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ONLINE ISSN: 1347-5460
PRINT ISSN: 0915-1559

ISIJ International Vol. 58 (2018), No. 1

  • Comparison of Agglomeration Behavior of Fine Particles in Liquid among Various Mixing Operations

    Syunsuke Sumitomo, Kota Yoshitomi, Md. Azhar Uddin, Yoshiei Kato

    pp. 1-9

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    DOI:10.2355/isijinternational.ISIJINT-2017-190

    Abstract

    In order to compare the agglomeration and breakup behavior of fine particles in liquid by various mixing operations, model experiments were carried out and a mathematical model was developed and compared with the experimental results. Three kinds of mixing operations were examined: mechanical stirring by impeller (impeller), gas blow mixing (gas), and gas and liquid jet blow mixing by RH degasser (RH). Polymethylmethacrylate (PMMA) particles of 2.8×10−6 m in mean diameter and 3.0×103 mol·m−3 of KCl solution were used in the experiment as solid and liquid phases, respectively. Total number of PMMA particles at each mixing process decreased with the increasing time, although the agglomeration rate decreased. The PMMA agglomeration rate at the same mixing energy input in the liquid was in the following decreasing order: impeller, gas, and RH mixing. The experimental results of the impeller mixing were able to be explained by a turbulence agglomeration model. A breakup model of particles was newly developed assuming that the agglomerated PMMA particles adhered to the surface of bubbles during bubble floating in the liquid was divided into two pieces on the gas/liquid free surface at the moment of bubble bursting. By introducing this breakup model in addition to the agglomeration one, the calculation results for both of the gas and RH mixing agreed well with the experiment.

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    2. Analysis of Cohesive Particle Percolation in a Packed Bed Using Discrete Element Method ISIJ International Vol.58(2018), No.1
    3. Evaporation of S from Liquid Fe–C–S Alloy ISIJ International Vol.58(2018), No.1

  • Evaporation of S from Liquid Fe–C–S Alloy

    Youn-Bae Kang, Fahmi Tafwidli

    pp. 10-16

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    DOI:10.2355/isijinternational.ISIJINT-2017-498

    Abstract

    Evaporation mechanism of S from liquid Fe–C–S alloys at 1873 K was proposed by analyzing available experimental data. It has been known that increasing C content in liquid alloy increases activity coefficient of S (fs), and it could raise driving force for the evaporation reaction S = S(g). However, experimental data of the evaporation of S in the Fe–C–S alloys could not be accounted for only by considering the increases of fs. In the present study, formation of carbosulfides, CS(g) and CS2(g), was additionally taken into account in order to explain role of C for the accelerated S evaporation. Surface adsorption of S was also taken into account, which retards the evaporation rate of S. An evaporation model equation was formulated. It can be applied to calculate the evaporation rate of S over wider C content (from zero to its saturation to liquid alloy).

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    2. Analysis of Cohesive Particle Percolation in a Packed Bed Using Discrete Element Method ISIJ International Vol.58(2018), No.1
    3. Development of Slag Flowability Prediction Formula for Blast Furnace Operation and Its Application ISIJ International Vol.58(2018), No.1

  • Modeling and Simulation of Iron Ore Sintering Process with Consideration of Granule Growth

    Bin Zhang, Jiemin Zhou, Mao Li, Yuan Li

    pp. 17-24

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    DOI:10.2355/isijinternational.ISIJINT-2017-342

    Abstract

    Granule growth is an important process for iron ore sintering process. Variation of granule size has a great influence on the quality of sinter and productivity of the process. In this study, a model of granule growth was proposed based on two dimensional homogeneous sphere packing theory. The sintering process was simulated by an unsteady two-dimensional mathematical model which incorporates most of the significant physical phenomena and chemical reactions. Numerical simulation was carried out by FLUENT software and C language programming via developing custom code. Sinter pot tests were performed and experimental data reasonably agreed with the simulation. Results showed that granules diameter changed from 3 mm to 31.9 mm, which increased nearly ten times, while sintering time and yield can be estimated. Simulations were conducted under different initial iron ore size to investigate its effect on sintering. Results showed that larger agglomeration were formed and thickness of molten zone was decreased under larger initial iron ore size, which shortened sintering time and increased productivity.

