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

ISIJ International Advance Publication

  • Multiscale Analysis of MnS Inclusion Distributions in High Strength Steel

    Ryota Sakaguchi , Takayuki Shiraiwa , Pornthep Chivavibul , Tadashi Kasuya , Manabu Enoki , Norio Yamashita , Hideo Yokota , Yutaka Matsui , Akira Kazama , Keita Ozaki , Hiroyuki Takamatsu

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    DOI:10.2355/isijinternational.ISIJINT-2019-739

    Abstract

    In the present study, manganese sulfide (MnS) inclusions in the high-strength steel were observed by mainly three observation methods (optical microscope, ultrasonic test and serial sectioning) to characterize the size, location and shape distributions across multiple length scales. For the inclusion size, ultrasonic C-scan imaging and three-dimensional internal structure observation with serial sectioning were used to measure the distributions of the square root of the projected area of the inclusion. The obtained size distributions were combined by setting the threshold of ultrasonic amplitude. The validity of the amplitude threshold was verified by observing several inclusions with X-ray CT. The spatial distributions of inclusions were also obtained by the three observation methods, and analyzed on the basis of the coefficient of variation of the mean near-neighbor distance of inclusions (COVd). The results of analyzing COVd in both 2D and 3D spaces revealed that the inclusions in this material were arranged in clusters. For the inclusion shape, the three-dimensional geometries of inclusions were reconstructed from the images obtained by the serial sectioning method, and simplified to ellipsoid by principal component analysis. From the above results, the distributions of inclusion size, aspect ratio and direction (angle between rolling direction and major axis) were successfully obtained. The inclusion distributions were applied to fatigue prediction model, and the fatigue crack initiation life and total fatigue life of the high-strength steel were calculated. The calculation results showed that the multiscale analysis of inclusions would be useful for fatigue life prediction.

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  • Modelling and Crystal Plasticity Analysis for the Mechanical Response of Alloys with Non-uniformly Distributed Secondary Particles

    Yelm Okuyama , Masaki Tanaka , Tetsuya Ohashi , Tatsuya Morikawa

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    DOI:10.2355/isijinternational.ISIJINT-2019-754

    Abstract

    The relationship between yield stress and the distribution of microscopic plastic deformation was numerically investigated by using a crystal plasticity finite element method (CP-FEM) in the model where particles were randomly distributed. It was in order to reveal which particle spacing. i.e., the maximum, minimum or average particle spacing, can be taken as the representative length which controls yielding. The critical resolved shear stress for the onset of the slip deformation in any element was defined under the extended equation in the Bailey-Hirsch type model. The model includes the term of the Orowan stress obtained from the local values of the representative length. Each particle spacing was distributed with a standard deviation of approximately 2 to 3 times larger than the average particle spacing. The macroscopic mechanical properties obtained with CP-FEM were in good agreement with those experimentally obtained. The onset of microscopic slip deformation depended on the particle distribution. Plastic deformations started first in the area where the particle size is larger, then the plastic region grows in the areas where the particle spacing is smaller. Slip deformation had occurred in 90% of the matrix phase by the macroscopic yield point. The length factor in the Orowan equation was the average spacing of the particles in the model, which is in good agreement with Foreman and Makin. The CP-FEM indicated that in dispersed hardened alloys, microscopic load transfer occurred between the areas where the large particles spacing and the small one at the yielding.

  • Effect of B2O3 on Structure of CaO–Al2O3–SiO2–TiO2–B2O3 Glassy Systems

    Feifei Lai , Wen Yao , Jiangling Li

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    DOI:10.2355/isijinternational.ISIJINT-2019-679

    Abstract

    Titanium-bearing blast furnace slag is an important metallurgical waste, but presently, it is difficult for it to be effectively utilized. B2O3 is an important modifier to greatly promote the mass diffusion of crystallization of Ti-enriched phases in molten slags. To furtherly understand the effect of B2O3 on the structure of Ti-bearing slag, CaO–Al2O3–SiO2–TiO2–B2O3 glasses of various B2O3 were investigated by combining Raman, FT-IR, and X-ray photoelectron spectroscopy. The results showed that BO3 was the dominant structure, which decreased slightly as the B2O3 content increased, while BO4 increased. Three coordination forms (TiO4, TiO5, and TiO6) of the Ti-structure were discovered in the prepared Ti-bearing glasses. The percentage of TiO4 gradually increased and became the main structural unit as the increased B2O3. The increase of BO4 and TiO4 leaded to an increased amount of network connection units, such as SiO4, to increase the degree of polymerization of the prepared Ti-bearing glasses.

  • Phase Composition and Properties Distribution of Residual Iron in a Dissected Blast Furnace Hearth

    Lei Zhang , Jianliang Zhang , Kexin Jiao , Cui Wang

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    DOI:10.2355/isijinternational.ISIJINT-2019-712

    Abstract

    Dissection research is the most meaningful way to understand the internal conditions of blast furnace. Because it can obtain samples from hearth after a blast furnace was shut down. In this paper, a 2200 m3 commercial blast furnace was shut down with residual iron remained inside. And then core drilling method was used to obtain a horizontal sample of residual iron, which was located 1610 mm below the centerline of taphole and had a length of 1840 mm. A variety of techniques, such as scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), Optical Microscope, X-ray diffraction (XRD) and Raman spectroscopy were applied to analysis the microscopic morphology, phase composition and properties distribution of residual iron samples at different position. The results show that complex phases appear near the cold side, including Fe, C, Ti3N2, KAlSi2O6 and Al2O3. And distribution of properties along the core sample from inside to cold side like density, degree of graphitization and thermal diffusion also have a big change. These results are considered to be related to the function of cooling system.

