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ONLINE ISSN: 1883-2954
PRINT ISSN: 0021-1575

Tetsu-to-Hagané Advance Publication

  • Enrichment of Phosphorus from Iron Ore to Dicalcium-silicate Phase by Partial Reduction

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    DOI:10.2355/tetsutohagane.TETSU-2020-082

    It is necessary to develop an innovative iron-making technology for low-grade iron ore containing a high concentration of P. In this study, we propose a new process for enriching phosphorus in the C2S phase by mixing high-P iron ore, CaO, and graphite in appropriate proportions and partially reducing it. In this study, high-P iron ore adjusted to various basicities and reducing agent ratios was heated at 1573 K in Ar atmosphere, and the obtained sample was analyzed by EPMA. The results showed that in the reduced sample obtained under the conditions of C/S = 2.0 and Target FetO = 60%, more than 95% of P was distributed to the C2S phase, and the P content in metallic iron was sufficiently low.
  • Effects of Microstructural Anisotropy on the Dwell Fatigue Life of Ti-6Al-4V bar

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    DOI:10.2355/tetsutohagane.TETSU-2020-109

    Cyclic fatigue, dwell fatigue and crack growth properties were evaluated in the axial direction (L) and transversal direction (T) of Ti-6Al-4V forged round bar. In the SN curve where the stress is normalized by 0.2% proof stress, the cyclic fatigue life in the L/T direction is almost the same, whereas the dwell fatigue life in the T direction is as short as 1/5. In dwell fatigue, ductile fracture occurred when the maximum stress was higher than 95% of 0.2% proof stress. At stresses below 870 MPa, the inelastic strain range and the strain increase rate in the T direction gradually decreased with decreasing stress, and the fracture mode transitioned to that with fatigue crack growth. The gradual change must have been caused by the mixture of anisotropic microtexture regions. At stresses below 825 MPa, the fracture mode transitioned rapidly in the L direction, where the soft oriented microtexture regions were dominant. In the low ΔK region (≤15MPa√m), the crack growth rate in the axial direction was about twice that in the radial direction of the bar. The shorter dwell fatigue life in the T direction under stress conditions showing fatigue crack growth was explained by the significantly earlier crack initiation compared to that in cyclic fatigue and the faster crack growth along the microtexture in the axial direction of the bar.
  • Accuracy Improvement of the XRD-Rietveld Method for the Quantification of Crystalline Phases in Iron Sintered Ores Through the Correction of Micro-absorption Effects

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    DOI:10.2355/tetsutohagane.TETSU-2020-098

    The mass fraction of each crystalline phase in inorganic materials can be investigated using the Rietveld refinement of the X-ray diffraction (XRD) patterns. For quantitative analysis, differences in the values of the linear absorption coefficient, μ, among the crystalline phases must be considered when certain X-ray sources are used, because such differences often affect their mass fractions. Herein, we evaluate the effects of the differences between the Cu and Co X-rays on the mass fractions of the crystalline phases in iron sintered ores using the XRD-Rietveld method by performing two types of XRD measurements. Type 1 samples modeled materials with two different particle size combinations of α-Fe2O3 and ZnO. Type 2 samples used powder mixtures to simulate iron sintered ores composed of α-Fe2O3, and synthesized SFCA and SFCA-I in various mass fractions. Moreover, a correction method was developed using the Taylor-Matulis (TM) correction that considers the μ of each phase and the average particle diameter of each crystalline phase determined by scanning electron microscopy with energy dispersive spectroscopy. For type 1 samples, results that were in good agreement with the initially-charged mass fractions could be obtained using the TM correction, even in the presence of significant differences in R between α-Fe2O3 and ZnO. The results for type 2 samples confirmed that quantitatively accurate mass fractions could be obtained using the TM correction with an accuracy of approximately ±3 mass% for Cu and Co sources, whereas the error was greater than ±3 mass% for Cu source when the TM correction was not applied.
  • In situ Observation of Reduction Behavior of Multicomponent Calcium Ferrites by XRD and XAFS

