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

ISIJ International Vol. 57 (2017), No. 12

  • Scale Recycling Through Self-Reducing Briquettes to Use in EAF

    Maurício Covcevich Bagatini, Victor Zymla, Eduardo Osório, Antonio Cezar Faria Vilela

    pp. 2081-2090

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    DOI:10.2355/isijinternational.ISIJINT-2017-242

    Abstract

    This work is part of a project which aimed to provide a theoretical and experimental basis for recycling of mill scale from mini-mill plants. The focus of the present study was to evaluate the kinetics and the mechanisms of reduction in self-reducing briquettes composed of scale, charcoal and binders, aiming its use in EAF. Such briquettes were submitted to the following tests: thermogravimetry in micro- and macro-thermobalances with analysis of the generated gas, evaluation of the temperature profile inside the briquette and the metallization degree obtained by tests carried out in muffle furnace at a high heating rate. Previous studies, concerning scale and charcoal taken together with the results of this work indicate that both, the kinetics of scale reduction and the heat transfer limit the overall reaction rate of the briquette. However, the relatively high metallization degree of 76% obtained in the high temperature tests indicates the interest in using such the briquettes for scale recycling in industrial plants. The risk of reoxidation is low due to the protective role of gas evolving from the briquette during self-reduction.

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    2. Lower SO2 Emissions in the Sintering Process Utilizing the Difference of Sulphur Contents of Iron Ores ISIJ International Vol.57(2017), No.12
    3. Temperature Dependence of Thermal Diffusivity and Conductivity of FeO Scale Produced on Iron by Thermal Oxidation ISIJ International Vol.57(2017), No.12

  • Influences of Na2O and K2O Additions on Electrical Conductivity of CaO-SiO2-(Al2O3) Melts

    Guo-Hua Zhang, Wei-Wei Zheng, Shuqiang Jiao, Kuo-Chih Chou

    pp. 2091-2096

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    DOI:10.2355/isijinternational.ISIJINT-2017-285

    Abstract

    The present study investigated the influences of Na2O and K2O on the electrical conductivity of CaO-SiO2-(Al2O3) melts by the four electrode method. From the experimental results, it was found that the temperature dependence of electrical conductivity obeys the Arrhenius law. As adding Na2O or K2O to CaO-SiO2-(K2O) melts, electrical conductivity monotonously decreases. Meanwhile, Na2O bearing melt always has a larger value of electrical conductivity than K2O bearing melt when the compositions are the same. By substituting K2O for Na2O, the mixed alkali effect occurs that electrical conductivity first decreases and then increases with the substitution amount of K2O. Furthermore, the mixed alkali effect is more evident for melts with Al2O3 than that without Al2O3.

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    2. Viscosity Measurement of SiO2–Na2O Melts with Addition of NaF ISIJ International Vol.54(2014), No.9
    3. Subsolidus Phase Relations in the CaO–SiO2–Nb2O5–La2O3 Quarternary System at 1273 K ISIJ International Vol.57(2017), No.12

  • Temperature Dependence of Thermal Diffusivity and Conductivity of FeO Scale Produced on Iron by Thermal Oxidation

    Mu Li, Rie Endo, Megumi Akoshima, Masahiro Susa

    pp. 2097-2106

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    DOI:10.2355/isijinternational.ISIJINT-2017-301

    Abstract

    The thermal diffusivity/conductivity of FeO scales produced on iron substrates by thermal oxidation have been determined as functions of temperature. Iron plates (99.99%) were oxidised at 973 K in air to obtain oxide scales of FeO, Fe3O4, and Fe2O3, and then were reduced at 1273 K in nitrogen to obtain FeO-only. The densities of these scales were 5.85–6.05 g cm−3. The laser flash method was used to measure the apparent thermal diffusivity of the whole sample from room temperature to 1164 K during the heating/cooling cycles. This was converted to the thermal diffusivity of the scale only, which in turn was converted to the thermal conductivity. However, these values depended on the scale thickness, which suggests an interfacial heat resistance occurs between the scale layer and iron substrate. In addition, scanning electron microscopy (SEM) observations revealed that the scales contained Fe and Fe3O4 phases after heating. The scale thermal diffusivity/conductivity were corrected considering the interfacial heat resistance and dispersed phases to derive the corresponding values for FeO only. The interfacial heat resistance derived from the thickness dependence of the scale thermal conductivity was 8.3 × 10−6 m2 K W−1. Using this value, the thermal diffusivity of FeO was derived as 3.7 × 10−7–5.8 × 10−7 m2 s−1 and the thermal conductivity as 1.8–2.5 W m−1 K−1 between room temperature and 1164 K. The temperature coefficients of the thermal conductivity were mostly negative, which would be dominated by the phonon mean free path.

