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

ISIJ International Vol. 61 (2021), No. 8

  • Effect of the Location of Tracer Addition in a Ladle on the Mixing Time through Physical and Numerical Modeling

    Mario Herrera-Ortega, José Ángel Ramos-Banderas, Constantin Alberto Hernández-Bocanegra, José Julián Montes-Rodríguez

    pp. 2185-2192

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    DOI:10.2355/isijinternational.ISIJINT-2021-094

    Abstract

    In the present work, the release of tracer location on the global mixing time in an agitated ladle furnace by gas bottom injection was analyzed. Then, a numerical multiphasic steel-slag-argon-air system of a prototype with a capacity of 150 tons was carried out. The simulation was validated by using a physical model with a 1/6 geometric scale using colorant, KCl dispersion measurements techniques and open slag eye opening. Four different tracer addition locations were strategically established to study the influence of tracer releasing location on chemical homogenization. From the results, it was found that the measurement of mixing times varies according to the location of the tracer addition, which to a greater extent is conditioned by the convective currents that at some extent were related to turbulent viscosity.

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    2. Formation and Evolution of Inclusions in High Chromium Steel ISIJ International Vol.61(2021), No.9

  • Effect of La2O3 on the Viscosity, Crystallization, and Structure of Calcium-silicate-based Mold Flux for Continuous Casting La-bearing FeCrAl Alloy

    Lei Fan, Chengjun Liu, Jie Qi, Maofa Jiang

    pp. 2193-2199

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    DOI:10.2355/isijinternational.ISIJINT-2021-112

    Abstract

    The influence of La2O3 on the properties and structure of calcium-silicate-based mold flux for continuous casting La-bearing FeCrAl alloy was studied through employing rotating viscometer, SEM-EDS, XRD, and Raman spectroscopy. The results showed that the viscosity of mold fluxes decreased with the increase of La2O3 content from 0 mass% to 15 mass%. The apparent activation energy for viscous flow decreased from 108.56 ± 1.96 kJ/mol to 87.29 ± 7.29 kJ/mol with increasing La2O3. Deconvolution Raman analysis showed that with increasing La2O3, the mole fraction of Q3 units decreased, while that of Q0, Q1, and Q2 units increased. Furthermore, the values of NBO/Si increased from 1.27 to 1.83 with the increase of La2O3, which indicated that the degree of polymerization of melt structure was reduced and lead to the decrease of viscosity. During the cooling process, cuspidine (Ca4F2Si2O7) was the main crystalline phase in calcium-silicate-based mold fluxes. Nevertheless, when La2O3 was excessively added, a new phase of CaLa2(SiO4)2 was formed owing to the charge balance of Ca2+ and La3+ on the simple structural units Q0 ([SiO4]4−). Therefore, with increasing La2O3 can increase the break temperature and accelerate the formation of crystalline phases Ca4F2Si2O7 and CaLa2(SiO4)2 at high temperature.

  • Strength and Gasification Reactivity of Coke Prepared by Blending a Ca/C Composite and Coal

    Yuuki Mochizuki, Miki Takahashi, Javzandolgor Bud, Yuting Wang, Naoto Tsubouchi

    pp. 2200-2210

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    DOI:10.2355/isijinternational.ISIJINT-2020-622

    Abstract

    In this study, a calcium/carbon composite (Ca/C) was prepared from porous CaO by the water vapor swelling method; its pores were filled with tar-derived carbonaceous material to produce high-strength and highly reactive coke. The properties of coke prepared by blending the Ca/C composite and caking-coal were then investigated. The mesopores in the swelling Ca disappeared and the crushing strength was developed by filling tar-derived carbonaceous material into the porous Ca. Thus, a Ca/C composite could be produced by the abovementioned method, wherein the tar-derived carbonaceous material and Ca species were in close proximity. When the Ca/C composite was blended into the caking-coal, the strength of the coke obtained increased by up to 50% of Ca/C blending, which made it possible to produce high-strength coke. On examining the C structure of the prepared coke by X-ray diffraction, that of the original coke was found to be almost unchanged by adding the Ca/C composite. Conversely, the Ca/C blended-coke showed higher CO2 gasification reactivity than the original coke prepared from caking-coal. Based on the CO2 gasification reactivity test of the demineralized coke, it was clear that an increase in the gasification reactivity of the Ca/C blended-coke depended upon the catalytic effect of Ca. Thus, this method helped produce high-strength and highly reactive coke.

