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

ISIJ International Advance Publication

  • Effect of Annealing Time on Oxides Phases and Morphology along Oxidized Depth of Fe-3%Si Steel during Decarburization

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    DOI:10.2355/isijinternational.ISIJINT-2018-441

    The decarburization experiments were carried out at different annealing temperatures, PH2O/PH2 and times. Under the annealing conditions in present work, the optimum annealing condition of decarburization was that annealing temperature was 1108 K under PH2O/PH2=0.317. The oxides morphology in oxidized layer was studied. The concentration distribution of silicon and oxygen along the oxidized depth was analyzed. The relationship between oxides phases, oxides morphology and concentration distribution of silicon and oxygen was established. Results showed four zones presented in oxidized layer from the atmosphere/steel interface to the steel matrix, which were enriched zone of oxides, depleted zone of oxides, spherical zone of oxides and lamellar zone of oxides in sequence. The oxidized layer of Fe-3%Si steel was composed of iron oxide, fayalite and silica. With the increase of oxidized depth, there was still some unreacted silicon atoms remained in the oxidized layer.
  • Ultrasonic Based Non-destructive Testing Technique for Predicting Shape Defects in Rolled Steel Sheets

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    DOI:10.2355/isijinternational.ISIJINT-2018-499

    Shape defect such as bow and crossbow, is one of the major defects in hot rolled sheets. These defects arise due to non-uniform plastic strain (thermal and mechanical) due to improper rolling process. In-turn this non-uniform strain induces residual stress in the rolled material. Hence measurement of residual stress in early stage helps as a Go/No Go tool, while supplying material to customers to whom shape defects are very much problematic during its downstream process. In this paper a non-destructive testing (NDT) technique has been developed to predict the magnitude of bow/crossbow based on residual stress measurement using ultrasonic technique. The technique employs the relationship between residual stress distribution and its corresponding effect towards bow/crossbow formation. The paper also elaborates about residual stress measurement using ultrasonic measurement based on the acousto-elastic theory. It was demonstrated that there exists a distinct relationship between crossbow and residual stress for high strength hot rolled steel sheets experimentally.
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    1. Mathematical Modelling of the Effects of Transient Phenomena on Steel Cleanness during Tundish Transfer Practices ISIJ International Advance Publication
  • Preparation of High-Carbon Metallic Briquette for Blast Furnace Application

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    DOI:10.2355/isijinternational.ISIJINT-2018-421

    Developments in blast furnace (BF) ironmaking have long focused on low-coke operation. In this study, high-carbon metallic briquettes (HCMB) were prepared using ultrafine iron oxide powders and coal fines for BF application. The preparation conditions were optimized, and the binding mechanism of the briquette was analyzed. The gasification behavior of the optimally prepared HCMB was investigated under conditions simulating the in-furnace environment of the BF, and its application in BF was evaluated through numerical simulations. The results showed that the optimal preparation condition was mhematite/mcoal = 2.0. The optimally prepared HCMB had a carbon content of 25.6 wt%, cold strength (CS) of 1300 N/briquette, and crushing strength after reaction (CSR) of 2500 N/briquette. The high strength of the briquette was attributed to the iron network binding. The threshold temperature and activation energy of the briquette gasification in the blast furnace were 973 K and 166 kJ/mol, respectively. Simulation results on the HCMB application in a BF of 2500 m3 indicated that mixing HCMB of 5% into the ore burden could save approximately 12.5 kg of coke for producing one ton hot metal from the ore.
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    1. Mathematical Modelling of the Effects of Transient Phenomena on Steel Cleanness during Tundish Transfer Practices ISIJ International Advance Publication
  • Flow Instabilities in the Horizontal Single Belt Casting Process with an Inclined Feeding System

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    DOI:10.2355/isijinternational.ISIJINT-2018-514

    Both physical experiments and mathematical simulations were employed to investigate the transport phenomena involved during Horizontal Single Belt Casting (HSBC) of AA6111 aluminum alloy, using an inclined feeding system. Flow instabilities in the metal delivery system were first analyzed, and it was found that the first impingement gives rise to instabilities in the melt film falling from the slot nozzle of the head box. Meanwhile, this impingement also has the potential to result in air suction. Using the Eulerian multiphase method, the start casting stage is shown to be very short. Its predictions are similar to those from the Volume of Fluid (VOF) method, and both are confirmed by physical experiments. During steady state casting, one can classify the melt into four regions. The "wavy contour" in "Region I" is an instability largely induced by impingement on an inclined refractory piece. "Region II" demonstrates the buffer effect of the inclined refractory wall and the flow must be continuous within it. The resistance force induced by the melt that has flowed just earlier onto the belt, gives rise to "Region III", which is a transition region. Its transient variations in width determine the quality of the strip's edges. The thickness of "Region IV" is associated with both "Region II" and "Region III".
  • Mathematical Modelling of the Effects of Transient Phenomena on Steel Cleanness during Tundish Transfer Practices

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    DOI:10.2355/isijinternational.ISIJINT-2018-527

    Transient phenomena during tundish transfer practices have shown to be detrimental for the significance of clean steel production. These have become a distress for steelmakers; for this reason, there is opportunity for innovation in molten steel transfer devices, such as the dissipative ladle shroud. In the present modelling study the performance of this devise is fully analysed in order to quantify its efficiency in the reduction of the emulsification phenomenon and the slag aperture areas using a mathematical model to simulate a real steel-slag-air multiphase system during the ladle change-over practice. The most relevant results show that the convectional ladle shroud delivers a very turbulent steel flow generating strong mixing patterns, entrapping massive amount of air and slag into the tundish bath promoting a continuous emulsification and a permanent aperture of the slag layer. These phenomena are significantly reduced by using the dissipative ladle shroud technology since this innovative design reduces the emulsification phenomenon in more than a 50% and could decrease the steel re-oxidation by the reduction of the slag layer aperture in about 80%, all in comparison to the conventional ladle shroud; these will represent a diminishment in the amount of declassed steel to a less demanding application.
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    1. Ultrasonic Based Non-destructive Testing Technique for Predicting Shape Defects in Rolled Steel Sheets ISIJ International Advance Publication
    2. Preparation of High-Carbon Metallic Briquette for Blast Furnace Application ISIJ International Advance Publication
  • Influence of Microsegregation on the Onset of the Martensitic Transformation

