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  • 151. Jayamani, Jayaraj
    et al.
    Sordelet, D. J.
    Kim, D. H.
    Kim, Y. C.
    Fleury, E.
    Corrosion behaviour of Ni–Zr–Ti–Si–Sn amorphous plasma spray coating2006In: Corrosion Science, ISSN 0010-938X, E-ISSN 1879-0496, Vol. 48, no 4, p. 950-964Article in journal (Refereed)
    Abstract [en]

    Ni59Zr20Ti16Si2Sn3 amorphous material was deposited by a vacuum plasma spraying technique onto steel and copper substrates in order to investigate their behaviour in a corrosive environment. For comparison, the same alloy was prepared as amorphous ribbons by melt spinning. The amorphous nature of the coatings and ribbons was characterized by XRD, DSC and TEM, while XPS and AES analyses were performed to understand the origin of passivation and mode of corrosion. The corrosion behaviour of the coating was studied in H2SO4 and HCl solutions open to air at room temperature. Potentiodynamic polarisation and galvanic coupling tests were carried out on the substrate and the coating. It was found that the formation of Zr-, Ti- and Si-rich passive oxide layers provide a high corrosion resistance in H2SO4 solution while the breakdown of the passive layer by chloride ion adsorption was responsible for pitting corrosion of the Ni59Zr20Ti16Si2Sn3 amorphous ribbons in HCl solution. Galvanic corrosion was the dominant corrosion mechanism for the coating/copper hybrid structure, in contrast to the Ni59Zr20Ti16Si2Sn3 amorphous coating, which efficiently protected the steel substrate in the corrosive environment.

  • 152. Jayamani, Jayaraj
    et al.
    Thinaharan, C.
    Ningshen, S.
    Mallika, C.
    Kamachi Mudali, U.
    Corrosion behavior and surface film characterization of TaNbHfZrTi high entropy alloy in aggressive nitric acid medium2017In: Intermetallics (Barking), ISSN 0966-9795, E-ISSN 1879-0216, Vol. 89, p. 123-132Article in journal (Refereed)
    Abstract [en]

    Corrosion behavior of TaNbHfZrTi high-entropy alloy (HEA) was investigated in nitric and fluorinated nitric acid at ambient (27 °C) and boiling (120 °C) conditions. The alloy passivated spontaneously during potentiodynamic polarization in 11.5 M HNO3 at ambient condition. The corrosion rate was negligible in boiling 11.5 M HNO3, exposed for 240 h. Scanning electron microscopic (SEM) studies did not show any significant corrosion attack. The high corrosion resistance of TaNbHfZrTi HEA was attributed to its single phase bcc structure. X-ray photoelectron spectroscopic (XPS) analysis revealed that the protective passive film formed in boiling nitric acid was predominantly composed of Ta2O5, in contrast to the presence of ZrO2 and HfO2 in air-formed native film. Potentiodynamic polarization studies indicated a pseudo-passivation behavior of the HEA in 11.5 M HNO3 + 0.05 M NaF at ambient condition. In boiling fluorinated nitric acid, SEM images of TaNbHfZrTi HEA displayed a severely corroded morphology indicating the instability of the metal-oxides of the alloying elements. XPS investigations confirmed the presence of ZrF4, ZrOF2 and HfF4 along with un-protective oxides of Ta, Nb and Ti on the film, resulting in decreased corrosion resistance of TaNbHfZrTi HEA in fluorinated nitric acid.

