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

ISIJ International Advance Publication

  • Microstructure Ti–Fe Phase Separation Mechanism in the Direct Reduction Process of Titanomagnetite with Coal by Microwave Heating

    Peng Liu, Siyu Gong, Chao Yuwen, Bingguo Liu, Libo Zhang, Aiyuan Ma

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    DOI:10.2355/isijinternational.0_ISIJINT-2022-106

    Abstract

    Although microwave heating has been used in the field of metallurgy since the 1980s, there are few reports on using microwave heating to strengthen Ti–Fe phase separation in the reduction process of titanomagnetite. Microstructure Ti–Fe phase separation by microwave heating was found to be beneficial to the reduction process of titanomagnetite through the investigation of formation enthalpy and reduction difficulties. The dielectric properties and energy band structure of Fe3O4, Fe2O3, and TiO2 were determined, the dielectric constant (ε′r: 20.00) and dielectric loss (ε″r: 2.82) of Fe3O4 were significantly superior to those of TiO2 (ε′r: 3.42, ε″r: 0.04), and the physical thermal stress between Fe3O4 and TiO2 phases in the reduction process was conducive to the microstructure Ti–Fe phase separation process. Besides thermal stress, microstructure Ti–Fe phase separation was mainly due to the ampere traction force generated between local isotropic ring current in adjacent iron atoms. This study revealed the microstructure Ti–Fe phase separation mechanism in the reduction process of titanomagnetite by microwave heating.

  • Thermodynamic Analysis of the Reduction of Vanadium-titanium Magnetite by Gasification Gas

    Wei-bin Chen, Zhaoqi Dong, Xi-dong Wang

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    DOI:10.2355/isijinternational.0_ISIJINT-2022-182

    Abstract

    Vanadium-titanium magnetite (VTM) has a high comprehensive utilization value. The gas-based reduction process combined with the electric furnace melting process has the advantages of a high recovery rate of precious metal elements in VTM, low cost, high-energy efficiency, and low environmental pollution. Gasification gas provided by coal gasification technology is a potential reducing agent. Through FACTSAGE calculations and experiments, the reduction thermodynamic properties of VTM oxidized pellets by gasification gas were systematically studied to illustrate the feasibility of the system before practical experiments. The reaction mechanism of the direct reduction of VTM by gasification gas was proved, and the conversion behavior of iron and titanium in the reduction system was also clarified. This work clearly describes the reduction process of VTM oxidation pellets and clarifies the essence of the direct reduction of gas groups of VTM oxidized pellets.

  • Synergistic Effect of Brightener and Solution Temperature on the Electrodeposition Behavior of Zn–Ni Alloy from Alkaline Zincate Solution

    Sung Hwa Bae, Satoshi Oue, Yu-ki Taninouchi, Injoon Son, Hiroaki Nakano

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    DOI:10.2355/isijinternational.ISIJINT-2022-160

    Abstract

    Zn–Ni alloys were electrodeposited on a Cu electrode at 10–5000 A·m-2, 5 × 104 C·m-2, 293 K, 313 K, and 333 K in unagitated zincate solutions containing the reaction product of epichlorohydrin and imidazole (IME) as a brightener. The synergistic effect of IEM and solution temperature on the deposition behavior of Zn–Ni alloys was investigated. The transition current density at which the deposition behavior shifted from normal to anomalous one decreased with IME at 293 K, but did not change regardless of IME addition at 313 K and 333 K. The suppression effect of IME on the Zn and Ni depositions during alloy deposition was observed at 293 K while at 313 K and 333 K, the suppression effect decreased on the Zn deposition but was maintained on the Ni deposition. Therefore, Ni content in deposits significantly decreased with IME as the temperature increased. The current efficiency of Zn deposition significantly decreased with IME at 293 K, with a small degree of decrease at 313 K and 333 K. The C content in deposits was the highest at 293 K and decreased with increasing solution temperature, indicating that the adsorption ability of IME on the cathode decreases with the increasing temperature. As a result, the suppression effect of IME on the Zn deposition decreases with the increasing temperature. The gloss of deposited films was the highest at 293 K, attributed to the IME adsorption ability being large at 293 K and deposited films with fine crystals becoming smooth.

  • Analysis of Process Signals of Resistance Spot Welding for DP590 Steel Using Numerical Calculation

    Kang Zhou, Gang Wang, Wenxiao Yu, Huan Li, Mikhail Ivanov

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    DOI:10.2355/isijinternational.ISIJINT-2022-100

    Abstract

    Although the finite element (FE) numerical calculation model has been extensively employed in analyzing metal characteristics, very few works use it to analyze features of the main process signals during the resistance spot welding (RSW) process. Hence, its generality was seriously restricted. In this work, a 2D FE model, which coupled thermal, electrical and mechanical fields, was established with reasonable meshing and parameters and boundary conditions. The parent metal used dual phase (DP) 590 steel, which is commonly employed in automobile lightweight manufacturing process. An actual experiment with the same conditions as the numerical calculation was conducted. The dynamic resistance and electrode displacement obtained from numerical calculation and actual experiment were seriously compared and analyzed. Many important characteristics of process signals have been reasonably explained by combining the results obtained from numerical calculation and experiments. The reasonability and accuracy of the FE numerical calculation were not only verified after the welding process but also examined in depth during the intermediate welding process. Hence, the work can effectively enlarge the applications of the FE model and strengthen the correlation between control strategy design, online quality estimation using main process signals and FE numerical calculation during the RSW process.