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    DOI:10.2355/tetsutohagane.TETSU-2020-077

    Reduction behavior of various multi-component calcium ferrites at 900°C were investigated by using in situ X-ray diffraction (XRD) and X-ray absorption spectroscopy. Intermediate components were determined by XRD, and change in X-ray absorption spectra of Fe and Ca K-edges were analyzed to determine reaction rate constants. SFCA-I (Ca3(Ca,Fe)(Fe,Al)16O28) and SFCA (Ca2(Fe,Ca)6(Fe,Al,Si)6O20) consist of layered structure of spinel and pyroxene. Early stage of reduction reaction, diffraction peaks of spinel structure were observed which indicating SFCA-I and SFCA decomposed into these units at the first step of the reduction reactions. The spinel was reduced sequentially into FeOx then Fe. Intermediate component, Ca2(Fe,Al)2O5 originated in pyroxene module was hard to reduce and reaction was controlled by decomposition of this phase. Reduction of SFCA-I started later than SFCA (with 5.7 mol% Al2O3) under hydrogen gas reduction condition at 900°C. SFCA with a high aluminum content indicated lower reducibility than that with a low one.
  • Numerical Simulation of Fine Particle Deposition in Layering Granulation

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    DOI:10.2355/tetsutohagane.TETSU-2020-079

    There is a great demand for understanding the layering granulation of coarse and fine iron ore particles. For the understanding, a numerical simulation can be powerful approach. We here proposed a numerical simulation method, by which the deposition of fine particles with water on the surface of a coarse particle can be simulated. In the proposed model, surface of a coarse particle was modeled as a flat surface. The fine particles and water droplets were then deposited on the flat surface with minimizing the surface energy of the liquid and potential energy of the particles, resulting in a bed of the deposited particles with water under the equilibrium state with considering the influence of the physicochemical properties of the particles and liquid. First, an experiment of the deposition of spherical polymer beads with water droplet on the flat polymer sheet was performed. The simulation results showed an agreement with the experimental result, demonstrating the validity of the proposed simulation method. Second, influences on the liquid amount and contact angle (i.e., wettability) of the particles were analyzed. The simulation results suggest that the smaller contact angle (good wettability) can result in more rigid bed with less ungranulated particles.
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    1. Effects of Iron Ore Type and Gangue MineralComponents on Strength of Sintered FinePowder Granule Tetsu-to-Hagané Advance Publication
  • Effects of Iron Ore Type and Gangue MineralComponents on Strength of Sintered FinePowder Granule

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    DOI:10.2355/tetsutohagane.TETSU-2020-061

    Depletion of high-grade iron ore resources leads to increasing use of ore concentrates as raw materials for sinter. One of the methods to effectively utilize such concentrates is Mosaic EmBedding Iron Ore Sintering (MEBIOS), which pre-granulated green pellets are charged into sintering bed with the mixture of other raw materials. In this study, effects of the ore type and gangue mineral components on the strength of sintered pellet prepared of fine concentrates were examined. Green pellets were prepared using hematite and magnetite ores, burnt lime and alumina and mullite reagents, and then sintered at 1300°C. The strength of sintered pellet increases with increasing basicity (CaO/SiO2, C/S) at lower basicity region. The pellet using hematite ore with C/S above 1.5 showed higher strength than 980 N. It can be attributed to the melt formation during sintering. On the other hand, when using magnetite ore, higher strength than 980 N was obtained above C/S = 1.0. The reason is an acceleration of solid-state sintering by the volume expansion due to oxidation of magnetite to hematite. Increasing Al2O3 content leads to decreasing the strength of pellet because oxidation of magnetite is prevented by the increasing amount of formed melt.
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    1. Numerical Simulation of Fine Particle Deposition in Layering Granulation Tetsu-to-Hagané Advance Publication
  • Recovery of Phosphorus from ModifiedSteelmaking Slag with High P2O5 Content via Leaching and Precipitation

