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

ISIJ International Vol. 51 (2011), No. 9

  • Solubility of Calcium and Oxygen in Molten Iron Equilibrated with Slag in CaO, Al2O3 or CaO-stabilized ZrO2 Crucible at 1873 K

    Ichiro Seki, Kazuhiro Nagata, Tetsuya Ashino, Jun Tanabe

    pp. 1369-1374

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    DOI:10.2355/isijinternational.51.1369

    Abstract

    The solubility of calcium and oxygen in molten iron equilibrated with CaO–Al2O3–ZrO2 molten slag in CaO, Al2O3 or 5.5 mass% CaO-stabilized ZrO2 crucible at 1873 K was measured by means of the slag-metal equilibrium partition method under Ar gas atmosphere. From the results by XRD and the phase diagram of CaO–Al2O3–ZrO2 system, the slag in a CaO crucible was in equilibrium with CaO·ZrO2 and CaO and the slag composition was 57.36 mass% CaO-34.86% Al2O3-7.78% ZrO2. The slag in a Al2O3 crucible was in equilibrium with CaO·2Al2O3 and ZrO2–CaO solid solution (Css) and the slag composition was 27.08 mass% CaO-53.42% Al2O3-19.50% ZrO2. The slag in a CaO-stabilized ZrO2 crucible was in equilibrium with ZrO2–CaO solid solution (Css) and CaO·ZrO2 and the slag composition was 30.38 mass% CaO- 51.56% Al2O3-18.06% ZrO2. The average concentrations of oxygen and calcium in molten iron in equilibrium with slag and compounds were 251 ppm and 3 ppm in a CaO crucible, 33 ppm and 4 ppm in an Al2O3 crucible and 21 ppm and 5 ppm in a CaO-stabilized ZrO2 crucible, respectively. The logarithm of equilibrium constant, logK, for the reaction of CaO(s) = Ca + O is –4.38 and the interaction parameter of eCaO is 31.8. The value is satisfied the thermodynamic phase stability.

  • Sulfide Capacity of the CaO–SiO2–MnO Slag at 1873 K

    Geun-Ho Park, Youn-Bae Kang, Joo Hyun Park

    pp. 1375-1382

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    DOI:10.2355/isijinternational.51.1375

    Abstract

    The sulfide capacity of the CaO–SiO2–MnO slag through the entire composition range was measured at 1873 K using a gas–slag equilibration method and the effect of basicity and the activity coefficient of sulfide on the sulfide capacity of molten slag was investigated. Furthermore, the relationship between the sulfide capacity and the optical basicity of MnO–containing slags was evaluated in view of industrial applications. Sulfide capacity of the slag linearly increased by increasing the content of MnO not only at a given silica content but also at a fixed Vee ratio (=CaO/SiO2). The capacity and the modified Vee ratio (=(CaO+MnO)/SiO2) showed a good linear relationship. Assuming that the basicity and the stability of sulfide ion in the slag are proportional to the activity of MnO (aMnO) and the activity coefficient of MnS (γMnS), respectively, the composition dependency of sulfide capacity was well described by the changes in the ratio of aMnO to γMnS. The iso–sulfide capacity of the CaO–SiO2–MnO slag at 1873 K was constructed in the present study. The capacity contours seemed to rotate clock–wisely from the CaO–SiO2 binary side to the MnO–corner. The sulfide capacity increased with increasing ratio of MnO to CaO at relatively acidic region in which silica content greater than about 40 mass%, while the substitution of CaO by MnO does not significantly affect the capacity in the low silica region. The sulfide capacity generally increased with increasing content of MnO regardless of changes in the content of other constituents in multicomponent MnO–containing slags. It is necessary to take different values for the theoretical optical basicity of MnO in order to estimate the sulfide capacity of MnO–containing slags depending on the content of silica.

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  • Kinetics and Mathematical Modeling of Hydrogen Reduction of NiO–WO3 Precursors in Fluidized Bed Reactor

    Hesham M. Ahmed, Abdel-Hady A. El-Geassy, Nurni Neelakantan Viswanathan, Seshadri Seetharaman

    pp. 1383-1391

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    DOI:10.2355/isijinternational.51.1383

    Abstract

    In the present work, Fluidized bed reduction of NiO–WO3 precursors was investigated isothermally at temperatures 973–1273 K. The reaction progress was monitored by analysis of H2O evolved during the reaction process using a gas chromatograph instrument. A theoretical model based on intrinsic chemical reaction rate constants and thermodynamic equilibria was developed to estimate the apparent reaction rate constant for the reduction reaction. In developing the model, the particles are considered to be in a completely mixed condition and gas flow is described as plug flow. The proposed model is also suitable for scale-up calculations.
    The interfacial chemical reaction model was found to fit the experimental results. The apparent activation energy values of the reduction process at different stages were calculated accordingly. The present investigation proved that the fluidized bed technique can be successfully utilized in bulk production of intermetallics containing W and a transition metal (or a composite material) wherein the process conditions would have a strong impact on the particle size of the end product.

