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

ISIJ International Vol. 55 (2015), No. 7

  • Water Model and CFD-PBM Coupled Model of Gas-Liquid-Slag Three-Phase Flow in Ladle Metallurgy

    Linmin Li, Zhongqiu Liu, Baokuan Li, Hiroyuki Matsuura, Fumitaka Tsukihashi

    pp. 1337-1346

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    DOI:10.2355/isijinternational.55.1337

    Abstract

    In ladle metallurgy, the role of argon gas purging in liquid steel is well recognized. One key aspect of this process is the prediction of gas volume fraction and gas bubble diameter. Calculation of bubble size is important as it is significantly modified by the injection system and gas flow rate, and it also directly determines the buoyancy which influences the physical mixing process and surface reactions. In this study, a porous plug was used for gas injection as the common practice in the steel industry and a one-third scale water model was established. Then a numerical model based on the Eulerian multiphase model was established and the population balance model (PBM) was used to calculate the gas bubble size distribution. The bubble coalescence and breakage were included and the phase interactions were coupled with the PBM to consider the effect of bubble diameter on the fluid flow. A user defined scalar (UDS) transport equation was added to simulate the solute transport in ladle to study the mixing efficiency. The mixing time, wall shear stress and slag entrapment probability were taken into consideration to find a suitable plug position to balance the mixing efficiency and steel cleanness. The results show that the mixing time decreases with increasing the plug radial distance and the maximum wall shear stress appears when plug radial distance is 0.67 R.

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  • Utilization of Waste Copper Slag to Produce Directly Reduced Iron for Weathering Resistant Steel

    Zhou Xian-Lin, Zhu De-Qing, Pan Jian, Wu Teng-Jiao

    pp. 1347-1352

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    DOI:10.2355/isijinternational.55.1347

    Abstract

    Waste copper slag is a refractory material with high iron content, but it is difficult to recovery iron minerals from the slag because the iron mainly occurs in fayalite. A new technology of coal-based direct reduction-magnetic separation process was developed to recover iron from the slag assaying 39.85% Fetotal and 0.33% Cu. The results show that the final iron concentrate, assaying 90.68% Fetotal, 94.01% metallization degree, 0.66% Cu and 0.058% S with overall iron and copper recoveries of 90.49% and 79.53%, respectively, was manufactured under the optimized conditions as follows: balling the mixture of copper slag with 20% compound additive at 0.3 of basicity, preheating the green pellets at 1000°C for 9 min, then reducing the preheated pellets at 1200°C for 70 min with coal to dried pellets mass ratio of 2, grinding the reduced pellets up to 95% passing 0.074 mm, and magnetically separating the ground product in Davi Tube at 0.08 T magnetic field intensity. The observation of the reduced pellets microstructure shows that the additive plays a role of nucleating agent, which enhances metallic iron grains migrating and coarsening during reduction process. The process is probably one of efficient ways to recover iron from copper slag to produce directly reduced iron (DRI), which can be used as the burden to produce weathering resistant steel by electric arc furnace to replace sponge iron or scrap steel. The process reduces the secondary environmental pollution of copper slag and has been applied well in Tongling Nonferrous Metals Group Holding Co., Ltd in China.

  • Low Computational-complexity Model of EAF Arc-heat Distribution

    Amirhossein Fathi, Yadollah Saboohi, Igor Škrjanc, Vito Logar

    pp. 1353-1360

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    DOI:10.2355/isijinternational.55.1353

    Abstract

    The paper presents a computational model and the corresponding algorithm for estimating the arc energy distribution to conductive, convective and radiative heat transfer in an electric arc furnace (EAF). The proposed algorithm uses channel arc model (CAM) in order to compute the distribution of the arc energy through empirical equations (to approximate arc radius), ideal gas law (to approximate arc density) and results of magneto-hydro-dynamic (MHD) models (to approximate arc pressure, temperature and velocity). Results obtained using the proposed algorithm are comparable with other similar studies; however, in contrast to other arc-energy distribution models, this model requires only two input variables (arc length and arc current) in order to calculate the energy distribution. Furthermore, simple algebraic equations used in the algorithm ensure minimal computational load and consequently lead to short calculation times which are approximately one hundred thousand (100000) times smaller than solving the MHD model equations, making the algorithm suitable for real-time applications, such as smart monitoring and model-based control. The algorithm has been validated by two different approaches. First, the simulation results have been compared to a study dealing with arc-heat distribution in plasma arc furnace; and second, the proposed arc module has been integrated into the frame of a comprehensive EAF model in order to estimate the EAF temperature levels and compare them with operational EAF measurements. Both validations show high levels of similarity with the comparing data.

