. Experimental methods used to both qualify and quantify the segregating phases included SEM, EDX analysis, manual point count and macro Vickers hardness tests.

    Main results show that there is a reduction in the segregating phases in both materials as homogenization proceeds hence a disappearance of the dendritic structure. In Allvac 718 Plus, plate like structures is observed to be closely associated with the Laves phase at low temperatures and dwell times. In addition, Nb is found to be segregating in the interdendritic areas. The expected trend of increase in Laves as a result of the dissolution of the plate like structures at the initial stage of homogenization is only detectable for few cases. In Haynes 282, white and grey phases are clearly distinguished and Mo is observed to be segregating in interdendritic areas.

  • 2.
    Engkvist, Josefin
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Canovic, Sead
    Hellström, Kristina
    Järdnäs, Anders
    Svensson, Jan-Erik
    Johansson, Lars-Gunnar
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Halvarsson, Mats
    Alumina scale formation on a powder metallurgical FeCrAl alloy (Kanthal APMT) at 900-1100 °C in dry O2 and in O2 + H2O2010Inngår i: Oxidation of Metals, ISSN 0030-770X, E-ISSN 1573-4889, Vol. 73, nr 1-2, s. 233-253Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A Rapidly Solidified Powder (RSP) metallurgical FeCrAl alloy, Kanthal APMT, was exposed in dry and humid O2 for 72 h at 900–1,100 °C. The formed oxide scales were characterized using gravimetry in combination with advanced analysis techniques (SEM, EDX, TEM, XRD, AES andSIMS). The oxide scales were at all exposures composed of two-layered α-Al2O3 scales exhibiting a top layer of equiaxed grains and a bottom layer containing elongated grains. A Cr-rich zone, originating in the native oxide present before exposure, separated these two layers. The top α-Al2O3layer is suggested to have formed by transformation of outwardly grown metastable alumina, while the inward-grown bottom α-Al2O3 layer had incorporated small Zr-, Hf- and Ti-rich oxide particles present in the alloy matrix. The scale also contained larger Y-rich oxide particles. Furthermore, in the temperature range studied, the presence of water vapour accelerated alloy oxidation somewhat and affected scale morphology.

  • 3.
    Hall, Josefine
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Berglund, Tomas
    Bexell, Ulf
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Influence of Microstructure and Hard Phase Content on the Mechanisms of Deformation and Wear of HIP:ed Stellite® 190 Composites2015Inngår i: Proceedings of 2015 European powder metallurgy congress, Euro PM 2015, Reims, France, 4-7 October 2015, 2015Konferansepaper (Fagfellevurdert)
  • 4.
    Ismail, Kasimagwa
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Brabie, Voicu
    The use of thermodynamic computations to predict the phase transformation in MgO-C refractories during steel refining2008Inngår i: Refractories Manual, s. 42-47Artikkel i tidsskrift (Fagfellevurdert)
  • 5.
    Jacobson, S
    et al.
    Uppsala Universitet.
    Beste, U
    Uppsala Universitet.
    Heinrichs, J
    Uppsala Universitet.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Wiklund, U
    Uppsala Universitet.
    On the nature of cemented carbide wear in rock drilling2014Inngår i: Hard Rock Tribology Course and Seminar, Tampere, Finland, November 4-5, 2014, 2014Konferansepaper (Annet vitenskapelig)
  • 6.
    Kasimagwa, Ismail
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    A study of slag corrosion of oxides and oxide-carbon refractories during steel refining2010Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The use of ceramic material as refractories in the manufacturing industry is a common practice worldwide. During usage, for example in the production of steel, these materials do experience severe working conditions including high temperatures, low pressures and corrosive environments. This results in lowered service lives and high consumptions of these materials. This, in turn, affects the productivity of the whole steel plant and thereby the cost. In order to investigate how the service life can be improved, studies have been carried out for refractories used in the inner lining of the steel ladles. More specifically, from the slag zone, where the corrosion is most severe. By combining thermodynamic simulations, plant trails and post-mortem studies of the refractories after service, vital information about the behaviour of the slagline refractories during steel refining and the causes of the accelerated wear in this ladle area has been achieved. The results from these studies show that the wear of the slagline refractories of the ladle is initiated at the preheating station, through reduction-oxidation reactions. The degree of the decarburization process is mostly dependent on the preheating fuel or the environment. For refractories without antioxidants, refractory decarburization is slower when coal gas is used in ladle preheating than when a mixture of oil and air is used. In addition, ladle preheating of the refractories without antioxidants leads to direct wear of the slagline refractories. This is due to the total loss of the matrix strength, which results in a sand-like product. Thermal chemical changes that take place in the slagline refractories are due to the MgO-C reaction as well as the formation of liquid phases from impurity oxides. In addition, the decrease in the system pressure during steel refining makes the MgO-C reaction take place at the steel refining temperatures. This reduces the refractory’s resistance to corrosion. This is a serious problem for both the magnesia-carbon and dolomite-carbon refractories. The studies of the reactions between the slagline refractories and the different slag compositions showed that slags rich in iron oxide lead mostly to the oxidation of carbon/graphite in the carbon-containing refractories. This leads to an increased porosity and wettability and therefore an enhanced penetration of slag into the refractory structure. If the slag contains high contents of alumina and or silica (such as the steel refining slag), reactions between the slag components and the dolomite-carbon refractory are promoted. This leads to the formation of low-temperature melting phases such as calcium-aluminates and silicates. The state of these reaction products during steel refining leads to an accelerated wear of the dolomite-carbon refractory. The main products of the reactions between the magnesia-carbon refractory and the steel refining slag are MgAl2O4 spinels, and calcium-aluminates, and silicates. Due to the good refractory properties of MgAl2O4 spinels, the slag corrosion resistance of the magnesiacarbon refractory is promoted.

