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

ISIJ International Advance Publication

  • Nanostructured Bainitic Bearing Steel

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    DOI:10.2355/isijinternational.ISIJINT-2018-693

    Bearing is the most important component for nearly all mechanical equipment. Nanostructured bainitic steel, which is a new bearing steel, not only possesses necessary hardness and higher toughness, but exhibits excellent wear resistance and rolling contact fatigue performance, making it suitable for bearing application. In recent years, the research on nanostructured bainitic bearing steel has gained great progress and obtained attentions from bearing industry. To make a clear knowledge on nanostructured bainitic bearing steel, and reveal the further research direction on this filed, this paper reviews the development of nanostructured bainitic bearing steel, including the design of chemical composition, the heat treatment process, the feature of microstructure, the properties involving conventional mechanical properties, wear resistance and rolling contact fatigue performance, the effect of retained austenite, and the distribution of residual stress.
  • A Review on Prevention of Sticking during Fluidized Bed Reduction of Fine Iron Ore

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    DOI:10.2355/isijinternational.ISIJINT-2019-392

    The fluidized bed ironmaking technology has attracted the attention of many researchers for decades as a direct reduction ironmaking method with many advantages. This process has been applied as a pretreatment method in many non-blast furnace ironmaking processes. However, the sticking problem hindered its development greatly. Defining the essential cause of sticking, and fundamentally solving this problem are the key steps encountered by this process. The research works related to the prevention of sticking problem during fluidized bed reduction of fine iron ore are comprehensively summarized in this article. The causes of sticking, the influencing factors of sticking and the solution of sticking are firstly discussed, followed by the analysis on the possible development direction of future fluidized bed ironmaking technology.
  • 3D Crystal Orientation Mapping of Recrystallization in Severely Cold-rolled Pure Iron Using Laboratory Diffraction Contrast Tomography

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    DOI:10.2355/isijinternational.ISIJINT-2019-405

    The mechanism of recrystallization texture development of cold-rolled metal and steel largely depends on the material chemical composition, cold-rolling reduction, and annealing treatment conditions. To clarify the mechanism, it is important to identify the locations where recrystallization starts and progresses within cold-rolled materials.Using laboratory diffraction contrast tomography (LabDCT), three-dimensional (3D) crystal orientation mapping corresponding to different stages of recrystallization has been successfully performed for pure iron sheets that were severely cold-rolled and heated at different temperatures.In cold-rolled iron with 99.2% reduction, the deformation texture was a strong α-fiber (RD//<110>). During annealing in the temperature range of 773–973 K, recrystallized grains were formed with textural components of {100}, {211}, {111} and {411}, and the α-fiber changed to the {100}<012> component. Recrystallized grains were generated at rather random locations within the sample. The size of recrystallized grains in the center region was 20–30% larger than that in the surface region. These results suggest that the nucleation is driven by the large strain caused by severe rolling. The number of recrystallization sites was larger in the surface region than in the center region and the competition of selective growth among recrystallized grains was more severe in the surface region, resulting in a smaller grain size.The volume data of the 3D crystal orientation mapping obtained by LabDCT provided crucial information for understanding the recrystallization mechanism including the nucleation and/or selective growth.
  • Fluid Dynamics Analysis of O2–CaO Jet with a Shrouding Flame for EAF Steelmaking

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    DOI:10.2355/isijinternational.ISIJINT-2019-207

    Compared with the traditional addition methods of lumpy lime into the electric arc furnace (EAF) for slag making, the technology of O2–CaO jet can deliver lime powder directly into the EAF molten bath with high speed carrier gas, which demonstrates much advantages in quick melting and effective phosphorus removal. Recently, the shrouding combustion flame was proposed and applied to strengthen the CaO import capability of the O2–CaO jet. In this study, combining the discrete particle model (DPM) and the Eddy Dissipation Concept (EDC) model with the detailed chemical kinetic mechanisms (GRI-Mech 3.0), computational fluid dynamics (CFD) models of the O2–CaO jet with shrouding flame, with shrouding O2 and without shrouding gas were developed. The numerical results of CFD models were firstly validated by the experimental data. The interaction between the particles and the gas jet of the O2–CaO jet was analyzed and how the shrouding combustion flame affected the fluid flow characteristics of the O2–CaO jet were clarified. The shrouding high-temperature combustion flame could delay the attenuation of the axial velocity of the O2–CaO jet, heat the CaO particles effectively and make the CaO particles cluster together in a much longer distance, which is helpful to strengthen the jet impact, accelerate the meltdown of CaO particles and improve the utilization efficiency of CaO.
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    1. Effect of High Nitrogen Addition on Microstructure and Mechanical Properties of As-cast M42 High Speed Steel ISIJ International Advance Publication
  • Behavior of V-Ti Elements in Warm-Rolled Transformation-Induced Plasticity Steel with Medium Manganese Content

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    DOI:10.2355/isijinternational.ISIJINT-2019-329

    To reveal the law governing V-Ti precipitation behavior in warm-rolled transformation-induced plasticity (TRIP) steel, two steel samples including 0.072V-0.051Ti steel (Bear-V-Ti steel) and 0.001V-0.001Ti steel (Free-V-Ti steel) are designed. Based on a comparative analysis, the former has an excellent combination of mechanical properties including a total elongation (TE) of 37%, ultimate tensile strength (UTS) of 935 MPa, and UTS×TE of 34 GPa·% after annealing at a temperature of 650°C. The superior mechanical properties are attributable to particles that precipitate in a composite form of (V-Ti)C/N at 650°C. These particles can refine the grains and improve the tensile strength of Bear-V-Ti steel. However, it should be noted that the two roles of precipitates in steel are size dependent. For sizes between 10–20 nm, the role mainly entails pinning the dislocation. This accounts for the precipitation strength. As the size increases to 20–60 nm, the role mainly involves pinning of the grain boundary, which leads to fine crystal reinforcement. These results provide useful data for the production of medium manganese steel using the warm-rolled process.
  • Effect of High Nitrogen Addition on Microstructure and Mechanical Properties of As-cast M42 High Speed Steel

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    DOI:10.2355/isijinternational.ISIJINT-2019-417