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  • Modeling on Dry Centrifugal Granulation Process of Molten Blast Furnace Slag

    Qingming Chang, Xianwang Li, Hongwei Ni, Wenyuan Zhu, Chenggang Pan, Shengde Hu

    pp. 1361-1366

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    DOI:10.2355/isijinternational.55.1361

    Abstract

    Lots of iron molten slag from blast furnace can be produced during iron making process. It is generally cooled by water quenching method which causes many problems, such as water consumption, serious pollution, energy wasting etc. To solve these problems, much more attention has been paid to various dry granulation methods. Among them, dry centrifugal granulation (DCG) method has its own advantages. In this study, a physical and mathematical model of slag flow behavior in DCG process is established. The DCG process with a flat disc at different mass flow rate, temperature or viscosity, surface tension of molten slag, rotating speed and surface roughness of disc is simulated. The influences of various factors on granulation process are analyzed and optimum parameters are obtained. The results show that the granulation can be greatly improved by increasing the rotating speed of the disc and by reducing the molten slag viscosity properly.

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    3. Controlled Disintegration of Multiple Jets of Molten Slag ISIJ International Vol.54(2014), No.12

  • Effect of Cr2O3 Addition on Viscosity and Structure of Ti-bearing Blast Furnace Slag

    Guibao Qiu, Long Chen, Jianyang Zhu, Xuewei Lv, Chenguang Bai

    pp. 1367-1376

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    DOI:10.2355/isijinternational.55.1367

    Abstract

    The viscous flow of CaO–SiO2–MgO–TiO2–Al2O3–Cr2O3 slag (CaO/SiO2=0.9–1.3, Cr2O3=0–4 mass%) were investigated to promote understanding of the effect of Cr2O3 addition and basicity (CaO/SiO2) on the viscous behavior of slag containing TiO2. The viscosity of slag was found to significantly increase with increasing Cr2O3 content at a fixed basicity. The increase in basicity could alleviate the viscosity of the slag to a particular extent. And this study involved the use of theoretical calculations and experiments to prove that Cr2O3 in the BF slag could easily react with MgO and Al2O3 to generate spinel phase (MgCr2O4, MgCrAlO4) with high melting points, there increasing the viscosity of the slag. The perovskite phase with high melting points is easily crystallized out at high temperatures with increasing Cr2O3 content and basicity which makes the viscosity of the slag increase sharply with increasing the CaO/SiO2 ratio. In addition, this study analyzed the silicate structure of the slag via infrared spectroscopy. The addition of Cr2O3 has little effect on the silicate structure of the slag. The increasing basicity enabled the slag to become simple in structure. However, the viscosity of the slag increased rapidly because of the precipitation of the high melting phase perovskite.

  • Injection of Pulverized Coal and Natural Gas into Blast Furnaces for Iron-making: Lance Positioning and Design

    Adrian Majeski, Allan Runstedtler, John D’alessio, Neil Macfadyen

    pp. 1377-1383

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    DOI:10.2355/isijinternational.55.1377

    Abstract

    Injecting pulverized coal and natural gas into blast furnaces for ironmaking decreases metallurgical coke requirements, providing a net decrease in the CO2 emissions and in many cases, operating costs associated with iron production. Ideally, the fuel would enter the raceway partially reacted and the injection would not have negative impacts on the equipment or process. Success in achieving this outcome is sensitive to the details of how the injection is implemented. Given this sensitivity and that it is difficult to make accurate, detailed observations in blast furnaces or devise representative pilot-scale experiments, computational fluid dynamics (CFD) has become a useful and complementary tool for the analysis and design of fuel injection methodologies. This study uses CFD to examine the interaction of the blast air and fuel flows in the blowpipe and tuyere nozzle for different fuel injection strategies. Important operating issues such as initiation of partial combustion and heat loads on the tuyere nozzle are examined. It was found that two key fuel injection strategies developed separately for coal and natural gas can be combined effectively in a single combined fuel lance that leverages a bluff body effect to help coal dispersion and has radial nozzles to improve natural gas combustion. The bluff body effect is a simple process whereby the interaction between the blast air flow and a thick-walled lance creates a wake that can impart coal dispersion without the complexity or costs of adding an auxiliary dispersive fluid, such as an annular swirling flow of air. The performance of this combined fuel lance is compared against two configurations for separate fuel lances.

