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

ISIJ International Vol. 52 (2012), No. 7

  • Chromium (VI) Biosorption from Aqueous Solutions by Free and Immobilized Biomass of Oscillatoria sp. H1 Isolated from Freshwater

    pp. 1173-1178

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    DOI:10.2355/isijinternational.52.1173

    The Oscillatoria sp. H1 (Cyanobacteria) isolated from Mogan Lake was researched for the removal of chromium (VI) ions from aqueous solutions and were used free (dry biomass), immobilized (in Ca-alginate) live and immobilized heat-inactivated biomass as biosorbents. Particularly, the effects of physico-chemical parameters like pH, the temperature change, initial concentration, biosorption time and biosorbent dosages on the biosorption of Cr (VI) ions were investigated. The biosorption of Cr (VI) ions for all biosorbents was determined as a highest value at pH 6.0. The temperatures which changed between 20 and 40°C did not affect the biosorption capacity.
    The biosorption of Cr (VI) ions on both free (dry) and immobilized (live and heat-inactivated) Oscillatoria sp. H1 biomass (mg/g) increased as the initial concentration of Cr (VI) ions was increased in the medium. Biosorption equilibrium was established in about 60 min. The retention of Cr (VI) increased with increasing the amount of the adsorbent up to 0.04 g and 30 bead. The results show that immobilized inactive cells (13.83 mg/g) and dry biomass (15.81 mg/g) had less biosorption capacity than that of the immobilized live form (20.82 mg/g). The Langmuir and Freundlich isotherm models were used to fit the equilibrium biosorption data. The biosorbent systems could be regenerated by washing with a solution of 10 mM HCl. The percent desorption achieved was as high as 98%. The biosorbents were reused in three biosorption-desorption cycles without significant loss of their initial biosorption capacity. The results indicated that the immobilized live Oscillatoria sp. H1 could be suitable for development of an efficient biosorbent for the removal of chromium (VI) from wastewater from some industrial processes and other ones.
  • Simulation and Characterization on Heat Transfer through Mould Slag Film

    pp. 1179-1185

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    DOI:10.2355/isijinternational.52.1179

    As one of the most important factors on product surface quality and casting practice, the heat transfer across the interfacial layers in continuous cast mould is greatly affected by the formation of mould slag film between the solidifying shell and the mould. So far, many methods have been presented to measure the heat transfer of mould slag; however, few of them could be easily applied to represent the real heat transfer across the mould interfacial gap. An apparatus used for mould slag film heat transfer measurement is presented in the current paper. The apparatus is used to simulate the heat transfer across the mould slag film. According to the measurement, four parameters are selected as a standard to characterize the heat transfer of the mould slag. The parameters include maximum heat flux (liquid slag), characteristic time, heat flux at meniscus, and average heat flux. Two measurements on different mould slags verify that: 1) the standard could represent the difference in heat transfer between medium carbon steel and low carbon steel mould slag; 2) the average heat flux is a key factor to indicate the overall heat transfer in casting mould; 3) the formed solid slag film in experiment is identical to the real mould, including the morphology, composition, grain size, and thickness. The experiment simulation offers an effective approach to study the formation and evaluation of slag film inside the mould.
  • Estimation of Effective Diffusion Coefficient of Gaseous Species in MgO–C Refractories by Shrinking Core Model

    pp. 1186-1195

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    DOI:10.2355/isijinternational.52.1186

    Different content of various anti-oxidants, Mg, Al, Si, SiC and B4C was added to MgO–C refractories, ranging from 1 to 7 wt.%. Exposed to the air at 1200°C, weight changes of cylindrical specimens were measured by a thermo gravimeter (TG). Based on shrinking core model, a mathematical model was modified by introducing anti-oxidant consumption factor. And the effective diffusion coefficient of gaseous species in refractories with different anti-oxidants was calculated by measuring results of weight change. The phase changes of the anti-oxidants' oxidation process were researched by XRD, and the volume expansions of this process were derived according to theoretical calculation. It was found that Mg had negative effect on diminishing the effective diffusion coefficient, while Al, Si, SiC and B4C had positive effect on it. For B4C's largest volume expansion at the oxidation process, effective diffusion coefficient in samples with B4C addition was smaller than that in samples with other additions.
  • Size Distribution of Multi-phase Deoxidation Particles for Heterogeneous Crystallization of TiN and Solidification Structure in Ti-Added Ferritic Stainless Steel

    pp. 1196-1205

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    DOI:10.2355/isijinternational.52.1196