  • Casting Defect and Process Optimization of Steel Crossing

    Dengyue Sun , Ruihao Lv , Jiuming Xie , Shimin Xu

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    DOI:10.2355/isijinternational.ISIJINT-2019-612

    Abstract

    The casting quality of crossing in a railway turnout is required to be higher because of the significant impact load on the rail. The simulation results of using different fever risers, the temperature field, solidification process and casting defects, were obtained by the implicit finite element method based on the ProCAST software. To improve the authenticity of the visualization of the casting process, a numerical simulation assumption of the mass flow rate attenuation was proposed for the overflow of molten metal from the risers during tilt pouring. The result shows that the temperature field is more uniform when the risers with exothermic energy of 1200 kJ/kg were chosen and the defects converge to the risers in accordance with the principle of sequential solidification. Compared with insulation riser, shrinkage porosity proportion decreased from 23.10% to 17.01%, and the shrinkage cavity proportion decreased from 1.002% to 0.530%. However, changing the burned time has no obvious effect on the casting. At the same time, the process optimization scheme of risers was put forward in this study and the casting defects such as shrinkage cavity and porosity are predicted according to the ‘V type' feeding area of the fever risers. This improvement has greatly improved the performance of the casting, and the passing gross tonnage could reach 300 million tons.

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  • Numerical Simulation of Impinging Gas Jet on a Liquid Bath Using SPH Method

    Jumpei Maruyama , Kazuki Ito , Makoto Ando , Jun Okada , Kimihisa Ito

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    DOI:10.2355/isijinternational.ISIJINT-2019-653

    Abstract

    As the basis of injection metallurgy, an impinging gas jet on a liquid bath surface was simulated and experimentally verified. The SPH simulation of the gas-liquid two phase flow was developed by using the XSPH method, and the calculation speed was considerably increased with the use of general-purpose computing on graphics processing units. For N2 gas – water bath system, the simulated shapes and penetration length of the cavity were in good agreement with the experimental results, and the three modes of cavity were reproduced by the calculation. N2 gas–molten iron bath system was also simulated. The cavity mode was "dimpling mode" for all calculations.

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    3. Multiscale Analysis of MnS Inclusion Distributions in High Strength Steel ISIJ International Advance Publication

  • Data Assimilation in the Welding Process for Analysis of Weld Toe Geometry and Heat Source Model

    Takayuki Shiraiwa , Manabu Enoki , Sota Goto , Takashi Hiraide

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    DOI:10.2355/isijinternational.ISIJINT-2019-720

    Abstract

    Finite element simulations are widely conducted to evaluate the heat transfer and deformation during welding. Basically these welding simulations require input variables such as shape parameters and heat source parameters, which are not directly measured by the experimental method. In this study, two methods were proposed to obtain these input parameters more efficiently: a method of automatically identifying toe radius and reinforcement angle from height profile, and a method of estimating a heat source model in welding simulation. In the first method, the toe radius and reinforcement angle were extracted from the height profile by Akaike's information criterion. The extracted results were consistent with the manual fitting results. In the second method, the optimal combination of the heat input parameters was automatically searched by Bayesian optimization. Comparing the accumulated regrets, it was found that the probability of improvement and upper confidence bound provide more efficient optimization than the other acquisition functions in the calibration of the heat input parameters. Both temperature history and shape of fusion zone and heat-affected zone calculated at the optimized condition were in good agreement with the experimental results. These results demonstrated that the two proposed methods are effective to create a numerical model for welding simulation.

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  • Sulfide Capacities of Solid Oxides in Calcium-Aluminate Systems

    Yosuke Baba , Xu Gao , Shigeru Ueda , Shin-ya Kitamura

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    DOI:10.2355/isijinternational.ISIJINT-2019-793

    Abstract

    To clarify the mechanism of CaS formation on the oxide inclusion of the CaO–Al2O3 system, the sulfide capacities of solid oxides was measured in the present study. The results show that the sulfide capacity of (12CaO·7Al2O3; C12A7) was much larger than of other compounds, and increased with temperature. The value for C12A7 was larger than that measured for the liquid oxide of the same composition. Furthermore, the diffusion behavior of sulfur in solid steel to the inclusion of the CaO–Al2O3 system, was investigated using a diffusion couple. After heating at 1473 K for 72 h, in the case of C12A7, the intensity of sulfur in the oxide was high, but the formation of CaS was not detected. This suggests that the formation of CaS was suppressed around the C12A7 particles by the diffusion of sulfur in the solid oxide.

  • Physico-chemical Properties of Mill Scale Iron Powders

    Kameswara Srikar Sista , Srinivas Dwarapudi , Deepak Kumar , Gourav Ranjan Sinha

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    DOI:10.2355/isijinternational.ISIJINT-2019-737

    Abstract

    Powdered form of iron typically < 250 microns is phrased as iron powder. Commercial manufacturing of iron powder is majorly restricted to atomization, carbonyl, electrolytic and reduction routes. Powders from the later three techniques generally cater to special iron powders applicable to non-powder metallurgy segments such as food fortification, chemical reagents, water purification, etc. In this work, mill scale iron powders are synthesized by thermo-chemical reduction of mill scale, a steel industry by product, and their properties are analysed and compared with commercial iron powders such as carbonyl, electrolytic and reduced. Chemical and physical characterizations such as Optical Microscopy, Scanning Electron Microscopy and X-ray Diffraction of the powders are performed. Obtained results reveal that, mill scale iron powders MIP and MIP45 possess good product properties. Especially, MIP45 grade exhibited finer particle size of D50< 30 microns and BET surface area of 0.63 m2/g along with Fe (T) > 98%, true density-7.55 g/cc, apparent density 2.67–2.83 g/cc, packed bulk density of 3.44 g/cc and good flowability. This product of mill scale with highest apparent density and good surface area is expected to qualify to new segment of applications along with other commercial iron powders.

