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  • 3701.
    Ånmark, Niclas
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Björk, Thomas
    Swerea KIMAB.
    Karasev, Andrey
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Jönsson, Pär Göran
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Effect of Different Inclusions on Mechanical Properties and Machinability of 20NiCrMo Carburizing Steels2015In: The 6th International Congress on the Science and Technology of Steelmaking (ICS2015), Beijing: The Chinese Society for Metals , 2015, p. 805-808Conference paper (Refereed)
    Abstract [en]

    In modern steelmaking, carburizing steels are often used for production of automotive components with elevated levels of toughness and fatigue strength. This study is focused on the link between the characteristics of non-metallic inclusions in the steel and the machinability of the given steel grades. For this purpose, inclusion characteristics (such as composition, number, size, morphology etc.) in steel samples were determined by common two-dimensional (2D) observations of inclusions on polished metal surface of samples as well as by three-dimensional (3D) investigations of inclusions after electrolytic extraction from steel samples. The inclusion characteristics were investigated in the three types of 20NiCrMo carburizing steel grades: Steel A ‑ reference steel (410ppm S) having a common level of mechanical properties and machinability, Steel B ‑ steel grade (having 340ppm S) with an improved machinability due to the Ca-treatment and modification of MnS inclusions and Steel C ‑ clean steel grade (40ppm S) having a small amount of inclusions and a higher fatigue strength. It was found that the number of inclusions in Steel B is smaller than that in Steel A and that the inclusion composition is different. At the same time, the estimated machinability (tool life) of the Ca‑treated steel was superior to that of the reference steel. However, the significant decrease of the number of inclusions in the clean steel (Steel C) resulted in a lower machinability in comparison to the reference steel grade.

  • 3702.
    Ånmark, Niclas
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy. Swerea KIMAB, Sweden.
    Karasev, Andrey
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Jönsson, Pär Göran
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    The Effect of Different Non-Metallic Inclusions on the Machinability of Steel2015In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 8, no 2, p. 751-783Article in journal (Refereed)
    Abstract [en]

    Considerable research has been conducted over recent decades on the role of non-metallic inclusions and their link to the machinability of different steels. The present work reviews the mechanisms of steel fractures during different mechanical machining operations and the behavior of various non-metallic inclusions in a cutting zone. More specifically, the effects of composition, size, number and morphology of inclusions on machinability factors (such as cutting tool wear, power consumption, etc.) are discussed and summarized. Finally, some methods for modification of non-metallic inclusions in the liquid steel are considered to obtain a desired balance between mechanical properties and machinability of various steel grades.

  • 3703.
    Åsberg, Mikael
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Fredriksson, Gunnel
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Hatami, Sepehr
    Swerea IVF AB.
    Fredriksson, Wendy
    Bodycote Hot Isostatic Pressing.
    Krakhmalev, Pavel
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics (from 2013).
    Influence of post treatment on microstructure, porosity and mechanical properties of additive manufactured H13 tool steel2019In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 742, p. 584-589Article in journal (Refereed)
    Abstract [en]

    Additive manufacturing (AM) is an attractive manufacturing technology in tooling applications. It provides unique opportunities to manufacture tools with complex shapes, containing inner channels for conformal cooling. In this investigation, H13, a widely used tool steel, was manufactured using a laser powder bed fusion method. Microstructure, tensile mechanical properties, hardness, and porosity of the AM H13 after stress relieve (SR), standard hardening and tempering (SR + HT), and hot isostatic pressing (SR + HIP + HT) were investigated. It was found that the microstructure of directly solidified colonies of prior austenite, which is typical for AM, disappeared after austenitizing at the hardening heat treatment. In specimens SR + HT and SR + HIP + HT, a microstructure similar to the conventional but finer was observed. Electron microscopy showed that SR and SR + HT specimens contained lack of fusion, and spherical gas porosity, which resulted in remarkable scatter in the observed elongation to break values. Application of HIP resulted in the highest strength values, higher than those observed for conventional H13 heat treated in the same way. The conclusion is that HIP promotes reduction of porosity and lack of fusion defects and can be efficiently used to improve the mechanical properties of AM H13 tool steel.