  • 7.
    Kasimagwa, Ismail
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Brabie, Voicu
    Thermo-calc and SEM analysis of the dolomite lining during steel refining2008Inngår i: Proceedings for the Third Nordic Symposium for Young Scientists in Metallurgy, 2008, s. 46-50Konferansepaper (Fagfellevurdert)
  • 8.
    Kasimagwa, Ismail
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Brabie, Voicu
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Jönsson, Pär G.
    Studies on decarburization of MgO-c refractories during ladle preheating2010Inngår i: Steel GRIPS Journal, ISSN 1611-4442, nr 8, s. 357-363Artikkel i tidsskrift (Fagfellevurdert)
  • 9.
    Kasimagwa, Ismail
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Eriksson, J.
    Brabie, Voicu
    Wahlberg, H.
    Slagline refractory2008Inngår i: Proceedings for the SCANMET III-3rd International Conference on Process Development in Iron and Steel making, 2008, s. 377-384Konferansepaper (Fagfellevurdert)
  • 10.
    Kellner, Hans
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. KTH, Tillämpad processmetallurgi.
    Study of Non-metallic Inclusion in Alloy 8252017Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    It is well known that inclusions affect the properties of steels and alloys. Therefore, it is important to understand what type of inclusions that exist and how they behave and especially with a focus on large size inclusions. Thus, the large size non-metallic inclusions in ferroalloy FeTi70R were investigated in two dimensions (2D) by using scanning electron microscopy (SEM) in combination with an energy dispersive technique (EDS). It was found that the FeTi70R ferroalloy contain complex oxide inclusions consisting mostly of CaO, SiO2 and TiOx. Furthermore, experimental trials were performed to investigate how these inclusions behaved when entering a melt. More specifically, a comparison between pure Fe and an Alloy 825 grade were made. These results determined the parameters effect on the transformation of the inclusions in the melt.

    The large size non-metallic inclusions in Alloy 825 during the ladle treatment were investigated during industrial trials by using both two dimensional (2D) and three dimensional (3D) microscopic investigations. The results showed that inclusions consisted of spherical oxides and clusters made up of oxides and nitrides. Further investigations found that the spherical inclusions were transformed from existing NMI in the FeTi70R ferroalloy and slag particles. As for the clusters, they originate from deoxidation products. Furthermore, small inclusions precipitated in the local zones around the added FeTi70R ferroalloy and titanium nitrides. Investigations also found that only Al2O3-MgO and TiN clusters exist after casting.

    Industrial trials were performed during the last period of the ladle treatment and using a combined electromagnetic (EMS) and gas (GS) stirring. The purpose to investigate the effect of different EMS directions on the agglomeration and on the removal of Al2O3-MgO and TiN clusters. The investigations were then performed in 3D after an electrolytic extraction of the metal samples. The results show that electromagnetic stirring in the upwards direction is best for the agglomeration of the Al2O3-MgO and TiN clusters. However, electromagnetic stirring in the downwards direction is more effective to remove clusters from the melt. This is in agreement with the theoretical predictions based on Stokes’, Brownian and Turbulent collisions. Also, the calculations showed that for Al2O3-MgO clusters with sizes <20 μm the Turbulent collision is the defining factor for agglomeration. However, both Stokes’ and Turbulent collisions are dominant for larger inclusions. For the TiN clusters, turbulent collisions is the dominant factor.

    Further investigations with more heats and stirring modes were done by using 2D microscopic investigations. More specifically, the number, size, composition and morphology of different inclusions were determined by using SEM in combination with EDS and Inca Feature analyses. The results show that the EMS in downwards direction with a 0.04 m3 min-1 gas flow rate promotes a general removal of Al2O3-MgO and TiN inclusions. Furthermore, that the upwards EMS direction promotes a drastically increase of inclusions having an equivalent size smaller than 11.2 μm. Moreover, the stirring with a 0.02 m3 min-1 gas flow rate has a better removal rate for both downwards and upwards stirring directions compared to the stirring with a 0.04 m3 min-1 gas flow rate. However, no influence on the inclusion composition and morphology could be seen from the different stirring modes.

