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

ISIJ International Advance Publication

  • Texture Evolution during Recrystallization and Grain Growth in Heavily Cold-rolled Fe-3%Si Alloy

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    DOI:10.2355/isijinternational.ISIJINT-2018-268

    Recrystallization and grain growth are important phenomena for controlling the mechanical and magnetic properties of steels through texture. Only a limited number of studies have been carried out on texture evolution during recrystallization and grain growth in heavily cold-rolled Si steel. The present study first focuses on clarifying the texture evolution during normal grain growth, followed by an investigation into the development of the {411}<148> component during recrystallization. The {411}<148> component is remarkably developed during normal grain growth after the completion of recrystallization. At just fully recrystallized stage, the diameters of the {411}<148> grains were larger than that of the grains with other orientations. Therefore, the {411}<148> grains significantly grew owing to the size advantage.Just at the commencement of recrystallization, differences in grain diameter of recrystallized grains in terms of crystal orientation were not detected. However, it is worthwhile to mention that the nucleation of {411}<148> recrystallized grains is unexpectedly fast in heavily cold-rolled Si steel. Recrystallized {411}<148> grains were observed to nucleate in the deformed α-fiber grains, especially near the grain boundaries. Nuclei with {411}<148> orientation grow easily due to the high mobility of the interface between the recrystallized/non-recrystallized grains and the high driving force. Consequently, the diameter of a {411}<148> recrystallized grain becomes relatively large upon the completion of recrystallization. This contributes to the selective grain growth during the normal grain growth stage because of the size effect.
  • The Optimization of Partial-least-square Regression for Determination of Manganese in Low-alloy Steel by Single-shot Laser-induced Breakdown Spectroscopy

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    DOI:10.2355/isijinternational.ISIJINT-2018-134

    Laser-induced breakdown spectroscopy (LIBS) is employed for ultra-high-speed determination of the manganese content in various steel specimens. LIBS is widely known as a method for elemental analysis with a rapid response. It has several advantages such that it can work under ambient pressure, and that specimens can be tested without any pre-treatment such as acid digestion, cleaning, or polishing of surface of the specimens. We applied a laboratory-build LIBS system for the determination of Mn in a series of low-alloy steel certified reference materials by a multivariate analysis using partial-least-square regression. Considering enough intensities of Mn emission lines and spectral interferences from emission lines of the iron matrix in these alloys, two wavelength ranges for the spectrograph could be employed. By minimizing the predicted residual sum of squares and the root mean square error of prediction, the analytical result of the Mn concentrations could be obtained with reasonable accuracy and precision.
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  • Holdup Characteristics of Melt in Coke Beds of Different Shapes

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    DOI:10.2355/isijinternational.ISIJINT-2018-369

    Numerical analysis was carried out on the dripping and holdup behaviors in the lower part of a blast furnace for coke bed structures having different shapes; a discrete element method smoothed particle hydrodynamics scheme was used considering the size distribution immediately above the raceway. Even for coke beds with similar void fractions, the averaged-coke-shape factors such as φ and (φD)2 give little clear correlation for holdup sites. Instead of averaged-coke-shape information, only the direct evaluation of the void shape of the packed bed can explicitly trace the holdup site.
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  • Effect of Si Content on the Microstructure and Wear Resistance of High Chromium Cast Iron

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    DOI:10.2355/isijinternational.ISIJINT-2018-099

    Effect of Si content on the wear resistance of high chromium cast iron was investigated. The result showed that the eutectic carbides were greatly refined and increased with the increase of Si addition from 0.5 to 1.5 wt.%. Meanwhile, the transformation of austenitic matrix to pearlite was observed. After destabilized treatment at 950°C for 3 h, denser secondary carbides precipitated from the matrix are observed in the alloy containing 1.5wt.%Si. Such microstructure changes leaded to the increase of hardness and improvement of abrasive wear resistance. An increase in load from 20 N to 100 N, the extent of carbide fragmentation was much greater and extended to a deeper distance. Severer fracture of carbides was observed in the alloy containing 0.5wt.%Si. The higher resistance with addition of Si was attributed to the denser secondary carbides, which strengthened the matrix between the eutectic carbides and in turn increased the mechanical support to the carbides against cracking.
  • Granulation Effectiveness of Iron Ore Sinter Feeds: Effect of Ore Properties