  • 3704.
    Åsenlund, Robin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering.
    Kartläggning av förvärmningsprocessen för gjutlåda och gjutrör.2018Independent thesis Basic level (university diploma), 10 credits / 15 HE creditsStudent thesis
    Abstract [sv]

    Denna rapport är ett examensarbete utfört på Ovako Bar AB i Smedjebacken, vilket är det avslutade momentet i utbildningen ”Materialteknik med inriktning metallurgi” på Bergsskolan i Filipstad.

     

    Grunden till detta arbete ligger hos ”frysningar” (att stålet slutar rinna från gjutlådan) som företrädesvis sker på yttersträngarna. Igensättning av denna typ orsakas generellt av två faktorer, för låg övertemperatur i förhållande till likvidustemperatur eller otillräcklig förvärmning av gjutlåda samt gjutrör.

     

    Syftet med detta arbete har varit att fokusera på förvärmningen, där målet var att utvärdera hur förvärmningstider ser ut i förhållande till de föreskrivna. Samt utvärdera prestandan hos värmningsutrustningen. Och utvärdera hur temperaturfördelningen ser ut i gjutlådan under gjutning.

     

    Arbetet utfördes med hjälp av termoelement som monterades in i gjutlådan vid 1: a sträng och 3:e sträng för att kunna se hur temperaturfördelning är i gjutlådan. Mätningarna visade tydligt att temperaturen skiljde sig mellan yttersträng (1: a) och centrumsträng (3:e) vilket kan var en orsak till att frysningar sker företrädesvis på yttersträng där temperaturen visat sig vara lägre än centrumsträng.

     

    Vid utvärdering av prestandan på värmningsutrustningen så användes en handpyrometer som möjliggjorde mätning av gjutrören för att ta fram en trendkurva, som visar när temperaturökningen avtar och upphör. Vilket visade brister i tid och prestanda i nuläget.

     

    Med en fullt fungerande förvärmning skulle igensättningsgraden kunna minskas.

  • 3705.
    Åstrand, Max
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control. ABB Corp Res, Control Optimizat & Analyt, Automat Solut, Vasteras, Sweden.
    Johansson, Mikael
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
    Greberg, J.
    Lulea Univ Technol, Dept Civil Environm & Nat Resources Engn, Div Min & Geotech Engn, Lulea, Sweden..
    Underground mine scheduling modelled as a flow shop: a review of relevant work and future challenges2018In: The Southern African Journal of Mining and Metallurgy, ISSN 2225-6253, E-ISSN 1543-9518, Vol. 118, no 12, p. 1265-1276Article, review/survey (Refereed)
    Abstract [en]

    Advanced planning and automation are increasingly important in modern mines. Sophisticated methods for long-term mine planning are often used, and the advent of autonomous machines makes the actual operation more predictable. However, the interface between these two timescales, i.e. the scheduling of the mobile production fleet, often limits the ability to operate mines at maximum profitability. We show how scheduling the production fleet in an underground mine can be modelled as a flow shop. A flow shop is a general abstract process formulation that captures the key properties of a scheduling problem without going into specific details. Thus, the flow shop enables mine scheduling to reap the benefits of scheduling research from other industries. We review recent results from the mining community and the flow shop community, and introduce scheduling methods used in these two fields. This work aims at providing value to researchers from the mining community who want to leverage their skill set, as well as to theoretical researchers by presenting the mining process as a potential application area. Lastly, we discuss the results, and outline some future challenges and opportunities facing the industry.

  • 3706.
    Åström, August
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Sten, Morgan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Macro segregation in continuous cast HSLA steels: With correlation to impact toughness2019Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The report reviews macro segregations in continuous cast steels and possible correlations to impact toughness. The purpose of the thesis is to investigate centreline segregates and V-segregates to see which of them that affect impact toughness the most. Apart from a literature study, Charpy-V data was collected with permission from SSAB for two steel types, grade A and grade B, each with respective dominant segregation type. The collected data was yielded in three individual Charpy-V tests at different spots on the metal sheet, derived within a close area. The average value of these tests were used in statistical analysis to observe the spread of values in different heats of the two steels. Additionally, the specimens were etched and captured in cross-section. Results indicated that for the data of grade A, where centreline segregates were dominant, the spread of values was higher than for the data of grade B. The conclusion is that centreline segregations are worse in relation to impact toughness, since higher deviations translates to less predictable properties from a customers perspective.

