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  • 251.
    Deng, Zhiyin
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Mikro-modellering. School of Metallurgy, Northeastern University, China.
    Study on the Interaction between Refractory and Liquid Steel Regarding Steel Cleanliness2016Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The present thesis focuses on the interaction between refractory and liquid steel. The aim of this work is to understand the interaction behavior between refractory and liquid steel regarding steel cleanliness. The effect of different refractories on different inclusions in Al-killed steel was studied in a furnace. The sintering mechanism of filler sand were also investigated in laboratory. In the industrial trials, the attachments of different oxides on the walls of submerged entry nozzle (SEN) were discussed in the cases of high strength low alloy steel (HSLA) and ultra-low carbon steel (ULC).

    It is found that the effect of alumina and spinel refractory on all the three types of inclusions is very little, while MgO refractory influences the inclusions depending on the activity of dissolved oxygen in liquid steel. At low oxygen level, alumina inclusions could transform into spinel inclusions with the help of MgO refractory, while the effect on spinel and calcium aluminate inclusions is not evident. On the other hand, when the activity of dissolved oxygen is high enough, the evolution of spinel inclusions from alumina inclusions could not be seen.

    The reaction between chromite and silica grains leading to liquid formation is the main mechanism for the sintering of filler sand. The factors viz. steel composition, silica size and content, operation temperature and process holding time have a strong influence on the sintering of the filler sand. Smaller size and higher content of silica in sand, steel grades containing higher Mn and Al contents, higher temperature and longer holding time would result in serious sintering. The choice of the sand needs to take those factors into account.

    The results show that solid alumina particles are always agglomerated on the inner wall of SEN in the case of ULC steel. The top slag with high FeO and MnO contents is considered as the main reason of this kind of attachments. The removal of slag might be a good method to avoid the attachments. In the case of HSLA steel, liquid calcium aluminate inclusions could attach on the inner wall of SEN as well. The smoothness of the inner wall of the SEN holds the key of liquid attachments. In addition, the attachment situation on the outer wall of SEN depends on the operations. The oxygen entrainment through the mold powder would result in the formation of plate-like alumina attachments. The control of reoxidation due to oxygen entrainment would help to avoid this situation.

  • 252.
    Deng, Zhiyin
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Mikro-modellering. School of Metallurgy, Northeastern University, China.
    Glaser, Björn
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Mikro-modellering.
    Bombeck, Marc André
    PURMETALL GmbH & Co. KG, 46049 Oberhausen, Germany.
    Du, Sichen
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Mikro-modellering.
    Effects of Temperature and Holding Time on the Sintering of Ladle Filler Sand with Liquid Steel2016Ingår i: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 87, nr 7, s. 921-929Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the present work the effects of temperature and holding time on the sintering of ladle filler sand are studied. Laboratory experiments are carried out using pellets made of chromite based filler sand and two steel grades containing different contents of Mn and Al. It is found that the liquid steel plays a major role in the sintering behavior. The results also show that the amount of liquid phase in the sintered sand pellets increases with the increase of temperature and holding time. The Al2O3 content increases substantially in the chromite phase (spinel), especially in the region close to the liquid phase, when the temperature is high enough or when the holding time is long enough. Higher content of dissolved Al would accelerate the formation of the alumina-rich chromite.

  • 253.
    Deng, Zhiyin
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. Northeastern University, China.
    Zhu, M.
    Zhou, Y.
    Sichen, Du
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Attachment of Alumina on the Wall of Submerged Entry Nozzle During Continuous Casting of Al-Killed Steel2016Ingår i: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 47, nr 3, s. 2015-2025Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The mechanisms of the formation of different attachments on the walls of submerged entry nozzle (SEN) were studied for the processes of Al-killed steel (Ca-treated, HSLA) and ultra-low carbon Al-killed steel (ULC). To understand the mechanism, the types of inclusions in the steel taken in tundish and in bloom (or slab) were identified. In the case of ULC, the reoxidation product, micro-alumina particles were found to be the source of attachment on the inner wall of the SEN. To avoid reoxidation of the steel by the top slag, removal of the slag could be considered in order to improve the situation. No attached layer was found on the outer surface of the SEN after casting of the ULC steel. In the case of HSLA steel, an attached layer composed of plate-like alumina crystals was found in some trials. The entrainment of oxygen through the mold powder due to improper operation would be the reason for the formation of this type of attachment. The formation of the plate-like crystals was discussed with the help of CFD calculation.

  • 254.
    Deng, Zhiyin
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Mikro-modellering. School of Metallurgy, Northeastern Unviersity, China.
    Zhu, Miaoyong
    School of Metallurgy, Northeastern Unviersity, China.
    Du, Sichen
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Mikro-modellering.
    Effect of Refractory on Nonmetallic Inclusions in Al-killed Steel2016Ingår i: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 47, nr 5, s. 3158-3167Artikel i tidskrift (Refereegranskat)
  • 255.
    Deng, Zhiyin
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. Northeastern University, China.
    Zhu, Miaoyong
    Zhong, Baojun
    Sichen, Du
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Attachment of Liquid Calcium Aluminate Inclusions on Inner Wall of Submerged Entry Nozzle during Continuous Casting of Calcium-Treated Steel2014Ingår i: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 54, nr 12, s. 2813-2820Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the present study, inclusions in calcium-treated steel after RH treatment, in the tundish and in bloom were studied. Only two types of inclusions were detected in all steel samples, namely liquid calcium aluminate inclusions and inclusions of two phases with spinel in the center surrounded by the liquid calcium aluminate. The attachment of the inclusions on the inner surface of SEN was investigated for two types of refractory materials. The results indicated that liquid calcium aluminate inclusions could attach on the wall of SEN, when the refractory had big grain size and big cavities on the surface. On the other hand, tiny grain size and smooth surface of the SEN showed no attachment of the inclusions. The different behaviors of the two types of SEN were well explained using the results of flow calculation in the nozzle. The mechanism of the attachment was also discussed based on the experimental results and the CFD calculation. The tiny nodules formed on the surface of the inner nozzle due to inclusion attachment could be a source of macro inclusions.

  • 256.
    Dilner, David
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Profitability = f(G): Computational Thermodynamics, Materials Design and Process Optimization2016Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The thesis starts by giving a motivation to materials modeling as a way to increase profitability but also a possibility decrease the environmental impact. Fundamental concepts of relevance for this work are introduced, this include the materials genome, ICME and of course the CALPHAD method. As a demonstration promising results obtained by an ICME approach using genetic algorithms and CALPHAD on the vacuum degassing process are presented. In order to make good predictive calculations and process models it is important to have good thermodynamic descriptions. Thus most part of the work has concerned the thermodynamic assessments of systems of importance for steelmaking, corrosion and similar processes. The main focus has been the assessment of sulfur-containing systems and thermodynamic descriptions of the Fe-Mn-Ca-Mg-S, Fe-Ca-O-S, Fe-Mg-O and Mg-Mn-O systems are presented. In addition, heat capacity measurements of relevance for the Mg-Mn-O system have been performed. To summarize the efforts some application examples concerning thermodynamic calculations related to steelmaking and inclusion formation are shown.

  • 257.
    Dilner, David
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Kjellqvist, Lina
    Mao, Huahai
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Selleby, Malin
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Improving Steel and Steelmaking - Computational Thermodynamics using a Sulphide and Oxide databaseManuskript (preprint) (Övrigt vetenskapligt)
  • 258.
    Dilner, David
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Termodynamisk modellering.
    Kjellqvist, Lina
    Mao, Huahai
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Termodynamisk modellering.
    Selleby, Malin
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Improving Steel and Steelmaking—an Ionic Liquid Database for Alloy Process Design2018Ingår i: Integrating Materials and Manufacturing Innovation, ISSN 2193-9764, Vol. 7, s. 195-201Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The latest development of a thermodynamic database is demonstrated with application examples related to the steelmaking process and steel property predictions. The database, TCOX, has comprehensive descriptions of the solution phases using ionic models. More specifically, applications involving sulphur and oxygen, separately as well as combined, are presented and compared with relevant multi-component experimental information found in the literature. The over-all agreement is good.