    Single (Ti and Mg) and multiple (Ti/M: M=Mg, Ca, Zr or Ce and Ti/M/M': Ti/Mg/Al, Al/Mg/Ti, Al/Ti/Ca, Ti/Al(Ca)/Ca(Al), Ti/Mg(Ca)/Ca(Mg), Ti/Zr/Ca(Mg) or Ti/Ce/(Ca) deoxidations were carried out at 1600°C to study the effect of TiN crystallization on the solidification structure in an Fe–17.5(11)%Cr–0.25%Mn–0.20%Si–0.2 to 0.3%Ti–0.01%C alloy containing 0.0030 to 0.04 ppm N on a mass percent basis. Planar size distributions of TiN, TiN+oxide and oxide particles above 1.5 μm in size and spatial size distributions of particles with different compositions greater than 0.1 μm in size were measured and the characteristics of these size distributions have been discussed. The crystallization and precipitation of TiN and TiN on oxide particles were studied as functions of particle number, [Ti]·[N] solubility product and composition of the deoxidation particles. It was found that the solidification structure was not influenced by the number of TiN and TiN+oxide particles of size greater than 1.5 μm, but by the deoxidation method. A very fine structure was observed in Ti/Mg, Ti/Mg/Al and Ti/Mg(Ca)/Mg(Ca) deoxidations and a fine structure was observed in Ti(Al)/Al(Ti)/Ca deoxidation using a MgO crucible both with and without the presence of CaO–MgO–Al2O3 slag.
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  • Thermodynamic Properties of the MnS–CuS0.5 Binary System

    pp. 1206-1210

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    DOI:10.2355/isijinternational.52.1206

    In order to discuss the formation of MnS–CuS0.5 inclusion in γ-Fe, the phase diagram of the MnS–CuS0.5 binary system has been determined by using a confocal scanning laser microscope (CSLM) and a chemical equilibration technique. In addition, the activities of MnS and CuS0.5 in the liquid phase at 1473 K were investigated by chemical equilibration with molten Cu. The phase diagram of the binary system was found to be of a eutectic type with mutual solid solubility between MnS and CuS0.5. The activities of MnS and CuS0.5 showed positive deviation from the ideality. Finally, the solid steel composition equilibrated with the inclusion was estimated by using the determined thermodynamic properties.
  • Recovery of Molybdenum from Copper Slags

    pp. 1211-1216

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    DOI:10.2355/isijinternational.52.1211

    Slags as the by-product of copper making have been produced in large amounts in Chile, and about 5 million tons of slags are estimated to be disposed every year and about 50 million tons have been already accumulated near the mine site. Typical Chilean copper slag contains about 0.3 mass% Mo which is the same to the grade of primary mine production of molybdenite and the copper slags also contain about 40 mass% of Fe and 1 mass% Cu. Recovery of Mo from Chilean copper slags is quite attractive to secure a stable Mo supply. The feasibility of the recovery of Mo from copper slags as Fe–Mo alloys by carbothermic reduction is investigated in the present study. Mo in the copper slag is found to be fully recovered as Fe rich Fe–Mo alloy. The recovered alloy contains about 0.60 mass% Mo and 2.4 mass% Cu. To use the recovered Fe–Mo alloy effectively in the special steel industry, which is the most important market for molybdenum, Cu in the produced Fe–Mo alloy is successfully decreased from 2.4 mass% to 0.1 mass% by using FeS–Na2S flux. Thus, Mo recovery from Chilean copper slag can be promising.
  • Recovery of Molybdenum from Spent Lubricant

    pp. 1217-1224

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    DOI:10.2355/isijinternational.52.1217