  • Effect of Silicon, Manganese and Heating Rate on the Ferrite Recrystallization Kinetics

    Vitesh Shah , Monika Krugla , Sven Erik Offerman , Jilt Sietsma , David Neal Hanlon

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    DOI:10.2355/isijinternational.ISIJINT-2019-475

    Abstract

    This study presents the effects of silicon (Si) and manganese (Mn) concentration and of heating rate on the ferrite recrystallization kinetics in seven model alloys with different Si and Mn concentrations, which are of relevance for the development of Advanced High Strength Steels (AHSS). The recrystallization kinetics were studied with in-situ 2D X-ray Diffraction (2D-XRD) and ex-situ microstructure observations using Scanning Electron Microscopy (SEM). The experimentally observed differences in the recrystallization start temperature (Ts), dependent on the Si and Mn concentrations and the heating rate, can be described by combining the non-isothermal JMAK-model with a modified version of Cahn's solute drag model. The modified Cahn model takes into account – in an approximate manner – that the interaction energy of the solute atoms with the grain boundary depends on the Si and Mn concentrations in the boundary and the Wagner interaction parameters. The collective contribution of the Si and Mn atoms to the increase in the Ts with respect to the reference alloy (without Si and with very little Mn) is higher than would be expected from the simple addition of the effects of the Si and Mn concentrations alone. This means that the interaction between Si and Mn atoms leads to an additional increase in Ts, i.e. a coupled solute drag effect. For the later stages of recrystallization, we have studied the change in the number density and the growth rates of the recrystallizing grains using SEM. The observations show non-random nucleation, early impingement of the grains in the normal-direction and non-constant growth rates of recrystallizing grains.

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  • In-situ Phase Identification of Crystallized Compound from 2CaO·SiO2–3CaO·P2O5 Liquid

    Masanori Suzuki , Sho Nakano , Honami Serizawa , Norimasa Umesaki

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    DOI:10.2355/isijinternational.ISIJINT-2019-449

    Abstract

    In dephosphorization process in steelmaking, phosphorus in molten iron is distributed into molten slag after oxidized, and it forms 3CaO·P2O5. It has been known that dicalcium silicate (2CaO·SiO2) formed in molten slag and 3CaO·P2O5 make a solid solution, which could promote dephosphorization efficiency from molten iron. It has been reported that 2CaO·SiO2–3CaO·P2O5 solid solution (α phase) is formed for entire composition range at higher temperatures than 1673 K, and many previous studies on dephosphorization behavior assumed that the α phase would be precipitated from molten slag. However, we found that the α phase cannot be obtained at low phosphorus concentrations when the pellet of 2CaO·SiO2 and 3CaO·P2O5 powders mixture is annealed and quenched to room temperature. In this study, we conduct high temperature in-situ X-ray diffraction analysis to the aerodynamically levitated sphere of the 2CaO·SiO2–3CaO·P2O5 liquid to identify primary crystallized phase. It has been verified that the α phase is precipitated from the liquid for wide phosphorus concentrations. In addition, a rapid phase transition of the 2CaO·SiO2–3CaO·P2O5 solid solution has been detected by the time-division X-ray diffraction with high resolutions when the levitated sample containing the α phase is quenched from the precipitated temperature.

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  • A Data-Driven Multiobjective Dynamic Robust Modeling and Operation Optimization for Continuous Annealing Production Process

    Yao Wang , Xianpeng Wang , Zhiming Dong , Zan Wang

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    DOI:10.2355/isijinternational.ISIJINT-2019-570

    Abstract

    There are many dynamic disturbances during the continuous annealing production line (CAPL) in iron and steel enterprise. Traditional robust operation optimization considers only the maximum disturbance range in previous production and overrides the dynamic changes of these disturbances, which often results in high production cost and low product quality. Therefore, this paper proposes a novel multiobjective dynamic robust optimization (MODRO) modeling method by further taking into account the dynamic changes of these disturbances and adopting a time series prediction model based on a least square support vector regression (LSSVR) to predict the range of disturbances in next time slot. The main feature of the model is that the robustness can be dynamically adjusted according to the disturbance range predicted by the LSSVR. To solve this model, an improved NSGA-II algorithm is developed based on a new crowding metric. Numerical results based on actual production process data illustrate that the proposed MODRO modeling method is obviously superior to traditional static robust operation optimization, and that it can significantly improve the strip quality and the capacity utilization of the CAPL, and reduce the total energy consumption.

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  • Segregation Mechanism of Al-based Oxides on Surface of Zn-0.2mass%Al Hot-dip Galvanized Steel Sheets

    Katsuya Hoshino , Katsunari Oikawa , Wataru Tanimoto , Masayasu Nagoshi , Masaki Koba

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    DOI:10.2355/isijinternational.ISIJINT-2019-749

    Abstract

    It is known that the Al added to the Zn coating layer of hot-dip galvanized steel sheets (HDG) segregates on the surface of temper-rolled HDG as Al-based oxides with increasing aging time in air at room temperature. In this study, the surfaces of Zn-0.2mass%Al HDG with and without temper rolling were investigated to clarify the segregation mechanism. Specimens with a Zn coating weight of 55–57 g/m2 including 0.19–0.20 mass% of Al were used. The specimens were aged in air at 20°C or held in liquid nitrogen, and the surface and cross sections of the specimens were then observed and analyzed by XRF, SEM-EDX and EBSD. As a result, it was found that the velocity of Al-based oxide segregation on the surface of the temper-rolled HDG was much higher than that of the HDG without temper rolling. This was attributed to the difference in the area where formation of Al-based oxides was possible. It was also found that the Zn crystal grains in the coating layer were refined by recrystallization due to contact with the temper roll, resulting in an increased number of grain boundaries that can serve as Al diffusion paths. Some unrecrystallized grains also remained after temper rolling and could increase the number of formation sites for Al-based oxides, as they contain numerous dislocations that can serve as Al diffusion paths. These two different formation sites could lead to difference in the segregation rates observed in this study.

