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  • 101. Hultquist, G.
    et al.
    Graham, M. J.
    Kodra, O.
    Moisa, S.
    Liu, R.
    Bexell, Ulf
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Smialek, J. L.
    Corrosion of copper in distilled water without O-2 and the detection of produced hydrogen2015Inngår i: Corrosion Science, ISSN 0010-938X, E-ISSN 1879-0496, Vol. 95, s. 162-167Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper reports on hydrogen pressures measured during similar to 19,000 h immersion of copper in oxygen-free liquid distilled water. Copper corrosion products have been examined ex-situ by SEM and characterized by XPS and SIMS. XPS strongly indicates a corrosion product containing both oxygen and hydrogen. SIMS shows that oxygen is mainly present in the outer 0.3 mu m surface region and that hydrogen penetrates to depths well below the corrosion product. Thermal desorption spectroscopy shows that the reaction product formed near room-temperature is less stable than that formed in air at 350 degrees C. 

  • 102. Hörnström, S. -E
    et al.
    Karlsson, E.
    Losch, A.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Bay, N.
    Forming of high-strength steels using a hot-melt dry lubricant2010Inngår i: 17th International Colloquium Tribology 2010 - Solving Friction and Wear Problems, 2010, Vol. 2, s. 958-971Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The increasing use of high strength steels in a variety of mechanical engineering applications has illuminated problems associated with galling in sheet metal forming operations. Galling is a tribological phenomenon associated with transfer of material from the steel sheet to the tool surface during forming resulting in seizure of the tool/steel sheet contact and extensive scratching of the steel sheet surface. As a result, a number of concepts have been developed in order to reduce the tendency to galling in metal forming, including the development of new dry lubricants, new forming tool steel grades and improved surface engineering treatments such as the deposition of low friction CVD and PVD coatings. In the present study the performance of a hot-melt dry lubricant in the forming of hot and cold rolled and hot-dip galvanized high strength steel has been evaluated and compared with a conventional rust protection oil using five different tests methods, i.e. a strip reduction test, a bending under tension test, a stretch-forming test, a pin-on disc test and a strip drawing test. In these tests, two different cold work tool steels, a conventional steel grade and a nitrogen alloyed PM steel grade were evaluated. The results show that the different tests used give consistent results and valuable information concerning the galling tendency of the steel sheet, tool steel and lubricant combinations investigated and when combined can be used to rank the galling resistance of lubricants and tool steels. The results clearly show that the dry lubricant provides better lubrication and generates less galling than the rust protection oil. Also, the nitrogen alloyed PM steel grade shows a significantly higher galling resistance as compared with the conventional steel grade and can, in combination with a dry lubricant, preferably be used in sheet metal forming operations to further improve the galling resistance.

  • 103. Ingemarsson, L.
    et al.
    Halvarsson, M.
    Engkvist, Josefin
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Jonsson, T.
    Hellstrom, K.
    Johansson, L. -G
    Svensson, J. -E
    Oxidation behavior of a Mo (Si, Al)(2)-based composite at 300-1000 degrees C2010Inngår i: Intermetallics (Barking), ISSN 0966-9795, E-ISSN 1879-0216, Vol. 18, nr 4, s. 633-640Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The oxidation behavior of a Mo (Si,Al)(2)-based composite of Mo(Si,Al)(2), Al2O3 and Mo-5(Si,Al)(3) (Kanthal Super ER) in synthetic air was investigated. The samples were oxidized isothermally for up to 72 h at 300-1000 degrees C using a thermobalance. The microstructure was analyzed by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Auger Electron Spectroscopy (AES) depth profiling. Broad ion beam milling (BIB) was used to prepare cross-sections. Oxidation behavior depended strongly on the composition of the substrate which consisted of a Mo(Si,Al)(2) matrix and the minority phases Mo-5(Si,Al)(3) and Al2O3. At 300-500 degrees C the mass gains were small with parabolic kinetics, oxidation resulting in a mixture of oxides that reflects the substrate composition. At 600 and 700 degrees C the oxide scale is thin and protective and depleted in molybdenum, a mass loss occurring due to MoO3 vaporization. At 1000 degrees C a protective alpha-alumina scale forms. (C) 2009 Elsevier Ltd. All rights reserved.

  • 104.
    Isgren, Peter
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Dragprovstavens geometripåverkan på mätresultatet2015Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [en]

    The thesis is based on a comparative investigation of standard SS 112113 with a geometry described as straight and standard SS-EN 1561:2011 with a geometry described as hourglass shaped. The study will provide deeper understanding of the effect that different tensile test geometries and different test speed has on the tensile strength and the variation. The purpose is to find a suitable geometry and test speed that results in a small dispersion on the measured tensile strength. Another purpose is to perform structural studies to investigate how the microstructure affects the measured result. Seventy tensile tests are included in this study and every bar is casted from the same gray iron melt in identical sand molds. The tensile test bars is lathed according respective standard and tensile tested in a Zwick tensile test machine. A light microscopy, LOM has been used for checking defects in the fracture surface, check the roughness of the surface and for graphite classification. A scanning electron microscope, SEM has been used to check rust on the tensile test piece. Hardness testing by Brinell has been performed since there is a connection between tensile strength and hardness. The tensile strength and the dispersion are lower for SS 112113. The fracture occurs at different positions for standard SS 112113. Different tensile test speed does not result in a significant difference in tensile strength or dispersion. For standard SS-EN 1561:2011 the fracture occurs where the cross-sectional area is minimum. Microstructure with regard to graphite type and graphite length does not explain the difference in tensile strength or deviation.

