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

ISIJ International Vol. 55 (2015), No. 12

  • Production and Development of Large Blast Furnaces from 2011 to 2014 in China

    Dong-dong Zhou, Shu-sen Cheng, Ying-sheng Wang, Xi Jiang

    pp. 2519-2524

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    DOI:10.2355/isijinternational.ISIJINT-2015-353

    Abstract

    This article reviews the production and technical characteristics of the large blast furnaces in China. The reasons for low level development of large blast furnace in past decades were analyzed. It introduces the production, raw materials and operation indexes of large blast furnaces from 2011 to 2014. On this basis, some thoughts on operations of large blast furnace were proposed. The affected factors on the development of large blast furnace were analyzed, the conclusion that the number of large blast furnace in China will increase in future was obtained.

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    1. Low Carbon Operation of Super-Large Blast Furnaces in China ISIJ International Vol.55(2015), No.6
    2. Injection of Flux into the Blast Furnace via Tuyeres for Optimising Slag Formation ISIJ International Vol.39(1999), No.7
    3. Development of Control Techniques for Mixing Small Coke at Bell-less Top Blast Furnace ISIJ International Vol.55(2015), No.6

  • Measurement and Characterization of the Apparent Viscosity of Fe–C Melts during Solidification

    Yan-Ling Zhang, Qi Li, Zhuo-Qing An, Zhan-Cheng Guo

    pp. 2525-2534

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    DOI:10.2355/isijinternational.ISIJINT-2015-389

    Abstract

    The rheology of Fe–C melts during solidification can give important insight into the process operations and product quality of the resulting alloys. Here, we investigated the apparent viscosity of Fe–C melts during solidification. The testing spindle of the traditional rotation method for measuring the viscosity of liquids was improved so that it could be used to measure the apparent viscosity of Fe–C melts during solidification. Further, the apparent viscosity of Al2O3 particles in methyl silicon oil, a representative liquid-solid slurry system, was measured. The effects of the particle fraction, particle shape and particle size on the apparent viscosity of the slurry were examined and the viability of a viscosity prediction model was tested. Finally, the apparent viscosity of Fe–C melts during solidification was measured. Our results showed that the apparent viscosity of Fe–C melts during solidification increased with increasing cooling rate and decreasing shear rate. The effect of precipitated particle structures on the apparent viscosity of Fe–C melts during solidification was similar to the effect that Al2O3 particles had on the methyl silicon oil–Al2O3 particle system. The viscosity model to predict the apparent viscosity of Fe–C melts under different solidification conditions was proposed.

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    1. Influence of Hydrogen on Local Mechanical Properties of Pure Fe with Different Dislocation Densities Investigated by Electrochemical Nanoindentation ISIJ International Vol.56(2016), No.12
    2. Effect of Na2SO4 on the Embedding Direct Reduction of Beach Titanomagnetite and the Separation of Titanium and Iron by Magnetic Separation ISIJ International Vol.55(2015), No.12
    3. Formation of Fine Austenite through Static Recrystallization in Low Carbon Micro-alloyed Steels ISIJ International Vol.55(2015), No.12

  • Concentrating of Iron, Slag and Apatite Phases from High Phosphorous Iron Ore Gaseous Reduction Product at 1473 K by Super Gravity

    Jintao Gao, Lei Guo, Zhancheng Guo

    pp. 2535-2542

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    DOI:10.2355/isijinternational.ISIJINT-2015-416

    Abstract

    According to the melting behavior of high phosphorous iron ore gaseous reduction product at 1473 K, the iron grains remain in solid state, and the other minerals have formed into slag phase, as well as the phosphorus mainly exist in the form of apatite coexisting with slag phase, while it is impossible to accomplish the iron-slag separation at that temperature under the conventional conditions. Hence, concentrating experiments of iron, slag and apatite phases from high phosphorous iron ore gaseous reduction product at 1473 K by super gravity were carried out in this study, and the results confirmed that it was a feasible and effective method. The layered structures appear significantly in the samples obtained by super gravity treatment, the iron grains and molten slag moved in opposite direction and concentrated at the bottom and upper of the sample, respectively, and the apatite crystals concentrated in the iron-slag interface. Moreover, increasing the gravity coefficient is definitely beneficial for the separating and concentrating of iron, slag and apatite phase. With the gravity coefficient of G=1200, the mass fraction of MFe in the iron rich phase is up to 90.50 wt%, and that of P is decreased to 0.061 wt% after removing the slag inclusion in iron rich phase.