  • 3707.
    Åström, Elin
    et al.
    LKAB Research and Development.
    Björkvall, Johan
    Swerea MEFOS AB.
    Björkman, Bo
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Minerals and Metallurgical Engineering.
    Hallberg, Dan
    LKAB, LKAB Research and Development.
    Vanadium oxide solubility in CaO–SiO2–VOX system2017In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 44, no 1, p. 42-51Article in journal (Refereed)
    Abstract [en]

    The solubility of vanadium oxide in the SiO2–CaO–VOX system was investigated as a function of basicity (CaO/SiO2) at a fixed temperature of 1600°C and oxygen partial pressure of 10−10 atm. Formed phases and microstructures of saturated samples were identified with SEM–EDS analysis and XRD. Maximum solubility of vanadium oxide was between 15 and 20% independent of basicity. Pure karelianite (V2O3) was formed in all samples at saturation of vanadium oxide. The morphology of karelianite changed with the change in basicity in the slag, where needles or threads were formed for slags with basicity B2 = 0.54 and B2 = 0.67 and stars or dendritic patterns were formed with basicity B2 = 1.0 and B2 = 1.22. Wollastonite (CaSiO3) was also formed in the slags with star or dendritic patterns.

  • 3708.
    Öberg, Christian
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Zhu, B. H.
    Jonsson, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Plastic deformation and creep of two ductile cast irons, simo51 and simo1000, during thermal cycling with large strains2018In: 11th International Symposium on the Science and Processing of Cast Iron, SPCI-XI 2017, Trans Tech Publications, 2018, Vol. 925, p. 361-368Conference paper (Refereed)
    Abstract [en]

    Cyclic deformations of two ferritic, ductile cast irons, SiMo51 and SiMo1000, were studied in air and Ar using a new method, SRTC (stress relaxation with thermal cycling). Locked specimens were thermally cycled up to 800 °C with isothermal holds, varying temperature interval, heating/cooling rates and hold times. A description of the mechanical response to thermal cycling of a locked specimen is given.

  • 3709.
    Öberg, Eva Alldén
    et al.
    LKAB, Research & Development, 983 81 Malmberget.
    Pålsson, Bertil
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Användning av processimulering för att identifiera flaskhalsar i malmbehandlingssystem2008In: Conference in Minerals Engineering 2008, Luleå: Luleå tekniska universitet, 2008, p. 1-14Conference paper (Other academic)
    Abstract [sv]

    LKAB beslöt 2004 att starta en grundläggande studie som underlag för framtida expansion av anläggningarna i Malmberget. En del processer och produktionslinjer riskerade att bli flaskhalsar i framtiden. I den här rapporterade studien är det sovringsverket som undersökts och resultatet visade att flera enhetsoperationer kommer att vara begränsande med nuvarande maskinpark. Därför var ett syfte med studien att undersöka hur byte av maskiner skulle påverka kapacitet och drift samt om de framtida produktionsplanerna kunde innehållas. Sovringsprocessen har genomgående simulerats med ModsimTM för ett antal olika fall, som har skilt sig åt i järnhalt och partikelstorleksfördelningar hos ingående malm. Modelleringsparametrarna har hämtats, till en del från existerande undersökningar i pilotskala, men i största möjliga utsträckning från mätningar i existerande kretsar. Simuleringarna visade att installation av nya siktar skulle ge en väsentligt förbättrad drift, men också att nya krossar skulle vara en förbättring eftersom de skulle kunna köras fullmatade med snävare ansättning, vilket skulle ge process-tekniska fördelar. Under 2007 har de flesta av de föreslagna åtgärderna genomförts och resultatet visar att flaskhalsarna är borta och att halter och massbalanser är till och med bättre än vad som förutsågs i simuleringarna.