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  • Selection of Atomic Emission Lines on the Mutual Identification of Austenitic Stainless Steels with a Combination of Laser-induced Breakdown Spectroscopy (LIBS) and Partial-least-square Regression (PLSR)

    Shunsuke Kashiwakura , Kazuaki Wagatsuma

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    DOI:10.2355/isijinternational.ISIJINT-2019-549

    Abstract

    Laser-induced breakdown spectroscopy (LIBS) is a promising method for the rapid determination of compositions of stainless steels in steel scrap. LIBS is widely known as a method for very rapid elemental analysis in open-air without any pretreatment. We applied a laboratory-build LIBS system for mutual identification of 5 types of austenitic stainless steels, SUS304, SUS310, SUS316, SUS321, and SUS347. The certified reference materials of JSM M 200 were employed for establishing supervised models, conducting partial-least-square regression (PLSR) for the determination of Cr, Ni, Mo, Ti, and Nb. Since it needed more than 10 minutes of calculation time when all the wavelength range were utilized for PLS2 regression, suitable emission lines in the determination were picked up for the reduction of calculation amount and time. When we select single emission lines having higher excitation levels to avoid an affection by self-absorption, the good determination results for Cr, Ni, Mo, and Nb could be obtained with reasonable accuracy and precision by the calculation with PLS1 regression.

  • Development of Low-fluoride Slag for Electroslag Remelting: Role of Li2O on the Crystallization and Evaporation of the Slag

    Dingli Zheng , Jing Li , Chengbin Shi

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    DOI:10.2355/isijinternational.ISIJINT-2019-575

    Abstract

    To reduce environmental pollution caused by fluoride from conventional electroslag remelting (ESR)-type slag and meet the requirements of vacuum ESR, it is strongly needed to develop low-fluoride and fluoride-free slag. The crystallization behaviors and evaporation of CaF2–CaO–Al2O3–MgO–Li2O slag as a candidate for low-fluoride ESR-type slag were studied. The sequence of crystal precipitation in CaF2–CaO–Al2O3–MgO–Li2O slag during cooling process was 11CaO·7Al2O3·CaF2 to CaO, followed by CaF2. The dominant crystalline phase in the slag was 11CaO·7Al2O3·CaF2. The liquidus temperature and crystallization temperature of slag decreased significantly with increasing Li2O content from 1.59 mass% to 4.46 mass%. Increasing Li2O contents suppressed the crystallization behaviors of ESR-type CaF2–CaO–Al2O3–MgO–Li2O slag. The weight loss of the slag melts increased with increasing Li2O content in the slag from 1.59 mass% to 4.46 mass%. The gaseous species evaporated from the slag melts were mainly LiF and contained a few amounts of CaF2. A proper amount of Li2O could be considered as an effective component for the design of low-fluoride ESR-type slag. Serious fluoride evaporation of LiF from CaF2–CaO–Al2O3–MgO–Li2O slag melts takes place when Li2O content exceeds a critical value.

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  • Modelling and Application of Signal Decoupling of Adjacent Channels of a Whole-Roller Seamless Flatness Meter

    Huaxin Yu , Dongcheng Wang , Hongmin Liu , Tongyuan Zhang , Lipo Yang

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    DOI:10.2355/isijinternational.ISIJINT-2019-472

    Abstract

    For ultra-thin and super-wide cold rolled strips, the flatness problem are still very conspicuous. To ensure that the surface of a strip is not scratched, a whole-roller seamless flatness meter (abbreviated as WRS flatness meter) is developed. Due to the structure of the measuring roll, which has cylindrical holes under its surface, both the signal of the measuring channels and the signal of the adjacent channels will be significantly interfered when a load is applied to a WRS flatness meter, causing flatness measurement errors. To eliminate mutual interference between channels, flatness measuring principle and channel coupling mechanism are analyzed, and the concept and model of coupling coefficient are proposed. Then, some examples are given to illustrate significant errors caused by coupling, which demonstrates the necessity of decoupling the channels. Coupling coefficients between the channels are obtained by experimental calibration, and interference between the channels is eliminated with a decoupling matrix equation. Through simulation and industrial applications, it is shown that the theoretical model proposed in this paper realizes decoupling of the channels of the WRS flatness meter, which improves flatness detection and controlling accuracy.

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  • Lowest Fatigue Limit Estimation of Ductile Cast Iron Joints by Considering Maximum Defect Size Toward Replacing Welded Joints

    Tetsuro Hidaka , Nao-Aki Noda , Yoshikazu Sano , Nobuhiro Kai , Hiroyoshi Fujimoto

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    DOI:10.2355/isijinternational.ISIJINT-2019-494

    Abstract

    In our earlier study, the authors revealed that the fatigue limit of ductile cast iron (DCI) specimens whose shapes are similar to the welded joint shapes is about three times larger than that of the welded joint specimens. However, since many defects are usually included in the DCI specimens, the fatigue limit of DCI joints decreases with increasing the maximum defect size. In this paper, therefore, the maximum defect size is estimated by using statistics of extremes. Then, the lowest fatigue limit corresponding to the maximum defect size is estimated from the 4 parameter model and compared with the lowest fatigue limit of the welded joint. As a result, it was confirmed that the lowest fatigue limit of the DCI specimens is about twice as large as the welded joint.