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    2. An Improved Methodology for Pulse Combustion with Programmable Timing Sequence Used in Reheating Furnaces ISIJ International Vol.57(2017), No.12
    3. Scale Recycling Through Self-Reducing Briquettes to Use in EAF ISIJ International Vol.57(2017), No.12

  • Subsolidus Phase Relations in the CaO–SiO2–Nb2O5–La2O3 Quarternary System at 1273 K

    Jiyu Qiu, Chengjun Liu

    pp. 2107-2114

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    DOI:10.2355/isijinternational.ISIJINT-2017-324

    Abstract

    The lack of phase diagrams and other related thermodynamic information for the silicate slag system with additions Nb and REE seriously restrict the comprehensive utilization of REE-Nb-Fe ore deposit resources in China. In this study, the equilibrium phase relations in the CaO–SiO2–Nb2O5–La2O3 quarternary system at 1273 K and 1473 K were investigated experimentally using the high-temperature equilibrium experiment followed by X-ray diffraction (XRD), scanning electron microscope (SEM), and energy dispersive spectrometer (EDS). Subsolidus phase relations in the CaO–SiO2–Nb2O5–La2O3 quarternary system and La2O3–SiO2–Nb2O5 ternary system were determined and presented in the form of independent tetrahedron regions and triangle regions, respectively, according to the Gibbs Phase Rule, the isothermal section for 5 wt%La2O3 and 10 wt%La2O3 at 1273 K were also constructed respectively.

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  • Lower SO2 Emissions in the Sintering Process Utilizing the Difference of Sulphur Contents of Iron Ores

    Junmao Qie, Chunxia Zhang, Xiuping Li, Yuhua Guo, Haifeng Wang, Shengli Wu

    pp. 2115-2123

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    DOI:10.2355/isijinternational.ISIJINT-2017-151

    Abstract

    The current treatment of sintering flue gas pollutants is mainly focused on the end-of-pipe treatment, but some problems still exist. It will be more simple and efficient to start from the source to control the pollutants elements. In this paper, the iron ores are classified into two parts utilizing the difference of sulphur contents of iron ores and their adding ratio, “High Sulphur” iron ores and “Low Sulphur” iron ores. Both parts of the iron ores are located inside or outside of the tested pellet, respectively, by granulating with other sintering materials. The experiment results of SO2 emissions reduction are similar in the tubular electric furnace experiment and the sinter-pot test. The sinter-pot test performed in this study reveals that about 41.02% and 34.20% of SO2 are reduced, respectively, through the method in which the “High Sulphur” iron ores are located inside and outside of the tested pellet compared with the traditional method. The falling strength and tumbler strength of sinter decrease by 3.04% and 1.51% when the “High Sulphur” iron ores are located inside of the tested pellet, respectively. While the falling strength and tumbler strength increase by 5.44% and 0.08% when the “Low Sulphur” iron ores are located inside of the tested pellet, respectively. Reduction index (RI) decreases by 1.38% and 4.96%, respectively, while the characteristic value (S) decreases by 19.89% and 70.50%, respectively. The reducibility of sinter decreases, but the softening-melting properties of sinter improve obviously. Compared with the traditional method, the methods introduced in this article have some advantages from the perspective of SO2 emissions reduction and the improvement of the softening-melting properties of sinter. In general, the method in which “High Sulphur” iron ores are located outside of the pellet would be more preferable than that of located inside.

