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

ISIJ International Advance Publication

  • Analysis of Billet Thermal Behavior and Temperature Setting Optimization in a Walking Beam Reheat Furnace

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    DOI:10.2355/isijinternational.ISIJINT-2016-471

    Aiming at the heating process of copper alloy billets, thermal behavior in a walking beam reheat furnace is investigated. A simplified thermal model is presented to predict billet temperature distribution considering specific heat transfer characteristics. Hot gas blackness is corrected basing on composition of chamber combustion atmosphere during the computation of heat flux boundary condition which improves the model accuracy. A fully implicit scheme is employed to solve the discretization of conduction equation in finite volume method. As an inverse application, a practical method to optimize the chamber gas setting temperature is introduced to make a billet temperature track the technical curve well. Design effects are calculated and simulated with Matlab software. Application results for the hot rolled coil production illustrate the effectiveness of the proposed approach.
  • Enhancement of Quicklime Dissolution in Steelmaking Slags by Utilizing Residual CO2 from Quicklime

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    DOI:10.2355/isijinternational.ISIJINT-2017-103

    In steelmaking processes, quicklime is generally used to produce CaO-based slags, and its dissolution rate is important for steel refining. The dissolution rate of quicklime is conventionally measured by the rotating cylinder method using dense and hard lime samples which gives rates that are slower than estimated rates from the actual operation. The authors established a new method to measure the dissolution rate of quicklime by measuring the variation of slag composition and reported that the quicklime used in the actual operation had a much higher dissolving rate than that of completely calcined quicklime. The significant increase of the dissolution rate was caused by gas formation from the quicklime due to the thermal decomposition of residual limestone existing in quicklime. In this study, the dissolution rate of quicklime with the accompanying gas formation is quantitatively investigated by using quicklimes with different CO2 contents produced by a rotary kiln process through the direct observation of the dissolution behavior of quicklime particles and the change of the CaO content in the slag. The results revealed that quicklime emits the gas in two steps, and the second occurrence of gas formation effectively enhances the quicklime dissolution. The weight of the CaCO3 core differed among particles from the same grade of quicklime, and the corresponding dissolution rates were different as well. The dissolution rates of quicklime during the second foaming, however, were 5–10 times higher than without foaming and were similar regardless of the CO2 content in a quicklime particle.
  • Intermediate-angle Neutron Scattering Instrument for Quantitative and Non-destructive Characterization of Nanostructures in Steels and Other Alloys

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    DOI:10.2355/isijinternational.ISIJINT-2017-226

    For characterizing nanostructures embedded in a metallic matrix, a newly designed intermediate-angle neutron scattering (iANS: "irons") instrument has been developed that shortens the distance between the sample and detector and is combined with a time-of-flight (TOF) technique. Since the momentum transfer (Q) resolution can be relaxed to provide an optimum Q-range when we focus on characterizing nanoscale heterogeneity, a much higher neutron flux can be utilized for the measurements than those available in a conventional small-angle neutron scattering (SANS) instrument. Consequently, iANS gives sufficiently high quality profiles for quantitative analysis on an absolute unit scale even using a compact accelerator driven neutron source (CANS). The results obtained at the Hokkaido University Neutron Source (HUNS) are compared to those obtained in large facilities. Some results obtained by iANS, are compared to those obtained by small angle X-ray scattering (SAXS) with respect to SAXS/SANS contrast variation.
  • Influence of P2O5 on Dissolution Behavior of Lime in Molten Slag

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    DOI:10.2355/isijinternational.ISIJINT-2017-094

    Dissolution of lime into molten slag is an important phenomenon in hot-metal dephosphorization treatment and should be suitably promoted in order to obtain an effective refining reaction and to recycle slag as some environmental resources. A lot of research has been conducted on the phenomenon, but the influence of P2O5 on the dissolution behavior of lime has never been studied despite the presence of P2O5 in the slag obtained during actual operation.In this study, the dissolution behavior of lime in CaO–SiO2–FeO or CaO-SiO2-FeO-5.2 mass% P2O5 molten slag was investigated via a high-temperature laser microscope, an optical microscope, and a scanning electron microscope/energy dispersive spectroscopy (SEM/EDS) in order to clarify the influence of P2O5 on the dissolution behavior of lime. We conclude that the addition of P2O5 to the slag accelerates the dissolution of lime in the molten slag mainly by increasing the CaO equilibrium content in the liquid slag saturated with 2CaO·SiO2.P2O5 is a product of the dephosphorization reaction, and basically, its content is preferred to maintain low content for dephosphorization based on equilibrium theory. However, the experimental results obtained in this study clarify that the presence of P2O5 in molten slag is effective for the promotion of the dephosphorization reaction when the reaction is limited by the dissolution of lime.
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  • Numerical Simulation of Thermal Field of Work Roll during Top Side-pouring Twin-roll Casting of Steel