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  • Development of High Accuracy Segmentation Model for Microstructure of Steel by Deep Learning

    Fumito Ajioka , Zhi-Lei Wang , Toshio Ogawa , Yoshitaka Adachi

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    DOI:10.2355/isijinternational.ISIJINT-2019-568

    Abstract

    We studied on automation of segmentation using deep learning, which has been remarkably developed in recent years.For the microstructural image of ferrite-martensite dual phase steel, we tried to segment the ferrite phase, martensite phase, and ferrite grain boundary in different colors individually. We created two models, SegNet and U-Net that can perform segmentation with high accuracy and compared the accuracy with an existing method.As a result, we demonstrated that models using deep leaning is more accurate than the existing method. In particular, U-Net model shows highly accuracy of segmentation for material microstructures.

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  • Non-equilibrium Precipitation Behavior of TiC during Rapid Solidification of TiC-reinforced Wear-resistant Steel

    Gang Du , Feng Liu

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    DOI:10.2355/isijinternational.ISIJINT-2019-535

    Abstract

    Precipitation behavior of TiC in TiC-reinforced wear-resistant steel was investigated using both thermodynamics and experiments. The carbide in TiC-reinforced wear-resistant steel is principally Ti-rich MC-type, which starts to precipitate at 1460°C in the solid–liquid zone. As the temperature decreased, there is no major change in the concentration of Ti and C in TiC. The results calculated by using equilibrium assumptions show that TiC can form when the solid fraction exceeds 0.24. However, the isolated primary TiC was observed in the sample cooled at rate of 162 K/s and 267 K/s, indicating that TiC can precipitate from the melts at the initial stage of solidification process. As an extension of Brody and Fleming's model, the interface response functions relating the cooling rate with the interface composition and interface temperature, which consider interface non-equilibrium effect on the basis of incomplete mixing of solute in the liquid during solidification, were used to evaluate TiC precipitation behavior during rapid solidification for different cooling rates. In comparison with lower cooling rate, the effect of non-equilibrium behavior is strengthened under the condition of higher cooling rate, so that primary TiC can precipitate from the melts at the initial stage of solidification when a high cooling rate is imposed.

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  • Establishment of Evaluation and Prediction System of Comprehensive State Based on Big Data Technology in a Commercial Blast Furnace

    Yong Deng , Qing Lyu

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    DOI:10.2355/isijinternational.ISIJINT-2019-545

    Abstract

    The application of big data in industry can solve industrial problems through data analysis. In order to establish the evaluation and prediction system of comprehensive state in a commercial blast furnace (BF), problems of ironmaking data were observed, standardized processing technologies were employed to process ironmaking data, big data platform of ironmaking was deployed based on the collected data. Hot metal production, hot metal production quality [Si+Ti] and fuel rate were selected as the target parameters to reflect the comprehensive state of BF. 26 key parameters that were most closely related to BF production and target parameters were screened out through Python 3.7. The relationship between 26 key parameters and hot metal production, [Si+Ti], fuel rate was analyzed, respectively. The first five parameters with strong correlation with target parameters were selected as important data for analysis and prediction. The comprehensive state was scored according to scoring rules derived from data analysis, the total score could be obtained to evaluate the comprehensive state of the commercial BF. The prediction of comprehensive state was realized based on a large number of historical data. The optimization of model was completed and the model could be run online, the evaluation and prediction system helped operators optimize BF operation.

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  • Vortex Dynamics and Fluctuations of Impinging Planar Jet

    Le Quang Phan , Andrew Dennis Johnstone , Buyung Kosasih , Wayne Renshaw

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    DOI:10.2355/isijinternational.ISIJINT-2019-566

    Abstract

    Smoothness of thin metallic coated strip produced in continuous galvanizing lines is influenced by fluctuations of the impinging wiping pressure. In this paper, vortex dynamics e.g. vortex production frequency and mixing of jet opposing shear layer vortices; and impinging pressure were numerically studied by Large Eddy Simulation (LES). The effects of jet nozzle width, d, and operational parameters (nozzle to strip distance, H, and mean jet velocity, Uo) were investigated. Vortex production rate is almost linearly correlated to Uo and mixing of shear layer vortices occurs when H/d ≥ 6. Dominant frequencies of impinging pressure fluctuation are significantly different between the two possible phenomena of i) Mixing of opposing shear layer vortices prior to jet impingement on the strip, or ii) No mixing of opposing shear layer vortices prior to jet impingement. The impinging pressure of a jet characterised by mixing of vortices is predominantly composed of frequencies lower than 10 kHz with the most significant components at less than 1 kHz. In contrast, for a jet with non-mixing of vortices, the impinging pressure fluctuations are comprised of frequencies greater than 10 kHz and the dominant frequency is approximately one half the vortex production frequency. Utilising existing model results for the coating thickness response to pressure and shear stress fluctuations12) the anticipated degree of coating thickness sensitivity to the mixing and non-mixing impinging jet cases of the present work has been elucidated. It is shown that a mixed vortices jet is most likely to cause surface ripples in the coating.