  • Effect of Na2SO4 on the Embedding Direct Reduction of Beach Titanomagnetite and the Separation of Titanium and Iron by Magnetic Separation

    Chao Geng, Tichang Sun, Huifen Yang, Youwen Ma, Enxia Gao, Chengyan Xu

    pp. 2543-2549

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    DOI:10.2355/isijinternational.ISIJINT-2015-420

    Abstract

    A novel process for separating iron and titanium from Indonesian beach titanomagnetite (TTM) concentrates is proposed. This process involves several steps, including mixing the TTM concentrate and additive, pressing the mixture into pellets, embedding direct reduction of the pellets, and magnetic separation. Given that coal and additives are the main factors influencing the coal-based direct reduction of beach TTM, this study employed embedding reduction, where pellets are embedded under the coal to be reduced, and Na2SO4 was used as an additive. The best result was obtained when the Na2SO4 dosage was 4%, and the direct reduction iron powder (DRI powder) with an iron grade of 94.45%, iron recovery of 85.18%, and TiO2 content of 0.44% were obtained. Titanium concentrate assay yielded 40.43% TiO2 containing main titanium minerals of ilmenite and ferrous pseudobrookite. The results showed that a suitable Na2SO4 addition (4–6%), DRI powder and titanium concentrate presented better iron recovery and TiO2 grade as compared without addition, while this advantage disappeared as Na2SO4 addition increased (>6%). The characteristics of roasted pellets were analyzed through X-ray diffraction, scanning electron microscopy, and energy dispersive spectrometry. Results showed that FeS and nepheline are formed by addition of Na2SO4, thereby benefiting the migration and growth of metallic iron particles in the redox system and separation of titanium and iron. While a suitable dosage of Na2SO4 could promote porosity and induce a reducing atmosphere, but more liquid phase formed by an excessive Na2SO4 was unfavorable and caused expansion of the pellets.

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  • Effect of Coke Breeze Distribution on Coke Combustion Rate of the Quasi-particle

    Hiroshi Ogi, Takayuki Maeda, Ko-ichiro Ohno, Kazuya Kunitomo

    pp. 2550-2555

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    DOI:10.2355/isijinternational.ISIJINT-2015-089

    Abstract

    Coke combustion rate in an iron ore sintering process is one of the most important factors for quality and productivity of sintering iron ore.
    In order to improve coke combustion efficiency, a new granulation method was developed. In the new granulation method, coke and limestone are segregated to the particle’s surface. The purpose of this study is to investigate the effect of coke distribution in the quasi-particle on coke combustion rate.
    Four kinds of samples, which have different coke distributions, were prepared. The samples consist of interior part and exterior part.
    Combustion experiments were carried out under air atmosphere at 1073 K, 1223 K, 1373 K and 1523 K. From the results, coke combustion rates were improved when added coke were segregated to sample’s surface. At higher experimental temperature, the combustion rates become faster. The results were analyzed by using unreacted-core model with one reaction interface.
    From the kinetic analysis, it was found that the coke distribution of the quasi-particle had effects on not the interfacial reaction rate but the oxygen diffusion. In other words, oxygen diffusion in the quasi-particle become faster when added coke was segregated to the quasi-particle’s surface. This is one of the main reasons that coke combustion rate in quasi-particle made from new granulation method was improved.

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    3. Dynamic Wettability of Liquids on Gasified Metallurgical Cokes ISIJ International Vol.57(2017), No.7

  • Factors Controlling High-temperature Zone Resistance to Airflow during Iron Ore Sintering

    Hao Zhou, Mingxi Zhou, Zihao Liu, Ming Cheng, Kunzan Qiu, Kefa Cen

    pp. 2556-2565

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    DOI:10.2355/isijinternational.ISIJINT-2015-311

    Abstract

    A fundamental study was carried out on the high-temperature zone flow resistance during iron ore sintering. In present work, firstly, quartz sand was used to replace iron ores to investigate the impact of temperature if bed structure has no change; then a three-layer bed structure was used to explore the primary factors controlling high-temperature zone structure for airflow. The zone where temperature above 700°C is defined as high temperature zone. High-temperature zone flow resistance depends on sinter bed temperature and high-temperature zone structure which was related to melt volume, melt properties, bed voidage, drive force and high temperature zone thickness. A new model [ This part of text is omitted ] which can suggest high-temperature zone flow resistance was established by using Support Vector Machine (SVM) model and predicted airflow rate well. Drive force has a very impact on high-temperature zone flow resistance. It can dilute gas channels in the high-temperature zone and increase or maintain sinter bed permeability. Sintering under lower suction has greater high-temperature zone resistance. Too much melt will deteriorate high-temperature zone permeability; sintering airflow rate with high coke rate in the bottom layer decreases by around 25% at a suction of 8 kPa. Similarly melt properties also have a great impact on high-temperature zone resistance; high viscosity is bad for gas channels formation in the high-temperature zone. Under a limited range increasing coke rate has little influence on high-temperature zone resistance.