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    DOI:10.2355/isijinternational.ISIJINT-2018-424

    Due to the volume change accompanying the fcc to bcc or bct crystal structures in steels, it is a common practice to determine phase transformation temperatures using dilatometry. The martensite start temperature (Ms) is often of particular interest. Experimentally, it is found that the start of the martensite transformation is not indicated by a sharp change in the slope of the dilatation curve as is predicted by the Koistinen – Marburger equation. Rather, there is a gradual change in the slope such that the martensite start temperature is ill-defined. The current work shows that this gradual change in slope can be related to chemical inhomogeneity in the steel caused by interdendritic microsegregation. It is shown that combining the Koistinen – Marburger equation with measured concentration profiles allows experimental dilatation curves to be well predicted.
  • Phase Transformation Behavior of Oxide Scale on Plain Carbon Steel Containing 0.4 wt.% Cr during Continuous Cooling

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    DOI:10.2355/isijinternational.ISIJINT-2018-365

    Pre-oxidation in air at 750°C for 10 min, the plain carbon steels without Cr and containing 0.4 wt.% Cr tended to rapidly form oxide scale composed of outer Fe3O4 layer and inner FeO layer. Moreover, a FeCr2O4 layer was observed at the FeO/substrate interface on the steel containing Cr. A comparative study was carried out between the scales on the two steels in inert gas cooled from 350–600°C to room temperature at the cooling rate range of 1–40°C/min, to determine the effect of low concentration Cr addition on the phase transformation of FeO. Based on the cross-sectional morphologies of oxide scale during various cooling conditions, the relationship between cooling rate and start cooling temperature were constructed, and the area fraction of eutectoid structure was analyzed. The result shows that the transformation rate and area fraction of eutectoid structure in oxide scale on steel containing Cr were greater than that on steel without Cr, and then the nucleation, growth and 100% transformation region of eutectoid structure in oxide scale on steel without Cr were delayed. This study proposed two mechanisms to discuss the experimental results. Firstly, the formation of FeCr2O4 layer reduced the consumption of O, and then prevented short-range uphill diffusion of Fe from FeO to substrate. Secondly, combined with the lamellar spacing in eutectoid structure and the Fe–Cr–O equilibrium phase diagram, the Cr addition increased the formation temperature of FeO in oxide scale, which provided sufficient driving force for eutectoid transformation during continuous cooling.
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    1. Influence of Microsegregation on the Onset of the Martensitic Transformation ISIJ International Advance Publication
    2. Fusion Zone Microstructural Evolution of Al-10% Si Coated Hot Stamping Steel during Laser Welding ISIJ International Advance Publication
  • Fusion Zone Microstructural Evolution of Al-10% Si Coated Hot Stamping Steel during Laser Welding

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    DOI:10.2355/isijinternational.ISIJINT-2018-489

    Fusion zone microstructural evolution of Al-10% Si coated hot stamping steel during laser welding and its mechanical properties were investigated in this study. During laser welding, a liquidized Al-10% Si coating penetrated along the fusion boundary to form δ-ferrite. After hot stamping heat treatment, the final microstructure was composed of a martensite-ferrite dual phase. The dual phase formation causes mixed mode fracture (brittle fracture + ductile fracture) at the fusion zone due to the hardness difference between the martensite and ferrite phases. This issue can be addressed by applying filler wire or by changing the coating system from an Al-based coating to a Zn-based coating.
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    1. Influence of Microsegregation on the Onset of the Martensitic Transformation ISIJ International Advance Publication
    2. Effect of Microsegregation on the Delayed Fracture of High Strength Steels Tetsu-to-Hagané Vol.69(1983), No.1
    3. 日本鉄鋼協会第105回講演大会 講演概要集(I) その3 Tetsu-to-Hagané Vol.69(1983), No.4
  • End-to-end Billet Identification Number Recognition System

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    DOI:10.2355/isijinternational.ISIJINT-2018-506

    In steel industry, product number recognition is necessary for factory automation. Before final production, the billet identification number (BIN) should be checked to prevent mixing billets of different material. There are two types of BINs, namely, paint-type and sticker-type BINs. In addition, the BIN comprises seven to nine alphanumeric characters except the letters I and O. The BIN may be rotated in various directions. Therefore, for proper recognition and accident prevention, end-to-end BIN recognition system that uses the deep learning is proposed. Specifically, interpretation and sticker extraction modules are developed. Furthermore, the fully convolutional network (FCN) with deconvolution layer is used and optimized. To increase the BIN recognition accuracy, the FCN was simulated for various structures and was transferred from the pre-trained model. The BIN is identified by the trained FCN model and interpretation module. If the BIN is sticker-type, it is inferred after the sticker region is extracted by the sticker extraction module. The accuracy of the proposed system was shown to be approximately 99.59% in an eight-day period.
  • Effect of Nb on the As-cast Structure and Compactness Degree of Ferritic Stainless Steel Dual Stabilized by Ti and Nb

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    DOI:10.2355/isijinternational.ISIJINT-2017-595