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    1. Analysis of Cohesive Particle Percolation in a Packed Bed Using Discrete Element Method ISIJ International Vol.58(2018), No.1
    2. Development of Slag Flowability Prediction Formula for Blast Furnace Operation and Its Application ISIJ International Vol.58(2018), No.1
    3. Preliminary Investigation on the Capability of eXtended Discrete Element Method for Treating the Dripping Zone of a Blast Furnace ISIJ International Vol.58(2018), No.1

  • Preliminary Investigation on the Capability of eXtended Discrete Element Method for Treating the Dripping Zone of a Blast Furnace

    Maryam Baniasadi, Bernhard Peters

    pp. 25-34

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    DOI:10.2355/isijinternational.ISIJINT-2017-344

    Abstract

    The role of molten iron and slag in the dripping zone of a blast furnace is very critical to reach a stable operational condition. The existence of several fluid phases and solid particles in the dripping zone of a blast furnace, makes the newly developed eXteneded Discrete Element Method (XDEM) as an Eulerian-Lagrangian approach, suitable to resolve the dripping zone of a blast furnace. In the proposed model, the fluid phases are treated by Computational Fluid Dynamics (CFD) while the solid particles are solved by Discrete Element Method (DEM). These two methods are coupled via momentum, heat and mass exchanges. The main focus of current study is to investigate the influence of packed properties such as porosity and particle diameters, calculated by the XDEM, on the fluid phases for isothermal. In order to present the capability of the XDEM for this application. The validity of the proposed model is demonstrated by comparing model prediction results with the available experimental data.

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    2. Analysis of Cohesive Particle Percolation in a Packed Bed Using Discrete Element Method ISIJ International Vol.58(2018), No.1
    3. Modeling and Simulation of Iron Ore Sintering Process with Consideration of Granule Growth ISIJ International Vol.58(2018), No.1

  • Exploring the Capability of Muon Scattering Tomography for Imaging the Components in the Blast Furnace

    Xianfeng Hu, Lena Sundqvist Ökvist, Elin Åström, Fredrik Forsberg, Paolo Checchia, Germano Bonomi, Irene Calliari, Piero Calvini, Antonietta Donzella, Eros Faraci, Franco Gonella, Joel Klinger, Davide Pagano, Andrea Rigoni, Pietro Zanuttigh, Paolo Ronchese, Michele Urbani, Sara Vanini, Aldo Zenoni, Gianni Zumerle

    pp. 35-42

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    DOI:10.2355/isijinternational.ISIJINT-2017-384

    Abstract

    Knowing the distribution of the materials in the blast furnace (BF) is believed to be of great interest for BF operation and process optimization. In this paper calibration samples (ferrous pellets and coke) and samples from LKAB’s experimental blast furnace (probe samples, excavation samples and core-drilling samples) were measured by the muon scattering tomography detector to explore the capability of using the muon scattering tomography to image the components in the blast furnace. The experimental results show that it is possible to use this technique to discriminate the ferrous pellets from the coke and it is also shown that the measured linear scattering densities (LSD) linearly correlate with the bulk densities of the measured materials. By applying the Stovall’s model a correlation among the LSD values, the bulk densities and the components of the materials in the probe samples and excavation samples was established. The theoretical analysis indicates that it is potential to use the present muon scattering tomography technique to image the components in various zones of the blast furnace.

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    2. Development of Slag Flowability Prediction Formula for Blast Furnace Operation and Its Application ISIJ International Vol.58(2018), No.1
    3. Analysis of Cohesive Particle Percolation in a Packed Bed Using Discrete Element Method ISIJ International Vol.58(2018), No.1

  • Analysis of Cohesive Particle Percolation in a Packed Bed Using Discrete Element Method

    Heng Zhou, Shengli Wu, Mingyin Kou, Zhi-guo Luo, Zong-shu Zou, Yansong Shen

    pp. 43-51

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    DOI:10.2355/isijinternational.ISIJINT-2017-373

    Abstract

    Many granular materials are in cohesive or wet state in pyrometallurgy processes. The present work systematically studies the cohesive particle percolation behaviour in a packed bed by discrete element method (DEM). The results indicate that the vertical velocity of percolating particles increases with increasing the cohesive force from 0 to 2 mg (the gravity force of percolating particle, given by ρgπd3/6). While for a higher cohesive force, e.g.fe=8 mg, insufficient percolation occurs and percolating particles stick in the packed bed. Percolating particles in the packed bed shows a diffusivity for the cases of smaller cohesive force. The transverse dispersion of fe=2 mg is smaller than that of fe=0, while the longitudinal dispersion becomes larger when the cohesive force changes from 0 to 2 mg. In addition, the influence of other key variables, such as diameter ratio, damping coefficient and rolling friction coefficient on percolation behaviour is also discussed. The transverse dispersion coefficient increases with the diameter ratio, while the longitudinal dispersion coefficient decreases with the diameter ratio. With the increase of damping coefficient or rolling friction coefficient, the transverse dispersion coefficient decreases but the longitudinal dispersion increases. The study provides a fundamental understanding on percolation behaviour of cohesive particles in a packed bed, and is useful for processes understanding and optimization in cohesive particles handling and mixing.

