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

ISIJ International Advance Publication

  • Heat Transfer Characteristic of Slit Nozzle Impingement on High-temperature Plate Surface

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    DOI:10.2355/isijinternational.ISIJINT-2018-576

    Heat transfer mechanism of a slit jet impingement was thoroughly studied to improve capacity and uniformity of a hot steel strip/plate during its ultrafast cooling or quenching. The impact angle has a significant influence on the heat transfer characteristics of the stationary slit jet impinging process. Heat transfer capability and rewetting front propagation, which include such parameters as qmax, tMHF, and TMHF, differ significantly between the upstream and downstream regions. Parallel flow and intense sputtering in the downstream region are apparent for the forward-moving inclined slit jet impingement cooling process. The antiparallel flow in the upstream region is thinner, and the sputtering is reduced and is relatively stable. As the plate moves forward, the wetting front expands and forms almost a straight line with synchronized and uniform heat transfer. The inclined angle increases from 0 to 45°, which significantly increases the heat transfer intensity and shortens the time to nucleate boiling stage as well as the width of the transitional boiling region. A higher moving velocity reduces and promotes qmax moving to the downstream region.
  • A Gibbs Energy Balance Model for Growth Via Diffusional Growth-Ledges

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    DOI:10.2355/isijinternational.ISIJINT-2018-621

    Growth ledges are commonly observed on interphase boundaries during diffusional phase transformations and are of great importance for understanding inter-sheet spacing of interphase precipitates. A simple model based on Gibbs Energy Balance (GEB) for describing growth kinetics via diffusional growth-ledges of height λ is presented for the case of ferrite growth into austenite. The model is validated against the case of austenite to ferrite transformation involving interphase precipitation in a V, Mn, Si alloyed HSLA steel where, λ is assumed to be equal to the inter-sheet spacing of interphase carbide precipitates. The presented model provides a computationally efficient and versatile method for predicting the ledge height, λ, and the growth kinetics of ferrite from initial nucleation through to final soft impingement considering the evolution of solute drag at growth ledge risers. It is suggested that the intrinsic mobility of growth ledge risers is: [ This part of text is omitted ], with R the gas constant and T the absolute temperature in K.
  • Selection of the Massive-like δ-γ Transformation due to Nucleation of Metastable δ Phase in Fe-18 Mass%Cr-Ni Alloys with Ni Contents of 8, 11, 14 and 20 Mass%

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    DOI:10.2355/isijinternational.ISIJINT-2018-726

    It has been realized that a massive-like transformation, in which δ phase (ferrite) transformed to γ phase (austenite) in the solid state during and after solidification, was selected in Fe–C steels. X-ray radiography confirmed that the massive-like transformation also occurred in Fe-18 mass%Cr-Ni alloys with Ni contents of 8, 11, 14 and 20 mass%Ni. According to the equilibrium phase diagram, δ phase is the primary phase in 8 and 11 mass%Ni alloys while γ phase in 14 and 20 mass%Ni alloys. Solidification was always initiated by nucleation of δ phase and consequently fine γ grains were formed by the massive-like transformation in 8 and 11 mass%Ni. On the other hand, nucleation of δ phase as a metastable phase was preferably selected at lower undercoolings (<50 K) in 14 and 20 mass%Ni and consequently the massive-like transformation occurred even in 14 and 20 mass%Ni alloys. Solidification of γ phase can be triggered by nucleation of δ phase followed by the massive-like transformation in the Fe–Cr–Ni with lower Cr/Ni values (the primary γ alloys). Moreover, the present study demonstrates that the massive-like transformation will be commonly observed in Fe-based alloys, in which δ and γ phases are competitive each other from a thermodynamic perspective.
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    1. A Gibbs Energy Balance Model for Growth Via Diffusional Growth-Ledges ISIJ International Advance Publication
  • Shear-Force Based Stainless Steel Slag Modification for Chromium Immobilization

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    DOI:10.2355/isijinternational.ISIJINT-2017-678