    The recovery of Mo from spent lubricant by applying carbothermic reduction was investigated. The carbothermic reduction of CaCO3–MoS2–C, CaCO3–MoS2–Fe2O3–C and the spent lubricant–CaCO3–Fe3O4–C mixtures at 1073 K, 1173 K, 1273 K, 1373 K and 1473 K were carried out to investigate the reduction mechanism of MoS2 under various conditions. The reduction process was anlayzed by using quadruple mass spectroscopy (QMS) analysis, differential thermal analysis (DTA) and X-ray diffraction (XRD) analysis. Based on the investigated reaction mechanism, the carbothermic reduction of the spent lubricant–CaCO3–Fe3O4–C mixtures at 1773 K was carried out to confirm the feasibility of the Mo recovery from the spent lubricant. Mo in the spent lubricant was found to be fully recovered as molten Fe–Mo alloy by the reaction, MoS2(s) + 2CaO(s) + 2C(s) → 2CaS(s) + 2CO(g) + Mo. The recovered Fe–Mo alloy contained about 40 mass% Mo and 4.3 mass% C. Thus, Mo recovery from the spent lubricant by carbothermic molten reduction is promising.
  • Modeling and Validation of the Radiative Heat Transfer in an Electric Arc Furnace

    pp. 1225-1232

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    DOI:10.2355/isijinternational.52.1225

    This paper presents an approach to the mathematical modeling and validation of the radiative heat-transfer processes in an electric arc furnace (EAF). This radiative heat transfer represents an important part of the complete EAF model, which is further composed of electrical, hydraulic, thermal, chemical and mass-transfer sub-models. These have already been addressed in our previous publications. It is well known that during the operation of an EAF all three types of heat transfer (conductive, convective and radiative) are present; however, a great portion of the heat is transferred between the surfaces by means of radiation. The model presented in this work uses a simplified internal geometry of the EAF to represent the relations between the defined EAF zones and is developed in accordance with fundamental thermodynamic laws. The parameters of the model were fitted using the geometrical relations in the EAF; theoretically, using the conclusions from different studies involved in EAF modeling; and experimentally, using the measured temperatures on the furnace roof and the water-cooled panels. Since the radiative heat mostly represents a negative impact on the furnace roof, walls and linings, the obtained model represents an important part of the complete EAF. The presented results show satisfactory levels of similarity between the measured and simulated temperatures of the roof and water-cooled panels, which suggest that the presented model is relatively accurate and follows the fundamental laws of thermodynamics. Possessing such a model is of special importance when enhancing the EAF process using different optimization techniques, since the radiative impacts on the furnace need to be taken into the account in order to maintain or reduce the wear on the furnace lining.
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    3. Arc Behaviour and Cathode Melting Process during VAR: an Experimental and Numerical Study ISIJ International Vol.53(2013), No.2
  • Experimental Study and Atomic Level Description of Adsorption Process of CO2 on Doped Alkaline Earth Oxides

    pp. 1233-1240

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    DOI:10.2355/isijinternational.52.1233

    To realize CO2 capture and storage, many methods for CO2 sequestration should be investigated from a long-term viewpoint. The development of novel CO2 absorbent material is considered to be a candidate for the effective CO2 sequestration. Investigation of CO2 absorbent material is usually based on the experiment with following thermodynamic analysis of obtained data. Recently, the introduction of large-scale simulation based on modern computational chemistry methods is found to be a powerful approach in order to explain and understand the experimental data. In the present study, the experimental measurements and ab-initio calculations were employed for studying the adsorption process of CO2 on both clean and doped CaO (001) surface. The effect of addition of other alkaline earth metal oxide to CaO on adsorption energy of CO2 was analyzed in detail. The relationship between the standard free energy change of carbonation of added alkaline earth metal oxide and extent of variation in the adsorption energy was not clear. However, the structural deformation of CaO surface caused by formation of compound or solid solution would vary the adsorption energy and in the case of CaO/BeO, it leads to significantly improve the capture of carbon dioxide during the first step of adsorption process. Reactivity of CaO with CO2 was investigated by experimental. The experimental results agree with calculation result. Atomistic level description of adsorption process of CO2 on the doped alkaline earth oxides was successfully carried out by ab-initio calculations.
  • Simulation Study on Performance of Z-path Moving-fluidized Bed for Gaseous Reduction of Iron Ore Fines

    pp. 1241-1249

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    DOI:10.2355/isijinternational.52.1241