    This study systematically investigated the influence of high nitrogen (N) addition (0.205 wt.%) on microstructure and mechanical properties of as-cast M42 high speed steel. The results demonstrate that the conventional and high-nitrogen M42 cast ingots are mainly composed of martensite, retained austenite and various precipitates (M2C, M6C as well as MC in M42 cast ingot or M(C, N) in M42N cast ingot). The addition of N could increase the retained austenite content, trigger the transformation of MC to M(C, N), favor the formation of M2C at the expense of M6C, and improve the distribution uniformity of M6C at the macroscopic scale. Moreover, the addition of N could lead to the reduction of the secondary dendrite arm spacing as well as the decrease of the thickness and area fraction of eutectic carbides, and improve the distribution uniformity of eutectic carbides at the microscopic scale. The M(C, N) particles form directly from the liquid phase prior to the formation of primary austenite, which could act as the heterogeneous nuclei of primary austenite and thus promote the refinement of the as-cast microstructure. The addition of N slightly decreases the macro-hardness and ultimate compression strength of the cast ingot but increases its ductility, which could be ascribed to the increase of retained austenite content and the reduction in the amount of eutectic carbides. Therefore, high N addition can significantly improve the as-cast microstructure of M42 high speed steel, which is promising for the further enhancement of the mechanical property and service life of the final product.
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    1. Fluid Dynamics Analysis of O2–CaO Jet with a Shrouding Flame for EAF Steelmaking ISIJ International Advance Publication
  • Multiphase Flow Behavior in a Single-Strand Continuous Casting Tundish during Ladle Change

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    DOI:10.2355/isijinternational.ISIJINT-2019-506

    The three-phase flow behavior in a single-strand continuous casting tundish during ladle change was investigated using physical modeling. These phenomena observed from physical modeling were explained by employing the multiphase model volume of fluid, which can track the interface behavior between the liquid steel, slag, and air during this operation. The effects of the refilling time and lowest operating level on the slag entrainment and the steel exposure during ladle change were analyzed and discussed, respectively. Increasing the refilling time significantly decreased the amount of entrained oil and the exposed area in the impact zone during ladle change. However, the increase in the lowest level had little influence on reducing the slag entrainment. To reduce the slag entrainment and the steel exposure during ladle change, the refilling time in the prototype should be larger than 3 minutes. Furthermore, the use of the turbulence inhibitor has also been evaluated. By diminishing the turbulence intensity in the impact zone and the velocity magnitude at the steel-slag interface, the turbulence inhibitor reduced considerably the amount of entrained slag and the steel reoxidation. The results indicated that the emulsification phenomenon during ladle change could be eliminated using TI-2, and the maximum exposed area fractions in the impact zone for different refilling times and lowest levels were less than 13% and 23%, respectively. Therefore, the TI-2 was recommended to improve the steel cleanliness during ladle change.
  • Agglomeration and Removal of Alumina Inclusions in Molten Steel with Controlled Concentrations of Interfacial Active Elements

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    DOI:10.2355/isijinternational.ISIJINT-2019-107

    In this study, Al deoxidation experiments have been performed in a mildly stirred steel bath with controlled O and S concentrations, to investigate the effects of interfacial active elements on the agglomeration and removal of Al2O3 inclusions in molten steel. The decrease rate constants of total Al2O3 inclusions, Al2O3 cluster inclusions, and Al2O3 single inclusions as well as the maximum average diameter of Al2O3 cluster inclusions decrease with increasing O and S concentrations in molten steel. However, the effect of O is much greater than that of S. These experimental results have been analyzed based on the kinetics of Al2O3 inclusion removal and the interfacial chemical interaction between Al2O3 inclusions in molten steel. The following findings have been obtained on the agglomeration and removal mechanisms of Al2O3 inclusions in molten steel. The Al2O3 inclusions in molten steel are removed by a mechanism whereby large Al2O3 cluster inclusions, formed by Al deoxidation, float and separate while repeatedly agglomerating and coalescing with fine Al2O3 single inclusions suspended in molten steel. The agglomeration of Al2O3 inclusions during floating and separation can also be explained by a mechanism whereby the agglomeration force due to the cavity bridge force is exerted between the Al2O3 inclusions and the Al2O3 inclusions come in complete contact when the Al2O3 inclusions with thermodynamically agglomerating tendency are approaching each other. The effects of O and S interfacial active elements are considered in both these mechanisms.
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    1. Multiphase Flow Behavior in a Single-Strand Continuous Casting Tundish during Ladle Change ISIJ International Advance Publication
    2. A Visual PCI Blockage Detection in Blast Furnace Raceway ISIJ International Advance Publication
    3. Melting Behaviour of Iron Ore Pellet Bed under Nut Coke Mixed Charge Conditions ISIJ International Advance Publication
  • A Visual PCI Blockage Detection in Blast Furnace Raceway

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    DOI:10.2355/isijinternational.ISIJINT-2019-367

    The pulverized coal injection (PCI) blockage detection is critical to the stable operation of blast furnace. In recent years, tuyere cameras have been widely applied, which provides a channel to detect the PCI blockage. However, the visual impression of images strongly varies between different raceways, it requires detection method should be robust and convenient to fine-tune for different blast furnace images. This paper presents an intelligent image-based method to detect the PCI blockage. An adaptive image preprocessing technique combining de-noising algorithm and image enhancement algorithm is applied to remove image noise and improve image quality, laying the foundation for subsequent work. The fitting ellipse based on Hough transform is used to locate the tuyere region, which can separate the tuyere region from the background. The adaptive threshold segmentation algorithm combining Otsu and Bernsen is used to obtain binarized image. However, it is difficult to obtain the pulverized coal cloud only by binarization due to the similarity between pulverized coal cloud and lance in gray-level. The multi-scale fully convolutional network (FCN) based on deep learning is investigated to detect the lance region, and pulverized coal cloud can be extracted by removing lance in binarized image. The flow rate of PCI can be characterized by the extracted area information to some extent, which can be used to detect PCI blockage. Extensive videos captured from real production lines are used to evaluate the detection method. The experiment results show that the method can accurately detect the PCI blockage.
  • Recycling Nickel Slag by Aluminum Dross: Iron-extraction and Secondary Slag Stabilization

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    DOI:10.2355/isijinternational.ISIJINT-2019-173

    Nickel slag is a metallurgical solid waste from nickel refineries, which can be recycled as one of excellent secondary sources due to valuable iron contents. In this work, the approach of recycling nickel slag by aluminum dross was proposed, and the processes of network modification of slags and reduction were successively investigated at 1773 K. Upon the thermodynamic calculations, CaO was chosen as the modifier in order to obtain a higher activity of ‘FeO', and basicity of the modified slag was determined as 1.0. Element mapping analysis of the modified slag showed that ‘FeO' had been separated from the structure of nickel slag. After aluminothermic reduction for 120 min, the recovery degree of iron and copper was 94.35% and 97.89%, respectively. In addition, the secondary slag stabilization was discussed, and the utilization of the produced Fe–Cu alloy and the secondary slag was analyzed.
  • Optimization of Discharge Parameters for a Glow Discharge Emission Spectrograph with Two-dimensional Spatial Resolution

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    DOI:10.2355/isijinternational.ISIJINT-2019-205