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    2. Combustion Behavior of Pulverized Coal and Ash Particle Properties during Combustion ISIJ International Vol.55(2015), No.6
    3. Carburization Degree of the Iron Nugget Produced by High Al2O3 Iron Ore ISIJ International Vol.57(2017), No.3

  • Comprehensive Mathematical Model for Particle Flow and Circumferential Burden Distribution in Charging Process of Bell-less Top Blast Furnace with Parallel Hoppers

    Guolei Zhao, Shusen Cheng, Wenxuan Xu, Chao Li

    pp. 2566-2575

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    DOI:10.2355/isijinternational.ISIJINT-2015-342

    Abstract

    Parallel hoppers type bell-less top is one kind of widely used charging apparatus, and it is essential to clarify particles flow behavior and circumferential burden distribution during charging process. Thus in this paper, a comprehensive mathematical model from flow control gate to stock surface has been established. In the model, the trajectory shape of particles colliding point on rotating chute with semi-circular section is firstly clarified, not simply an ellipse shape, and the mathematical model of particles flow behavior on rectangular type chute is initiatively presented. The model is then validated by measured results of coke particles falling trajectory in the freeboard using laser grids method during the blow-in stage of an actual 2500 m3 blast furnace. Based on the established model, the projected trajectories of particles colliding point on rotating chute are clarified for semi-circular type chute and rectangular type chute respectively, and circumferential variations of particles effective motion length and motion time on the chute are investigated. In addition, circumferential burden falling point distribution and mass flow rate distribution on stock surface are deeply analyzed, and the phenomenon that semi-circular type chute tends to cause larger nonuniformity than rectangular type chute is realized. The model has great significance and application value in predicting and recognizing nonuniform burden distribution in parallel hoppers type blast furnace and further improving blast furnace operation.

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  • Dynamic Migration Process and Mechanism of Phosphorus Permeating into Metallic Iron with Carburizing in Coal-based Direct Reduction

    Cheng Cheng, Qingguo Xue, Yuanyuan Zhang, Fei Han, Jingsong Wang

    pp. 2576-2581

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    DOI:10.2355/isijinternational.ISIJINT-2015-386

    Abstract

    The uneven distribution of phosphorus in direct reduction iron (DRI) was found in a carbothermal reduction experiment at 1200°C. The results showed that phosphorus creates reticular distribution in DRI, and its content is high where carbon distributes intensively. The microstructure of eroded iron at room temperature was observed, and it was found that phosphorus is distributed mainly in the ledeburite and rarely in the ferrite or cementite. Ultimately, the process of the phosphorus migration with carburization into DRI was revealed: First, the austenite grain boundary melts and absorbs significant amounts of phosphorus while carburizing; meanwhile, the internal austenite remains solid, and the process of phosphorus entering into austenite is blocked, then, the austenite melted completely, therefore, the processes of carburizing and absorption of phosphorus occurred rapidly and phosphorus was mainly absorption at this stage. Based on these studies, low phosphorus DRI can be obtained by lowering the temperature and reducing the reducing agent, which preventing melted of DRI and inhibiting the absorption of phosphorus.

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  • Emission Behavior and Physicochemical Properties of Aerosol Particulate Matter (PM10/2.5) from Iron Ore Sintering Process

    Min Gan, Zhiyun Ji, Xiaohui Fan, Xuling Chen, Qiang Li, Liang Yin, Xiangning He, Yang Zhou, Tao Jiang

    pp. 2582-2588

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    DOI:10.2355/isijinternational.ISIJINT-2015-412

    Abstract

    Iron ore sintering process is the major emission source of PM10/2.5 (aerosol particulate matters less than 10 µm/2.5 µm in aerodynamic diameter) in integrated steelworks. The aim of this investigation is to obtain the emission behavior and major inorganic characteristics of PM10/2.5 from typical sintering stages. Particulate matters were collected and classified into different size fractions with a cascade impactor, and the properties of PM10/2.5 were analyzed by XRF, SEM-EDS techniques. The results show that sintering stages initiated from the gradual disappearing process of over-wetted layer to the burning through point are the main emitting area of PM10, and sintering bed has potential ability to scrub PM10 from flue gas. The main chemical composition of PM2.5 emitted from the beginning of an integrated sintering process to the point where flue gas temperature began to rise characterizes high contents of Fe and low contents of volatile trace elements; PM2.5 emitted from the flue gas temperature rising process characterizes high contents of K, Pb, Cl and S, and low content of Fe for the first half, while characterizes high contents of Al, Si, and low content of Fe for the second half. Such information can be helpful in exploiting controllable technologies on disposing PM-related pollutants in practice.

