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  • 101.
    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. 

  • 102. 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. 

  • 103. 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, ISSN 2589-1529, Vol. 5, article id 100193Article in journal (Refereed)
  • 104.
    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 (Print), 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.

  • 105.
    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.

  • 106.
    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.

  • 107.
    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.

  • 108. 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)
  • 109.
    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.

  • 110.
    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.

  • 111.
    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.

  • 112.
    Mattsson, Amanda
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Lindholm, Malin
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Friction and wear mechanisms of PCBN in sliding contact with tool steel2011Independent thesis Basic level (degree of Bachelor)Student thesis
  • 113.
    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.

  • 114.
    Michael, Lindgren
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Experimental investigations of the roll load and roll torque when high strength steel is roll formed2007In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 191, no 1-3, p. 44-47Article in journal (Refereed)
    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.

  • 115.
    Molnar, David
    Dalarna University, School of Technology and Business Studies, Materials Technology. KTH, Tillämpad materialfysik.
    Generalised stacking fault energy and plastic deformation of austenitic stainless steels2018Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Austenitic stainless steels are primarily known for their exceptional corrosion resistance. They have the face centred cubic (FCC) structure which is stabilised by adding nickel to the Fe-Cr alloy. The Fe-Cr-Ni system can be further extended by adding other elements such as Mn, Mo, N, C, etc. in order to improve the properties. Since austenitic stainless steels are often used as structural materials, it is important to be able to predict their mechanical behaviour based on their composition, microstructure, magnetic state, etc.

    In this work, we investigate the plastic deformation behaviour of austenitic stainless steels by theoretical and experimental approaches. In FCC materials the stacking fault energy (SFE) plays an important role in the prediction of the deformation modes. Based on the magnitude of the SFE different deformation modes can be observed such as martensite formation, deformation twinning, dissociated or undissociated dislocation glide. All these features influence the behaviour differently, therefore it is desired to be able to predict their occurrence. Alloying and temperature have strong effect on the SFE and thus on the mechanical properties of the alloys. Several models based on the SFE and more recently on the so called generalised stacking fault energy (GSFE or γ-surface) are available to predict the alloy's affinity to twinning and the critical twinning stress representing the minimum resolved shear stress required to initiate the twinning deformation mechanism. One can employ well established experimental techniques to measure the SFE. On the other hand, one needs to resort to ab initio calculations based on density functional theory (DFT) to compute the GSFE of austenitic steels and derive parameters like the twinnability and the critical twinning stress. 

    We discuss the effect of the stacking fault energy on the deformation behaviour for two different austenitic stainless steels. We calculate the GSFE of the selected alloys and based on different models, we predict their tendency for twinning and the critical twinning stress. The theoretical predictions are contrasted with tensile tests and electron backscatter diffraction (EBSD) measurements. Several conventional and in situ tensile test are performed to verify the theoretical results. We carry out EBSD measurements on interrupted and fractured specimens and during tensile tests to closely follow the development of the microstructure. We take into account the role of the intrinsic energy barriers in our predictions and introduce a new and so far unique way to experimentally obtain the GSFE of austenitic stainless steels. Previously, only the SFE could be measured precisely by well-designed experiments. In the present thesis we go further and propose a technique that can provide accurate unstable stacking fault energy values for any austenitic alloy exhibiting twinning. 

  • 116.
    Molnar, David
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology. KTH.
    Engberg, Göran
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Li, Wei
    Lu, Song
    Hedström, Peter
    Kwon, Se Kyun
    Vitos, Levente
    Experimental study of the gamma-surface of austenitic stainless steels2019In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 173, p. 34-43Article in journal (Refereed)
    Abstract [en]

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

  • 117.
    Molnar, David
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology. KTH.
    Engberg, Göran
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Li, Wei
    Vitos, Levente
    Deformation properties of austenitic stainless steels with different stacking fault energies2018In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 941, p. 190-197Article in journal (Refereed)
    Abstract [en]

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

  • 118.
    Molnar, David
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology. KTH.
    Sun, Xun
    Lu, Song
    Li, Wei
    Engberg, Göran
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Vitos, Levente
    Effect of temperature on the stacking fault energy and deformation behaviour in 316L austenitic stainless steel2019In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 759, p. 490-497Article in journal (Refereed)
    Abstract [en]