    This paper describes a specified measuring system for glow discharge emission spectrograph, which can provide a spatial/radial distribution of analyte atoms on the sample surface, while the conventional system provides only the information on the elemental distribution in depth direction. For this purpose, a spectrometer system consisting of an image spectrograph and an intensified charge coupled device (ICCD) detector was employed. The delay time and gate width of the ICCD detector was principally selected to improve the spatial resolution of the emitting zone. The objective of this paper was to determine an optimized set of the experimental parameter for better spatial resolution. The best spatial resolution was obtained when the gate width was 1 μs and the delay time was 60 μs. Better spatial resolution was obtained at narrower gate width, because the re-emission from the analyte atoms could be observed to a less extent when the observation was conducted more instantly just after start of the pulsed discharge.
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    1. Melting Behaviour of Iron Ore Pellet Bed under Nut Coke Mixed Charge Conditions ISIJ International Advance Publication
  • Melting Behaviour of Iron Ore Pellet Bed under Nut Coke Mixed Charge Conditions

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    DOI:10.2355/isijinternational.ISIJINT-2019-246

    The melting and dripping behaviour of an iron ore pellet bed mixed with nut coke are investigated through a series of quenching, melting and dripping experiments. In the melting bed of iron ore pellets, nut coke acts as a frame to maintain the passage for the gas flow. The iron carburisation level of the pellet shell is found to control the melting temperature of the pellet bed. Simultaneous and layer-wise melting is observed for the pellet bed with and without mixed nut coke, respectively.In the case of pellet bed mixed with nut coke, the liquid dripping starts at a lower temperature (1500°C) compared to the case when nut coke is absent (1518°C). Subsequently, a steady rate of liquid dripping is observed for the pellet bed mixed with nut coke. However, in the case of the pellet bed without nut coke, most of the liquid drips (~50 wt%) at high temperature (1550°C). The difference in carbon content of the quenched pellets and the dripped metal reveals that a substantial iron carburisation occurs when liquid iron flows over the regular coke particles.The nut coke is noticed to consumed preferentially in place of the regular coke. Additionally, the total coke consumption decreases with an increase in nut coke addition in the pellet bed. These results give support for more extensive use of nut coke as a replacement of the regular coke in the ironmaking blast furnace.
  • A Novel On-Line Model for the Prediction of Strip Profile in Cold Rolling

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    DOI:10.2355/isijinternational.ISIJINT-2019-233

    This paper presents a new on-line model for the prediction of the roll force profile across the strip in cold rolling. Also presented is a new on-line model for the prediction of roll deformed profile in a six-high mill. It is shown that an integrated model may be formed for the prediction of the strip profile on the basis of them. The prediction accuracy of the proposed models is examined through comparison with the predictions from Finite Element simulation.
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    1. Decoupling Strategy and Dynamic Decoupling Model of Flatness Control in Cold Rolling Strip ISIJ International Advance Publication
    2. Solubility of Sulfur in the Solid Oxide of the Calcium-Aluminate System ISIJ International Vol.59(2019), No.10
  • Effect of Single Power Two Circuits Electroslag Remelting Process on the Cleanliness of the Remelted Ingot

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    DOI:10.2355/isijinternational.ISIJINT-2019-450

    Single power two circuits electroslag remelting process with current carrying mould (ESR-STCCM) has been developed to remelt high alloy. In the present work, the laboratory experiments, physical simulations and numerical simulations were set up to systematically investigate the droplet size and cleanliness of the remelted ingot for ESR withdrawing process (ESRW) and ESR-STCCM. The results indicated that ESR-STCCM can change the distribution of electromagnetic force, thereby reducing the droplet size in the case of the same remelting power. ASPEX explorer was utilized to investigate the non-metallic inclusions of the remelted ingot for different remelting processes, and the result indicated that the types of the non-metallic inclusions for the different remelting processes were not changed, however, the number decreased by 42.3% for ESR-STCCM. Compared with the ESRW, the deoxidation ability of ESR-STCCM increased by 10.7% meanwhile, the desulfurization ability increased by 24.5%.
  • Molecular Dynamics Study of the Effect of Carbon Atoms on the Surface Tension of Silicon–carbon Alloy

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    DOI:10.2355/isijinternational.ISIJINT-2019-308

    We conducted molecular dynamics simulations of Si–C alloy to understand the atomistic behavior of solute C atoms near the melt surface and to estimate the surface tension. The surface tensions of liquid Si and C were first evaluated and compared with experimental values and those for other metals. The composition dependence of the surface tension of Si–C alloy was then evaluated, and compared with estimates obtained using the modified Butler's model. The behavior of C atoms at the surface of liquid Si–C alloys is also discussed.
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    1. Effect of Initial Microstructure on Creep Strength of ASME Grade T91 Steel ISIJ International Advance Publication
  • Decoupling Strategy and Dynamic Decoupling Model of Flatness Control in Cold Rolling Strip

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    DOI:10.2355/isijinternational.ISIJINT-2019-328

    Taking a 1420 mm UCM six-high cold rolling mill as the research object, by calculating and analyzing the relative gain array of flatness adjustments, the flatness control strategy of independent control primary flatness, decoupling control quadratic and quartic flatness is proposed, which simplifies the complex three-loop decoupling to the two-loop decoupling, and facilitates the design of flatness control system. In order to overcome the shortcomings of the long response time and the process fluctuation of the static matrix decoupling control, based on the multi-input and multi-output decoupling control theory, a method and model for the whole process decoupling of quadratic and quartic flatness control loops is proposed by introducing dynamic decoupling matrix instead of static decoupling matrix. The simulation results show that the dynamic matrix decoupling control method can make the system adjust quickly and smoothly, and by controlling the primary, quadratic and quartic flatness, the cubic flatness can also be controlled effectively. This paper opens up a new way and method for developing a simple, practical and high performance flatness control system.
  • Effects of Alloy Elements on Carbon Partitioning in Early Stages of Proeutectoid Ferrite Transformation in Low Carbon Mn–Si Steels

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    DOI:10.2355/isijinternational.ISIJINT-2019-395

    Controlling the carbon concentration and distribution among constituent phases is one of the most important issues for achieving high strength and ductility in the design of steel. The carbon distribution near the α/γ interface in the early stage of isothermal holding at 750°C was measured and visualized in Fe–C–Mn–Si alloys containing 2 mass% Si and 1.5 or 2 mass% Mn using a high precision FE-EPMA developed recently by the authors, and the results were compared with the theory of ferrite growth in multi-component low alloy steel. The carbon concentrations at α/γ interfaces in austenite were generally between the NPLE/PLE and paraequilibrium α/(α + γ) boundary concentrations. In alloys with carbon contents smaller than the NPLE/PLE boundary, the α/γ interfaces appeared to migrate under a condition close to paraequilibrium or with partially developed spikes of alloy elements in the early stages. On the other hand, in alloys with a bulk composition on the boundary and its higher carbon concentration side, Mn enrichment was observed at the interfaces, and the carbon concentrations tended to be higher than those in alloys with lower carbon contents, albeit there were variations at individual interfaces.
  • Extraction of Phosphorus and Recovery of Phosphate from Steelmaking Slag by Selective Leaching

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    DOI:10.2355/isijinternational.ISIJINT-2019-298