    Performance of the Z-path moving-fluidized bed reactor for gaseous reduction of iron ore fines was numerically investigated. The proposed mathematical model was developed by analyzing the gas-solid transport phenomena and chemical reactions in the reactor. The model was solved by a new solving approach - integration of FLUENT package (V6.3) and PHOENICS (V3.3). Numerical simulation results of cold state were compared with the experimental data and the simulation results including pressure drop per perforated plate, gas flow pattern and solid flow pattern agreed well with the experimental ones. The developed CFD model then conducted some hot state predictions of gaseous reduction of iron ore fines using reformed COG gas and purified COREX export gas in this reactor. Results indicate that under hot state, the performance of the reactor depends on the reducing gas supplied. Pressure drop per perforated plate decreases one by one from the bottom plate to the top plate and some improvements are needed for the perforated plate arrangement in the reactor. For ore fines gaseous reduction, the reactor displays a high utilization efficiency of gas sensible heat and gas reduction potential. The Z-path moving fluidized bed has the advantage that it realizes a gradient utilization of heat and reduction potential of the gas in iron ore fines reduction with a comparatively simple structure. In the cases simulated, the top two plates play a role of preheating the ore fines and the bottom three plates reducing the ore fines. For operation control, the reactor with three inclined perforated plates is reasonable and preheating ore fine may be carried out by other means.
  • Determination of Size of Representative Volume Element for Coke Using Homogenization Method Based on Digital Image of Actual Microstructure

    pp. 1250-1256

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    DOI:10.2355/isijinternational.52.1250

    When the homogenization method based on the digital image of actual microstructure is used to analyze the strength of coke, the representative volume element (RVE) is a crucial input to predict reliable results. The shape of RVE was identified as square, due to the two-dimensional numerical analysis with the research object being a section image of a coke sample was studied. The variation of multi-scale mechanical properties of coke according to a large number of unit cells with various scales was investigated to determine the proper RVE size. The resolution of calculation equaling original resolution was considered as Case 1. The other low resolution of calculation was considered as Case 2. The results showed that, in the macro-scale (homogenization) analysis, the proper size of RVE on coke's sample should be chosen larger than 874.8 μm, due to the mean calculated homogenized Young's modulus was almost constant in the case of unit cell larger than 874.8 μm. In the micro-scale (localization) analysis, in Case 1, unit cell of a large scale was prone to stress concentration which happened at the relative thin parts of structure around large pores. In Case 2, it was considered that high resolution was necessary, because low resolution changed the structural characteristic. Finally, the optimum size of RVE on coke's sample was determined as 2624.4 μm, which could represent the structural relativity of the research object.
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  • Dynamic and Isothermal Reduction Swelling Behaviour of Olivine and Acid Iron Ore Pellets under Simulated Blast Furnace Shaft Conditions

    pp. 1257-1265

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    DOI:10.2355/isijinternational.52.1257

    Pellet swelling has been widely studied, being simultaneous with reduction reactions and common in the operation of blast furnaces. A tube furnace equipped with a camera recording system was used here to study the dynamic and isothermal reduction swelling behaviour of olivine and acid pellets under simulated BF shaft conditions. The olivine pellets were magnetically separated into three fractions, containing low, medium and high amounts of magnetite in the core. The divalent iron (FeO) content of these fractions was 0.1 wt-%, 0.2 wt-% and 2.9 wt-%, respectively. Pellets with a large magnetite nucleus were observed to encompass numerous cracks, which was reflected in a poor LTD test value, while SiO2-rich reference pellets with a different slag chemistry had more restrained swelling and cracking behaviour in dynamic reduction. Swelling in the olivine pellets was associated with cracking at the boundary between the original magnetite nucleus and the hematite shell.
    The dynamic reduction swelling test results showed lower reduction swelling indices (max 17% in volume) than under isothermal conditions (max 51% in volume), in which case the pellets were suddenly exposed to a strongly reducing atmosphere. It is thus suggested that the reduction swelling behaviour of iron ore pellets should preferably be studied dynamically under simulated blast furnace conditions in order to achieve a realistic understanding of their swelling behaviour in a blast furnace.
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    3. Swelling of Iron Ore Pellets by Statistical Design of Experiment ISIJ International Vol.32(1992), No.12
  • Effect of the Roll Surface Profile on Centerline Segregation in Soft Reduction Process

    pp. 1266-1272

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    DOI:10.2355/isijinternational.52.1266