  • 105.
    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)
  • 106.
    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)
  • 107. Jansson, S.
    et al.
    Brabie, Voicu
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Jonsson, P.
    Magnesia-carbon refractory dissolution in Al killed low carbon steel2006Inngår i: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 33, nr 5, s. 389-397Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The effects of rotation speed, steel temperature and steel composition on the rate of dissolution of MgO-C refractory into Al deoxidised molten steel were investigated using the rotating cylinder method. Cylinders or rods of MgO-C refractory material were immersed in an Al deoxidised molten steel. Experiments were performed for steel temperatures between 1873 and 1973 K and rotation speeds between 100 and 800 rev min(-1) as well as for different immersion times. For each case, the dissolution rate of MgO-C material was determined from measurement of the decrease in the rod radius. The experimental results showed that the dissolution rate of the MgO-C refractory material increased with an increase in steel temperature and rotation speed. The findings strongly suggest the diffusion of magnesium through the slag layer formed around the refractory rods to be a rate determining step. This thin oxide layer at the steel/refractory interface was found to be owing to reaction between magnesium vapour and CO generated by the reaction between MgO and C in the refractory. Oxide inclusions were also found in the steel melt and they were shown to mainly consist of MgO and Al2O3 or a mixture of the two.

  • 108. Jansson, Sune
    et al.
    Brabie, Voicu
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Jonsson, P.
    Corrosion mechanism of commercial doloma refractories in contact with CaO-Al2O3-SiO2-MgO stag2008Inngår i: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 35, nr 2, s. 99-107Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The dissolution of three doloma based refractories in liquid CaO-Al2O3-SiO2-MgO slag was studied. Cylindrical refractory specimens of doloma, carbon bonded doloma, and magnesia doloma were rotated in a stationary crucible of molten slag under forced convection conditions. Slag composition, temperature, rod rotation speed and rod immersion time were varied. The refractory dissolution rate was determined from the change in diameter of the cylindrical specimens. The corrosion rate was found to increase with temperature and rod rotation speed and decrease when the slag was nearly saturated with MgO. The findings of the study substantiate the assumption that the diffusion of magnesium oxide through the slag boundary layer controls the corrosion process. The results indicated the overall corrosion process to be the dissolution of refractory material into the slag, followed by slag penetration of the pores and grain boundaries and finally, dispersion of the grains into the slag.

  • 109. Jansson, Sune
    et al.
    Brabie, Voicu
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Josson, Par
    Corrosion mechanism of commercial MgO-C refractories in contact with different gas atmospheres2008Inngår i: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 48, nr 6, s. 760-767Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Corrosion of MgO-C refractories in different gas atmospheres consisting of air, Ar, CO or Ar/CO was studied in laboratory experiments. In total, 103 experiments were carried out in the temperature range 1 173 to 1 773 K and for holding times between 2 to 120 min. The reaction rate of the MgO-C material was determined from measurements of the weight loss of the samples. The results showed that the refractory weight loss increased with an increased temperature or an increased holding time. The thermodynamic conditions and the experimental results showed that magnesium gas and carbon monoxide gas should form during ladle refining of steel when the refractory material consists of MgO-C. It was suggested that the reaction rate is directly dependent on the oxygen potential in the ambient atmosphere.

  • 110. Jansson, Sune
    et al.
    Brabie, Voicu
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Jönsson, Pär
    Corrosion mechanism and kinetic behaviour of MgO-C refractory material in contact with CaO-Al2O3-SiO2-MgO slag2005Inngår i: Scandinavian journal of metallurgy, ISSN 0371-0459, E-ISSN 1600-0692, Vol. 34, nr 5, s. 283-292Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The rate of dissolution of solid MgO-C into liquid CaO-Al2O3-SiO2-MgO slag at different temperatures was studied under conditions of forced convection by rotating cylindrical refractory specimens in a stationary crucible containing molten slag. The corrosion rate was calculated from the change in diameter of the cylindrical refractory specimens. The specimens were rotated for 15-120 min at a speed of 100-400 rpm in the molten slag. The rate of corrosion was found to increase with an increase in temperature and rod rotation speed, and to decrease when the slag was nearly saturated with MgO. The experimental results support the assumption that the diffusion of magnesium oxide through the slag-phase boundary layer controls the corrosion process. The corrosion mechanism seems to be the dissolution of refractory material into the slag followed by penetration of pores and grain boundaries and dispersion of the grains into the slag.

  • 111.
    Johansson, Per
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Mekanisk och tribologisk karakterisering av ferrokrombaserat kompositmaterial för tribologiska användningsområden2014Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
  • 112.
    Johansson, Robert
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Finite element modeling of straightening of thin-walled seamless tubes of austenitic stainless steel2016Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [en]

    During this thesis work a coupled thermo-mechanical finite element model (FEM) was builtto simulate hot rolling in the blooming mill at Sandvik Materials Technology (SMT) inSandviken. The blooming mill is the first in a long line of processes that continuously or ingotcast ingots are subjected to before becoming finished products.

    The aim of this thesis work was twofold. The first was to create a parameterized finiteelement (FE) model of the blooming mill. The commercial FE software package MSCMarc/Mentat was used to create this model and the programing language Python was used toparameterize it. Second, two different pass schedules (A and B) were studied and comparedusing the model. The two pass series were evaluated with focus on their ability to healcentreline porosity, i.e. to close voids in the centre of the ingot.

    This evaluation was made by studying the hydrostatic stress (σm), the von Mises stress (σeq)and the plastic strain (εp) in the centre of the ingot. From these parameters the stress triaxiality(Tx) and the hydrostatic integration parameter (Gm) were calculated for each pass in bothseries using two different transportation times (30 and 150 s) from the furnace. The relationbetween Gm and an analytical parameter (Δ) was also studied. This parameter is the ratiobetween the mean height of the ingot and the contact length between the rolls and the ingot,which is useful as a rule of thumb to determine the homogeneity or penetration of strain for aspecific pass.

    The pass series designed with fewer passes (B), many with greater reduction, was shown toachieve better void closure theoretically. It was also shown that a temperature gradient, whichis the result of a longer holding time between the furnace and the blooming mill leads toimproved void closure.