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  • Development of Slag Flowability Prediction Formula for Blast Furnace Operation and Its Application

    Jia-Shyan Shiau, Shih-Hsien Liu, Chung-Ken Ho

    pp. 52-59

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    DOI:10.2355/isijinternational.ISIJINT-2017-394

    Abstract

    In this study, the effects of MgO content, Al2O3 content, TiO2 content and C/S (=CaO/SiO2) on slag flowability are investigated for blast furnace (BF) operation. The liquidus temperature and the viscosity of semi-synthetic slags are measured using an optical softening temperature detector and a viscometer, respectively. Based on the measured data, equations of the liquidus temperature and the viscosity for the semi-synthetic slags (SiO2–Al2O3–CaO–MgO–TiO2) were formulated via the multiple-regression method. In operation practice of BF, the slag flowability is mainly determined by both viscosity and liquidus temperature. A combined slag flowability index, including viscosity and liquidus temperature, has been designed in this research to indicate appropriate slag flowability. This index has been incorporated into the tapping system of CSC (China Steel Corporation) BF. Based on the calculated liquidus temperature and viscosity of the final slag inside BF, the system is able to predict the difficulty of slag flow for the coming tapping. It can immediately provide BF staffs some information to control the variation of slag flowability via the effective operation practice such as enforcing management of thermal state or adjusting the chemical composition of final slag via the burden of BF.

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    3. Modeling and Simulation of Iron Ore Sintering Process with Consideration of Granule Growth ISIJ International Vol.58(2018), No.1

  • Micro-bubble Formation under Non-wetting Conditions in a Full-scale Water Model of a Ladle Shroud/Tundish System

    Sheng Chang, Xiangkun Cao, Zongshu Zou, Mihaiela Isac, Roderick Ian Lawrence Guthrie

    pp. 60-67

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    DOI:10.2355/isijinternational.ISIJINT-2017-390

    Abstract

    The effect of interfacial wettability on the size of gas bubbles releasing from orifices submerged in high velocity cross flow coupled with strong turbulence, was investigated in a full-scale water model of a commercial ladle/tundish/mold system, located at the McGill Metals Processing Centre. The present work attempted to simulate bubble formation in liquid steel passing through a ceramic (non-wetting) ladle shroud, with a high velocity and strong turbulence. This was accomplished by using a hydrophobic coating, sprayed onto the inner surface of the vertical acrylic ladle shroud, forming a contact angle of 150° at the three-phase line of contact, versus an angle of ~45° on the bare plexiglas surface.As such, the poor wettability of the treated acrylic surface of the ladle shroud led to slight increases in the diameters of micro-bubbles of 8.0%–22.4%, vs wetting systems, depending on gas flow rate and gas injection position. The present results indicate that the cross flows of liquid and their associated kinetic energy of turbulence within a ladle shroud flow can effectively refine bubbles into the micron size range, and prevent bubble growth caused by the poor wettability of liquid steel. Thus, argon gas injection through a ladle shroud could be an effective approach of producing small bubbles in liquid steel, even under the non-wetting conditions associated with such flows, which cannot be achieved by conventional gas curtain technique.

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  • Effect of Argon Injection in Meniscus Flow and Turbulence Intensity Distribution in Continuous Slab Casting Mold Under the Influence of Double Ruler Magnetic Field

    Sandip Sarkar, Vikas Singh, Satish Kumar Ajmani, Ranjay Kumar Singh, Elanjickal Zachariah Chacko

    pp. 68-77

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    DOI:10.2355/isijinternational.ISIJINT-2017-448

    Abstract

    In the present investigation, an experimentally validated coupled two phase Magnetohydrodynamics (MHD) flow and turbulence model has been developed to analyse the combined implications of Argon injection and double ruler electromagnetic breaking (EMBr) in continuous casting flow control (FC) mold of the Tata Steel plant. The numerical model essentially solves transient Euler–Euler two-phase model, turbulence, and MHD Maxwell equations for prescribed experimentally plant measurement of magnetic field boundary conditions data at various Argon flow rates, casting speeds, and submerged entry nozzle (SEN) depths. The numerical model primarily validated with the plant experimental measurement data and found to be in good agreement. The computational results demonstrate that the application of magnetic field suppresses turbulence and meniscus velocity decrement. However, increasing Argon flow rate is found to magnify meniscus velocity and turbulence intensity at the mold. The Argon gas injected from the ports clusters nearer to the SEN and a local chunk of it gradually escapes from the meniscus by short-circuiting its path. Effect of EMBr is not found to be prominent at the higher Argon gas flow rate values. Maximum meniscus level disturbance is noticed at an Argon flow rate of 10 L/min.