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

  • 119.
    Molnar, David
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology. KTH.
    Vida, Ádám
    Huang, Shuo
    Chinh, Nguyen Q
    The effect of cooling rate on the microstructure and mechanical properties of NiCoFeCrGa high-entropy alloy2019In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 54, no 6, p. 5074-5082Article in journal (Refereed)
    Abstract [en]

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

  • 120.
    Nilsson, Maria
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Tribology in Metal Working2012Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

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

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

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

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

  • 121.
    Nilsson, Maria
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    An investigation of worn work roll materials used in the finishing stands of the hot strip mill for steel rolling2012Conference paper (Refereed)
    Abstract [en]

    The surface failure characteristics of different work roll materials, i.e. High Speed Steel, High Chromium Iron and Indefinite Chill Iron, used in the finishing stands of a hot strip mill have been investigated using stereo microscopy, 3D optical profilometry, scanning electron microscopy and energy dispersive X-ray spectroscopy. The results show that the surface failure mechanisms of work rolls for hot rolling are very complex, involving plastic deformation, abrasive wear, adhesive wear, mechanical and thermal induced cracking, material transfer and oxidation. Despite the differences in chemical composition and microstructure, the tribological response of the different work roll materials was found to be strongly dependent on the material microstructure and especially the presence and distribution of microstructural constituents, such as the different carbide phases and graphite (in the case of Indefinite Chill Iron). Cracking and chipping of the work roll surfaces, both having a negative impact on work roll wear, are strongly influenced by the presence of carbides, carbide networks and graphite in the work roll surface. Consequently, the amount of carbide forming elements as well as the manufacturing process must be controlled in order to obtain an optimised microstructure and a predictable wear rate.

  • 122.
    Nilsson, Maria
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    An investigation of worn work roll materials used in the finishing stands of the hot strip mill for steel rolling2013In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 227, no 8, p. 837-844Article in journal (Refereed)
    Abstract [en]

    The surface failure characteristics of different work roll materials, i.e. High Speed Steel, High Chromium Iron and Indefinite Chill Iron, used in the finishing stands of a hot strip mill have been investigated using stereo microscopy, 3D optical profilometry, scanning electron microscopy and energy dispersive X-ray spectroscopy. The results show that the surface failure mechanisms of work rolls for hot rolling are very complex, involving plastic deformation, abrasive wear, adhesive wear, mechanical and thermal induced cracking, material transfer and oxidation. Despite the differences in chemical composition and microstructure, the tribological response of the different work roll materials was found to be strongly dependent on second phase constituents such as the size, morphology and distribution of different carbide phases and graphite (in the case of Indefinite Chill Iron) which was found to promote cracking. Cracking and chipping of the work roll surfaces, both having a negative impact on work roll wear, are strongly influenced by the presence of carbides, carbide networks and graphite in the work roll surface. Consequently, the amount of carbide forming elements as well as the manufacturing process must be controlled in order to obtain an optimised microstructure and a predictable wear rate.

  • 123.
    Nilsson, Maria
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology. Tribomaterials group, The Ångström Laboratory, Uppsala University, Sweden.
    Microstructural, mechanical and tribological characterisation of roll materials for the finishing stands of the hot strip mill for steel rolling2013In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 307, no 1-2, p. 209-217Article in journal (Refereed)
    Abstract [en]

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

  • 124. Olofsson, J.
    et al.
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Jacobson, S.
    Tribofilm formation of lightly loaded self mated alumina contacts2012In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 289, p. 39-45Article in journal (Refereed)
    Abstract [en]

    A tribofilm is formed on alumina surfaces that have been slid against alumina surfaces. The tribofilm is formed by alumina wear particles that have been ground, agglomerated and tribosintered to a film. The tribofilm smoothens out the surface topography and fills up cavities. Tribofilms on alumina surfaces have been investigated with respect to surface appearance, hardness and chemical composition. Surface preparation and surrounding humidity have shown to affect the character and lateral distribution of the tribofilm. The tribofilm that was formed in humid air was softer than the tribofilm formed in dry air. XPS analysis revealed the chemical shift of the Al 2p peak did not differ between the tribofilms that was formed in different humidity, nor the unworn reference surface, finding that no hydroxide was found on the alumina surfaces. Also, no tribochemical changes could be detected by ToF-SIMS analysis. (C) 2012 Elsevier B.V. All rights reserved.