  • 113. Karasev, A. V.
    et al.
    Kellner, Hans
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. KTH.
    Sundqvist, O.
    Memarpour, A.
    Jönsson, P. G.
    Estimation of non-metallic inclusions in industrial Ni based alloys 8252017Inngår i: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 88, nr 4, artikkel-id 1600024Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    It is well known that inclusions affect the properties of the steel and other alloys. The importance of understanding the behavior of the inclusions during production can never be overstated. This study has examined the main types of big size (>10μm) inclusions that exist in Ni-based Alloy at the end of ladle treatment and after casting during industrial production of Ni based Alloys 825. Sources, mechanisms of formation and behavior of different type large size inclusions in Alloy 825 are discussed based on 2 and 3D investigations of inclusion characteristics (such as, morphology, composition, size, and number) and thermodynamic considerations. The large size inclusions found can be divided in spherical (Type I and II) inclusions and in clusters (Type III-V). Type I-A inclusions (Al2O3-CaO-MgO) originate from the slag. Type I-B inclusions and Type II inclusions consist of CaO-Al2O3-MgO and Al2O3-TiO2-CaO, respectively. Both types originate from the FeTi70R alloy. Type III clusters (Al2O3-MgO-CaO) are formed during an Al deoxidation of the Ni-based alloy. Type IV clusters (Al2O3-TiO2-CaO) formed from small inclusions, which are precipitated in local zones which contain high Ti and Al levels. These clusters are transformed to Type III clusters over time in the ladle. Finally, Type V clusters are typical TiN clusters. 

  • 114.
    Karimi Bakhshandi, Reza
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Corrosion Study of yellowmetals in Biodiesel and Test fuel2014Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Biodiesel is a promising substitute fuel for fossil fuels that derived from renewable resources like vegetable oils and animal fats. Rapeseed methyl ester, RME, is the most common biodiesel used in Scandinavia. Chemically, biodiesel is unstable and degradation of biodiesel results in formation of corrosive degradation products such as short chain fatty acids (SCFA) and water.Degradation of biodiesel is a continuous process which takes place even during corrosion studies in laboratory and results in too aggressive fuel. In order to investigate how increasing acidity of degraded fuel influence corrosion of metals and to avoid too corrosive environment, a stable test fuel simulating degraded biodiesel with certain amount of corrosive degradation products but resistance to additional degradation was needed to be developed.In the first part of this project a stable test fuel has been prepared and doped by adding impurity (methanol) and corrosive degradation products such as SCFA and water to a saturated methyl ester in order to simulate the corrosive environment and avoid excessive aggressiveness during the corrosion testing .Then four batches of test fuel were blended to see how increasing acidity and water content will influence the metallic corrosion.In the second part, samples of copper, brass and aluminium, with focus on copper, were exposed to prepared test fuels and RME in order to investigate corrosion behaviour of the metals and their effect on the test fuels.In order to investigate the stability of test fuel and effect of metals on it, developed test fuels were evaluated regarding to its water content using Karl Fischer volumetric titration, SCFA using extraction ion chromatography, structure using GC-MS and methanol using GC-FID. Targeted acceptance criteria for developed test fuel; such as solubility of degradation products, oxidation stability, toxicity, melting point were fulfilled by test fuel.Corrosion rate of the copper samples was calculated and their surfaces were analysed with SEM-EDS and FTIR. Metal content of fuel samples were analysed after exposure using ICP-OES method.As expected copper accelerated the oxidation of biodiesel effectively and copper ions were released into RME or low acidic test fuel but with increasing the acidity in test fuel copper samples were corroded and the corrosion rate increased. The results showed that the developed test fuel enabled accelerated corrosion testing comparable with aged RME.

  • 115.
    Karlsson, P
    et al.
    Karlstads Universitet.
    Eriksson, Jenny
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Gaard, A
    Karlstads Universitet.
    Krakhmalev, P
    Karlstads Universitet.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Bergstrom, J
    Karlstads Universitet.
    Galling resistance evaluation of tool steels by two different laboratory test methods for sheet metal forming2012Inngår i: Lubrication Science, ISSN 0954-0075, E-ISSN 1557-6833, Vol. 24, nr 6, s. 263-272Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Adhesive accumulation of work material on the tool surface is today a major problem in many sheet metal-forming applications. Different laboratory test methods are used to investigate galling with respect to different tool materials, lubricants and process conditions. In the present study, the galling resistance of a modern nitrogen-alloyed powder metallurgy tool steel and an conventional ingot cast D2 type tool steel was evaluated under lubricated sliding against ferritic stainless steel sheets using a commercial pin-on-disc (POD) and an in-house made slider-on-flat-surface (SOFS) tribotester. The investigated tool steels ranked similarly in terms of galling resistanc in both test methods. However, sliding distances to galling were longer for the SOFS equipment due to continuous sliding on new lubricated sheet surface. Best performance was demonstrated by the powder metallurgy tool steel treated to 65?HRC. Differences in friction behaviour and galling initiation were analysed on the basis of the two different working conditions, i.e. open (SOFS) and closed (POD) tribosystems. Copyright (c) 2012 John Wiley & Sons, Ltd.

  • 116. Karlsson, P. G.
    et al.
    Richter, J. H.
    Blomquist, J.
    Uvdal, P.
    Grehk, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Sandell, A.
    Metal organic chemical vapor deposition of ultrathin ZrO2 films on Si(1 0 0) and Si(1 1 1) studied by electron spectroscopy2007Inngår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 601, nr 4, s. 1008-1018Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The growth of ultrathin ZrO2 films on Si(100)-(2x1) and Si(111)-(7x7) has been studied with core level photoelectron spectroscopy and X-ray absorption spectroscopy. The films were deposited sequentially by chemical vapor deposition in ultra-high vacuum using zirconium tetra-tert-butoxide as precursor. Deposition of a > 50Å thick film leads in both cases to tetragonal ZrO2 (t-ZrO2), whereas significant differences are found for thinner films. On Si(111)-(7x7) the local structure of t-ZrO2 is not observed until a film thickness of 51Å is reached. On Si(100)-(2x1) the local geometric structure of t-ZrO2 is formed already at a film thickness of 11Å. The higher tendency for the formation of t-ZrO2 on Si(100) is discussed in terms of Zr–O valence electron matching to the number of dangling bonds per surface Si atom. The Zr–O hybridization within the ZrO2 unit depends furthermore on the chemical composition of the surrounding. The precursor t-butoxy ligands undergo efficient C–O scission on Si(100), leaving carbonaceous fragments embedded in the interfacial layer. In contrast, after small deposits on Si(111) stable t-butoxy groups are found. These are consumed upon further deposition. Stable methyl and, possibly, also hydroxyl groups are found on both surfaces within a wide film thickness range.