  • 153. Jayamani, Jayaraj
    et al.
    Thirathipviwat, Pramote
    Han, Junhee
    Gebert, Annett
    Microstructure, mechanical and thermal oxidation behavior of AlNbTiZr high entropy alloy2018In: Intermetallics (Barking), ISSN 0966-9795, E-ISSN 1879-0216, Vol. 100, p. 9-19Article in journal (Refereed)
    Abstract [en]

    The developed as-cast AlNbTiZr high entropy alloy (HEA) resulted in the formation of solid solution bcc dendrites along with the inter-dendritic Zr2Al intermetallic phase. Due to low-density of 5.74 g/cm3 and high yield strength of about 1650 MPa (under compression testing), the alloy exhibited high specific yield strength of approximately 287 kPa m3/kg. Further, the AlNbTiZr HEA showed high fracture strength of 1950 MPa and substantial plastic strain of approximately 17.9%. During the isothermal thermo-gravimetry analysis in the synthetic air, at 873, 973, 1073, 1173 and 1273 K for 3 h, the mass gain behavior of the alloy was nearly parabolic indicating the formation of the protective oxide layer. Further, the long-term oxidation studies of the AlNbTiZr HEA carried out in open air atmosphere for 50 h at 873, 1073 and 1273 K confirmed that the oxide layers formed were protective, intact, and spallation did not occur. Formation of complex oxides such as AlNbO4 and Ti2ZrO6 along with Al2O3, NbO, ZrO2, and TiO2 as confirmed by X-ray diffraction could have led to the sluggish oxidation kinetics of the AlNbTiZr HEA. In contrast, the HfNbTiZr HEA showed poor oxidation resistance at 873 K.

  • 154. Jayamani, Jayaraj
    et al.
    Thyagarajan, K.
    Mallika, C.
    Mudali, U. Kamachi
    Corrosion Behavior of Zirconium, Titanium, and Their Alloys in Simulated Dissolver Solution of Fast Breeder Reactor Spent Nuclear Fuel Using Zircaloy-4 Mock-Up Dissolver Vessel2015In: Nuclear Technology, ISSN 0029-5450, E-ISSN 1943-7471, Vol. 191, no 1, p. 58-70Article in journal (Refereed)
  • 155.
    Johansson, Per
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Mekanisk och tribologisk karakterisering av ferrokrombaserat kompositmaterial för tribologiska användningsområden2014Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
  • 156.
    Johansson, Robert
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Finite element modeling of straightening of thin-walled seamless tubes of austenitic stainless steel2016Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    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.

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  • 157.
    Kamachi Mudali, U.
    et al.
    Corrosion Science and Technology Group Indira Gandhi Center for Atomic Research Kalpakkam, Tamilnadu.
    Jayamani, Jayaraj
    Corrosion Science and Technology Group Indira Gandhi Center for Atomic Research Kalpakkam, Tamilnadu.
    Bulk Metallic Glassy Alloys for Nitric Acid Applications2014Conference paper (Refereed)
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  • 158. Kamachi Mudali, U.
    et al.
    Jayamani, Jayaraj
    Corrosion Science and Technology Group, Indira Gandhi Centre for Atomic Research, Kalpakkam, India.
    Raman, R.K. Singh
    Raj, Baldev
    Corrosion: An Overview of Types, Mechanism, and Requisites of Evaluation2019In: Non‐Destructive Evaluation of Corrosion and Corrosion‐assisted Cracking / [ed] Raman Singh, Baldev Raj, U. Kamachi Mudali, Prabhakar Singh, John Wiley & Sons, 2019Chapter in book (Refereed)
    Abstract [en]

    Corrosion of metals and alloys in an aqueous environment is generally an electrochemical process that requires four essential components: an aqueous electrolyte, an anode, a cathode, and a current carrying pathway (i.e. circuit). In electrochemical corrosion, the anodic oxidation reaction should be compensated by the reduction reaction at cathode. The basis for the types of corrosion is their appearance and propagation mode. The eight well-known forms of corrosion are uniform or general corrosion, galvanic corrosion, pitting corrosion, crevice corrosion, intergranular corrosion, dealloying or selective leaching, erosion corrosion, and environmentally assisted cracking. Apart from these eight forms, the microbiologically influenced corrosion is also considered as one of the important corrosion forms. Nondestructive technique plays a vital role for damage assessment and life extension of the component as it is suitable in detection of the early stages of corrosion so that corrective measures can be taken before damage becomes severe.