  • 3710.
    Öberg, Eva Alldén
    et al.
    LKAB.
    Pålsson, Bertil
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Tano, K.T.
    LKAB.
    The use of process simulation methodology in de-bottlenecking of production lines2008In: Proceedings of XXIV International Mineral Processing Congress: Beijing, China 24-28 September 2008 / [ed] Wang Dian Zuo; Sun Chuan Yao; Wang Fu Liang; Zhang Li Cheng; Han Long, Beijing: American Science Press Inc., 2008, p. 2388-2395Conference paper (Refereed)
  • 3711.
    Ökvist, Lena Sundqvist
    Luleå tekniska universitet.
    Co-injection of basic fluxes or BF flue dust with PC into a BF charged with 100% pellets: effects on slag formation and coal combustion2004Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Based on 100% pellets operation at BF No. 3 at SSAB Tunnplåt in Luleå a new pellet with CaO/SiO2=1 was developed during early nineties. The pellet showed good results in metallurgical laboratory test but caused slag formation problems in the bosh. A high basicity slag was formed during interaction with basic fluxes and its melting point was increased when the slag was finally reduced. By injection of basic fluxes, the slag formation problems in the bosh can be avoided. Without a sinter plant, dusts have to be recycled in a cold bonded briquette. Injection of some of BF flue dust would improve the properties of the briquette and may be beneficial for the BF process. Based on top charging or tuyere-injection of basic fluxes and the injection of BF flue dust studies have been done. The studies carried out will clarify some phenomena of slag formation and the effect of co- injection on coal combustion in the blast furnace, including the effect of: 1) basic fluxes on slag formation in the blast furnace, if they are top- charged; 2) basic fluxes on slag formation in the blast furnace, if they are tuyere injected; 3) chemical composition and metallurgical properties of pellet and fluxes on slag formation; 4) reduction conditions on (reduction temperature, reducing gas composition) on bosh slag formation; 5 co- injection of BOF slag or BF flue dust on coal combustion efficiency and BF performance. From the results, it can be concluded that the interaction between pellets and fluxes starts when softening and melting starts in the cohesive layer. By choosing fluxes of a high melting point the dissolution of them in the bosh slag can be delayed and the excessive basicity of the bosh slag can be limited. A basic flux with a low melting point will easily dissolve into the bosh slag causing its basicity to increase, which is beneficial to S refining when acid pellets are used. The formation of a bosh slag of excessive basicity (which causes BF operation disturbances, because its high melting point, increases further during reduction) can be avoided by tuyere injection of basic fluxes with the coal. The positive effect is greatest when a fluxed pellet of basicity B21 and with a high Fe content is used as ferrous burden. In this case, the slag amount can be significantly decreased. BOF slag has suitable high-temperature properties for use as a basic flux in combination with e.g., olivine pellets. It has a low softening and melting temperature, does not shrink, is slowly reduced in the BF shaft and its properties are almost unaffected by the partial reduction occurring in the shaft of the BF. BOF slag absorbs a low content of alkalies, which causes volume increase at elevated temperatures, when the basicity is still high. The results indicate that co-injection of BOF slag or BF flue dust with PC has positive effects on the BF operation. The injection of BOF slag decreases the Si content in HM by an increased basicity of the slag formed during combustion leading to a decreased activity of SiO2 in the slag and by an increased FeO content in the tuyere slag that will be reduced by SiFe in the metal at the tuyere level, if the SiFe is initially high. The consumption of reducing agents can be reduced because of a decreased Si content in HM and a decreased slag amount. The permeability is improved by prohibiting the formation of a shell at the raceway end because of improved melting properties of tuyere slag caused by an increased basicity and FeO content, consumption of coal and coke fines by FeO and improved radial transport of tuyere slag. The injection of BOF slag improves the bosh slag because an excessive basicity caused by top-charged fluxes added for neutralisation of coal and coke ashes and non-uniform slag formation caused by uneven distribution of top-charged fluxes are avoided. The productivity increases because of the possibility to decrease the slag amount. The injection of BOF slag can be done without negative effects on combustion efficiency by using very finely ground BOF slag and because of improved total consumption of coal and coke fines by direct reduction in the coke bed. The injection of BF flue dust decreases the Si content in HM by an increased FeO content of the tuyere slag that will be reduced by SiFe in the metal at the tuyere level, if the SiFe is initially high. The consumption of coal and coke is decreased because of a high of C content in BF flue dust and the decreased Si content in HM. The permeability is improved by prohibiting the formation of a shell at the raceway end because of consumption of coal and coke fines by FeO and improved melting properties of tuyere slag promoting the radial transport of the tuyere slag. The injection of BF flue dust can be done without negative effects on the total consumption of coal and coke fines by direct reduction in the coke bed. Injected BF flue dust supplies oxygen for combustion, but because of endothermic reactions as reduction of hematite and calcination of limestone occurring in the BF flue dust at the same temperatures as release and disintegration of VM, it will have a negative effect on the combustion of HV coal. SSAB Luleå and SSAB Oxelösund have started up projects aiming to make tuyere- injection of BF flue dust part of the standard BF operation.