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  • Characterisation of Typical Indian Iron Ore Slime through Quantitative Mineralogy to Evaluate Beneficiation Prospect

    Atanu Banerjee, Asim Kumar Mukherjee

    pp. 1392-1395

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    DOI:10.2355/isijinternational.51.1392

    Abstract

    The current work was taken up to predict the yield of the concentrate with 2 mass% target alumina from the available iron ore slime material. It was found that the conventional method was not suitable for characterisation of the slime. As an alternative method, a third generation of automated mineral analysis machine named “QEMSCAN” is used to find out the liberation characteristics. However, data generated through this routine method was also inadequate for the assigned job. The routine method predicted a low yield for the concentrate. This was due to skewed distribution of mineral phases and wide variation in chemical composition of the major mineral phases. The database of this machine was then modified so that it recognises three broad subtypes of the major mineral phase. The new set of data was used to establish the yield–grade relation for the concentrate from the slime. This vital information on liberation characteristics depicted the beneficiation prospect of the slime.

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  • Crystallization Behavior of Rutile in the Synthesized Ti-bearing Blast Furnace Slag Using Single Hot Thermocouple Technique

    Jing Li, Xidong Wang, Zuotai Zhang

    pp. 1396-1402

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    DOI:10.2355/isijinternational.51.1396

    Abstract

    The present paper constructed the time-temperature-transformation (TTT) diagram of the synthesized titanium-bearing blast furnace (Ti-BF) slag using single hot thermocouple technique (SHTT) in order to study the crystallization behavior of rutile. A combination of X-ray Diffraction (XRD), Electron Probe Micro Analysis (EPMA) and Scanning Electron Microscope (SEM) equipped with Energy-dispersive X-ray spectroscopy (EDX) were applied to determine the structure and the composition of the crystals in the synthesized Ti-BF slag. It was found that rutile with rod shape was formed in the wide range of isothermal temperatures from 1160°C to 1320°C, and CaMgSi2O6, CaAl2Si2O8 as well as CaTiSiO5 were precipitated with further decreasing isothermal temperature. At a fixed isothermal temperature, the diameter of rutile increased slightly, whereas the length of rutile increased linearly with holding time. When increasing the isothermal temperature, the diameter of rutile increased linearly, while the growth rate of the length of rutile initially increased and followed by a decrease with further increasing isothermal temperature. The growth rate of the length of rutile had a maximum value (7.74 μm/s) at 1260°C. The mechanism of crystal growth was also discussed, and the results indicated that rutile with one-dimensional growth was observed in the slag melt.

  • Relation between Sticking and Metallic Iron Precipitation on the Surface of Fe2O3 Particles Reduced by CO in the Fluidized Bed

    Ben Zhang, Xuzhong Gong, Zhi Wang, Zhancheng Guo

    pp. 1403-1409

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    DOI:10.2355/isijinternational.51.1403

    Abstract

    The Fe2O3 particles (150–224 μm diameter) were reduced in a laboratory fluidized bed with CO–N2 mixture gas at 700–900°C to investigate the relation between sticking and iron precipitation. As a result, the sticking tended to occur with acceleration of the reduction rate, judging from the fluidization time. The sticking depended strongly on the metallization ratio signifying the probability of iron-iron contact that estimated the contact area of precipitated iron when particles collide together, whereas the reduction degree had indirect influence on it. Many tiny iron grains with the diameter of approximately 20–40 nm were found on the surface of particles by SEM and EDS. According to theory of microcrystal melting point, the grains reached Tammann temperature easily, leading to higher surface energy of iron, producing higher adhesion force among the reduced particles.