    Immobilization of chromium in a stable spinel by modification is a powerful way to prevent chromium pollution of stainless steel (SS) slags. The precipitated spinel grain size is usually smaller than 30 µm, however, which limits the effectiveness of the modification. In the literature, very few efforts have been reported on promotion of spinel growth rate by optimizing the dynamic conditions. In this study, the effects of shear force on the spinel grain size evolution under isothermal conditions and during cooling were investigated. The experimental results indicate that the employment of shear force significantly changes the growth behavior of spinel at 1500°C. The growth mechanism of spinel was studied by using crystal size distribution (CSD) theory, showing different regimes of supply-controlled Ostwald ripening, surface-controlled growth with decaying nucleation rate, and constant rate nucleation and growth at shear rates of 0 s-1, 10.83 s-1, and 21.67 s-1, respectively. On the other hand, at a cooling rate of 5°C·min-1, the shear force was found to have little effect on the crystallization behavior of spinel. The results of static leaching tests indicated that hardly any chromium had leached, which makes the modified SS slag more environmentally friendly when used as a raw material.
  • Effect of MnS Inclusions Distribution on Intragranular Ferrite Formation in Medium Carbon Non-Quenched and Tempered Steel for Large-Sized Crankshaft

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    DOI:10.2355/isijinternational.ISIJINT-2018-509

    A novel quantitative characterization method of MnS distribution was proposed based on the data from automatic inclusions analysis software to evaluate their effects on intragranular polygonal ferrite (IPF) formation in medium carbon non-quenched and tempered steels. The results show that agminated MnS inclusions in the steel are less effective to promote the IPF formation and lots of inclusions are actually wasteful because their space distances are too small to act as nucleation sites individually, even their number is larger than that in the steel with plentiful uniformly distributed MnS inclusions. Due to the difference of observation method, three-dimensional dendritic MnS inclusions would be revealed as several agminated small-sized ones in two-dimensional observation. In order to avoid misunderstanding, the characteristics of the nearest space distances between inclusions in widely used two-dimensional observation could be applied to recognize and define these agminated MnS inclusions to more accurately evaluate their effects on IPF formation.
  • Improving Blast Furnace Raceway Blockage Detection. Part 1: Classification of Blockage Events and Processing Framework

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    DOI:10.2355/isijinternational.ISIJINT-2018-530

    The present paper is the first part of a three paper series discussing raceway blockages in blast furnaces for ironmaking. During raceway blockages the hot blast flow rate can be reduced significantly and in such cases it is beneficial to shut down additional fuel systems like pulverized coal injection (PCI) on that specific tuyere. Currently this is mainly done by a simple threshold comparison of the hot blast flow rate data. Using a constant threshold level cannot account for drifting sensor levels or local changes in burden permeability around the raceway. Thus, the authors investigate various strategies to find more reliable solutions for blockage detection and the shutdown of PCI branches. Part 1 discusses the different nature of various blockage events on the basis of tuyere camera images and hot blast flow rate data. For the detailed testing of signal processing (part 2) and image processing algorithms (part 3) a universal test-bench is presented which also includes a common quality assessment of the results. Based on the collection of tuyere camera images a simple classification of blockage events is established. The analysis of 1500 hours of blast furnace operation data delivers a proper statistics about the frequency of occurrence of blockages on a small size blast furnace. The detailed analysis of hot blast signals and tuyere camera images presented in this paper series aims to improve the understanding of the raceway regions and their influence on optimal blast furnace operation.
  • Improving Blast Furnace Raceway Blockage Detection. Part 2: Signal Processing of Hot Blast Pressure Data

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    DOI:10.2355/isijinternational.ISIJINT-2018-531

    The present paper is part 2 of a three paper series discussing raceway blockages and various approaches for automated detection based on blast furnace (BF) plant data. Blockages of the raceway areas occur on a regular basis and in cases where the hot blast flow rate is reduced significantly, it is beneficial to shut down additional fuel systems like pulverized coal injection (PCI) on that specific tuyere. While part 1 gave an overview on the different appearances of raceway blockages and presented a common test-bench used for signal and image processing, part 2 focuses on the discussion of various signal processing algorithms and their applicability for raceway blockage detection. The algorithms are tested on data from a real BF with supplementary tuyere camera images to validate the results. Beyond this test dataset, a long-term test is performed by processing three month of BF data offline.
  • Improving Blast Furnace Raceway Blockage Detection. Part 3: Visual Detection Based on Tuyere Camera Images