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    3. Acceleration of Carburization and Melting of Reduced Iron in Iron Ore–Carbon Composite Using Different Types of Carbonaceous Materials ISIJ International Vol.57(2017), No.11

  • Role of MgO in Sinter from Perspective of MgO Distribution between Liquid and Magnetite Phases in FeOx–CaO–SiO2–MgO System

    Miyuki Hayashi, Hiroki Tanaka, Takashi Watanabe, Masahiro Susa

    pp. 2124-2130

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    DOI:10.2355/isijinternational.ISIJINT-2017-305

    Abstract

    The chemical compositions of liquid in equilibrium with FeOx in the FeOx–CaO–SiO2–MgO system at 1573 K and oxygen partial pressures of 10−7 atm and 10−6 atm have been determined along with the MgO concentrations in the liquid and FeOx phases to understand the role of MgO in improvement of reducibility of the sinter produced from deteriorated iron ores. The liquid area in the FeOx–rich side was decreased with additions of MgO over the measurement range of C/S ratios between 0.32 and 2.28, and was separated into silicate–based and calcium ferrite–based liquid phases, where 2CaO·SiO2 phase becomes stable thermodynamically in the C/S ratios between 1.66 and 1.96. The ratio of MgO concentration in the liquid phase to that in the FeOx phase decreased with increasing C/S ratio from 0.36 to 2.28, which trend has been explained from the viewpoint of basicity. On the basis of these findings, the role of MgO in improvement of reducibility of the sinter has been discussed to conclude that additions of MgO make the cohesive zone thinner and improves the gas permeability in a blast furnace.

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  • Slag/Metal Separation from H2-Reduced High Phosphorus Oolitic Hematite

    Dong Zhao, Guangqiang Li, Henghui Wang, Jianghua Ma

    pp. 2131-2140

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    DOI:10.2355/isijinternational.ISIJINT-2017-304

    Abstract

    A process of H2 reduction followed by the slag/metal separation for the utilization of high-phosphorus oolitic hematite has been proposed. The H2 reduction was conducted at 1073 K in a horizontal rotary electric resistance furnace, which significantly promotes the metallization ratio of reduced ore fines. Thermodynamic calculation of H2 reduction for apatite and XRD analysis of ore samples before and after H2 reduction confirmed that gangue minerals containing P, Al and Si in oolitic hematite hardly be reduced. The slag/metal separation was carried out in an induction furnace at 1873 K. After separation, metal block and slag were obtained, and most of gangue minerals combined with lime and calcium fluoride formed the slag, but some impurities remained in the form of slag inclusions in the metal. Based on the SEM-EDS examination of P-containing slag inclusions and ternary phase diagram of Fe–P–O system computed by FactSageTM 6.4 at 1873 K, phosphorus in the metal product can be precipitated as iron phosphate or iron phosphide, and the evolution of P-containing slag inclusions is Fe2P(l) + Fe3(PO4)2(l)→Fe3(PO4)2(l)→FeO(l) along with the increase of slag basicity, melt separation time and additive CaF2. A satisfactory metal product with 99.80 wt% T. Fe, 0.027 wt% P, 0.0013 wt% Si, 0.004 wt% Al and 0.05 wt% O was achieved by the slag/metal separation under the optimum conditions: slag basicity of 2, melt separation time of 10 min, CaF2 mixing ratio of 4 wt% and metallization ratio of reduced fines of 85.9%.

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    3. Reconstruction of Three-dimensional Temperature Distribution with Radiative Image by Monte Carlo Method in Blast Furnace Raceway ISIJ International Vol.57(2017), No.12

  • Reconstruction of Three-dimensional Temperature Distribution with Radiative Image by Monte Carlo Method in Blast Furnace Raceway

    Yan Li, Shusen Cheng, Ruixuan Zhang, Dongdong Zhou, Tian Chen

    pp. 2141-2147

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    DOI:10.2355/isijinternational.ISIJINT-2017-317

    Abstract

    This paper presented reconstruction of three-dimensional temperature distribution of raceway from radiative images based on Monte Carlo method and image processing techniques in the blast furnace. The Monte Carlo method was introduced to describe radiative heat transfer of raceway for its efficiency. Color CCD camera was used to obtain radiative information in visible spectrum of raceway. An efficient numerical inverse reconstruction model was established by the relationship between three-dimensional thermal radiation and two-dimensional radiative image. Because the reconstruction was an ill-posed inverse problem, a hybrid Tikhonov regularization method was used to determine the meaningful reconstruction. The numerical simulations were utilized for checking the validity of inverse reconstruction model before each experimental reconstruction. Experiment was done to reconstruct three-dimensional temperature distribution of 2500 m3 blast furnace raceway. Ultimately, this method could restore temperature distribution of the raceway effectively. Moreover, computational fluid dynamics (CFD) technology was applied to simulate combustion process and obtain temperature distribution of blast furnace raceway, which was compared with the reconstructed temperature distribution. All results show that the temperature distribution of raceway can be reconstructed reasonably using Monte Carlo method and image processing techniques.