  • 159. Karasev, A. V.
    et al.
    Kellner, Hans
    Dalarna University, School of Technology and Business Studies, Materials Technology. KTH.
    Sundqvist, O.
    Memarpour, A.
    Jönsson, P. G.
    Estimation of non-metallic inclusions in industrial Ni based alloys 8252017In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 88, no 4, article id 1600024Article in journal (Refereed)
    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. 

  • 160.
    Karimi Bakhshandi, Reza
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Corrosion Study of yellowmetals in Biodiesel and Test fuel2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    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.

  • 161.
    Karlsson, P
    et al.
    Karlstads Universitet.
    Eriksson, Jenny
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Gaard, A
    Karlstads Universitet.
    Krakhmalev, P
    Karlstads Universitet.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Bergstrom, J
    Karlstads Universitet.
    Galling resistance evaluation of tool steels by two different laboratory test methods for sheet metal forming2012In: Lubrication Science, ISSN 0954-0075, E-ISSN 1557-6833, Vol. 24, no 6, p. 263-272Article in journal (Refereed)
    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.

  • 162. Karlsson, P. G.
    et al.
    Richter, J. H.
    Blomquist, J.
    Uvdal, P.
    Grehk, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    Sandell, A.
    Metal organic chemical vapor deposition of ultrathin ZrO2 films on Si(1 0 0) and Si(1 1 1) studied by electron spectroscopy2007In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 601, no 4, p. 1008-1018Article in journal (Refereed)
    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.

  • 163.
    Karlström, Klaudia
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Värmebehandling av kättingstål: Inverkan på slagsegheten och mikrostrukturen2014Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    One of Ovako:s internal steel grades 9209 is used for chains and thus has high demands on toughness and hardness. After several quality controls has been implemented, among others impact toughness and grain size after martensite hardening, the result of the impact strength was not satisfactory. Several hardening tests in a wide temperature range has been made without satisfactory results. On a few rare occasions, the material had been annealed at 720 °C before hardening. This has resulted in surprisingly high values of impact strength. It’s also been noted that the hardness increases with annealing temperature.

    The main objective of this work is to carry out heat treatments in a temperature range to find the most ideal annealing temperature that maximizes the steel properties and to study the effect of heat treatment on microstructure.

    The result of heat treatment showed that a temperature of 700 °C was the only heat treatment method that resulted in satisfactory impact strength combined with strength requirements.The study of microstructure showed that annealing affects the precipitated particles, which is of probable significance for the ductility and thus improves the impact toughness. Hardness measurements showed that hardness increased with annealing temperature.

  • 164. Kasimagwa, I.
    et al.
    Brabie, Voicu
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Jonsson, P. G.
    Slag corrosion of MgO-C refractories during secondary steel refining2014In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 41, no 2, p. 121-131Article in journal (Refereed)
    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)

  • 165.
    Kasimagwa, Ismail
    Dalarna University, School of Technology and Business Studies, Material Science.
    A study of slag corrosion of oxides and oxide-carbon refractories during steel refining2010Doctoral thesis, comprehensive summary (Other academic)
    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.

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  • 166.
    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 refining2008In: Proceedings for the Third Nordic Symposium for Young Scientists in Metallurgy, 2008, p. 46-50Conference paper (Refereed)
  • 167.
    Kasimagwa, Ismail
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Brabie, Voicu
    Dalarna University, School of Technology and Business Studies, Material Science.
    Jönsson, Pär G.
    Studies on decarburization of MgO-c refractories during ladle preheating2010In: Steel GRIPS Journal, ISSN 1611-4442, no 8, p. 357-363Article in journal (Refereed)
  • 168.
    Kasimagwa, Ismail
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Eriksson, J.
    Brabie, Voicu
    Wahlberg, H.
    Slagline refractory2008In: Proceedings for the SCANMET III-3rd International Conference on Process Development in Iron and Steel making, 2008, p. 377-384Conference paper (Refereed)
  • 169.
    Kellner, Hans
    Dalarna University, School of Technology and Business Studies, Materials Technology. KTH, Tillämpad processmetallurgi.
    Study of Non-metallic Inclusion in Alloy 8252017Doctoral thesis, comprehensive summary (Other academic)
    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.