  • 3712.
    Ökvist, Lena Sundqvist
    Luleå tekniska universitet.
    High temperature properties of BOF slag and its behaviour in the blast furnace2004In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 75, no 12, p. 792-799Article in journal (Refereed)
    Abstract [en]

    Slag formation in the bosh and raceway is an important issue in the blast furnace process. SSAB works in Lulea operate with 100 % olivine pellets. A small amount of basic fluxes is added from the top, slag and limestone are used. To improve the control of slag formation, a concept with injection of BOF slag was evaluated and tested in the LKAB etxperimental blast furnace (EBF). In this paper, the behaviour of BOF slag as a slag former, when it is top-charged or tuyere-injected, is evaluated based on the results from a laboratory study including reduction tests, softening and melting tests, XRD analyses and SEM analyses. Samples taken from the EBF during excavation, and with a burden probe during operation, are examined. The evaluations show that the melting point of BOF slag is quite low and will not be increased, because of the partial reduction that occurs in the BF shaft. When carbon is present at high temperatures, reduction proceeds and a high basicity slag with a high melting point, consisting of di- and tricalcium silicates, is formed. When pellets with a basicity of B2 - 1 are used, a slag with similar properties can be formed as a result of interaction with the BOF slag. BOF slag in combination with olivine pellets with a low basicity generates a slag with intermediate basicity and the reduction of iron oxides in the slag has a small effect on the melting temperature. The BOF slag decreases the melting point of coal and coke ashes.

  • 3713.
    Ökvist, Lena Sundqvist
    Luleå tekniska universitet.
    Optimisation of the slag formation in a blast furnace charged with 100% pellets2001Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    This work is based on experiences from industrial blast furnaces. Process irregularities when testing self-fluxed pellets Process disturbances when charging increased proportions of coarse pellets Laboratory tests to evaluate the effect of basic fluxes on the slag formation in the bosh and in the raceway have been carried out. Pilot scale tests have been performed to verify the effect of coarse pellets. The effect of reduction degree and the reduction behaviour on the slag formation and blast furnace performance have been evaluated It was found that decreased degree of reduction of pellets or lowly reduced core of coarse pellets decrease the melting temperature and increase the softening and melting temperature interval. Basic fluxes have a negative effect on the melting properties of the self-fluxed pellets and a positive effect on the melting properties of the olivine pellets. Basic fluxes have a positive effect on the melting properties of tuyere slags.

  • 3714.
    Ökvist, Lena Sundqvist
    et al.
    Luleå tekniska universitet.
    Cang, Danqiang
    SSAB Tunnplåt AB.
    Zong, Yanbing
    SSAB Tunnplåt AB.
    Bai, Hao
    University of Science and Technology, Beijing.
    The effect of BOF slag and BF flue dust on coal combustion efficiency2004In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 44, no 9, p. 1501-1510Article in journal (Refereed)
    Abstract [en]

    Injection into a BF of BOF slag to improve the slag formation and of BF flue dust to improve the recycling of in-plant fines has previously been tested. The effects on the PC combustion efficiency at different conditions, when these materials are co-injected with coal, have so far not been tested. Combustion efficiencies at varied temperature, O2 enrichment, amount of PC, amount of added BOF slag or BF flue dust and particle size of the added material are measured in a fixed bed and a blowpipe model. The established facts that an increased temperature and O2 enrichment or a decreased amount of coal increase the combustion efficiency are valid also when BOF slag or BF flue dust are added to the coal. By adjusting the combustion conditions, a decreased combustion efficiency can be counteracted, when a second material is co-injected with coal. The effect of BOF slag addition on coal combustion efficiency measured in the blowpipe model is in-significant, if a fine fraction is used. The combustion efficiency is higher in the fixed bed compared with that in the blowpipe model. The addition of BF flue dust increases the combustion efficiency in the fixed bed

  • 3715.
    Örnek, Cem
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science. The University of Manchester, United Kingdom.
    Burke, M. G.
    Hashimoto, T.
    Engelberg, D. L.
    748 K (475 A degrees C) Embrittlement of Duplex Stainless Steel: Effect on Microstructure and Fracture Behavior2017In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 48A, no 4, p. 1653-1665Article in journal (Refereed)
    Abstract [en]