    The effect of Nb on the as-cast structure and compactness degree of ferritic stainless steel (FSS) dual stabilized by Ti and Nb are investigated. In this study, the as-cast structure of experimental ingots were almost composed of equiaxed grains and Ti-Mg-Al-oxide enveloped by Ti(C,N) or (Ti,Nb)x(N,C)y, namely complex nucleus, was found in the interior of FSS grain. When Nb was added to FSS, the as-cast grain size became smaller and the grain boundary precipitates (BP) became smaller and more dispersed. In addition, the composition of the outer layer of the complex nucleus and the BP both converted from Ti(C,N) to (Ti,Nb)x(N,C)y. Thermodynamics analysis showed that, the solidification region will be extended by Nb, which will be beneficial to the nucleation of complex nucleus. Complex nucleus is theoretically possible to form and exhibits good nucleation effect on δ-Fe as well as TiN according to the disregistry calculation. What's more, (Ti,Nb)x(N,C)y particles in BP will be formed at the end of solidification and will prevent the grain merging by pinning effect.
  • Off-line Model of Blast Furnace Liquid Levels

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    DOI:10.2355/isijinternational.ISIJINT-2018-417

    An off-line simulation model of the blast furnace hearth is developed based on mass balances for iron and slag, expression of the liquids outflow rates and logical conditions for the start and the end of the outflow of liquids. The dynamic model divides the furnace hearth into two regions of sizes that may change during the tapping process. It provides a description of the time evolution of the liquid levels and predicts the duration and the periods of iron- or slag-only flow in the beginning of the taps. The values of some model parameters are estimated on the basis of measurements in a reference blast furnace, while others are fixed. A sensitivity analysis of the model is provided, revealing the role of some key parameters. The model is demonstrated to describe the overall drainage behavior of the reference furnace reasonably well, and the presence of pools with different liquid levels can also be deduced from the real data. Finally, some recommendations for future work are suggested.
  • Recovery of Fe, Ni, Co, and Cu from Nickel Converter Slag through Oxidation and Reduction

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    DOI:10.2355/isijinternational.ISIJINT-2018-533

    The conventional method of nickel converter slag dilution is reduction–sulfurization by adding coal and pyrite into the slag. In this study, the effect of sulfur content in the initial slag ((pct S)0) on the slag dilution process was determined by producing metal, which is significantly different from the conventional method producing matte. Analysis of the nickel converter slag showed that nickel, cobalt, and copper were mainly present in the form of sulfides, which are difficult to separate from the slag. The NiO, CoO, and Cu2O in the slag are easily reduced into metal using carbon, while the presence of sulfur inhibits the reduction reaction. In a vertical resistance furnace, the desulfurized slags with different sulfur contents were reduced using carbon. The sulfur distribution rate increased with the decrease in (pct S)0; the distribution of nickel, cobalt, and copper decreased with the decrease in (pct S)0. The nickel recovery rate increased with the decrease in (pct S)0, while (pct S)0 almost had no effect on the recovery of iron, cobalt, and copper. The distribution rates of sulfur, nickel, and copper increased with the increase in mole ratio of carbon to reducible oxygen (nC/nO), while the distribution rate of iron and cobalt decreased with the increase in nC/nO. In addition, the recovery rates of iron, nickel, cobalt, and copper increased with the increase in nC/nO.
  • Gasification and Migration of Phosphorus from High-phosphorus Iron Ore during Carbothermal Reduction

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    DOI:10.2355/isijinternational.ISIJINT-2018-372

    The effect of different gangue oxides(Al2O3, SiO2 and Fe2O3) on the gasification and migration of phosphorus during the carbothermal reduction of fluorapatite has been investigated. The vaporization of phosphorus during the carbothermal reduction of synthesized model sample demonstrating a high-phosphorus iron ore was analyzed by gas mass spectrometry. Results revealed that the dephosphorization of fluorapatite was promoted by Al2O3 and SiO2 to form CaAl2O4 and CaSiO3, respectively. The promotion effect of SiO2 was larger than that of Al2O3. With the increase in the addition of gangues, the thermodynamic conditions for the reduction of fluorapatite were continuously optimized, thereby accelerating the dephosphorization of fluorapatite. At a C/O (O originated from fluorapatite and Fe2O3) of larger than 1 in molar ratio, P2 was the the dephosphorization product. Whereas, at a C/O of less than 1, the dephosphorization product turn to PO. With the addition of Fe2O3 to fluorapatite, a large amount of phosphorus was absorbed by liquid iron, resulting in a decrease of the amount of volatilized P2, leading to the slow increase or decrease in the dephosphorization ratio of the pellets. Phosphorus was absorbed by liquid iron as P2, whereas PO gas was completely volatilized. Gasification dephosphorization mainly occured from 10 min to 25 min at 1200°C. These findings leads to a new idea on the dephosphorization of a high -phosphorous iron ore, that is, decreasing the reduction temperature to retard melting of iron and simultaneously adding the additives to promote the dephosphorization of fluorapatite.
  • Degradation and Microstructure Changes of Tuyere Coke Behavior of a COREX-3000 Furnace

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    DOI:10.2355/isijinternational.ISIJINT-2018-409