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  • Penetration Effect of Injected Gas at Shaft Gas Injection in Blast Furnace Analyzed by Hybrid Model of DEM-CFD

    Shungo Natsui, Shigeru Ueda, Hiroshi Nogami, Junya Kano, Ryo Inoue, Tatsuro Ariyama

    pp. 1410-1417

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    DOI:10.2355/isijinternational.51.1410

    Abstract

    Shaft gas injection of reducing gas in the blast furnace is one of favorable ways to greatly decrease CO2 emissions from steel works, and this approach is used for the top gas recycling and oxygen blast furnace processes. In these processes, the penetration effect of the gas injected from the auxiliary tuyeres is important for attaining effective gas reduction or making up the heat balance in the upper part, and so it is useful to analyze the dynamic behavior of the gas injected into the shaft.
    In the present study, the penetration effect of injected gas was three-dimensionally simulated by a hybrid model of the discrete element method (DEM) and continuum model (CFD). In particular, the CFD model was used to quantitatively analyze the dynamic gas flow and the pressure distribution in the burden layers calculated by DEM. Although the area influenced by the injected gas from the auxiliary tuyeres was restricted to a specific area due to insufficient horizontal inertial force of the gas, the penetration area gradually enlarged as the gas velocity from the auxiliary tuyeres increased. In a small blast furnace, the injected gas can easily reach the center with the higher gas velocity, and it was shown that the relative penetration depth of the injected gas depends on the inner volume of the blast furnace. However, the overall behavior of the injected gas did not show any remarkable change. In conclusion, the penetration area of shaft gas was almost proportional to the ratio of shaft gas and the upward gas from the conventional tuyeres.

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  • Ideal Behavior of Sinter Block Densification and Relation Thereof to Yield and Strength in Iron Ore Sintering

    Masanori Nakano, Jun Okazaki

    pp. 1418-1424

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    DOI:10.2355/isijinternational.51.1418

    Abstract

    The authors assumed an ideal manner of sinter block densification due to increase in melt volume, and explained thereby changes in sinter strength and yield with operational factors such as ore porosity, CaO/Fe2O3 ratio and coke content.
    Based on knowledge of liquid phase sintering, they drew polygonal lines to describe the change of sinter block strength with melt volume, which comprised two line segments for rapid and slow densification regions, where the position of broken point and the slope of later line segment reflected ore porosity as more porous ores sifted the broken point to more melt volume side and less strength and allowed the slope to turn from negative to positive.
    After assuming a block strength distribution in sinter cake, they illustrated that relative location of the distribution curve to a polygonal line was to determine a sinter strength and a sintering yield, and predicted a disaccording manner of sinter strength to sintering yield and overmelting phenomena as a result of pairing of distribution curve's transformation to line segment's slope in the slow densification region.

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  • Coking Pressure Control by Selective Crushing of High Coking Pressure Coal

    Seiji Nomura, Takashi Arima, Atsushi Dobashi, Kazuhide Doi

    pp. 1425-1431

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    DOI:10.2355/isijinternational.51.1425

    Abstract

    Controlling coking pressure is one of the most important aspects of the cokemaking process, since excessive coking pressure increases the force needed for coke cake pushing and in some cases leads to operational problems such as hard pushes or “stickers,” causing wall damage. Against this backdrop, we investigated the selective fine crushing of high coking pressure coal as a way to reduce coking pressure. It was shown on a laboratory scale that the fine crushing of high coking pressure coal increases the permeability of the plastic coal layer, which decreases coking pressure (internal gas pressure). Based on the basic investigation, we tried the fine crushing of high coking pressure coal at commercial cokemaking plants, and it was confirmed during a long-term commercial-scale experiment that the fine crushing of high coking pressure coal decreases coking pressure and decreases the maximum power current of coke pushing. Thus, the selective fine crushing of high coking pressure coal is a promising way to reduce coking pressure and prolong coke oven life.

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  • Indication of the Measurement of Surface Area on Iron Ore Granulation

    Xuewei Lv, Xiaobo Huang, Jaqing Yin, Chenguang Bai

    pp. 1432-1438

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    DOI:10.2355/isijinternational.51.1432

    Abstract

    The characterization of the surface area of iron ore is of vital importance for the studies of the mineral processing. The specific surface area of iron ore particles can be measured by nitrogen adsorption, laser diffraction, and mathematical models based on the size distribution. The difference among these three methods and its indication on the granulation process were discussed. It was found that the shapes of the particles influences the specific surface area apparently. The roughness of the particle influences the specific surface area apparently, and the samples with like-slice and like-layer particles have high specific surface area. The granulation experiments shows that the efficiency of granulation increases with increasing the water saturation and the iron ore with more fine adhesive particles can get a higher efficiency of granulation easily. The usage of iron ore with big and rough particles can improve the permeability of the bed of granules. The iron ore with smooth and sphere particles has poor ability of granulation.