  • 259.
    Dilner, David
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Pavlyuchkov, Dmytro
    Zienert, Tilo
    Kjellqvist, Lina
    Fabrichnaya, Olga
    Thermodynamics of the Mg-Mn-O system - Modeling and Heat Capacity Measurements2016Ingår i: Journal of The American Ceramic Society, ISSN 0002-7820, E-ISSN 1551-2916Artikel i tidskrift (Refereegranskat)
  • 260.
    Dilner, David
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Selleby, Malin
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Thermodynamic Description of the Fe-Ca-O-S systemManuskript (preprint) (Övrigt vetenskapligt)
  • 261.
    Ding, Wei
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. School of Material and Metallurgy, Inner Mongolia University of Science and Technology; Bayan Obo multimetallic resource comprehensive utilization Key lab, Inner Mongolia University of Science and Technology.
    Hedström, Peter
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Li, Yan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. Bayan Obo multimetallic resource comprehensive utilization Key lab, Inner Mongolia University of Science and Technology.
    Heat treatment, microstructure and mechanical properties of a C-Mn-Al-P hot dip galvanizing TRIP steel2016Ingår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 674, s. 151-157Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Heat treatments of a hot dip galvanizing TRIP (Transformation induced plasticity) steel with chemical composition 0.20C-1.50Mn-1.2Al-0.07P(mass%) were performed in a Gleeble 3500 laboratory equipment. The heat treatment process parameters were varied to investigate the effect of intercritical annealing temperature as well as isothermal bainitic transformation (IBT) temperature and time, on the microstructure and the mechanical properties. The microstructure was investigated using scanning electron microscopy, transmission electron microscopy and x-ray diffraction, while mechanical properties were evaluated by tensile testing. Furthermore, to generate a better understanding of the phase transformations during heat treatment, dilatometry trials were conducted. The desired microstructure containing ferrite, bainite, retained austenite and martensite was obtained after the heat treatments. It was further found that the IBT is critical in determining the mechanical properties of the steel, since it controls the fraction of bainite. With increasing bainite fraction, the fraction of retained austenite increases while the fraction of martensite decreases. The mechanical properties of the steel are excellent with a tensile strength above 780 MPa (expect in one case) and elongation above 22%.

  • 262.
    Ding, Zong-Hai
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Huml, Pavel
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Influence of stress path change on the resistance to plastic deformation of cold rolled sheets2005Ingår i: Journal of University of Science and Technology Beijing, ISSN 1005-8850, E-ISSN 2212-6430, Vol. 12, nr 6, s. 521-526Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Flat workpieces have been tested in order to investigate the influence of stress path change (loading mode) while keeping strain path unchanged. These investigations are pertinent to the testing of cold rolled strips and to subsequent forming. The workpieces which first compressed by plane strain compression in thickness direction were then tested in perpendicular direction in order to measure the influence of strain and stress path. The tension workpieces came from flat die compression test at different deformation histories. Two different materials were investigated: 18/8 Ti stainless steel and AW-1050 aluminium. The results show that the plastic flow by tension in lengthwise direction after pre-strain by compression in thickness direction will begin at an appreciably lower stress than that of the workpieces unloaded after pre-compression. Comparing with two materials, it can be seen that both 18/8 Ti stainless steel and AW-1050 aluminium behave similarly. The drop in yield stress is lower for AW-1050 aluminium than that for 18/8 Ti stainless steel. However, reloading in different directions than in the precious step results in significantly higher strain hardening.

  • 263.
    Doddapaneni, Venkatesh
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Zhao, Yichen
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Funktionella material, FNM.
    Ye, Fei
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Funktionella material, FNM.
    Gati, R.
    Edin, Hans
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Toprak, Muhammet S.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Funktionella material, FNM.
    Improving Uv Radiation Absorption by Copper Oxide NPs/PMMA Nanocomposites for Electrical Switching Applications2015Ingår i: Powder metallurgy and metal ceramics, ISSN 1068-1302, E-ISSN 1573-9066, Vol. 54, nr 7-8, s. 397-401Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Nanocomposites based on the radiation absorbing polymer (PNCs) are of interest for a variety of applications including circuit breakers, UV-shielding windows, contact lenses, and glasses among others. Such PNCs can be made by incorporating suitable radiation absorbing nanoparticles into a polymeric matrix by in situ polymerization. In this study, spherical nanoparticles (5-6 nm) of oleic acid (OA) surface modified cupric oxide (CuO) are synthesized and used to improve the ultra-violet (UV) radiation absorption property of a polymer matrix, i.e., polymethylmethacrylate (PMMA). The synthesis of spherical CuO nanoparticles, surface modification using OA, dispersion of CuO nanoparticles with different concentrations in PMMA, and UV radiation absorption property of the resultant PNC are investigated. Two different PNCs are produced using OA modified CuO nanoparticles with different concentrations. As synthesized CuO nanoparticles and OA modified CuO nanoparticles are examined by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FT-IR) techniques. The UV absorption edges are evaluated from the UV-Vis absorption spectra by using UV-Visible absorption spectroscopy. The results show that the UV radiation absorption of the PNC with higher concentration of CuO nanoparticles is improved compared with PMMA and the absorption edge moved towards longer wavelengths i.e., from 271 to 281 nm. These PNCs are successful in arc interruption process by absorbing a broad range of radiation emitted from high-energy copper arcs produced in the circuit breakers.

  • 264.
    Donaj, Pawel
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Energi- och ugnsteknik.
    Conversion of biomass and waste using highly preheated agents for materials and energy recovery2011Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    One of the greatest challenges of human today is to provide the continuous and sustainable energy supply to the worldwide society. This shall be done while minimizing all the negative consequences of the operation(s) to the environment and its living habitants including human beings, taking from the whole life cycle perspective. In this thesis work new solutions for treatment biomass and waste are analyzed.

     

    Based on the fundamental research on the conversion of various materials (biomass: straw pellets, wood pellets; and waste: plastic waste, ASR residues after pyrolysis), converted by means of different systems (pyrolysis in a fluidized bed reactor, gasification in a fixed-bed reactor using highly preheated agents) it is recommended to classify materials against their charring properties under pyrolysis, in order to find the best destination for a given type of fuel. 

     

    Based on phenomenological research it was found that one of the important effects, affecting performance of downdraft gasifiers, is the pressure drop through the bed and grate. It affects, directly, the velocity profile, temperature distribution and of the height of the bed, especially for the grate with restricted passage surface, although it was not investigated in literature. The lower grate porosity, the higher conversion of fuel and heating value of gas is produced. However, the stability of the process is disturbed; therefore reducing the grate porosity below 20% is not recommended, unless the system is designed to overtake the consequences of the rising pressure inside the reactor. This work proposed the method for prediction of a total pressure drop through the fixed-bed downdraft gasifier equipped with a grate of certain porosity with an uncertainty of prediction ±7.10.  

     

    Three systems have been proposed; one for the treatment of automotive shredder residue (ASR), one for the treatment of plastic waste (polyolefins) and one for biomass (wood/straw pellets). Pyrolysis is an attractive mean of conversion of non-charring materials (like plastic waste) into valuable hydrocarbons feedstock. It gives directly 15-30% gaseous olefins while the residue consisting of naphtha-like feedstock has to be reformed/upgraded to olefins or other chemicals (e.g. gasoline generation) using available petrochemical technologies. Pyrolysis of complex waste mixture such as ASR is an attractive waste pretreatment method before applying any further treatments, whereby useful products are generated (gaseous and liquid fuel) and char, rich in precious metals. The solid residues are meant for further treatment for energy and metals recovery. Gasification is a complementary method for handling pyrolysis residues. However, metals can be removed before gasification. Pyrolysis of charring materials, like biomass, is a very important step in thermo-chemical conversion. However, the char being approximately 25%wt. contains still very high caloric value of about 30MJ/kg. This in connection with the High Temperature Steam Gasification process is a very promising technology for biomass treatment, especially, above 900oC. This enhances the heat transfer towards the sample and accelerates kinetics of the gasification. This, in turn, improves the conversion of carbon to gas, increases the yield of the producer gas and reduces tar content. At higher steam to fuel ratio the process increases the yield of hydrogen, making it suitable for second-generation biofuels synthesis, whereas at lower steam to fuel ratio (S/F<2) the generated gas is of high calorific value making it suitable for power generation in a combined cycle.