  • Evaluation of Deep Network-based Methods for Crack Detection of Iron Ore Green Pellet

    Shuyi Zhou, Xiaoyan Liu, Yuru Chen, Xihan Sun

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    DOI:10.2355/isijinternational.ISIJINT-2022-108

    Abstract

    Crack detection for iron ore green pellet is an essential step in the measuring process of drop strength, which is one of the important quality metrics of green pellet. However, current method for crack detection of green pellet is manual inspection, which is rather laborious, tedious and subjective. Although various deep network-based methods are proposed to automatically detect cracks in tunnel, pavement and wall, little effort has been made on pellet crack detection. Therefore, it is still unknown whether the current deep network-based methods can solve the crack pellet detection problem. In the present work, we perform comparison study to evaluate the performance of six state-of-the-art deep networks, using our green pellet dataset with various crack types and complex background. Comprehensive comparatives are conducted to evaluate the performance and computing efficiency of six deep networks on pellet crack detection. Moreover, task-driving comparison is performed to show what to extent the six deep networks affect the measuring accuracy of drop strength. Our experimental analyses demonstrate that CrackSegNet achieves better crack detection accuracy than other five networks (DeepCrack-Z, DeepCrack-L, U-net, CrackSegNet, GCUnet), and thereby performs better in the task of drop strength measurement. However, computing time needed by CrackSegNet (0.26 seconds per image) is longer than other networks (0.05–0.20 seconds per image) in processing one image with the size of 512×512. In future work, the performance of deep networks needs to be improved in crack detection accuracy as well as computing efficiency to ensure more accurate and fast measurement of pellet quality.

  • Wettability of Molten Fe–Al Alloys against Oxide Substrates with Various SiO2 Activity

    Tomoki Furukawa, Ziyao Zhang, Taro Hirosumi, Noritaka Saito, Kunihiko Nakashima

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    DOI:10.2355/isijinternational.ISIJINT-2022-093

    Abstract

    The contact angle between molten Fe–Al alloy with 0.03, 0.3, and 3 mass% Al composition, and Y2O3 matrix oxide substrate with 0.002, 0.32, and 1 SiO2 activity was measured using sessile drop method in Ar atmosphere at 1873 K, and the interfacial tension was evaluated. The contact angle and interfacial tension between the molten Fe-0.3 Al alloy and the Y2Si2O7 + SiO2 (aSiO2 = 1) substrate decreased over time during 60 s after the molten alloy was dropped onto the substrate. The decrease of the contact angle was 20°, and that of the interfacial tension was 628 mN·m-1 Conversely, the other contact angles and the other interfacial energies were almost stable during the same period. The decrease of the contact angles ranged between 0° and 7°, and that of the interfacial tensions ranged 4 and 195 mN·m-1. By observing the wetting behavior for 60 min, it was recognized that the interfacial reaction between the Fe–Al alloy and the oxide substrate was the redox reaction between Al composition in the alloy and SiO2 composition in the substrate, composed of SiO2 decomposition reaction and Al2O3 formation reaction between oxygen absorbed at the interface and Al composition in the alloy. In addition, it was indicated from the interfacial tension dependence on SiO2 activity that the medium SiO2 volume slag for the molten low-Al steel and the low SiO2 volume slag for the molten high-Al steel were effective in preventing the small droplets of molten slag into the molten steel.

  • Application of Heat Transfer Coefficient Estimation Using Data Assimilation and a 1-D Solidification Model to 3-D Solidification Simulation

    Toshihiko Oikawa, Yukinobu Natsume, Munekazu Ohno

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    DOI:10.2355/isijinternational.ISIJINT-2022-095

    Abstract

    Solidification simulations are effective in designing a casting process to improve the quality of steel slabs and ingots. In this study, a new method was developed to efficiently estimate multiple heat transfer coefficients to improve the accuracy of three-dimensional (3-D) solidification simulation for a casting process. The heat transfer coefficients for the two heat transfer directions—side and bottom—of a prismatic mold were independently estimated by data assimilation using one-dimensional solidification simulations near the boundaries. The optimum values of the heat transfer coefficients at the side and bottom boundaries were elucidated by comparing the 3-D solidification simulation and experimental cooling curves. The maximum and average errors between the cooling curves of the 3-D solidification simulation with the optimum values and those of the experiment were less than 1.8% and 0.2%, respectively.