    This study investigates the effect of roll surface profile on the centerline segregation of the molten metal (bloom) being solidified in the soft reduction process, where the molten metal (bloom) thickness is reduced consecutively by a set of rolls. The roll surface profiles are convex and flat. Finite element analysis was performed to examine the variations in solidus line contour, the phase state across the bloom cross-section and stress state of the bloom in the mushy zone to the casting direction when high carbon bloom (400 mm in thickness and 500 mm in width) was solidified and plastically deformed at the same time. To verify the finite element analysis results, soft reduction test with an actual bloom caster was also carried out.
    Results reveal that a convex roll surface profile is much more effective than a flat roll surface profile in decreasing the centerline segregation and the internal cracks in the bloom. The convex roll surface profile compresses the mushy zone from both directions (bloom thickness and width) and subsequently compensates efficiently the solidification shrinkage of molten metal. In addition, the convex roll can save energy required in deforming the bloom in the soft reduction process.
  • Numerical Modelling of Inclusion Behaviour in a Gas-stirred Ladle

    pp. 1273-1280

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    DOI:10.2355/isijinternational.52.1273

    The treatment of liquid metal in gas-stirred ladles has long been identified as the main process responsible for the inclusion cleanness in special steels. Four university teams and three steels developers have combined their efforts through a project, supported by French National Research Agency, in order to improve the understanding of the complex mechanisms involved during the ladle treatment. In this paper, the contribution of the Institut Jean Lamour to this program, that bears the acronym CIREM, is presented. Using a commercial CFD code as a basis, a three-dimensional simulation model is developed that includes the geometry and industrial operating conditions. The hydrodynamics of the turbulent metal/bubbles mixture is well represented along with the coupled mechanisms of transport, aggregation and surface entrapment of inclusions.
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  • Corrosion of Nozzle Refractories by Liquid Inclusion in High Oxygen Steels

    pp. 1281-1288

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    DOI:10.2355/isijinternational.52.1281

    In order to understand the corrosion mechanism of stopper refractories by liquid MnO–SiO2–FeO–MnS inclusion in high oxygen steels, the chemical reaction between the liquid MnO–SiO2–FeO–MnS slag and several refractories including Al2O3–C, Spinel–C, Al2O3–AlN–C and ZrO2–C were performed at 1550°C. It is found that the reduction of the liquid inclusion can occur by C in the refractories to produce Mn–Fe–Si metallic phase and the degree reduction is important factor influencing to the chemical composition and amount of liquid inclusion. From this experimental and thermodynamic study and in plant test, it is found that ZrO2–C(13%) refractory has excellent corrosion resistance against high oxygen steel containing liquid MnO–SiO2–FeO–MnS inclusion.
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  • Current, Magnetic Field and Joule Heating in Electroslag Remelting Processes

    pp. 1289-1295

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    DOI:10.2355/isijinternational.52.1289

    A three-dimensional (3D) finite element model was developed to simulate the current density, magnetic field, electromagnetic force and Joule heating for a system of electrode, slag and ingot in electroslag remelting processes. Especially, the skin effect is taken into account in electromagnetic field model by magnetic vector potential method. Simulated magnetic flux density is compared with experiment and obtained a good agreement. Numerical results show that the skin effect becomes strong and the maximum current occurs at the surface of electrode and ingot, the maximum of electromagnetic force is at the upper surface nearby the electrode in the slag and the maximum of Joule heating is at the interface of electrode and slag. The parametric study shows that the eddy current flow occurs in interior of electrode and ingot if the current frequency is more than 40 Hz. With the increasing of electrode immersion depth or decreasing of slag cap thickness, the maximum of the Joule heating in slag increases.
  • Directional Solidification of Ti6Al4V Ingots with an Electromagnetic Cold Crucible by Adjusting the Meniscus

    pp. 1296-1300

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    DOI:10.2355/isijinternational.52.1296

    Two different Ti6Al4V ingots were directionally solidified with an electromagnetic cold crucible using same parameters except the meniscus. Macrostructures of the two ingots were similar at the beginning of crystal growth, but became opposite at the end of crystal growth - the solid/liquid (S/L) interface is convex for one and concave for the other. Analysis of heat transfer during this cold crucible directional solidification showed that the meniscus influenced the macrostructure by changing the type of lateral heat transfer and the distance of heat conduction in axial direction. By increasing the mass of the meniscus, the lateral heat transfer changes from radiation to the combined action of radiation and heat conduction, and finally to heat conduction only. The distance of heat conduction increases at the same time. In order to achieve directional solidification, the meniscus must be kept at an optimal position in the electromagnetic field and must have appropriate size.
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  • Solidification Structure and Compactness Degree of Central Equiaxed Grain Zone in Continuous Casting Billet Using Cellular Automaton-Finite Element Method

    pp. 1301-1309

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    DOI:10.2355/isijinternational.52.1301