    The behavior of tuyere coke obtained from a COREX-3000 process was investigated in the present study for an in-depth understanding for the condition of raceway. The coke samples was obtained in a dissection process of the furnace, and coke samples at P1 (200 mm from tuyere sleeve towards the furnace center), P2 (400 mm from tuyere sleeve towards the furnace center), P3 (600 mm from tuyere sleeve towards the furnace center), P4 (800 mm from tuyere sleeve to the furnace center), P5 (1000 mm from tuyere sleeve to the furnace center) and P6 (1200 mm from tuyere sleeve to the furnace center) were sieved, and the particles size distribution and average size of different position has been calculated. Microstructure of coke samples at P2, P4 and P6 was examined using scanning electron microscopy, and carbon structure and mineral phases of coke samples at P6 were identified using X-ray diffraction (XRD) analysis. The results showed that the percentage of small coke particles (<10 mm) was higher at P5 and P6, and the average particle size of coke samples at P5 and P6 were 12.04 mm and 7.71 mm, which is much smaller than that of other samples indicating a severe degradation of coke. The amount of pores of tuyere coke increased compared with charged coke, and more pores were found in coke sample at P6 than P2 and P4, indicating a violent reaction at this position. The graphitization degree of tuyere cokes at P6 were much higher than that of charged coke, and coke particle (10–16 mm) possess the highest graphitization degree, indicating the much higher temperature in the raceway zone. The main minerals in the tuyere coke were gehlenite and akermanite, and the slag was melt to be spherical particles confirming the higher temperature in raceway zone in COREX-3000 process.
  • Experimental Investigation of Relationship between Enthalpy Change and Viscosity in Blast Furnace Type Slags

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    DOI:10.2355/isijinternational.ISIJINT-2018-572

    The effects of MgO, Al2O3 and basicity on the heat capacity and enthalpy change of CaO–SiO2–MgO–Al2O3 slags at 1673 K and 1773 K as well as the thermal stability were investigated. The enthalpy change at 1773 K increased with the addition of Al2O3 and MgO, but decreased with increasing basicity. Thus, the higher basicity helped to reduce the heat consumption and fuel ratio of blast furnace. With increasing MgO content, the fluctuations of the temperature and viscosity caused by the reduction of the slag heat quantity decreased. Furthermore, the slag will have a better fluidity and thermal stability when MgO content is greater than 8 mass%. The increase of Al2O3 content deteriorated the fluidity and thermal stability of the slag to some extent. When the reduction of the slag heat quantity was fixed, as the basicity increased, the slag temperature increased obviously and the viscosity significantly decreased. Also, the fluctuations of slag temperature and viscosity became less pronounced with increasing basicity. The increase of the basicity was favorable to improve the fluidity and thermal stability of the slag. For the slag system of this experiment, the suitable basicity was 1.10–1.15.
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    2. Effect of TiO2 and MnO on Viscosity of Blast Furnace Slag and Thermodynamic Analysis ISIJ International Advance Publication
    3. Off-line Model of Blast Furnace Liquid Levels ISIJ International Advance Publication
  • Effect of Size of Ferrotitanium on the Melting Behavior and the Yield in the Refining of Interstitial Free Steel by RH De-gasser

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    DOI:10.2355/isijinternational.ISIJINT-2018-292

    The reduction of ferroalloy consumption used in the steel making is an important approach to high-performance and low-cost steel manufacture. In this paper, the effect of size of ferrotitanium on the yield in the refining of interstitial free steel by RH de-gasser was investigated. Motion trajectory of ferrotitanium after the addition into molten steel in RH de-gasser was investigated through water model experiment. The effect of size of ferrotitanium on the melting time was investigated by numerical simulation. Combining water model experiment with numerical simulation, the loss mechanism and effect of size on the yield of ferrotitanium were discussed. It was found that the size of ferrotitanium larger than a certain value has a great opportunity of floating up to the interface of molten steel and slag in ladle and being oxidized there. Results of industrial experiment verified the mechanism. As for a 300 tons RH de-gasser, Fe-70%Ti alloy whose size was larger than 43 mm had a low yield because of oxidation by the ladle slag.
  • Vanadium Alloy Steel DIN 30MnVS6 Applied in Cold Forming Manufacture

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    DOI:10.2355/isijinternational.ISIJINT-2018-342

    Vanadium alloy steels are still little known and debated when applied to the cold forming process, it is not clear what the performance of their mechanical performance is compared to traditional steels that the market already uses.The possibility of reducing costs and generating competitiveness, are the basis for studies that generate new opportunities for industries. In this article, the possibility of withdrawing the heat treatment process, directed the performance of the tests presented here.This paper deals with the performance comparison of DIN 30MnVS6 steel compared to ISO 898-1, which deals with mechanical performance for bolts. The tests were correlated with the bolts of resistance class 8.8, which currently have heat treatment. It is possible to evaluate the positive performance of the vanadium-alloyed steel DIN 30MnVS6, despite the occasional performance limitations in some attributes addressed in ISO 898-1.
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    1. Effect of TiO2 and MnO on Viscosity of Blast Furnace Slag and Thermodynamic Analysis ISIJ International Advance Publication
  • Effect of TiO2 and MnO on Viscosity of Blast Furnace Slag and Thermodynamic Analysis

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    DOI:10.2355/isijinternational.ISIJINT-2018-379

    The effect of TiO2 and MnO on the viscous behavior and structure of CaO–SiO2–MgO–Al2O3–TiO2–MnO slags were studied using rotating cylinder method and FTIR spectroscopic analysis. Furthermore, the heat capacity and enthalpy change of the slag were calculated to clarify the influence of TiO2 and MnO on the heat quantity of the slag at elevated temperatures, and then the equilibrium temperatures and corresponding viscosities of the slag under various fixed heat quantities were also analyzed. The higher TiO2 and MnO contents resulted in lower viscosity. The FTIR results revealed that TiO2 and MnO depolymerized the slag by modifying the silicate network structure and breaking the linkage between the silicate and aluminate structure, while have little effect on aluminate structure of the slag. In the temperature range of interest, the enthalpy change of the slag increased with increasing TiO2 content, but remained basically unchanged with MnO additions. The fluctuations of the slag heat quantity had a significant influence on the slag temperature and viscosity. With the increase of TiO2 content, the equilibrium temperature of the slag at fixed heat quantity decreased and the corresponding viscosity increased. However, as the MnO content increased, the equilibrium temperature of the slag at fixed heat quantity was almost constant and the corresponding viscosity decreased.
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    3. Vanadium Alloy Steel DIN 30MnVS6 Applied in Cold Forming Manufacture ISIJ International Advance Publication
  • Mathematical Model and Plant Investigation to Characterize Effect of Casting Speed on Thermal and Solidification Behavior of an Industrial Slab Caster