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  • Enhancement of Rutile Formation by ZrO2 Addition in Ti-bearing Blast Furnace Slags

    Zhongmin Li, Yongqi Sun, Lili Liu, Xidong Wang, Zuotai Zhang

    pp. 1384-1389

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    DOI:10.2355/isijinternational.55.1384

    Abstract

    Enhancement of rutile crystallization in Ti-bearing Blast Furnace (Ti-BF) Slag caused by various ZrO2 additions was clarified by Single Hot Thermocouple Technique (SHTT). Time-temperature-transformation (TTT) curves were obtained to analyze the variation trend of crystallization behavior. The results showed that the incubation time of primary crystal, i.e., rutile, at high temperature was first prolonged with increasing ZrO2 addition from 0 to 3 wt.%, and then visibly shortened with further addition of ZrO2 up to 5 wt.%. However, final amount of crystal precipitated was monotonously enhanced by the increasing ZrO2 addition. Meanwhile, Fourier Transform Infrared spectroscopy (FTIR) test was applied to investigate structure of the slag and it was found that degree of polymerization (DOP) for the slag was enhanced and the structural group related to Zr–O–Zr group became more pronounced with increasing ZrO2 concentration, which agreed well with the variation trend of the crystallization behaviors of slags. These results have highlighted that addition of ZrO2 could enhance rutile crystallization, which is of great importance for potentially extracting Ti element from the slag.

  • Development of Heated Ore Addition Technology Using Burner in Chromium Ore Smelting Reduction Converter

    Goro Okuyama, Futoshi Ogasawara, Yuichi Uchida, Yuji Miki, Yasuo Kishimoto, Hisashi Ogawa, Yohei Kaneko

    pp. 1390-1397

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    DOI:10.2355/isijinternational.55.1390

    Abstract

    In order to increase the heat efficiency of the chromium ore smelting reduction furnace, a heated ore addition technology using a burner in the converter was developed. 5 ton scale pilot converter tests were conducted. Based on the results of the pilot converter tests, this technology has been applied to the actual process. The results are summarized as follows:
    1) Compared with the conventional process (without burner), the amount of effective heat transfer increased by 18% with addition of heated ore using the burner in 5 ton converter.
    2) A decrease in the off-gas temperature and reduction of the thermal load on the refractory were also confirmed in 5 ton converter.
    3) The heat transfer ratio of burner combustion with addition of heated ore increased up to about 90%, depending on the increase of the ore feeding rate in 5 ton converter.
    4) From the results of a numerical simulation, it was revealed that the total sensible heat of all particles increases as the ore feeding rate increases. As a result, the ore particles heated by the flame function as a medium of heat transfer from the flame to the molten metal and slag.
    5) This technology was applied to an actual smelting reduction furnace at JFE Steel East Japan Works (Chiba). As in the tests with 5 ton converter, the heat transfer ratio of burner combustion with addition of heated ore was about 90%. The supplied energy per unit of chromium ore added to the furnace decreased by 17%.

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  • Effect of Flux Addition Method on Hot Metal Desulfurization by Mechanical Stirring Process

    Yoshie Nakai, Yuta Hino, Ikuhiro Sumi, Naoki Kikuchi, Yuichi Uchida, Yuji Miki

    pp. 1398-1407

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    DOI:10.2355/isijinternational.55.1398

    Abstract

    The effects of three flux addition methods on hot metal desulfurization with mechanical stirring were investigated in a 1/12-water model test and a 70 kg hot metal desulfurization test. The flux addition methods studied here were top addition on the bath surface in the first period of desulfurization (batch addition), continuous addition from the top, and powder blasting with nitrogen gas. The desulfurization rate when powder blasting is applied is larger than that of either continuous addition or batch addition. The obtained aggregated slag (desulfurization flux) particle diameters after desulfurization were 0.76 mm (batch addition) and 0.38–0.44 mm (powder blasting). Desulfurization behavior was analyzed assuming that the interfacial area between the flux and the hot metal is proportional to the estimated size of the aggregated slag. Based on this analysis, the effect of powder blasting with nitrogen gas on improvement of desulfurization efficiency was interpreted to be the combined result of a) promotion of flux dispersion and avoiding aggregation during flux addition and b) prevention of slag particle aggregation in the hot metal during stirring.