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  • Influence of Refractory-Steel Interfacial Reaction on the Formation Behavior of Inclusions in Ce-containing Stainless Steel

    Sun Kuk Kwon, Jun Seok Park, Joo Hyun Park

    pp. 2589-2596

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    DOI:10.2355/isijinternational.ISIJINT-2015-125

    Abstract

    Effect of Ce addition on the interfacial reaction between alumina refractory and 25wt%Cr-20wt%Ni-4wt%Si-0.5wt%Mn stainless steel deoxidized by Al at 1873 K was investigated to understand the contribution of the refractory-steel reaction to the inclusion evolution processes. The oxygen content markedly decreased by Al deoxidation, followed by a sluggish decrease by Ce addition greater than 0.5 wt%. The Ce content continuously decreased, but the higher the initial Ce content, the lower the Ce-decreasing rate was obtained. The content of Al initially decreased due to the formation of Al-rich inclusions, followed by an abrupt increase mainly due to a reduction of alumina refractory by Ce at the steel-refractory interface. The content of Al decreased again because of the formation of CeAlO3 compound not only as inclusions but also as refractory-steel reaction products. The CeAl11O18 and CeAlO3 were formed at the refractory side, while the Ce2O3 and CeAlO3 were formed at the steel side in the 0.5 wt% and 1.0 wt% Ce added systems. From the refractory-steel reaction mechanism, the process of inclusion evolution was proposed to three steps as follows. The initial SiO2-rich oxides are reduced by Al, resulting in the formation of aluminosilicates inclusions (Step 1). The Al2O3 in the inclusions are reduced by cerium, resulting in the formation of Ce-rich oxides (Step 2). Because the Ce content continuously decreased due to the refractory-steel reaction, the inclusions transform from Ce–Al complex oxides to Al-rich aluminosilicates and from Ce2O3 to Ce–Al complex oxides in the 0.1 wt% and 0.5 wt% Ce added systems (Step 3).

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  • Suppression of Swirl Motion of a Bottom Blown Bath using a Circular Disk

    Kazuya Kinoshita, Yoshiaki Ueda, Manabu Iguchi

    pp. 2597-2603

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    DOI:10.2355/isijinternational.ISIJINT-2015-356

    Abstract

    A swirl motion of a bubbling jet is induced in a cylindrical reactor under a certain gas injection condition. Mixing in the bath is highly enhanced in the presence of the swirl motion, whereas the swirl motion itself sometimes causes severe oscillation of the reactor and slopping of the molten metal contained in the reactor. A simple method of suppressing the swirl motion was proposed in this water model study. A circular disk in contact with the bath surface was found to successfully suppress the swirl motion for the disk diameter greater than a certain critical value. Empirical equations were derived for the critical disk diameter.

  • Fluid Flow Characterization in Asymmetric Tundish

    Heng Cui, Yang Liu, Dongxia Li

    pp. 2604-2608

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    DOI:10.2355/isijinternational.ISIJINT-2015-409

    Abstract

    If the combined model is used to calculate the residence time distribution (RTD) curves of different outlets of multi-strand or asymmetric tundishes, there may exist negative dead volume fraction or bigger calculation errors. The flow characteristics (the volume fractions of dead region, plug flow, and well-mixed flow) are analyzed mainly on the basis of the tracer concentration versus time curve (C curve) or E curve. In the present work, the E curve obtained by “pulse stimulus-response” tests was translated into F curve generated by step input of the tracer; then based on F curve, an analysis model for dead volume fraction in multi-strand or asymmetric tundishes was established. The dead volume fraction was used to evaluate metallurgical effect, and the flow uniformity of molten steel in dual asymmetric tundishes was evaluated by comparing the flow concentration difference and the maximum difference of F curves between the two strands. This model was used to analyze the flow characteristics of dual-strand asymmetric tundishes. As for the experiment condition in the paper, there is a linear relationship between the dead volume fraction and the volumetric flow rate difference of the two strands. The maximum concentration difference between the two strands is not significantly affected by the volumetric flow rate difference of the two strands. Dual-strand asymmetric tundishes are not fit for casting with small volumetric flow rate. If the total volumetric flow rate is small, the volumetric flow rate difference between two strands should be reduced.