    At the refining temperature of steelmaking slag, phosphorus is distributed between the liquid phase and solid solution phase of 2CaO·SiO2-3CaO·P2O5. By exploiting the differences in water solubilities between the solid solution and other phases, we are developing an acid leaching process to separate out phosphorus. In this paper, we determined the optimum conditions of leaching with nitric acid by investigating the control over Fe valency in the slag and the recovery of phosphorus from the leachate. pH of 3 was found to dissolve the solid solution, while a solid solution containing FeO showed a lower phosphorus dissolution ratio. To avoid the formation of a glassy phase, slow cooling was necessary which suppressed the dissolution of other phases at this pH. Leaching was further studied in artificially prepared steelmaking slags of compositions representing commercial slag fertilizers. The dissolution ratio of phosphorus reached about 91% while the phosphorus content in the residue was sufficiently low. After separating from the residue, the pH of the leachate was increased to precipitate the phosphate. At a pH of 7, over 80% of the phosphorus in the leachate was precipitated, and the phosphate content of the precipitate was approximately 25% after calcination.
  • Removal of Fine SiO2 Composite Inclusions from 304 Stainless Steel Using Super-gravity

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    DOI:10.2355/isijinternational.ISIJINT-2019-301

    The super-gravity technique was used to remove the SiO2 composite inclusions from 304 stainless steel. The effects of different super-gravity coefficients and super-gravity treatment time on the removal effect of inclusions were studied. It was found that the SiO2-based composite inclusions floated up to the top of the sample after the super-gravity treatment, and the inclusions in the lower part of the sample were largely removed. The volume fraction and number density of inclusions presented a gradient distribution along the direction of the super-gravity, which became steeper with increasing gravity coefficient and treatment time. The total oxygen content at the bottom of the sample was reduced from 150 ppm to 93 ppm within 15 min of super-gravity treatment under the gravity coefficient of G = 80.
  • Effect of Initial Microstructure on Creep Strength of ASME Grade T91 Steel

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    DOI:10.2355/isijinternational.ISIJINT-2019-358

    To clarify the cause of heat-to-heat variation in the creep strength of Grade T91 steels, the influence of the initial microstructure on creep strength was investigated. The distribution of chromium concentration considered to be remaining segregation was observed as corresponding to lamellar contrasts parallel to the longitudinal direction of the boiler tube. Standard deviation (SD) of ΔCr was employed as an indicator of the degree of segregation, and a good correlation was found between the SD of ΔCr and the creep rupture life at 650°C. Remaining segregation was reduced by renormalizing heat treatment at 1200°C instead of 1250°C. The creep rupture life of steel subjected to renormalizing heat treatment at 1200°C and tempering at 760°C, followed by normalizing and tempering under standard heat treatment conditions for Grade T91 steel, was prolonged by a factor of 2.3–2.8. The strengthening effect of renormalizing at 1200°C to reduce the remaining segregation was confirmed by creep tests up to about 10000 h at 600°C and 650°C. Decreases in the number density of M23C6 carbide particles, length of high-angle boundaries and average KAM values during creep exposure are promoted by the presence of remaining segregation. Since diffusion is enhanced by the concentration gradient of elements, degradation due to microstructural change is promoted by the presence of remaining segregation. Segregation should be reduced to obtain high creep strength with homogenized concentration of chemical composition.
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    1. Molecular Dynamics Study of the Effect of Carbon Atoms on the Surface Tension of Silicon–carbon Alloy ISIJ International Advance Publication
  • Tracking the Burden Surface Radial Profile of a Blast Furnace by a B-mode Mechanical Swing Radar System

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    DOI:10.2355/isijinternational.ISIJINT-2019-362

    To continuously track the burden surface radial profile inside a blast furnace in every noncharging period, a new organizing structure for the scanned data of a mechanical swing radar system was proposed. The detection results of the radial shape of the burden surface in one scanning period can be organized into a matrix and represented by a composite image. Then, the extraction of the burden surface radial profile can be achieved by the segmentation of a featured region in the composite image. To address the incorrect segmentation results caused by the deterioration of the image quality in the later stage of each noncharging period, a priori curve-based image segmentation algorithm was proposed. The shape prior was constructed by a priori shape function and a current state function decomposed from the contours of the priori and current segmented regions, respectively. Compared with the classical region-scalable fitting segmentation algorithm, the proposed algorithm has the ability to provide more reasonable segmentation results during the entire noncharging period. The tracking of the burden surface radial profile can be accomplished by calculating the corresponding shape function from the contour of the segmented image region. Compared with the results produced by the existing A-mode radar data processing method, oscillations and local outliers can be avoided in the results of the proposed method. The goal of the continuous tracking of the burden surface radial profile was accomplished.
  • Effects of Temperature and Phase Transformation on Post-buckling Behavior of Non-oriented Electric Steel during Hot Finishing Rolling

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    DOI:10.2355/isijinternational.ISIJINT-2019-383

    The traditional buckling model is based on the assumption of homogeneous material. However, for non-oriented electrical steel with high-temperature phase transformation, the transverse differences of temperature and phase transformation during the hot finishing rolling result in uneven distribution of material properties in the dual-phase region. In order to study the effect of inhomogeneous material on the post-buckling behavior of strip, the relationships between tangent modulus and temperature in the austenite region and ferrite region are firstly obtained by hot compression experiments. Secondly, the transverse distribution function of tangent modulus is calculated according to the distributions of temperature and phase structure in the dual-phase region. Finally, the large deflection theory of thin plate is modified, and the elastic modulus constant is replaced by the distribution function of tangent modulus. The post-buckling model considering inhomogeneous material is established to analyze the effect of temperature and phase transformation on the wave height. The results show that strip thickness and tension have great effect on the post-buckling deformation of global longitudinal wave, but little effect on local longitudinal wave. The temperature drop and phase transformation at the strip edge have no significant effect on the wave heights of global and local center waves, but they reduce the wave heights of global and local edge waves by 6% and 20%, respectively.
  • Study of Sinter Strength and Pore Structure Development using Analogue Tests

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    DOI:10.2355/isijinternational.ISIJINT-2019-247

    Iron ore sinter quality is important for productive and efficient operation of the modern iron blast furnace. Understanding the driving mechanisms of industrial sinter quality is complicated by the variability in the product. Variability arises due to many factors including heterogeneous raw material distribution, spatial variation in temperature profile and gas atmosphere down the bed. To reduce product variability iron ore sinter analogues were created from the -1.0 mm fraction of an Australian iron ore. Samples were fired under tightly controlled thermal and atmospheric conditions in an infra-red rapid heating furnace. Maximum temperature was found to have a strong influence on the porosity of the fired tablets and hence their strength. The more commonly used integrated time at temperature above 1100°C (EA, enclosed area) was found to be not as useful a predictor of sinter strength for these analogue tests. Analogues fired to 1320°C showed a minimum in porosity and maximum strength after holding for 1 min. With longer firing, over-sintering occurred caused by pore swelling, leading to a decrease in strength. The proposed mechanisms of pore swelling are bubble coalescence and gas generation from hematite decomposition to magnetite. Extrapolating these results suggests over-sintering may occur in the lower part of the industrial sinter bed if the temperature is too high for too long, leading to lower strength product.
  • Formation Mechanism of Dislocation Walls during Cyclic Deformation in an Fe–Si Alloy