  • 117.
    Karlström, Klaudia
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Värmebehandling av kättingstål: Inverkan på slagsegheten och mikrostrukturen2014Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [sv]

    En av Ovakos interna stålsorter 9209 används till kättingar och har därmed höga krav på slagseghet och hårdhet. Efter ett antal kvalitetskontroller, där bland annat slagseghet och kornstorlek kontrollerats efter härdning med efterföljande anlöpning, har resultatet med slagsegheten vid -20 °C inte varit tillfredsställande. För att utreda orsaken till problemet har ett flertal härdtester i ett brett temperaturintervall utförts utan tillräckligt bra resultat. Vid ett tillfälle har materialet enkelglödgats i 720 °C i 135 minuter innan härdning. Detta har resulterat i förvånande höga värden på slagseghet. Det har även noterats att hårdheten ökar med ökad glödgningstemperatur.

    Huvudsyftet med arbetet är att genomföra värmebehandlingar i ett temperaturintervall för att hitta värmebehandlingstemperaturen som maximerar stålets egenskaper och att studera värmebehandlingens inverkan på mikrostrukturen.

    Resultatet av värmebehandlingarna visade att glödgningstemperaturen 700 °C var den enda som resulterade i godkända resultat på alla parametrar på den undersökta chargen.Den undersökta mikrostrukturen visade att glödgningens inverkan på utskiljda partiklar påverkar duktiliteten och på så vis förbättrar slagsegheten.Hårdhetsmätningarna visade att hårdheten ökade med glödgningstemperaturen.

  • 118. Kasimagwa, I.
    et al.
    Brabie, Voicu
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Jonsson, P. G.
    Slag corrosion of MgO-C refractories during secondary steel refining2014Inngår i: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 41, nr 2, s. 121-131Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Studies of the reactions between the MgO-C refractory and a CaO-Al2O3-SiO2-MgO slag system have been carried out through thermodynamic simulations, laboratory experiments and microscopy studies of the microstructure of the refractory samples after the experimental procedures. Corrosion experiments were conducted using the rotating immersion method of the MgO-C refractory rods in a liquid slag: in the temperature range of 1773-1923 K, revolution speed of 200 rev min(-1), with varying slag compositions and times ( 2700-8100 s). Laboratory experiments have shown that the time during which the ladle lining is exposed to a liquid slag with high stirring and slag composition are two important parameters which have large effect on the kinetics of the refractory wear. The rate constants calculated in the present work are in the range of 4 x 10(-7) to 1 x 10(-6) ms(-1). The estimated activation energy from the experimental results is 26 kJ mol(-1)

  • 119.
    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.

  • 120.
    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)
  • 121.
    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)
  • 122.
    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)
  • 123.
    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.

  • 124.
    Kellner, Hans
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Karasev, A. V.
    Memarpour, A.
    Jönsson, P. G.
    Evolution of non-metallic inclusions from FeTi70R alloys during alloying of Fe-40Ni-20Cr steels2016Inngår i: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 87, nr 11, s. 1461-1468Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this study, the composition, size, and number of large non-metallic inclusions (&gt;20μm) are investigated in a commercial refined FeTi70R alloy, which is used for deoxidation and alloying of different industrial high-quality steels. It is found that this ferroalloy contains different complex oxide inclusions, which sizes vary from 20 to 260μm. These different complex inclusions contain mostly CaO, SiO2, and TiOx. When adding FeTi70R alloy in the steel during the final stage of ladle treatment, these large size inclusions can significantly decrease the cleanliness and mechanical properties of steel. Therefore, the evolution and behavior of these inclusions after addition of this ferroalloy into the liquid iron or Fe-40Ni-20Cr steel are investigated in laboratory experiments. In addition, the results from the laboratory scale experiments are compared to results obtained from industrial heats using Alloy 825. A consideration of the evolution mechanism of large inclusions after an addition of a FeTi70R alloy helps to understand their behavior in the melt. It also helps to estimate their possible harmful effects on the quality of this steel grade during commercial production. 

  • 125.
    Kellner, Hans
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. KTH.
    Karasev, A. V.
    Sundqvist, O.
    Jönsson, P. G.
    Effect of the Stirring Mode on the Behavior of Al2O3–MgO Particles and Clusters during Ladle Treatment of Ni-based Alloy 8252017Inngår i: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 88, nr 12, artikkel-id 1700165Artikkel i tidsskrift (Fagfellevurdert)
  • 126.
    Kellner, Hans
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. KTH.
    Karasev, Andrey Vladimirovich
    KTH Royal Inst Technol, S-10044 Stockholm, Sweden..
    Sundqvist, Olle
    Sandvik Mat Technol AB, S-81181 Sandviken, Sweden..
    Jönsson, Pär Göran
    KTH Royal Inst Technol, S-10044 Stockholm, Sweden..
    TiN Particles and Clusters during Ladle Treatments of Ni-based Alloy 825 using Different Stirring Modes2018Inngår i: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 58, nr 2, s. 292-298Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Today, titanium is often used in steelmaking not only for deoxidation but also for micro-alloying and alloying for a wide range of steel grades. Therefore, many studies are focused on investigations on the formation and behavior of Ti-containing non-metallic inclusions (such as oxides, nitrides and carbides) during production of different Ti-containing steels and their effect on final steel properties. This study has examined the behavior of TiN clusters and particles in the melt during the ladle treatment of Alloy 825 containing up to 1.2 wt% of Ti. The industrial trials were performed at the end of the ladle treatment by using argon gas in combination with electromagnetic stirring using an upwards or a downwards stirring direction. Metal samples were taken before and after ladle treatment to enable three-dimensional investigations of non-metallic inclusions and clusters. The composition, size and number of particles and clusters were determined after electrolytic extraction of the metal samples by using SEM in combination with EDS. It was found that agglomerations of TiN clusters and particles in the melt are faster during an upwards stirring in comparison to a downwards stirring. However, the removal of clusters from the melt is more effective when using a downwards stirring direction compared to when using an upwards stirring in combination with gas stirring. It was also found that the Turbulent collision is the dominant factor for the agglomeration of TiN particles in the melt.