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  • 170.
    Kellner, Hans
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Karasev, A. V.
    Memarpour, A.
    Jönsson, P. G.
    Evolution of non-metallic inclusions from FeTi70R alloys during alloying of Fe-40Ni-20Cr steels2016In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 87, no 11, p. 1461-1468Article in journal (Refereed)
    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. 

  • 171.
    Kellner, Hans
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology. 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 8252017In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 88, no 12, article id 1700165Article in journal (Refereed)
  • 172.
    Kellner, Hans
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology. 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 Modes2018In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 58, no 2, p. 292-298Article in journal (Refereed)
    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.

  • 173.
    Keränen, Elias
    Dalarna University, School of Technology and Business Studies, Material Science.
    Experimental and modelling ofmachining behavior of stainlesssteel in interrupted cutting withcoated cemented carbide2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

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

  • 174.
    Khoshkhoo, Mohsen Samadi
    et al.
    IFW Dresden, Institut für Komplexe Materialien, Postfach 27 01 16, D-01171 Dresden, Germany.
    Scudino, Sergio
    IFW Dresden, Institut für Komplexe Materialien, Postfach 27 01 16, D-01171 Dresden, Germany.
    Thomas, Jürgen
    IFW Dresden, Institut für Komplexe Materialien, Postfach 27 01 16, D-01171 Dresden, Germany.
    Surreddi, Kumar Babu
    IFW Dresden, Institut für Komplexe Materialien.
    Eckert, Jürgen
    IFW Dresden, Institut für Komplexe Materialien, Postfach 27 01 16, D-01171 Dresden, Germany.
    Grain and crystallite size evaluation of cryomilled pure copper2011In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 509, p. S343-S347Article in journal (Refereed)
  • 175.
    Khraisat, Walid
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Graphite pore filling and surface blistering of sintered Fe-C-Si2012In: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 55, no 3, p. 242-247Article in journal (Refereed)
    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.

  • 176.
    Kolvereid, Anneli
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Framtagande av fördelningsfaktorer för säkrare beräkning vid skrotlastning2014Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    This work is performed at the company Ovako Sweden AB in Hofors as a degree project for the engineering education in materials technology.  In steel industry, the cost of raw materials such as scrap and alloys is the by far largest, and requires resources for the best utilization. By using a program to optimize the loading of scrap, large savings can be made. The thesis presents the compiling of distribution factors for more secure calculations for the scrap loading. These factors are used in the optimization program RAWMATMIX as large savings can be made since this program chooses the most economically advantageous raw material. The results show that the distribution factors differ between different scrap classes, which require a new model for the distribution factors for each class. Furthermore, the optimization program must be adapted to calculate with a certain amount of steel left in the electric arc furnace. 

  • 177. Kumar, S.
    et al.
    Ramesh, M. R.
    Jeyaraj, P.
    Powar, Satvasheel
    Dalarna University, School of Information and Engineering, Energy Technology. Indian Institute of Technology Mandi, Himachal Pradesh, Mandi, India.
    Doddamani, M.
    Buckling behavior of non-uniformly heated 3D printed plain and functionally graded nanocomposites2023In: Polymer Composites, ISSN 0272-8397, E-ISSN 1548-0569, Vol. 44, p. 5450-5463Article in journal (Refereed)
    Abstract [en]