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    DOI:10.2355/isijinternational.ISIJINT-2019-314

    Low–cycle fatigue tests of a polycrystalline Fe–3 mass%Si alloy were performed at room temperature under a constant total strain amplitude of 1 × 10-2. Dislocation structures were observed by high–voltage scanning transmission electron microscopy. The development of dislocation walls parallel to (110) started during the first few tens cycles of fatigue. The activation of a set of double slip systems, (211)[111] and (112)[111], contributed to the formation of (110) walls. The (110) walls lie in the directions bisecting the angles between the Burgers vectors of the two active dislocations of the double slip systems.
  • Erosion of Carbon Brick by Zinc in Hearth of Blast Furnace

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    DOI:10.2355/isijinternational.ISIJINT-2019-142

    The service life of a blast furnace (BF) is affected by the accumulation of zinc. To clarify the erosion mechanism of the carbon bricks, due to the zinc action, a dissection investigation of a commercial BF was carried out. The results show that the zinc content reaches up to 10.59% in the tuyere coke. The carbon bricks were sampled in a region characterized by high erosion levels and molten iron was detected. More interestingly, zinc was detected between the molten iron and the carbon bricks: the high zinc content of the bosh gas of the BF induces the zinc vapor to penetrate into the molten iron surface. The zinc vapor and the molten iron mix together, and zinc migrates from the molten iron into the carbon bricks. The thermodynamic behavior of zinc was analyzed and the volume expansion rate (56.94%) was calculated when Zn oxidizes into ZnO. The oxidation process may be the main reason behind the carbon brick erosion. The results show that molten zinc flows to the brittle layer of the carbon bricks, and finally solidifies, the carbon bricks become easy to break at the brittle layer. Countermeasures to reduce the harm of zinc have been suggested based on the zinc balance calculation.
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    2. Supergravity-Induced Separation of Oxide and Nitride Inclusions from Inconel 718 Superalloy Melt ISIJ International Advance Publication
    3. Time Change in Scale Microstructure of Fe-5 mass%Ni Alloy at 1200°C ISIJ International Advance Publication
  • Time Change in Scale Microstructure of Fe-5 mass%Ni Alloy at 1200°C

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    DOI:10.2355/isijinternational.ISIJINT-2019-252

    Ni containing steel is known to form a complex oxide scale, which consists of an outer layer of Fe-oxides and an inner layer of FeO with complicated distribution of Ni(Fe) metal particles. Due to the complex microstructure, descaling of the oxide scale formed on Ni containing steel during a hot-rolling process is very difficult. In order to improve the descaling process, microstructural control of the inner oxide layer to eliminate its detrimental effect is necessary.In this study, the change in microstructure of the outer and inner layers formed on Fe-5 mass%Ni alloy during oxidation is investigated. In particular, the change in the microstructure of the metal particles in the inner layer with oxidation time is considered.The inner layer consisted of FeO, Ni(Fe), and voids. The concentration of Ni in the Ni(Fe) was found to increase across the inner layer from the scale/steel interface toward the outer/inner scale interface due to the equilibrium Ni concentration in the Ni(Fe) particles with FeO, which corresponded to the oxygen potential gradient in the inner layers. The number and area fraction of the Ni(Fe) metal particles decreased, whereas the size of the particles increased with oxidation time. This coarsening of the metal particles was proposed to be due to Ostwald ripening.
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    1. Supergravity-Induced Separation of Oxide and Nitride Inclusions from Inconel 718 Superalloy Melt ISIJ International Advance Publication
    2. Erosion of Carbon Brick by Zinc in Hearth of Blast Furnace ISIJ International Advance Publication
  • Supergravity-Induced Separation of Oxide and Nitride Inclusions from Inconel 718 Superalloy Melt

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    DOI:10.2355/isijinternational.ISIJINT-2019-321

    Herein, a method of supergravity-enhanced separation was used to remove oxide and nitride inclusions from Inconel 718 superalloy melt, with elucidating the inclusion removal behavior by varying the gravity coefficients (G) and separation times (t) used for melt treatment. Under supergravity conditions, inclusions concentrated at the sample top and are almost absent at the sample bottom. Moreover, the inclusion number density and average size showed a gradient distribution along the supergravity direction, and the steepness of this gradient rapidly increased with increasing G and t. The experimentally determined inclusion movement velocities agreed well with those calculated using Stokes's law at G ≤ 210 and t ≤ 10 min. At G = 210 and t = 10 min, the total oxygen and nitrogen contents of the sample decreased from 34.4 to 8.7 ppm and 133.4 to 34.1 ppm, respectively, corresponding to oxide and nitride removal efficiencies of 74.7% and 74.4%, respectively.
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    1. Time Change in Scale Microstructure of Fe-5 mass%Ni Alloy at 1200°C ISIJ International Advance Publication
    2. Erosion of Carbon Brick by Zinc in Hearth of Blast Furnace ISIJ International Advance Publication
  • Coupled Experimental Study and Thermodynamic Modeling of the Al2O3–Ti2O3–TiO2 System

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    DOI:10.2355/isijinternational.ISIJINT-2019-006

    A complete critical evaluation and re-optimization of phase diagrams and thermodynamic properties of the Al2O3–Ti2O3–TiO2 system at 1 atm pressure has been performed. Equilibration and quenching experiment in the Al2O3–TiO2 system in air was also performed to constrain the solubility limit of Al2O3 in TiO2 rutile solution at high temperatures. The molten oxide phase was described by the Modified Quasichemical Model considering the short-range ordering in molten oxide. While Al2TiO5 and Ti3O5 were treated as separate stoichiometric phases in the previous optimization, they were described in this study, using the Compound Energy Formalism, as part of pseudobrookite solid solution with a miscibility gap based on new experimental data. Corundum and rutile solutions were also described based on their crystal structures. New high temperature phase, Al6Ti2O13, was also considered for the first time. A set of optimized model parameters of all phases was obtained, which reproduces all available and reliable literature data within experimental error limits from 25°C to above the liquidus temperatures under oxygen partial pressures from metallic saturation to 1 atm. The newly optimized database was applied to calculate the inclusion diagram and reoxidation of Al-killed and Ti bearing steels.
  • Research and Application of Model and Control Strategies for Hot Rolled Strip Cooling Process Based on Ultra-Fast Cooling System

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    DOI:10.2355/isijinternational.ISIJINT-2019-104