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  • Effect of Ti–V Magnetite Concentrate Pellet on the Strength of Green Pellets and the Quality of Sinter by Composite Agglomeration Process (CAP)

    Yanan Lu, Shengli Wu, Heng Zhou, Liming Ma, Zhengjian Liu, Yang Wang

    pp. 2211-2219

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    DOI:10.2355/isijinternational.ISIJINT-2021-005

    Abstract

    The composite agglomeration process is one of the most potential methods to effectively produce blast furnace burden with vanadium-titanium magnetite. In this work, the effects of V–Ti magnetite particle size, coke breeze ratio of green pellets, coke breeze of pelletized feed, and pelletized feed basicity on quality of CAP products were studied. The results shown that the drop strength and compressive strength of green pellets are improved when the vanadium-titanium magnetite is pretreated by high-pressure grinding roll compared with those prepared from raw material. With the increase of basicity of flux green pellets, the strength of green pellets, the permeability of mixed layer and the sinter yield increase. When the basicity of green pellets is 0.9, the economic and technical indexes of sintering are the best. After finely grinding coke powder for sintering and adding vanadium-titanium magnetite to prepare carbon-containing green pellets, the amount of coke powder should be controlled at about 0.4 mass%, considering the drop strength and compression strength of green pellets,. However, sintering with pellets containing 0.4% coke breeze in the core produces perforated pellets or molten pellets. Therefore, it is not recommended to use coke powder in CAP pellet.

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    3. Thermal Stability of Molten Slag in Blast Furnace Hearth ISIJ International Vol.61(2021), No.8

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

    Nobuhiro Maruoka, Hironari Kubo

    pp. 2220-2226

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    DOI:10.2355/isijinternational.ISIJINT-2021-038

    Abstract

    Due to the low quality of available iron ore, it is necessary to develop a new technology to produce high quality steel from ore containing a high concentration of phosphorous. In this study, we propose a new process for producing low-P steel by concentrating P in the dicalcium silicate phase through a partial reduction process. High-P iron ore was mixed with varying quantities of CaO and graphite and heated at 1573 K in an Ar atmosphere, and the obtained product was analyzed by electron probe microanalysis. It was found that in the reduced product mixture that was obtained under specific conditions of high basicity and a lower amount of added carbon, more than 95% of P was concentrated in the dicalcium silicate phase, and the P content in metallic iron was sufficiently low.

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    3. Modeling of Wall Shear Stress Induced Inclusion Transport and Removal in Multi-Strand Tundish ISIJ International Vol.61(2021), No.9

  • Thermal Stability of Molten Slag in Blast Furnace Hearth

    Jian Zhang, Kexin Jiao, Jianliang Zhang, Hengbao Ma, Yanbing Zong, Ziyu Guo, Zhongyi Wang

    pp. 2227-2236

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    DOI:10.2355/isijinternational.ISIJINT-2021-066

    Abstract

    The thermal stability of the molten slag plays an extremely important role in the smooth production of the blast furnace. In this paper, the effects of basicity, Al2O3 content and MgO content on the thermal stability of the slag during heat fluctuations were investigated. The effect of slag basicity and composition on slag viscosity behavior was measured by the rotating cylinder method under the condition of heat fluctuation and constant temperature. The slag temperature and solid phase precipitation under thermal fluctuations were calculated. The effect of thermal fluctuations of the slag on viscosity was clarified. The results show that the specific heat capacity of the slag first decreases and then increases as the slag basicity increases, and it increases with the rise of Al2O3 as well as MgO. The average viscosity change rate of slag under fixed heat is much more pronounced than that of at a constant temperature with the variation of slag basicity as well as Al2O3, while it is inverse for the effect of MgO. When the slag heat is reduced, the change in slag basicity has the greatest effect on the slag temperature, followed by the Al2O3 content and MgO content. It indicates that MgO helps to maintain a stable slag temperature. Therefore, appropriately increasing the basicity of the slag, controlling a lower Al2O3 content and maintaining a suitable MgO content will help to improve the thermal stability of the slag.