  • 265.
    Donaj, Pawel J.
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Energi- och ugnsteknik.
    Kaminsky, W.
    Buzeto, F.
    Yang, Weihong
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Energi- och ugnsteknik.
    Pyrolysis of plastic waste for recovery of monomers and naphtha-like feedstockIngår i: Journal of Waste Management, ISSN 2356-7724, E-ISSN 2314-6052Artikel i tidskrift (Övrigt vetenskapligt)
    Abstract [en]

    Pyrolysis of plastic waste is an alternative way of plastic recovery and could be a potential solution for the increasing stream of solid waste. The objective of this work was to increase the yield the gaseous olefins (monomers) as feedstock for polymerization process and to test the applicability of a commercial Ziegler-Natta (Z-N): TiCl4/MgCl2 for cracking a mixture of polyolefins consisted of 46 % wt. of LDPE, 30% wt. ofHDPE and 24 % of PP. Two sets of experiments have been carried out at 500oC and 650oC via catalyticpyrolysis (1% of Z-N catalyst) and at 650oC and 730oC via only-thermal pyrolysis. These experiments have been conducted in a lab-scale, fluidized quartz-bed reactor of a capacity of 1-3kg/h at Hamburg University. The results revealed a strong influence of temperature and presence of catalyst on the product distribution. The ratios of gas/liquid/solid mass fractions via thermal pyrolysis were: 36.9/48.4/15.7%wt. and 42.4/44.7/13.9%wt. at650oC and 730oC while via catalytic pyrolysis were: 6.5/89.0/4.5%wt. and 54.3/41.9/3.8%wt. at 500oC and 650oC, respectively. At 650oC the monomer generation increased by 55% up to 23.6 %wt. of total pyrolysis products distribution while the catalyst was added. Obtained yields of olefins were compared with the naphtha steam cracking process and other potentially attractive processes for feedstock generation. The concept of closed cycle material flow for polyolefins has been discussed, showing the potential benefits of feedstock recycling in a plastic waste management.

  • 266.
    Donaj, Pawel J.
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Energi- och ugnsteknik.
    Kaminsky, W.
    Buzeto, F.
    Yang, Weihong
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Energi- och ugnsteknik.
    Pyrolysis of polyolefins for increasing the yield of monomers' recovery2012Ingår i: Waste Management, ISSN 0956-053X, E-ISSN 1879-2456, Vol. 32, nr 5, s. 840-846Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Pyrolysis of plastic waste is an alternative way of plastic recovery and could be a potential solution for the increasing stream of solid waste. The objective of this work was to increase the yield the gaseous olefins (monomers) as feedstock for polymerization process and to test the applicability of a commercial Ziegler-Natta (Z-N): TiCI4/MgCl2 for cracking a mixture of polyolefins consisted of 46% wt. of low density polyethylene (LDPE), 30% wt. of high density polyethylene (HDPE) and 24% wt. of polypropylene (PP). Two sets of experiments have been carried out at 500 and 650 C via catalytic pyrolysis (1% of Z-N catalyst) and at 650 and 730 degrees C via only-thermal pyrolysis. These experiments have been conducted in a lab-scale, fluidized quartz-bed reactor of a capacity of 1-3 kg/h at Hamburg University. The results revealed a strong influence of temperature and presence of catalyst on the product distribution. The ratios of gas/liquid/solid mass fractions via thermal pyrolysis were: 36.9/48.4/15.7% wt. and 42.4/44.7/13.9% wt. at 650 and 730 degrees C while via catalytic pyrolysis were: 6.5/89.0/4.5% wt. and 54.3/41.9/3.8% wt. at 500 and 650 degrees C, respectively. At 650 degrees C the monomer generation increased by 55% up to 23.6% wt. of total pyrolysis products distribution while the catalyst was added. Obtained yields of olefins were compared with the naphtha steam cracking process and other potentially attractive processes for feedstock generation. The concept of closed cycle material flow for polyolefins has been discussed, showing the potential benefits of feedstock recycling in a plastic waste management.

  • 267. Dong, H.
    et al.
    Zhao, Zhe
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. School of Materials Science and Engineering, Shanghai Institute of Technology, Shanghai, 201418, China.
    Wang, C.
    Effect of powder characteristics on the thermal conductivity and mechanical properties of Si 3 N 4 ceramics sintered by Spark plasma sintering2019Ingår i: Journal of materials science. Materials in electronics, ISSN 0957-4522, E-ISSN 1573-482X, Vol. 30, nr 8, s. 7590-7599Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The effect of powder characteristics on the thermal conductivity and mechanical properties of silicon nitride (Si 3 N 4 ) ceramics were investigated systematically by using two α-Si 3 N 4 powders as raw materials and using MgSiN 2 or MgO + Y 2 O 3 as sintering additives. The Si 3 N 4 ceramics with a higher density were obtained by α-Si 3 N 4 powders with lower oxygen content and impurities and using none-oxide sintering additive MgSiN 2 . The α–β phase transformation completely taken place in all the specimen at 1750 °C. The specimens sintered by powders with lower levels of oxygen and impurities show higher mechanical properties than other specimens. The Y 2 O 3 and MgO sintering additives lead to higher flexural strength and fracture toughness than MgSiN 2 . The Vickers’ hardness is just the opposite. The thermal conductivity value of powders with lower oxygen content is higher than that of the materials prepared by the other type of powder at the same conditions. The effects of the Si 3 N 4 particle size, native oxygen and impurities on the thermal conductivity of resultant materials were discussed in detail. This work demonstrates that the improvement in thermal conductivity of Si 3 N 4 can be obtained by using none-oxide sintering additive MgSiN 2 and the Si 3 N 4 powder with lower oxygen content, and impurities.

  • 268.
    Dong, Pengli
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Measurements of the thermodynamic activities of chromium  and vanadium oxides in CaO-MgO-Al2O3-SiO2 slags2009Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    In the present work, the thermodynamic activities of chromium and vanadium oxide in CaO-SiO2-MgO-Al2O3 slags were measured using gas-slag equilibration technique. The slag was equilibrated with a gas mixture of CO, CO2 and Ar gases enabling well-defined oxygen partial pressures in the gas mixture (PO2=10-3,10-4,10-5 Pa) at temperatures 1803, 1823K, 1873, 1923 K. The slags were kept in Pt crucibles during the equilibration and the duration of which was 20 h. From a knowledge of the thermodynamic activity of chromium and vanadium in Cr or V in Pt alloy, obtained from literature, and the oxygen partial pressure in the gas stream calculated by Thermo Calc software, the thermodynamic activity of chromium, vanadium oxide in the slags could be observed.An assessment of the experimental studies in earlier works reveal that, the activities of chromium at low chromium contents and vanadium in their respective alloys in platinum exhibits a strong negative deviation from ideality, the logarithms of activity coefficient of these elements were found to increase with increasing mole fractions of these metals in the Pt-alloys.Regarding the slag phase, all the chromium in the slags was assumed to be present in the divalent state in view of the low Cr contents and the low oxygen potentials employed in the present studies. Analogously, vanadium in the slag was assumed to be in the trivalent state in view of the low vanadium contents in the slag and the low oxygen partial pressure in the gas phase. Activity of chromium oxide, CrO decreases with increasing temperature and decreasing content of chromium oxide in slag and oxygen partial pressure in the gas phase. Activity of vanadium oxide, VO1.5 in slag phase shows a negative deviation from ideality. Activity coefficient of vanadium oxide shows a decrease with basicity of slag and the “break point” occurs at about slag basicity of 1 under the oxygen partial pressure of 10-3 Pa and temperature of 1873 K.A relationship for estimating the actual content of chromium, vanadium in slag as a function of activities of chromium or vanadium, temperature, oxygen partial pressure and slag basicity were developed from the present results, the agreement between the estimated and experimental values is satisfactory, especially at lower oxygen partial pressure.

  • 269.
    Dong, Pengli
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Wang, X. D.
    Seetharaman, Seshadri
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processvetenskap.
    Activity of VO1.5 in CaO-SiO2-MgO-Al2O3 Slags at Low Vanadium Contents and Low Oxygen Pressures2009Ingår i: Steel Research International, ISSN 1611-3683, Vol. 80, nr 4, s. 251-255Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the present work, the gas-slag equilibration technique was employed for the measurement of the thermodynamic activity of vanadium oxide. The vanadium-containing slag kept in a platinum crucible was equilibrated with a gas mixture of CO, CO2 and Ar, with well-defined oxygen partial pressure at a pre-determined temperature. The slag sample was quenched and the composition of the final slag was determined by chemical analysis. From the value of the oxygen partial pressure, the thermodynamic activity of VO1.5 could be calculated using the value for the activity of vanadium in V-Pt alloy. The measurements were carried out in the temperature range 1823 similar to 1923K and the oxygen partial pressures employed were 10(-3), 10(-4), 10(-5) Pa. The present results show that the activity of vanadium(III) oxide in slag exhibits a negative deviation from ideality in the present composition range. With increasing basicity of the slag, the final content of vanadium oxide in the slag was found to show an initial increase followed by a constant content. The activities of vanadium(III) oxide did not exhibit any significant change with increasing temperature. The activity coefficient of vanadium(III) oxide decreased sharply with slag basicity approximately up to a basicity of 1, beyond which it showed a near-constant value. Increase in basicity was found to cause a change in the distribution of vanadium between the slag and the alloy phases even though this effect was less pronounced. From the present results, a mathematical relationship for estimating the vanadium content in slag for a given activity of vanadium in the molten metal phase was developed.