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  • Coupling of Multiple Numerical Models to Simulate Electroslag Remelting Process for Alloy 718

    Nils Giesselmann, Antje Rückert, Moritz Eickhoff, Herbert Pfeifer, Jürgen Tewes, Jutta Klöwer

    pp. 1408-1415

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    DOI:10.2355/isijinternational.55.1408

    Abstract

    The Electroslag Remelting (ESR) process concerns the use of a consumable metal electrode, which is used to melt through a slag layer into a water-cooled mold by applying an alternating electric current. The ESR process produces large ingots of a high quality. This is achieved by controlled solidification and chemical refinement. An understanding of the solidification, heat and fluid flow in the ESR process is essential in order to predict the presence of defects in the solidified ingot. Due to the transient nature of the multiphase, non-isothermal fluid flow problem with magneto-hydrodynamic effects, melting and solidification modeling is a complex task.
    This paper presents the combination of two coupled computational fluid dynamics (CFD) models to simulate both the fluid flow in the slag layer, including metal droplet formation, and solidification in the metal pool. The simulation has been performed for Alloy 718 and compared to experimental data. The presented 3d-model is able to simulate both the steady state and the transient ESR process.

  • Formation of Slag ‘eye’ in an Inert Gas Shrouded Tundish

    Saikat Chatterjee, Kinnor Chattopadhyay

    pp. 1416-1424

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    DOI:10.2355/isijinternational.55.1416

    Abstract

    Inert gas shrouding is a common practice in tundish metallurgy and has manifold benefits. However, there are a few detrimental aspects associated with it, and one of them is the formation of an exposed ‘eye’ around the ladle shroud which results in higher heat losses, and more importantly re-oxidation of the liquid steel and inclusion formation. Hence, it is essential to gain proper insights about the formation, and evolution of slag ‘eye’s in tundishes so as to improve the operations, and enhance liquid metal quality. In the present work, the behavior of slag ‘eye’ in tundishes have been simulated using the finite volume based program ANSYS-FLUENT 15. The mathematical modeling was performed using the Volume of Fluid (VOF) method, and discrete phase method, coupled with the standard k–ε turbulence model. The predictions from mathematical modeling were validated against one-third scale water model experiments. Although the present numerical results over-predicted the experimental results by ~17%, they are well within reasonable limits considering the complexity, and stochastic nature of the problem.

  • Analysis of Cr with Various Valence States in Industrial EAF Slag for Making Stainless Steel

    Hui Wang, Baijun Yan, Fan Li

    pp. 1425-1431

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    DOI:10.2355/isijinternational.55.1425

    Abstract

    Slags of stainless steel making by EAF process in one plant from south and the other from north China were selected. The qualitative and quantitative analysis of all elements in samples were investigated first, the possible phases were identified by diffraction. Micro-morphology and composition analysis showed that Cr exist in iron-based alloy, chromite phase and Cr-containing silicate phase. It inferred that Cr (0) would be in iron-based alloy drops, Cr (III) would be in chromite phase. The Cr valence states in slag were assumed as 0, +2, +3 and +6. The caustic plus carbonate sodium solution was adopted to leach Cr(VI) as CrO42−; oxalic acid was applied to leach the Cr(0) in alloy drops; FeCl3–HCl–NH4Cl combined with V2+-HCl leaching process, the Cr(II) in slag would change to Cr2+ in solution; the resident containing Cr(III) was smelting by Na2O2. Cr in different valence states were separated and detected. The optimized leaching processes of Cr (VI) and Cr (0) were investigated. The influence of the leaching process on existence of other phase was checked also. The analysis results showed the route of separation and analysis is suitable for the slag samples. Both slag samples were with the same trend of contents in various Cr states. Among the states, Cr (0) content is highest, about 2.0–4.5 mass%; the second highest content is Cr (III), about 1.4–2.7 mass%; the content of toxic Cr (VI) is about 80–310 ppm, the lest one is Cr (II), about 1.0–2.1 ppm. This study would provide an experimental method and basis for the utilization and environmental impact of stainless steel smelting slag.