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  • Development of a Stand-alone Powered Exoskeleton Robot Suit in Steel Manufacturing

    Ho Yu, Il Seop Choi, Kyung-Lyong Han, Jae Yeon Choi, Goobong Chung, Jinho Suh

    pp. 2609-2617

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    DOI:10.2355/isijinternational.ISIJINT-2015-272

    Abstract

    Handling heavy-load materials is the most common operation in iron and steel making processes. There are numerous operations in which workers directly deal with heavy loads without equipment. The refractory constructions in the converter and AOD (Argon Oxygen Decarburization) furnaces are representative examples. Transferring thousands of heavy materials repeatedly over a long period of time can not only cause musculoskeletal diseases, which occur 70% on the waist and 30% on other parts such as wrists, elbows, shoulders, etc. but also contain latent risks of safety accidents.
    In this paper, a novel stand-alone powered exoskeleton robot suit was developed for assisting the strength of waist, lower back, and hip joints that are physically vulnerable during handling heavy-load materials. The simple robot structure reduces the frame weight as well enabling easy motion control. The robot is capable of moving freely due to the stand-alone actuators. The developed novel clutch system generates a smooth transition against various working conditions. This technology significantly diminishes the physical fatigue of operators and will subsequently prevent further muscular skeletal disorders as well as safety accidents.

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  • Simultaneous Characterisation of Precipitates and Matrix in a Steel Using Small-Angle Neutron Scattering and Bragg-Edge Transmission Analysis

    Yojiro Oba, Satoshi Morooka, Hirotaka Sato, Nobuhiro Sato, Kazuki Ohishi, Jun-ichi Suzuki, Masaaki Sugiyama

    pp. 2618-2623

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    DOI:10.2355/isijinternational.ISIJINT-2015-315

    Abstract

    A new technique for the quantitative characterisation of the microstructure in steels has been developed. Using a small-angle neutron scattering (SANS) instrument at a pulsed neutron source, both a SANS profile and a Bragg-edge transmission spectrum could be simultaneously measured. The SANS analysis provides structural information about the precipitates in steels, while the Bragg-edge transmission analysis reveals the crystal structure of the steel matrix. As a demonstration, Fe–C–Cu–V alloys were measured and analysed. The SANS profiles showed that nanosized precipitates were grown when the alloys were aged at 823 K. The Bragg-edge of the corresponding transmission spectra clearly revealed that the ferritic matrix was kept with the aging time. The experimental results confirmed that this new technique provides a new possibility of efficient characterisation of the steel microstructures.

  • Convenient Debonding Strength Evaluation for Spray Coating Based on Intensity of Singular Stress

    Nao-Aki Noda, Takumi Uchikoba, Masayasu Ueno, Yoshikazu Sano, Kazuki Iida, Zefeng Wang, Guohui Wang

    pp. 2624-2630

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    DOI:10.2355/isijinternational.ISIJINT-2015-458

    Abstract

    Hearth rolls are used in continuous annealing furnace to produce thin steel sheet. The roll surface is usually coated by using thermal spraying, which has high adhesive strength and wears resistance. However, in the ceramics coating, thermal stress caused during heating and cooling process in the furnace may lead to debonding due to the low toughness of ceramics. In order to improve the heat resistance of the thermally sprayed coating, it is essential to evaluate the debonding strength. Generally, heat resistance of thermal spray coating is evaluated by thermal shock test prescribed by JIS H8304 although few research is available in terms of singular stress at the end of the interface for JIS specimen under thermal shock. This paper focuses on the intensity of the singular stress at the end of interface. Then, the most suitable conditions are discussed with varying the coating material and the coating thickness.

  • Deposition of DLC/oxynitriding Films onto JIS SKD11 Steel by Bipolar-pulsed PECVD

    Shih-Hsien Chang, Chun-Cheng Yu, Kuo-Tsung Huang, Chung-Ming Liu

    pp. 2631-2638

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    DOI:10.2355/isijinternational.ISIJINT-2015-350