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  • Effect of Operating Conditions on Inclusion of Die Steel during Electroslag Remelting

    Gang Du, Jing Li, Zhong-Bing Wang

    pp. 78-87

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    DOI:10.2355/isijinternational.ISIJINT-2017-429

    Abstract

    The current paper focuses on the effect of different operating conditions on the content of inclusions and cleanliness of remelting ingots. For these investigations, eight ingots were remelted with two slag amount and with two current intensity under otherwise comparable remelting conditions. A two-dimensional (2D) coupled mathematical model was employed to simulate the velocity field, solidification and inclusion motion for a system of electrode, slag and ingot in electroslag remelting (ESR) processes, to reveal the inclusion removal mechanism. The results showed that the content of large-sized inclusions in ESR ingot was decreased by approximately 66.18% when the slag amount was increased from 17.85 kg to 20.50 kg. Because of the increase of slag amount, the metal and slag flow faster and the maximal velocity increases by 10.3%, thus there is an increasing trend in trajectories of inclusions (i.e., inclusion motion) in slag pool resulted from the stronger natural convective flow, which is beneficial for the inclusion removal. When the average current was increased from 4 kA to 5 kA, the content of large-sized inclusions in ESR ingot was decreased by approximately 51.38%. Because of the increasing of current, the flow in the middle of the slag pool becomes stronger and the maximal downward velocity increases by 2.7%, thus there is an increasing trend in the renewal rate of the metal film surface due to the stronger washing by slag flow, which can promote the inclusion removal.

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  • Effect of CaO/Al2O3 Ratio of Ladle Slag on Formation Behavior of Inclusions in Mn and V Alloyed Steel

    Jae Hong Shin, Joo Hyun Park

    pp. 88-97

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    DOI:10.2355/isijinternational.ISIJINT-2017-456

    Abstract

    The effect of CaO/Al2O3 (=C/A) ratio of the ladle slag on the formation behavior of non-metallic inclusions in the Mn-V-alloyed steel was investigated using both the experimental method and refractory-slag-metal-inclusion (ReSMI) multiphase reactions simulation. The formation behavior of inclusion was strongly affected by the activity of MgO in the initial slag at the early stage of the reaction. However, since the MgO activity converged to unity due to MgO dissolution from refractory to slag during the reaction, the formation behavior of inclusion was affected by the activity of CaO and Al2O3 in the slag rather than that of MgO at the final stage of the reaction. From the experimental results and ReSMI multiphase reaction model, the formation behavior of inclusions could be divided into three cases according to the C/A ratio of the slag as follows; 1) C/A < 1.5; Alumina → Spinel → Spinel + Liquid oxide, 2) 1.5 < C/A < 2.5; Alumina → Spinel → Liquid oxide, 3) C/A > 3.0; Alumina → Spinel → Liquid oxide → Magnesia. Therefore, it was concluded that the C/A ratio of the ladle slag should be controlled from about 1.5 to 2.5 in order to suppress the harmful solid inclusions such as spinel during secondary refining processes.

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  • Effect of Super-gravity Field on Grain Refinement and Tensile Properties of Cu–Sn Alloys

    Yuhou Yang, Bo Song, Jin Cheng, Gaoyang Song, Zhanbing Yang, Zeyun Cai

    pp. 98-106

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    DOI:10.2355/isijinternational.ISIJINT-2017-233

    Abstract

    In this paper, the effect of super-gravity field on the grain refinement and tensile properties of as-cast Cu–Sn alloys were investigated systematically. The experimental results revealed that the as-cast grains of Cu–Sn alloys can be significantly refined in super-gravity field. In normal gravity field, the average grain size is 2.13 mm, while in super-gravity fields of G=100, 300 and 600, they are 0.35 mm, 0.173 mm and 0.074 mm, respectively. Accordingly, both the tensile strength and the plasticity are enhanced with the increasing gravity coefficient. The ultimate tensile strength of Cu-11wt%Sn sample in normal gravity field is 265 MPa, while in super-gravity fields of G=100, 300 and 600, they are 449 MPa, 487 MPa and 521 MPa, respectively. The fracture morphology transforms from fragility to plasticity with the increasing gravity coefficient. The mechanism for the grain refinement is that super-gravity promotes the falling of crystal nuclei within the solidifying melt only at the early solidification period, which can be called the “Crystal Rain”. As a result, the crystal nuclei multiply within the solidifying melt and a refined grain structure was obtained. Besides, the refining effect by super-gravity increases with the increasing solute Sn concentration because of the increased nucleation rates and a decrease in crystal growth.