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  • Distribution and Anisotropy of Dislocations in Cold-drawn Pearlitic Steel Wires Analyzed Using Micro-beam X-ray Diffraction

    Shigeo Sato, Takahisa Shobu, Kozue Satoh, Hiromi Ogawa, Kazuaki Wagatsuma, Masayoshi Kumagai, Muneyuki Imafuku, Hitoshi Tashiro, Shigeru Suzuki

    pp. 1432-1438

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    DOI:10.2355/isijinternational.55.1432

    Abstract

    To characterize the distribution and anisotropy of dislocations in cold-drawn pearlitic steel wires, X-ray diffraction line-profile analysis was performed using synchrotron radiation micro-beams. An analytical procedure for correcting the instrumental line broadening for highly directional micro-beams was developed using diffraction profiles of standard CeO2 powder. Although the CeO2 powder line profile includes line broadening due to its microstructural imperfections, the instrumental broadening can be obtained by estimating the effect of the microstructural imperfections on the line broadening. The plastic shear strain was generally more severe near the surface than the center of the wire, whereas the dislocation density distribution was almost constant from the center to the surface. On the other hand, the dislocation rearrangement, which evolves the dislocation cell structure, progressed closer to the surface. It was also revealed that a difference between the hardness in axial and transverse wire directions could be explained by anisotropic dislocation density. Line-profile analysis based on diffraction data at elevated temperatures was performed. Whereas the cementite recovery progressed at a constant rate, the ferrite phase recovery rate was temperature-dependent, suggesting that the ferrite phase recovery was less related to that of the cementite phase.

  • Enhancement of Microstructural and Mechanical Properties by Pulse Mode of Metal Transfer in Welded Modified Ferritic Stainless Steel

    Manidipto Mukherjee, Anupama Dutta, Prasanta Kanjilal, Tapan Kumar Pal, Sunil Sisodia

    pp. 1439-1447

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    DOI:10.2355/isijinternational.55.1439

    Abstract

    The present study describes the enhancement of microstructural and mechanical properties by pulse mode of metal transfer in welded modified ferritic stainless steel (409 M) sheets (as received) of 4 mm thickness. The welded joints were prepared by varying modes of metal transfer at different heat input conditions (i.e. pulse mode at 0.5 kJ/mm and 0.9 kJ/mm and spray mode at 0.5 kJ/mm), using austenitic filler wire (i.e. 308 L) under Ar + 10% CO2 atmosphere. It has been observed that the pulse mode of metal transfer significantly alters the weld metal composition compare to spray mode which promotes comparatively stable austenite in the welds and also depicts significant enhancement in grain structure even with the higher heat input condition. Present study clearly shows that pulse mode enhances micro-hardness of welded joints and toughness values of weld metals compare to spray mode of metal transfer for a particular heat input.

  • Finite-element Simulation of Low-alloy High Strength Steel Welding Incorporating Improved Martensite Transformation Kinetics and Recrystalization Annealing

    Yongzhi Li, Mengjia Xu, Yujing Jin, Hao Lu

    pp. 1448-1453

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    DOI:10.2355/isijinternational.55.1448

    Abstract

    An experimental and numerical investigation was conducted to study the continuous cooling transformation kinetics for the welding simulation of low-alloy steels. A modified Koistinen-Marburger (K-M) equation was proposed based on the transformation kinetics characteristic of low-alloy steels. The modified K-M equation was proved to be more accurate in predicting the stress evolution of low-alloy by a cyclic uniaxial test. Finite-element simulation of Weldox960 steel welding incorporating the improved martensite transformation kinetics and recrystallization annealing was performed to predict the stress evolution and residual stress. The simulation results indicated that the transformation kinetic equations and the recrystalization annealing both had non-ignorable effects on the stress evolution. In addition, the simulated residual stress based on the modified K-M equation and annealing model compared well with the data measured by the hole drilling method.

  • Growth of Fe2Al5 Phase on Pure Iron Hot-Dipped in Al–Mg–Si Alloy Melt with Fe in Solution

    Naoki Takata, Manamu Nishimoto, Satoru Kobayashi, Masao Takeyama

    pp. 1454-1459

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    DOI:10.2355/isijinternational.55.1454

    Abstract

    We have examined the growth and morphology of the Fe–Al alloy layer (Fe2Al5-η and FeAl3-θ phases) on pure Fe sheets hot-dipped at 750°C in an Al-8.2Mg-4.8Si–Fe (wt.%) and Al–Fe alloy melts which are saturated with Fe where the effect of Fe dissolution from the solid Fe can be eliminated. In both the Al–Mg–Si–Fe and Al–Fe melts, the total thickness of Fe sheets increased during the dipping, indicating that the diffusion of Al from the melt side is dominant in the growth of the Fe–Al alloy layer. The growth rate constant of the η phase layer in the both melts was close to 0.5 while the growth rate in the Al–Mg–Si–Fe alloy melt was approximately one order of magnitude slower than that in the Al-Fe melt. The θ phase layer appeared continuous in the Al–Mg–Si–Fe alloy melt, whereas the layer was discontinuous in the Al–Fe melt. The sluggish growth of the η phase layer in the Al–Mg–Si–Fe alloy melt is discussed.