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    DOI:10.2355/isijinternational.ISIJINT-2018-423

    Development of a validated 3D transient mathematical model for modeling the fluid flow and solidification process in an industrial continuous slab caster has been demonstrated. The model couples thermo-fluid aspect of mold and sub-mold region by utilizing a standard Enthalpy-porosity method. Extensive plant level measurements of mold heat fluxes and thermocouples data, breakout shell thickness profile, and macrostructures were carried out to evaluate proper input of heat transfer and other conditions for the model. A suitable validation of the model is established with slab surface temperature and solidified shell thickness profile as measured from a breakout shell in the caster plant. An insight is drawn for an industrial slab caster from the model results analysis for a range of operating parameters of casting speed and SEN submergence depth as employed in the caster. Evolution of a solidified shell thickness profile is simulated. Slab surface temperature mapping is drawn from the model and discussed its variation originating due to fluid flow inside the solidified shell. Casting speed is shown to have a dominant effect as temperature rise of order of 50°C are observed as it is increased from an average plant value of 1.4 m/min to peak of 1.8 m/min. Similar effect is also reflected in the solidified shell thickness profile as shell thickness gets thinner by an order of 6 mm in the sub-mold region due to increase in casting speed from an average to peak value. The effect of SEN submergence depth is also outlined.
  • Effects of Sulfur and Titanium Interaction in Molten Pig Iron on Erosion of Carbon Brick

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    DOI:10.2355/isijinternational.ISIJINT-2018-467

    The service life of blast furnace is largely determined by the erosion of carbon brick. The experiments were carried out to investigate effects of sulfur and titanium interaction in molten pig iron on erosion of carbon brick. The experimental results show that the erosion of carbon brick was enhanced when the sulfur content increased separately in molten pig iron, however, this effect could be made up by addition of titanium in molten pig iron. The control standard of sulfur content and titanium content in molten pig iron was proposed, which was combined with the operation to delay the erosion of carbon brick. The quantitative relationship between the erosion rate and sulfur and titanium interaction at 1773 K was obtained based on experimental data, when sulfur content increased by 0.01%, the increment of titanium content by 0.015% would be needed to compensate for the effect of sulfur content on the erosion. The mechanism of sulfur and titanium interaction was analyzed through the erosion process of carbon brick, the difference between the influences of two elements on the surface tension and viscosity of molten is the essential cause of the interaction.
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    2. Image-based Method for Measuring Pellet Size Distribution in the Stable Area of Disc Pelletizer ISIJ International Advance Publication
    3. Effect of TiO2 and MnO on Viscosity of Blast Furnace Slag and Thermodynamic Analysis ISIJ International Advance Publication
  • A Kinetic Model on Oxygen Transfer at a Steel/Slag Interface under Effect of Interfacial Tension

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    DOI:10.2355/isijinternational.ISIJINT-2018-303

    A kinetic model was developed to predict the dynamic change of the oxygen content in the sub-interface region as well as the dynamic change of the interfacial tension between molten steel and slag. The dynamic steel/slag interfacial phenomena are very complex, where the combined effect of thermodynamics and kinetics on the interfacial tension needs to be accounted for. As a first step, the current model only considers the SiO2 decomposition, oxygen adsorption and desorption at the steel/slag interface to realize the modeling of the dynamic change of the steel/slag interface phenomena. The oxygen desorption rate was derived based on the slope of the interfacial tension change over oxygen content. Specifically, the oxygen change with time in a sub-interface was predicted by the current model. The oxygen desorption rate was found to have an important influence on the dynamic change of the oxygen content in the sub-interface region. Furthermore, a low slag viscosity was found to increase the oxygen content at the interface due to the fast supply of SiO2 from the slag bulk to the interface. In addition, the equilibrium constant for the oxygen adsorption at an interface due to the interfacial tension effect increases the oxygen content in the sub-interface region.
  • The Effect of Manganese on the Thermodynamic Property of Tellurium in Molten Iron

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    DOI:10.2355/isijinternational.ISIJINT-2018-315

    The effect of manganese on the thermodynamic property of tellurium in molten iron was experimentally evaluated as an interaction parameter using a vapor-liquid equilibration technique, where the vapor pressure of tellurium was controlled using the transpiration method. Manganese was found to stabilize tellurium in molten iron and its effect was relatively small compared to other alloying elements.
  • Characterization on Microstructure and Carbides in an Austenitic Hot-work Die Steel during ESR Solidification Process

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    DOI:10.2355/isijinternational.ISIJINT-2018-370