  • Role of Interfacial Properties in the Evolution of Non-metallic Inclusions in Liquid Steel

    Lichun Zheng, Annelies Malfliet, Baiqiang Yan, Zhouhua Jiang, Bart Blanpain, Muxing Guo

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    DOI:10.2355/isijinternational.ISIJINT-2022-079

    Abstract

    The evolution of non-metallic inclusions in liquid steel involves a series of processes, including nucleation, growth by diffusion and Ostwald ripening, growth by collisions, floating up and removal of relatively large inclusions, as well as pushing and engulfment of remaining inclusions during solidification. All the evolution processes occur uniquely at the interface between inclusions and liquid steel. Therefore, interfacial properties between inclusions and liquid steel, such as interfacial energy and contact angle, play a crucial role in the evolution of inclusions, thus determining the inclusion characteristics. To effectively control the inclusion characteristics, the role of interfacial properties in the evolution processes of non-metallic inclusions is systematically reviewed in this work, based on theoretical analysis and published experimental results. In the early and middle stages of deoxidation, inclusions should have as high interfacial energy or contact angle as possible to enhance inclusion removal. In the later stage, however, the interfacial energy should be decreased as much as possible to weaken the clustering and pushing of inclusions, favoring the formation of small-sized and uniformly-distributed inclusions. To optimize the characteristics of Al2O3 inclusions, which are the most common in steel, several control strategies are proposed.

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    2. Solute Concentration Distribution in the Vicinity of Solid-Liquid Interface under the Imposition of a Time-Varying Force ISIJ International Advance Publication
    3. Water Model Study on the Flotation Behaviors of Inclusion Clusters in Molten Steel ISIJ International Advance Publication

  • Hierarchical Deformation Heterogeneity during Lüders Band Propagation in an Fe-5Mn-0.1C Medium Mn Steel Clarified through in situ Scanning Electron Microscopy

    Motomichi Koyama, Takayuki Yamashita, Satoshi Morooka, Zhipeng Yang, Rama Srinivas Varanasi, Tomohiko Hojo, Takuro Kawasaki, Stefanus Harjo

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    DOI:10.2355/isijinternational.ISIJINT-2022-098

    Abstract

    In-situ deformation experiments with cold-rolled and intercritically annealed Fe-5Mn-0.1C steel were carried out at ambient temperature to characterize the deformation heterogeneity during Lüders band propagation. Deformation band formation, which is a precursor phenomenon of Lüders band propagation, occurred even in the macroscopically elastic deformation stage. The deformation bands in the Lüders front grew from both the side edges to the center of the specimen. After macroscopic yielding, the thin deformation bands grew via band branching, thickening, multiple band initiation, and their coalescence, the behavior of which was heterogeneous. Thick deformation bands formed irregularly in front of the region where the thin deformation bands were densified. The thin deformation bands were not further densified when the spacing of the bands was below ~10 µm. Instead, the regions between the deformation bands showed a homogeneous plasticity evolution. The growth of the thin deformation bands was discontinuous, which may be due to the presence of ferrite groups in the propagation path of the deformation bands. Based on these observations, a model for discontinuous Lüders band propagation has been proposed.

  • Evaluation of Cleavage Fracture Behavior of C14 Fe2W Laves Phase by First-principles Calculations and Crystal Orientation Analysis

    Shigeto Yamasaki, Tatsuya Morikawa, Masaki Tanaka, Yasuaki Watanabe, Mitsuo Yamashita, Sakae Izumi

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    DOI:10.2355/isijinternational.ISIJINT-2022-122

    Abstract

    In this study, the cleavage fracture of the C14 Fe2W Laves phase was investigated by first-principles calculations and crystal orientation analysis using scanning electron microscopy. Trace analysis of the orientations of cleavage planes revealed that cleavage fracture occurred in five types of crystal planes: (0001), {1100}, {1120}, {1101}, and {1122}. Among these fractures, the fracture at (0001) is the most preferable. From, the first-principle calculations of the surface energy for fracture, Young's modulus, and Poisson's ratio, the minimum fracture toughness value of 1.62 MPa·m1/2 was obtained at (0001). The tendency of the calculated fracture toughness to become larger with high indexed planes is almost the same as the frequency of the types of cleavage planes in the trace analysis. It was concluded that the fracture toughness of the C14 Fe2W Laves phase is controlled by the surface energy for fracture and Young's modulus.

  • Analysis of Dephosphorization Thermodynamics Based on the Melt Structure of CaO–SiO2–FeO–MgO System

    Rui Zhang, Jixiang Jia, Shixiong Li, Yongyu Zhang, Lin Jing, Yi Min, Chengjun Liu

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    DOI:10.2355/isijinternational.ISIJINT-2022-073

    Abstract

    To reduce the phosphorus content in steel, the CaO–SiO2–FexO–MgO-based dephosphorization slag was designed to clarify the microscopic reaction behavior of phosphorus. In the present study, Raman spectra of final slag were measured and deconvoluted. The spectral analysis showed that P5+ ions removed from liquid iron existed in the form of Q0(P) and Q1(P) groups. According to the result, phosphate capacity and phosphorus distribution ratio (LP*) were redefined. The results showed that lgLP* was proportional to molar ratio of Q0(P)/Q1(P), indicating that Q0(P) exerted a significant influence on LP* compared with Q1(P). As the increases of CaO/SiO2 from 0.15 to 1.25 and FeO from 7.2 to 21.9 mass% in the final slag, lgLP* gradually increased, whereas lgLP* showed a downward trend when FeO increased to 29.2 mass%. This was because the increase of O2- ions generated by the dissociations of CaO, MgO and FeO continuously destroyed the network structure and formed more Q0(P) units, which were compensated by the increasing Ca2+, Mg2+, and Fe2+ cations to form stable groups. Meanwhile, the Q0(Si) units formed by slag depolymerization further played a role in fixing Q0(P). However, due to the stronger polarization of Fe2+ than Ca2+ and Mg2+, Q0(P) and Q1(P) units were easily deformed and decomposed by Fe2+. The excessive Fe2+ diluted the proportion of Ca2+ and Mg2+, and made Q0(P) and Q1(P) lose stability. The P5+ ions in the Q0(P) and Q1(P) units were reduced to liquid iron, and the rephosphorization phenomenon occurred, resulting in a decrease of lgLP*.