    22Cr-5Ni duplex stainless steel (DSS) was aged at 748 K (475 A degrees C) and the microstructure development correlated to changes in mechanical properties and fracture behavior. Tensile testing of aged microstructures confirmed the occurrence of 748 K (475 A degrees C) embrittlement, which was accompanied by an increase of strength and hardness and loss of toughness. Aging caused spinodal decomposition of the ferrite phase, consisting of Cr-enriched alpha aEuro(3) and Fe-rich alpha' and the formation of a large number of R-phase precipitates, with sizes between 50 and 400 nm. Fracture surface analyses revealed a gradual change of the fracture mode from ductile to brittle delamination fracture, associated with slip incompatibility between ferrite and austenite. Ferrite became highly brittle after 255 hours of aging, mainly due to the presence of precipitates, while austenite was ductile and accommodated most plastic strain. The fracture mechanism as a function of 748 K (475 A degrees C) embrittlement is discussed in light of microstructure development.

  • 3716.
    Örnek, Cem
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science. University of Manchester, UK.
    Burke, M. G.
    Hashimoto, T.
    Lim, J. J. H.
    Engelberg, D. L.
    475 degrees C Embrittlement of Duplex Stainless Steel-A Comprehensive Microstructure Characterization Study2017In: Materials Performance and Characterization, ISSN 2379-1365, Vol. 6, no 3, p. 409-436Article in journal (Refereed)
    Abstract [en]

    The effect of 475 degrees C embrittlement on microstructure development of grade 2205 duplex stainless steel was investigated. Spinodal decomposition products and associated precipitates in ferrite, austenite, and at interphase boundaries were characterized using analytical transmission electron microscopy (TEM) and scanning electron microscopy (SEM) techniques. Microanalyses confirmed the presence of Cr-enriched alpha'' and Cr-depleted alpha' spinodal structures in the ferrite after 5 h of aging at 475 degrees C. Long-term aging for 255 h resulted in heavily-faulted R-phase precipitates with sizes of similar to 50-400 nm, chi-phase, and epsilon-Cu in the ferrite, TiN and Cr2N precipitates in the austenite, and a continuous network of M23C6-carbides at interphase boundaries. A significant hardness increase was observed after 255 h of aging, which was accompanied by a reduction of ferrite fraction. X-ray diffraction (XRD) stress measurements showed a general reduction of residual stresses in both ferrite and austenite with aging. Electron backscatter diffraction (EBSD) showed increased local misorientations, primarily close to precipitate interfaces within the ferrite, indicating the development of strain heterogeneities in the microstructure. The data presented provided a better understanding of 475 degrees C embrittlement in duplex stainless steel, suggesting that not only the ferrite alone is responsible for embrittlement. A comprehensive microstructure characterization study has been provided and the explanation for 475 degrees C embrittlement of duplex stainless steel has been discussed.

  • 3717.
    Örnek, Cem
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Surface and Corrosion Science.
    Leygraf, Christopher
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Surface and Corrosion Science.
    Pan, Jinshan
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Surface and Corrosion Science.
    Passive film characterisation of duplex stainless steel using scanning Kelvin probe force microscopy in combination with electrochemical measurements2019In: npJ Materials Degradation, ISSN 2397-2106, Vol. 3, no 1, p. 1-8Article in journal (Refereed)
    Abstract [en]

    The characterisation of passive oxide films on heterogeneous microstructures is needed to assess local degradation (corrosion, cracking) in aggressive environments. The Volta potential is a surface-sensitive parameter which can be used to assess the surface nobility and hence passive films. In this work, it is shown that the Volta potential, measured on super duplex stainless steel by scanning Kelvin probe force microscopy, correlates with the electrochemical properties of the passive film, measured by electrochemical impedance spectroscopy and potentiodynamic polarisation. Natural oxidation by ageing in ambient air as well as artificial oxidation by immersion in concentrated nitric acid improved the nobility, both reflected by increased Volta potentials and electrochemical parameters. Passivation was associated with vanishing of the inherent Volta potential difference between the ferrite and austenite, thereby reducing the galvanic coupling and hence improving the corrosion resistance of the material. Hydrogen-passive film interactions, triggered by cathodic polarisation, however, largely increased the Volta potential difference between the phases, resulting in loss of electrochemical nobility, with the ferrite being more affected than the austenite. A correlative approach of using the Volta potential in conjunction with electrochemical data has been introduced to characterise the nobility of passive films in global and local scale.