    The current work was undertaken to systematically examine the as-cast microstructure and carbides in a developed austenitic hot work die steel produced by conventional electroslag remelting (ESR) and continuous directional solidification of electroslag remelting (ESR-CDS). In addition, the growth pattern of carbides was also discussed. A combination of optical microscopy (OM) and scanning electron microscopy (SEM) were used to characterize microstructure and carbides. The segregation was analyzed using an original position analyzer (OPA) and electron probe microanalysis (EPMA). The electrolytically extracted carbides were analyzed by SEM and x-ray diffraction (XRD) to identify their three-dimensional microstructure and compositions. The microstructure of electroslag remelted austenitic die steel was composed of austenite matrix and primary carbides V8C7-type and Mo2C-type. Compared with conventional ESR, ESR-CDS contributed to a finer as-cast microstructure, a smaller amount and smaller size of carbides in remelted steel. Meanwhile, the alloying elements segregation was reduced through ESR-CDS. The enrichment of carbide-forming elements was reduced through directional solidification of ESR, resulting in the change in the morphology of V-rich carbides from rod-like to lamellar-shaped. The hardness and V-notched impact energies of remelted ingot (produced by ESR-CDS) after heat treatment (solution temperature 1180°C for 2 hours, aging temperature 720°C for 2 hours) was increased by 3 to 5HRC and 4 to 6 J/cm2 respectively, in comparison with that produced by conventional ESR.
  • Effect of Rb2O on Inclusion Removal in C96V Saw Wire Steels Using Low-Basicity LF Refining Slag

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    DOI:10.2355/isijinternational.ISIJINT-2018-385

    A novel Rb2O-containing synthetic LF refining slag has been developed in order to produce ultraclean C96V saw wire steel. In addition, the thermodynamic and kinetics mechanism of Rb2O on inclusion removal have been discussed fully. The results indicated that (1) Rb2O additions (≤10.00 wt%) seems to significantly enhance inclusion removal in steel melts. ① The average diameter of nonmetallic inclusions decreased significantly with the Rb2O addition in synthetic LF refining slag increasing. In particular, the diameter of most of inclusions was less than 3.0 × 10-6 m (3.0 µm) when Rb2O addition was 10.00 wt% ② The number of nonmetallic inclusions decreased sharply with the content of Rb2O in synthetic LF refining slag raising. ③ Both of the MnO–SiO2–Al2O3, CaO–SiO2–Al2O3 inclusions system mainly concentrated in the low melting point zone. (2) For the 15.00 wt% Rb2O-containing synthetic LF refining slag, not only the average diameter of inclusion increases slightly with reaction times increasing, but also the number. This is due to the fact that, the effect of Rb2O on the ability of refining slag to absorb inclusions is a double-edged sword: On the one hand, Rb2O addition would promote the thermodynamic conditions of inclusion removal, then, inclusions would enter the slag spontaneously easier. On the other hand, Rb2O addition could also exacerbate the kinetic conditions of inclusion removal by increasing the viscosity of slag at the same time.
  • Numerical Simulation of Desulfurization Behavior in Ladle with Bottom Powder Injection

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    DOI:10.2355/isijinternational.ISIJINT-2018-406

    A computation fluid dynamics–population balance model–simultaneous reaction model (CFD–PBM–SRM) coupled model was used to predict the reaction kinetic and desulfurization behavior in 80 ton ladle with bottom powder injection. The reaction rate and evolution of multi-components including Al, S, Si, Mn and Fe at the powder droplet–liquid steel interface, bubble–liquid steel interface, top slag–liquid steel interface and air–liquid steel interface were revealed. Then, the effects of different kinetic conditions on the desulfurization efficiency were investigated, and the importance of various mechanisms was discussed and clarified. The results show that at the lower powder injection rate, the desulfurization is mainly attributed to the joint effort of both powder–liquid steel reaction and top slag–liquid steel reaction which is the prevailing mechanism. At the higher powder injection rate, the powder particle–liquid steel and bubble–liquid steel interface reaction become more important and then predominate the desulfurization behavior. With the increase of gas flow rate, the total desulfurization ratio gradually decreases, and with the increasing of powder injection rate, the total desulfurization ratio increases.
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  • Numerical Study of Inclusion Removal in Steel Continuous Casting Mold Considering Interactions Between Bubbles and Inclusions

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    DOI:10.2355/isijinternational.ISIJINT-2018-319

    Bubble coalescence-breakup and bubble-inclusion interaction models were implemented into Eulerian-Lagrangian models of steel liquid flow and discrete particles transport, which was applied to examine the interaction and removal of discrete bubbles and inclusions during continuous casting. Bubble distribution affected by coalescence-breakup and its connection with the inclusion removal rate were analyzed. The inclusion removal rates at different initial bubble diameters and inclusion diameters were predicted. Larger inclusions have a higher removal rate and the predicted removal rates ranging from 14% to 30% agree well with industrial experiment measurements. It is also found that smaller bubbles have a higher capacity to remove inclusions and very small bubbles may cause more production defects when it is attached to inclusions. These results show that the developed model can reasonably predict the behaviors of discrete bubbles and inclusions and their interactions in molten steel. Such a model should be useful for the operation of steel continuous casting.
  • Effect of Introducing Coke into Ore Layer on Softening-melting-dropping Characteristics of Vanadium-titanium Mixed Burden under Simulating BF Conditions

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    DOI:10.2355/isijinternational.ISIJINT-2018-175

    Coke-ore mixed charging is a well-known and effective measure to strengthen BF operation and realize low reducing agent BF ironmaking. The objective of this paper is to investigate the effect of coke-ore mixing ratio on softening-melting dropping performance and permeability of vanadium-titanium mixed burden and to clarify the interaction mechanism between mixed nut coke and iron-bearing burden under BF simulating conditions. It was found that the softening-melting-dropping behaviors and permeability of mixed burden get improved obviously with a coke-ore mixing ratio of 20%. However, the generation of carbide of V and Ti would be accelerated with further increasing coke-ore mixing ratio to 50%, which would deteriorate the fluidity of slag and worsen the dropping behavior of mixed burden and lower the yield of V in liquid iron. The interaction between nut coke and vanadium-titanium mixed burden could be summarized as four parts, namely reduction strengthen, carburization promotion, permeability improvement, and the precipitation of the carbide of titanium.
  • Using Red Mud-based Flux in Steelmaking for High Phosphorus Hot Metal