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  • An Online Sintering Batching System Based on Machine Learning and Intelligent Algorithm

    Song Liu, Yadi Zhao, Xin Li, Xiaojie Liu, Qing Lyu, Liangyuan Hao

    pp. 2237-2248

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    DOI:10.2355/isijinternational.ISIJINT-2020-522

    Abstract

    Aiming at the problem that the accuracy and economy of the traditional off-line batching method are not high, the online batching system (BSMLIA) based on machine learning and intelligent algorithms was put forward from three aspects: real-time, technical requirements and economic benefits. The accurate solution and on-line fast calculation of sintering raw material ratio under the influence of multiple factors are solved. Specifically, a BSMLIA architecture with three levels of data communication layer (DCL), parameter prediction and batching optimization layer (PPBOL), and diagnostic decision layer (DDL) was first designed to realize online monitoring and abnormal diagnosis of sinter performance. Then, the sintering batching adjustment and optimization module (SBAOM) was elaborated. The mixture performance prediction model was developed by MLR and LightGBM algorithm, the model can be based on sinter composition and quality index requirements and current sintering production process parameters to calculate the appropriate mixture performance. In addition, the pre-batching model and the sintering batching model were established to achieve the solution of the lowest raw material cost ratio for a given mixture performance. Finally, the actual production data was used to verify the SBAOM. The results proved that the online batching system can not only quickly calculate the batching plan that meets the requirements, but also reduce the batching cost by RMB 29.54/ton.

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  • Phase Quantification of Regular and Turbo-stratified Graphite in Cast Iron by X-ray Diffractometry/Rietveld Refinement

    Atsushi Ohbuchi, Kosuke Otori, Kenta Hagiwara, Yuya Koike, Toshihiro Nakamura

    pp. 2249-2255

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    DOI:10.2355/isijinternational.ISIJINT-2021-070

    Abstract

    A method to quantify regular graphite and turbo-stratified graphite (TS-graphite) forming the free carbon in ductile cast iron was developed using X-ray powder diffractometry. Iron in accurately sampled 2–4 g of the ductile cast iron powder was decomposed using hydrochloric acid without heating, and the residue was centrifugally separated. Graphite, TS-graphite, wustite (FeO), and amorphous silicate were identified in the residue. Calibration-standard mixtures were prepared by mixing corundum (α-Al2O3), griceite (LiF), and graphite powder which showed the most similar full-width at half-maximum value of (002) line to that of graphite in the ductile cast iron sample. The calibration curve of graphite showed good linearity, with a range of 0–200 mg corresponding to the 0–5.0 mass% of graphite in the 4.00 g of the cast iron sample. The quantitative value of total graphite in the ductile cast iron sample was 3.17 mass% with 8.0% of relative standard deviation for n = 5. The peak area ratio of graphite and TS-graphite was calculated using Rietveld refinement by assuming the same atomic scattering factor for each graphite measurement. The concentration ratio of graphite and TS-graphite were 67.8 and 32.2%, respectively. The analytical values of graphite were in good agreement with those of the NIST gray cast iron standard material, with concentration ratio of 53.7% and 46.3% for graphite and TS-graphite, respectively.

  • Effect of Reaction Product of Epichlorohydrin and Imidazole on the Electrodeposition Behavior of Zn–Ni Alloy from Alkaline Zincate Solution

    Sung Hwa Bae, Satoshi Oue, Injoon Son, Hiroaki Nakano

    pp. 2256-2263

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    DOI:10.2355/isijinternational.ISIJINT-2021-080

    Abstract

    A Zn–Ni alloy was electrodeposited on a Cu electrode at a current density of 10–5000 A·m−2, a charge of 5 × 104 C·m−2, and temperature of 293 K in an unagitated zincate solution containing the reaction product of epichlorohydrin and imidazole (EI polymer) as a brightener. The effect of the EI polymer on the deposition behavior of the Zn–Ni alloy was investigated. The transition current densities at which the deposition behavior shifted from the normal type to anomalous were 50–100 A·m−2 and 10–20 A·m−2 in the EI polymer-free solution and polymer containing solutions, respectively, indicating that the EI polymer decreased the transition current density. The transition current density corresponded to the current density at which the potential of the total polarization curve significantly shifted from the more noble region than the equilibrium potential of Zn to the less noble region. The decrease in transition current density with EI polymer was attributed to the suppression of hydrogen evolution. In addition, the current efficiency for alloy deposition in the high-current-density region decreased due to the suppression of both Zn and Ni depositions. The Ni content of deposited films decreased with EI polymer, indicating that Ni deposition was more suppressed with the EI polymer addition than Zn deposition. With increasing current density, the crystals of the films deposited from the EI polymer-containing solution smoothened and showed significant brightness. The oxidation reaction of the films deposited from the EI polymer-containing solution was suppressed, thus causing the corrosion potential to shift to a noble direction.