  • Quantitative Evaluation of the Relationship between Strain and Color Change in Opal Photonic Crystal Films and Application into Complex Specimen Geometries

    Yutao Zhou, Zhipeng Yang, Motomichi Koyama, Saya Ajito, Tomohiko Hojo, Hiroshi Fudouzi, Eiji Akiyama

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    DOI:10.2355/isijinternational.ISIJINT-2022-054

    Abstract

    The color change of opal photonic crystal films (OPCFs) due to deformation was quantitatively evaluated using digital image correlation (DIC) analysis. OPCFs were pasted on specimens of three different gauge geometries, and random patterns were formed on the opposite side of each specimen for DIC analysis. To assess the applicability of using OPCFs-based strain characterization for analyzing steel structural components and associated metallurgical analyses, smooth, width-gradient, and holed specimens were prepared in this study. As deformation increased in the smooth specimen, the color of the OPCFs changed significantly. The color change in the OPCFs could be quantitatively converted into strain values through Hue value analysis. Heterogeneous strain distributions could also be quantitatively analyzed using OPCFs-based analysis at the submillimeter or millimeter scale. When the strain gradient is too high, for example, near a stress concentration site such as a hole, local peeling of the OPCFs away from the specimen surface can occur. Consequently, for quantitative characterization, we must take proper care when measuring this upper limit of the "strain gradient" as well as strain, which would depend on the adhesion and surface condition of the specimen.

  • Simultaneous Analysis of Soluble and Insoluble Oxygen Contents in Al-Killed Steels of Various C Contents and Supersaturation Phenomena in the Steel

    Yong-Min Cho, Dong-Jun Lee, Hyun-Jin Cho, Wan-Yi Kim, Sang-Woo Han, Youn-Bae Kang

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    DOI:10.2355/isijinternational.ISIJINT-2022-059

    Abstract

    Soluble and insoluble O contents ([S. O] and [I. O], respectively) in Al-killed steels of various C contents (0 to ~2 mass pct.) were simultaneously measured using "two-stage" inert gas fusion infrared absorptiometry, where majority of the inclusions was alumina. Several steel specimens were used for the O content analysis where the specimens were either taken from a steel plant or prepared in this laboratory. In addition to this, several pretreatment methods of the specimens were tested in order to provide reliable analysis results. It was found that mechanical grinding of the specimen's surface should be carefully carried out in order not to induce unwanted surface oxidation. This resulted in overestimation of the O content of the specimen. [S. O] and [I. O] in the steel specimens were successfully analyzed using the "two-stage" gas fusion method in the context of inert gas fusion infrared absorptiometry. Considerable portion of total O content ([T. O] = [S. O] + [I. O]) was the [S. O], which was higher than the equilibrium O content of the known Al deoxidation equilibria. Therefore, the supersaturation in the Al deoxidation was confirmed. The analyzed [I. O] was independently validated by measuring area of the exposed alumina inclusions on the polished section of the specimen using SEM. It was also found that increasing C content in the steel lowered the [S. O] while [I. O] hardly changed. It is concluded that C in the steel, mechanical stirring, and remelting, could relieve the supersaturation.

  • Comparative Study of Shear Fracture between Fe-based Amorphous and Ultrafine-grained Alloys Using Micro-tensile Testing

    Yuki Tampa, Kosuke Takagi, Shohei Ueki, Motoki Ohta, Yoji Mine, Kazuki Takashima

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    DOI:10.2355/isijinternational.ISIJINT-2022-088

    Abstract

    Micro-tensile tests were employed to clarify the post-plastic-instability behavior in the shear fractures of specimens with the dimensions of 18×25×50 µm3 made from iron-based amorphous (AM) and ultrafine-grained (UFG) alloys. The AM specimen yielded by localized shear bands with an inclination angle of ~52° with respect to the loading axis, followed by sliding off almost throughout the entire specimen thickness. Micro-tensile and micro-shearing tests revealed that the Mohr failure envelope of the AM specimens could be described by a quadratic equation rather than a linear equation. Therefore, the sliding-off process is assisted by the applied normal stress, which suggests that it is caused by free-volume coalescence. For the UFG specimen, yielding set in by shear band formation with an inclination angle of ~45° with respect to the loading axis, following the Tresca criterion. Necking after shear band diffusion formed a triaxial stress state, which resulted in a final shear fracture plane via void coalescence in the UFG specimens. Voids formed along the intersection of the primary shear bands with secondary shear bands during the necking process. This indicates that the deviation of the shear fracture plane in the UFG specimen was determined by the strain development process. A comparison of the post-plastic-instability behavior between the AM and UFG specimens suggests that the external control of triaxial stress conditions is key to improving the formability of AM specimens.