  • 270.
    Dong, Pengli
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Wang, X. D.
    Seetharaman, Seshadri
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processvetenskap.
    Thermodynamic Activity of Chromium Oxide in CaO-SiO2-MgO-Al2O3-CrOx Melts2009Ingår i: Steel Research International, ISSN 1611-3683, Vol. 80, nr 3, s. 202-208Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Thermodynamic activities of chromium oxide contained in CaO-SiO2-MgO-Al2O3 melts were measured in the present work using gas-slag equilibrium technique. The oxygen partial pressure was varied (10(-)3, 10(-4), 10(-5) Pa). Gas mixture of CO, CO2 and Ar were used and investigated at 1803, 1873 and 1923 K. The activities of CrO showed a strong positive deviation from ideality and a decrease with increasing temperature and oxygen partial pressure. A mathematical expression relating the amount of chromium oxide in the slag phase with the activity of Cr in the metal phase based on the present experimental results is presented.

  • 271.
    Dong, Zhihua
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Temperature dependent mechanical properties of as-cast steels: Experimental and theoretical studies2015Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The temperature-dependent mechanical properties of steels are important to avoid processing defects, to understand and to improve the high-temperature performance. At the same time, having access to thermal properties gives us opportunity to assess the first-principles theoretical predictions at elevated temperatures. These properties are directly bound up with the performance of individual phase and also the evolving microstructure states at different thermalmechanical processes. In the present thesis, the temperature-dependent mechanical properties of continuously cast steels and iron are investigated using experimental and theoretical methods. Experimental studies are performed centering on the influence of thermal cycles occurring in secondary cooling.

    The temperature reversion in secondary cooling makes the hot ductility trough occurring at higher temperatures with greater depth. Increasing the reversion rate, the low temperature end of the ductility trough slightly extends to lower temperatures. As indicated by microstructure examinations, the intergranular fracture contributed from the thin film-like ferrite and (Fe,Mn)S particles slightly changes with the varying thermal cycles; however, the widmanstatten ferrite observed in the temperature reversion process seriously deteriorates the ductility. Due to the temperature reversion process, the peak stress slightly declines and the peak of strain to peak stress moves to higher temperatures. On the other hand, the sequential formations of ferrite and pearlite in the austenite transformation are indicated by two distinct peaks on the thermal expansion coefficient. By applying the developed concise model, the volume fractions of ferrite, pearlite, and austenite are quantitatively monitored in the phase transformation. Either increasing the cooling rate or the content of austenite stabilizing atoms Ni and Cu, the austenite transformation occurs at relatively low temperatures and indicates a greater phase transformation rate for both ferrite and pearlite. In addition, the final fraction of ferrite/pearlite increases/decreases with increasing the cooling rate, increasing the alloying atoms like Ni, Cr and Cu or lowering the carbon content.

    The temperature dependence of the polycrystalline Young’s modulus and the tetragonal shear modulus c0 of iron is predicted using ab initio calculations within the exact muffin-tin orbitals formalism. The dependence exhibits a good consistency with that of the peak stress observed in the experiments for the commercial steel. Despite the significant effects of magnetic sate and crystal structure on the elastic property of iron, the magneto-volume coupling primarily determines the temperature dependence for the single phase. In contrast, the dominant role of the volume expansion is observed for both the paramagnetic (PM) face centered cubic (fcc) and body centered cubic (bcc) Fe, although they show different magneto-elastic behaviors. Based on the theoretically predicted thermal expansion for PM bcc Fe, both the lattice vibrations and the magnetic evolution contribute to the thermal expansion, and the former is dominant.

  • 272.
    Dong, Zhihua
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Chongqing University, China.
    Chen, D.
    Long, M.
    Li, Wei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Chen, H.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala University, Sweden; Wigner Research Center for Physics, Hungary.
    Computation of Phase Fractions in Austenite Transformation with the Dilation Curve for Various Cooling Regimens in Continuous Casting2016Ingår i: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 47, nr 3, s. 1553-1564Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A concise model is applied to compute the microstructure evolution of austenite transformation by using the dilation curve of continuously cast steels. The model is verified by thermodynamic calculations and microstructure examinations. When applying the model, the phase fractions and the corresponding transforming rates during austenite transformation are investigated at various cooling rates and chemical compositions. In addition, ab initio calculations are performed for paramagnetic body-centered-cubic Fe to understand the thermal expansion behavior of steels at an atomic scale. Results indicate that by increasing the cooling rate, the final volume fraction of ferrite/pearlite will gradually increase/decrease with a greater transforming rate of ferrite. The ferrite fraction increases after austenite transformation with lowering of the carbon content and increasing of the substitutional alloying fractions. In the austenite transformation, the thermal expansion coefficient is sequentially determined by the forming rate of ferrite and pearlite. According to the ab initio theoretical calculations for the single phase of ferrite, thermal expansion emerges from magnetic evolution and lattice vibration, the latter playing the dominant role. The theoretical predictions for volume and thermal expansion coefficient are in good agreement with the experimental data.

  • 273.
    Dong, Zhihua
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Chongqing University, China.
    Chen, Dengfu
    Long, Mujun
    Li, Wei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Chen, Huabiao
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala University, Sweden.
    Computation of Phase Fractions in Austenite Transformation with the Di-latation Curve for Various Cooling Regimes in Continuous CastingManuskript (preprint) (Övrigt vetenskapligt)
  • 274.
    Dong, Zhihua
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Chongqing University, China.
    Li, Wei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Long, Mujun
    Gui, Lintao
    Chen, Dengfu
    Huang, Yunwei
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala University, Sweden.
    Effect of Temperature Reversion on Hot Ductility and Flow Stress-Strain Curves of C-Mn Continuously Cast Steels2015Ingår i: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 46, nr 4, s. 1885-1894Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The influence of temperature reversion in secondary cooling and its reversion rate on hot ductility and flow stress-strain curve of C-Mn steel has been investigated. Tensile specimens were cooled at various regimes. One cooling regime involved cooling at a constant rate of 100 degrees C min(-1) to the test temperature, while the others involved temperature reversion processes at three different reversion rates before deformation. After hot tensile test, the evolution of mechanical properties of steel was analyzed at various scales by means of microstructure observation, ab initio prediction, and thermodynamic calculation. Results indicated that the temperature reversion in secondary cooling led to hot ductility trough occurring at higher temperature with greater depth. With increasing temperature reversion rate, the low temperature end of ductility trough extended toward lower temperature, leading to wider hot ductility trough with slightly reducing depth. Microstructure examinations indicated that the intergranular fracture related to the thin film-like ferrite and (Fe, Mn)S particles did not changed with varying cooling regimes; however, the Widmanstatten ferrite surrounding austenite grains resulted from the temperature reversion process seriously deteriorated the ductility. In addition, after the temperature reversion in secondary cooling, the peak stress on the flow curve slightly declined and the peak of strain to peak stress occurred at higher temperature. With increasing temperature reversion rate, the strain to peak stress slightly increased, while the peak stress showed little variation. The evolution of plastic modulus and strain to peak stress of austenite with varying temperature was in line with the theoretical prediction on Fe.

  • 275.
    Doostmohammadi, Hamid
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    A Study of Slag/Metal Equilibrium and Inclusion Characteristics during Ladle Treatment and after Ingot Casting2009Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Today, there is a high demand on clean steel for high performance materialproperties. Thus, steel producers try to deliver a steel product with the highestquality and cleanliness to the market. The number of parameters that affect thesteel cleanliness may vary depending on the required material properties of thefinal product. However, the non-metallic inclusion characteristics represent one ofthe most important parameters. More specifically, the composition, size, numberand morphology affect steel cleanliness. In this work, selected parameters affectingthe inclusion characteristics were studied using the following methods: i)thermodynamic calculations (including computational thermodynamiccalculations), ii) inclusion determinations using a cross sectional (CS) method (2Dinvestigations) and iii) inclusion determinations using an electrolytic extraction(EE) method (3D investigations).