  • 11.
    Memarpour, Arashk
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    An Experimental Study of Submerged Entry Nozzles (SEN) Focusing on Decarburization and Clogging2011Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The submerged entry nozzle (SEN) is used to transport the molten steel from a tundish to a mould. The main purpose of its usage is to prevent oxygen and nitrogen pick-up by molten steel from the gas. Furthermore, to achieve the desired flow conditions in the mould. Therefore, the SEN can be considered as a vital factor for a stable casting process and the steel quality. In addition, the steelmaking processes occur at high temperatures around 1873 K, so the interaction between the refractory materials of the SEN and molten steel is unavoidable. Therefore, the knowledge of the SEN behaviors during preheating and casting processes is necessary for the design of the steelmaking processes  The internal surfaces of modern SENs are coated with a glass/silicon powder layer to prevent the SEN graphite oxidation during preheating. The effects of the interaction between the coating layer and the SEN base refractory materials on clogging were studied. A large number of accretion samples formed inside alumina-graphite clogged SENs were examined using FEG-SEM-EDS and Feature analysis. The internal coated SENs were used for continuous casting of stainless steel grades alloyed with Rare Earth Metals (REM). The post-mortem study results clearly revealed the formation of a multi-layer accretion. A harmful effect of the SENs decarburization on the accretion thickness was also indicated. In addition, the results indicated a penetration of the formed alkaline-rich glaze into the alumina-graphite base refractory. More specifically, the alkaline-rich glaze reacts with graphite to form a carbon monoxide gas. Thereafter, dissociation of CO at the interface between SEN and molten metal takes place. This leads to reoxidation of dissolved alloying elements such as REM (Rare Earth Metal). This reoxidation forms the “In Situ” REM oxides at the interface between the SEN and the REM alloyed molten steel. Also, the interaction of the penetrated glaze with alumina in the SEN base refractory materials leads to the formation of a high-viscous alumina-rich glaze during the SEN preheating process. This, in turn, creates a very uneven surface at the SEN internal surface. Furthermore, these uneven areas react with dissolved REM in molten steel to form REM aluminates, REM silicates and REM alumina-silicates.

    The formation of the large “in-situ” REM oxides and the reaction of the REM alloying elements with the previously mentioned SEN´s uneven areas may provide a large REM-rich surface in contact with the primary inclusions in molten steel. This may facilitate the attraction and agglomeration of the primary REM oxide inclusions on the SEN internal surface and thereafter the clogging. The study revealed the disadvantages of the glass/silicon powder coating applications and the SEN decarburization.

    The decarburization behaviors of Al2O3-C, ZrO2-C and MgO-C refractory materials from a commercial Submerged Entry Nozzle (SEN), were also investigated for different gas atmospheres consisting of CO2, O2 and Ar. The gas ratio values were kept the same as it is in a propane combustion flue gas at different Air-Fuel-Ratio (AFR) values for both Air-Fuel and Oxygen-Fuel combustion systems. Laboratory experiments were carried out under nonisothermal conditions followed by isothermal heating. The decarburization ratio (α) values of all three refractory types were determined by measuring the real time weight losses of the samples. The results showed the higher decarburization ratio (α) values increasing for MgO-C refractory when changing the Air-Fuel combustion to Oxygen-Fuel combustion at the same AFR value. It substantiates the SEN preheating advantage at higher temperatures for shorter holding times compared to heating at lower temperatures during longer holding times for Al2O3-C samples. Diffusion models were proposed for estimation of the decarburization rate of an Al2O3-C refractory in the SEN.

    Two different methods were studied to prevent the SEN decarburization during preheating: The effect of an ZrSi2 antioxidant and the coexistence of an antioxidant additive and a (4B2O3 ·BaO) glass powder on carbon oxidation for non-isothermal and isothermal heating conditions in a controlled atmosphere. The coexistence of 8 wt% ZrSi2 and 15 wt% (4B2O3 ·BaO) glass powder of the total alumina-graphite refractory base materials, presented the most effective resistance to carbon oxidation. The 121% volume expansion due to the Zircon formation during heating and filling up the open pores by a (4B2O3 ·BaO) glaze during the green body sintering led to an excellent carbon oxidation resistance.

    The effects of the plasma spray-PVD coating of the Yttria Stabilized Zirconia (YSZ) powder on the carbon oxidation of the Al2O3-C coated samples were investigated. Trials were performed at non-isothermal heating conditions in a controlled atmosphere. Also, the applied temperature profile for the laboratory trials were defined based on the industrial preheating trials. The controlled atmospheres consisted of CO2, O2 and Ar. The thicknesses of the decarburized layers were measured and examined using light optic microscopy, FEG-SEM and EDS. A 250-290 μm YSZ coating is suggested to be an appropriate coating, as it provides both an even surface as well as prevention of the decarburization even during heating in air. In addition, the interactions between the YSZ coated alumina-graphite refractory base materials in contact with a cerium alloyed molten stainless steel were surveyed. The YSZ coating provided a total prevention of the alumina reduction by cerium. Therefore, the prevention of the first clogging product formed on the surface of the SEN refractory base materials. Therefore, the YSZ plasma-PVD coating can be recommended for coating of the hot surface of the commercial SENs.