  • Solute Concentration Distribution in the Vicinity of Solid-Liquid Interface under the Imposition of a Time-Varying Force

    Guangye Xu, Kazuhiko Iwai

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    DOI:10.2355/isijinternational.ISIJINT-2021-177

    Abstract

    Mass transfer is often the rate determining step for solid-liquid reaction, such as an electroplating process in automotive industry and a refining process in metallurgical industry. The decrease of concentration boundary layer thickness through the excitation of convection is adapted to enhance the solid-liquid chemical reaction rate. Therefore, traditional methods excite a macro-scale flow in the bulk liquid. Because the concentration boundary layer exists in the velocity boundary layer, the traditional methods have the limitation in enhancing mass transfer rate. Therefore, a new method was proposed, which imposes force directly near the solid-liquid interface. In the past research, force, with or without an oscillating component was imposed near the solid-liquid interface during the dissolution of a Cu anode into a Cu2+ aqueous solution. The increase of Cu2+ concentration under the force imposition with oscillating component was suppressed compared to that by imposing the force without oscillating component just above the center of the anode. This research evaluated the dissolved Cu2+ concentration distribution and the liquid flow pattern in the whole vicinity of the solid-liquid interface under the force imposition with or without oscillation component. The results indicated that by imposing the force with oscillating component, the increase of the Cu2+ concentration was suppressed in the whole vicinity of the solid-liquid interface, and the Cu2+ concentration distributed more uniformly near the solid-liquid interface. This might be because of the excitation of circulating micro-scale flows near the side parts of the anode surface.

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  • A Novel Process for Separation of Magnetite and Phosphorous Phases from a CaO–SiO2–FeO–P2O5 Slag

    Guoxuan Li, Jinshan Liang, Jun Long, Dong Guan, Zushu Li, Seetharaman Sridhar, Juncheng Li

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    DOI:10.2355/isijinternational.ISIJINT-2021-578

    Abstract

    Iron and phosphorus were successfully separated from CaO–SiO2–FeO–P2O5 slag through atmospheric control, B2O3 addition and a combination of magnetic separation and flotation. For the slag with basicity (CaO/SiO2) of 2.5 and B2O3 addition of 6% (weight percentage), iron and phosphorus in the slag were enriched in the form of magnetite (Fe3O4) and calcium phosphate (Ca10P6O25) phases respectively under Ar atmosphere. Using a combination of magnetic separation and flotation, the concentrates were obtained with Fe3O4 and P2O5 content of 92.84% and 37.66% respectively, corresponding to the recovery ratios of 85.8% for iron and 91.3% for phosphorus.

  • Ironmaking Using Municipal Solid Waste (MSW) as Reducing Agent: A Preliminary Investigation on MSW Decomposition and Ore Reduction Behavior

    Hiroki Hasegawa, Ade Kurniawan, Itsuki Iwamoto, Rochim Bakti Cahyono, Arief Budiman, Yoshiaki Kashiwaya, Takahiro Nomura

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    DOI:10.2355/isijinternational.ISIJINT-2021-552

    Abstract

    The iron and steel industries currently face the depletion of high-grade ore and high CO2 emissions. Some initiatives that effectively utilize alternative carbon sources and abundant low-grade ores become the preferable solutions. This novel study aims to utilize municipal solid waste (MSW) as a reducing agent in ironmaking using low-grade (goethite) ores. As an initial fundamental approach, the comparison of decomposition behaviors between the model and actual MSW was investigated in thermogravimetric analysis. Both model and actual MSWs mainly decompose at 300–500°C. As for reduction tests, pellets containing MSWs and ores with different pretreatments were prepared. The pellets were reduced in an Ar atmosphere at different temperatures. The effect of different ores: high-grade and low-grade ones, on the decomposition of MSW and the iron reduction, were investigated. As a result, interestingly, the low-grade, goethite ore-containing pellet exhibits a more significant reduction degree than the high-grade ones. The reduction is completed in 5 minutes at 700°C and above, indicating a significant reduction by the decomposed carbon. The reduction degree extends at elevated temperature, which reaches more than 94% at 900°C.

  • Comparison of Oxidation Behavior of Various Reactive Elements in Alloys during Electroslag Remelting (ESR) Process: An Overview

    Sheng Chao Duan, Joo Hyun Park

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    DOI:10.2355/isijinternational.ISIJINT-2022-015

    Abstract

    The oxidation behavior of various reactive elements, such as Al/Ti, B/Si, and rare earth metals (REM), by electroslag remelting (ESR) type slag has been investigated utilizing the systematic thermodynamic analysis based on the calculated activity in the fluoride-containing slags by the ion and molecule coexistence theory (IMCT). The results indicate that the IMCT model can be reliably applied to calculate the activity of each component in the ESR type slag. The oxidation behavior of the various reactive elements is completely different by changing the same component in the slag, such as CaO and Al2O3, during the ESR process. Therefore, it is indispensable to find a key parameter to control the homogeneity of the reactive elements in remelted ingots by comparing the effects of the activity of each component and temperature on the equilibrium content of the various reactive elements in alloy melts. The results demonstrate that the oxidation loss of Al/Ti, B/Si, and REM (Ce and La) can be effectively prevented by employing TiO2, B2O3/SiO2, and CaO during the ESR process. Oxidation behavior of B/Si and Ce(La)/Al is weakly susceptible to temperature fluctuation compared with that of Al/Ti in alloy melts, which can be controlled by adding TiO2.