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  • Effect of Solidification Pressure on Interfacial Heat Transfer and Solidification Structure of 19Cr14Mn0.9N High Nitrogen Steel

    Zhouhua Jiang, Hongchun Zhu, Huabing Li, Guohai Liu, Pengbo Wang, Junhui Zhu, Shucai Zhang, Hao Feng

    pp. 107-113

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    DOI:10.2355/isijinternational.ISIJINT-2017-356

    Abstract

    The effect of solidification pressure (0.5, 0.85 and 1.2 MPa) on heat transfer between ingot and mould was investigated with the measurement of cooling curves and calculation of heat transfer coefficient. Combined with cooling rate, temperature gradient and local solidification time (LST), the influence of pressure on solidification structure of 19Cr14Mn0.9N was revealed by macrostructure observation. The calculation results of heat transfer coefficient, obtained by the Beck-Nonlinear estimation technique, indicate that increasing solidification pressure obviously enhances heat transfer at the ingot/mould interface. And higher solidification pressure is benefit to increase cooling rate and temperature gradient of ingot. Meanwhile, increasing solidification pressure considerably suppresses nitrogen gas pore, and reduces the whole area of dispersing porosity and shrinkage, which is favorable to obtain a sound ingot. With the solidification pressure increasing from 0.5 to 1.2 MPa, the columnar zone is lengthened, the columnar-to-equiaxed transition (CET) position gradually moves to the ingot center, and both dendritic arm spacing (λ1 and λ2) and local solidification time (LST) gradually decrease. The solidification structure is significantly refined and compressed under higher solidification pressure.

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  • Acceleration of Macrosegregation Simulation Based on Lattice Boltzmann Method

    Munekazu Ohno, Hayato Sato

    pp. 114-122

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    DOI:10.2355/isijinternational.ISIJINT-2017-375

    Abstract

    Lattice Boltzmann Method (LBM), newly developing technique of computational fluid dynamics, is coupled with solute and energy conservation equations to develop a macrosegregation simulation model (LBM-coupled model) with high computational efficiency. LBM does not require time-consuming calculations for correction of velocity and pressure of fluid in contrast to methods directly solving Navier-Stokes (NS) equation and, therefore, LBM is computationally efficient. In this study, the accuracy of the LBM-coupled model is investigated by calculating the steady state flows and by comparing the results with those of analytical solutions and a conventional model based on the NS equation. The results between them are almost identical with each other and it indicates that the accuracy of the LBM-coupled model is sufficiently high. Moreover, a macrosegregation simulation is carried out for a simple case where the macrosegregation emerges only by natural convection, by means of the LBM-coupled and conventional models. The LBM-coupled model yields almost the same result with the one of NS-based model. Importantly, however, the simulation of LBM-coupled model is about five times faster than the one of NS-based model.

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  • Heterogeneous Nucleation of Graphite on Rare Earth Compounds during Solidification of Cast Iron

    Kok Long Ng, Hideaki Sasaki, Hisao Kimura, Takeshi Yoshikawa, Masafumi Maeda

    pp. 123-131

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    DOI:10.2355/isijinternational.ISIJINT-2017-398

    Abstract

    To investigate the heterogeneous nucleation of graphite on rare earth non-metallic inclusions during the solidification of cast iron, Fe-4.1mass%C-2.5mass%Si and S-added Fe-4.1mass%C-2.5mass%Si-0.01mass%S alloys are contact-melted and solidified on RE2O3 (RE; La, Yb) substrates. Regarding the Fe-4.1mass%C-2.5mass%Si alloy, XRD analysis and SEM observation results show that graphite, with an overall orientation in the [0001] direction, precipitates at the alloy/substrate interface. In addition, formation of nodular graphite with rare earth sulfides as the heterogeneous nuclei is observed in the bulk alloy. In the 0.01%S-added specimens, precipitation of graphite at the alloy/substrate interface is observed to be significantly weakened compared to reference specimens. Such precipitation behavior is considered to be due to the increased formation of nodular graphite in the bulk as a result of S addition. Based on these results, the precipitation behavior of graphite on rare earth compounds is discussed.