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    DOI:10.2355/isijinternational.ISIJINT-2018-339

    To smelt high phosphorus hot metal effectively, a new flux named Red Mud (RM) was applied in steelmaking to form CaO–FeO–SiO2–Al2O3–Na2O slag. Good slag fluidity and dephosphorization effects can be achieved when using RM-based flux in simulated steelmaking for high phosphorus hot metal. The dephosphorization rates of the RM-based flux were all greater than 82%. Especially, when RM:CaO=1:1.2, high dephosphorization rate (~95%) and low final [P] (=0.02%) was achieved in the situation of high [C] =1.36%. This is of great importance for the production of clean steel. The P2O5 content in the P-rich phase in RM-based slag can reach 29.1 wt%, far higher than the 9.1 wt% in lime-based slag.
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    1. Phosphorus Partition and Phosphate Capacity of Basic Oxygen Steelmaking Slags ISIJ International Advance Publication
  • Image-based Method for Measuring Pellet Size Distribution in the Stable Area of Disc Pelletizer

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    DOI:10.2355/isijinternational.ISIJINT-2018-384

    Disc pelletizer is widely used in the agglomeration process to form powdered iron ore into iron ore green pellets. The pellet size distribution (PSD) is one of the major measures of product quality. An imaging system is developed for measuring PSD in the stable area of the disc pelletizer. Image pre-processing is performed to extract the densely distributed pellets as foreground, followed by identifying surface pellets using pellet markers and K-means clustering method. Then a marker-controlled watershed algorithm is applied to segment overlapping pellets in the image. The pellet sizes and thus PSD are then obtained using circumscribed circle fitting. The proposed image-based measuring method was tested in a steel company. The measured PSD was compared with manual sieving results. It shows good accuracy for different size ranges under different pelletizing conditions. The proposed method also makes it possible to evaluate online the pellet quality.
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    3. Effect of TiO2 and MnO on Viscosity of Blast Furnace Slag and Thermodynamic Analysis ISIJ International Advance Publication
  • Phosphorus Partition and Phosphate Capacity of Basic Oxygen Steelmaking Slags

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    DOI:10.2355/isijinternational.ISIJINT-2018-129

    The phosphorus partition (LP) and phosphate capacity (CPO43−) were measured for slags in the CaO–SiO2–MgO–FetO–(MnO–Al2O3–TiO2–P2O5) system over temperatures representative of basic oxygen steelmaking. The measured LP values were found to be in good agreement with those predicted from the model of Assis et al. The oxygen potential of the slag-metal systems studied was also evaluated and used in combination with the measured LP to calculate the CPO43− of the slags. Capacity values in the range of 7.77×1016 to 4.27×1019 for temperatures 1550°C to 1700°C were obtained.Correlations of CPO43− with common measures of slag basicity (v-ratio and optical basicity) were sought and reported. Consistent with other researchers it was found that the LP and CPO43− increased with increasing slag basicity and decreasing temperature.
  • Radar Detection-based Modeling in a Blast Furnace: a Prediction Model of Burden Surface Shape after Charging

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    DOI:10.2355/isijinternational.ISIJINT-2018-267

    Radar detection is an advanced method for monitoring a blast furnace's inner burden surface shape, which is an important factor that largely affects the production efficiency of the iron-making process. In this paper, a radar detection-based model for the prediction of burden surface shape was developed for assisting operators in developing a charging strategy. The data used are composed of both the detection and controlling records of a real, working-state blast furnace obtained by mechanical swing radar and a furnace database system, respectively. By defining and analyzing the stacking density function, the physical meanings of the modeling principles were revealed. Combined with the classical force charging trajectory sub-model and detection-driven burden descent calculation, the proposed model adopts Gaussian radius basis functions to approximate the stacking mechanism of the burden charging process. The parameter identification results show that the model can approximate the burden surface radius profile well. Compared with the results obtained for coke layers, the parameters' ranges for the ore layers are narrower. Performance comparison shows that the proposed model has the advantages of higher prediction accuracy for both local details and global shape over the classical polygonal line model.
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    3. Effects of Sulfur and Titanium Interaction in Molten Pig Iron on Erosion of Carbon Brick ISIJ International Advance Publication
  • In-situ Analysis and Numerical Study of Inclusion Distribution in a Vertical-bending Caster

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    DOI:10.2355/isijinternational.ISIJINT-2018-283

    Based on a fast-detection platform (FDP) founded by us, an in-situ measurement of inclusion distribution in slab is successfully performed. The inclusion distribution is obviously asymmetry and non-uniform. Specially, due to the structure differences in the vertical and bending part of a slab caster, the inclusion distribution in these two parts are quite different: In the vertical part, the inclusions entrapped in the outer arc is much more than that in the inner arc, while in the bending part, the inclusions entrapped in the outer arc is a little less than that in the inner arc. Large inclusions are tend to be found near the surface, and sometimes in the center, but they're very few. Then in order to interpret the inclusion distribution in practical measurements, a new LES model is established using Euler-Lagrange approach. A new entrapment criterion is also defined to calculate the entrapped inclusions. Big inclusions are tend to float up to the mold top, and aggregate near the outer arc, which can explain the differences of inclusion distribution in the vertical part; Smaller inclusions are easier to flow deep into the mold, and become clusters when they're getting near, which can explain the big inclusions in the central part. What's more, the drag effect of bending slab is proven to be responsible for the differences of inclusion distribution in the bending part. This mathematical model is helpful for understanding the inclusion movements in slab.
  • A Novel Measurement of Voidage in Coke and Ferrous Layers in Softening and Melting under Load Test Using Synchrotron X-ray and Neutron Computed Tomography