  • 12.
    Memarpour, Arashk
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Brabie, Voicu
    Jönsson, Pär
    Studies of Yttria Stabilized Zirconia (YSZ) plasma-PVD coated Al2O3-C refractory base materials of a commercial SEN with respect todecarburization and clogging2011Inngår i: Steel Grips - Journal of Steel and Related Materials, ISSN 1866-8453Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Carbon oxidation is a main industrial problem for alumina-graphite refractory base materials used in commercial Submerged Entry Nozzles (SEN) during preheating. Thus, the effects of the plasma spray-PVD coating of the Yttria Stabilized Zirconia (YSZ) powder on the carbon oxidation were investigated. Laboratory preheating trials were performed at non-isothermal heating conditions in a controlled atmosphere. Also, the applied temperature profile for the laboratory trials were defined based on industrial preheating trials. The controlled atmospheres consisted of CO2, O2 and Ar. The (CO2/O2) ratios were kept the same as for a propane combustion flue gas at an Air-Fuel-Ratio (AFR) value equal to 1.5 for heating in an air-fuel mixture and in air. The thicknesses of the decarburized layers were measured and examined using light optic microscopy, FEG-SEM and EDS. The YSZ plasma-PVD coated alumina-graphite refractory base materials, presented the effective resistance to carbon oxidation at different coating thicknesses from 160-480 μm in both combustion flue gas and air atmospheres. For the YSZ plasma coating that contained a thinner coating layer such as 160 μm, the uneven surface of the substrate may be reflected more than it could be reflected for a thicker coating. However, for the YSZ plasma coating with a coating thickness of 290 μm, the uneven surface of the substrate may be reflected much less than it could be reflected for thinner coatings. A 250μm and a 290μm YSZ coating may prevent the decarburization of an alumina-graphite refractory base materials during preheating in air at a maximum heating temperature of 1020°C. Moreover, in an oxidizing atmosphere with an AFR value equal to 1.5 at a maximum temperature of 1020°C and a holding time of 7200 seconds. A 250-290 μm YSZ coating is suggested to be an appropriate coating, as it provides both an even surface and prevention of the decarburization even during heating in air. In addition, the interactions between the YSZ coated alumina-graphite refractory base materials in contact with a cerium alloyed molten stainless steel were surveyed. The YSZ coating provided a total prevention of the alumina reduction by cerium. Therefore, the prevention of the first clogging product formed on the surface of the SEN refractory base materials. Therefore, the YSZ plasma-PVD coating can be recommended for coating of the hot surface of thecommercial SENs.

  • 13.
    Molnar, David
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. KTH.
    Engberg, Göran
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Li, Wei
    Lu, Song
    Hedström, Peter
    Kwon, Se Kyun
    Vitos, Levente
    Experimental study of the gamma-surface of austenitic stainless steels2019Inngår i: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 173, s. 34-43Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We introduce a theory-guided experimental approach to study the γ-surface of austenitic stainless steels. The γ-surface includes a series of intrinsic energy barriers (IEBs), which are connected to the unstable stacking fault (USF), the intrinsic stacking fault (ISF), the unstable twinning fault (UTF) and the extrinsic stacking fault (ESF) energies. The approach uses the relationship between the Schmid factors and the effective energy barriers for twinning and slip. The deformation modes are identified as a function of grain orientation using in situ electron backscatter diffraction measurements. The observed critical grain orientation separating the twinning and slip regimes yields the USF energy, which combined with the universal scaling law provides access to all IEBs. The measured IEBs and the critical twinning stress are verified by direct first-principles calculations. The present advance opens new opportunities for modelling the plastic deformation mechanisms in multi-component alloys.

  • 14.
    Molnar, David
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. KTH.
    Engberg, Göran
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Li, Wei
    Vitos, Levente
    Deformation properties of austenitic stainless steels with different stacking fault energies2018Inngår i: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 941, s. 190-197Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In FCC metals a single parameter – stacking fault energy (SFE) – can help to predict the expectable way of deformation such as martensitic deformation, deformation twinning or pure dislocation glide. At low SFE one can expect the perfect dislocations to dissociate into partial dislocations, but at high SFE this separation is more restricted. The role of the magnitude of the stacking fault energy on the deformation microstructures and tensile behaviour of different austenitic steels have been investigated using uniaxial tensile testing and electron backscatter diffraction (EBSD). The SFE was determined by using quantum mechanical first-principles approach. By using plasticity models we make an attempt to explain and interpret the different strain hardening behaviour of stainless steels with different stacking fault energies.

  • 15.
    Molnar, David
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. KTH.
    Sun, Xun
    Lu, Song
    Li, Wei
    Engberg, Göran
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Vitos, Levente
    Effect of temperature on the stacking fault energy and deformation behaviour in 316L austenitic stainless steel2019Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 759, s. 490-497Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The stacking fault energy (SFE) is often used as a key parameter to predict and describe the mechanical behaviour of face centered cubic material. The SFE determines the width of the partial dislocation ribbon, and shows strong correlation with the leading plastic deformation modes. Based on the SFE, one can estimate the critical twinning stress of the system as well. The SFE mainly depends on the composition of the system, but temperature can also play an important role. In this work, using first principles calculations, electron backscatter diffraction and tensile tests, we show a correlation between the temperature dependent critical twinning stress and the developing microstructure in a typical austenitic stainless steel (316L) during plastic deformation. We also show that the deformation twins contribute to the strain hardening rate and gradually disappear with increasing temperature. We conclude that, for a given grain size there is a critical temperature above which the critical twinning stress cannot be reached by normal tensile deformation, and the disappearance of the deformation twinning leads to lower strain hardening rate and decreased ductility.