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  • Kinetic Analysis of Aluminum and Oxygen Variation of G20CrNi2Mo Bearing Steel during Industrial Electroslag Remelting Process

    Shi-jian Li, Guo-guang Cheng, Zhi-qi Miao, Lie Chen, Cheng-wei Li, Xin-yan Jiang

    pp. 2148-2156

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    DOI:10.2355/isijinternational.ISIJINT-2017-227

    Abstract

    Kinetics of slag-metal reactions was investigated in order to elucidate the mechanism of Al-oxidation and oxygen increase during industrial electroslag remelting (ESR) process. G20CrNi2Mo bearing steel was utilized as the consumable electrode and remelted using a 2400-kg industrial ESR furnace. It was found that with the content of FeO in the slag increasing from 0.20 wt% to 0.45 wt%, the content of oxygen increased from 12 ppm in electrode to 16 ppm, 21 ppm in the ingot while Al decreased from 0.040 wt% in the electrode to 0.031 wt%, 0.019 wt% in the ingot. Based on penetration and film theories, a kinetic model has been developed. The model indicates that Al in the electrode is mainly oxidized by FeO at the metal film. Increase of soluble oxygen mainly occurs during the time of droplet formation and falling. The content of soluble oxygen occupies about fifty percent of the total oxygen. The rate-determining step of Al-oxidation is the mass transfer of Al at metal side, whereas oxygen increase lies in the mass transfer of FeO at slag side. With the content of FeO increasing from 0.20 wt% to 0.45 wt%, the mass transfer resistance of FeO decreases obviously, thus would result in an increase of Al-oxidation and total oxygen. In order to improve the cleanliness of refined ingot, it is more effective to decrease the oxygen potential of slag pool to a minimum level, or decrease the time of droplet formation and the temperature of slag pool to some extent, rather than improve the Al content in the electrode.

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  • Influences of the Transverse Static Magnetic Field on the Droplet Evolution Behaviors during the Low Frequency Electroslag Remelting Process

    Huai Wang, Yunbo Zhong, Qiang Li, Wanqin Li, Weili Ren, Zuosheng Lei, Zhongming Ren, Qiong He

    pp. 2157-2164

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    DOI:10.2355/isijinternational.ISIJINT-2017-267

    Abstract

    To visualize the electroslag remelting (ESR) process, a transparent experimental model was adopted. The droplet evolution process at the consumable electrode tip was recorded by a high-speed camera. Different intensities of the transverse static magnetic field (TSMF) were imposed during the ESR process with a low frequency current of 5 Hz. The representative processes of formation and detachment of the droplets under different conditions were given. The results showed that when the intensities of the TSMF were equal or greater than 0.3 T, the droplet evolution processes would be influenced remarkably. When the TSMF reached 0.5 T, the liquid neck would be broken up into two arrays of smaller droplets. The mechanism of the breakup phenomenon appearing on the droplet neck was discussed. Statistical analysis of the videos captured by the high-speed camera under different conditions had been done. The results showed that the separation degree of the droplet necks and the remelting rate could be increased to a certain extent as the increase of the TSMF. The features of the collected droplets with the TSMF of 0.7 T showed a smaller average size and more tiny droplets comparing with what were obtained without the external magnetic field. The decrease of the droplet size and the generation of numerous tiny droplets enlarged the interfacial area between metal and slag tremendously.

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  • Numerical Study on the Capture of Large Inclusion in Slab Continuous Casting with the Effect of In-mold Electromagnetic Stirring

    Yanbin Yin, Jiongming Zhang, Shaowu Lei, Qipeng Dong

    pp. 2165-2174

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    DOI:10.2355/isijinternational.ISIJINT-2017-347

    Abstract

    Large inclusions captured by the solidifying shell deteriorate the surface quality of interstitial free steel. To investigate the capture of large inclusion in slab continuous casting, a three-dimensional model coupling flow field, solidification and inclusion motion has been developed. Additionally, to study the effect of in-mold electromagnetic stirring (M-EMS) on large inclusion capture, the electromagnetic field has been also coupled in the model. The results of electromagnetic field indicates its centrally symmetrical distribution on the cross-section, and the electromagnetic force swirls on the cross-section. The effects of M-EMS on flow pattern, solidification and inclusion capture have been discussed. The M-EMS significantly changes the flow pattern and solidifying shell thickness. The inhomogeneous distribution of large inclusions existing in the slab surface in the slab surface are different between the cases with and without M-EMS. Furthermore, the number of captured inclusions increases at 0–0.02 m beneath the wide surface and decreases at 0.02–0.04 m beneath the wide surface in response to the application of M-EMS. Large inclusions in steel were quantitatively analyzed by the galvanostatic electrolysis method. The experimental results are in agreement with the simulation results, suggesting that the model is valid.