    The computational thermodynamic calculations of the slag-steel and inclusion-steelequilibriums were carried out using the Thermo-Calc software. With the help ofthese calculations, the influence of the slag carryover on the top slag, aluminumcontent in steel and sulfur distribution ratio as well as predictions of stable phasesof inclusions were studied. In addition, inclusion determinations of tool steel gradesamples collected during various stages of the ladle treatment in a scrap-based steelplant were carried out using both 2D and 3D methods. Furthermore, inclusiondeterminations of bearing steel grade samples from a runner system after ingotcasting were performed using a 2D metallographic method (CS-method). Also, theINCAFeature software was used, when using cross sectional method, in order tocollect more statistics of the inclusion characteristics.

    It was found that slag carryover has a large influence on the composition of theactual top slag as well as the aluminum content in the steel as well as the sulfurdistribution ratio. In addition, steel and slag were found to be in “near”-equilibriumconditions, after the completion of the vacuum degassing operation. Furthermore,the composition of small-size inclusions in samples taken from tool steel was foundto be very scattered. Moreover, the composition of the large-size inclusions wasfound to be less scattered. Furthermore, closer to the top slag composition insamples collected after vacuum degassing. Finally, the accuracy of the inclusioncomposition determinations of tool steel samples using the electrolytic extractionmethod was found to be better than for the cross sectional method. The worseaccuracy of the CS-method is due to a considerable effect of matrix elements oninclusion composition.

  • 276.
    Doostmohammadi, Hamid
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Andersson, Margareta A. T.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Steneholm, Karin
    Uddeholm Tooling AB.
    Jönsson, Pär
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Effect of EAF Slag Carryover on Slag-metal Equilibrium Calculations for Ladle Degassing Process2009Ingår i: EPD CONGRESS 2009, PROCEEDINGS    / [ed] Howard SM, 2009, s. 695-702Konferensbidrag (Refereegranskat)
    Abstract [en]

    During the tapping of liquid steel from Electric Arc Furnace (EAF), some slag is carried over into the ladle. High levels of FeO and MnO in slag carryover increase the oxygen activity in steel melt leading to oxide inclusion formation during the ladle treatment. The demand on cleaner steels requires minimization of carryover slag. In this work, the effect of EAF slag carryover on ladle slag-steel equilibrium calculations for a hot working tool steel was studied. Steel and slag sampling were done in Uddeholm Tooling AB in Sweden. XRF and OES techniques were used to determine chemical composition of samples. The quantity of slag carryover was calculated based on a mass balance followed by thermodynamic calculations on metal-slag equilibrium using Thermo-Calc software. The agreement between predictions and experimentally determined compositions was good. This leads to the development of a prediction method for optimizing the production of other tool steel grades.

  • 277.
    Doostmohammadi, Hamid
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Andersson, Margareta
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Karasev, Andrey
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Jönsson, Pär
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Use of Computational Thermodynamic Calculations in Studying the Slag/Steel Equilibrium during Vacuum Degassing2010Ingår i: STEEL RES INT, ISSN 1611-3683, Vol. 81, nr 1, s. 31-39Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The effectiveness of a ladle refining process for production of tool steel with focus on the top slag is studied using computational thermodynamic calculations. The theoretical assessment was based on compositional data of steel and slag samples collected during trials in a plant equipped with a 65-t EAF, a ladle furnace and a vacuum degasser The calculation of slag-metal equilibrium during ladle treatment was performed for top slag excluding (Case A) and including (Case B) slag carryover and deoxidation products. The predictions showed that slag carryover and deoxidation products in the ladle significantly affect the composition of the top slag. Thus, these conditions must be taken into consideration when predicting the actual top slag composition. It was also found that it is possible to predict the final aluminium and sulphur content in steel based on the same calculation approach.

  • 278.
    Doostmohammadi, Hamid
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Jönsson, Pär
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Komenda, J
    Hagman, S
    Inclusion Characteristics of Bearing Steel in a Runner after Ingot Casting2010Ingår i: STEEL RES INT, ISSN 1611-3683, Vol. 81, nr 2, s. 142-149Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the uphill teaming method of ingot casting molten metal from the ladle goes into the runner system, which feeds one or several ingot moulds. This method is still important for production of bearing steel. In order to make clean steel, which has a controlled amount of inclusions, good understanding of inclusions characteristics is necessary In this work non-metallic inclusions of steel left in the runner part of an ingot casting system were studied. Inclusion type, size, and morphology were the main focus of this study A scanning electron microscope (SEM) was used to assess inclusion size and morphology The chemical composition of inclusions was determined by SEM equipped with EDS. An automated program called 'INCAFeature' was used to collect statistics of inclusion characteristics. Based on the statistical analysis of inclusion composition, four types of inclusions including oxides, sulfides, carbonitrides and complex inclusions were defined. The inclusion characteristics in the runner were also compared to literature data of inclusions found in ladle and mould samples.

  • 279.
    Doostmohammadi, Hamid
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Karasev, Andrey
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Jönsson, Pär G
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    A Comparison of a Two-Dimensional and a Three-Dimensional Method for Inclusion Determinations in Tool Steel2010Ingår i: STEEL RES INT, ISSN 1611-3683, Vol. 81, nr 5, s. 398-406Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    To produce clean commercial tool steel the non-metallic inclusions characteristics have to be known, since they influence the mechanical properties of steel. In this work, inclusion characteristics in steel samples from plant trials were studied. The samples were collected in the steel plant according the two following methods: (a) 2D investigations of inclusions by a cross sectional method and (b) 3D investigations of inclusions collected on a film filter after electrolytic extraction. More specifically, the chemical composition, morphology, number and size distribution of inclusions in tool steel samples taken from ladle during melt treatment were determined by both methods. In both methods SEM equipped with EDS was used for compositional analysis of inclusions. In addition, in the cross sectional method an automated detection program called 'INCAFeature' was used to collect more statistics of non-metallic inclusions. The composition of inclusions larger than 5 mu m was found to contain 49% CaO based on the results from both methods. However, for smaller inclusions it was found that the accuracy of the 2D method was less than that of the 3D method due to the influence of the metal matrix on the results. In addition, it was found that a critical inclusion size of 4 mu m could be defined for the 3D method, above which the standard deviation in composition determination was very low.

  • 280.
    Drahorad, Nicolò
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Quantification of tribological effects in expansion fasteners2019Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Eftermonterade fästankare i byggnader säkerställer byggnadsstrukturernas integritet, även under de mest allvarliga statiska, seismiska och chockbelastningar. Trots stor användning och popularitet  på byggarbetsplatser över hela världen är det nuvarande kunskapsläget av denna teknik begränsat och det finns en stor potential för betydande förbättringar.

    Specifikt bygger expansionsankringsmekanismen på ren friktion. Därför är möjligheten att manipulera och optimera fästankarnas tribologiska beteende nyckeln till att uppfylla strikta säkerhetsbestämmelser och kunna utveckla bättre prestanda och designlösningar.

    Detta forskningsprojekt har utförts på Hilti Corporation i Schaan (Liechtenstein) och presenterar en undersökning av flera antifriktionsbeläggningslösningar. Laboratorieprov har utförts för att kvantifiera olika friktionskoefficienter, och efter fullskaliga standardiserade tester (med fästankare i betong) har det varit möjligt att utvärdera de övergripande mekaniska prestationerna av dessa. Erhållna data har analyserats numerisk och proverna har undersökts ytterligare med optisk mikroskopi.

    Resultatet av detta examensarbete är viktigt för utvecklingen av nästa generation expansionsfästen och ger även ytterligare insikt och en djupare förståelse av tribologin av funktionella beläggningar.

  • 281.
    Du, Hongying
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    THE EVALUATION OF NON-METALLIC INCLUSIONS IN CALCIUM-TREATED STEEL BY USING ELECTROLYTIC EXTRACTION2016Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    This study aims on characterization of non-metallic inclusions (oxides and sulfides) in steel with and without Calcium treatment. In this paper, the three-dimensional (3-D) investigation method of inclusions on film filter after Electrolytic Extraction (EE) of steel samples is applied on two different steel grades (280, 316L). Image analysis of non-metallic inclusions is carried out on Scanning Electron Microscope (SEM) images following with inclusion characteristic analysis. Steel samples with calcium treatment in the production process and reference samples was investigated and compared in density, size and composition.