    Ultra-fast cooling technology as an effective method for control microstructure and property, is widely used in hot rolled strips. For precise control of strip temperature in cooling process, a mathematical model based on UFC is established to calculate UFC-T and CT in high pressure mode, or only CT in low pressure mode. Temperature calculation compensation strategy is obtained to solve the situation that re-reddening after UFC process affects CT calculation. Furthermore, for existing self-learning strategy care less about evolution of strip temperature and has no ability to eliminate errors quickly, a multi-dimensional self-learning control strategy is proposed including dynamic self-learning gain, distributed temperature self-learning strategy and velocity coefficient for heat transfer self-learning. With help of proposed control strategies, strip temperature in cooling process is precise calculated and controlled. The model and strategies have been applied successfully in a 2050 HSM for development of low cost and feature strip products.
  • Observation of Chemical State for Interstitial Solid Solution of Carbon in Low-carbon Steel by Soft X-ray Absorption Spectroscopy

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    DOI:10.2355/isijinternational.ISIJINT-2019-206

    The near-edge X-ray absorption fine structure at the carbon K edge was measured for determining the chemical state of interstitial carbon in a low-carbon steel. In addition, the wavelength dependence of the photoelectron spectrum of the surface of the steel was evaluated, and a contamination and oxidation layer of 3 nm thickness was found. As a result, it was possible to observe a change in the chemical state of carbon existing in bulk iron located deeper than the oxidation and contamination layers, by evaluating the difference spectra between the sample and a reference. Furthermore, by evaluating the shape change of the difference spectra based on the heat treatment time, it was found that the chemical state of carbon in bulk iron changes with heat treatment.
  • Optimization of Thermal Soft Reduction on Continuous-Casting Billet

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    DOI:10.2355/isijinternational.ISIJINT-2019-409

    Thermal soft reduction (TSR) is an effective technique to improve the inner quality of continuous-casting billet, but it may lead to undesired internal and surface cracks. In this work, the technologic parameters of TSR were optimized to ensure its effect and control the cracks of 82A tire cord steel billet. A heat transfer model with comprehensive thermo-physical parameters was established to simulate the thermal behavior of continuous-casting billet. The model was verified by comparing the measured surface temperatures and the calculated ones. According to the mechanism of TSR on billet, both the location and water flow rate were comparatively optimized. TSR was determined to locate at 6.96 m–8.46 m from meniscus, where the temperature of billet center dropped rapidly to liquid impenetrable temperature. The water flow rate of TSR was set to 2.2 m3/h, which allowed the reheating rate and surface temperature in a reasonable range and prevented the formation of the cracks. Plant trials were conducted to verify the effect of the optimized TSR. The results showed that the central porosity, V segregation and central segregation of the billet were obviously improved by applying TSR. Meanwhile, the internal and surface cracks were well controlled in the billet.
  • Thermal Decomposition Reaction Kinetics of Hematite Ore

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    DOI:10.2355/isijinternational.ISIJINT-2019-129

    In order to understand the thermal decomposition kinetics of hematite particles in inert atmosphere, thermogravimetriy was employed for isoconversional analysis. The kinetic triplet was estimated from the experimental data and the isothermal reaction kinetics was predicted. The results indicated that the thermal decomposition could be divided into two stages, of which the activation energies were 636 kJ/mol and 325 kJ/mol, respectively. The exponential form of pre-exponential factor, ln(A/s-1), for the two stages were estimated to be 42.9±6.6 and 14.1±3.08. At last, the kinetic mechanism of the first stage was suggested to match Sestak-Berggren model as f(α)=(1-α)1.38. The relatively slow reaction rate of the second stage was due to the slag formation during the reaction.
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    3. Determination of Free Lime Contents in Slags by Solution Calorimetry ISIJ International Vol.36(1996), No.Suppl
  • Modeling of Surface Crack Defects Developed on Shear Edge in High-strength Automotive Steel Sheets

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    DOI:10.2355/isijinternational.ISIJINT-2019-326

    Surface crack defects developed on the shear edge cause a problem in shearing of high-strength steels. The surface crack formation mechanism was clarified by microstructural examinations and numerical simulation. Two types of 780 MPa grade hot-rolled steel sheets with a thickness of 2.6 mm were chosen for the evaluations because the materials show different surface crack susceptibilities. Cleavage fracture was responsible for the surface cracks, and micro-ductile cracks with a length of 30 µm to 40 µm were detected in the interrupted punching samples. A numerical simulation demonstrated that a tensile stress was developed in the direction of the micro-ductile cracks opening during punching process. The critical length of the micro-ductile crack for cleavage fracture as a crack initiation site was given by linear fracture mechanics; for example, the critical length is 23 µm or longer under the applied tensile stress of 910 MPa. The tensile stress causing cleavage fracture decreased by reducing the tool clearances, and it was shown experimentally that surface crack defects can be prevented by controlling the clearance appropriately.
  • Development of Analysis Method for Sulfide in Steel with Chelating Agent of Copper

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    DOI:10.2355/isijinternational.ISIJINT-2019-327

    Copper sulfide (CuxS) has been frequently observed in steel samples, prepared using selective potentiostatic etching by electrolytic dissolution (SPEED). It is often the case that CuxS is detected unexpectedly from the precipitates extracted from steel samples by selective potentiostatic etching, although such CuxS formation during the heat treatment conducted is not anticipated by the thermodynamic equilibrium calculations. In this study, we observed such artificial CuxS along with manganese sulfide (MnS) precipitates, which were extracted from steel materials by SPEED, using secondary electron microscope (SEM) equipped with energy dispersive X-ray spectroscopy (EDX) and Auger electron spectroscopy. These CuxS–MnS sulfide complex would be formed by the following mechanism: as the solubility of CuxS is far bigger (i.e. 10 times or more) than that of MnS, Cu2+ ion dissolved from steel matrix would be exchanged with Mn2+ ion on the MnS surface during the etching process, leading to a formation of CuxS–MnS sulfide complex.In order to suppress the formation of such CuxS, we propose the use of following electrolyte: a non-aqueous solution of 4% methyl salicylate + 1% salicylic acid + 1% tetramethylammonium chloride (TMAC) + 5% Triethylenetetramine (TET) in volume fraction, in methyl alcohol (Cu ion selective hold etching by electrolytic dissolution, abridged as CUSH electrolyte). Then, this electrolyte was applied to precipitates in steel samples. It was effective to prevent the formation of sulfides in electrolyte, with the effect of metallic (Cu2+, Ag+, Pb+, etc.) chelating ability of TET.
  • Accuracy Evaluation of Phase-field Models for Grain Growth Simulation with Anisotropic Grain Boundary Properties

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    DOI:10.2355/isijinternational.ISIJINT-2019-305