    Abstract

    In this study, diamond-like carbon (DLC) films are coated by bipolar-pulsed PECVD onto oxynitriding-treated JIS SKD11 steel. In order to evaluate the properties of the DLC/oxynitriding films on SKD11 steel, Raman spectroscopy analysis, wear tests, adhesion tests, hardness tests and corrosion resistance inspections are performed. The experimental results show that the DLC/oxynitride duplex layers possess ideal wear and corrosion resistance when DLC films are deposited by unbalanced bipolar-pulsed voltage, with a coating time of 90 min and duty cycles maintained at 15%. The highest surface hardness (Hv0.025 2830.7) and lowest wear volume loss (when the load of 2 N and sliding speed of 0.05 m·s−1 is 4.07 × 10−3 mm3 and the load of 5 N and sliding speed of 0.25 m·s−1 is 5.83 × 10−3 mm3, respectively) are obtained. In addition, the optimal DLC/oxynitride films also possess the lowest corrosion current (Icorr = 2.66 × 10−6 A·cm−2) and highest polarization resistance (Rp = 1.57 × 104 Ω·cm2) in 3.5 wt% NaCl solutions.

  • Discontinuous Precipitation during Isothermal Transformation in a 9–12% Chromium Ferritic Steel

    Xingang Tao, Lizhan Han, Jianfeng Gu

    pp. 2639-2647

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    DOI:10.2355/isijinternational.ISIJINT-2015-197

    Abstract

    A study of discontinuous reaction in a 9–12% chromium ferritic steel was performed by means of many characterization methods, such as physicochemical phase analysis, electron backscatter diffraction, electron probe microanalysis. Isothermal aging treatments at 700°C after solution annealing were carried out for the period over 216 h. Cr-rich M2N were formed as the main precipitates, together with a small amount of Cr-rich M23C6 and Nb-rich MN. With the increase of isothermal aging time, precipitates were observed to be preferentially nucleated at the prior austenite grain boundaries and grew toward the interior of grains with the morphology of pearlite, and eventually formed a lamellae structure. The characterization of carbide and nitride was presented in detail. Besides, the growth of the discontinuous reaction was also documented. It was found that the isothermal decomposition reaction of over-cooled austenite could be summarized as: γ→α+Cr-rich carbonitrides. The growth of discontinuous precipitation involved the diffusion of chromium (short range) and nitrogen (long range).

  • Improvement of Anti-aging Property at Low Temperature by Cr Addition in Bake Hardenable Ultra Low Nitrogen Steels

    Naoki Maruyama, Naoki Yoshinaga, Hideaki Sawada, Manabu Takahashi

    pp. 2648-2656

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    DOI:10.2355/isijinternational.ISIJINT-2015-146

    Abstract

    The effect of Cr, Mn, Mo, V, Nb, and Al on bake hardenability (BH) at 170°C and anti-aging properties, i.e. the inhibition of the appearance of yield point elongation (YPE) after low temperature aging, in ultra low N steels was investigated. It was found that Cr addition of 0.5–1.0 mass% apparently inhibit the appearance of YPE after aging for 3.6 ks at 100°C without much decreasing the amount of 2%BH at 170°C. The reason for the inhibition by Cr addition was discussed on the diffusion trap model, by using the interactions among Cr atom, N atom, and vacancy evaluated by first-principles calculation. The estimation indicates that (1) Cr would not inhibit the diffusion of N atoms as a repulsive interaction was expected for Cr–N complexes, (2) a small amount of vacancies introduced by skinpass rolling, which attracts strongly with N atoms, seems to play a main role on the inhibition of the diffusion of N atoms, (3) Cr could retard the annihilation of vacancies which trap N atoms during aging, since Cr atom attractively interacts with vacancy–N complexes. Moreover, the effect of annealing temperature and coiling temperature on bake hardenability was investigated, and the effect was found to be understood by the change of solute N, owing to the precipitation of CrN which has a precipitation nose at 650–700°C.

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  • Formation of Fine Austenite through Static Recrystallization in Low Carbon Micro-alloyed Steels

    Xinjun Shen, Shuai Tang, Jun Chen, Zhenyu Liu, Guodong Wang

    pp. 2657-2660

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    DOI:10.2355/isijinternational.ISIJINT-2015-160

    Abstract

    The feasibility of further refinement of recrystallized austenite in a low carbon micro-alloyed steel was investigated through warm deformation of the overcooled austenite followed by reheating to the austenite non-recrystallization region. The results showed that static recrystallization of the deformed austenite happened at a higher degree of overcooling due to the increased driving force by warm deformation. The fraction of recrystallized austenite during reheating increased with increasing degrees of overcooling. After warm deformation at 550°C, the fraction of recrystallized austenite reached about 20.9%, and the average grain size was less than 5 µm. In addition, if a second deformation was imposed to the overcooled austenite at 550°C, considerable recrystallization was activated, resulting in a dramatically higher fraction of recrystallized austenite (94.0%) and a finer austenite grain size of 3.3 µm.