    A Cellular Automaton-Finite Element (CAFE) coupling model was developed to analyze the evolution of solidification structure of high-carbon steel continuous casting billet and the compactness degree of central equiaxed grain zone. Comparison between the simulated and actual solidification structure was first made under three different conditions, i.e., without MEMS (mould electromagnetic stirring), with MEMS and with MEMS plus intensive cooling. It is indicated that the model can provide a good simulation of the actual solidification structure. Thereafter, the model was used to simulate the solidification structure under different superheats and casting speeds. It is shown that the width of equiaxed grain zone increases with the decrease of the superheat, and decreases with the decrease of the casting speed. The compactness degree of central equiaxed grain zone is also evaluated by the grain number in the same area under different conditions in this study. It is demonstrated that the compactness degree of central equiaxed grain zone in the billet is increased obviously when the MEMS is applied, and is further increased with MEMS plus intensive cooling. In addition, it is also increased when decreasing the casting speed. However, the compactness degree of central equiaxed grain zone is decreased when decreasing the superheat. Moreover, it is found that the compactness degree of central equiaxed grain zone in the billet is closely related to the centre solidification time, i.e., it decreases with the increase of the centre solidification time.
  • Influence of Mold Flux on Initial Solidification of Hypo-Peritectic Steel in a Continuous Casting Mold

    pp. 1310-1319

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    DOI:10.2355/isijinternational.52.1310

    Continuous casting of hypo-peritectic steel was conducted with a pilot slab caster. Such experimental data as local heat flux, thickness of solidified shell or mold flux film, and dendrite primary arm spacing were obtained. On the basis of these experimental results, influence of mold flux on initial solidification in the mold was discussed.
    With mild cooling by crystallization of mold flux, local heat flux and solidification rate decreased in the mold. The changes in them quantitatively correspond to each other. Dendrite primary arm spacing increased with the mild cooling. Relationship between the arm spacing and cooling rate was established and cooling rate on quite initial stage of solidification was stimated. Cooling rate at 1 mm thickness of solidified shell was estimated as about 10000–17000 K/min and changed by mold flux. Unevenness of the solidified shell thickness becomes remarkable when the shell grows to be 1 mm thick. Relation between the unevenness and the cooling rate was discussed, and critical cooling rate against the uneven solidification was observed around 17000 K/min. Thermal resistance of mold flux film was also evaluated and it was clarified that thermal resistance in the film is larger than that by air gap, and Crystallization in the film contributes to increase of both resistances. It is also considered that increase of casting speed makes air gap thinner, so reduction of radiation by crystallization of mold flux becomes more important in high speed continuous casting.
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  • Shape Reconstruction of Plate Thinning Using Reflection Coefficients of Ultrasonic Lamb Waves: a Numerical Approach

    pp. 1320-1327

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    DOI:10.2355/isijinternational.52.1320

    This paper presents an inverse method for the shape reconstruction of local surface-thinning flaws on a 2-D isotropic plate using ultrasonic guided Lamb waves. The problem considered is to determine the function representing a plate thinning shape from reflection coefficients of Lamb waves obtained over a range of frequency, when a single Lamb wave mode is incident upon the thinning part in a plate. The formulation is based on the integral expression of scattered waves by flaws in a plate. Introducing the far field approximation and Born approximation into the integral expression, we obtain the Fourier transform pair between the shape function of plate thinning and reflection coefficients in frequency domain. Thus the shape of a plate-thinning flaw can be reconstructed by performing the inverse Fourier transform of reflection coefficients of Lamb waves with respect to frequency. Some numerical examples are illustrated to show the validity and effectiveness of the inverse approach. Reflection coefficients of the first symmetric Lamb wave mode are calculated by a forward analysis, and are used for the inverse analysis. It is found that although the reconstructed flaw shapes do not perfectly agree with the original shapes due to the approximations induced in the inverse approach, the flaw location and depth are well estimated if the frequency range for the inverse Fourier transform is chosen properly, corresponding to the flaw configurations.
  • T-bar Universal Rolling and Its Deformation Properties

    pp. 1328-1334

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    DOI:10.2355/isijinternational.52.1328