  • 16.
    Molnar, David
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. KTH.
    Vida, Ádám
    Huang, Shuo
    Chinh, Nguyen Q
    The effect of cooling rate on the microstructure and mechanical properties of NiCoFeCrGa high-entropy alloy2019Inngår i: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 54, nr 6, s. 5074-5082Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The effect of cooling rate on the microstructure and mechanical properties of equimolar NiCoFeCrGa high-entropy alloy (HEA) was studied by scanning electron microscopy, energy-dispersive X-ray spectroscopy and electron backscatter diffraction (EBSD), as well as by microhardness tests. Experimental results show that the cooling rate has a crucial impact on the developing microstructure which has a mixture of two—FCC and BCC—phases, leading to a self-similarity of the solidified structure formed in the sample. Furthermore, the cooling rate influences both the composition of the two phase-components and the ratio of their volume fractions, determining the mechanical properties of the sample. The present results confirm the grouping of Co, Fe and Cr in the FCC phase and that of Ni and Ga in BCC phase in the NiCoFeCrGa high-entropy alloy system. An empirical rule is suggested to predict how the phase-components can be expected in this complex high-entropy alloy.

  • 17.
    Nilsson, Maria
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Tribology in Metal Working2012Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This thesis focuses on the tribological performance of tool surfaces in two steel working operations, namely wire drawing and hot rolling. In all forming operations dimensions and surface finish of the products are of utmost importance. Forming basically includes three parts – forming conditions excluded – that may be changed; work material, tool and (possibly) lubricant. In the interface between work material and tool, the conditions are very aggressive with – generally or locally – high temperatures and pressures. The surfaces will be worn in various ways and this will change the conditions in the process. Consequently, the surface finish as well as the dimensions of the formed product may change and in the end, the product will not fulfil the requirements of the customer. Therefore, research and development in regard to wear, and consequently tribology, of the forming tools is of great interest.

    The investigations of wire drawing dies focus on coating adhesion/cohesion, surface characteristics and material transfer onto the coated steel both in laboratory scale as well as in the wire drawing process. Results show that it in wire drawing is possible to enhance the tribological performance of drawing dies by using a lubricant together with a steel substrate coated by a polished, dual-layer coating containing both hard and friction-lowering layers.

    The investigations of hot rolling work rolls focus on microstructure and hardness as well as cracking- and surface characteristics in both laboratory scale and in the hot strip mill. Results show that an ideal hot work roll material should be made up of a matrix with high hardness and a large amount of complex, hard carbides evenly distributed in the microstructure. The surface failure mechanisms of work rolls are very complex involving plastic deformation, abrasive wear, adhesive wear, mechanical and thermal induced cracking, material transfer and oxidation.

    This knowledge may be used to develop new tools with higher wear resistance giving better performance, lower costs and lower environmental impact.

  • 18.
    Nilsson, Maria
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. Tribomaterials group, The Ångström Laboratory, Uppsala University, Sweden.
    Microstructural, mechanical and tribological characterisation of roll materials for the finishing stands of the hot strip mill for steel rolling2013Inngår i: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 307, nr 1-2, s. 209-217Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The microstructure, mechanical and tribologicalproperties for three different materials, High Speed Steel, High Chromium ironand Indefinite Chill iron, used for hot strip mill work rolls have beenevaluated. Microstructural characterisation was performed using light opticalmicroscopy, scanning electron microscopy and energy dispersive X-rayspectroscopy. The mechanical and tribological properties were evaluated usingmicro Vickers indentation and scratch testing in combination with post-testmicroscopy. The microstructures of the investigated materials were found to berather complex with a number of secondary phases andalso materials with similar nominal composition display significant differenceswith respect to distribution, size and morphology of carbides. Scratch testing,including detection of friction coefficient, acoustic emission and penetrationdepth, gives valuable information concerning the mechanical and tribologicalresponse on a microscopic level of the investigated materials. Type,amount, distribution, size and morphology of the secondary phases in thematerials have a strong impact on the surface deformation and wear mechanismsduring scratching. Cracking and chipping are frequently observed in connectionto the ridges surrounding the scratches. However, cross-sectional analyses ofthe scratched microstructures reveal that cracking of the brittle carbidephases may extend to significant depths, >100 µm, reducing the mechanicalstrength of the material. Based on the results, it is believed that a moreisotropic microstructure, e.g. obtained via a powder metallurgy process, withfiner carbides would result in improved properties and performance in a hotrolling application.