  • 127.
    Keränen, Elias
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Experimental and modelling ofmachining behavior of stainlesssteel in interrupted cutting withcoated cemented carbide2014Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    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.

  • 128.
    Khraisat, Walid
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Graphite pore filling and surface blistering of sintered Fe-C-Si2012Inngår i: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 55, nr 3, s. 242-247Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Different alloys of the system Fe-C-Si were sintered to obtain a grey iron microstructure and then hardened by post-sintering heat treatment to obtain a martensitic structure. The main problem in the development of this approach is related to the occurrence of surface blistering in the as sintered material when sintering in N2 atmosphere. Surface blistering is explained by the increase in entrapped gas pressure in pores caused by graphite pore filling. A mechanism has been proposed to explain graphite pore filling. According to this mechanism, graphite pore filling is caused by the C activity difference between the gas entrapped in pores and the matrix, which is a consequence of Boudouard’s reaction. This difference in C activity causes C to diffuse from the matrix to the pores, thus filling pores with graphite. © 2012 Institute of Materials, Minerals and Mining.

  • 129.
    Kolvereid, Anneli
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Framtagande av fördelningsfaktorer för säkrare beräkning vid skrotlastning2014Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [sv]

    Detta arbete är utfört på Ovako Sweden AB i Hofors som en examinationsuppgift för ingenjörsutbildning i materialteknik. I stålindustrin är kostnaden för råvaror såsom skrot och legeringar den överlägset största och något som kräver hjälpmedel för att utnyttja på bästa sätt. Genom att använda ett optimeringsprogram vid lastning av skrot går det att gör stora besparingar. I examensarbetet presenteras framtagande av fördelningsfaktorer för säkrare beräkning vid skrotlastning. Dessa faktorer används i optimeringsprogrammet RAWMATMIX då det vid lastning av skrot går att göra besparingar genom att programmet väljer det mest ekonomiskt fördelaktiga råmaterialet. Resultaten visar att fördelningsfaktorerna skiljer sig åt mellan olika skrotklasser vilket medför att en ny fördelningsmodell måste tas fram för varje klass. Vidare måste optimeringsprogrammet anpassas för körning med ”sump” dvs. den mängd stål från föregående charge som är kvar i ljusbågsugnen.

  • 130. Larsson, C.
    et al.
    Holden, T. M.
    Bourke, M. A. M.
    Stout, M.
    Teague, J.
    Lindgren, Lars-Erik
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Measurement andniodeling of residual stress in a welded Haynes (R) 25 cylinder2005Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 399, nr 1-2, s. 49-57Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An experimental and simulation study of residual stresses was made in the vicinity of a gas tungsten arc weld, used to join a hemispherical end cap to a cylinder. The capped cylinder is used in a satellite application and was fabricated from a Co-based Haynese (R) 25 alloy. The cylinder was 34.7 mm in outer diameter and 3.3 mm in thickness. The experimental measurements were made by neutron diffraction and the simulation used the implicit Marc finite element code. The experimental resolution was limited to approximately 3 rum parallel to the axis of the cylinder (the weld was 6 mm in the same direction) and comparison over the same volume of the finite element prediction showed general agreement. Subject to the limited spatial resolution, the largest experimentally measured tensile residual stress was 180 MPa, located at the middle of the weld. However, the predictions suggest that there are regions in the weld where average tensile residual stresses as much as 400 MPa exist. One qualitative disparity between the model and the experiments was that the measurement included a larger degree of asymmetry on either side of the weld than predicted by the model. 

  • 131. Lindgren, L. -E
    et al.
    Gyhlesten Back, Jessica
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Elastic properties of ferrite and austenite in low alloy steels versus temperature and alloying2019Inngår i: Materialia, ISSN 2589-1529, Vol. 5, artikkel-id 100193Artikkel i tidsskrift (Fagfellevurdert)
  • 132.
    Lindgren, Lars-Erik
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Domkin, Konstantin
    Högskolan Dalarna, Akademin Industri och samhälle, Maskinteknik.
    Hansson, Sofia
    Dislocations, vacancies and solute diffusion in physical based plasticity model for AISI 316L2008Inngår i: Mechanics of materials (Print), ISSN 0167-6636, E-ISSN 1872-7743, Vol. 40, nr 11, s. 907-919Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A physical based model for the evolution of flow stress of AISI 316L from room temperature up to 1300 °C, strains up to 0.6 and strain rates from 0.0005 up to 10 s-1 is developed. One set of tests have been used for model calibration and another more complex set of tests for its validation. The model is based on a coupled set of evolution equations for dislocation density and (mono) vacancy concentration. Furthermore, it includes the effect of diffusing solutes in order to describe dynamic strain ageing (DSA). The model described the overall flow stress evolution well with exception of the details of the effect of the DSA phenomenon. Its numerical solution is implemented in a format suitable for large-scale finite element simulations.