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  • Inclined Jetting and Splashing in Electric Arc Furnace Steelmaking

    Morshed Alam, Gordon Irons, Geoffrey Brooks, Andrea Fontana, Jamal Naser

    pp. 1439-1447

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    DOI:10.2355/isijinternational.51.1439

    Abstract

    In Electric Arc Furnace (EAF) steelmaking, liquid metal splashes on the furnace wall due to the impingement of high speed oxygen jet on molten metal surface. The splashed metal droplets cause wear of furnace wall and loss of production. Optimization of the operating condition (lance angle, lance height and flow rate) may reduce splashing and increase productivity. In the present study, the effect of different operating conditions on the wall splashing rate was investigated. Air was injected on water surface in a small-scale thin slice model at different lance angles, lance heights and flow rates. Splashed liquid in the forward direction was collected and measured in each case. The forward splashing rate was found to increase with the increase of lance angle from the vertical and flow rate. The critical depth of penetration as well as the impact velocity for the onset of splashing was found to decreases with the increase of lance angle from the vertical. The effect of lance angle on the dimensionless Blowing number (NB), which is a measure of droplet generation rate, was quantified. A new approach has been proposed for modelling the gas jet impinging phenomenon inside the real furnace using room temperature water model.

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  • Modeling Solidification Microstructures of Steel Round Billets Obtained by Continuous Casting

    Giovanni Straffelini, Luca Lutterotti, Matteo Tonolli, Massimo Lestani

    pp. 1448-1453

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    DOI:10.2355/isijinternational.51.1448

    Abstract

    The knowledge of the position of the columnar to equaxial transition (CET) is of paramount importance to evaluate the internal quality of continuous casting (CC) products. One way to control the operational CC conditions with the objective of assuring a given quality level is to develop a numerical program able to calculate the local solidification rate (R), the local thermal gradient (G) and the local time of solidification (tf) and to relate these parameters to the CET by means of a predictive model. In the present investigation, the dendritic morphology and the CET transition of three round billets made of a low carbon steel (0.14%C) and produced by CC are characterized, and a computer model is developed to evaluate the R, G and tf-parameters. Referencing the well-known CET transition model developed by Hunt, a simple prediction equation is thus obtained for the steel under study and it is used to propose guidelines for the optimization of the CC operational parameters.

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  • Development of Hard Secondary Cooling by High-pressure Water Spray in Continuous Casting

    Yoichi Ito, Takeshi Murai, Yuji Miki, Masayuki Mitsuzono, Takatoshi Goto

    pp. 1454-1460

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    DOI:10.2355/isijinternational.51.1454

    Abstract

    Cooling intensity in secondary cooling is an important factor for achieving high-speed casting. In this study, we investigated the effects of the hydraulic pressure and water flow rate of a cooling water spray on cooling intensity, and developed a more efficient secondary cooling system with a high-water pressure spray. In laboratory experiments, a test plate was heated to 1273 K and then cooled below a certain temperature by one nozzle under various experimental conditions. The heat transfer coefficient was estimated using the temperature data from thermocouples 3 mm below the cooled surface. The average heat transfer coefficient with a hydraulic pressure of 5 MPa was 2.8 times larger than that of a conventional water spray nozzle at the same water flow rate. On the basis of the laboratory results, plant trials were carried in the Kurashiki No. 2 CCM at JFE West Japan Works. A high-pressure water supplying device (maximum 5 MPa) with high pressure type nozzles was installed in one segment at a position from 2.5 to 4.0 m below the meniscus and the water flow rate of the high-pressure spray was the same as that of the conventional one. It was confirmed that casting speed was increased by 30% without any inner cracks or surface cracks for several steel grades. In addition, the measurements of slab surface temperature were in good agreement with the thermal calculation results from the laboratory heat transfer coefficient data.

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  • Mathematical Modeling of Initial Filling Moment of Uphill Teeming Process Considering a Trumpet

    Zhe Tan, Mikael Ersson, Pär G. Jönsson

    pp. 1461-1467

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    DOI:10.2355/isijinternational.51.1461

    Abstract

    The flow pattern in the uphill teeming process has been found to be closely related to the quality of ingots and further affects the yield of ingots production, which is crucial for steel making process. The formation of non-metallic inclusion and entrapment of mold flux has been considered to be affected by the flow pattern in the gating system and molds by many previous researchers. The emphasis of this study is focused on the flow pattern of steel in the gating system and molds during the initial stage of the mold filling process. A three dimensional model of two molds gating system for 6.2 ton ingots from Scana Steel is adopted in the present work. A reduced geometry including one mold and a runner is also used for comparison with the present results. In addition, the realizable k-ε model was used to study the flow pattern in uphill teeming process. The predictions were compared with practical filling information from industrial data and results from previous researches. It concludes that a reduced geometry with homogenous inlet condition fails to describe the fluctuating conditions present as the steel enters the mold. However, the trends are very similar when comparing the (hump height-surface height) evolution over time. The maximum wall shear stress fluctuates with a descending trend. A special attention should be made in choosing refractory at center stone, the horizontal runner and the vertical runner at elbow, where the wall shear stress values are highest or with long exposure time.