    It shows that higher magnification and larger inclusion size correspond to more accurate result. With restriction of equipment and measurement, 2μm is the smallest size could be measured in ×500 magnification within 5% error.

    The comparison of distribution of inclusions varies with different zones: center has the largest size with least number of NMI; surface has the smallest size with largest number of NM; middle part has the median properties.

    In 316L steel, Ca treatment increases the number of oxides inclusions significantly; the content of Ca and Si in oxides inclusions is also increased. Two shapes of oxides inclusions, oval and elongated ones, are found with Ca treatment.

    In 280 steel, the total amount of NMI decreases slightly with Ca treatment; CaS is found in spherical inclusions; Because of earlier formation of larger size spherical inclusions, higher Ca content is found than that in smaller size spherical inclusions.

  • 282.
    Du, Sichen
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Mikro-modellering.
    Improving process design in steelmaking2005Ingår i: Fundamentals of Metallurgy, Elsevier Inc. , 2005, s. 369-398Kapitel i bok, del av antologi (Övrigt vetenskapligt)
  • 283.
    Edström, John Olof
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Steel research in Sweden2005Ingår i: Revue de métallurgie (Imprimé), ISSN 0035-1563, E-ISSN 1156-3141, Vol. 102, nr 1, s. 103-105Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The author describes the steel research organisation that has been developed in Sweden from the middle of the twentieth century and reports on the most recent assessments of its cost effectiveness. Jernkontoret has been the central organization of the Swedish steel industry since1747. Jernkontoret originated several famous Swedish Institutes or Universities, such as the Royal Institute of Technology (KTH), Lulea University of Technology, Dalarna University, the Swedish Institute for Metal Research and MEFOS. The work of the institutes is funded by commissions from the Swedish or the foreign industry, and grants from the Swedish state and the European Union. Total costs of steel research in Sweden is on the order of 100 M-C per year. A recent Jernkontoret report concluded that the state aided joint research in the Swedish steel industry generated at least a fivefold return.

  • 284.
    Edvartsen, Mattias
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    A desulphurization study of hot metal at SSAB Europe Luleå with added bottom stirring of nitrogen gas2015Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [en]

    This bachelor degree project is about determining the impact that additional bottom stirring may have on the desulphurization process at SSAB Luleå. During one week of field work steel samples were collected from 39 different heats. 31 of the heats were samples with the bottom stirring function enabled and the remaining 8 heats without the bottom blowing function, which is the standard method today at SSAB Luleå and they can be referred as references. Data from 15 old reference heats were also used for analysis.Two different behaviors of bottom stirring appeared and they were therefore separated to type 1 and type 2 bottom stirring. Type 1 bottom stirring turned out to have highest possibility of all methods to reach dissolved sulfur content of maximum 0.001%. If the ingoing dissolved sulfur content is around 0.03% has type 1 bottom stirring 33% chance to reach 0.001% dissolved sulfur content already after 13.3 minutes of injection and that can save sulfur reagents. The method with highest reagent efficiency showed type 1 bottom stirring to have, on second place came type 2 bottom stirring and the references showed to have lowest reagent efficiency.

  • 285.
    Edvartsen, Mattias
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Steel Cleanliness: Deviations during the CAS-OB process2017Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Different types of deviations in the CAS-OB (composition adjustment by sealed argon bubbling - oxygen blowing) process at SSAB in Luleå are known to occur. Therefore, SSAB Europe in Luleå started this project with the task to investigate deviations during the CAS-OB process, to see how the deviations affect the steel cleanliness in terms of non-metallic inclusions. The aim of this project has been to locate unwanted deviations from the standard practice associated with the CAS-OB process. This study is restricted to Al-killed and calcium treated steel grades only.

    In this study has 34 different steel heats, including four references, 25 deviations and five steel heats from previous studies and reclaims been investigated. Totally, 18 steel samples have been retrieved from 14 different steel heats. The steel samples have been prepared and analyzed per the standards SS111114 and SS111116 to retrieve inclusion drawings and PC-mic results.

    Several types of unwanted deviations in the CAS-OB process has been detected, including; cooling the steel heats with steel scrap after calcium treatment and multiple of small additives of aluminum late in the process. The results indicate that cooling with scrap after the calcium treatment worsen the steel cleanliness in terms of non-metallic inclusions and should therefore be avoided. Furthermore, multiple of small aluminum additions late in the process is likely a contributing parameter to increase the projected length of the inclusions.

    Adding alloying elements after the calcium treatment to adjust the composition is another frequently occurring deviation from the practice, and in many cases, extra calcium is added after the alloys. The results from this study implies that it is preferable not to add any extra calcium if extra additions of alloying elements are necessary, since it seems to generate larger inclusions.

    Publikationen är tillgänglig i fulltext från 2027-09-14 13:00
  • 286.
    Edwards, Dan
    et al.
    Pacific North West Laboratories, Richland, WA. USA.
    Garner, Frank
    Pacific North West Laboratories, Richland, WA. USA.
    Bruemmer, Steve
    Pacific North West Laboratories, Richland, WA. USA.
    Efsing, Pål
    Nano-cavities observed in a 316SS PWR flux thimble tube irradiated to 33 and 70 dpa2009Ingår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 384, s. 249-255Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The radiation-induced microstructure of a cold-worked 316SS flux thimble tube from an operating pressurized water reactor (PWR) was examined. Two irradiated conditions, 33 dpa at 290 °C and 70 dpa at 315 °C were examined by transmission electron microscopy. The original dislocation network had completely disappeared and was replaced by fine dispersions of Frank loops and small nano-cavities at high densities. The latter appear to be bubbles containing high levels of helium and hydrogen. An enhanced distribution of these nano-cavities was found at grain boundaries and may play a role in the increased susceptibility of the irradiated 316SS to intergranular failure of specimens from this tube during post-irradiation slow strain rate testing in PWR water conditions.

  • 287.
    Edwards, Dan
    et al.
    Pacific North West Laboratories, Richland, WA. USA.
    Simonen, Ed
    Pacific North West Laboratories, Richland, WA. USA.
    Bruemmer, Steve
    Pacific North West Laboratories, Richland, WA. USA.
    Efsing, Pål
    MICROSTRUCTURAL EVOLUTION IN NEUTRON-IRRADIATED STAINLESS STEELS: COMPARISON OF LWR AND FAST-REACTOR IRRADIATIONS2005Ingår i: 12th International Conference on Environmental Degradation of Materials in Nuclear Power System – Water Reactors / [ed] Todd Allen, Peter King, Larry Nelson, The Minerals, Metals, and Materials Society, 2005, s. 419-428Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    A series of Bor-60 fast-reactor irradiations have been completed on commercial and laboratory heats of 304SS and 316SS irradiated at 330°C to doses from 5 to 20 dpa. A quantitative comparison has been made to assess critical changes in material microstructure due to differences in fast-reactor versus lightwater-reactor irradiation environments. Direct comparisons are also made between cold-worked 316SS baffle-bolt materials irradiated in Bor-60 to similar cold-worked 316SS heats removed from the PWR service after moderate to high irradiation exposures. The evolution of Frank loops, precipitates and cavities will be documented and evaluated with respect to differences in irradiated spectrum, dose rate and temperature.

  • 288.
    Efsing, Pål
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Forssgren, Björn
    Ringhals AB.
    Bengtsson, Bengt
    OKG AB.
    Jonsson, Alf
    Forsmarks KraftGrupp AB.
    Jenssen, Anders
    Studsvik Nuclear AB.
    Sundberg, Johan
    Studsvik Nuclear AB.
    Jansson, Christer
    Vattenfall Utveckling.
    IGSCC DISPOSITION CURVES FOR ALLOY 82 IN BWR NORMAL WATER CHEMISTRY2007Ingår i: 13th International Conference on Environmental Degradation of Materials in Nuclear Power Systems, 2007, s. 1353-1363Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    In many nuclear power plants, areas of susceptible material in the reactor systems are replaced or mitigated. Many of the areas where the nickel-based weld metal Alloy 182 have been used, are not replaceable but need to be mitigated. One possibility to mitigate is to make known susceptible material non-accessible for the reactor coolant water by covering it with less susceptible materials. One such possibility that has been utilized frequently in the Swedish Boiling Water Reactor (BWR) fleet is in-lay welding of butt welds in the main circulation and feed water loops with the less susceptible Alloy 82, which has fewer reported failure cases under these conditions.