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  • An Experimental Investigation on Rate Sensitivity of Fracture-Mechanical Characteristics in 304 Austenitic Stainless Steel under Bending Deformation

    Hang Thi Pham, Takeshi Iwamoto

    pp. 2661-2666

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    DOI:10.2355/isijinternational.ISIJINT-2015-397

    Abstract

    It is considered that the martensitic transformation in austenitic stainless steel is responsible for its high fracture toughness. A mechanism for fracture mechanical characteristics in the steel at higher rate of deformation might become quite complicated because a quick temperature rise may suppress the martensitic transformation as well as thermal softening. An investigation on fracture-mechanical characteristics of austenitic stainless steel at the higher rate and its rate sensitivity is indispensable. Recently, J-integral of 304 austenitic stainless steel is determined by three-point bending tests at various deflection rates. However, the tests carried out on small specimens might derive some errors for its evaluation because the plane strain condition is not ensured for J-integral. Additionally, the validity of the measured J-integral is not confirmed by other fracture parameters and it is obvious that measured value does not become a critical value of J-integral. In this study, J-integral of the steel is evaluated at different deflection rate by three-point bending tests on larger specimens. As a result, a higher value of J-integral is obtained compared with previous investigation on smaller specimens at the same normalized deflection rate. Additionally, the results indicates that the relationship between value of J-integral and normalized deflection rate is roughly a linear function in a semi-logarithmic plot in the range of normalized deflection rate from 4×10−4 to 10.5/s. The obtained values of the stretch zone width (SZW) are suitable for observation of a positive rate sensitivity of J-integral. Thus, the validity of the results for J-integral is confirmed.

  • Influence of Hydrogen on Fatigue Property of Suspension Spring Steel with Artificial Corrosion Pit after Multi-step Shot Peening

    Manabu Kubota, Takahisa Suzuki, Daisuke Hirakami, Kohsaku Ushioda

    pp. 2667-2676

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    DOI:10.2355/isijinternational.ISIJINT-2015-438

    Abstract

    In order to reduce the weight of the suspension springs by increasing the strength level of the steels used, improvement of the corrosion fatigue property is the most important issue. This study investigated, the effect of residual stress, artificial corrosion pit depth and diffusible hydrogen on rotary bending fatigue properties of specimens after double shot and triple shot peening. The following conclusions were obtained:
    (1) Fatigue limits of specimens having the artificial corrosion pit of 250 µm depth with and without the charged hydrogen are improved remarkably by the triple shot peening.
    (2) Fish-eye fatigue fracture with an inclusion as the fatigue crack initiation site occurs frequently due to the charged hydrogen.
    (3) A good relationship between fatigue limit after shot peening and compressive residual stress at the bottom of the artificial corrosion pit is obtained regardless of the depth of the artificial corrosion pit.

  • New Interpretation to Disputed Matter of 300 to 400 Degrees Celsius Peak in Hydrogen-detecting Thermal Desorption Spectrum and Potentiality of Hydrogen Generation through this Phenomenon

    Yasuhide Ishiguro, Shinji Ootsuka, Daisuke Mizuno, Kazuki Fujimura

    pp. 2677-2685

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    DOI:10.2355/isijinternational.ISIJINT-2014-667

    Abstract

    This paper provides an answer to the ever-lasting discussion concerning the interpretation of the hydrogen-related peak at 300 to 400°C in hydrogen-detecting Thermal Desorption Spectrum which often appears in a hydrogen-introduced steel sample, particularly which has undergone an outdoor exposure or wet/dry cyclic accelerated-corrosion test and/or by acid immersion. Up to now, the focus of the discussion of the peak has been held with respect to whether the reaction is caused by diffusible hydrogen or not. However, the peak does not correspond either to a typical diffusible hydrogen peak at around 200°C or to a typical non-diffusible peak at over 400°C. Rather, the 300 to 400°C peak in TDS comes from the formation of hydrogen through a rust-related chemical reaction where iron (III) oxide-hydroxide (oxyhydroxide) of goethite “FeOOH” reacts into iron (III) oxide of hematite “Fe2O3”. It should be noted that the origin of FeOOH comes from rust which is too small to detect and which, even if you are sure that the surface is perfectly smooth and cleaned off by hand-polishing, is not removed due to deeply-rooted and small-diameter rust particles, and cannot be detected by the naked eye. In addition, following on from this new interpretation of the controversial spectrum, this phenomenon is re-interpreted as a new process to produce hydrogen gas, and the potentiality and the mechanism are also discussed.