  • 125.
    Olovsjö, S
    et al.
    Atlas Copco.
    Johanson, R
    Atlas Copco.
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    On the understanding of cemented carbide degradation in rock drilling: the importance of metallographic sample preparation2012In: Proceedings of Euro PM 2012 Congress & Exhibition Vol. 2, 2012Conference paper (Refereed)
  • 126.
    Olovsjö, S
    et al.
    Atlas Copco.
    Johanson, R
    Atlas Copco.
    Falsafi, M
    Atlas Copco.
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Surface failure and wear of cemented carbide rock drill buttons: the importance of sample preparation and optimized microscopy settings2013In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 302, no 1-2, p. 1546-1554Article in journal (Refereed)
    Abstract [en]

    The combination of suitable mechanical properties and wear resistance makes cemented carbide one of the most interesting engineering composite materials for tribological applications, such as in rock drilling. Despite the fact that cemented carbide buttons have been used in rock drilling applications for a long time the detailed understanding of the prevailing wear mechanisms is far from complete and wear and breakage of rock drill buttons are still one of the lifetime-limiting factors for rock drill bits. Consequently, further research in this area, including detailed characterization of worn drill button surfaces and sub-surface regions, is needed in order to support the future development of new cemented carbide grades with improved failure and wear resistance. In the present paper, high resolution scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and Auger electron spectroscopy (AES) have been used to characterize the wear and failure mechanisms of worn drill buttons and samples exposed to well controlled impact and scratch tests performed in the laboratory. The most important mechanisms of surface failure and wear were found to be severe plastic deformation, cracking, crushing of individual WC grains and mechanical/tribochemical degradation of the Co binder phase including Co depletion. Fracture cross-sectioning under tensile stress-state was found to be the best method for achieving large and reliable sub-surface cross-sections within a short time and to a low cost. The importance of optimized microscopy and spectroscopy settings for enhanced surface sensitivity for the examination of small-scale tribological phenomena is illuminated and discussed.

  • 127.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    On the use of scratch testing as a model experiment for evaluating the initial wear of cemented carbidein rock drilling2013Conference paper (Refereed)
  • 128.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Surface and wear characteristics of electrical discharge machined (EDM) cemented carbide drawing dies2014In: Jernkontorets Forskning, ISSN 0280-2481Article, review/survey (Other academic)
  • 129.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Tribological aspects of conventional wire drawing - A case study2014In: Jernkontorets Forskning, ISSN 0280-2481Article, review/survey (Other academic)
  • 130.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Tråddragningens tribologi2015In: Nordisk Trådteknisk Förening: Årsbok 2015 / [ed] Leif Eriksson, NTTF , 2015Chapter in book (Other academic)
  • 131.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Wear resistant materials in mining, drilling and rock handling2014Conference paper (Other academic)
  • 132.
    Olsson, Mikael
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Friction characteristics and material transfer tendency in metal powder compaction2011In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 271, no 9-10, p. 1903-1908Article in journal (Refereed)
    Abstract [en]

    The friction characteristics and material transfer tendency between metal powder and die tool material in metal powder compaction play an important role in the production of near-net-shape components of high density. A natural step to further increase the green density and simplify the sintering process is to reduce the amount of internal lubricant in the powder since the volume fraction of an organic lubricant will result in a significant contribution to the resulting porosity. However, this will significantly increase the adhesive contact and thus the friction between the die and the powder/green body during the powder compaction process. As a result, the compaction and ejection forces as well as the wear rate of the die and punch surfaces will increase. Consequently, improved knowledge concerning the friction mechanisms prevailing at the metal powder/die tool material interface is needed. The present paper will present data regarding the influence of type of tool and coating material on the friction characteristics and material transfer tendency during simulated powder compaction of a water atomized plain iron powder under no or starved lubrication conditions using two different laboratory tribo tests. Tool materials investigated include ingot cast tool steel, powder metallurgy (PM) tool steel and TiAlN and DLC-type PVD coatings. Post-test characterization using scanning electron microscopy and energy dispersive X-ray spectroscopy was used to analyse the tribo surfaces and especially the tendency to material transfer and tribo film formation. The results show that the material transfer tendency is mainly controlled by strong adhesive metal–metal contacts and that a PVD coating showing intrinsic low-friction properties and a smooth surface topography may significantly reduce the interaction between the mating surfaces promoting a stable friction and a low material transfer tendency.