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  • Microstructure and Mechanical Properties of a Hot-rolled High Manganese TWIP Steel Containing 0.3%V

    Xinjun Sun , Xiaojiang Wang

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    DOI:10.2355/isijinternational.ISIJINT-2019-578

    Abstract

    In this paper, the microstructure, precipitates and mechanical properties of a 0.3%V-alloying high Mn austenitic TWIP steel after hot rolling and aging treatment were investigated, aimed to improve the yield strength of high Mn austenitic steel. Experimental results showed that an elongated and unrecrystallized grain structure could be obtained at a finish rolling temperature of 850°C or below in 0.3V steel. The amount of VC precipitates was very small and most vanadium remained in solution after hot rolling. Therefore, the solute drag effect of dissolved vanadium rather than the Zener pinning effect of VC precipitates was mainly responsible for the inhibition of recrystallization. The yield strength increase of 0.3V steel with deceasing finish rolling temperature was much more remarkable than that of V-free steel. Quantifying possible strengthening mechanisms revealed that most of the YS increase was due to the dislocation strengthening in 0.3V steel. The aging treatment for 30 min promoted the precipitation of VC, but the precipitation amount was still much less than the equilibrium precipitation amount. The comparative analysis on precipitation kinetics of VC in high Mn and low Mn steels indicated that the former had a more sluggish precipitation rate than the latter. This result was further analyzed in terms of the effect of Mn on the solubility product of VC in austenite.

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  • Simultaneous Broadening Analysis of Multiple Bragg Edges Observed by Wavelength-resolved Neutron Transmission Imaging of Deformed Low-carbon Ferritic Steel

    Hirotaka Sato , Kenji Iwase , Takashi Kamiyama , Yoshiaki Kiyanagi

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    DOI:10.2355/isijinternational.ISIJINT-2019-656

    Abstract

    With the goal of real-space mapping of dislocation information using a wavelength-resolved (spectroscopic) neutron transmission imaging method, broadenings of multiple Bragg-edges in neutron transmission spectrum were investigated in detail for the first time. Data of time-of-flight (TOF) neutron transmission imaging and diffraction experiments on a polycrystalline low-carbon ferritic steel sample while undergoing tensile testing were analysed. The Bragg-edge neutron transmission spectroscopy was combined with the classical Williamson-Hall method corrected by the crystal elastic anisotropy using the ratio of diffraction Young's modulus, namely, the corrected classical Williamson-Hall (ccWH) method. As a result, the broadening values evaluated from the ccWH analysis of Bragg-edge data were consistent with results of both our TOF neutron diffraction experiments and previous reports. In addition, it was deduced that the line-broadenings appearing in the plastic deformation condition during tensile testing in our experiment were mainly caused by micro-strain (dislocation density) effect and not by crystallite size effect. Finally, a Bragg-edge broadening mapping method, using a simultaneous multiple Bragg-edges profile analysis based on the ccWH method, could identify plastically deformed zones in the sample more clearly than a traditional single Bragg-edge broadening analysis method.

  • Time-resolved and In-situ Observation of δ–γ Transformation during Unidirectional Solidification in Fe–C Alloys

    Tomohiro Nishimura , Kohei Morishita , Masato Yoshiya , Tomoya Nagira , Hideyuki Yasuda

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    DOI:10.2355/isijinternational.ISIJINT-2019-636

    Abstract

    Time-resolved and in-situ observations using synchrotron radiation X-rays successfully proved that a massive-like transformation, in which the γ phase was produced through the solid–solid transformation and partitioning of substitute elements such as Mn and Si at the δ–γ interface was negligible, was selected in the unidirectional solidification of 0.3 mass% C steel at a pulling rate of 50 μm/s. The massive-like transformation produced fine γ grains near the front of the δ–γ interface. The coarse γ grains also grew behind the fine γ grains along the temperature gradient. Distance between the δ–γ front and the advancing front of coarse γ grains was as short as 200 μm. Namely, the fine γ grains disappeared within 10 s owing to growth of coarse γ grains. In addition, the observation of the δ–γ interface confirmed that a transition from the diffusion-controlled γ growth to the massive-like γ growth occurred at a growth velocity of 5 μm/s. Thus, the massive-like transformation is dominantly selected in the carbon steel during conventional solidification processes.

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  • Characterisation of Binary Phase Mixtures of Magnesium-Aluminate Spinel and Calcium-Aluminates Using Time-Gated Raman Spectroscopy

    Francis Gyakwaa , Matti Aula , Tuomas Alatarvas , Tero Vuolio , Qifeng Shu , Marko Huttula , Timo Fabritius

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    DOI:10.2355/isijinternational.ISIJINT-2019-576

    Abstract

    The modification of MgO·Al2O3 spinel inclusions into less detrimental mixture phases of CaO–MgO–Al2O3 plays an essential role in refining calcium-treated aluminium killed steels. This study uses Raman spectroscopy for the characterisation of binary phase samples that contain MgO·Al2O3 spinel and calcium aluminate (CaO)x–(Al2O3)y phases. Samples were synthesised from MgO·Al2O3 spinel (MA), Al2O3 and calcium aluminate phases to achieve binary samples of CA–MA, C3A–MA, C12A7–MA and Al2O3–MA with varying phase fractions. The study also examined the possibility of a slight variation for non-stoichiometric spinel samples below the 1600°C region in an MgO–Al2O3 binary system. The relative intensities of the Raman band were used for the quantification of the phase fractions. For a quantitative prediction, linear regression calibration models were identified for each of the studied systems. This work demonstrates the use of Raman spectroscopy for the characterisation of calcium aluminate phases of CA, C3A, C12A7 and magnesium aluminate spinel phases along with Al2O3 and its potential application in inclusion characterisation.