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    3. Quantitative Evaluation Methods for Surface Processing Technology Using Microbial Biofilm: Microbial Biofilm on Iron and Steel Slag, and the Effects of Slag Attached Biofilm on pH Buffering Action ISIJ International Vol.62(2022), No.5

  • Removal of Inclusions using Swirling Flow in a Single-Strand Tundish

    Wenxin Huang, Sheng Chang, Zongshu Zou, Hao Song, Yingxia Qu, Lei Shao, Baokuan Li

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    DOI:10.2355/isijinternational.ISIJINT-2021-600

    Abstract

    Swirling flow tundish was developed to enhance the coalescence of inclusions, so as to deeply clean the liquid steel. Inclusions would gather to the center of the swirling flow by centripetal force, due to the density difference between inclusions and liquid steel. Thus, small inclusions can coalesce into larger ones, and then float to the free surface by their self-buoyance. Physical experiments were carried out in a 1/2.5 scale single strand tundish to study the flow characteristics of tundish with swirling chamber. Numerical modeling was developed to simulate the movements of small inclusions in swirling flow. Discrete phase model was employed together with the O'Rourke algorithm to characterize the coalescence of the inclusions in the swirling flow. The removal of inclusions was investigated, considering the absorption by upper slag and trapping by outside wall of ladle shroud. Compared with a turbulence inhibitor, a swirling chamber shows a similar effect on flow improvement, while performs better in inclusion removal, owing to the inclusion coalescence caused by centripetal force. The results revealed that swirling chamber in diameter of 450 mm is an optimized scheme for deep cleaning of liquid steel, with only 1.66% of the inclusions flowing out of the tundish nozzle.

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    2. Exploration of the Relationship between the Electromagnetic Field and the Hydrodynamic Phenomenon in a Channel Type Induction Heating Tundish Using a Validated Model ISIJ International Vol.62(2022), No.4
    3. Comparison of Oxidation Behavior of Various Reactive Elements in Alloys during Electroslag Remelting (ESR) Process: An Overview ISIJ International Advance Publication

  • Weld Defect Cascaded Detection Model Based on Bidirectional Multi-scale Feature Fusion and Shape Pre-classification

    Haoying Yang, Hongbing Wang, Haihua Li, Xiaoping Song

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    DOI:10.2355/isijinternational.ISIJINT-2022-035

    Abstract

    Object detection algorithms like Faster R-CNN have been widely used in the field of industrial defect detection. For weld defect detection, its detection accuracy for some small targets and difficult-to-classify defects is not high. This paper proposes a Cascade R-CNN detection model for weld defects based on bidirectional multi-scale feature fusion and shape pre-classification. There are defects of different sizes in the weld. In order to improve the detection ability of the model for multi-size defects, the model adopts the bidirectional feature pyramid network, in which an extra bottom-up path after the top-down path aggregation network and an extra edge from the original input to output node are added. According to the statistics of the proportion distribution of long and short axes of weld defects, the defects can be divided into two categories: long strip defects with the proportion of about 2:1 and approximate circle defects with a much bigger proportion. Therefore, each cascade detector is connected in parallel with a two-categories classifier for long strip and approximate circle defects and a five-categories classifier for five specific defects, so as to realize the pre-classification of two morphological defects and mine the difference between the two shapes of defects. In order to avoid over fitting caused by small datasets. Firstly, noise is added to augment the data. Then the training samples are expanded by random flip and mirror in the training, and OHEM is introduced to balance the selection of positive and negative samples. The experimental results show that the detection accuracy of the model on small targets and difficult-to-classify defects is significantly improved. The mAP value is increased by about 9.3% compared with the traditional Faster R-CNN and about 3.3% compared with the traditional Cascade R-CNN.

  • Surface Quality Evaluation of Heavy and Medium Plate Using an Analytic Hierarchy Process Based on Defects Online Detection

    Dongdong Zhou, Yujie Zhou, Xuemin Zhang, Ke Xu

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    DOI:10.2355/isijinternational.ISIJINT-2021-585

    Abstract

    Heavy and medium plate (HMP) is a valuable and irreplaceable material that is widely used in pipelines, bridges, ships, building construction, and power plants. The quality of a plate's surface is closely related to its strength, hardness, and corrosion resistance. HMP is still trimming to length after the continuous casting process. The goal of this research is to evaluate surface quality quickly by combining online detection information of normal and periodic defects with professional quality control skills. To begin, this study creates a set of assessment criteria for HMP surface quality based on length, total defect area, and total area of various types of surface defects on the plate. The analytic hierarchy process (AHP) is then developed to identify based on the operator's experience and expert knowledge, the weights of the classified defects are then determined using the analytic hierarchy process (AHP). Finally, the evaluation grades for each plate may be calculated. The evaluation findings may benefit not only in improving production efficiency, lessening labor intensity, and reducing waste caused by cutting to length, but also in boosting the intelligent control capability of the HMP manufacturing technique.