  • 133.
    Olsson, Mikael
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Heinrichs, J
    Uppsala Universitet.
    Yvell, Karin
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Jacobson, S
    Uppsala Universitet.
    On the relevance of hardness as a material parameter in the deformation and wear of  cemented carbides in rock drilling2014Conference paper (Refereed)
  • 134.
    Olsson, Mikael
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Heinrichs, J
    Uppsala Universitet.
    Yvell, Karin
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Jacobson, S
    Uppsala Universitet.
    Towards a better understanding of the wear of cemented carbide drill bit inserts in rock drilling2014Conference paper (Other academic)
  • 135.
    Olsson, Mikael
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Heinrichs, Jannica
    Yvell, Karin
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Jacobson, Staffan
    Initial degradation of cemented carbides for rock drilling: model studies of the tribological contact against rock2015In: International journal of refractory metals & hard materials, ISSN 0958-0611, E-ISSN 2213-3917, Vol. 52, p. 104-113Article in journal (Refereed)
    Abstract [en]

    Hardness and fracture toughness are often used as the prime material parameters to characterise cemented carbides used in rock drilling. However, the deformation and wear of cemented carbide are too complicated to be described by these parameters alone. The cemented carbide and the wearing rock mineral are both composite materials, containing phases with widely varying hardness. Moreover, the deformation behaviour of the individual phases may be strongly anisotropic, as for the WC grains in the cemented carbide. The wear of the cemented carbide typically occurs on the scale of individual grains or smaller. Contrastingly, the hardness stated for both is typically a macroscopic value, averaged over numerous grains, orientations, etc. The present investigation aims to contribute to the understanding of the relations between microstructure, properties and wear mechanisms of cemented carbide buttons in rock drilling. It is focused on the role of scale of deformation in relation to size of the different phases of the cemented carbide. This is achieved by simplifying the contact situation of the rock drill button to a single stylus sliding contact between a granite stylus and a polished cemented carbide surface. The deformation and wear of this well controlled contact is then evaluated on the sub-micrometer scale; using high resolution FEG-SEM with EBSD, FIB cross-sectioning and AFM. The results show that even an extremely local deformation, such as slip within individual WC grains, affects the tribological contact, and that the nominally much softer granite may cause deformation both within individual WC grains, and on the composite scale. The results are discussed with respect to their significance for wear of cemented carbides in rock drilling. (C) 2015 Elsevier Ltd. All rights reserved.

  • 136.
    Olsson, Mikael
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Högman, B
    Uddeholms.
    Influence of tool steel microstructure on the prevailing wear mechanisms in metal powder compaction2012In: TOOL 2012 : proceedings of the 9th international tooling conference, developing the world of tooling, Montanuniversität Leoben 11-14 September 2012 / [ed] Herald Leitner, Regina Kranz, Angelika Tremmel, Knittelfeld: Gutenberghaus , 2012, p. 409-416Conference paper (Refereed)
  • 137.
    Olsson, Mikael
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Karlsson, P.
    Eriksson, Jenny
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Gåård, A.
    Krakhmalev, P.
    Bergström, J.
    Galling resistance evaluation of tool steels by two different laboratory test methods for sheet metal forming2011In: Proceedings of the 18th International Conference on Wear of Materials, Philadelphia, USA, 2011Conference paper (Other academic)
  • 138.
    Olsson, Mikael
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Surreddi, Kumar Babu
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Scratch testing of cemented carbides - Influence of Co binder phase and WC grain size on surface deformation and degradation mechanisms2018In: Proceedings of The 18th Nordic Symposium on Tribology - Nordtrib 2018 / [ed] Staffan Jacobson, Uppsala: Uppsala University, 2018Conference paper (Refereed)
    Abstract [en]

    In the present study, the microstructural response of some commercial cemented carbide grades during scratchinghas been analyzed and evaluated by a number of post-test characterization techniques. The influence of Co binder phase content and WC grain size on the deformation and degradation on a WC grain size scale and on a composite scaleare evaluated. The results clearly illustrate the complexity of deformation, degradation and wear of cemented carbide and the dynamics of the diamond stylus / cemented carbide contact during the scratching event. For all cementedcarbide grades the microstructure has a strong impact on the observed degradation mechanisms and the resistance to deformation and degradation was found to increase with decreasing Co content and decreasing WC grain size.