    A new method of rolling T-bars using a common universal mill for H-beams was investigated. To study its deformation properties, model rolling experiments and finite element analyses were carried out. Before the experiment, there was concern about large side camber of the rolled T-bars due to the asymmetric section shape in universal rolling. However, it was shown that the side camber could be controlled by adjusting the balance of the web and flange thickness reductions. The spreading behavior of the flange and web were then studied in detail by experiments and numerical simulations. Linear relationships between reduction balance and spread parameters were found, enabling the spread deformation to be predicted by using model equations. Moreover, the similarity of the flange spread behavior between T-bar and H-beam universal rolling was investigated by numerical analysis. The result of this research suggested the high potential of this rolling method for flexible T-bar production.
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  • Microstructure and Toughness of Friction Stir Weld of Thick Structural Steel

    pp. 1335-1341

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    DOI:10.2355/isijinternational.52.1335

    Friction stir welding (FSW) was performed with single-sided one-pass butt welding using 12 mm thick structural steel plates with 400 N mm–2 grade of tensile strength. The microstructures and mechanical properties such as the Vickers hardness, tensile strength, and Charpy V-notch toughness of the weld joint were investigated, which verified the inhomogeneous features of the microstructure and toughness within the stir zone (SZ). Thermal cycle examinations with or without deformation at the peak temperature were undertaken using a thermomechanical testing apparatus in order to study the predominant factors on the microstructural evolution and resulting toughness within the SZ. It is indicated that the variation in the thermal cycle, especially the peak temperature, within the SZ plays a predominant role in defining the inhomogeneous features within the SZ.
  • Formation Behavior of an Intermetallic Compound Layer during the Hot Dip Aluminizing of Cast Iron

    pp. 1342-1347

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    DOI:10.2355/isijinternational.52.1342

    Hot dip aluminizing (HDA) is an effective way to improve the high temperature corrosion resistance and scaling resistance of ferrous materials. The formation of intermetallic compound layers between the two materials is a dominant factor in determining the properties of hot dip aluminized steel. The formation behavior of the intermetallic compound layer between a Si alloyed Al melt and cast iron has been investigated.
    The thickness of the intermetallic compound layer was significantly reduced as a result of the increased carbon content of the cast iron matrix. The thickness of the intermetallic compound layer formed in the Al–Si–Fe three-component alloy system remains constant in the early stage of the reaction, and it becomes increasingly rough with increased reaction time. The increased roughness could be attributed to the increased Fe concentration in the Al–Si melt near the cast iron surface, which is a result of the increased inter-diffusion of Al, Si and Fe atoms with increased reaction time by which the formation, melting and spallation of the intermetallic compound layer is enhanced.
  • Effect of Chemical Compositions of Case Hardening Steels for Distribution of Carbon and Cementite during Vacuum Carburizing

    pp. 1348-1355

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    DOI:10.2355/isijinternational.52.1348

    In order to develop the model to predict the microstructures of case hardening steels during vacuum carburizing, the effects of chemical compositions such as Cr and Si on carburizing behaviors were investigated using three steels based on Fe–1.1Cr–0.8Mn–0.25Si–0.2C (in mass%). The distributions of carbon near the carburized surface and grain boundary cementite (θ) were analyzed by Glow Discharge Optical Emission Spectroscopy (GD-OES) and image analysis of microstructures respectively. It was revealed that the distributions of carbon and the volume fractions of θ were affected by the chemical compositions i.e. they increased with increasing amount of Cr and decreased with increasing amount of Si. The results by X-ray Diffraction (XRD) and field emission electron probe microanalyzer (FE-EPMA) showed the carbon content in the retained austenite(γ) near the surface was around 1.4–1.6 mass% which was higher than the equilibrium condition.
    By the comparing the experimental and calculation results obtained using the commercial multi-elemental diffusion solver, DICTRA, it was confirmed that the carbon in the γ was supersaturated during vacuum carburizing and the surface condition was estimated to be equal to the carbon activity of the meta-equilibrium border of γ/(γ+graphite). Additionally the result of θ distribution suggests that the volume fraction of θ cannot be predicted by equilibrium calculations; rather, a kinetic model for θ growth is required.
  • Growth Process of Passive Films on Austenitic Stainless Steels under Wet-dry Cyclic Condition

    pp. 1356-1361

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    DOI:10.2355/isijinternational.52.1356