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    DOI:10.2355/isijinternational.ISIJINT-2018-257

    For the first time, the bed voidage of samples from interrupted softening and melting (S&M) under load tests was measured directly using computed tomography (CT). The large size, fused structure and high metallic iron content of the samples required the very high energy synchrotron X-ray source for scanning; samples produced at higher temperatures, e.g., 1450°C, required neutron CT to allow adequate penetration of the samples. This method was able to uniquely and accurately identify the volumes, distributions, and structures of coke, ferrous, and void in the S&M samples, and quantify the tortuosity of the voids. This information is critical for analysis of the pressure drop–contraction relationship in the S&M under load test, and will allow the improvement of the treatment of the cohesive zone in numerical models of the blast furnace.
  • Influence of Agitating Conditions on Agglomeration and Collapse of Iron Ore Mixture

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    DOI:10.2355/isijinternational.ISIJINT-2018-359

    The influence of agitating conditions on agglomeration and collapse of wet iron ore mixture was investigated in the view of kinetics and matrix model analysis. At the initial stage of mixing behavior, it was found that average particle size was dependent on the mixing rate constant defined as the deviation degree of particle size and water distribution from initial state. Mixing rate constants of powder and water were almost consistent with each other and expressed by power function of Froude number of impeller. It was presumed that the water and fine particle moved together as wet granules during mixing at a given water level. According to the analysis of entire mixing behavior based on matrix model, it was found that the collapse indexes defined by matrix parameters increased as particle size and impact force increased. Minimum particle size at initial mixing state decreased as collapse index increased and the size of long term mixing state was expected by intrinsic increasing rates defined by maximum eigenvalue of matrix parameters.
  • Local Buckling of Steel Plates in Composite Structures under Combined Bending and Compression

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    DOI:10.2355/isijinternational.ISIJINT-2018-202

    In this paper, explicit local buckling analysis of steel plates in composite structures under combine bending and compression and with elastic restraint against rotation is presented. Unique displacement function, which combines sinusoidal and cosine functions along x- and y-directions and satisfies boundary and loading conditions, is proposed to account for the effect of restraint of concrete and the elastic rotational restraint stiffness along both the loaded and unloaded edges of the steel plates. The explicit local buckling solution for the elastically restrained steel plates in composite structures is simplified to several special cases (e.g., the CS, CC, SS and KS steel plates) subjected to combined bending and compression. To verify the accuracy of the explicit solutions, experimental data, available solutions in the literature, and finite element results are compared, and reasonable agreement has been observed, particularly for the simplified cases. Parametric study is further conducted, and the effects of different parameters such as the aspect ratio and the loading stress gradient parameter on the local buckling stress resultants of steel plates with different boundary conditions are discussed.
  • Transient Thermo-fluid and Solidification Behaviors in Continuous Casting Mold: Oscillation Behaviors

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    DOI:10.2355/isijinternational.ISIJINT-2018-169

    A computational model of the continuous casting process has been developed, which includes transient heat transfer, multiphase flow, solidification, and mold oscillation. Succeeding the previous report on the evolution phenomena in the mold, this article describes fluctuations in the pressure, heat flux, and slag films during the oscillation cycle and the coupling effect of these variables on slag flow and shell growth. The results show that the predicted flux pressure is decided by the combined effect of mold velocity and liquid film thickness. The presence of slag rim enhances the nonuniform pressure flow near the meniscus during mold oscillation. Increases in pressure and heat flux occur in the negative strip time while the mold and slag rim move downwards approaching the lowest position, which squeezes the slag flow to be divided into two tributaries, promoting the slag infiltration and the initial shell solidification. Negative consumption rate is identified partly in the cycle based on the velocity distributions of liquid slag. The model provides quantitative analysis regarding the influence of meniscus shape and slag films related to the casting speed on slag consumption and oscillation mark formation.
  • Numerical Investigation of Coke Collapse and Size Segregation in the Bell-less Top Blast Furnace

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    DOI:10.2355/isijinternational.ISIJINT-2018-415

    The coke collapse phenomenon significantly affects the burden and gas distributions, and further gas utilization and CO2 emission. Therefore, it is necessary to investigate the coke collapse in blast furnace. A three dimensional model of bell-less top blast furnace is established based on discrete element method (DEM). The effects of chute angle, rotating speed and sinter amount on the coke collapse charateristics are then investigated based on this model. The results show that coke profile changes a lot after its collapse and the collapse region is more than 40% of the furnace radius. Sinter amount affects the coke collapse amount much, followed by chute angle and chute rotating speed. The coke collapse region is affected most by sinter amount, followed by chute rotating speed and chute angle. Large chute angle, higher rotating speed and small sinter amount are recommended for practical operation since they help to obtain a lighter coke size segregation along radius.
  • Improving the Desulphurization in COREX-3000 Process by the Optimization of Chemical Compositions of Slag

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    DOI:10.2355/isijinternational.ISIJINT-2018-427

    To improve the desulfurization in the COREX-3000 process, several aspects are studied and practiced. The work documented in the present paper focuses on the effects of chemical compositions of slag, such as CaO/SiO2, MgO, MgO/Al2O3 and MnO, on desulfurization. Theoretical calculations of sulfide capacity and viscosity of slag and diffusion coefficient of S2- in the slag are given to study the effects of slag chemical compositions on the thermodynamics and dynamics of desulfurization. After that, experiments are carried out to verify the theoretical analyses and give the appropriate ranges of these four parameters. The suggested suitable ranges of CaO/SiO2, MgO content, MgO/Al2O3 and MnO content for COREX-3000 are 1.20–1.30, 10 wt%–12 wt%, 0.80–0.90 and 0.4 wt%–0.7 wt%, respectively.

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