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  • Local Heat Transfer Characteristics of Multi Jet Impingement on High Temperature Plate Surfaces

    Bingxing Wang, Dong Lin, Bo Zhang, Lei Xiong, Zhaodong Wang, Guodong Wang

    pp. 132-139

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    DOI:10.2355/isijinternational.ISIJINT-2017-154

    Abstract

    In order for the hot plate TMCP ultra-fast cooling technology to be optimized, the local heat transfer characteristics of multi jet impinging on hot plate surfaces were investigated. The experiments were performed for double and three jet impingement cooling study as cooling header primary units in the industrial scale. The jet velocity at the nozzle exit ranged between 1.99 m/s and 6.63 m/s. The results demonstrated that both the hydrodynamic structure and the heat transfer region distribution of multi jet impingement cooling were distinct from the single jet case. The parallel flows with a sufficient kinetic energy collided and intensified the heat transfer efficiency in the interference region. The higher-sized nozzle spacing magnified the heat exchange differences in the interference region, whereas the jet velocity increased both the heat flux and the rewetting velocity acceleration outside the stagnation region. The surface temperature in the interference region dropped slightly faster than the parallel flow region at the same spatial distance from the stagnant point, second only to the stagnant point, which was interpreted that the parallel flows interaction and agitation enhanced the heat transfer intensity. The results were valuable in the nozzle arrays arrangement and the heat transfer ability and cooling uniformity improvement of the ultra-fast cooling technology in industrial applications.

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  • Boiling Heat Transfer Characteristics of Vertical Water Jet Impinging on Horizontally Moving Hot Plate

    Kenta Morisawa, Jun-ya Nakahara, Keisuke Nagata, Hitoshi Fujimoto, Takayuki Hama, Hirohiko Takuda

    pp. 140-145

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    DOI:10.2355/isijinternational.ISIJINT-2017-383

    Abstract

    This study investigates the heat transfer characteristics of a circular jet pointing upward that impinges on a moving hot steel sheet by using a laboratory-scale setup. The test liquid was water at 17°C, and the volumetric flow rate of the coolant was set to 450, 960, and 1480 mL/min. The test solid was 0.3 mm thick stainless steel (SUS430) with an initial temperature in the range 300–700°C. The moving velocity of the solid was set to 0.5, 1.0, and 1.5 m/s, and its temperature profile was measured by an infrared camera. The results showed that a region of high heat flux appeared in the area impacted by the jet. The heat transfer characteristics relied heavily on the initial temperature of the solid associated with the boiling patterns—namely, nucleate, transition, and film boiling. Along the boundary between the strong nucleate and the transition boiling regimes, the heat flux took peak values. The local minimum values of heat flux obtained between the transition and the film boiling regimes. The initial temperatures of the solid exhibiting these values were influenced by its moving velocity and the jet impact velocity. Moreover, the heat fluxes in the jet impact region for upward-impinging jets were compared with reported data for downward-impinging jets under the condition whereby the jet impact velocity and diameter in the two cases were nearly identical prior to impact. The two sets of results showed very similar trends, although the flow motions of water varied because of the effect of gravity.

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  • Visualization and Analysis of Groove Residual Magnetism for Narrow Gap Arc Welding

    Jiayou Wang, Ping Huang, Jie Zhu, Xiaoyu Zhu

    pp. 146-152

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    DOI:10.2355/isijinternational.ISIJINT-2017-067

    Abstract

    Residual magnetism obviously exists in welding groove of high strength steel and thus influences narrow gap arc welding quality. The present work investigates the characteristics of residual magnetism for U-shape welding groove, and reveals its formation mechanism by physically modeling the residual magnetism. An experimental data based visualization approach is then proposed to characterize dominant distributions of residual magnetism. It is shown that residual magnetism is much stronger in groove width and at groove bottom respectively than in groove length and at groove top, as well as of bar magnet features for each groove sidewall. Two-dimensional visualization of residual magnetism vector is realized by plane and curved surface cloud maps of equivalent color bars, while three-dimensional visualization is expressed by assembling six outermost plane cloud maps of residual magnetism in groove measuring space. The built models and digital visualizations well contribute to understand the phenomena of residual magnetism.

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  • Effect of Welding Process Conditions on Angular Distortion Induced by Bead-on-plate Welding

    Masahito Mochizuki, Shigetaka Okano

    pp. 153-158

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    DOI:10.2355/isijinternational.ISIJINT-2017-306

    Abstract

    In this study, the effect of welding process and heat input conditions on the angular distortion induced by bead-on-plate welding was investigated through a numerical approach. Numerical models of gas metal arc welding (GMAW) and gas tungsten arc welding (GTAW), which were developed in a previous study, were utilized for accurate distortion analyses. The calculated relation between welding conditions and angular distortion was quantified by using the conventional heat input parameter derived from welding thermal conduction theory. The results clarified the limits of applying the heat input parameter to quantify angular distortion under the various welding process and heat input conditions. In addition, the effect of the weld reinforcement generated in GMAW on angular distortion was coordinately examined by using a parameter, defined as the ratio of the area of weld reinforcement to the square of plate thickness. The effect was generally negligible except for in the case of a thin plate. Then, a parameter of the mechanical melting region on the plate thickness section was applied to quantify the angular distortion induced by GMAW and GTAW. As the results, a unified evaluation of the effect of welding process and heat input conditions on angular distortion was successfully achieved. Thus, it can be concluded that the developed parameter of the mechanical melting region on the plate thickness is the dominant factor for accurately quantifying angular distortion.