  • 139.
    Olsson, Mikael
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Surreddi, Kumar Babu
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Thin hard CVD and PVD coatings and their potential in steel wire drawing applications2018In: Proceedings of The 18th Nordic Symposium on Tribology - NORDTRIB 2018 / [ed] Staffan Jacobson, Uppsala: Uppsala University, 2018Conference paper (Refereed)
    Abstract [en]

    In the present work, the potential of using thin hard CVD and PVD coatings in order to improve the performance of cemented carbide steel wire drawing nibs is evaluated. Coating materials include some state-of-the-art CVD and PVD coatings and pre- and post-coating treatments were used to improve the surface topography of the coated functional surfaces. The tribological performance of the coatings has been evaluated by sliding wear tests and wire drawing experiments under well controlled conditions. Post-test characterization of the coated nibs using 3D optical surface profilometry, scanning electron microscopy and energy dispersive X-ray spectroscopy illustrates the pros and cons of the two deposition techniques but also that the coatings have a potential to improve the performance of cemented carbide nibs in steel wire drawing applications.

  • 140.
    Olsson, Mikael
    et al.
    Dalarna University, School of Technology and Business Studies, Material Science.
    Wadman, B.
    Eriksson, Jenny
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Schedin, E.
    Madsen, E.
    Bay, N.
    Influence of stainless steel surface texture on galling2011In: Proceedings of the 18th International Conference on Wear of Materials, Philadelphia, USA, 2011Conference paper (Other academic)
  • 141.
    Olsson, Mikael
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology. Ångström Tribomaterials Group, Uppsala University.
    Yvell, Karin
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Heinrichs, J.
    Bengtsson, M.
    Jacobson, S.
    Surface degradation mechanisms of cemented carbide drill buttons in iron ore rock drilling2017In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 388-389, p. 81-92Article in journal (Refereed)
    Abstract [en]

    The wear behavior of cemented carbide rock drill buttons is influenced by many factors, which include the composition and microstructure of the cemented carbide material, the nature of the rock material, and the conditions of the rock drilling operation. Depending on the type of rock and on the drilling procedure used, the cemented carbide is exposed to substantially differing mechanical and thermal conditions. In the present study, the surface degradation and wear mechanisms of cemented carbide drill buttons exposed to iron ore rock drilling have been characterized based on a combination of high resolution scanning electron microscopy (SEM), focused ion beam cross-sectioning (FIB), energy-dispersive X-ray spectroscopy (EDS) and electron back scatter diffraction (EBSD).The results show a significant difference in surface degradation and wear between the front and peripheral buttons of the drill bits. While the front buttons display a relatively smooth worn surface with shallow surface craters the peripheral buttons display a reptile skin pattern, i.e. plateaus, 200-300. μm in diameter, separated by valleys, typically 40-50. μm wide and 15-30. μm deep, The reptile skin pattern is obtained in regions where the peripheral buttons are in sliding contact against the drill hole walls and exposed to high surface temperatures caused by the frictional heating. The results indicate that the reptile skin pattern is related to friction induced thermal stresses rather than mechanical contact stresses, i.e. the reptile skin pattern is formed due to thermal fatigue, rather than mechanical fatigue, caused by the cyclic frictional heating generated at the cemented carbide button/iron ore interface.

  • 142.
    Olsson, Mikael
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Yvell, Karin
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Heinrichs, Jannica
    Uppsala University.
    Bengtsson, Maria
    LKAB Wassara AB.
    Jacobson, Staffan
    Uppsala University.
    Surface degradation mechanisms of cemented carbide drill buttons exposed to iron ore rock drilling2016In: Proceedings of the 17th Nordic Symposium on Tribology - Nordtrib 2016, 2016Conference paper (Refereed)
    Abstract [en]

    The wear behavior of cemented carbide rock drill buttons is influenced by many factors, which include the composition and microstructure of the cemented carbide material, plus the conditions of the rock drilling operation, such as drilling parameters, drill button geometry and the nature of the rock material. Depending on the type of rock and on the drilling procedure used, the cemented carbide is exposed to substantially differing mechanical and thermal conditions. Under conditions of high mechanical stress and high temperatures, typical for drilling in highly abrasive rocks such as granite, the worn cemented carbide buttons are usually very smooth, with the roughness limited to within the size of individual WC grains. When drilling under conditions of moderate mechanical stress and high temperatures, typical for drilling in low-abrasive rock, such as ores with e.g. magnetite, the surface damage of the buttons usually includes a macroscopic surface wear pattern, commonly referred to as “reptile skin”, in an otherwise smooth surface. The crack growth associated to the valleys of the reptile skin pattern eventually leads to catastrophic fracture of the button, unless the cracked surface layer is repeatedly ground off before the cracks grow too deep. So despite the low general wear rate, the wear life of drill buttons becomes severely restricted by the surface cracks. The present study focuses on revealing the degradation mechanisms behind the formation of the reptile skin. This is done by analyzing drill buttons exposed to different stages of degradation and wear from drilling in iron ore. The work is based on a combination of high resolution scanning electron microscopy (SEM), focused ion beam microscopy (FIB), energy-dispersive X-ray spectroscopy (EDS) and electron back scatter diffraction (EBSD).