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  • The Optimal Design for the Production of Hot Rolled Strip with “Tight Oxide Scale” by Using Multi-objective Optimization

    Tao Jia, Zhenyu Liu, Hengfa Hu, Guodong Wang

    pp. 1468-1473

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    DOI:10.2355/isijinternational.51.1468

    Abstract

    Recently, customers are demanding for hot rolled strip products to have tight oxide scales on the surfaces. Therefore, high finishing rolling temperature, low coiling temperature and fast finishing rolling speed have to be used to obtain tight oxide scale, which is different from conventional controlled rolling. In order to ensure the mechanical properties at the same time, a framework consisting of the Bayesian neural network and multi-objective particle swarm optimization has been established to determine the optimal hot strip rolling parameters. Due to excellent generalization ability, the Bayesian neural network was employed to develop the model for the prediction of mechanical properties of hot rolled automotive beam steels. The accuracy between the measured and predicted values was within ±30 MPa and ±4% for strength and elongation, respectively, providing a reliable model for the optimal process design. By applying multi-objective particle swarm optimization, the optimized hot rolling process was obtained for the production of hot rolled automotive beam steel with “Tight Oxide Scale”. Industrial trials have been carried out, which showed good agreement with the optimized hot strip rolling processes. It has been theoretically and practically proven that the optimal process design framework can effectively locate the optimal processing window for hot strip rolling.

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  • Optional SVM for Fault Diagnosis of Blast Furnace with Imbalanced Data

    Limei Liu, Anna Wang, Mo Sha, Xiyan Sun, Yunlu Li

    pp. 1474-1479

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    DOI:10.2355/isijinternational.51.1474

    Abstract

    Fault diagnosis for blast furnace is actually a multi-class classification problem because the blast furnace may appear usually many kinds of abnormal states. Moreover, those abnormal states should be monitored and diagnosed timely and what can help workers take effective measures. Support vector machine (SVM) is state-of-the-art for many classification problems currently. But many classification tasks involve imbalanced training examples in practice. Imbalanced dataset learning is an important practical issue in machine learning, especially in support vector machine (SVM). Fault diagnosis for blast furnace is such an imbalanced data problem. A novel algorithm named optional support vector machine is proposed to solve this imbalanced data classification by pruning training sets and adding the unlabeled data and applying edited nearest neighbor (ENN) rules. Firstly, training sets of majority class are pruned in order to reduce the training time. Secondly, the algorithm selects some useful unlabelled training data and adds them to the training sets. Those samples are used to replenish the lack of training samples so that the training sets are representative. However, they may contain some noisy examples. Finally, the edited nearest neighbor rule is removed the noisy examples. The algorithm adds the unlabelled (testing) samples to balance the number of samples between the minority class and the majority one. The real-time producing data of blast furnace are used to running experiment. In order to more accurately diagnose which kinds fault happened, a binary tree multi-class classification method is adopted based on blast furnace characteristics. Simulation results show that the proposed algorithm is feasible and effective.

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  • Fatigue Crack Length Measurement of Sputtered Metal Film for RFID-based Smart Stress Memory Patch

    Takayuki Shiraiwa, Manabu Enoki

    pp. 1480-1486

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    DOI:10.2355/isijinternational.51.1480

    Abstract

    A new sensor, which can estimate fatigue damage parameters such as number of cycles and stress amplitude, was proposed and fabricated based on smart stress memory patch. This sensor composed of an ion-sputtered metal film deposited on the smart stress memory patch (a thin copper specimen). The crack extension of the sensor during fatigue test could be estimated by measuring the electrical resistance change of the ion-sputtered metal film. The relationship between normalized electrical resistance and the crack extension obtained from the experiment showed a good agreement with that predicted by FEM analysis. This new sensor was combined with two wireless systems using commercially available wireless module and RFID tag. The capability of these systems was evaluated and the results showed that both systems were successfully applied to measure the crack length of the smart stress memory patch. It demonstrated that the proposed systems have potential as a wireless sensor for structural health monitoring, which enable long-term fatigue evaluation with features of easy configuration, wireless and powerless.