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  • Effect of Surface Nano-crystalline Layer Formed by Heavy Plastic Deformation Process on Rolling Contact Fatigue

    Nozomu Adachi, Yoshikazu Todaka, Tashika Masaki, Yoshinori Shiihara, Takuya Suzuki, Masahiro Tsukahara, Osamu Idohara

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    DOI:10.2355/isijinternational.ISIJINT-2021-512

    Abstract

    This study developed a deformation process to form a uniform nano-crystalline layer with relatively high thermal stability that can retain even after an induction heating and quenching process on a surface of cylinder-shaped sample. The effect of the surface nano-crystalline layer on rolling contact fatigue life of carbon steels (JIS S45C and S55C) was investigated. The sample with the surface nano-crystalline layer showed lower friction coefficient under cylindrical rolling contact condition comparing to that without the layer. The rolling contact fatigue life was extended to 4 times higher cycles by forming the nano-crystalline layer. It is presumable that the improvement of a rolling contact fatigue is owing to not only the high hardness but also the reduction of friction coefficient during the test followed by a suppression of dynamic tempering softening and variation of stress distribution.

  • Determining Optimum Water Content for Iron Ore Granulation using Agitation Torque of Wet Ore Powder

    Tomotaka Otsu, Hideya Nakamura, Shuji Ohsaki, Satoru Watano, Shohei Fujiwara, Takahide Higuchi

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    DOI:10.2355/isijinternational.ISIJINT-2022-009

    Abstract

    Wet granulation of iron ore powders is a key process in ironmaking. In wet granulation, it is important to determine the optimum content of water added to the original ore powders. To determine the optimum water content, it is important to understand the saturation state in wet ore powder, which can be done by measuring the agitation torque of the wet powder. This study proposes a methodology for determining the optimum water content of various iron ore powders using the agitation torque of wet ore powders. First, measurement of the agitation torque and wet granulation of various iron ore powders were conducted. By comparing the results, it was found that the optimum water content, which was defined as the minimum water content required to diminish fine particles in the original powder, corresponded to the water content exhibiting the maximum agitation torque, regardless of the original powder. Using the agitation torque at different water contents, the saturation degree S, which is the volume ratio of water to the interparticle voids, was calculated, resulting in a range of 0.999 ≤ S ≤ 1.173 at the optimum water content. This suggests that the state between the funicular and capillary states is a suitable saturation state for the wet granulation of ore powders. Consequently, it was demonstrated that it is possible to determine the optimum water content for wet granulation of various iron ore powders based on the water content exhibiting the maximum agitation torque of wet ore powders.

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  • Water Model Study on the Flotation Behaviors of Inclusion Clusters in Molten Steel

    Yulin Zhu, Tao Li, Guozhang Tang, Yingjian Gu, Henan Cui

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    DOI:10.2355/isijinternational.ISIJINT-2021-551

    Abstract

    To improve the performance of steel and produce clean steel with higher quality, the inclusions in the molten steel should be removed and controlled strictly. The removal behaviors of the inclusions, such as flotation, are largely dependent on their size and morphology, which determines the cleanliness of molten steel. It is thus of great importance to clarify the floating behaviors of inclusion clusters with different morphologies. However, the previous work on the floating behaviors of the inclusions is mostly on basis of the spherical inclusions and the influence of the morphology of the inclusions has not been clarified systematically. In this study, the 3D structure of inclusion clusters was established by 3D modeling and fabricated by 3D Printing Technology. A series of water model experiments were performed to investigate the influence of diameter and fractal dimension of inclusion clusters on the terminal floating velocity. In this study, the formula of the terminal floating velocity of the inclusion clusters is derived from the experimental results based on the previous work, which considers the influence of the fractal dimension of the inclusion clusters. It would provide fundamental supports for the research on the removal behaviors of inclusion clusters in molten steel.

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  • Microstructure and Plasticity Evolution During Lüders Deformation in an Fe-5Mn-0.1C Medium-Mn Steel

    Motomichi Koyama, Takayuki Yamashita, Satoshi Morooka, Takahiro Sawaguchi, Zhipeng Yang, Tomohiko Hojo, Takuro Kawasaki, Stefanus Harjo

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    DOI:10.2355/isijinternational.ISIJINT-2021-510

    Abstract

    The local plasticity and associated microstructure evolution in Fe-5Mn-0.1C medium-Mn steel (wt.%) were investigated in this study. Specifically, the micro-deformation mechanism during Lüders banding was characterized based on multi-scale electron backscatter diffraction measurements and electron channeling contrast imaging. Similar to other medium-Mn steels, the Fe-5Mn-0.1C steel showed discontinuous macroscopic deformation, preferential plastic deformation in austenite, and deformation-induced martensitic transformation during Lüders deformation. Hexagonal close-packed martensite was also observed as an intermediate phase. Furthermore, an in-situ neutron diffraction experiment revealed that the pre-existing body-centered cubic phase, which was mainly ferrite, was a minor deformation path, although ferrite was the major constituent phase.