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  • Corrosion Behavior of Laser-clad Mo2NiB2 Cermet Coating on Low Carbon Steel Substrate

    Qianlin Wu, Wenge Li, Ning Zhong, Chunhua Fan, Boyang Liu

    pp. 1460-1467

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    DOI:10.2355/isijinternational.55.1460

    Abstract

    A Mo2NiB2 cermet coating on low carbon steel substrate was fabricated by laser cladding technique. The coating consisted of γ-(Fe, Ni) as a metallic matrix binder and Mo2NiB2 particles as a reinforced phase distributed uniformly in the microstructure. Corrosion behavior of the coating was investigated and the commercial 1Cr, 304SS, and G3 were used for comparison. G3 exhibited the highest corrosion resistance and 1Cr the lowest corrosion resistance, whereas 304SS and the coating exhibited the intermediate and similar corrosion resistance. However, the severe pitting corrosion which was observed in 304SS did not exist for the coating.

  • Formation of Acicular Ferrite in Mg Treated Ti-bearing C–Mn Steel

    Ming-ming Song, Bo Song, Chun-lin Hu, Wen-bin Xin, Gao-yang Song

    pp. 1468-1473

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    DOI:10.2355/isijinternational.55.1468

    Abstract

    The effects of Mg content, inclusion size and austenite grain size on the acicular ferrite nucleation in Mg treated Ti-containing C–Mn steel were studied by high temperature experiment and metallurgical analysis. The composition analysis and size distribution counting of the inclusions and nucleuses were carried out on scanning electron microscope (SEM) with energy dispersive spectrometer (EDS) and image process software, separately. The effectiveness of inclusions with different size and the influence of heat treatment on acicular ferrite formation were statistically investigated. The results obtained are as fellows: the optimal Mg content for acicular ferrite nucleation is 0.0015–0.0026 mass%. The best austenite grain size for acicular ferrite nucleation is about 120 µm. The inclusions for nucleating acicular ferrite mainly consist of spherical Ti–Mg oxide covered by MnS, and there is a Mn-depleted zone (MDZ) around them. The optimized size of inclusions for acicular ferrite nucleation is between 1–4 µm in this study. The effectiveness of inclusions inducing acicular ferrite would be increased after heat treatment.

  • In Situ Observation of Void Nucleation and Growth in a Steel using X-ray Tomography

    Dowon Seo, Hiroyuki Toda, Masakazu Kobayashi, Kentaro Uesugi, Akihisa Takeuchi, Yoshio Suzuki

    pp. 1474-1482

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    DOI:10.2355/isijinternational.55.1474

    Abstract

    In situ synchrotron X-ray computed tomography has been applied to visualize and quantify the void nucleation, growth and coalescence leading to ductile fracture in a free-cutting steel. Uniaxial tensile test was performed and interrupted at different strain levels in order to understand the sequential damage process. Each void detected by the absorption contrast was sequentially tracked with increasing strain. Quantitative data obtained by this method was then used to compare and validate the several pre-existing models predicting the damage evolution. The gap between the void nucleation predictions and the experimental results was widened with increasing strain at high strain regime, because of the restrictive observation of voids and the void coalescence. The models predicting the void growth were also discussed with reassessing the constant α to take the reduction in equivalent diameter by nucleating voids.

  • Three-Dimensional Investigation of Void Coalescence in Free-Cutting Steel using X-ray Tomography

    Dowon Seo, Hiroyuki Toda, Masakazu Kobayashi, Kentaro Uesugi, Akihisa Takeuchi, Yoshio Suzuki

    pp. 1483-1488

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    DOI:10.2355/isijinternational.55.1483

    Abstract

    Synchrotron X-ray computed tomography has been applied to visualize and quantify the void coalescence leading to ductile fracture in a free-cutting steel. In situ tensile test was carried out and interrupted at different strains in order to observe the sequential damage process. Each void detected by the absorption contrast was sequentially tracked with increasing strain. The results showed that the occurrence frequency of void coalescence was increased exponentially with increasing the strain. Quantitative data obtained by this method was then used to compare and validate the several pre-existing models predicting the void coalescence. Both the Thomason and the Pardoen and Hutchinson models calculated with an average intervoid distance gave a reasonable prediction for large scale coalescence of voids leading to failure.