    The functionalized multi-walled carbon nanotubes (MWCNTs) (0.5–5 wt.%) are compounded with high density polyethylene (HDPE), and, subsequently, used for extruding nanocomposite filaments to fabricate nanocomposites (NCs) and functionally graded nanocomposites (FGNCs) through 3D printing. The 3D printed NCs are investigated for coefficient of thermal expansion (CTE), and buckling under different non-uniform temperature distributions (case-1: left edge heating, case-2: centre heating, and case-3: left and right edge heating). A significant reduction in CTE is observed with MWCNT addition and gradation. The highest reduction in CTE is observed for H5 (5 wt.% of MWCNT in HDPE) NC and H1 ⟶ H3 ⟶ H5 (FGNC-2) among the NCs and the FGNCs. It is noted that Tcr (critical buckling temperature) is highest for case-3 and lowest for case-2. The highest deflection is noticed in case-2, while no significant difference is observed in case-1 and case-3 heating conditions. It is also observed that Tcr increases with gradation and MWCNTs addition. The H5 NC and FGNC-2 exhibited the highest Tcr among the NCs and FGNCs, respectively. The maximum deflection is noticed for HDPE, whereas the minimum deflection is noticed for FGNC-2 and H-5 NC among the tested samples. The results also revealed that Tcr is very sensitive to type of heating. © 2023 Society of Plastics Engineers.

  • 178. Larsson, C.
    et al.
    Holden, T. M.
    Bourke, M. A. M.
    Stout, M.
    Teague, J.
    Lindgren, Lars-Erik
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Measurement andniodeling of residual stress in a welded Haynes (R) 25 cylinder2005In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 399, no 1-2, p. 49-57Article in journal (Refereed)
    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. 

  • 179. Lin, Z.
    et al.
    Surreddi, Kumar Babu
    Dalarna University, School of Information and Engineering, Materials Technology.
    Hulme, C.
    Dadbakhsh, S.
    Rashid, A.
    Influence of Electron Beam Powder Bed Fusion Process Parameters on Transformation Temperatures and Pseudoelasticity of Shape Memory Nickel Titanium2023In: Advanced Engineering Materials, ISSN 1438-1656, E-ISSN 1527-2648, Vol. 25, no 12, article id 2201818Article in journal (Refereed)
    Abstract [en]

    Electron beam powder bed fusion (PBF-EB) is used to manufacture dense nickel titanium parts using various parameter sets, including the beam current, scan speed, and postcooling condition. The density of manufactured NiTi parts is investigated in relation to the linear energy input. The results imply that the part density increases with increasing linear energy density to over 98% of the bulk density. With a constant energy input, a combination of low power and low scan speed leads to denser parts. This is attributed to lower electrostatic repulsive forces from lower number density of the impacting electrons. After manufacturing, the densest parts with distinct parameter sets are categorized into three groups: 1) high power with high scan speed and vacuum slow cooling, 2) low power with low scan speed and vacuum slow cooling, and 3) low power with low scan speed and medium cooling rate in helium gas. Among these, a faster cooling rate suppresses phase transformation temperatures, while vacuum cooling combinations do not affect the phase transformation temperatures significantly. Herein, all the printed parts exhibit almost 8% pseudoelasticity regardless of the process parameters, while the parts cooled in helium have a higher energy dissipation efficiency (1 − η), which implies faster damping of oscillations. © 2023 The Authors. Advanced Engineering Materials published by Wiley-VCH GmbH.

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  • 180. Lindgren, L. -E
    et al.
    Gyhlesten Back, Jessica
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Elastic properties of ferrite and austenite in low alloy steels versus temperature and alloying2019In: Materialia, E-ISSN 2589-1529, Vol. 5, article id 100193Article in journal (Refereed)
  • 181.
    Lindgren, Lars-Erik
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Domkin, Konstantin
    Dalarna University, School of Technology and Business Studies, Mechanical Engineering.
    Hansson, Sofia
    Dislocations, vacancies and solute diffusion in physical based plasticity model for AISI 316L2008In: Mechanics of materials, ISSN 0167-6636, E-ISSN 1872-7743, Vol. 40, no 11, p. 907-919Article in journal (Refereed)
    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.

  • 182.
    Lindgren, Lars-Erik
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Material Science.
    Carlsson, Per
    Dalarna University, School of Technology and Business Studies, Material Science.
    Simulation of hydroforming of steel tube made of metastable stainless steel2010In: International journal of plasticity, ISSN 0749-6419, E-ISSN 1879-2154, Vol. 26, no 11, p. 1576-1590Article in journal (Refereed)
    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. 