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    DOI:10.2355/isijinternational.ISIJINT-2018-141

    This paper developed a quantitative understanding of the effect of ore properties on granulation effectiveness for different iron ore types based on the mechanistic model proposed by J.D. Litster et al. The granulation effectiveness was measured by the magnitude of x0.5, which was postulated to be a function of the layer binding strength. Water was adopted as the only binder for all granulation tests. A wide range of moisture contents, up to the optimum moisture content that yielded an optimum permeability, was tested for each ore type. The typical structure of granules made from different ores was investigated to reveal the effect of mineralogical properties of ore particles on the growth of granules. The results indicate that the granulation effectiveness x0.5 varies markedly with ore type and moisture content. Feed particle size distribution and moisture for granulation are paramount factors determining the granulation effectiveness x0.5, which has a single relationship with the mass mean size of layering particles independent of ore type. The mass mean size of layering particles is dependent on the inherent size distribution of raw materials and the mass fraction of layering particles, while the latter is linear to available moisture content. The model works well for some ore types except for those with unreasonable size distributions: 1) excessive intermediate particles meanwhile lacking of fine particles; or 2) excessive ultrafine particles. An effective criteria closely related to layer binding strength, (1-ε)S/εd, is proposed to determine the applicability of the model.
  • Strip Edge Defects and Comprehensive Control Technology in Trimming Process

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    DOI:10.2355/isijinternational.ISIJINT-2017-708

    In the strip trimming process, defects such as buckle edge, burr, and imbalance of cutoff ratio often occur. This study investigated the mechanism of these defects and analyzed the influence of disc shears process parameters, including overlap, clearance, fron and back tension on the quality of strip edge. On this basis, a comprehensive evaluation function of strip trimming quality is proposed. Furthermore, the process parameter optimization technology of the disc shears is developed. Subsequently, an on-line grinding device for strip edge is designed to fundamentally control burr defect. Via field application of this technology and this device, the comprehensive treatment of buckle edge, burr, and imbalance of cutoff ratio is realized. Therefore, improving the quality of finished strip is helpful and has the value of further popularization and application.
  • Properties of Low-MgO Ironmaking Blast Furnace Slags

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    DOI:10.2355/isijinternational.ISIJINT-2018-022

    Low slag volume ironmaking blast furnace (BF) operation can reduce the cost of ironmaking by lower flux rate and fuel ratio, meanwhile the operation should be maintained safely in terms of operational temperature, fluidity and desulphurization. One of the approaches for low slag volume BF operation is to decrease MgO content in the slag. In this study, the properties of BF slag have been experimentally investigated in the CaO–SiO2–Al2O3–MgO system from the aspects of phase equilibria, viscosity and sulphide capacity. The liquidus temperature of slag is not sensitive to the MgO concentration. The viscosity of slag increases slightly with decreasing MgO concentration. The sulphide capacity of slag decreases slightly with decreasing MgO concentration. It is suggested that the MgO concentration in the BF slag can be reduced to 5 wt% at the CaO/SiO2 weight ratio of 1.10 to 1.30 and Al2O3 of around 15 wt% under stable BF operation.
  • Effect of MgO on Formation and Crystallization Behaviors of Calcium Ferrite during Heating and Cooling Processes

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    DOI:10.2355/isijinternational.ISIJINT-2018-028