  • Diffusion Behavior of Al in Zn Coating Layer of Zn-0.2mass%Al Hot-dip Galvanized Steel Sheets with and without Temper Rolling during Aging after Production

    Katsuya Hoshino, Katsunari Oikawa, Yusuke Okumura, Shoichiro Taira

    pp. 2264-2273

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    DOI:10.2355/isijinternational.ISIJINT-2021-096

    Abstract

    It is known that Al added to the Zn coating layer of hot-dip galvanized steel sheets (HDG) diffuses to the surface at room temperature and forms Al-based oxides in air. In order to understand the diffusion behavior of Al in Zn coating layer, this study investigated the effect of the aging temperature on the segregation behavior of Al-based oxides in HDG with and without temper rolling (skinpass rolling) using a material with a Zn coating weight of about 56 g/m2 with an Al content of approximately 0.20 mass%. The specimens were aged at −15, 5, 20, 38, 100 or 200°C in air after production, and the surface and cross sections were observed and analyzed by XRF, SEM-EDX, EBSD and TEM. As a result, up to the aging temperature of 38°C, the amount of Al-based oxides increased linearly to the square root of aging time, suggesting that the formation rate is determined by the diffusion of Al in Zn coating layer in this temperature range. However, this linear relationship did not hold at aging temperatures above 100°C. In addition, in the temper-rolled HDG, the formation rate of Al-based oxides is larger than that without temper rolling up to the aging temperature of 38°C, and then decreased drastically at aging temperatures above 100°C. The segregation behavior of Al-based oxides is discussed in view of the diffusion behavior of Al and the changes in the macrostructure of the Zn coating layer during the aging after production.

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  • Effect of Carbon Content on Three-body Abrasive Wear Characteristics of 28Cr-3Ni Cast Alloys

    Takayuki Todaka, Kazumichi Shimizu, Kenta Kusumoto, Riki Hendra Purba, Yila Gaqi

    pp. 2274-2283

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    DOI:10.2355/isijinternational.ISIJINT-2021-099

    Abstract

    Abrasive wear resistance of white cast iron can be improved by adding transition metals due to carbide formation and matrix stabilization. However, it must also be affected by carbon content which has received little attention from researchers. Therefore, this study would investigate the influence of (1.4 and 2.8 wt.%) C on three body abrasive wear characteristics of 28Cr-3Ni cast alloys. High Cr-based multi-component white cast irons (Hi–Cr MWCIs) were used as comparison materials to estimate the life-service of each material. The abrasion test was performed using a rubber wheel abrasion machine test with two different sizes of silica sands (1100HV1).As results, the microstructure consists of martensite (the main matrix) and M7C3 carbide. Additionally, M2C carbide was also precipitated on the microstructure of Hi–Cr MWCIs. Meanwhile, Ni or Co was embedded in the matrix area of materials microstructure. In the case of 28Cr-3Ni, the higher amount of C has a higher carbide volume fraction and hardness leading to be better abrasive wear resistance at high loads. However, the reverse trend occurred at low loads with different sizes of abrasive particles. By comparing to Hi–Cr MWCIs, its abrasive wear resistance is lower owing to the fewer carbide types. In the case of Hi–Cr MWCIs, the higher Cr addition significantly consumes C content during the solidification process resulting to lower hardness and wear resistance. Therefore, it can be concluded that the three abrasive wear performance of materials is strongly influenced by C content, applied load, and abrasive particle size.