  • 183.
    Lindgren, Michael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    An improved model for the longitudinal peak strain in the flange of a roll formed U-channel developed by FE-analyses2007In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 78, no 1, p. 82-87Article in journal (Refereed)
    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.

  • 184.
    Lindgren, Michael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Cold roll forming of a U-channel made of high strength steel2007In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 186, no 1-3, p. 77-81Article in journal (Refereed)
    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.

  • 185.
    Lindgren, Michael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Experimental and computational investigation of the roll forming process2009Doctoral thesis, monograph (Other academic)
    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.

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  • 186. Lindgren, Michael
    et al.
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Comparison of Roll Forming Using Different Forming Strategies and Bending2014In: IDDRG 2014, conference proceedings: Innovations for the sheet metal industry, June 1-4 2014, Paris, France / [ed] SFAR Hedi, MAILLARD André, 2014Conference paper (Other academic)
  • 187.
    Lindgren, Michael
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Wikström, Lars
    Roll forming of partially heated cold rolled stainless steel2009In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 209, no 7, p. 3117-3124Article in journal (Refereed)
    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.

  • 188.
    Lindgren, Michael
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Edberg, Jonas
    Lindgren, Lars-Erik
    Roll forming2015In: Handbook of Manufacturing Engineering and Technology, Springer-Verlag London Ltd , 2015, p. 285-307Chapter in book (Other academic)
    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.

  • 189. Lindgren, Michael
    et al.
    Ingmarsson, Lars-Olof
    3D roll-forming of hat-profile with variable depth and width2009In: Rollform09 1st International congress on roll forming, Bilbao, Spain, 2009Conference paper (Other academic)
    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.

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  • 190. Lissel, Linda
    et al.
    Engberg, Göran
    Dalarna University, School of Technology and Business Studies, Material Science.
    Prediction of the microstructural evolution during hot strip rolling of Nb microalloyed steels2007In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 558-559, no 2, p. 1127-1132Article in journal (Refereed)
    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%.

  • 191.
    Ljungberg, Adam
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Schmidt, Nathalie
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Deformationsstrukturer i ett duplext rostfritt stål (SAF 2507)2014Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    In order to improve the processes and the use of the duplex stainless steel SAF 2507, its deformation properties has to be investigated and explained. Through EBSD-analysis deformation structures and pole figures have been developed to describe the behavior of the material during deformation. Also Taylor factors, Young’s modules and Poisson's ratio have been developed in order to investigate the material's anisotropy.

    The experiments have been performed on samples of SAF 2507 which has been plastically deformed at different strains. The strains studied are undeformed sample, samples drawn uniaxial drawn to 7.7 % and 24.3 % elongation, and one sample which is cyclically loaded to 3% elongation. The steel we have investigated is produced by two different methods, but in this report, only the extruded steel is investigated.

    By comparing how different mechanical properties of the steel behave during plastic deformation, the result shows that the steel’s ferrite phase behaves anisotropically with a hint of increasing isotropy when the deformation is increasing. The austenite phase behaves isotropic and does not become more or less isotropic with increasing deformation. The substructures in the ferrite phase are clearly increasing with increasing deformation, and are seen mainly in the austenite phase after 24 % deformation.