  • Reduction Test of Hydrogen Sulfide in Silty Sediment of Fukuyama Inner Harbor Using Steelmaking Slag

    Yasuhito Miyata, Akio Hayashi, Michihiro Kuwayama, Tamiji Yamamoto, Norito Urabe

    pp. 2686-2693

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    DOI:10.2355/isijinternational.ISIJINT-2015-114

    Abstract

    Fukuyama inner harbor is an inlet located in the city area of Fukuyama, Hiroshima, Japan, where the offensive odor of the hydrogen sulfide released from organically enriched, anoxic sediments has become a social issue. Since hydrogen sulfide is also highly toxic and reactive with oxygen, its presence may cause further oxygen depletion in the bottom waters and ultimately, the total decay of local aquatic ecosystems. To evaluate its effects on dissolved sulfide formed in the sediments, steelmaking slag was applied in two different experimental treatments, capping the sediments and mixing with the sediments. The results revealed that both uses of the steelmaking slag significantly suppressed hydrogen sulfide gas by reducing the dissolved sulfide in the sediment interstitial water. This was clearly much more effective than the results obtained by capping with natural stones that was conducted as a control method. The examination with a SEM-EDX suggested that iron sulfide may form on the slag surface after immersing in the sulfide-containing Fukuyama harbor sediments. It was concluded that applying steelmaking slag would be an effective method to suppress the annoying odor of hydrogen sulfide gas generated from the sediments of coastal areas due to its chemical reaction with sulfide ions.

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  • Interfacial Kinetics of Nitrogen Dissolution in Molten Fe–Mn–C Alloys Using 15N–14N Isotope Exchange Reaction

    Chang-Ho Eom, Min-Ho Song, Dong-Joon Min

    pp. 2694-2696

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    DOI:10.2355/isijinternational.ISIJINT-2015-321

    Abstract

    The kinetics of the dissolution of nitrogen into molten Fe–Mn–C alloys through the isotope exchange reaction at 1673 K was investigated. The rate of nitrogen dissolution into a molten Fe–Mn–C alloy at low oxygen concentrations ([mass% O] < 0.001) indicated a first-order reaction with respect to the partial pressure of nitrogen. In a molten Fe–Mn–C alloy, Mn had a positive effect on the dissolution rate of nitrogen owing to a strong thermodynamic affinity with nitrogen, while carbon produced the opposite effect. The present work on nitrogen dissolution in molten Fe–Mn–C alloys was compared to previous studies on the carbon-free Fe–Mn binary alloy, providing empirical evidence for the proportionality of the rate constant to the square of the Mn alloying element activity. It should also be noted that nitrogen dissolution into the molten Fe–Mn–C alloy could be described using a parallel reaction model for the ideal mixing between Fe and Mn, which is also discussed in detail.

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  • Measurement of Trace Amount of Cadmium Using a Portable Total Reflection X-Ray Fluorescence Spectrometer

    Shinsuke Kunimura, Katsuyuki Amagasu

    pp. 2697-2699

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    DOI:10.2355/isijinternational.ISIJINT-2015-267

    Abstract

    This note describes a method for detecting Cd L-lines from a trace amount of cadmium using a portable total reflection X-ray fluorescence spectrometer. When the measurement was carried out in vacuum, the Ar K-lines (Ar Kα line: 2.96 keV, Ar Kβ line: 3.19 keV) that overlap with the Cd L-lines (Cd Lα line: 3.13 keV, Cd Lβ line: 3.32 keV) were remarkably reduced and the Cd L-lines from an analyte containing 1 ng of cadmium were detected. Although the K Kα line (3.31 keV) also overlaps with the Cd L-lines, solid-phase extraction for removing potassium from a sample solution containing both cadmium and potassium led to significant reduction in the intensity of the K Kα line. A combination of solid-phase extraction and measurement in vacuum makes it possible to analyze a trace amount of cadmium using the portable spectrometer.

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  • Synthesis and Identification of Allophane from Waste Blast Furnace Slag

    Teruhisa Hongo

    pp. 2700-2702

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    DOI:10.2355/isijinternational.ISIJINT-2015-195

    Abstract

    Blast furnace slag is expected to be applied for a mineral carbonation process. This process produces a new waste of undissolved residue by acid treatment. The waste is mainly consists of SiO2, and the development of a utilization system for the waste would be desirable. In the current study, the undissolved residue was successfully used as raw material for the synthesis of allophane, which is a functional material as pollutants adsorbent.

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  • © 2015 The Iron and Steel Institute of Japan

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