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  • A Simple Method for Observing ω-Fe Electron Diffraction Spots from <112>α-Fe Directions of Quenched Fe–C Twinned Martensite

    Dehai Ping, Alok Singh, Shuqi Guo, Takahito Ohmura, Masato Ohnuma, Taichi Abe, Hidehiro Onodera

    pp. 159-164

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    DOI:10.2355/isijinternational.ISIJINT-2017-270

    Abstract

    In twinned martensite, a metastable hexagonal ω-Fe phase always exists in the twin boundary region of the body-centered cubic (bcc) {112}<111>-type twin. The ω-Fe electron diffraction spots at the 1/3{112}α-Fe and 2/3{112}α-Fe positions have been treated as the twinning double diffraction effect previously. The ω-Fe spots fully cover the spots of the bcc matrix, twin and their double diffraction. Due to this, it is difficult to practically distinguish the ω-Fe diffraction spots from the sum of matrix + twin + double diffraction. Here, a simple method for observing the ω-Fe spots is introduced based on the twinning crystallographic analysis.In this method, at first a [011] zone axis is found in twinned martensite, containing the diffraction spots of twin and ω-Fe (previously double diffraction spots). It is then confirmed that the twin plane is inclined to the incident electron beam by means of the dark field observation. The reciprocal <222>* direction (containing spots at 1/3{222} and 2/3{222} positions), is noted. A tilting is then performed keeping this direction un-tilted, i.e., tilting about this direction, to <112> zone axis. This requires about 30° tilting. If the ω-Fe spots are absent at the 1/3{222} and 2/3{222} positions when the zone axis reaches <112>, then an opposite tilt is performed (since there are two tilting directions: clockwise and counter-clockwise), then, the ω-Fe diffraction spots can be seen at the 1/3{222} and 2/3{222} positions. A large twinned martensite at the TEM specimen edge is better for tilting to avoid any overlapping.

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  • Effect of Carbon Content on Bainite Transformation Start Temperature in Middle–High Carbon Fe–9Ni–C Alloys

    Hiroyuki Kawata, Toshiyuki Manabe, Kazuki Fujiwara, Manabu Takahashi

    pp. 165-172

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    DOI:10.2355/isijinternational.ISIJINT-2017-387

    Abstract

    Bainite in steel is an industrially useful structure. However, the controlling factor of its transformation start point is not clearly known. In this study, we measured the bainite transformation start temperature (Bs) in Fe–9Ni–C alloys containing 0.3–0.9 mass%C via microstructure observation of the specimens held isothermally between 600 K and 798 K. Bs existed between 758 K and 773 K in all alloys used, and was independent of carbon content. Especially, Bs was higher than T0, at which fcc and bcc of the same composition have the same free energy, at more than 0.3 mass%C. This result was completely different from that of our previous study on low carbon Fe–9Ni–C alloys, in which Bs decreased with the increase in carbon and kept the certain driving force of partitionless transformation from fcc to bcc. Bs in middle–high carbon alloys corresponded to the temperature of the intersection point between T0′, at which the driving force is 400 J/mol, and the γ/(γ + θ) phase boundary. This suggests that the nucleation and growth of bainitic ferrite in austenite containing solute carbon higher than T0′ is promoted by the precipitation of cementite in austenite.

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  • Hydrogen Embrittlement Behavior of Ultra-high Strength Dual Phase Steel Sheet under Sustained Tensile-loading Test

    Katsutoshi Takashima, Yuma Yoshioka, Ken'ichi Yokoyama, Yoshimasa Funakawa

    pp. 173-178

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    DOI:10.2355/isijinternational.ISIJINT-2017-315

    Abstract

    The hydrogen embrittlement behavior of an ultra-high strength (1180 MPa grade) dual phase steel sheet composed of ferrite and tempered martensite, as compared with that of a single phase steel sheet composed of tempered martensite, has been investigated by a sustained tensile-loading test. No fracture of the dual phase steel occurs under the low hydrogen-charging current density of 5 A/m2 except under high applied stress substantially larger than the yield stress. With the high current density of 50 A/m2, the time to fracture of the dual phase steel varies widely, but is almost the same as that of the single phase steel. The critical applied stress for fracture of the dual phase steel is higher than that of the single phase steel. Under the high applied stress, however, the time to fracture of the dual phase steel is shorter than that of the single phase steel, and a unique intergranular-like morphology is observed at the crack initiation area on the fracture surface. Upon plastic deformation before the sustained tensile-loading test under the high applied stress, the time to fracture of the dual phase steel increases and the initiation area on the fracture surface exhibits typical quasi-cleavage features. The results of the present study indicate that the hydrogen embrittlement of the dual phase steel displays some anomalous behavior.