  • 3718.
    Örnek, Cem
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Surface and Corrosion Science. Swerea KIMAB AB, Isafjordsgatan 28A, Kista, 164 40, Sweden.
    Liu, Min
    Univ Sci & Technol Beijing, Natl Ctr Mat Serv Safety, Xueyuan Rd 30, Beijing 100083, Peoples R China..
    Pan, Ying
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Surface and Corrosion Science.
    Jin, Y.
    Univ Sci & Technol Beijing, Natl Ctr Mat Serv Safety, Xueyuan Rd 30, Beijing 100083, Peoples R China..
    Leygraf, Christopher
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Surface and Corrosion Science.
    Volta Potential Evolution of Intermetallics in Aluminum Alloy Microstructure Under Thin Aqueous Adlayers: A combined DFT and Experimental Study2018In: Topics in catalysis, ISSN 1022-5528, E-ISSN 1572-9028, Vol. 61, no 9-11, p. 1169-1182Article in journal (Refereed)
    Abstract [en]

    In this work, first-principle density functional theory (DFT) was used to calculate the work function and Volta potential differences between aluminum alloy matrix and two intermetallic phases (Mg2Si and Al2Cu) with varying surface terminations as a function of adhering monolayers (ML) of water. The calculated data were compared with experimental local Volta potential data obtained by the scanning Kelvin probe force microscopy (SKPFM) on a commercial aluminum alloy AA6063-T5 in atmospheric environments with varying relative humidity (RH). The calculations suggest that the surface termination has a major effect on the magnitude and polarity of the Volta potential of both intermetallic phases (IMP's). The Volta potential difference between the IMP's and the aluminum matrix decreases when the surface is gradually covered by water molecules, and may further change as a function of adhering ML's of water. This can lead to nobility inversions of the IMP's relative to the aluminum matrix. The measured Volta potential difference between both IMP's and their neighboring matrix is dependent on RH. Natural oxidation in ambient indoor air for 2 months led to a nobility inversion of the IMP's with respect to the aluminum matrix, with the intermetallics showing anodic nature already in dry condition. The anodic nature of Al2Cu remained with the introduction of RH, whereas Mg2Si became cathodic at high RH, presumably due to de-alloying of Mg and oxide dissolution. The DFT calculations predicted an anodic character of both IMP's in reference to the oxidized aluminum matrix, being in good agreement with the SKPFM data. The DFT and SKPFM data were discussed in light of understanding localized corrosion of aluminum alloys under conditions akin to atmospheric exposure.

  • 3719.
    Örnek, Cem
    et al.
    KTH.
    Reccagni, Pierfranco
    Kivisakk, Ulf
    Bettini, Eleonora
    Engelberg, Dirk L.
    Pan, Jinshan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Hydrogen embrittlement of super duplex stainless steel - Towards understanding the effects of microstructure and strain2018In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 43, no 27, p. 12543-12555Article in journal (Refereed)
    Abstract [en]

    The effects of austenite spacing, hydrogen charging, and applied tensile strain on the local Volta potential evolution and micro-deformation behaviour of grade 2507 (UNS 532750) super duplex stainless steel were studied. A novel in-situ methodological approach using Digital Image Correlation (DIC) and Scanning Kelvin Probe Force Microscopy (SKPFM) was employed. The microstructure with small austenite spacing showed load partitioning of tensile micro-strains to the austenite during elastic loading, with the ferrite then taking up most tensile strain at large plastic deformation. The opposite trend was seen when the microstructure was pre-charged with hydrogen, with more intense strain localisation formed due to local hydrogen hardening. The hydrogen-charged microstructure with large austenite spacing showed a contrasting micro-mechanical response, resulting in heterogeneous strain localisation with high strain intensities in both phases in the elastic regime. The austenite was hydrogen-hardened, whereas the ferrite became more strain-hardened. SKPFM measured Volta potentials revealed the development of local cathodic sites in the ferrite associated with hydrogen damage (blister), with anodic sites related to trapped hydrogen and/or micro voids in the microstructure with small austenite spacing. Discrete cathodic sites with large Volta potential variations across the ferrite were seen in the coarse-grained microstructure, indicating enhanced susceptibility to micro-galvanic activity. Microstructures with large austenite spacing were more susceptible to hydrogen embrittlement, related to the development of tensile strains in the ferrite.