  • 19.
    Pirouznia, Pouyan
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. KTH Royal Institute of Technology; voestalpine Precision Strip AB, Munkfors.
    Andersson, N. ÅI.
    Tilliander, A.
    Jönsson, P. G.
    The impact of the gas inlet position, flow rate, and strip velocity on the temperature distribution of a stainless-steel strips during the hardening process2019Inngår i: Metals, E-ISSN 2075-4701, Vol. 9, nr 9, artikkel-id 928Artikkel i tidsskrift (Fagfellevurdert)
  • 20.
    Safara Nosar, Nima
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. KTH Royal Institute of Technology.
    Engberg, Göran
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Ågren, John
    KTH Royal Institute of Technology.
    Modeling microstructure evolution in a martensitic stainless steel subjected to hot working using a physically based model2019Inngår i: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 50, nr 3, s. 1480-1488Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The microstructure evolution of a martensitic Stainless steel subjected to hot compression is simulated with a physically based model. The model is based on coupled sets of evolution equations for dislocations, vacancies, recrystallization and grain growth. The advantage of this model is that with only a few experiments, the material dependent parameters of the model can be calibrated and used for a new alloy in any deformation condition. The experimental data of this work is obtained from a series of hot compression, and subsequent stress relaxation tests performed in a Gleeble thermo-mechanical simulator. These tests are carried out at various temperatures ranging from 900 to 1200⁰C, strains up to 0.7 and strain rates of 0.01, 1 and 10 s-1. The grain growth, flow stress, and stress relaxations are simulated by finding reasonable values for model parameters. The flow stress data obtained at the strain rate of 10 s-1 were used to calibrate the model parameters and the predictions of the model for the lower strain rates were quite satisfactory. An assumption in the model is that the structure of second phase particles does not change during the short time of deformation. The results show a satisfactory agreement between the experimental data and simulated flow stress, as well as less than 5% difference for grain growth simulations and predicting the dominant softening mechanisms during stress relaxation according to the strain rates and temperatures under deformation.

  • 21.
    Safara Nosar, Nima
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. KTH Royal Institute of Technology, Stockholm.
    Golpayegani, Ardeshir
    Sandvik Materials Technology, Sandviken.
    Engberg, Göran
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Ågren, John
    KTH Royal Institute of Technology, Stockholm.
    Study of the mean size and fraction of the second-phase particles in a 13% chromium steel at high temperature2019Inngår i: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, s. 1-17Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The mean size and fraction of the second-phase particles in a 13% chromium steel are investigated, while no plastic deformation was applied. The results of the measurement are compared with the modelling results from a physicallybased model. The heating sequence is performed on samples using a Gleeble thermo-mechanical simulator over the temperature range of 850?1200°C. Using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), the size distribution and composition of the carbides were evaluated, respectively. For obtaining particle size distribution (PSD), an image-processing software was employed to analyse the SEM images. Additionally, the relation between the 2D shape factor and size of the particles is also studied at different temperatures and most of the particles turned out to have a shape factor close to two. In order to measure the carbide weight fraction, electrochemical phase isolation was employed. The Ms and fraction of the martensite phase after quenching of samples are calculated and the results were comparable with the measured hardness values at corresponding temperatures. The measured hardness of the samples is found to comply very well with the measured mean size of the precipitates. The calculated mean size of the particles from the model shows very good agreement with both hardness value and experimentally measured mean size, while the calculated volume fraction from simulation follows a slightly different trend.

  • 22.
    Safara Nosar, Nima
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Sandberg, Fredrik
    Sandvik Materials Technology.
    Engberg, Göran
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Characterization of hot deformation behavior in a 13% chromium steel2018Inngår i: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 941, s. 458-467Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The behavior of a 13% chromium steel subjected to hot deformation has been studied by performing hot compression tests in the temperature range of 850 to 1200 ⁰C and strain rates from 0.01 to 10 s-1. The uniaxial isothermal compression tests were performed on a Gleeble thermo-mechanical simulator. The best function that fits the peak stress for the material and its relation to the Zener-Hollomon parameter (Z) is illustrated. The average activation energy of this alloy for the entire test domain was reviled to be about 557 [kJ mol-1] from the calculations and the dynamic recrystallization (DRX) kinetic were studied to find the fraction DRX in the course of deformation.

  • 23.
    Svensson, Jennie
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. KTH, Tillämpad processmetallurgi.
    An Experimental Study to Improve the Casting Performance of Steel Grades Sensitive for Clogging2017Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    In this study, the goal is to optimize the process and to reduce the clogging tendency during the continuous casting process. The focus is on clogging when the refractory base material (RBM) in the SEN is in contact with the liquid steel. It is difficult or impossible to avoid non-metallic inclusions in the liquid steel, but by a selection of a good RBM in the SEN clogging can be reduced.