  • Selective Backscattered Electron Imaging of Material and Channeling Contrast in Microstructures of Scale on Low Carbon Steel Controlled by Accelerating Voltage and Take-off Angle

    Tomohiro Aoyama, Masayasu Nagoshi, Hideki Nagano, Kaoru Sato, Shigeaki Tachibana

    pp. 1487-1491

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    DOI:10.2355/isijinternational.51.1487

    Abstract

    We studied the behaviors of contrast in backscattered electron (BSE) images of cross-sectional heat-treated steel under various accelerating voltages and take-off angles. Changes in these conditions resulted in dramatic changes in contrast. Low accelerating voltage and low take-off angle improved the surface information and channeling contrast, whereas high accelerating voltage and high take-off angle enhanced the bulk information and reduced channeling contrast, resulting in improved Z contrast. Such behavior can be understood by the ratio of low-loss electrons (LLEs), which are related to channeling contrast, to the inelastic BSE components detected. The distribution of these components varies with the accelerating voltage and take-off angle: the detection ratio of LLE to inelastic BSE increases with decreasing accelerating voltage and take-off angle. The results obtained in this study will be useful for obtaining Z and crystallographic information separately in BSE images for the material of interest.

  • Combined XRD and XRF Technique for the Quantification of the Mass Balance in a Si Carbothermic Production Experiment

    Elena Dal Martello, Gabriella Tranell, Ola Raaness, Lars Arnberg

    pp. 1492-1496

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    DOI:10.2355/isijinternational.51.1492

    Abstract

    The production of metallurgical grade silicon is based on carbothermic reduction of silica in the submerged arc-furnace. Small scale silicon production experiments have been performed aiming at investigating the kinetics and the reaction mechanisms occuring in the furnace. This paper describes a new combined quantitative technique for the analysis of reaction products from silicon experiments. The method is based on a combination of XRD and XRF techniques and can be used to estimate the total phase mass balance in silicon experiments.

  • Flow Characteristics of Circular Liquid Jet Impinging on a Moving Surface Covered with a Water Film

    Hitoshi Fujimoto, Yuhei Suzuki, Takayuki Hama, Hirohiko Takuda

    pp. 1497-1505

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    DOI:10.2355/isijinternational.51.1497

    Abstract

    The flow characteristics of a single circular water jet impinging on a moving surface covered with a water film have been investigated by means of experiments and three-dimensional computer simulations. The experiments were conducted by varying the jet velocity, nozzle-to-plate distance, and flow rate of the water film. It was found that the following three types of flow structures existed: an almost steady flow structure, an unsteady flow structure, and a transition flow structure between the steady and the unsteady flows. The critical boundary, at which the almost steady flow structure appears, is discussed using a simple potential flow theory. In the numerical simulation, the liquid flow was assumed to obey the Navier-Stokes equation in the three-dimensional Cartesian coordinate system. The effects of viscosity, gravity, and the presence of a free liquid surface were taken into account. The predictions were in reasonable agreement with the experimental results. Each flow structure has been studied in detail for a better understanding of the physics of the phenomena.

  • Neural Network Prediction of Hardness in HAZ of Temper Bead Welding Using the Proposed Thermal Cycle Tempering Parameter (TCTP)

    Lina Yu, Yuma Nakabayashi, Masato Sasa, Shinsuke Itoh, Masashi Kameyama, Shinro Hirano, Naoki Chigusa, Kazuyoshi Saida, Masahito Mochizuki, Kazutoshi Nishimoto

    pp. 1506-1515

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    DOI:10.2355/isijinternational.51.1506

    Abstract

    A new thermal cycle tempering parameter (TCTP) to characterize the tempering effect during multi-pass thermal cycles has been proposed by extending the Larson-Miller parameter (LMP) to non-isothermal heat treatment. Experimental results revealed that the hardness in synthetic HAZ of low-alloy steel subjected to multi-pass tempering thermal cycles has a good linear relationship with the TCTP. The new hardness prediction system was constructed by using a neural network taking into consideration of the tempering effect during multi-pass welding, estimated by using the TCTP. Based on the thermal cycles numerically obtained by FEM and the experimentally obtained hardness database, the hardness distribution in HAZ of low-alloy steel welded with temper bead welding method was calculated. The predicted hardness was in good accordance with the experimental results. It follows that our new prediction system is effective for estimating the tempering effect in HAZ during multi-pass welding and hence enables us to assess the effectiveness of temper bead welding.