  • Residual Stress Analysis of Cold-drawn Pearlite Steel Wire Using White Synchrotron Radiation

    Masayoshi Kumagai, Shigeo Sato, Shigeru Suzuki, Muneyuki Imafuku, Hitoshi Tashiro, Shin-ichi Ohya

    pp. 1489-1495

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    DOI:10.2355/isijinternational.55.1489

    Abstract

    Measurement of the residual stresses in cold-drawn pearlitic steel wire was conducted using an energy dispersive X-ray diffraction technique. The residual stresses of the ferrite and cementite phases were determined for different crystal orientations and large residual stresses were found to exist in the cold-drawn pearlitic steel wire. The residual stresses in the ferrite phase were compressive in the axial direction but nearly zero in the hoop and radial directions. In addition, the residual stresses of the reflection indices for the ferrite phase were similar to one another. For the cementite phase, while tensile residual stress existed in the axial direction, compressive residual stress existed in the hoop and radial directions. These stresses in the ferrite phase in the axial direction and cementite phase in all directions decreased along the radial positions. A residual stress state model was proposed on the basis of the aligned lamellar structure along the drawing direction; the model explains the effect of the lamellar direction on residual stress. Reanalysis of the wire sample using the proposed model provided residual strains and stresses in the lamellar direction that were different from the average values estimated using the simple stress analysis method.

  • Effects of Temperature and Strain Rate on Deformation Twinning in Fe–Si Alloy

    Takashi Mizuguchi, Kento Ikeda, Naoki Karasawa

    pp. 1496-1501

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    DOI:10.2355/isijinternational.55.1496

    Abstract

    In this study, the effects of temperature and strain rate on the deformation twinning behavior in Fe–5%Si alloy were investigated. Tensile tests at various temperatures (198–248 K) and strain rates (0.1–0.01 s−1) were carried out up to a strain of 0.8%. The presence of deformation twins was confirmed in all the tensiled specimens. The results of crystal orientation analysis by SEM–EBSP indicated that the {112} plane is the twinning plane for the twins formed in the grains. The area fraction and the width of deformation twin increased with decreasing temperature or with increasing strain rate. This tendency can be explained by the relationship between the resolved shear stress and the dislocation velocity.

  • Influence of Tensile Strain on Young’s Modulus in High-strength Cold-rolled Steel Sheets

    Taro Kizu, Kaneharu Okuda, Yasunobu Nagataki, Toshiaki Urabe, Kazuhiro Seto

    pp. 1502-1511

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    DOI:10.2355/isijinternational.55.1502

    Abstract

    The change of Young’s modulus accompanying tensile deformation was investigated for an anisotropic high-strength cold-rolled steel sheet with a high Young’s modulus value in the transverse direction and an isotropic steel sheet with no prominent development of texture. The characteristic phenomenon was the decrease in Young’s modulus in the transverse direction by tensile deformation in the transverse direction in the anisotropic steel sheet. The drop of Young’s modulus in the transverse direction was attributable to a decrease in the ODF intensity around {112}<110>. Young’s modulus in the diagonal direction also decreased somewhat as a result of tensile deformation in the rolling and diagonal directions in the anisotropic steel sheet. This change was caused mainly by an increase in ODF intensity around {001}<110>. Young’s modulus in the rolling direction displayed little change as a result of tensile deformation because the texture on the α-fiber and γ-fiber, which were mainly developed in cold-rolled steel sheets, showed an almost constant Young’s modulus in the rolling direction. In the isotropic steel sheet, Young’s modulus showed little change in any direction as a result of tensile deformation. Young’s modulus calculated by the Voigt model had relatively good correspondence with the measured results. Concerning simulation of crystal rotation, the Taylor model indicated that the crystals around the α-fiber from {112}<110> to {111}<110> rotated to the vicinity by tensile deformation in the transverse direction. The remarkable change of Young’s modulus was explained by the crystal rotation simulated by the Taylor model.