  • 133.
    Lindgren, Lars-Erik
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Carlsson, Per
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Simulation of hydroforming of steel tube made of metastable stainless steel2010Inngår i: International journal of plasticity, ISSN 0749-6419, E-ISSN 1879-2154, Vol. 26, nr 11, s. 1576-1590Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Olson-Cohen model for strain-induced deformation, further developed by Stringfellow and others, has been calibrated together with a flow stress model for the plastic deformation of metastable stainless steel. Special validation tests for checking one of the limitations of the model have also been carried out. The model has been implemented into a commercial finite element code using a staggered approach for integrating the stress-strain relations with the microstructure model. Results from a thermo-mechanical coupled simulation of hydroforming of a tube have been compared with corresponding experiments. The agreement between experimental results of radial expansion and martensite fraction and the corresponding computed results is good. 

  • 134.
    Lindgren, Michael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    An improved model for the longitudinal peak strain in the flange of a roll formed U-channel developed by FE-analyses2007Inngår i: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 78, nr 1, s. 82-87Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Today one can find cold roll forming (CRF) products in many applications, for example vehicles, furniture and in the building industry. Though CRF is a well known sheet metal process, it is still not entirely understood due to the geometrically complex forming. There are several computer aided engineering (CAE) programs on the market that can assist the tool maker when designing a new CRF machine. However, they are often based on simple formulas when predicting the stress and the strain in the strip. The main objective of this study is to improve formulas for the longitudinal peak membrane strain and the deformation length when a U-channel is formed. These are important since they can be used to determine the number of forming steps and the distance between them. A twolevel factorial design is done using the finite element analysis to investigate which parameters affect the peak strain and the deformation length. The parameters are then used to build models for the peak strain and the deformation length.

  • 135.
    Lindgren, Michael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Cold roll forming of a U-channel made of high strength steel2007Inngår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 186, nr 1-3, s. 77-81Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Cold roll forming is a bending process where the bending occurs gradually in several forming steps from an undeformed strip to a finished profile. The process is very interesting for the sheet metal industry due to the high speed in which the profile can be produced. High strength steel has, in recent years, become more common in cold roll forming. These materials have advantages but also disadvantages that affect the design of the process. Simple models in literature [K.F. Chiang, Cold roll forming, ME Thesis, University of Auckland, August 1984] predict that the longitudinal peak membrane strain in the flange of a profile is independent of the material properties. However, Ingvarsson [L. Ingvarsson, F¨orenklad teori f¨or rullforming av element¨ar v-profil, j¨amf¨orelse mellan normalt och h¨ogh°allfast st°al, VAMP 15- rullforming 23 april 2001] compared mild and ultra high strength in a roll forming experiment and the conclusion was that the material properties will affect the finished profile. This paper is a fundamental study performed in order to understand the observation by Ingvarsson [L. Ingvarsson, F¨orenklad teori f¨or rullforming av element¨ar v-profil, j¨amf¨orelse mellan normalt och h¨ogh°allfast st°al, VAMP 15- rullforming 23 april 2001]. The objectives of this study are to investigate the change in the longitudinal peak membrane strain at the flange edge and the deformation length when the yield strength increases. These are important since they can be used to determine the number of forming steps and the distance between them when designing the cold roll forming machine. The result from the simulations show that the longitudinal peak membrane strain decreases and the deformation length increases when the yield strength is increased.

  • 136.
    Lindgren, Michael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Experimental and computational investigation of the roll forming process2009Doktoravhandling, monografi (Annet vitenskapelig)
    Abstract [en]

    One of the first questions to consider when designing a new roll forming line is the number of forming steps required to produce a profile. The number depends on material properties, the cross-section geometry and tolerance requirements, but the tool designer also wants to minimize the number of forming steps in order to reduce the investment costs for the customer. There are several computer aided engineering systems on the market that can assist the tool designing process. These include more or less simple formulas to predict deformation during forming as well as the number of forming steps. In recent years it has also become possible to use finite element analysis for the design of roll forming processes. The objective of the work presented in this thesis was to answer the following question: How should the roll forming process be designed for complex geometries and/or high strength steels? The work approach included both literature studies as well as experimental and modelling work. The experimental part gave direct insight into the process and was also used to develop and validate models of the process. Starting with simple geometries and standard steels the work progressed to more complex profiles of variable depth and width, made of high strength steels. The results obtained are published in seven papers appended to this thesis. In the first study (see paper 1) a finite element model for investigating the roll forming of a U-profile was built. It was used to investigate the effect on longitudinal peak membrane strain and deformation length when yield strength increases, see paper 2 and 3. The simulations showed that the peak strain decreases whereas the deformation length increases when the yield strength increases. The studies described in paper 4 and 5 measured roll load, roll torque, springback and strain history during the U-profile forming process. The measurement results were used to validate the finite element model in paper 1. The results presented in paper 6 shows that the formability of stainless steel (e.g. AISI 301), that in the cold rolled condition has a large martensite fraction, can be substantially increased by heating the bending zone. The heated area will then become austenitic and ductile before the roll forming. Thanks to the phenomenon of strain induced martensite formation, the steel will regain the martensite content and its strength during the subsequent plastic straining. Finally, a new tooling concept for profiles with variable cross-sections is presented in paper 7. The overall conclusions of the present work are that today, it is possible to successfully develop profiles of complex geometries (3D roll forming) in high strength steels and that finite element simulation can be a useful tool in the design of the roll forming process.