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  • 192. Mahade, S.
    et al.
    Björklund, S.
    Govindarajan, S.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Joshi, S.
    Novel wear resistant carbide-laden coatings deposited by powder-suspension hybrid plasma spray: Characterization and testing2020In: Surface and Coatings Technology, ISSN 0257-8972, Vol. 399, article id 126147Article in journal (Refereed)
  • 193.
    Malakizadi, Amir
    et al.
    Department of Materials and Manufacturing Technology, Chalmers University of Technology, Gothenburg, Sweden .
    Cedergren, Stefan
    Department of Materials and Manufacturing Technology, Chalmers University of Technology, Gothenburg, Sweden .
    Surreddi, Kumar Babu
    Nyborg, Lars
    Department of Materials and Manufacturing Technology, Chalmers University of Technology, Gothenburg, Sweden .
    A methodology to evaluate the machinability of Alloy 718 by means of FE simulation2013In: International Conference on Advanced Manufacturing Engineering and Technologies. Stockholm: NEWTECH, 2013, p. 95-106Conference paper (Refereed)
  • 194. Malmberg, P.
    et al.
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Material Science.
    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 sources2007In: Rapid Communications in Mass Spectrometry, ISSN 0951-4198, E-ISSN 1097-0231, Vol. 21, no 5, p. 745-749Article in journal (Refereed)
    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.

  • 195.
    Mane, Mayur
    Dalarna University, School of Information and Engineering.
    Mechanical and tribological characterization of additivemanufactured Co-free tool steels aimed for cutting tool bodies2021Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Additive manufacturing (AM) is an emerging and interesting technology that enables some of theproduct development projects (PDPs) to produce products that have mechanical and tribologicalproperties comparable to products that are conventionally manufactured. Selective laser melting(SLM) is an additive manufacturing technology that is predominantly used for the production of metalbased components (i.e. it could be pure metal, alloys, and metal matrix composites). This workevaluates and ranks two different steel grades produced with SLM technology in tribological andcutting tool applications at AB Sandvik Coromant. The two steel grades used in this work were Cofree maraging steel alloy and Co-free W360 AMPO alloy. Both the grades are Cobalt free, hencedeveloped as a sustainable alternative for the future. The W360 AMPO alloy is a hot-work tool steelwith high temperature wear resistance and heat resistance. The work covers the characterization ofmicrostructure and chemical composition, mechanical properties, and tribological properties toevaluate the performance of the tool steel grades when used as tool bodies in drilling applications.The microstructure and chemical composition of the additive manufactured and heat-treated tool steelswere analyzed using SEM and EDS. The mechanical properties were evaluated using micro-Vickersindentation and scratch testing while the tribological properties were evaluated using pin-on-disctesting where counter material used was quenched and tempered steel. The application test included asimulated chip wear test using chip breakers (CB’s) and an actual drilling test, both performed at ABSandvik Coromant. To study the effect of surface topography on the adhesion tendency, the simulatedchip wear test was performed on both milled and grounded chip breaker (CB) samples. The drillingtest was done with three different test-set ups; function test, 30° inclined exit, and forced tool life test.The cellular microstructure was observed on Co-free maraging steel alloy sample, while themicrostructure was tempered martensite in W360 AMPO alloy. Elemental analysis revealed thechemical composition of the two steel grades. The measured hardness for both the samples Co-freemaraging steel alloy and W360 AMPO was found to be within the specification of demands (50-52HRC), although the hardness of W360 AMPO was a bit higher than Co-free maraging steel alloy. Theresults of the pin-on-disc tests showed that the wear resistance of the W360 AMPO alloy issignificantly higher than that of the Co-free maraging steel alloy, the tribo-system used was similarwhen compared to the actual application. Also, after analyzing the pin made up of quenched andtempered steel 34CrNiMo6 (SS2541) it can be seen that due to the W360 AMPO sample the volumeloss of the pin is almost 4 times when compared to Co-free maraging steel alloy. The result from thesimulated chip wear test showed that W360 AMPO has better wear characteristics. Adhesion ofworkpiece material (SS2541) was observed on both samples. In the simulated chip wear test, thesurface topography effect was studied by performing a test on milled and grounded CBs. GroundedCBs showed less adhesion tendency compared with milled CBs on both samples but the wearcharacteristics were similar irrespective of the surface roughness. The result from the drilling testshowed wear scar was predominant on a drill with Co-free maraging steel alloy and a drill with W360AMPO alloy was intact. Future possible investigations proposed after findings from experimentalresults may lead to future work.