     

    Different process steps were evaluated during the casting process in order to reduce the clogging tendency. First, the preheating of the SEN was studied. The results showed that the SEN can be decarburized during the preheating process. In addition, decarburization of SEN causes a larger risk for clogging. Two types of plasma coatings were implemented to protect the RBM, to prevent reactions with the RBM, and to reduce the clogging tendency. Calcium titanate (CaTiO3) mixed with yttria stabilized zirconia (YSZ) plasma coatings were tested in laboratory and pilot plant trials, for casting of aluminium-killed low-carbon steels. For casting of cerium alloyed stainless steels, YSZ plasma coatings were tested in laboratory, pilot plant and industrial trials. The results showed that the clogging tendency was reduced when implementing both coating materials.

     

    It is also of importance to produce clean steel in order to reduce clogging. Therefore, the steel cleanliness in the tundish was studied experimentally. The result showed that inclusions originated from the slag, deoxidation products and tundish refractory and that they were present in the tundish as well as in the final steel product.

  • 24.
    Svensson, Jennie
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. KTH, Tillämpad processmetallurgi.
    The submerged entry nozzle: a study of how to reduce decarburization and clogging2014Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    During continuous casting the submerged entry nozzle (SEN) is one of the critical points. This since sequence casting is favourable, clogging of the SEN results in fever sequences or aborted castings. In this study the preheating of SEN has been evaluated at different steel plants. This since it earlier  has been found, preheating resulted in decarburisation of  the refractory base material (RBM)  which in turn resulted in clogging of the SEN. During the industrial preheating trials it was found that decarburisation of  the SEN is possible.The decarburisation results in a higher oxygen potential near the SEN wall. This in turn makes it possible for aluminum in the molten steel to form alumina particles. For low carbon aluminum killed steel grades, accretion of alumina clusters on the SEN internal wall result in clogging which hinder or reduces the steel flow through the SEN. For this reason, laboratory trials were performed to establish the formation of a liquid phase. Thus simulating the formation of liquid inclusions when alumina clusters attaches to the SEN wall, and which can be washed away by the steel flow. Formation of a liquid phase was indicated at the temperatures 1550-1600°C, and plasma coated nozzles were tried in pilot plant trials. The coating contained of 5-9 pct, 99.9 pct pure, calcium titanate (CaTiO3) mixed with yttria stabilized zirconia (YSZ).

  • 25.
    Svensson, Jennie
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Larsson, F.
    Memarpour, A.
    Ekerot, S.
    Brabie, Voicu
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Jönsson, P.G.
    Implementation of an YSZ coating material to prevent clogging of the submerged entry nozzle (SEN) during continuous casting of Ce-treated steels2018Inngår i: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 45, nr 2, s. 105-113Artikkel i tidsskrift (Annet vitenskapelig)
    Abstract [en]

    The possibility to reduce clogging in the submerged entry nozzle (SEN) during continuous casting of Ce alloyed stainless steels has been studied. This was done by implementing a new plasma coating material, consisting of yttria stabilized zirconia (YSZ). The coating was first tested in pilot-plant trials; where the amount of steel teemed through the plasma coated nozzles was monitored. Thereafter, samples of the coatings from the nozzles were studied using a FEG-SEM equipped with EDS. In addition, the coating material was tested in industrial trials where the performance was judged with respect to the clogging tendency detected as the movement of the stopper rod. The results from both the pilot-plant trials and industrial trials showed that the use of an YSZ coating led to a decreased clogging tendency during the casting in comparison to when using an uncoated SEN. Specifically, the pilot-plant trials showed that the clogging factor was lowered when implementing the YSZ coatings. Furthermore, the industrial trials showed that the clogging tendency, measured by the stopper rod movements, were lower when implementing the YSZ coating.

  • 26.
    Svensson, Jennie
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Larsson, Fredrik
    Outokumpu, Avesta SE-774 22, Sweden.
    Memarpour, Arashk
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. Sandvik Materials Technology, Sandviken SE-811 81, Sweden.
    Brabie, Voicu
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Jönsson, Pär
    Royal Institute of Technology, Brinellvägen 23, Stockholm SE-100 44, Sweden.
    Post-mortem Studies of Submerged Entry Nozzles (SEN) Coated with Yttria Stabilized Zirconia (YSZ)2015Inngår i: The 6th International Congress on the Science and Technology of Steelmaking (ICS2015), China, May 12-14, 2015 in Beijing / [ed] Organized by The Chinese Society for Metals (CSM), 2015Konferansepaper (Fagfellevurdert)
    Abstract [en]

    During continuous casting of Ce-treated stainless steel grades an accumulation of inclusions at the submerged entry nozzle’s (SEN) internal wall can cause disturbances or even prevent the molten steel flow. Plasma sprayed yttria stabilized zirconia (YSZ) coating of the SEN’s inlet and stopper rod have been implemented in order to decrease the clogging effect. The coating thickness was 210 µm and the plant trials were conducted during continuous casting of slabs. The clogging tendency was measured by the stopper rod position during the casting process. The results of the measured positions were then compared to experimentally determined information from samples cut out from the SEN’s inlet after casting. Specifically, the samples were analysed using a field emission gun scanning electron microscope (FEG-SEM) equipped with an energy dispersive X-ray spectrometry (EDS). Sample with the dimensions of ̴15x10x5 mm were electrolytic extracted before analysis. The chemical composition at the interface between the solidified steel and refractory base materials were analysed, and traces of the YSZ coating were determined.