  • In-situ Observation of Cracking and Healing Behavior of High-carbon Steel during Oxide Scale Growth

    Guangming Cao, Xinyu Gao, Shuai Pan, Wenchao Shan, Hao Wang, Zhenyu Liu

    pp. 2284-2291

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    DOI:10.2355/isijinternational.ISIJINT-2020-658

    Abstract

    This study investigates cracking and healing behavior during the oxide scale formation on high-carbon steel. The steel was heated to 1000°C at a rate of 2°C/s in the air atmosphere. The surface morphology of the oxide scale was monitored in situ using Laser Scanning Confocal Microscopy (LSCM) and oxide phases in the scale were analyzed by X-ray diffraction (XRD). The microstructures of scale cross-sections were analyzed by Electron Probe Micro-analysis (EPMA). Based on the surface morphology of the oxide scale at different temperatures, we established a relationship between blistering and the “state” of the oxide scale. Blistering occurs during the scale growth due to the decarburization process, since evolved gaseous products cause swelling and eventual rupturing of the oxide scale, forming cracks on the surface. Thermal stress induced by the difference in FeO/Fe3O4 thermal expansion coefficients causes crack expansion. Subsequent crack healing consists of the following steps: (1) oxygen penetrates the oxide scale through the cracks and reacts with FeO to form Fe3O4. This reduces the difference in the thermal expansion coefficients and decreases the thermal stress, restraining the crack expansion; (2) at a certain temperature, the oxidation rate increases and oxygen reacts with the substrate to form new oxides, which fill in the formed blisters. The mechanism of crack expansion and healing was developed by monitoring the evolution of oxide scale morphologies during the blistering process.

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  • Influence of High-pressure Quenching on the Microstructure, Martensite Transformation, and Mechanical Properties of 0.2 Mass% C Steel

    Qing Cui, Jie Liu, Chang Xu, Yujun Xu, Hao Huang, Bin Wen, Xiaoping Lin

    pp. 2292-2298

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    DOI:10.2355/isijinternational.ISIJINT-2020-784

    Abstract

    Low-carbon steel (0.2 mass%) samples were austenitized and quenched at a cooling rate of 10°C/s under GPa level high pressure. The morphology, lattice constant, and order degree of C atom distribution of high-pressure quenching martensite were characterised and analyzed by TEM, EBSD, XRD, and Mössbauer. Besides, the transformation characteristics and strengthening mechanisms were discussed. The results show that the microstructure of 0.2 mass% C steel is fine hierarchical lath martensite with almost no residual austenite, and its laths mostly follow {112} <111> twin relationship, indicating the self-accommodation effect among martensite variants. Compared to atmospheric pressure, the order degree of carbon atom distribution increases in high-pressure quenched martensite, meanwhile the tetragonality (c/a) of martensite lattice increases from 1.009 at atmospheric pressure to 1.012 at 4 GPa. The significant promotion of hardness in 0.2 mass% C steel subjected to high-pressure treatment can be ascribed to a large number of dislocations in the structure, grain refinement strengthening caused by twin boundary, and solution strengthening caused by large distortion due to the increase of the order degree for C atom distribution and the decrease of lattice constant. These findings provide new insights into the carbon steel martensite transformation mechanism, and a new martensite transformation technique can be developed.

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  • Evaluation of Multiaxial Low Cycle Creep-fatigue Life for Mod.9Cr-1Mo Steel under Non-proportional Loading

    Yuta Nakayama, Fumio Ogawa, Noritake Hiyoshi, Ryuta Hashidate, Takashi Wakai, Takamoto Itoh

    pp. 2299-2304

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    DOI:10.2355/isijinternational.ISIJINT-2020-780

    Abstract

    This study discusses the creep-fatigue strength for Mod.9Cr-1Mo steel at a high temperature of 823 K under multiaxial loading. Low cycle fatigue tests in various strain waveforms were performed with a hollow cylindrical specimen. The tests were conducted under a proportional loading with a fixed axial strain and a non-proportional loading with a 90-degree phase difference between axial and shear strains. The tests at different strain rates and the creep-fatigue tests at different holding times were also conducted to discuss the effects of stress relaxation and strain holding on the failure life. In this study, two types of multiaxial creep-fatigue life evaluation methods were proposed: the first method is to calculate the strain range using Manson’s universal slope method with considering a non-proportional loading factor and creep damage; the second method is to calculate the fatigue damage by considering the non-proportional loading factor using the linear damage law and to calculate the creep damage from the improved ductility exhaustion law. The accuracy of the evaluation methods is much better than that of the methods used in the evaluation of actual machines such as time fraction rule. The second method proposed by the authors showed the highest evaluation accuracy. The first evaluation equation is slightly less accurate than the second, but it is useful in that the evaluation procedure is easy.