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    DOI:10.2355/isijinternational.ISIJINT-2018-532

    The present paper is part 3 of a paper series discussing raceway blockages and various approaches for automated detection based on blast furnace (BF) plant data. While part 11) gave an overview on the different appearances of raceway blockages and part 22) focussed on signal processing of hot blast data, this third part discusses various approaches for image processing of tuyere camera data. The visual impression of raceway blockages strongly varies between different events. This makes automated detection based on digital image processing of tuyere cameras a difficult task. On one hand the image processing algorithm should be robust and easy to tune for different tuyeres or different blast furnaces, on the other hand it should be fast enough, so that all tuyeres of a blast furnace can be processed on-line with a sufficiently high image frame rate. While algorithms optimized for motion detection fail due to the lack of a homogeneous background, adaptive thresholding of the grey-level histograms delivers useful results. Due to the nature of chaotic motion of coke particles inside the raceway also line based processing methods can extract the information from tuyere images in a sufficient manner and are very fast with regards to online implementation in a process control system. However, image processing of tuyere camera data has some disadvantages compared to the signal processing of hot blast data as discussed in part 2 of this paper.
  • Formation and Evolution of Silicate Inclusions in Molten Steel by Magnesium Treatment

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    DOI:10.2355/isijinternational.ISIJINT-2018-543

    The effect of magnesium addition on the formation and evolution of inclusions in Mn–Si killed steel is studied by laboratory experiments and thermodynamic calculation. Samples were taken at different holding time after magnesium addition to study the transient evolution of inclusions. The morphology, composition, number and diameter of inclusions were thoroughly analyzed by SEM-EDS. The results show that four types of inclusions (MgO–SiO2–MnO liquid inclusion, MgO–SiO2–MnO complex inclusion, MgO–SiO2 and MgO solid inclusion) form with different amount of magnesium addition. Liquid inclusion of MnO–SiO2 is promptly modified to MgO–SiO2–MnO liquid inclusion with 0.0005% magnesium addition. As the amount of magnesium is increased to 0.0011%, intermediate product MgO forms immediately and then gradually transforms to MgO–SiO2 solid inclusion with holding time. While MgO solid inclusion keeps stable throughout with 0.0019% magnesium addition.
  • Design of a Kind of Backup Roll Contour Used in Four-High CVC Hot Strip Mill

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    DOI:10.2355/isijinternational.ISIJINT-2018-674

    The phenomenon of uneven contact pressures between cylindrical backup roll and CVC (Continuously Variable Crown) work roll in four-high hot strip mill has always existed, which can lead to seriously uneven wear of cylindrical backup roll and even spalling defect. In order to obtain an available solution plan for above mentioned problem, a new kind of backup roll contour called reverse CVC backup roll contour is proposed in this paper. Reverse CVC backup roll contour is generated by fitting four cubic chamfer contours and one backup roll surface contour designed by CVC work roll contour. And one roll elastic deformation simulating software coded based on Influence Function Method has been used to calculate and study the contact pressure distributions between CVC work roll and reverse CVC contour backup roll or cylindrical contour backup roll. Compared with cylindrical contour backup roll, contact pressures between CVC work roll and reverse CVC contour backup roll are much smoother without steep peak. Simulating results meet well with data collected from the application field, wear of new reverse CVC contour backup roll is more well-distributed than cylindrical contour backup roll.
  • Effect of Carbonization Conditions on the Property and Structure of Bamboo Char for Injection in Blast Furnace

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    DOI:10.2355/isijinternational.ISIJINT-2018-460