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  • Optical Microscopy-Based Damage Quantification: an Example of Cryogenic Deformation of a Dual-Phase Steel

    Nao Uehata, Motomichi Koyama, Shusaku Takagi, Kaneaki Tsuzaki

    pp. 179-185

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    DOI:10.2355/isijinternational.ISIJINT-2017-468

    Abstract

    We evaluated the availability of an optical-microscopy-based damage quantification method in a ferrite/martensite dual-phase steel, and interpreted the obtained results toward screening damage evolution behavior under various test conditions. In this study, we employed this method for tensile deformation at 20, −100, and −180°C to analyze the temperature dependence of damage evolution in cryogenic regime as a case study. The damage evolution behavior was classified into regimes of damage nucleation, damage arrest, and damage growth to fracture, irrespective of the deformation temperature in a cryogenic temperature range. Coupled with some high-resolution observations, the damage nucleation and damage arrest sites were identified to be martensite and ferrite, which are common regardless of the deformation temperatures. This indicates that ferrite acted as a damage arrest site even at −180°C. However, a critical strain for damage growth to fracture decreased drastically by decreasing the temperature to −180°C. The distinct reduction in the critical strain is attributed to the transition of ferrite cracking mode from ductile to brittle mechanisms.

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  • Viscosity-structure-crystallization of the Ce2O3-bearing Calcium-aluminate-based Melts with Different Contents of B2O3

    Jie Qi, Chengjun Liu, Maofa Jiang

    pp. 186-193

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    DOI:10.2355/isijinternational.ISIJINT-2017-252

    Abstract

    In order to restrain the slag-metal interface reaction in the process of heat resistant steel continuous casting, the aluminate-based mold flux was devised. The effect of B2O3 on the viscosity, structure and crystallization property of the aluminate-based melts was studied. Appropriately adding B2O3 could decrease the viscosity of the melts. However, the viscosity could remain relatively constant when the addition of B2O3 exceeded 5 mass%. The structures of the melts, which were correlated to the viscosity, were confirmed through Fourier transformed infrared spectroscopy. The main network former of the melts was AlO4-tetrahedral unit. With adding B2O3, B2O3 formed 2D BO3-triangular unit, the bridging oxygen of the network combined by AlO4-units was broken, the polymerization of the melts decreased, and the viscosity, the apparent activation energy decreased consequently. With no B2O3 addition, the main crystalline phase was CaO. Because of Ca–O have the strongest interaction force and the weakest irregular thermal motion. The crystallization of CaO could be restrained by adding B2O3, the crystalline phase transferred from CaO to LiAlO2 and CaCeAlO4. CaCeAlO4 precipitated later than LiAlO2 because of the different interactions and the irregular motion ability of different structure units.

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  • Recovery of Soluble Potassium from Electric Arc Furnace Dust of Manganese Alloy Production: Characterization and Water Leaching Kinetics

    Yiwei Zhong, Xinle Qiu, Jintao Gao, Zhancheng Guo

    pp. 194-200

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    DOI:10.2355/isijinternational.ISIJINT-2017-421

    Abstract

    As an environmentally hazardous waste, electric arc furnace (EAF) dust had a potential to provide a wider resource of potassium if recycled due to high potassium content. In this study, the chemical and mineralogical characteristics of the EAF dust, especially the existing state of potassium, were analyzed. The results showed that the dust consisted dominantly of manganese oxides (Mn3O4, MnO, MnO2) and manganese silicate (MnSiO3). The K element existed in the dust was in the form of potassium permanganate (K2Mn4O8, insoluble) and potassium sulfate/sulfite (soluble). Then the soluble potassium salts in the dust were recovered by water leaching and crystallization. The recovery ratio of K reached 88.2%, and the products K2SO4 and KCl with the K2O content of 65.25% were obtained. During leaching, the Mn3+ and Mn4+ components were reduced to Mn2+ by sulfide (S2−) or sulfite (SO32−), and the S2− and SO32− components were oxidized to SO42−. The leaching kinetics was studied by the specific electrical conductivity method. The apparent activation energy was 7.76±0.65 kJ/mol, suggesting that the rate controlling step of leaching process was the diffusion of K+ through the diffusion layer.

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  • © 2018 The Iron and Steel Institute of Japan

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