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    DOI:10.2355/isijinternational.ISIJINT-2017-191

    During the top side-pouring twin-roll casting (TSTRC) of steel, the thermal field of the roll and the effects of parameters on the cooling power of roll surface were investigated using a two-dimensional model. The temperature and heat flux curves of roll surface appeared double-peak, especially when the rolling speed was high. The theories for the first and second peak of the curves and the relationship between the curve shape and the rolling speed were both discussed. Temperature variation curves in a revolution for different locations under the bottom roll surface were analyzed to reveal the temperature distribution of the roll. Besides, the cooling power of roll surface, measured by average temperature of roll surface, was of great significance in the TSTRC process. The influence of the rolling speed and the cooling water flux on the cooling power had been discussed and they were believed having positive and negative relativity with average temperature of roll surface, respectively. By comparison of average temperature range between two groups of simulation results, the cooling water flux was believed to affect the cooling power more than the rolling speed did. Furthermore, the increase of the cooling water flux was less effective in reducing the average temperature of roll surface especially when the water flux of the bottom roll was more than 6 m3/h. And to balance average surface temperature of two rolls, the suitable cooling water flux would be 4 m3/h and 6 m3/h for the upper and bottom roll respectively.
  • A Molecular Dynamics Study of Partitionless Solidification and Melting of Al–Cu Alloys

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    DOI:10.2355/isijinternational.ISIJINT-2017-221

    The partitionless solidification and melting in Al–Cu alloy system are investigated by means of molecular dynamics simulations with an embedded atom method (EAM) potential. The solid-liquid interfacial velocity for solid-liquid biphasic systems of Al-rich alloys is examined with respect to temperature and Cu composition. The kinetic coefficient is then derived from the slope of the interfacial velocity with respect to temperature. Our results show that the kinetic coefficient is largely dependent on the Cu composition. It sharply decreases with addition of small amount of Cu. There is almost no partition at the solid-liquid interface within the time scale of the simulation since the solid-liquid interfacial velocity is very fast at temperatures away from the equilibrium temperature. Since it is not straightforward to measure the kinetic coefficient directly from experiments, it is significant in this study to derive the composition dependence of the kinetic coefficient for binary alloys directly from the MD simulation without any phenomenological parameters.
  • Effect of Carbon Content on Bainite Transformation Start Temperature in Low Carbon Fe–9Ni–C Alloys

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    DOI:10.2355/isijinternational.ISIJINT-2017-239

    Bainite in steel is an industrially useful structure. However, the controlling factor of its transformation start point is not known clearly. In this study, to clarify the effect of carbon content on the bainite transformation start temperature (Bs), we evaluated the dilatation curve and the microstructure in low carbon Fe–9Ni alloys. As a result, Bs decreased with increasing of carbon content. Furthermore, the driving force of partitionless transformation from fcc to bcc at Bs, which was calculated considering nickel segregation, was approximately constant at 400 J/mol in all alloys. This value is consistent with the driving force required for partitionless growth of ferrite, as reported in a previous study. This consistency suggests that Bs depends on the martensitic growth behavior of lath-shaped ferrite, which is determined by the supercooling starting from the T0 line.
  • Selective Enrichment and Separation of Ti–Fe Enriched Mineral from Ti-bearing Electric Furnace Slag with Metallic Iron as Carrier

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    DOI:10.2355/isijinternational.ISIJINT-2017-159

    A new process of selective enrichment and separation of Ti-bearing minerals from the Ti-bearing electric furnace slag (TEFS) with metallic iron as carrier was proposed in this paper. The thermodynamic analysis, melting process and selective reduction were carried out, with an emphasis on the effects of Fe2O3/slag ratio and H2 partial pressure on the processes. The results indicated that the major Ti-bearing mineral in TEFS was pseudobrookite after adding Fe2O3 into the molten slag. In the selective reduction process, the pseudobrookite particle in the modified slag was selectively reduced to the magnetic Ti–Fe enriched mineral particle embedded with metallic iron. Then the magnetic Ti–Fe enriched mineral particle was separated from the nonmagnetic silicate particle in magnetic separation process. Finally, the Ti–Fe enriched mineral with 61.1 wt% TiO2 and 18.31 wt% Total Fe was obtained. Furthermore, the recovery ratio of TiO2 and Total Fe were 85% and 78.6%, respectively. The contents of CaO and SiO2 of the Ti–Fe enriched mineral were 1.4 wt% and 1.9 wt%, which were much less than that of TEFS. The Ti-bearing mineral in TEFS was effectively concentrated as using the new selective enrichment and separation method.

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