    To evaluate the effect of carbonization conditions on the bamboo, the relationship between carbonization parameter and physicochemical characteristics was studied. The results indicated that the volatile matter drastically decreased with the increase of carbonization temperature, while the fixed carbon and fuel ratio (fixed carbon/volatile matter) increased. Excellent linearity between the fuel ratio and carbonization temperature was obtained. The energy yield decreased gradually when rising the carbonization temperature, whereas the change of heating value was not obvious. A new calculation model of higher heating value (HHV) was developed, and it could be used to predict HHV of the bamboo char more precisely at temperatures above 300°C. The positive impact of functional groups, specific surface area as well as catalysis of alkali metal may contribute to the combustion of bamboo char. The results showed that there is a feasible operating condition for the transformation of bamboo into char with the carbonization parameter at 400°C for 30 min.
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    1. Kinetics of Dissolution of SiO Gas in Liquid Fe–C Alloys ISIJ International Vol.58(2018), No.12
    2. Effect of Silica on Reduction Behaviors of Hematite-carbon Composite Compact at 1223–1373 K ISIJ International Advance Publication
    3. Development and Validation of Kinematical Blast Furnace Model with Long-term Operation Data ISIJ International Vol.58(2018), No.12
  • Effect of Silica on Reduction Behaviors of Hematite-carbon Composite Compact at 1223–1373 K

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    DOI:10.2355/isijinternational.ISIJINT-2018-613

    The influence of compositional changes in the SiO2–Fe2O3 binary oxide system on the reduction behavior of carbon-bearing compact was investigated at 1223–1373 K. Density functional theory (DFT) calculations were employed to investigate the adsorption behaviors of O–Si–O on various FeO surfaces in order to explore the mechanism of the conversion of FeO to Fe–Si–O phase. Chemical analysis, SEM-EDX, and XRD were carried to characterize the conversion mechanisms. According to experimental results, silica causes the decrease of the metallization ratio by hindering the reduction of FeO to Fe and facilitating the reaction of FeO to Fe–Si–O phases. The size of metallic iron granules diminishes gradually and the boundary between the iron phase and the slag phase becomes less obvious with increasing silica content, which greatly increases the contact probability of SiO2/liquid phases and FeO. For the three adsorption sites, the adsorption energies of Si atoms onto FeO surfaces are all obviously larger than that of the reducing gases, making it extremely difficult for the reducing gases to remove O atoms from FeO surfaces, as the DFT results show. Moreover, it is easier to form the Fe–O–Si phase on the FeO (110) surface since the adsorption energy of O–Si–O onto this surface is greater than that onto the FeO (100) and FeO (111) surfaces. Additionally, the charge of the O (FeO) 2p orbital, the Si 3p orbital, as well as the 3s, 3p, and 3d orbitals of the Fe atom take charge of the formation of Si–O–Fe bond.
  • Curling of Sheet in Asymmetric Rolling Investigated by Profile Measurement of Partly Rolled Sheet

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    DOI:10.2355/isijinternational.ISIJINT-2018-528

    The curling of a sheet in cold asymmetric rolling was investigated experimentally by interrupted rolling. Influences of speed difference as well as entry table height were studied. The upper and lower profiles of the aluminum sheet obtained by interrupted rolling were measured by a laser profilometer. The contact lengths on both upper and lower surfaces LU and LL were detected from the profiles. The curvature radius of sheet was calculated from the curling profiles. Under differential-speed rolling, the sheet curled to the slower roll side at low reduction in thickness, while it curled to the faster roll side at higher reduction. Meanwhile, LU on the faster (upper) roll surface was longer than LL on the slower (lower) roll surface at low reduction. On the other hand, LU was shorter than LL at higher reduction in thickness. It is found that the ratio of contact length LL/LU is correlated with the curling direction in the differential-speed rolling. If LL/LU < 1, the sheet curls towards the slower roll side, while the sheet curls towards the faster roll side in case of LL/LU > 1.
  • Effect of Mineral Elements Migration on Softening–melting Properties of Ti–bearing High Basicity Sinter

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    DOI:10.2355/isijinternational.ISIJINT-2018-498