    MgO is one of essential component in blast furnace slag for improving the fluidity and desulfurization. Generally it is added via sintering process. It has been also proved in practice that the addition of MgO affects the quality of sinter significantly. However, the effect of MgO on formation and crystallization behaviors of calcium ferrite in sintering had been scarcely discussed. In this work, the crystalline products in CaO–Fe2O3 system with different content of MgO were identified by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). In order to follow the reactions during heating and cooling, differential scanning calorimetry (DSC) was also conducted. It was found that addition of MgO restrained the formation of CaFe2O4 leading to the decrease in content of original melt during sintering process. The contents of Ca2Fe2O5 and solid solution of magnetite (magnetite s.s) were increased and the crystallization of Ca2Fe2O5 was also promoted with increasing MgO. Compared with forming Ca2Fe2O5, addition of MgO facilitated to form magnetite s.s. Content of initial liquid phase was decreased with increasing MgO, whereas new liquid phase was generated at 1609 K when the content of MgO exceeded 7 mass%, due to the reaction between Ca2Fe2O5 and magnetite.
  • Bend Failure Mechanism of Zinc Coated Advanced High Strength Steel

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    DOI:10.2355/isijinternational.ISIJINT-2018-132

    Local formability is one of the most critical properties of Advanced High Strength Steels for successful implementation in automotive applications. However, attaining satisfactory local formability is a challenge for many Advanced High Strength Steels. In the present study, a hot dip galvannealed dual-phase steel with 980 MPa minimum tensile strength was selected as the AHSS and its local formability was evaluated by conducting 90-degree V-bend tests. The bend samples, particularly those that experienced failure during testing, were subjected to intense characterization using Scanning Electron Microscope, Cathodoluminescence Microscope and Thermal Desorption Analyzer. Fractography study indicated that the bend failure is associated with the interaction between inclusions near the steel surface and the diffusible hydrogen in the steel. The same underlying failure mode was also observed in two additional zinc coated AHSS grades. Improved steel cleanliness resulted in reduction of inclusions and diffusible hydrogen amounts, and facilitated enhanced steel bendability. Diffusible hydrogen content in the steel could be reduced by removing the surface zinc coating or by heat treatment; such treatments also led to a significant improvement in bendability.
  • Effect of Annealing Temperature on the Selective Oxidation and Reactive Wetting of a 0.1C-6Mn-2Si Advanced High Strength Steel During Continuous Galvanizing Heat Treatments

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    DOI:10.2355/isijinternational.ISIJINT-2017-688

    The effects of peak annealing temperature and annealing time on the selective oxidation and reactive wetting of a prototype medium-Mn Fe-0.1C-6Mn-2Si third generation advanced high strength steel were investigated. Annealing heat treatments were carried out in a N2-5 vol% H2 243 K (-30°C) dew point process atmosphere at 963 K (690°C) and 1073 K (800°C) for 120 s and 600 s. TEM observations of the sample cross-sections revealed internal oxidation of the subsurface grains and grain boundaries. EELS results showed that the internal oxide network had a multi-layered structure with SiO2 at the oxide core and MnSiO3 as the surrounding shell; however, MnO was the only species detected at the surface of all samples. The effect of annealing temperature on the surface structure development and its impact on reactive wetting of the substrates annealed for 120 s at both peak annealing temperatures by a Zn-0.20 wt% Al (dissolved) galvanizing bath was also determined. In contrast to the 1073 K steel, the 963 K substrate showed superior reactive wetting, owing to the much thinner, finer and wider spacing of the MnO nodules on the pre-immersion surface. TEM+EELS analysis of the coated steels showed that infiltration of the bath alloy and partial reduction of MnO resulted in lift-off of the surface oxides and partial formation of Fe2Al5ZnX interfacial layer, indicating that reactive wetting had occurred for the 963 K × 120 s substrate.
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  2. Bend Failure Mechanism of Zinc Coated Advanced High Strength Steel ISIJ International Advance Publication
  3. Effect of Annealing Temperature on the Selective Oxidation and Reactive Wetting of a 0.1C-6Mn-2Si Advanced High Strength Steel During Continuous Galvanizing Heat Treatments ISIJ International Advance Publication
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  6. In Situ Temperature Measurement of Sinter Beds at High Spatial and Time Resolution ISIJ International Vol.58(2018), No.5
  7. Effect of MgO on Formation and Crystallization Behaviors of Calcium Ferrite during Heating and Cooling Processes ISIJ International Advance Publication
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  9. Granulation Effectiveness of Iron Ore Sinter Feeds: Effect of Ore Properties ISIJ International Advance Publication
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