  • Effects of Cu Addition on Hydrogen Absorption and Diffusion Properties of 1470 MPa Grade Thin-walled Steel Tube under Atmospheric Corrosion

    Shunsuke Toyoda, Hideto Kimura, Masayasu Nagoshi, Isamu Kage, Naotake Yoshihara, Jun'ichi Sakai

    pp. 1516-1523

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    DOI:10.2355/isijinternational.51.1516

    Abstract

    Hydrogen embrittlement is caused by the introduction of hydrogen into steel and is critical for high strength steels. To clarify the effects of Cu addition on hydrogen absorption and diffusion properties of steel under atmospheric condition, corrosion test was conducted on a 1470 MPa grade thin-walled low carbon martensite steel tube. To this end, a martensite steel tube bearing 0.18% C, 0.4% Si, 1.5% Mn, 0.15% Cu, 0.01% Nb was prepared and compared with Cu free steel tube. As a result of EPMA mapping for the rust layer, Cu accumulated discretely on the rust/steel interface, especially in the bottom of pits of 0.15% Cu bearing steel tubes after the atmospheric corrosion test over 12 years. According to x-ray absorption near-edge structure (XANES) spectra, the valence of Cu in the rust layer was mainly +2 as Cu-(O, OH, SO4). The average and maximum diffusible hydrogen content level of 0.15% Cu bearing steel was lower than that of Cu free steel after the atmospheric corrosion test. The quantity of non-diffusible hydrogen was much higher than that of diffusible hydrogen. According to diffusion calculation results, hydrogen diffusion was so rapid that the long-term corrosion hysteresis seemed to have little influence on the diffusible hydrogen content. Furthermore, the short-term corrosion hysteresis may be the main determinant of diffusible hydrogen concentration. Having regard to the fact that the valance of Cu could also be 0 as reported by Shimizu et al., an inhibition mechanism from accumulated Cu on hydrogen-induced cracking was proposed. Eluted Cuy+ ions in the rust layer may precipitate as metallic Cu at the microscopic cathode during the corrosion test. As a result, the microscopic cathode becomes inactivated as an electrochemical reaction site for hydrogen. The Cu alternates between precipitates and Cu ions depending on the relative humidity, and the condensation and pH of the water in the rust layer.

  • Effects of Soluble Ti and Zr Content and Austenite Grain Size on Microstructure of the Simulated Heat Affected Zone in Fe–C–Mn–Si Alloy

    Andrey Vladimirovich Karasev, Hideaki Suito, Pär Göran Jönsson

    pp. 1524-1533

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    DOI:10.2355/isijinternational.51.1524

    Abstract

    The effect of soluble Ti and Zr contents on the microstructure in a simulated heat affected zone of a Fe-0.05mass%C-1.5mass%Mn-0.20mass%Si alloy was studied. This was done as a function of the austenite grain size as well as the number and size of TiN, Ti2O3, MgO(+Ti2O3), TiN(+MgO) and ZrO2(+Ti2O3) particles under different peak temperature (1300 and 1400°C), peak holding time (0, 60 and 600 s) and a constant time of cooling (70 s) from 800 to 500°C. The effectiveness of inclusion phases for intragranular ferrite (IGF) formation was studied from the area fraction of IGF for a given austenite grain size and soluble Ti content. For a given austenite grain size, the primary ferrite decreases and the IGF increases with an increased soluble Ti content up to about 100 ppm. After going through a maximum the replacement of IGF by lath bainitic ferrite occurs with an increased soluble Ti content. It is found that the effect of soluble Zr content on the microstructure is much stronger than that of a soluble Ti content. The area fraction of IGF decreases gradually with an increase in the austenite grain size (50–1000 μm) for a given soluble Ti content (50–400 ppm). By using the hardenability parameter based on the non-equilibrium grain-boundary segregation model, it is observed that the IGF formation is encouraged in the following order: TiN>{Ti2O3, MgO(+Ti2O3)}>ZrO2(+Ti2O3).

  • Hydrogen Behavior in an Ultrafine-Grained Electrodeposited Pure Iron

    Yuhua Su, Yo Tomota, Junichi Suzuki, Masato Ohnuma

    pp. 1534-1538

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    DOI:10.2355/isijinternational.51.1534

    Abstract

    The behavior of hydrogen in an ultrafine-grained electrodeposited pure iron with Lankford (r) value larger than 7.0 was studied by small angle neutron scattering (SANS) and thermal desorption spectroscopy (TDS). Nano-sized inhomogeneity consisting of hydrogen bubble exists in the deposited specimen. The bubble size increases a little by 673 K annealing and then all the bubbles disappear after 973 K annealing. With rolling at room temperature (RT), the bubble size and number density are found to decrease, which must be caused by the change in the status of hydrogen location during plastic deformation. Crystal rotation and grain coalescence are revealed to occur after rolling deformation from electron backscattered diffraction (EBSD) results.