    The mineral elements migration behaviours of Ti–bearing high basicity sinter during softening–melting process, as well as its effect on softening–melting properties, are studied using scanning electron microscope and X–ray diffractometer. We can conclude that both MgO and Al2O3 content increase while TiO2 content increases first and decreases later overall in the slag phase from the original state to melting end. At softening stage, some perovskite dissolves into the slag phase and part of TiO2 and MgO in wustite phase transfer into the slag phase. The low melting temperature of the slag phase is the main factor for the low softening temperatures of Ti–bearing sinter. At melting stage, TiO2 in the slag phase is tiny and changes little. The low liquidus temperature and viscosity of the slag phase result in the low melting start temperature of Ti–bearing sinter. The slag phase melts great earlier than metallic iron while the unfused sponge iron still bounds large amounts of perovskite crystals. And then, iron collapses and releases the restrained crystals at a higher temperature, resulting in the second rise of pressure drop.
  • Experimental Study on the Physical Properties of Iron Ore Granules Made from Australian Iron Ores

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    DOI:10.2355/isijinternational.ISIJINT-2018-508

    A fundamental experimental study was conducted to measure the physical properties of iron ore granules made from three types of Australian iron ores. In this study, some key physical property parameters, including apparent density, Young's modulus and the coefficients of static and rolling frictions, of the iron ore granules with varying moisture content were investigated. The effect of granule size on the considered property parameters was also studied for the iron ore granules at the optimal moisture content which was determined by permeability pot packing test. The measurement results showed that both apparent density and Young's modulus of iron ore granules generally decreased with moisture content due to the growth of adhering layer around the nuclei particles. The static friction coefficient generally increased with moisture content but, at lower moisture contents, its variation differed between the granule types. The rolling friction coefficient generally experience a minimum value as moisture content increased within the considered range. The moisture content for the minima varied with granule type due to the different characteristics of the ore types. At the optimal moisture content for each granule type, the apparent density of different granule size fractions showed variable values because of the heterogeneous composition of the raw mixture in each size fraction. The Young's modulus and static friction coefficient showed slight downward and upward trends with the increase of granule size, respectively. The rolling friction coefficient is nearly independent of granule size.
  • Coating Film Profiles Generated by Fluctuating Location of the Wiping Pressure and Shear Stress

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    DOI:10.2355/isijinternational.ISIJINT-2018-413

    Impinging planar jets are a widely used means of removing excess drag-out coating material from steel strip in order to control the final thickness of the applied coating. A wide range of possible coating defects are known to occur for this process, many of which are suspected to have their origin in the spatio-temporal characteristics of the air jets. It is therefore of interest to improve understanding of the link between the unsteady flow behaviour inherent to impinging jets and the evolution of the coating free surface produced by the gas-wiping process. In this paper, the coating response, characterised by the amplitude and frequency of the coating thickness fluctuation, throughout both the active region of the gas-wiping jets and the region immediately downstream, is investigated using a numerical model. The pressure and shear stress profiles acting on the coating surface along the strip are imposed as time-varying inputs such that for both the pressure and shear the vertical location of the entire profile undergoes sinusoidal oscillation parallel to the strip. A range of amplitude-frequency combinations for the vertical oscillation of the profiles are employed to assess the combined effect of these parameters on the coating response. Additionally, the strip speed is a varied parameter. Both the magnitude of the coating thickness fluctuation and the corresponding shape of the coating surface profile along the strip are found to be dependent on the strip speed and the oscillation amplitude and frequency of the vertical location of the pressure and shear stress profiles.
  • Numerical Simulation of Decarburization Kinetics for Fe-3%Si Steel during Annealing

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    DOI:10.2355/isijinternational.ISIJINT-2018-547