    The study focuses on the development of a Factor of Improvement between Alloy 182 and the replacement, Alloy 82 material. As part of this, a disposition curve under conditions relevant for Normal Water Chemistry, NWC, in the Swedish BWRs is presented.

  • 289.
    Efsing, Pål
    et al.
    Ringhals AB.
    Jansson, Christer
    Vattenfall Utveckling.
    Embring, Gören
    Ringhals AB.
    Mager, Tom
    TRM International Consulting.
    Analysis of the Ductile-to-Brittle Transition Temperature Shift in a Commercial Power Plant With High Nickel Containing Weld Material2007Ingår i: Journal of ASTM International, ISSN 1546-962X, E-ISSN 1546-962X, Vol. 4, nr 7Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Plant specific surveillance programs that ideally include all relevant materials and materials combinations that are subjected to neutron irradiation during operation address the degradation due to irradiation of the reactor pressure vessel material for nuclear electric power plants. Plant specific surveillance programs are not unique to the two power plants treated in this study. The current Swedish regulatory system does, however, call for a fairly rigid approach within the surveillance program. In the Swedish case, this means that there is a plant specific predetermined inspection∕test program that has to be followed in order to verify the operability of the power plant and also to verify the operational limits with respect to pressure∕temperature effects on a repetitive basis. The two pressurized water reactor plants Ringhals 3 and 4 have in common that the weld metal used for the butt welds of the reactor pressure vessel is a high nickel type material, above the current limits of the NUREG Reg. Guide 1.99, rev. 2. In the original state, the high nickel content provides excellent fracture toughness in the unirradiated material condition and a low ductile-to-brittle transformation temperature (DBTT). It has, however, been highlighted in several studies that high nickel materials exhibit a very large DBTT shift as a consequence of irradiation, and also that the precipitates that form during the irradiation are not as easily controlled during a heat treatment to remove the irradiation damage as are the copper rich clusters. This paper will present the current state of the art regarding these effects as observed in the weld metal specimens. The paper will present the results from the Charpy V notched and fracture mechanics specimen test encapsulated in the Ringhals Units 3 and 4 surveillance programs. The results from the Ringhals Units 3 and 4 surveillance programs show that there is a need for corrective action to be taken in order to ensure 60 y of operability for the two power plants.

  • 290.
    Efsing, Pål
    et al.
    Research and Nuclear Development, Vattenfall/Ringhals AB, Väröbacka,.
    Roudén, Jenny
    Ringhals AB.
    Green, Eva-Lena
    Ringhals AB.
    Ringhals Units 3 and 4 - Fluence determination in a historic and future perspective2012Ingår i: Journal of ASTM International, ISSN 1546-962X, E-ISSN 1546-962X, Vol. 4, s. 1-9Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Ringhals site is situated on the Swedish southwest coastline. At the site, there are four operating nuclear power plants. Historically, the Swedish policy has been that the nuclear power plants were to be closed in 2010. The present position is to operate the units until their technical and economic lifetime has run out. The units shall be maintained and invested in to ensure a lifetime of at least 50 years, but the actions taken shall not limit the time to this date. When the initial surveillance capsules were evaluated, it was noted that the material properties of the weld material of unit 3 and 4 showed some deviations from the expected behaviour. Currently there is an extensive project running for re-evaluating the embrittlement situation from a long-term operating perspective. One part of the project is aimed at more accurately determining the fluence levels of the reactor pressure vessels (RPVs). The basis for the early evaluations of the dosimeters in the surveillance capsules and the corresponding fluence evaluation had an operating lifetime of 25 years as a target value. Therefore, the accuracy and refinement of the measurement and calculation were taken to be good enough to suit this life span. Looking back at the results from the dosimetry measurements there are a few discrepancies. Some of the dosimeters were disintegrated and some measurements had comparatively large uncertainties. When starting this project there were some re-evaluations done with the old fluence prediction model. For every new run and refinement there appeared new difficulties, and the decision was to start the evaluation from scratch.

    Then there are two questions remaining regarding the fluence: What is the current fluence level? What will the resulting fluence be after 60 years of operation, when we have up-rated output power of both reactors? This paper aims to describe the view of the fluence evaluation in the surveillance program of the RPV, both in a historical and prospective view.

  • 291.
    Efsing, Pål
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Roudén, Jenny
    Ringhals AB.
    Lundgren, Martin
    Epsilon AB.
    Long term irradiation effects on the mechanical properties of reactor pressure vessel steels from two commercial PWR plants 2013Ingår i: ASTM Special Technical Publication, ASTM International, 2013, Vol. 1547, s. 52-68Konferensbidrag (Refereegranskat)
    Abstract [en]

    The Swedish nuclear power plants all have plant specific surveillance programs which includes samples from all relevant materials that are subjected to a fluence-level that exceeds 1*1017 n/cm2 over the estimated period of operation for the specific power plants. The Swedish pressurized water reactor (PWR)-plants are currently planning for a service period beyond 50 years of operation. As a portion of that, two of the three PWR units at the Ringhals site are conducting a major effort to verify the fitness to service of the reactor pressure vessel (RPV). In this case it is the weld in the belt-line region of the RPV, which is the apparent limiting factor. The weld metal contains high Nickel and high Manganese levels, not commonly used in other PWR-reactors. The effort includes a densified testing of the available surveillance capsule material in order to better understand the degradation phenomena and also an extended testing scope. A spin off effect of this program is that high fluence data for the base material also is made available from the testing. The chemical composition of the base metal is valid for many of the currently operating PWR-vessels. This study is an analysis of both the weld and the base material data extracted from the surveillance program. The results are evaluated against currently available data and correlation curves. In general, the results point out that the current Regulatory Guide 1.99 revision 2-correlation regarding the prediction of as-irradiated transition temperature is under-conservative for the tested material. The transition temperature shift, here evaluated as the temperature shift at 41J, is under-predicted by the correlation by as much as 70°C in some cases and increases with increasing fluences. However, prediction made by the French average irradiation embrittlement prediction formula, FIM-formula, is consistently better but still slightly under conservative.

  • 292.
    Ejenstam, Jesper
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap. Sandvik Heating Technology AB.
    Jonsson, Bo
    Szakalos, Peter
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Optimizing the Oxidation Properties of FeCrAl Alloys at Low Temperatures2017Ingår i: Oxidation of Metals, ISSN 0030-770X, E-ISSN 1573-4889, Vol. 88, nr 3-4, s. 361-370Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    FeCrAl alloys are proposed candidate materials for liquid lead applications. Chromium is needed to assist the formation of a protective alumina layer, albeit has to be limited to avoid alpha' precipitation. Reactive elements (RE) improve oxidation properties, but little is known about the RE effects at lower temperatures. An alloy matrix based on Fe-10Cr-4Al (wt%), with varying Zr, Y and Ti contents, was exposed to liquid lead up to 1 year in the temperature interval of 450-550 A degrees C. It was found that the formation of protective alumina was dependent on the RE/carbon ratio. All alloys with ratios lower than unity showed poor oxidation properties due to the formation of Cr-carbides in the metal-oxide interface. A sufficiently high amount of Zr and Ti was shown to significantly improve the oxidation properties at both temperatures. The positive effect is related to the suppression of Cr-carbides by addition of stronger carbide formers.

  • 293.
    Ejenstam, Jesper
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Szakalos, Peter
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Long term corrosion resistance of alumina forming austenitic stainless steels in liquid lead2015Ingår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 461, s. 164-170Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Alumina forming austenitic steels (AFA) and commercial stainless steels have been exposed in liquid lead with 10-7 wt.% oxygen at 550 °C for up to one year. It is known that chromia forming austenitic stainless steels, such as 316L and 15-15 Ti, have difficulties forming protective oxides in liquid lead at temperatures above 500°C, which is confirmed in this study. By adding Al to austenitic steels, it is in general terms possible to increase the corrosion resistance. However this study shows that the high Ni containing AFA alloys are attacked by the liquid lead, i.e. dissolution attack occurs. By lowering the Ni content in AFA alloys, it is possible to achieve excellent oxidation properties in liquid lead. Following further optimization of the microstructural properties, low Ni AFA alloys may represent a promising future structural steel for lead cooled reactors.