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  • Dissolution of Iron Oxides Highly Loaded in Oxalic Acid Aqueous Solution for a Potential Application in Iron-Making

    Phatchada Santawaja, Shinji Kudo, Atsushi Tahara, Shusaku Asano, Jun-ichiro Hayashi

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    DOI:10.2355/isijinternational.ISIJINT-2020-726

    Abstract

    Oxalic acid has been identified as a sustainable chemical enabling an efficient recovery of target metals from industrial minerals by dissolution. The dissolution process recently has attracted attention as a key reaction in a potential clean iron-making. In this application to efficiently produce a high-purity iron, the dissolution is required to occur in the absence of light, with no addition of other chemical reagents, and to produce high concentration iron oxalate aqueous solution as fast as possible. To reveal the chemistry of iron oxide dissolution for this application, in the present study, the dissolution experiments are carried out under various conditions with a particular focus on the iron oxide highly loaded in the oxalic acid aqueous solution. Highly acidic oxalic acid solution for dissolving the highly loaded iron oxide enabled the production of iron oxalates aqueous solution with the concentration of up to 0.56 mol-Fe/L. Different from conventional studies under diluted conditions with pH control, the dissolution followed a non-reductive mechanism, producing [Fe3+HC2O4]2+ as a dominant iron species, and highly correlated with a concentration of proton in the solution. The experimental results and proposed stoichiometries identified a minimum amount of oxalic acid required for the complete dissolution of iron oxide independently from the concentration and type of loaded iron oxide. Among iron oxides tested (α-Fe2O3, FeOOH and Fe3O4) as the feedstock, Fe3O4 had an advantage in the dissolution rate, but showed a relatively low iron recovery in the solution (80–90%) because of an unavoidable formation of FeC2O4·2H2O precipitates.

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  • An Empirical Comparative Study of Renewable Biochar and Fossil Carbon as Carburizer in Steelmaking

    Ryan ROBINSON, Liviu BRABIE, Magnus PETTERSSON, Marko AMOVIC, Rolf LJUNGGREN

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    DOI:10.2355/isijinternational.ISIJINT-2020-135

    Abstract

    Approximately 60–70% of the direct greenhouse gas emissions in electric arc furnace (EAF) steelmaking originate from the use of fossil carbon charge during melting of steel scrap. Regarding short-term solutions to mitigate the climate impact of steelmaking, there is greater potential to replace fossil carbon charge with renewable carbon in the EAF than in integrated blast furnace steelmaking where mechanical strength requirements on carbon charge are too demanding. Therefore, the present study aims to provide an experimental and practical foundation for using renewable biochar in the EAF as a relatively simple step to decrease the climate impact of steelmaking.In order to evaluate the inherent performance of biochar as a carburizing agent, lab-scale tests where completed using four different types of carbonaceous materials: synthetic graphite, anthracite coal and two types of biochar from woody biomass (BC1 and BC2). The first order dissolution rate constants from experiments ranged between 0.7 to 1.9 × 10-4 m/s, which agrees well with previously reported results. Furthermore, lab-scale results show that biochar properties commonly seen as detrimental, such as low carbon crystallinity and high porosity, do not necessarily constitute a disadvantage for biochar utilization as carburizer in steelmaking.In order to further assess the results from lab-scale tests, an industrial trial including six consecutive heats was performed in a 50 t EAF at the Höganäs Halmstad Plant. Results show that 33% substitution of standard Anthracite carbon charge with biochar BC2 gave no deviation from normal operating conditions in the EAF.

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  • © The Iron and Steel Institute of Japan

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06 Jul. (Last 30 Days)

  1. Production and Technology of Iron and Steel in Japan during 2021 ISIJ International Vol.62(2022), No.6
  2. Role of Interfacial Properties in the Evolution of Non-metallic Inclusions in Liquid Steel ISIJ International Advance Publication
  3. Preface to the Special Issue on “Frontier in Characterization of Materials and Processes for Steel Manufacturing” ISIJ International Vol.62(2022), No.5
  4. Application of Heat Transfer Coefficient Estimation Using Data Assimilation and a 1-D Solidification Model to 3-D Solidification Simulation ISIJ International Advance Publication
  5. Wettability of Molten Fe–Al Alloys against Oxide Substrates with Various SiO2 Activity ISIJ International Advance Publication
  6. Reduction of CO2 Emissions from Blast Furnace Applying Reactive Coke Agglomerate and Hydrogen Reduction Tetsu-to-Hagané Vol.108(2022), No.6
  7. Nitrogen Solubility and Gas Nitriding Kinetics in Fe–Cr–Mo–C Alloy Melts under Pressurized Atmosphere ISIJ International Vol.62(2022), No.6
  8. Comparison of Oxidation Behavior of Various Reactive Elements in Alloys during Electroslag Remelting (ESR) Process: An Overview ISIJ International Advance Publication
  9. Influence of Al2O3/SiO2 and BaO/Al2O3 Ratios on Rheological and Crystallization Behavior of CaO–BaO–Al2O3-Based Mold Slags ISIJ International Vol.62(2022), No.6
  10. Synergistic Effect of Brightener and Solution Temperature on the Electrodeposition Behavior of Zn–Ni Alloy from Alkaline Zincate Solution ISIJ International Advance Publication

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