    In order to reduce the magnetic aging produced in the use of oriented silicon steels, the carbon content in the steel matrix of products is less than 50 ppm. In this study, the decarburization reaction kinetics on Fe-3% Si steel surface and the diffusion mechanism of carbon in the steel were analyzed during decarburization annealing. Based on the balance between carbon diffusion flux in the steel matrix and the decarburization reactions on steel surface, the mathematical model for decarburization of Fe-3% Si steel with oxidation behavior was established. The boundary conditions of the model were given and the model was solved by numerical method. The decarburization experiments were carried at different annealing time, annealing temperature and PH2O/PH2. Results showed that the residual carbon content in the steel decreased and oxygen content increased continuously as the annealing time increased. With the increase of annealing temperature and PH2O/PH2, the residual carbon content in the steel first decreased and then increased. But the oxygen content increased continuously. Based on the experimental results, the decarburization model was modified from three aspects, which were phase transition in steel matrix, temperature change of steel in heating process and parameters change of decarburization kinetics. When the decarburization model was modified, the values of simulated results were in good agreement with the experimental results, which proved the validity of the model.
  • Effects of Coke Ash on Erosion of Carbon Composite Brick

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    DOI:10.2355/isijinternational.ISIJINT-2018-562

    Carbon composite brick has attracted increased attention because it is widely used on the hot face of blast furnace hearth. In order to reduce the erosion rate of carbon composite brick and investigate effects of coke ash on the erosion of carbon composite brick, the minerals CaO·Al2O3, CaO·2Al2O3, and CaO·6Al2O3 (CA, CA2, and CA6), which were considered to be the main components of coke ash in hearth, were prepared by heating a mixture of CaCO3 and Al2O3. Experiments of the minerals coupled with carbon composite brick were carried out at different temperatures in a high temperature tube furnace. The mass change fraction of the experimental assembly was calculated using mass measurements before and after the experiment. The reaction products at different temperatures were predicted on the basis of ternary phase diagrams, and the thickness of the reaction layer was measured using scanning electron microscopy (SEM). The results show that the reaction rate of carbon composite brick with the minerals increased with an increase of the Ca content in the minerals. The results of reaction interface analysis show that the diffusion of Ca2+ was the dominant process during reaction. Cation diffusion was considered to be the rate determining step, and this was in agreement with experimental results. Therefore, reducing the ash content of coke, especially the CaO in ash, is the key to reduce the erosion rate of carbon composite bricks below the centerline of taphole.
  • A Mechanism Model for Accurately Estimating Carbon Emissions on a Micro Scale of Iron-making System

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    DOI:10.2355/isijinternational.ISIJINT-2018-239

    The research from the Reclaim Program in Los Angels and Tsinghua University shows the estimation error reaches up to 27%–50% via using the emission coefficient approach offered by IPCC. In principle, this approach only concerns the categories and amount of fuels though ignoring the systemic parameters and many process details. Therefore it is only applicable to the carbon emission estimation on a macro scale of an industry or a zone with a tolerable accuracy while the amount of carbon emissions is large. For more accurate estimation, a mechanism model considering the systemic parameters and the carbon metabolic processes of the iron-making system is established on a micro scale. In order to simplify the mechanism model, the iron-making system is divided into processing sectors and subsequently the carbon metabolic behaviors on systemic boundaries of sectors are parameterized for constructing the multiple agents. All agents are assembled by using the Petri net that indicates the links of sectors and the corresponding operation sequences. The mechanism model based on Hybrid PN–MaS formulates the quantitative relation between the carbon emission and systemic parameters and therefore can be used to accurately estimate the carbon emission from the iron-making system with multiple blast furnaces. Subsequently the systemic parameters including the allocation of materials, fuels, and the processing control parameters are discussed considering the objective of carbon emission reduction for the iron-making system on a micro-scaled level.
  • Effect of Brazing Temperature on Microstructure and Mechanical Property of High Nitrogen Austenitic Stainless Steel Joints Brazed with Ni–Cr–P Filler

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    DOI:10.2355/isijinternational.ISIJINT-2018-442