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  • Application of a Swirling Flow Producer in a Conventional Tundish during Continuous Casting of Steel

    Peiyuan Ni, Lage Tord Ingemar Jonsson, Mikael Ersson, Pär Göran Jönsson

    pp. 2175-2184

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    DOI:10.2355/isijinternational.ISIJINT-2017-377

    Abstract

    A swirling flow producer was designed for a conventional tundish in order to produce a swirling flow in the SEN driven by the steel flow potential. CFD simulations were carried out to investigate the flow phenomena in the new tundish system. The results show that a swirling flow in the tundish SEN was successfully obtained. The swirl number of the obtained steel flow inside the SEN can reach a value of 1.34, with a tangential velocity of around 2.8 m/s. The possibility of slag entrainment at the top of the tundish was estimated by analyzing the steel flow characteristics near the top surface. The calculated Weber Number is around 0.3 outside the cylinder, which indicates a low possibility of slag entrainment. A high value of shear stress was found on the SEN wall. This is due to the rotational steel flow in SEN. Also, non-metallic inclusions were tracked in the fully developed steel flow field. It was found that the number of inclusions that touch the top surface increases with an increased inclusion size. Small size inclusions mainly move into the cylinder from the left side of tangential inlet. Therefore, methods like installing a dam at the tundish bottom may be helpful to change the inclusion trajectories to move towards the top of the tundish.

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  • Effect of Microstructure on Surface Roughening in Stretch Forming of Steel Sheets

    Masahiro Kubo, Yoshiaki Nakazawa, Takayuki Hama, Hirohiko Takuda

    pp. 2185-2193

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    DOI:10.2355/isijinternational.ISIJINT-2017-320

    Abstract

    Surface quality is an important requirement in outer automobile panels, and to obtain products with an excellent surface quality the development of surface roughening during press forming should be prevented. However, the influence of microstructures on surface roughening is not yet sufficiently understood, and thus it is difficult to control surface roughening during press forming. In this study, the mutual effect of the development of texture and the surface profile variation is examined in detail using two types of tests: a Marciniak type test used for surface roughening observation, and a microscopic biaxial tensile test in a vacuum chamber of scanning electron microscope. The latter test enables in-situ continuous observations of microstructure evolution under biaxial deformation, which is a typical deformation mode in press forming. Interstitial free (IF) steel sheets are used in this study because these sheets are mainly used for outer panels. Results show that surface roughening becomes large for sheets which have a larger number of crystal grains with orientations in the vicinity of ND(001) due to inhomogeneous deformation derived from their lower deformation resistance. It is therefore suggested that surface quality after press forming may be further improved by reducing the number of grains with crystal orientation of ND(001) in IF steel sheets.

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  • Effects of Welding Procedures on Resistance Projection Welding of Nuts to Sheets

    Xiaopei Wang, Yongqiang Zhang

    pp. 2194-2200

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    DOI:10.2355/isijinternational.ISIJINT-2017-219

    Abstract

    In this study, experiments were conducted to investigate the effects of welding current, welding time, electrode force and types of nuts on resistance projection welding of nuts to sheets. The microstructures and welded joint size of welded joints in different welding procedures have been analyzed. The failure mode of welded joints was also discussed. It is found the microhardness distribution of the fusion zone gradually becomes homogeneous with the increase of the welding current or the welding time. Lower electrode force causes the occurrence of splash and large fluctuations of the microhardness in fusion zone. Different types of nuts lead to different heat distribution in the projection welding process. The welded joint in nut is deeper than that in base metal for welding nut with higher electrical resistivity. Button pull fracture, partial thickness fracture and interfacial fracture are the three failure modes of nut projection welded joints. The interfacial fracture is brittle rupture and the partial thickness fracture is ductile rupture.