    The phase-field method has been widely employed recently for simulating grain growth. Phase-field grain growth models are classified into two types according to their conservation constraints for phase-field variables: the multi-phase-field model and the continuum-field model. In addition, within the multi-phase-field model framework, three models with different formulations exist. These models are reported to accurately simulate grain growth under conditions of isotropic or weakly anisotropic grain boundary energy and mobility. However, for cases of strongly anisotropic grain boundary properties, the accuracy of these models has not yet been examined in detail. In this study, using the continuum-field model and three different multi-phase-field models, systematic grain growth simulations with anisotropic grain boundary energies and mobilities are performed. Through the detailed investigation of the accuracy of the simulated results, the suitability of each model for anisotropic grain growth simulations is revealed. Furthermore, based on the higher-order terms, accuracy improvement of the phase-field models is attempted.
  • Reaction Behavior of Coke in a High Alumina Slag

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    DOI:10.2355/isijinternational.ISIJINT-2019-180

    The reaction behaviors between coke and CaO–SiO2–MgO–Al2O3–Cr2O3 slag at different immersion time, temperature and rotation speeds were studied in this work. The diameter decrement of the coke increased as increasing the immersion time, temperature and rotation speed. When the coke was in contact with the molten slag, the slag could infiltrate into the coke and further flow to the interior of the coke through pore channels, which will fill up the coke pores. During the penetration process of slag into the coke, the carbon could be oxidized by Cr2O3 and SiO2 in the slag. Furthermore, the penetrated slag could also dissolve the coke ash minerals and react with that to form new phase. The comprehensive effects of slag penetration, slag-carbon reaction and slag-mineral reaction eventually resulted in the coke degradation.
  • Artificial MnS Inclusions in Stainless Steel: Fabrication by Spark Plasma Sintering and Corrosion Evaluation by Microelectrochemical Measurements

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    DOI:10.2355/isijinternational.ISIJINT-2019-408

    Spark plasma sintering was used to fabricate type 304L stainless steel specimens containing artificial manganese sulfide (MnS) inclusions, and a microelectrochemical technique was used to characterize the pit initiation behavior at the MnS. A 200 μm square electrode area that included an artificial MnS particle was potentiodynamically polarized in 0.1 M NaCl, and the electrode surface was observed in situ by optical microscopy. The anodic dissolution of the MnS particle was observed in the passive region of the stainless steel. The pit occurred at the boundary between the particle and the steel matrix after the particle dissolved slightly. The dissolution potential and pit initiation behavior at the artificial MnS particles in the sintered stainless steel were confirmed to be similar to those at MnS inclusions in commercial stainless steels.
  • Atomic and Effective Pair Interactions in FeC Alloy with Point Defects: A Cluster Expansion Study

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    DOI:10.2355/isijinternational.ISIJINT-2019-019

    The Cluster Expansion Method (CEM) is used to investigate the pair interactions in body centered cubic (BCC) FeC alloy in the presence of vacancies. Within the CEM framework, the relation of cluster (point and pair) probabilities and set of independent correlation functions are derived. These are then applied to calculate the effective cluster interaction and atomic pair interaction energies for Fe, C and vacancy in FeC system. We found that, in this alloy, the interaction mostly comes from the first nearest neighbor pairs, and, to some degree, from the third nearest neighbor pairs. Detailed analysis shows that, within the first nearest neighbor pair interactions approximation, the C–C and Fe–C pair interactions are repulsive where the former one is more dominant. This is attributed to the local stress field formed in the vicinity of C atoms which pushes the first nearest neighbor atoms away to maintain the equilibrium distances. Moreover, there is an attractive interaction between C and vacancy which implies the possibility of C atoms to be trapped at vacancy site.
  • Reduction and Gasification Characteristics of A Unique Iron Ore/carbon Composite Prepared from Robe River and A Coal Tar Vacuum Residue

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    DOI:10.2355/isijinternational.ISIJINT-2019-048

    We have prepared a unique iron ore/carbon composites (IOC) from a low grade iron ore called Robe River and a thermoplastic carbonaceous material. When Robe River which contains iron as goethite, FeOOH, is heated up to 250 to 300°C, the OH groups are removed as H2O, leaving flat pore spaces of 0.8 nm wide between 2.0 nm thick Fe2O3 layers. The pore spaces are, however, closed over 300°C by the sintering of the Fe2O3 layers. The idea proposed is to insert the thermoplastic carbonaceous material into the pore space of 0.8 nm wide while the pore spaces are opened and to carbonize it to form carbon in the pore space below 500°C. The iron oxide in the IOC thus prepared is reduced very rapidly in inert atmosphere and the carbon retained in the pore space is gasified by CO2 very rapidly also. In this work the reaction characteristics of the unique iron ore/carbon composite prepared from Rove River and a coal tar vacuum residue, CTVR, were examined for its direct reduction, indirect reduction in a H2 atmosphere, and coke gasification in a CO2 atmosphere from the viewpoints of reaction enthalpies and rate parameters. The examinations clarified that the carbonaceous material retained as coke in the pore space of iron ore are very reactive and show reaction characteristics different from bulk carbon.
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    1. Atomic and Effective Pair Interactions in FeC Alloy with Point Defects: A Cluster Expansion Study ISIJ International Advance Publication
  • Influence of Ambient and Oxygen Temperatures on Fluid Flow Characteristics Considering Swirl-type Supersonic Oxygen Jets

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    DOI:10.2355/isijinternational.ISIJINT-2019-030

    In vanadium extraction converter steelmaking, the swirl-type oxygen lance has been applied to improve the dynamic condition of the molten bath reaction to achieve a higher oxidation rate of vanadium and better vanadium slag quality, because the swirl-type jet can generate not only axial and radial forces but also tangential ones. Recently, the swirl-type supersonic jet with preheated oxygen was proposed to further enhance the agitation ability of the oxygen jet on the molten bath. In this study, the effects of the ambient temperature and oxygen temperature on the swirl-type supersonic jet behavior were analyzed to achieve better formulation and optimization of the process parameters. The flow characteristics of swirl-type oxygen jets were simulated by computational fluid dynamics software at 300 K, and 1700 K ambient and 300 K, 450 K and 600 K oxygen temperature, and partial results were validated against data from a preheating jet experiment. An analysis of the results shows that the centerline jet velocity was increased by preheated oxygen, and at higher ambient temperature, a longer core length was formed and the velocity fluctuation was aggravated. The influence of the preheating temperature on the core length was more evident at lower ambient temperature. From a dynamic perspective, the molecular motion was improved and with respect to energy, the internal energy of the oxygen jets could be preserved at higher ambient temperature.
  • Effect of a Novel Hot-core Heavy Reduction Rolling Process after Complete Solidification on Deformation and Microstructure of Casting Steel

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    DOI:10.2355/isijinternational.ISIJINT-2019-125