    In this study, Ni–Cr–P filler was used for vacuum brazing of high nitrogen austenitic stainless steels (HNS). The microstructure and shear strength of HNS joints were investigated by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction analysis (XRD) and universal testing machine. The results exhibit that Cr2N compounds are formed at the HNS/filler interface when the brazing temperature is lower than 1000°C. The brazing seam is composed of Ni–Fe solid solution and (Ni, Cr)3P compounds, and the content of (Ni, Cr)3P compounds decrease with the increasing of brazing temperature. The formation of Cr2N and (Ni, Cr)3P compounds is adverse to the joint strength due to their brittleness. The optimal shear strength of joints is 163 MPa when the brazing temperature is 1050°C.
  • Evolution of Inclusions and Associated Microstructure in Ti–Mg Oxide Metallurgy Steel

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    DOI:10.2355/isijinternational.ISIJINT-2018-445

    Evolution of inclusions from laddle furnace (LF) to continuous casting in Ti–Mg oxide metallurgy treatment were studied. The resuluts suggested that the composition of inclusions changed from MnS- MnO·SiO2 to (Ti–Ca–Mg–Al–O)–MnS. Furthermore, EDS results indicated that the content of Mg decreased because of reduction reaction, float and gasification. The average size of inclusions was decreased from 0.73 µm to 0.47 µm and the number density decreased from 977/mm2 to 595/mm2 after continuous casting. The microstructures changed from polygonal ferrite (PF) and ferrite side plate (FSP) to acicular ferrite (AF), PF and bainite (B) gradually after inclusion treatment (Ti–Mg oxide metallurgy) in LF furnace and Ca treatment in RH furnace. Heterogeneous nucleation of AF was observed on the surface of Ti–Mg oxides.
  • Molecular Dynamics Simulation of Carbon Effect on the Thermal Physical Properties of the Molten Iron

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    DOI:10.2355/isijinternational.ISIJINT-2018-513

    In this paper, the effect of the carbon on the thermal physical parameters of the molten iron at 1500 K–2500 K is studied using a molecular dynamics method based on the hybrid inter-atomic potentials. Results show that density of molten iron decreases linearly in accordance with the carbon or temperature rise, and such correlation is derived using a least square method. The viscosity of molten iron is also indicated to decrease with the temperature increase. In addition, the self-diffusion coefficient of molten iron is reducing with the carbon content rise. While the overall phonon thermal conductivity decreases along with the carbon content increase, the process appears to be fluctuating significantly.
  • Slow Strain Rate Tensile Test Properties of Iron-Based Superalloy SUH660 in Hydrogen Gas

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    DOI:10.2355/isijinternational.ISIJINT-2018-539

    To investigate dependence of strain rate of tensile test for iron-based superalloy SUH660 (A286), tensile tests were conducted for the specimens in 70 MPa hydrogen gas and air at 150°C. Nominal stress-nominal strain curve of each strain rate in 70 MPa hydrogen gas showed same behavior to maximum load via yield point in comparison with that in air, however, each elongation at breaking point in 70 MPa hydrogen was a little shorter than that in air. The values of tensile strength didn't depend on the strain rate in 70 MPa hydrogen as well as those in air. In addition, the difference in tensile strength wasn't observed between that in 70 MPa hydrogen gas and that in air for the strain rate. However, it's proved that relative reduction of area in 70 MPa hydrogen to that in air was significantly affected by strain rate of tensile test. Those values were 80%, 51%, and 32% in the case of strain rate 5.0×10-5, 7.5×10-6, and 1.25×10-6 s-1, respectively. The morphology of fracture surface also changed from dimple to quasi-cleavage (QC), with a decrease in strain rate. Simulation of hydrogen gas diffusion from surface to inside during experiment showed that the hydrogen diffusion layer of specimen with QC fracture surface (RRA 51%, strain rate 7.5×10-6 s-1) was only 0.25 mm in depth. That implies that hydrogen content at crack tips is much higher than that of simulation due to hydrogen concentration by a couple of defects. That tendency seems to become stronger with a decrease in strain rate.
  • Dynamic Distributions of Mold Flux and Air Gap in Slab Continuous Casting Mold

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    DOI:10.2355/isijinternational.ISIJINT-2018-609