  • 137. Lindgren, Michael
    et al.
    Bexell, Ulf
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Comparison of Roll Forming Using Different Forming Strategies and Bending2014Inngår i: IDDRG 2014, conference proceedings: Innovations for the sheet metal industry, June 1-4 2014, Paris, France / [ed] SFAR Hedi, MAILLARD André, 2014Konferansepaper (Annet vitenskapelig)
  • 138.
    Lindgren, Michael
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Bexell, Ulf
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Wikström, Lars
    Roll forming of partially heated cold rolled stainless steel2009Inngår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 209, nr 7, s. 3117-3124Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Today you will find roll formed details in many different products, for example buildings, household appliances and vehicles. The industry, in order to save weight, tends to use more and more high strength steel. The disadvantage with these materials is that they can be difficult to form due to reduced ductility. A way to increase the ductility in the forming areas is by partially heat the steel. It is shown that partial heating substantially increases the ductility of high strength steel and make it possible to roll form large bend angles. When roll forming, the material will work hardening almost to the as-received condition in the outer and inner radius of the roll formed profile. Furthermore, the heating power decides the bend angle obtained. Finally, the mechanical properties after heating and roll forming are discussed.

  • 139.
    Lindgren, Michael
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Edberg, Jonas
    Lindgren, Lars-Erik
    Roll forming2015Inngår i: Handbook of Manufacturing Engineering and Technology, Springer-Verlag London Ltd , 2015, s. 285-307Kapittel i bok, del av antologi (Annet vitenskapelig)
    Abstract [en]

    Roll forming is cost-effective compared to other sheet metal forming processes for uniform profiles. The process has during the last 10 years developed into forming of profiles with varying cross sections and is thereby becoming more flexible. The motion of the rolls can now be controlled with respect to many axes enabling a large variation in the profiles along the formed sheet, the so-called 3D roll forming or flexible roll forming technology. The roll forming process has also advantages compared to conventional forming for high-strength materials. Furthermore, computer tools supporting the design of the process have also been developed during the last 10 years. This is quite important when designing the forming of complex profiles. The chapter describes the roll forming process, particularly from the designer’s perspective. It gives the basic understanding of the process and how it is designed. Furthermore, modern computer design and simulation tools are discussed. © Springer-Verlag London 2015. All rights reserved.

  • 140. Lindgren, Michael
    et al.
    Ingmarsson, Lars-Olof
    3D roll-forming of hat-profile with variable depth and width2009Inngår i: Rollform09 1st International congress on roll forming, Bilbao, Spain, 2009Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    The use of roll-formed products in automotive, furniture, buildings etc. increases every year due to the low part-production cost and the complicated cross-sections that can be produced. The limitation with roll-forming until recent years is that one could only produce profiles with a constant cross-section in the longitudinal direction. About eight years ago ORTIC AB [1] developed a machine in which it was possible to produce profiles with a variable width (“3D roll-forming”) for the building industry. Experimental equipment was recently built for research and prototyping of profiles with variable cross-section in both width and depth for the automotive industry. The objective with the current study is to investigate the new tooling concept that makes it possible to roll-form hat-profiles, made of ultra high strength steel, with variable cross-section in depth and width. The result shows that it is possible to produce 3D roll-formed profiles with close tolerances.

  • 141. Lissel, Linda
    et al.
    Engberg, Göran
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Prediction of the microstructural evolution during hot strip rolling of Nb microalloyed steels2007Inngår i: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 558-559, nr 2, s. 1127-1132Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A physically based model is used to describe the microstructural evolution of Nb microalloyed steels during hot rolling. The model is based on a physical description of dislocation density evolution, where the generation and recovery of dislocations determines the flow stress and also the driving force for recrystallization. In the model, abnormally growing subgrains are assumed to be the nuclei of recrystallized grains and recrystallization starts when the subgrains reach a critical size and configuration. The model is used to predict the flow stress during rolling in SSAB Tunnplåt’s hot strip mill. The predicted flow stress in each stand was compared to the stresses calculated by a friction-hill roll-force model. Good fit is obtained between the predicted values by the microstructure model and the measured mill data, with an agreement generally within the interval ±15%.

  • 142.
    Ljungberg, Adam
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Schmidt, Nathalie
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Deformationsstrukturer i ett duplext rostfritt stål (SAF 2507)2014Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [sv]

    För att kunna förbättra processer och användning av det duplexa rostfria stålet SAF 2507 måste dess deformationsegenskaper undersökas och förklaras. Genom EBSD-analyser har deformationsstrukturer och polfgurer tagits fram för att kunna beskriva materialets beteende vid deformation. Även Taylorfaktorer, E-moduler och Poissons tal har tagits fram för att kunna undersöka materialets anisotropi.

    Experimenten har utförts på prov av SAF 2507 som har deformerats plastiskt till olika töjningar. Det som undersökts är odeformerat prov, prov som dragits enaxligt till 7,7 % och 24,3 % töjning, samt ett prov som är cykliskt belastat till 3 % töjning. Det undersökta stålet tillverkas genom två olika metoder, men i denna rapport har enbart det extruderade stålet undersökts.

    Genom att jämföra hur stålets olika mekaniska egenskaper beter sig under plastisk deformation har resultatet blivit att stålets ferritfas beter sig anisotropt med en antydan till ökande isotropi vid ökande deformation. Austenitfasen beter sig däremot isotropt och blir varken mer eller mindre isotropt vid ökande deformation. Substrukturerna i ferritfasen ökar tydligt vid ökande deformation, och ses framför allt i austenitfasen efter 24 % deformation.

  • 143. Malmberg, P.
    et al.
    Bexell, Ulf
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Eriksson, C.
    Nygren, H.
    Richter, K.
    Analysis of bone minerals by time-of-flight secondary ion mass spectrometry: a comparative study using monoatomic and cluster ions sources2007Inngår i: Rapid Communications in Mass Spectrometry, ISSN 0951-4198, E-ISSN 1097-0231, Vol. 21, nr 5, s. 745-749Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Time-of-flight secondary ion mass spectrometry (TOF-SIMS) is an important tool for the analysis of bone minerals at implant surfaces. Most studies have been performed with monoatomic primary ion sources such as Ga+ with poor secondary molecular ion production efficiency and only elemental distributions and minor fragments of bone minerals have been reported. By using cluster ion sources, such as Au and Bi, identification of larger hydroxyapatite species at m/z 485, 541, 597 and 653, identified as Ca5P3O12, Ca6P3O13, Ca7P3O14 and Ca8P3O15, respectively, became possible. The ions appear to be fragments of the hydroxyapatite unit cell Ca10(PO4)6(OH)2. Each ion in the series is separated by 55.9 m/z units, corresponding to CaO, and this separation might reflect the columnar nature of the unit cell. Copyright © 2007 John Wiley & Sons, Ltd.