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    DOI:10.2355/tetsutohagane.TETSU-2020-030

    The P contained in steelmaking slag is regarded as a potential phosphate source, especially with regard to slag with high P2O5 content, which is generated from the utilization of high P iron ores. If P can be efficiently extracted from slag, the obtained P can be used as a phosphate fertilizer. Moreover, the remaining slag can be recycled inside the steelmaking process. Compared with other phases, the P-condensed C2S– C3P solid solution in slag is more easily dissolved in water; therefore, selective leaching was applied to recover P from slag with high P2O5 content. In this study, the effect of K2O modification on P dissolution in the citric acid solution was investigated, and subsequently, a process for extracting phosphate product from the leachate, via precipitation, was explored. It was determined that K2O modification promoted dissolution of the solid solution, resulting in a higher dissolution ratio of P. By modification, the majority of the solid solution was dissolved at pH 6, and other phases remained in residue, indicating that a better selective leaching of P occurred. As the pH decreased, the dissolution ratios of both P and Fe increased. Following leaching at pH 5, a residue with a higher Fe2O3 content and lower P2O5 content was obtained. When the pH of the leachate increased, the dissolved P in the aqueous solution was precipitated. Through separation and calcination, a phosphate product with a P2O5 content of 30% was obtained, which has the potential to be used as a phosphate fertilizer.
  • Evaluation of the Compressive ResidualStress Relaxation Behavior by in situ X-rayStress Measurement

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    DOI:10.2355/tetsutohagane.TETSU-2020-059

    To clarify the relaxation behavior of compressive residual stress during the first push and pull loading cycle, an in situ X-ray stress measurement method was formulated, in which a fine particle peening-treated hourglass-shaped specimen was fixed on an axial-loading fatigue testing machine, and the surface stress of the specimen—which is the sum of applied stress and residual stress—was directly measured via X-ray diffraction without removing the specimen from the testing machine. A noticeable relaxation in compressive residual stress occurred under the first compressive loading process, and slight relaxation was observed then onward. During the first compressive loading, the surface stress decreased almost linearly as the applied compressive stress increased; however, when the stress exceeded a certain threshold value, the relation between the applied stress and the surface stress deviated from the linear relation. This threshold value is important with regard to compressive residual stress relaxation. Furthermore, the relaxation behavior during the first compressive loading process can be explained by a master diagram that shows the relationship between the applied stress and the stress measured via X-ray diffraction. The diagram consistently shows that with an increase in the applied compressive stress, there is an increase in the amount of relaxed residual stress.
  • Sinter Pot for Temperature Measurement of the Top Layer during and After the Ignition

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    DOI:10.2355/tetsutohagane.TETSU-2020-068

    For achieving high sinter yield and quality, various technologies are being implemented and developed to control the heat pattern during the sintering reaction. Further improvements in these technologies necessitate detailed time-course profiles of temperature at all sinter-bed heights; however, no technique has yet been reported for determining the temperature distribution in the top layers of the sinter bed at high spatial and time resolutions. Herein, detailed heat patterns in these layers were visualized by a newly developed pot test apparatus having ~300-mm sinter-bed height. The developed apparatus demonstrated the effect of ignition time on heat patterns during combustion and immediately after ignition. Ignition times of 30, 60, and 90 s demonstrated that the high-temperature holding time increased with an increase in ignition time, and this effect is more evident in the top layer. All parameters, including high-temperature holding time, flue gas composition, and sinter yield, suggest that a longer ignition time intensified coke combustion in the top half layer. The developed technique to measure the temperature in the top layer will quantitatively clarify the effect of segregation or ignition condition on the heat pattern in the top layer.

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  8. In situ Observation of Reduction Behavior of Multicomponent Calcium Ferrites by XRD and XAFS Tetsu-to-Hagané Advance Publication
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