    The distributions of mold flux and air gap in shell/mold gap have significant influences on the shell heat transfer in slab continuous casting mold. To describe the dynamic distribution characteristics of the mold flux and air gap, a three-dimensional thermo-mechanical model coupling with a complex interfacial heat transfer model was developed, in consideration of the interactions between the thermo-mechanical behaviors of solidified shell and distributions of mold flux and air gap. Based on these, the contact and heat transfer behaviors between the shell and mold copper plates, as well as the influence of wide face mold taper on the distributions of mold flux and air gap during a peritectic steel continuous casting were studied. The results show that the temperatures of copper plate hot faces beneath the bolt columns are higher than those beneath the deeper channels, and the calculated temperatures of copper plates coincide well with the measured data by thermocouples. Due to the thermal contraction, the shell corners in mold shrink away from mold corners as the slab moving downward, which causes the thick mold flux film and air gap concentrate around the corners and off-corners. As a result, the hot spots form at the shell off-corners. With greater wide face tapers, the thicknesses of mold flux film and air gap at wide face corner decrease. When the wide face taper increases to 4 mm, the air gap on shell wide face corner disappears near the mold exit.
  • Fabrication of Superoleophobic Surface on Stainless Steel by Hierarchical Surface Roughening and Organic Coating

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    DOI:10.2355/isijinternational.ISIJINT-2018-569

    Stainless steels is practically important corrosion-resistant metallic materials, and additional surface functionalities including self-cleaning, anti-fouling, anti-ice and snow sticking and fluid drag reduction by the introduction of superhydrophobic and superoleophobic surfaces are of recent interest. Here, we report the micro-/nano-hierarchical roughening of type 304 stainless steel surface by chemical and electrochemical etching and anodizing. Chemical etching in HCl + FeCl3 aqueous solution containing a surfactant introduces surface roughness of several tens micrometers scale and the electrochemical etching in HCl + HNO3 aqueous solution produces a number of etch pits of ~1 µm in size. Then, a porous anodic layer of the pore size of ~20 nm is formed on the etched surface by anodizing in ethylene glycol electrolyte containing 0.1 mol dm-3 NH4F and 0.1 mol dm-3 H2O. After fluoroalkylsilane (FAS) coating of the hierarchically rough surface to reduce the surface energy, the surface becomes superhydrophobic and superoleophobic; the advanced contact angle for hexadecane (surface tension of 27.6 mN m-1) is ~160° and the contact angle hysteresis is less than 10°. Since the FAS-coated flat surface is oleophilic, so that such hierarchically rough surface is of significant importance to achieve the superoleophobicity even for low surface tension liquids.
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  • Change in Composition of Inclusions through the Reaction between Al-killed Steel and the Slag of CaO and MgO Saturation

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    DOI:10.2355/isijinternational.ISIJINT-2018-584

    The inclusion of CaO–Al2O3 is occasionally observed during the secondary refining of Al-killed steel. In this study, MgO and CaO saturated slag was reacted with Al-killed steel in a MgO crucible, and the dissolution behaviors of Mg and Ca from the slag and the change in composition of inclusions were considered. Both the MgO and CaO in the slag were reduced from the presence of Al in the steel, and the concentration of dissolved Mg and Ca increased with the reaction time and Al concentration. When the Al concentration in the steel was 0.25 mass%, the concentration of dissolved Mg was 30 ppm or higher, whereas that of Ca was only 0.3 ppm. The initial Al2O3 inclusions transformed into a MgO·Al2O3 spinel, and finally changed into MgO inclusions rather than CaO–Al2O3 type inclusions. When the Al concentration was 0.75 mass%, the dissolved Ca concentration increased to 0.9 ppm, and the CaO–Al2O3 type inclusion with MgO was observed at 120 min. When the Al concentration further increased to 2.5 mass%, the concentrations of dissolved Mg and Ca increased to 110 and 3 ppm, respectively. The initial Al2O3 inclusions transformed into MgO inclusions within 5 min, and a CaO-Al2O3-type inclusion with MgO was observed after a 10 min reaction period. Finally, all inclusions transformed into a CaO-Al2O3-type inclusion with MgO at 120 min.
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