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  • Hydrogen Effects on the Migration of Nanoscale Cavities in Iron

    Kazuto Arakawa, Akira Kageyama, Hideto Hiroshima, Hidehiro Yasuda, Shigenobu Ogata

    pp. 2305-2307

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    DOI:10.2355/isijinternational.ISIJINT-2021-140

    Abstract

    Accurate knowledge of the influence of hydrogen on the behavior of vacancies and vacancy clusters is crucial for understanding the mechanism of hydrogen embrittlement of α-iron and its alloys. Using in-situ transmission electron microscopy, we examined the effects of hydrogen on the behavior of nanoscale cavities under heating, by comparison between the behaviors of cavities without hydrogen produced upon high-energy electron irradiation and those with hydrogen produced upon electro-deposition. It is revealed that hydrogen promotes the migration of cavities, in contrast to a traditional notion.

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  • Effect of Aging on Low-temperature Tensile Properties of Ultra-low Carbon Steel

    Norimitsu Koga, Yuki Kanehira, Pham Thi Thanh Huyen, Kazuya Hori, Osamu Umezawa

    pp. 2308-2316

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    DOI:10.2355/isijinternational.ISIJINT-2021-143

    Abstract

    The microstructural changes and low-temperature tensile properties of ultra-low carbon steel aged at 443 K were examined, and the relationship between the low-temperature tensile properties and ultra-low carbon state was discussed. Fine cementites of approximately 60 nm were observed at 0.6 ks and coarsened to approximately 800 nm at 600 ks. The yield and tensile stresses at 77 K increased until 6 ks and then decreased. The nominal stress-strain curves of all the specimens at 77 K exhibited low elastic limits, the nominal stress plateaued from an approximate nominal strain of 0.002 and, subsequently, work hardening occurred. In the unaged and 6 ks aged specimens, several twins were generated after the elastic limit, and which increased dramatically in the nominal stress plateau regime, and corresponded to macroscopic yielding. In contrast, the number of twins in the 600 ks aged specimen negligibly increased during macroscopic yielding. Macroscopic yielding occurred in the unaged and 6 ks aged specimens by deformation twinning, while in the 600 ks aged specimen it occurred by slip deformation. In the 6 ks aged specimen, the fine cementites and/or decrease in solid solute carbon enhanced the critical resolved shear stresses of deformation twinning, resulting in the highest strength. In the 600 ks aged specimen, the coarse cementites negligibly enhanced the critical resolved shear stress for slip deformation. Hence, the strength of the specimen aged for 600 ks decreased as compared to the specimen aged for 6 ks, and slip deformation occurred.

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  • Improvement of Filtration Performance of Foam Ceramics Using External Electric Field

    Chen Tian, Lei Yuan, Lei Jia, Yan Li, Zhenli Liu, Hao Zhang, Tianpeng Wen, Jingkun Yu

    pp. 2317-2319

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    DOI:10.2355/isijinternational.ISIJINT-2021-172

    Abstract

    To enhance filtration performance of foam ceramics, effects of electric field on filtration performance of foam ceramics were studied. Results show that external electric field can change the wettability between melt and foam ceramics and can improve filtration performance of foam ceramics. Meanwhile, chemical composition of melt is not affected by external electric field.

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  • Hydrogen Permeation Property of Bulk Cementite

    Nozomu Adachi, Haruki Ueno, Katsuhiko Onoe, Satoshi Morooka, Yoshikazu Todaka

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    DOI:10.2355/isijinternational.ISIJINT-2021-134

    Abstract

    This study investigated the hydrogen permeation property of cementite by fabricating bulk cementite sample using the process combining the mechanical ball milling and subsequent pulse current sintering. The bulk cementite sample having a 96 vol% of cementite was successfully fabricated. The prepared bulk cementite showed no signal of hydrogen permeation during the 3.5 day of electrochemical hydrogen permeation test. The morphology of blister formed in the sample indicated that diffusion coefficient of hydrogen in cementite is very small.
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