    Hot-core Heavy Reduction Rolling (HHR2) is a novel technology designed for eliminating center defects of casting steel by using the large temperature gradient, which performed heavy reduction to bloom or slab with rolling mill after the position of solidification end of the strand. This works mainly focus on the effect of HHR2 process on the shrinkage elimination and microstructure evolution. Firstly, bonding plate rolling experiment were carried out, which proved HHR2 process with large temperature gradient in thickness direction could improve the internal deformation of workpiece. Meanwhile, the deformation permeability was beneficial to the microstructure refinement of center layer. Secondly, the HHR2 process was studied by analysis of the results of FEM to explore the influence of some process parameters on shrinkage closure. In this study, the Gm index and volumetric residual percentage V/V0 were used as evaluation index in mechanical analyses and quantitative comparison, the results reflected the void tend to closing with the reduction ratio and roll diameter increasing, as well as with the reduction position moving towards the solidification end after complete solidification. Finally, the pilot plant trail of HHR2 was carried out before industrial application, and the results reflects the HHR2 process can eliminate the large central shrinkage cavity and refine the center microstructure.
  • Fabrication of Iron Oxide Nanoparticles via Submerged Photosynthesis and the Morphologies under Different Light Sources

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    DOI:10.2355/isijinternational.ISIJINT-2019-188

    Recently, metal oxide nanocrystallites have been synthesized through a new pathway, i.e., the submerged photosynthesis of crystallites (SPSC), and flower-like ZnO and CuO nanostructures have been successfully fabricated via this method. In this work, the SPSC process was applied for the fabrication of iron oxide and hydroxide nanoparticles. The experiments were conducted under visible light, ultraviolet light, and gamma-ray irradiation conditions and the morphologies of the obtained nanoparticles were observed and compared with that obtained without illumination. Then, the mechanism of the SPSC process for the fabrication of iron oxide nanoparticles was discussed. The results show that various kinds of morphologies of nanocrystallites were obtained on the Fe plate surface and the main morphologies are different under different conditions. For example, most FeOOH with the morphologies of nanorod and nanofiber exist by visible light irradiation; most faceted crystals of FeOOH and Fe2O3 with the morphologies of nanograular and nanorod exist by ultraviolet irradiation. In the SPSC process, light irradiation generates ·OH at the crystal tips and promote the crystallization in apical growth of FeOOH.
  • Characterization and Properties of Scaffold in a Dissected Blast Furnace Hearth

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    DOI:10.2355/isijinternational.ISIJINT-2019-199

    The blast furnace scaffold can only be obtained while the blast furnace shut down after operating for many years. Its characteristics and properties are important for the blast furnace campaign life. The key to delaying the carbon brick corrosion in blast furnace hearth is the scaffold formed between the melt and the carbon brick. In an emergency shutdown blast furnace, the scaffold in hearth is completely preserved, and the scaffold on the surface of the carbon brick above and below the taphole in hearth are sampled. The purpose of this study is to describe the characterization and properties of the scaffold in hearth. The paper presents results from investigations using electron imaging techniques such as Transmission Electron Microscopy (TEM), Optical Microscope (OM), Scanning Electron Microscope combined with Energy Dispersive Spectrometer (SEM-EDS), Raman analysis and X-ray Diffraction (XRD). The main component of the slag skull above the taphole is similar to the final slag and is rich in harmful elements. The thermal conductivity of the scaffold is about 2 W/(m·K) and the viscosity as well as the solidus temperature are higher than the final slag. The slag skull acts to isolate and contain harmful elements. The phase on the hot surface of the carbon brick below the taphole is mainly consist of graphite and the large-grained graphite phase has a random spatial network distribution in the iron matrix. The slag skull and the graphite serves to segregate the melt and harmful element, thereby protecting the carbon brick and extending hearth life.
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    3. Three-dimensional Mathematical Modeling and Designing of Hot Stove ISIJ International Vol.50(2010), No.7
  • Numerical Analysis of the Effect of Water Gas Shift Reaction on Flash Reduction Behavior of Hematite with Syngas

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    DOI:10.2355/isijinternational.ISIJINT-2019-215

    The water gas shift reaction (WGSR) is the most important side reaction in direct iron reduction processes in syngas. In this study, an Euler-Lagrange model has been developed to simulate the flash reduction behavior of hematite with syngas in a drop tube reactor. Based on model validation, the effect of WGSR on the flash reduction is investigated by comparing results predicted by models with and without WGSR. Results indicate that the WGSR has a minor effect in CO–H2 system while a major effect in H2–CO–CO2–H2O system. The difference of gas composition caused by WGSR leads to a difference of gas reduction capacity, which results in different reduction behavior. The relationship between the composition of gas mixture and the equilibrium constant of WGSR determines the direction of WGSR and thus determines the positive or negative effect of WGSR on the reduction process. The higher oxygen partial pressure and temperature, the stronger influence of WGSR can be considered to have.
  • Numerical Simulation of Multiphase Flow and Mixing Behavior in an Industrial Single Snorkel Refining Furnace: Effect of Bubble Expansion and Snorkel Immersion Depth

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    DOI:10.2355/isijinternational.ISIJINT-2019-280

    A coupled mathematical model is used to simulate the multiphase flow in an industrial Single Snorkel Refining Furnace (SSRF). Based on the present model, the evolution characteristics of bubble size, density, and velocity are analysed during the long-distance rising process. The comparative studies indicate that the expansion of bubbles has an enormous impact on the circulation rate and free surface in the vacuum chamber. Furthermore, the effect of snorkel immersion depth (SID) on the circulation rate, mixing time, and fluid flow are investigated. The results indicate that the circulation rate decreases with the increase of SID, while the mixing time shows an uptrend with the increase of SID. Particularly, when the SID exceeds 0.4 m, the scope of dead zone around the snorkel dramatically increases, which further decreases the flow velocity of slag layer in the ladle.
  • Effect of Laminated Structure on Mechanical Properties of Composition-modulated Co–Ni Laminated Plating

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    DOI:10.2355/isijinternational.ISIJINT-2019-293

    A composition-modulated Co–Ni laminated plating has been developed to prolong the lifetime of molds to be employed in continuous steel casting. We have investigated the relationship between the laminated structure and the mechanical properties of the plating films. The tensile strength of as-plated film was enhanced by the thinned thickness of the constituent layers, while the elongation received no effect of the thickness change of the constituent layer and remained almost stable in the range from 3 to 5%. Heat treatment at 400°C have brought about the improvement both in the tensile strength and the elongation. The improvement in the elongation was as remarkable as reached 13% in the film composed of layers with a thickness of 0.8 µm. The layer with low Ni content had an hcp structure, and that with high Ni content produced two phases of the hcp and fcc structures in the as-plated state. By the heat treatment, the high Ni-content layer turned into the single fcc phase, while the low Ni-content layer kept the hcp phase, and accordingly, the film structure changed into the one where the lamination of the hcp and fcc layers was distinct. The fact that the fcc layers, which was easily deformed, were formed continuously in the lateral direction, was seemed to contribute to the significant improvement in the elongation after heat treatment.

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  3. blast furnace productivity
  4. cohesive zone
  5. hot rolling
  6. pellet
  7. basicity
  8. alternating current electrolyzing method for colored stainless steel
  9. steel
  10. argon bubbles