  • 3720.
    Östklint, Mattias
    et al.
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.
    Wessén, Magnus
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.
    Microstructure characteristics and semi-solid slurry formation in binary Mg-Al alloys produced by the RheoMetal process2013In: Solid State Phenomena, ISSN 1012-0394, E-ISSN 1662-9779, Vol. 192/193, p. 482-487Article in journal (Refereed)
    Abstract [en]

    The RheoMetal process, previously also called the Rapid Slurry Forming process (“Rapid S”) or RSF process, is a novel method to produce high quality, cost effective, semi-solid magnesium slurries for component casting. The RheoMetal process uses an Enthalpy Exchange Material (EEM) as internal cooling to produce the slurry. Typical critical process parameters in the RheoMetal process are alloy content, stirring speed, superheat and EEM to melt ratio. In this study the effects of EEM to melt ratio and superheat on the slurry characteristics was examined for binary Mg-Al alloys in the range 5.8 - 11.2 wt % Al. Samples were quenched after slurry preparation and the microstructure was studied with respect to solid fraction and a-Al grain diameter. The solid fraction increased with an increasing EEM to melt ratio for all Al-contents investigated. Further, it was found that the solid fraction as well as the grain diameter decreased with increasing aluminium content (at constant EEM to weight ratio).

  • 3721.
    Överstam, Henrik
    et al.
    Örebro University, Department of Technology.
    Lundberg, Sven-Erik
    Örebro University, Department of Technology.
    A new approach to roll force and torque modelling in wire rod and bar mills2008In: Der Kalibreur, ISSN 0022-796X, Vol. 69, p. 61-72Article in journal (Refereed)
  • 3722. Sköld, Börje (Editor)
    Forssberg, Eric (Editor)
    Datorer inom mineraltekniken: Luleå 20-21 november 19851986Report (Other academic)
  • 3723. Sköld, Börje (Editor)
    Forssberg, Eric (Editor)
    Konferens i mineralteknik: Luleå 10-12 februari 19871988Report (Other academic)
  • 3724. Sköld, Börje (Editor)
    Forssberg, Eric (Editor)
    Konferens i mineralteknik: Luleå, 13-14 februari 19901990Report (Other academic)
  • 3725. Sköld, Börje (Editor)
    Forssberg, Eric (Editor)
    Konferens i mineralteknik: Luleå 14-16 februari 19891989Report (Other academic)
  • 3726. Sköld, Börje (Editor)
    Forssberg, Eric (Editor)
    Konferens i mineralteknik: Luleå, 4-5 februari, 19921992Report (Other academic)
  • 3727. Sköld, Börje (Editor)
    Forssberg, Eric (Editor)
    Konferens i mineralteknik: Luleå, 5-7 februari 19911991Report (Other academic)
  • 3728. Thomaeus, Marianne (Editor)
    Forssberg, Eric (Editor)
    Konferens i mineralteknik: Luleå, Sweden February 3-4, 20042004Report (Other academic)
  • 3729. Thomaeus, Marianne (Editor)
    Forssberg, Eric (Editor)
    Konferens i mineralteknik: Luleå, Sweden February 4-5, 20032003Report (Other academic)
  • 3730. Thomaeus, Marianne (Editor)
    Forssberg, Eric (Editor)
    Konferens i mineralteknik: Luleå, Sweden February 7-8, 20062006Report (Other academic)
  • 3731. Thomaeus, Marianne (Editor)
    Forssberg, Eric (Editor)
    Konferens i mineralteknik: Luleå, Sweden February 8-9, 20052005Report (Other academic)
  • 3732. Andersson, Lennart (Editor)
    Forssberg, Eric (Editor)
    Seminarium i mineralteknik i Luleå 6-8 februari 19851985Report (Other academic)
  • 3733. Sköld, Börje (Editor)
    Forssberg, Eric (Editor)
    Workshop i mineralteknik: Luleå 11-12 februari 19861986Report (Other academic)
72737475 3701 - 3733 of 3733
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