  • 144.
    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.

  • 145.
    Memarpour, Arashk
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Brabie, Voicu
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Jönsson, Pär
    Studies of effect of glass/silicon powder coatings on clogging behaviour of submerged entry nozzles when using REM alloyed stainless steels2011Inngår i: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 38, nr 3, s. 229-239Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The internal surfaces of modern submerged entry nozzles (SENs) were coated with a glass/silicon powder layer to prevent SEN graphite oxidation during preheating. The effects of the interaction between the coating layer and the SEN base refractory materials on clogging were studied. The results indicated that penetration of the formed alkaline rich glaze into the alumina/graphite base refractory occurs during preheating. More specifically, the glaze reacts with graphite to form carbon monoxide gas. Thereafter, dissociation of CO at the SEN/molten metal interface takes place. This leads to reoxidation of dissolved rare earth metals, which form ‘in situ’ rare earth metal oxides at the interface between the SEN and the molten steel. In addition, 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. The ‘in situ’ formation of the rare earth metal oxides together with the uneven internal surface of the SEN may facilitate the accumulation of the primary inclusions on the refractory walls.

  • 146.
    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.

  • 147.
    Memarpour, Arashk
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Brabie, Voicu
    Jönsson, Pär G.
    Decarburization and clogging behaviour of yttria stabilized zirconia coatings applied to SEN´s Al2O3-C refractories by plasma PVD2012Inngår i: Steel Grips - Journal of Steel and Related Materials, ISSN 1611-4442, E-ISSN 1866-8453, Vol. 10, s. 353-363Artikkel 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 the commercial SENs.

  • 148.
    Memarpour, Arashk
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Brabie, Voicu
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Jönsson, Pär G.
    Post-mortem study of the internal coated SENs (Submerged Entry Nozzle) respecting clogging phenomena2011Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A large number of accretion samples formed inside alumina/graphite clogged Submerged Entry Nozzles (SEN) were examined using FEG-SEM-EDS and Feature analysis. The SENs were used for continuous casting of stainless steel grades alloyed by Rare Earth Metals (REM). The internal surfaces of the SENs were coated by a glass/silicon powder layer to prevent the SEN decarburization during the preheating process. The results indicated a harmful effect of the SENs decarburization on the accretion thickness. In addition, the post-mortem results clearly revealed the formation of a multi-layer accretion. Also, the study indicated the penetration of the protecting glaze into the Alumina/graphite refractory materials. The interaction of the penetrated glaze with alumina in the SEN refractory materials leads to formation of high viscous alumina-rich glaze during the SEN preheating process. This interaction may lead to formation of an uneven surface inside the SEN. These areas consist of alumina particles, silica particles and the penetrated glaze in between. The results showed that these areas react with dissolved REM in molten steel to form REM aluminates, REM silicates and REM alumina-silicates. Furthermore, the penetration of the glaze may lead to reactions between alkalines in the glaze and the graphite. This leads to a supply of oxygen at the interface between the SEN and the molten steel. This, in turn, may lead to reoxidation of the REM alloying elements in molten steel under the formation of “in situ” REM oxides. The formation of the large “in-situ” REM oxides and the reaction of the REM alloying elements with the SEN´s uneven inside surface, may create 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 oxides inclusions on the SEN internal surface and thereafter the clogging.

  • 149.
    Memarpour, Arashk
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Brabie, Voicu
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Jönsson, Pär G.
    The effect of zirconium disilicide (ZrSi2) additions on the carbon oxidation behavior of alumina/graphite refractory materials2010Inngår i: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 50, nr 11, s. 1612-1621Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Carbon oxidation is a main industrial problem for Alumina/Graphite Submerged Entry Nozzles (SEN) during pre-heating. Thus, the effect of ZrSi2 antioxidants and the coexistence of antioxidant additive and (4B2O3 •BaO) glass powder on carbon oxidation were investigated at simulated non-isothermal heating conditions in a controlled atmosphere. Also, the effect of ZrSi2 antioxidants on carbon oxidation was investigated at isothermal temperatures at 1473 K and 1773 K. The specimens’ weight loss and temperature were plotted versus time and compared to each others. The thickness of the oxide areas were measured and examined using XRD, FEG-SEM and EDS. The coexistence of 8 wt% ZrSi2 and 15 wt% (4B2O3 •BaO) glass powder of the total alumina/Graphite base refractory 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 (4B2O3 •BaO) glaze during green body sintering led to an excellent carbon oxidation resistance.

  • 150.
    Michael, Lindgren
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Experimental investigations of the roll load and roll torque when high strength steel is roll formed2007Inngår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 191, nr 1-3, s. 44-47Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The cold roll forming process is a highly efficient process used to produce profiles for many applications, for example vehicles, buildings, domestic machines, etc. Therefore, its market share is increasing every year. Many of the above products are already today made of high strength steel and the usage of these materials will likely continue to increase. The objectives of this project are to find howthe roll load and roll torque are influenced by the yield strength of the material. Full-scale experiments have been performed. U-channels made of different materials from mild to ultra high strength steels have been formed. The roll torque is measured during the process using a torque sensor mounted between the tool and the power transmission. Used power is also calculated with help of the motor current. The roll load is measured with load cells mounted on both side of the roll forming tool. The experimental result will increase the understanding of the specific conditions for roll forming steels with increasing yield strength. The result can be used to support the roll machine designer to choose machine elements and power unit for these applications. Furthermore, the result can also be compared with finite element simulations in order to improve and validate simulation models.

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