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  • Microstructure and Micro Strain in the CGHAZ of 2.25Cr-1.6W Steel after Intercritical Heat Treatment

    Yujing Jin, Jiangping Liu, Wei Zhou

    pp. 2201-2206

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    DOI:10.2355/isijinternational.ISIJINT-2017-258

    Abstract

    Multiple microscopic analysis techniques, such as transmission electron microscope (TEM), electron backscatter diffraction (EBSD) and transmission-EBSD (T-EBSD), were used to study the microstructure and micro strain in the coarse-grained heat-affected zone (CGHAZ) of 2.25Cr-1.6W steel after strain-to-fracture (STF) tests under intercritical heat treatment temperature. This study was a supplement of previous research, which was helpful for understanding the mechanism of reduced susceptibility of reheat cracking by intercritical heat treatment. The result showed that transformation products were retained austenite and twin martensite which had many variants with different crystallographic orientation. Twin boundaries were found both in recrystallized grains and matrix near the recrystallized grains. They were not conventinal parallelling interfaces and the misorientation was not exactly equal to 60°. Transformation resulted in large strain in recrystallized grains and the strain concentration kept away from the prior austenite grain boundaries (PAGBs). Besides transformation strain, the position of recrystallization was another factor which led to different mechanisms of reduced susceptibility to ductility-dip cracking (DDC) in Ni-based alloy and reheat cracking in 2.25Cr-1.6W steel, respectively.

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  • Influence of Metallic Powder Contents on Corrosion Resistance of Galvanized Steel with Metal Powder-containing Organic Coatings for Automobile Fuel Tanks

    Hiroyuki Ogata, Hiroki Habazaki

    pp. 2207-2213

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    DOI:10.2355/isijinternational.ISIJINT-2017-244

    Abstract

    Pb- and Cr(VI)-free galvanized steel sheets for fuel tanks are coated with epoxy-resin films (thickness: approx. 3 µm) containing particulate Ni powder and flaky Al powder to provide a combination of weldability and degraded gasoline resistance (sour gasoline resistance). The corrosion behavior of galvanized steel specimens coated with epoxy resin containing different amounts of the two types of metal powders was investigated in a solution containing acetic acid, formic acid and NaCl at pH 3.2 and 40°C to elucidate the mechanism of corrosion protection by the coatings. The oxygen gas permeability and water vapor permeability of the coatings were also examined. The results indicated that the addition of particulate Ni powder promoted galvanic corrosion between the Ni and the Zn coating. Voids generated around the embedded Ni powder particles also appeared to accelerate the penetration of the corrosive solution through the coating. On the other hand, the addition of the flaky Al powder improved corrosion resistance. This improved corrosion resistance is associated with the suppression of direct contact between the Ni powder and the Zn coating and also with increased barrier properties, which could be confirmed from oxygen gas and water vapor permeation measurements.

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  • Effects of Si Solid Solution in Fe Substrate on the Alloying Reaction between Fe Substrate and Liquid Zn

    Satoru Kobayashi

    pp. 2214-2219

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    DOI:10.2355/isijinternational.ISIJINT-2017-410

    Abstract

    Effects of Si solid solution in Fe substrate on the formation of Fe–Zn intermetallic phase layers between the Fe(-Si) substrate and liquid Zn were investigated using a combinatorial technique. The formation of ζ-FeZn13 layer was promoted by Si solid solution up to 2 at.% in the Fe substrate but retarded by further solution. The formation of δ1-FeZn7-10 phase and Γ-Fe3Zn10 phase was retarded by Si solid solution up to 10 at.%. The rate of Fe dissolution from the Fe substrate to the liquid Zn region and the Fe/Zn/Si contents in the δ1 phase were analyzed as a function of Si content in the substrate. The results obtained suggest that the retardation of the Fe–Zn phase formation is caused by a difficulty in the nucleation of δ1 phase at lower Si contents less than 3 at.% and by a decrease in the rate of Fe dissolution at higher Si contents.