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  • Feasibility Investigation for Online Elemental Monitoring of Iron and Steel Manufacturing Processes using Laser-Induced Breakdown Spectroscopy

    Zhenzhen Wang , Yoshihiro Deguchi , Fangjung Shiou , Seiya Tanaka , Minchao Cui , Kai Rong , Junjie Yan

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    DOI:10.2355/isijinternational.ISIJINT-2019-317

    Abstract

    The metallurgical industries are very important for social development. In order to improve the metallurgical techniques and quality of products, the real-time analysis and monitoring of iron and steel manufacturing processes are very significant. Laser-induced breakdown spectroscopy (LIBS) has been studied and applied for the contents measurement of iron and steel. In this paper, the remote open-path LIBS measurement was studied under different sample temperature, lens to target distance (LTD), sample angle conditions to clarify its online measurement features. The 3D profile measurement system of parallel laser beam fringes projection was also developed to measure the sample profile at different sample temperature. The measurement results demonstrated the robustness of remote open-path LIBS system and 3D profile measurement system. However, the correction is necessary to enhance the detection ability of LIBS online measurement. In order to improve the precision and accuracy of real-time elemental measurement, an innovative co-axial laser beam measurement system combining LIBS and 3D profile techniques is proposed to automatically adjust the focus unit and measure the sample components. The further study of this promising method will be developed for online application of iron and steel manufacturing processes.

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  • Determination of Size Distribution of Nanoparticles Using Asymmetric Flow Field-flow Fractionation (AF4)

    Daisuke Itabashi , Reiko Murao , Shunsuke Taniguchi , Kazumi Mizukami , Hideaki Takagi , Masao Kimura

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    DOI:10.2355/isijinternational.ISIJINT-2019-387

    Abstract

    To investigate the performance of the size measurement by asymmetric flow field-flow fractionation (AF4), the measurement results of gold nanoparticles were compared among AF4, transmission electron microscopy (TEM), and small-angle X-ray scattering (SAXS) in terms of the average size and full width at half maximum (FWHM) of the size distribution. Although the average size was almost the same for the three methods, the FWHM measured using AF4 was larger than those measured using TEM and SAXS. This is attributed to the diffusion of the gold nanoparticles inside the AF4 instruments. The broadening coefficient of AF4 analysis was determined as 2.08 by the average of FWHM ratio of AF4 to TEM measured using the several sphere-like gold nanoparticles. In addition, the effect of particle shape on the above broadening coefficient was investigated using the sphere-like and plate-like silver nanoparticles. The broadening coefficient for plate-like particles apparently became smaller than that for sphere-like particles, possibly because the Brownian motion of plate-like particles was suppressed.Furthermore, the AF4 analysis with the FWHM correction method using the broadening coefficient was applied to niobium carbide (NbC) precipitates in steels. The average size measured by AF4 was mostly consistent with the results obtained in regions observed by TEM. Moreover, an increase in the number density of nanometer-sized NbC by heat treatment was successfully detected. The effect of particle shape on FWHM should be further investigated and improved; however, AF4 with the broadening coefficient can semi-quantitatively analyze the size distribution of nanoprecipitates in steels.

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  • Numerical Analysis of Effects of Different Blast Parameters on the Gas and Burden Distribution Characteristics Inside Blast Furnace

    Mingyin Kou , Heng Zhou , Zhibin Hong , Shun Yao , Shengli Wu , Haifa Xu , Jian Xu

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    DOI:10.2355/isijinternational.ISIJINT-2019-389

    Abstract

    Blast parameters are easy to be changed and are often applied to control the gas distribution in blast furnace. However, the effects of blast parameters on the gas and solid distribution characteristics were seldom investigated. Therefore, a 3D model considering gas and solid fluid phases is developed and used to analyze effects of blast parameters on the gas and solid distributions in the blast furnace B of Baiyi Steel. The results show that the gas temperature increases a little in the lower part while decreases in the middle and top parts of blast furnace when the oxygen enrichment ratio and blast temperature increase. The CO utilization ratio increases with the increase of oxygen enrichment ratio, humidified blast amount and blast temperature, and it increases most for the case of blast temperature. The metallization ratio at the bottom of the blast furnace increases with the increase of oxygen enrichment ratio and humidified blast amount while it decreases with the increase of gas temperature.

  • Utilization Rate of Magnesium in Hot Metal Desulfurization by Magnesium Vapor Injection

    Jian-ming Su , Zhi-he Dou , Ting-an Zhang , Yan Liu

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    DOI:10.2355/isijinternational.ISIJINT-2019-471

    Abstract

    To solve the technical problems such as serious splashing and low utilization rate of the desulfurizer in the traditional hot metal desulfurization by granular magnesium injection, a new idea of hot metal desulfurization with continuously controllable bottom blowing magnesium vapor is presented in this paper. An estimation model of the utilization rate of magnesium vapor was established based on the double-film theory, which shows that the utilization rate of magnesium vapor decreases with the increase of the flow rate of the carrier gas, and increases significantly with the decrease of the bubble radius of the magnesium vapor. The theoretical calculation results show that when the desulfurization temperature reaches 1573 K and the bubble radius of the magnesium vapor is refined to 0.175 mm, the residence time of magnesium vapor in the molten iron is equal to the reaction time, and the theoretical utilization rate of magnesium vapor can reach 100%. The model was validated by high temperature experiments using bottom blowing method. The experimental results indicate that the utilization rate of magnesium vapor in the desulfurization process is inversely proportional to the desulfurization temperature, the flow rate of the carrier gas and the mass of magnesium injection. Under the condition of 1573 K, the mass of hot metal 4.5 kg, the flow rate of 3 L/min and the injection mass of magnesium 1.55 g, the utilization rate of magnesium vapor can reach 83%. The calculated results of the model are well matched with the experimental data.