    The movement of the stopper position indicated that the clogging tendency was reduced for the coated SEN. However, the FEG-SEM analyses showed that clogging of the SEN had occurred during the casting.

  • 27.
    Svensson, Jennie
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. KTH.
    Memarpour, Arashk
    Brabie, Voicu
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. KTH.
    Jönsson, Pär
    KTH.
    Studies of the decarburisation phenomena during preheating of submerged entry nozzles (SEN) in continuous casting processes2017Inngår i: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 44, nr 2, s. 108-116Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Decarburisation of the submerged entry nozzles (SEN) during the preheating process wasinvestigated based on plant trials and thermodynamic modelling at three different steel plants.During the trials the preheating processes were mapped, the temperature profiles wereregistered and post-mortem studies of the SENs with scanning electron microscopy wereperformed. Typically, the glass/silicon powder will form a dense and protective layer inside theSEN when heated over 1100°C. However, this study found that the temperature distributioninside the SEN did not always reach this critical temperature. Thus, decarburisation of the SENwas found at all steel plants. The overall results illustrate that the control of the preheatingprocess needs to be improved at all steel plants. It is suggested that future research should befocused on the development of new coating materials to prevent decarburisation of therefractory base material, which would decrease the chances of clogging during casting.

  • 28.
    Svensson, Jennie
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. KTH, Tillämpad processmetallurgi.
    Memarpour, Arashk
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Brabie, Voicu
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Jönsson, Pär
    KTH, Tillämpad processmetallurgi.
    Studies of the decarburization phenomena during heating of submerged entry nozzles (SEN) in continuous casting processesManuskript (preprint) (Annet vitenskapelig)
  • 29.
    Svensson, Jennie
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Memarpour, Arashk
    Ekerot, Sven
    Brabie, Voicu
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Jönsson, Pär
    Tillämpad processmetallurgi, KTH.
    Studies of new coating materials to prevent clogging of the submerged entry nozzle (SEN) during continuous casting of Al killed low carbon steels2017Inngår i: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 44, nr 2, s. 117-127Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The possibility to reduce clogging in the submerged entry nozzle (SEN) when casting Al killed low carbon steel has been evaluated. The coating materials have been tested in laboratory trials and pilot plant trials. Totally, 2 mixes of the coating material has been tested; containing 4.8 and 9.1 % CaTiO3 mixed with yttria stabilised zirconia (YSZ) powder. The chemical composition was analysed by using an FEG-SEM equipped with EDS.The major result showed that alumina reacted with CaTiO3 in the temperature interval from 1550-1600°C. In addition, the clogging ratio showed a decreased clogging tendency for coated nozzles compared to standard nozzles. Also, the results showed that an approximately three times higher steel mass could be teemed through the coated nozzles before clogging occurred compared to trials with uncoated standard nozzles. Overall, it is concluded that plasma sprayed CaTiO3 coatings can reduce the clogging tendency during the continuous casting process.

  • 30.
    Vattur Sundaram, Maheswaran
    et al.
    Chalmers University of Technology.
    Surreddi, Kumar Babu
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Hryha, Eduard
    Chalmers University of Technology.
    Veiga, Angela
    CEIT, Pº Manuel Lardizábal 15, 20018 San Sebastián, Spain.
    Berg, Siguard
    Höganäs AB, SE-263 83 Höganäs, Sweden.
    Castro, Francisco
    CEIT, Pº Manuel Lardizábal 15, 20018 San Sebastián, Spain.
    Nyborg, Lars
    Chalmers University of Technology.
    Full Densification in PM Steels Through Liquid Phase Sintering and HIP Approach2018Inngår i: Euro PM2018 Proceedings, 2018Konferansepaper (Fagfellevurdert)
    Abstract [en]

    High-density powder metallurgy (PM) components are required for high-performance applications. Liquid phase sintering (LPS) is one such method to improve the densification, especially the master alloy route is preferred due to the flexibility in tailoring the alloying contents. In this study, gas atomised Ni-Mn-B master alloy powder of size fraction < 45 µm was admixed with water atomised iron and Mo-prealloyed powder. During sintering, there was a significant densification due to LPS where the liquid formation occurred in two stages, one from the master alloy melting and another from the eutectic liquid formation, enabling densities > 95%. The microstructural investigation revealed that the surface densification was achieved after sintering in H2 containing atmosphere. Capsule free hot isostatic pressing was performed on these samples to achieve full density. This approach of combining LPS and capsule free hot isostatic pressing demonstrates the potential in reaching full densification in high-performance PM steel components.

  • 31. Wang, Z.
    et al.
    Prashanth, K. G.
    Surreddi, Kumar Babu
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Suryanarayana, C.
    Eckert, J.
    Scudino, S.
    Pressure-assisted sintering of Al–Gd–Ni–Co amorphous alloy powders2018Inngår i: Materialia, ISSN 2589-1529, Vol. 2, s. 157-166Artikkel i tidsskrift (Fagfellevurdert)
1 - 31 of 31
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