    Passive films formed on Type 304 and 316 stainless steels under a wet-dry cyclic condition were characterized using X-ray photoelectron spectroscopy (XPS). Cr enrichment in the passive films during early stage of the wet-dry cycles occurred due to the preferential oxidation of Cr and the selective dissolution of Fe. However, the Cr fraction of hydroxide layer in passive film gradually decreased with time, because Fe(OH)aq dissolved in the thin water layer were accumulated into the outermost hydroxide layer of a passive film during the dry condition. Chloride in thin water layer facilitated selective dissolution of Fe ions. On the other hand, the Mo in Type 316 stainless steel suppressed the dissolution of Fe ions. Consequently, Cr fraction in passive film on Type 316 became smaller than that of Type 304 stainless steel.
  • Topological Approach to Ferrite/Martensite Dual-phase Microstructures

    pp. 1362-1365

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    DOI:10.2355/isijinternational.52.1362

    In this study, three different microstructures of dual-phase (DP) steel obtained by varying the intercritical annealing temperature were observed three dimensionally by a serial-sectioning method and their metrics and topological properties were quantified. The results demonstrated that martensite in DP steels has various morphologies such as layers, particles, holes, and voids. The fraction of these characteristic morphologies was examined as a function of the intercritical annealing temperature.
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  • Effect of Magnetic Field on Successive γε′→α′ Isothermal Martensitic Transformation in a SUS304L Stainless Steel

    pp. 1366-1369

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    DOI:10.2355/isijinternational.52.1366

    Effect of magnetic field on the TTT diagram of a successive γε′→α′ isothermal martensitic transformation in a solution-treated SUS304L stainless steel has been investigated. The TTT diagram corresponding to 0.5 vol.% transformation of the α′ martensite induced in the ε′ phase shows a C-curve under a magnetic field (0–7T) with a nose temperature located at 103 K. Incubation time of the successive γε′→α′ martensitic transformation shortens as the strength of magnetic field increases although the nose temperature does not depend on the magnetic field. Moreover, the width of the ε′ martensite including α′ martensite becomes thinner as the strength of the applied magnetic field increases at a fixed temperature. This result implies that the potential barrier for the ε′→α′ transformation decreases with increasing magnetic field. We have explained this behaviour based on a model previously proposed by our group.
  • Structural and Wear Characterization of Heat Treated En24 Steel

    pp. 1370-1376

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    DOI:10.2355/isijinternational.52.1370

    Ni–Cr–Mo steels such as En24 steel are widely used in machine part members, gears and shafts. En24 steel is generally used in the hardened and tempered condition to achieve an optimum combination of hardness and ductility. In the present study, heat treatment response of En24 steel was investigated by variation of hardening and tempering temperature in relation to microstructure and hardness. The microstructures were studied through a combination of scanning electron microscopy (SEM) and X-ray diffraction (XRD). The hardness decreased with the increase in hardening temperature from 1123 to 1273 K, whereas it increased slightly with the increase in hardening temperature after tempering at 823 K. The martensitic microstructure (laths) became coarser with increase in hardening temperature. The hardness results were well supplemented by XRD results (Williamson-Hall (WH) & modified WH plots and qualitatively by dislocation density). The specimens tempered at different temperatures (in the range 473–823 K) exhibited decreasing hardness with increase in tempering temperature. The abrasive wear tests were carried out on hardened and tempered specimens. The abrasive wear volume loss decreased with increase in tempering temperature, which was attributed to coarsening of martensite. The worn out specimens were observed under SEM, which revealed micro ploughing and cutting as important mechanisms of material removal during abrasive wear.
  • Role of Silicon in Quenching and Partitioning Treatment of Low-carbon Martensitic Stainless Steel

    pp. 1377-1382

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    DOI:10.2355/isijinternational.52.1377

    Quenching and partitioning (Q&P) treatment was applied to 12%Cr low-carbon martensitic stainless steels containing different amount of silicon, and then the effect of silicon content on the formation of retained austenite was discussed in terms of the behaviors of phase transformation and carbide precipitation during the partitioning treatment. It was suggested that the nearly ideal constrained carbon equilibrium (CCE) condition was realized in the specimens used in this study because a large amount of chromium suppressed bainitic transformation during the partitioning treatment, although cementite was partly observed at the retained austenite/martensite interface. The cementite precipitation was greatly retarded with increasing silicon content, resulting in an increase in the amount of retained austenite and an enhancement of the thermal stability of austenite. Tensile testing for the Q&P-treated specimens revealed that the increment of silicon content leads to a marked improvement of strength-ductility balance of the 12%Cr steels through the increase of retained austenite.

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