  • Influence of Selenium on the Internal Oxidation of Fe–Si–Al–C Alloy

    Darja Steiner Petrovič

    pp. 1539-1544

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    DOI:10.2355/isijinternational.51.1539

    Abstract

    The effect of selenium on the oxidation of Fe–Si–Al–C alloy during decarburization at 840°C in wet hydrogen was studied. Selenium was found to change the morphology of internal oxides of an Fe–Si–Al–C alloy. The long penetrating internal oxides of Si and Al in the alloy containing 0.034 at.% Se demonstrate an obvious preferential growth perpendicular to the steel substrate. FEG-SEM/EDX was performed to analyze the scale and the subscale. It was assumed that columnar morphology of internal oxides could be induced by selenium surface segregation. Therefore, in-situ AES analysis using a resistive heating of specimen in UHV was used to obtain more accurate data on temperature dependence of selenium surface segregation in silicon steel. Additionally, the kinetics of the selenium surface segregation was investigated in-situ during annealing at 840°C in the ultra-high vacuum chamber of a field-emission Auger electron spectrometer.

  • Effect of Warm Rolling on the Rolling and Recrystallization Textures of Non-oriented 3% Si Steel

    Seil Lee, Bruno Charles De Cooman

    pp. 1545-1552

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    DOI:10.2355/isijinternational.51.1545

    Abstract

    The effect of warm rolling in the 50°C–300°C temperature range on the microstructure, stored energy and crystallographic texture of a 3 mass-% Si steel was analyzed. Both rolling and annealing texture were significantly affected by warm rolling. Dynamic strain aging (DSA) was observed in the temperature range 150°C–300°C. The stored energy, ES<hkl>, of <hkl> || ND oriented grains in the steel warm rolled at 200°C was found to decrease in the following order: ES<111> > ES<110> >> ES<100> ≥ ES<112>. A pronounced {110}<001> recrystallization annealing texture was observed in specimens warm rolled in the DSA temperature range. The effect is due to the formation of {110}<001> oriented nuclei in deformation bands occurring in <110> || ND oriented grains after warm rolling. The deformation bands are believed to be caused by the strain localization associated with dynamic strain ageing.

  • Monitoring of Particulate Emissions to Assess the Outcomes of Retrofitting Measures at an Ironmaking Plant

    Marco Boscolo, Elio Padoano

    pp. 1553-1560

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    DOI:10.2355/isijinternational.51.1553

    Abstract

    This paper, deriving from a joint effort of its authors, reports the results of a wide-ranging survey on particulate matter (PM) emissions from the operation of ironmaking plants, where this type of emissions is especially problematic and, if not properly addressed, may lead to environmental deterioration conditions that are totally incompatible with the protection standards set at the European Union level. With reference to the Lucchini Severstal plant in Servola (Trieste – Italy), the description of its operating cycle and the relevant flows of materials is followed by an estimation of PM emissions from each of its main activities. Technical and economic efforts were focused on the most critical ones. These efforts led to the implementation of plant retrofitting measures, presently completed, which are illustrated in the paper together with the environmental performances shown by the monitoring activity performed on its systems within the framework of the Integrated Environmental Authorisation required by the regional authority. The analysis of air quality in the areas surrounding the manufacturing plant performed through the monitoring of PM10 concentrations for a significant period of time, before and after the actions taken, shows a positive trend that confirms, on the one hand, the absolute relevance of this source of emissions and, on the other hand, the effectiveness of the aforementioned measures.

  • Relationship between Mixing Time and the Number of Holes of a Top Blowing Immersion Nozzle in a Cylindrical Bath

    Hirofumi Ooyabu, Koji Mori, Manabu Iguchi

    pp. 1561-1563

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    DOI:10.2355/isijinternational.51.1561

  • Formation of {001} Fiber Texture in Fe-3mass%Si Alloy during Uniaxial Compression Deformation at Elevated Temperatures

    Yusuke Onuki, Kazuto Okayasu, Hiroshi Fukutomi

    pp. 1564-1565

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    DOI:10.2355/isijinternational.51.1564

  • Experimental Determination of Elastic Modulus during Martensitic Transformation of Low Transformation Temperature Steel

    Hidenori Terasaki, Hideki Yamagishi, Koji Moriguchi, Yusaku Tomio, Yu-ichi Komizo

    pp. 1566-1568

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    DOI:10.2355/isijinternational.51.1566

  • © 2011 The Iron and Steel Institute of Japan

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