  • 143.
    Osterman, Jesper
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Skarp, Kent
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Tong, Au Ping
    Zhukov, Andrey
    Chigrinov, Vladimir
    Kwok, Hoi Sing
    Mechanically stabilized bistable FLC cells on plastic substrates2005In: Proceedings of the twenty-fifth international display research conference, Eurodisplay 2005, 2005Conference paper (Refereed)
    Abstract [en]

    The electro-optical properties of a full v flexible photo-aligned FLC cell are investigated. Two different methods, sticky spacers together with a photo-sensitive monomer and polymer spacers in a regular pattern formed by photo-lithography, are proposed to stabilize the structure in order to increase the bending tolerance of the FLC material during deformation of the cell.

  • 144.
    Osterman, Jesper
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Tong, Au Ping
    Skarp, Kent
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Chigrinov, Vladimir
    Kwok, Hoi Sing
    Properties of azo-dye alignment layer on plastic substrates2005In: Journal of the Society for Information Display, ISSN 1071-0922, E-ISSN 1938-3657, Vol. 13, no 12, p. 1003-1009Article in journal (Refereed)
    Abstract [en]

    The alignment properties of the azo dye photo-alignment material SD-1/SDA-2 on plastic substrates are investigated. Excellent alignment with high anchoring energy can be achieved with a polarized UV dose less than 1.0 J/cm2. A reflective 6-digit flexible passive matrix driven TN-LCD for smart card applications showing excellent electro-optical properties is demonstrated.

  • 145.
    Pejryd, Lars
    et al.
    Örebro University.
    Larsson, Joakim
    Örebro University.
    Olsson, Mikael
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Process monitoring of wire drawing using vibration sensoring2017In: CIRP - Journal of Manufacturing Science and Technology, ISSN 1755-5817, E-ISSN 1878-0016, Vol. 18, p. 65-74Article in journal (Refereed)
    Abstract [en]

    Automating the detection of processing conditions that may lead to defects in the wire during the wire drawing process is of high interest to the industry. Current practise is based primarily on operator experience. Increasing demands on product quality and process robustness emphasises the need for development of robust in-process detection methods. This work is focusing on investigating the potential of using vibration monitoring to detect process deficiencies or variations that may lead to defects in the product. Wire drawing of a carbon steel in different lubricating situations was used to investigate vibration signal response together with force measurements and surface investigation of the wire product. The results show that vibration measurement is capable of detecting loss of lubrication that leads to poor surface quality of the wire.

  • 146.
    Persson, Petter
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Finite element analysis of hot rolling in the blooming mill2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 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.

  • 147.
    Persson, Petter
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Mätsystemanalys av mätmetod för kontroll av anoljningsgrad2014Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    At the end of the continuous annealing line at SSAB´s production plant in Borlänge a large portion of the produced sheet metal is oiled. Oiling of sheet metal is performed when a higher corrosion resistance is desirable, for example during transportation in a ship where it is exposed to a corrosive environment. To ensure that the correct amount of oil is applied, a visual inspection is done three times a day and each time the degree of oiling is changed. In addition, controls are done six times a year with a consumption measuring device. 

    The purpose of this thesis is to evaluate the current measurement method and to consider its use in the future. Possible improvements of this method are sought. Also, an oil thickness sensor is evaluated as an alternative.

    Three different measurement methods are used during the work with this thesis and a measurement systems analysis is carried out. This is done by compiling data in the statistical software Minitab 16 and the results were interpreted with regards to accuracy and precision.

    The results show that the consumption measuring device delivers more stable values than the oil thickness sensor when used during production. This is due to the sensors small measurement area and the drop-like way the oiling device applies oil. 