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    2. Electrical Properties and Melting Treatment Rate of a Continuous Induction Waste Melter ISIJ International Vol.39(1999), No.4
    3. Modeling of the Effect of Aluminum Content on the Kinetics of Iron Enrichment in Hot-dip Galvannealed Coatings on IF Steel Sheets ISIJ International Vol.38(1998), No.12

  • Effect of Annealing Before Cold Forging on the Behavior of Abnormal Grain Growth during Carburizing

    Yuta Imanami, Takako Yamashita, Kunikazu Tomita, Kazukuni Hase

    pp. 2220-2228

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    DOI:10.2355/isijinternational.ISIJINT-2017-131

    Abstract

    In order to clarify the mechanism of abnormal grain growth in steel for cold forging and carburizing, the effect of spheroidizing annealing on the behavior of abnormal grain growth during carburizing was investigated. Abnormal grain growth was observed in annealed steel, whereas it was suppressed in normalized steel. However, since both the normalized steel and the annealed steel have almost the same size distribution of Nb(C,N) nano-precipitates, the effect of annealing on abnormal grain growth was not explained by the conventional theory based on the pinning force by nano-precipitates.Spheroidized cementite was remained in the annealed steel which was immediately quenched from the quasi-carburizing temperature of 1203 K. Dissolution of spheroidized cementite and abnormal grain growth took place simultaneously. Spheroidized cementite was thermally stabilized by Cr concentration. A DICTRA simulation was carried out to discuss the kinetics of cementite dissolution. Cr concentration affects the dissolution rate of spheroidized cementite through the relationship between the Cr content and the cementite size. The Cr content in cementite has a wide distribution, and the dissolution time is different in each cementite. This dissolution time lag among cementites causes a local and non-uniform decrease of the pinning force by cementite. As a consequence, abnormal grain growth is likely to occur in annealed steel.

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  • Prediction of Ac3 and Martensite Start Temperatures by a Data-driven Model Selection Approach

    Hoheok Kim, Junya Inoue, Masato Okada, Kenji Nagata

    pp. 2229-2236

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    DOI:10.2355/isijinternational.ISIJINT-2017-212

    Abstract

    Four different information criteria, which are widely used for model selection problems, are applied to reveal the explanatory variables for phase transformation temperatures of steels, austenitise temperature (Ac3) and martensite-start temperature (Ms). Using existing datasets for CCT diagram for various steels, the predictive equations for these critical temperatures are derived. A number of empirical equations have been proposed to enable efficient prediction of the the Ac3 and Ms temperatures of steels. However, the key parameters in those equations are usually chosen based on researchers’ trials and errors. In this study, the performance of the information criteria is evaluated first using a simulated dataset mimicking the characteristics of those for the Ac3 and the Ms temperatures. Then the criteria are applied to the experimental data obtained from two different sources. The key parameters are chosen for the Ac3 and Ms temperatures and the derived equations are found to be in better agreement with experimental data than the previous empirical equations. Thus, it was clarified that the methods can be applied to automatically discover the hidden mechanism from complex multi-dimensional datasets of steels’ chemical composition.

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    2. Effect of Niobium on Precipitates and Texture Evolution of Fe-3% Si Grain-oriented Electrical Steel Annealed Hot Band ISIJ International Vol.57(2017), No.12
    3. Subsolidus Phase Relations in the CaO–SiO2–Nb2O5–La2O3 Quarternary System at 1273 K ISIJ International Vol.57(2017), No.12

  • In situ Observations of Transformation Behavior upon Heating for a 1.5Mn-1.5Si-0.2C Steel -Comparison between Neutron Diffraction, XRD, EBSD and Dilatometry-

    Yo Tomota, Nobuaki Sekido, Stefanus Harjo, Takuro Kawasaki, Wu Gong, Akira Taniyama

    pp. 2237-2244

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    DOI:10.2355/isijinternational.ISIJINT-2017-272

    Abstract

    The austenite reverse transformation behavior in a 1.5Mn-1.5Si-0.2C steel was in situ monitored using dilatometry, electron back scatter diffraction (EBSD), X-ray diffraction and neutron diffraction. The austenite reversion kinetics showed excellent agreements between dilatometry and neutron diffraction, whereas the austenite formation was observed to start at much higher temperature in cases of EBSD and X-ray diffraction measurements. Such discrepancy in transformation temperature is attributed to the change in chemical compositions near the surface of a specimen heated to elevated temperatures either in vacuum (EBSD) or in a helium gas atmosphere (X-ray); Mn and C concentrations were found to decrease with heating. In situ neutron diffraction enables us to investigate the changes in lattice constants of ferrite and austenite, showing not only thermal expansion but also suggesting carbon enrichment and phase stresses during the decomposition of the retained austenite and austenite reversion upon heating.