  • 294.
    Ejenstam, Lina
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap. SP Technical Research Institute of Sweden.
    Swerin, Agne
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap. SP Technical Research Institute of Sweden.
    Pan, Jinshan
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Claesson, Per
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap. SP Technical Research Institute of Sweden.
    Corrosion protection by hydrophobic silica particle-polydimethylsiloxane composite coatings2015Ingår i: Corrosion Science, ISSN 0010-938X, E-ISSN 1879-0496, nr 99, s. 89-97Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this study, the time-dependent corrosion protection ability of 10–15 µm thin polydimethylsiloxane -nanoparticle composite coatings was evaluated using mainly open circuit potential and electrochemical impedance spectroscopy measurements. The best result was obtained for the coating containing 20 wt% hydrophobic silica nanoparticles, where it was possible to achieve protection for almost 80 days in 3 wt% NaCl solution. The protective properties offered by this coating are suggested to be due to a synergistic effect of the hydrophobicity of the polydimethylsiloxane matrix and the prolonged diffusion path caused by addition of hydrophobic silica particles.

  • 295.
    Ek, Mattias
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Mikro-modellering.
    A study of some aspects of gas-slag-metal interactions: Towards dynamic process model and control2012Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The present thesis deals with the development of a new type of dynamic model for metallurgical reactors. It also covers some of the theoretical aspects of steelmaking that is necessary to include in such an application. The thesis consists of modeling work, high temperature experiments and cold model experiments.

    Two different aspects of slags in the oxygen steelmaking were investigated. In the first study, slag samples were equilibrated with copper at 1923K in order to study their capacities in capturing phosphorous. Some of the samples were liquid-solid mixtures. The solid phases in these samples were identified by SEM analysis. The identified phases were found to agree well with Thermocalc calculations while the amount of solid fractions didn’t. The phosphorous distribution between the different phases was examined. The phosphate capacities of the samples were evaluated. The MgO content didn’t show any appreciable impact on the phosphate capacity. Furthermore the activities of FeO in the liquid slag samples were calculated and were found to deviate positively from ideality. In the second study the foaming height of CaO-SiO2-FeO slags by the reaction with hot metal was investigated. It was found that the foaming height increased with increasing FeO content up to 20-25%. The foaming height was seen to decrease with increased viscosity. The present results indicated that simply using foaming index for converter slag might lead to wrong conclusion.

    Simulation experiments using cold model at room temperature were conducted. Cold model experiments were carried out in order to study the penetration depth due to an impinging gas jet on the surface of a liquid metal. The liquid alloy Ga-In-Sn was used to simulate steel. And an HCl solution was used to simulate the slag. A comparison with predictions of existing models was made and a new model parameter was suggested. The observation of the movement of metal droplets generated by the gas jet was also made. The low velocity of droplets suggested that the turbulent viscosity played important role and the droplets could have long resident time in the slag.

    Furthermore a study of the effect of gas flow rate on homogenization and inclusion removal in a gas stirred ladle was carried out. Both industrial trials and cold model experiments were conducted. As an auxiliary tool CFD was used to predict the mixing times and was found to agree well with both the model experiments and industrial data. The increase of flow rate of inert gas would not improve the mixing substantially at higher flow rates. The water model study showed also that the gas flow rate had negligible effect on the rate of inclusion removal. Both the experiments and CFD calculation strongly suggested that low gas flow rate should be applied in the ladle treatment.

    Lastly a new approach to a dynamic process model of 300 ton BOF converter was made. The main feature was to utilize the velocity vectors obtained by CFD simulation. In the standalone model, the steel melt domain was sliced into 1000 cells. Based on the imported velocity vectors from the CFD calculation, the mass transfer of carbon and phosphorus was calculated taking into account the slag metal reactions. The mass exchange between slag and metal was considered to be dominated by the metal droplet formation due to oxygen jet. The convergence of the model calculation and the promising comparison between the model prediction and the industrial data strongly suggested that the proposed approach would be a powerful tool in dynamic process control. However, more precise descriptions of other process aspects need to be included before the model can be practically employed in a dynamic controlling system.

  • 296.
    Ek, Mattias
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Mikro-modellering.
    Du, Sichen
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Mikro-modellering.
    Study on foaming of CaO-SiO2-FeO slag by the reaction with hot metal2012Manuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    In the present study the foaming of CaO-SiO2-FeO slags is investigated. The foaming height induced by the reaction between slag and hot metal were carried out. It was found that the foaming height increases with increased FeO content up to 20-25%. The foaming height was seen to decrease with increased viscosity. The present results indicated that simply using foaming index for converter slag might lead to wrong conclusion.

  • 297.
    Ek, Mattias
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Mikro-modellering.
    Huber, Jean-Christophe
    Brosse, Guillaume
    Du, Sichen
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Mikro-modellering.
    Capacities of some CaO-SiO2-FeO-MnO-MgO slags and slag-solid mixtures in capturing phosphorous2013Ingår i: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 40, nr 4, s. 305-311Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Slag is of great importance for dephosphorisation in converter steelmaking. In the present study, slag samples were equilibrated with copper at 1923 K to study their capacities in capturing phosphorous. The phosphate capacities of the slags were calculated. Some of the samples were liquid-solid mixtures. The solid phases in these samples were identified by SEM analysis, and the identified phases were found to agree well with Thermocalc calculations. On the other hand, the fractions of the solid phase did not agree with the Thermocalc calculation. Phosphorous distributions in the different phases were examined, and the phosphate capacities of the samples were evaluated. The MgO content did not show any appreciable impact on the phosphate capacity. The activities of FeO in the pure liquid slag samples were calculated and found to deviate positively from ideality.

  • 298.
    Ek, Mattias
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Mikro-modellering.
    Sichen, Du
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Mikro-modellering.
    Study of Penetration Depth and Droplet Behavior in the Case of a Gas Jet Impinging on the Surface of Molten Metal using Liquid Ga-In-Sn2012Ingår i: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 83, nr 7, s. 678-685Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    To study the penetration depth in the case of a gas jet impinging on the surface of liquid steel, cold model experiments were carried out using a liquid alloy GaInSn, which had similar physical properties as liquid steel. A HCl solution was used to simulate the top slag. The top phase was found to have appreciable effect on the penetration depth. Comparison of the experimental data with the predictions of the existing models indicated that most the model predictions deviated from the experimental results at higher lance heights and gas flow rates. New model parameter was suggested based on the present experimental data. The observation of the formation and movement of metal droplets generated by the gas jet was also made. The velocity of the droplet was found to be at a level only about 1% of the terminal velocity. This low velocity suggested that the turbulent viscosity played important role and the droplets could have long resident time in the slag.

  • 299.
    Ek, Mattias
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Mikro-modellering.
    Wu, Liushun
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Mikro-modellering.
    Valentin, Peter
    Sichen, Du
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Mikro-modellering.
    Effect of Inert Gas Flow Rate on Homogenization and Inclusion Removal in a Gas Stirred Ladle2010Ingår i: STEEL RES INT, ISSN 1611-3683, Vol. 81, nr 12, s. 1056-1063Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the present study, the effect of gas flow rate on homogenization and inclusion removal in a gas stirred ladle was investigated. Both industrial trials and cold model experiments were conducted. CFD calculation was also carried out as an auxiliary tool. The mixing times predicted by CFD simulation agreed well with both the model experiments and industrial data. 99% mixing could be achieved in about 2-3 minutes. The increase of flow rate of inert gas would not improve the mixing substantially, while the mixing time decreased somewhat with the increase of gas flow rate. The water model study showed also that the gas flow rate had a negligible effect on the rate of inclusion removal. Both the experiments and CFD calculation strongly suggested that a low gas flow rate should be applied in the ladle treatment.

  • 300.
    Ekbom, Lars B.
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Antonsson, Tomas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Ekbom, M
    Computer simulation of solution and growth processes during the initial stage of liquid phase sintering of tungsten heavy metal2005Ingår i: Scandinavian journal of metallurgy, ISSN 0371-0459, E-ISSN 1600-0692, Vol. 34, nr 5, s. 312-316Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the initial stage of liquid phase sintering, particle dissolution and growth processes occur. The melting matrix penetrates the solid particle agglomerates. A fraction of the particles dissolves in the liquid matrix phase and the original powder size will initially be reduced. At the same time the agglomerates of particles are effectively separated. In a second stage larger particles grow in equilibrium with the matrix, whilst smaller, pure particles dissolve into the matrix and the mean particle size increases. When an equilibrium is reached, the solid particles start to grow in the liquid matrix phase in accordance with the ripening process. The initial stages of liquid phase sintering have been investigated by short time sintering under microgravity and are presented in a series of micrographs. Mathematical models for the 3 stages have been developed. Computer simulations of these different stages in the solution and growth processes have been used to visualise the change in particle size distribution.

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