  • 148.
    Persson, Tomas
    et al.
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Riedel, Jochen
    Berghel, Jonas
    Karlstads Universitet.
    Bexell, Ulf
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Win, Kaung Myat
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Emissions and deposit properties from combustion of wood pellet with magnesium additives2013In: Journal of Fuel Chemistry and Technology, ISSN 1872-5813, Vol. 41, no 5, p. 530-539Article in journal (Refereed)
    Abstract [en]

    This work studies the amount of gaseous and particleemissions and deposits on heat exchanger surfaces in a boiler fired withcommercially available pellets and with pellets primed with magnesium oxide andmagnesium hydroxide. The combustion experiments were performed on a residentialboiler of 20 kW. Substrates placed in the heat exchanger was analysed withSEM-EDX-mapping to evaluate the chemical composition of the deposits. Theresults show that particle emissions (PM 2.5) using the additives increased byabout 50% and the mass of the deposits in the flue gas heat exchanger (excludingloose fly ash) increased by about 25% compared to the combustion of pelletswithout additives. The amount of additives was found to be eight times higherthan the amount of the main alkali metals potassium (K) and sodium (Na) whichleads to the assumption that the additives were overdosed and therefore causedthe problems reported. The SEM analysis of the substrates placed in the fluegas heat exchanger indicate that the deposits of sodium (Na), potassium (K),chlorine (Cl) and sulphur (S) decrease using the additives. If this was due tothe expected chemical reactions or due to the loose fly ash covering thesubstrates after the test, could not be determined in this study.

  • 149.
    Pirouznia, Pouyan
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology.
    Andersson, N. A. I.
    Tilliander, A.
    Jonsson, P. G.
    A mathematical model of martempering of thin martensitic stainless steel strips2015In: Proceedings of the 6th International Congress on the Science and Technology of Steelmaking, ICS 2015, 2015, p. 1027-1030Conference paper (Refereed)
    Abstract [en]

    The martempering process produces thin martensitic stainless steel strips and is widely used for production of valve- and spring steel. Industrial trials were conducted in collaboration with Böhler Uddeholm Precision Strip, Munkfors, Sweden. These trials suggested that the quenching step is critical to control, in order to reduce uneven temperature gradients which will lead to distortions or unevenness. To investigate this, computational modelling of the temperature was performed to estimate the current situation for the conventional martempering process based on physical theories together with Comsol Multiphysics and using a steady state modeling approach. The model boundary conditions were based upon temperature measurements in the real process. Furthermore, the strip was modelled as it comes out of the heating furnace, which is filled with hydrogen gas and continues into a molten lead-bismuth bath for quenching. Thus, the temperature profile was obtained for the strip as well as its surroundings; The results show that a better insight of the martempering line could be achieved. The model results can be used to investigate disturbances in the normal operation. Furthermore, the temperature profiles can be used to optimize the process and possibly to reduce the energy consumption.

  • 150.
    Pirouznia, Pouyan
    et al.
    Dalarna University, School of Technology and Business Studies, Materials Technology. KTH; Voestalpine Precis Strip AB, .
    Andersson, Nils Å. I
    KTH Royal Inst Technol, Dept Mat Sci & Engn, Div Proc, SE-10044 Stockholm, Sweden..
    Tilliander, Anders
    KTH Royal Inst Technol, Dept Mat Sci & Engn, Div Proc, SE-10044 Stockholm, Sweden..
    Jonsson, Par G.
    KTH Royal Inst Technol, Dept Mat Sci & Engn, Div Proc, SE-10044 Stockholm, Sweden..
    An investigation of the temperature distribution of a thin steel strip during the quenching step of a hardening process2019In: Metals, ISSN 2075-4701, Vol. 9, no 6, p. 1-14Article in journal (Refereed)
    Abstract [en]

    The dimension quality of the strip within the hardening process is an essential parameter, which great attention needs to be paid. The flatness of the final product is influenced by the temperature distribution of the strip, specifically across the width direction. Therefore, based on physical theories, a numerical model was established. The temperature of the strip for the section before the martensitic transformation was objected in the predicted model by using a steady state approach. In addition an infrared thermal imaging camera was applied in the real process in order to validate the results and to improve the boundary conditions of the numerical model. The results revealed that the temperature of strip decreased up to 250 degrees C within the area between the furnace and the quenching bath. This, in turn, resulted in significant temperature difference across the width of the strip. This difference can be up to 69 degrees C and 41 degrees C according to the numerical results and thermal imaging data, respectively. Overall, this study gave a better insight into the cooling step in the hardening process. In addition, this investigation can be used to improve the hardening process as well as an input for future thermal stress investigations.

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