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  • Effect of Niobium on Precipitates and Texture Evolution of Fe-3% Si Grain-oriented Electrical Steel Annealed Hot Band

    Ruogu Hou, Chengyi Zhu, Guangqiang Li, Bowen Zhou, Juan Jia

    pp. 2245-2254

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    DOI:10.2355/isijinternational.ISIJINT-2017-335

    Abstract

    Precipitation behavior of inhibitors, microstructure and texture evolution in annealed hot band of grain-oriented Fe-3%Si electrical steel with niobium addition were analyzed, and compared with that of common grain-oriented electrical steel. Stoichiometric ratio of C and N in Nb(C, N) was determined by their lattice parameters. Inhibitors precipitated in the hot rolled band with niobium addition are mainly Nb(C, N). Their average size was 34.1 nm and number density was 3.80×107/mm2, with stronger inhibition effect than inhibitors in common grain oriented electrical steel. Stoichiometric ratio of C and N in Nb(C, N) changed from Nb(C0.85, N0.15) to Nb(C0.71, N0.29) which means NbC is dominant in Nb(C, N) of current study. After niobium addition, recrystallization of annealed hot band was incomplete while more Goss texture is preserved. Addition of niobium is proved helpful to obtain precipitates with higher inhibition effect during hot rolling, instead of adopting hot band annealing.

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  • Industrial Application of Large Rotary Kiln for Recovery of Vanadium from Vanadium Slag Added MnVO4 in Calcium Roasting Process

    Jin Wang, Shaodong Wang, Lin Zhang, Guangchao Du, Wenyi He

    pp. 2255-2262

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    DOI:10.2355/isijinternational.ISIJINT-2017-097

    Abstract

    Calcification roasting was an effective and environment-friendly way to extract vanadium from vanadium slag. This paper presents a comprehensive study on industrial application of calcium roasting process for large rotary kiln. The study has highlighted the importance of temperature stability using MnVO4 for maximizing the recovery of the vanadium. The optimum conditions for recover 87.48–89.65% of vanadium (V) by using MnVO4 at M·Fe concentration 1±0.5%, CaO to V2O5 ratio 0.58–0.64, MnVO4 concentration 50–55%, feed rate 4.44±0.56 kg/s, rotate speed 87–90 s/r, temperature of T2 865±10°C, temperature control curves TE, TF, TG, negative pressure −10±5 Pa and volume flow ratio of the combustion air to coke oven gas (5–5.5). It was possible MnVO4 was not only the additive but also play a key auxiliary effect for CaO with vanadium (V) to Ca2V2O7 by studying on the oxidation reaction mechanism.

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  • A Novel Texture Improving Young’s Modulus in Rolling Direction of Hot Rolled Low Carbon Sheet Steel

    Naoki Yoshinaga, Natsuko Sugiura, Shunji Hiwatashi

    pp. 2263-2265

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    DOI:10.2355/isijinternational.ISIJINT-2017-372

    Abstract

    A novel texture, which improves Young’s modulus in rolling direction, has been found in a hot rolled low carbon sheet steel. This unique texture is observed in sheet surface area, which consists of sharply developed {110}<111>–{110}<112> fiber without {110}<001>. Together with {112}<111> orientation, this fiber can significantly contribute to increase Young’s modulus in rolling direction. The measured Young’s modulus in rolling direction in the present material is 236 GPa, which is more than 10% increase, compared to the one in conventional steels.

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    3. Generation of Heterogeneous Nucleus in Carbon Steel during Solidification by Magnesium Vapor Injection ISIJ International Vol.56(2016), No.8

  • An Improved Methodology for Pulse Combustion with Programmable Timing Sequence Used in Reheating Furnaces

    Lingyan Hu, Yana Lv, Kai Tang, Gwynfor Richards

    pp. 2266-2268

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    DOI:10.2355/isijinternational.ISIJINT-2017-020

    Abstract

    This work introduces a programmable pulse combustion controller. It has two main parts, namely burner flame switch timing sequence and burner startup sequence; and the sequences being controlled by three groups of programmable timers. Burner output capacities for high and low flames are adjustable online, and the corresponding working periods for different flame sizes can be computed automatically using the proposed equations tested in practice. Proper cooperation between the burner flame size and its working period can achieve the required control objective well. Comparison results in several projects of reheat furnaces show the proposed methodology can optimize chamber temperature distribution and improve control precision effectively.

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    3. Influences of the Transverse Static Magnetic Field on the Droplet Evolution Behaviors during the Low Frequency Electroslag Remelting Process ISIJ International Vol.57(2017), No.12
  • © 2017 The Iron and Steel Institute of Japan

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