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  • Elastic Properties of Fe–C and Fe–N Martensites

    Maaouia Souissi, Hiroshi Numakura

    pp. 1512-1521

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    DOI:10.2355/isijinternational.55.1512

    Abstract

    Single-crystal elastic constants of bcc iron and bct Fe–C and Fe–N alloys (martensites) have been evaluated by ab initio calculations based on the density-functional theory. The energy of a strained crystal has been computed using the supercell method at several values of the strain intensity, and the stiffness coefficient has been determined from the slope of the energy versus square-of-strain relation. Some of the third-order elastic constants have also been evaluated. The absolute magnitudes of the calculated values for bcc iron are in fair agreement with experiment, including the third-order constants, although the computed elastic anisotropy is much weaker than measured. The tetragonally distorted dilute Fe–C and Fe–N alloys exhibit lower stiffness than bcc iron, particularly in the tensor component C33, while the elastic anisotropy is virtually the same. Average values of elastic moduli for polycrystalline aggregates are also computed. Young’s modulus and the rigidity modulus, as well as the bulk modulus, are decreased by about 10% by the addition of C or N to 3.7 atomic per cent, which agrees with the experimental data for Fe–C martensite.

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  • Effect of Iron Powder on Inhibition of Carbonation Process in Cementitious Materials

    Jeong-Jin Kim, Young-Sun Heo, Takafumi Noguchi

    pp. 1522-1530

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    DOI:10.2355/isijinternational.55.1522

    Abstract

    Addition of a pore blocker to cementitious materials is one of the known measures for protection from carbonation. However, the connected pore network inherent to cementitious materials can make conventional pore blockers ineffective, but these connected pores can be advantageous when iron powder is used. This study found that ionised iron powders can diffuse along the connected pores and fill the neighbouring pores that mostly range in diameter from 0.075 to 7.500 µm, which is equivalent to the range that harmful ionic species can penetrate. Under the severe condition of accelerating carbonation and corrosion-accelerating curing, the replacement of sand with 2% iron powder is found to reduce the total porosity by up to 50% compared to that of the control specimen without iron powder. An electron probe micro-analyser was used to visually confirm the corrosion, ionisation, and diffusion of the iron powder that filled the pores in the cementitious materials.

  • Synthesis of Ca-based Layered Double Hydroxide from Blast Furnace Slag and Its Catalytic Applications

    Yasutaka Kuwahara, Hiromi Yamashita

    pp. 1531-1537

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    DOI:10.2355/isijinternational.55.1531

    Abstract

    A Ca-based layered double hydroxide (LDH) was synthesized from blast furnace slag (BFS) via a facile and low-cost manufacture process. The synthesis was performed through a two-step method including (i) an acid-dissolution and (ii) an alkali-precipitation process using BFS as a sole metal source. The formation of Ca–Al LDH crystals occurred above pH 9, and under the optimal synthetic conditions (at 373 K and pH 11.5) a well-crystallized stoichiometric hydrocalumite (Ca:Al:Cl=2:1:1) incorporating the slag-derived metallic elements in its structure was obtained with a metal recovery rate of 85%. The impacts of synthesis pH and temperature on the material structures were investigated in detail. The catalytic properties of the thus synthesized LDH material was demonstrated on industrially important several chemical reactions including (1) oxidation of alkyl aromatics with O2, (2) CO2 fixation reaction and (3) biodiesel synthesis from vegetable oil. These results open up a new route to fabricate a low-cost LDH compound and its potential availability as an alternative solid base catalyst.

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  • Simplified Simulation Method of Round Steel Bar Cooling

    Yuri Vjacheslavovich Yudin, Mikhail Vasiljevich Maisuradze, Maxim Alexandrovich Ryzhkov, Pavel Dmitrievich Lebedev, Sergey Alexandrovich Musikhin

    pp. 1538-1540

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    DOI:10.2355/isijinternational.55.1538

    Abstract

    Applying the finite difference method for numerical solution of one dimensional heat transfer equation provides a simple way for cooling process simulation of hypoeutectoid low alloy steel rod (round long length bar). The obtained results are comparable with ones calculated using finite element modeling commercial software. The temperature difference of the proposed model and literature experimental data for 50…270 mm diameter bars cooled in still air and conventional oil does not exceed 25°C for the whole examined time-temperature regions before the phase transformation.

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  • © 2015 The Iron and Steel Institute of Japan

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