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  • 196. Maurya, H. S.
    et al.
    Jayamani, Jayaraj
    Dalarna University, School of Information and Engineering, Materials Technology.
    Vikram, R. J.
    Juhani, K.
    Sergejev, F.
    Prashanth, K. G.
    Additive manufacturing of TiC-based cermets: A detailed comparison with spark plasma sintered samples2023In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 960, article id 170436Article in journal (Refereed)
    Abstract [en]

    The present work is a comparative study on the TiC-430 L ferritic stainless steel (FSS) cermets manufactured via two powder metallurgical processes, namely, conventional spark plasma sintering (SPS) and metal additive manufacturing (AM) process (laser powder-bed fusion process (LPBF)/selective laser melting (SLM)). The rescanning strategy has been used to preheat and melt the powder bed with different laser parameters during the SLM process to suppress the presence of residual thermal stress leading to the fabrication of cermets without cracks. The as-fabricated SPS samples (95 %) show a relatively lower density than the SLM-built parts (~98 %). A study of their mechanical properties such as hardness, compressive strength, and fracture toughness was conducted and discussed in detail. Further, the corrosion behavior of the fabricated cermets parts was evaluated in 3.5 wt% NaCl. The SLM-prepared specimens reveal finer microstructures and better mechanical properties (compressive strength and fracture toughness) due to the presence of fine microstructure. Furthermore, the corrosion current density of TiC-430 L fss-based cermets fabricated by SLM is approximately 270 times lower than that of cermets parts fabricated by SPS, indicating excellent corrosion resistance. On the other hand, the hardness shows an opposite trend, where the SPS samples show the maximum hardness as compared to the SLM counterparts due to the presence of hard and coarse TiC particles along with some metallic carbides formed during the SPS process. The results reveal that AM processes not only can fabricate cermets with intricate shapes but can also fabricate them with improved mechanical and corrosion properties.

  • 197. Maurya, H. S.
    et al.
    Jayamani, Jayaraj
    Dalarna University, School of Information and Engineering, Materials Technology.
    Wang, Z.
    Juhani, K.
    Sergejev, F.
    Prashanth, K. G.
    Investigation of the tribological behavior of the additively manufactured TiC-based cermets by scratch testing2023In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 959, article id 170496Article in journal (Refereed)
    Abstract [en]

    This study deals with the tribological behavior of the TiC-430 L SS cermets fabricated via an additive manufacturing process such as laser powder bed fusion/selective laser melting. A gradient microstructure (finer and coarser morphology) can be observed in the fabricated parts due to SLM's complex thermal history. Using Rockwell indenter, single and multiple passes scratch tests have been performed as a function of applied load to study the wear mechanism of the binder and matrix phase. A surface 3D profilometer was used to analyze the scratch track variation in terms of scratch width and depth. Scanning Electron microscopy (SEM) analysis was performed on the scratched cermet parts to study the wear mechanism and microstructural analysis. It has been observed that the scratch hardness increases with increasing load and the same decreases with increasing the number of passes. Similarly, the coefficient of friction increases with increasing load. Cermets with complex microstructural features exhibit high wear resistance under low loads and for higher loads, multiple passes can lead to tribolayer formation.

  • 198.
    Memarpour, Arashk
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    An Experimental Study of Submerged Entry Nozzles (SEN) Focusing on Decarburization and Clogging2011Doctoral thesis, comprehensive summary (Other academic)
    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.

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  • 199.
    Memarpour, Arashk
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Brabie, Voicu
    Dalarna University, School of Technology and Business Studies, Material Science.
    Jönsson, Pär
    Studies of effect of glass/silicon powder coatings on clogging behaviour of submerged entry nozzles when using REM alloyed stainless steels2011In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 38, no 3, p. 229-239Article in journal (Refereed)
    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.

  • 200.
    Memarpour, Arashk
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    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 clogging2011In: Steel Grips - Journal of Steel and Related Materials, ISSN 1866-8453Article in journal (Refereed)
    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.

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