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  • Development of In-situ Orientation Mapping and Microstructure Observation System for Ferrite/Austenite and Martensitic Transformations in Steel

    Akira Taniyama , Takafumi Amino , Kengo Hata , Junpei Miki

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    DOI:10.2355/isijinternational.ISIJINT-2019-534

    Abstract

    The unique in-situ SEM/EBSD observation system, which is available to carry out orientation mapping and microstructure observation at high temperature, was developed to observe ferrite/austenite and martensitic transformation of carbon steel directly. The system has the heating capacity over 1000°C and rapid cooling ability of the cooling rate faster than 100°C/s. The SIM imaging shows very good performance to observe quick change in crystalline grain's shape, and microstructural evolution of secondary recrystallization grains was successfully observed. Furthermore, the in-situ observation system was applied to observe martensitic transformation of plain carbon steel and nickel contained carbon steel. Crystalline grain shape and its orientation before and after martensitic transformation of the steel are observed at the same sample position. And direct comparison of the microstructures between austenite and martensite is successfully realized.

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  • Scheduling in Continuous Steelmaking Casting: A Systematic Review

    David García-Menéndez , Henar Morán-Palacios , Francisco Ortega-Fernández , Marina Díaz-Piloñeta

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    DOI:10.2355/isijinternational.ISIJINT-2019-574

    Abstract

    The converter furnace and the continuous casting are the most important stages in steel production. Modern integrated processes directly connect the converter furnaces and the continuous casting machines with a flow of molten metal, and the steel is manufactured synchronously between the various machines. Starting from the traditional handmade programs for the management of these processes, during the last two decades there has been a notable increase in studies and publications in this field, trying to formulate scheduling in a rational and automatic way. The process has been approached for years through the development of both physical and operational research models, many of them theoretically. The main purpose of this study is to present a critical and in-depth evaluation of the previous studies, so that the state of the art of scheduling in steelworks can be evaluated. An approach based on a Systematic Literature Review (SLR) has been used, trying to search, evaluate, synthesize and analyze all the relevant studies for this specific field. As a result, the conclusions of the various analyses are presented and a study route is proposed for the design of the optimal planning methodology in the steelworks.

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  • Study on the Reaction between CO2–O2 Mixture Gas and Fe–C Melts by Isotope Tracing Method

    Yuewen Fan , Xiaojun Hu , Rong Zhu , Kuochih Chou

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    DOI:10.2355/isijinternational.ISIJINT-2019-589

    Abstract

    In order to clarify the role of O2 and CO2 which are applied to steelmaking, the isotope tracing method has been used to study the decarburization reactions between CO2–O2 mixed gas and Fe–C melts containing different carbon contents at 1873 K. When the mixture of two isotope gases of 18O2 and 13CO2 reacts with melts, the isotopic composition of the reacted gas is monitored online by a mass spectrometer. According to the change of isotopic gas composition, the ratio of various reactions and the decarburization rate can be calculated, and the effects of gas flowrate and carbon content on the decarburization reaction can be discussed. The results showed that the utilization of CO2 was more than 97%, and approximately 52% of oxygen formed to CO, 17% to CO2, and 31% for post combustion under the conditions of 30 ml/min of flowrate, 1 cm of the gas injection height and the 4.00 to 1.00 wt% of original carbon content. And with the increase of the flowrate from 30 ml/min to 40 ml/min, the amount of CO2 generated by O2 increased, while the amount of CO decreased. In particular, the post combustion ratio improved significantly from 47% to 77%.

  • Exploring the Behavior of a Coherent Flow Field Produced by a Shrouding Laval Nozzle Structure

    Fuhai Liu , Dongbai Sun , Rong Zhu , Shaoyan Hu

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    DOI:10.2355/isijinternational.ISIJINT-2019-182

    Abstract

    For achieving a better stirring effect, the coherent jet technology has been widely adopted in the metallurgy field; a key feature of this technology is the use of a combustion flame to protect the main oxygen jet. In this paper, a shrouding nozzle with a Laval nozzle structure using preheating technology is introduced. The effect of the shrouding gas flow rate on the behavior of the main oxygen jet is investigated at room and high ambient temperatures. A computational fluid dynamics model has been built to investigate the flow field of the coherent jet in simulation studies. In addition, an experimental study has been carried out to verify the results of the numerical simulation. Based on the results, the new method improves the shrouding gas velocity and forms a low-density zone, which makes its velocity potential core length 178% and 174% longer than that generated by the traditional method at room and high ambient temperature, respectively. However, the shrouding jet forms a shock wave at the exit of the Laval nozzle, which results in removing kinetic energy from the main oxygen jet. As a result, the axial velocity of the coherent jet is smaller than that of the conventional jet, and the velocity variation increases as the flow rate increases.

  • Review on the High-Temperature Thermophysical Properties of Continuous Casting Mold Fluxes for Highly Alloyed Steels

    Zhanjun Wang , Il Sohn

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    DOI:10.2355/isijinternational.ISIJINT-2019-522

    Abstract

    Several recently developed highly alloyed steel grades have shown unsurpassed performance in terms of physical, chemical, and electromagnetic properties. However, broader commercialization of these steels has been hampered by limitations in mold flux performance. Newly developed steels containing considerable amounts of dissolved Al, Mn, and Ti actively react with typical CaO-SiO2-based mold fluxes, which severely changes the composition and subsequently the thermophysical properties of the mold flux that determine the external and internal quality of the as-cast steels. These dynamic changes result in nonuniform heat transfer, lubrication issues, surface defects, and caster breakouts. This work critically assesses the current status of the high-temperature thermophysical properties of CaO-SiO2-based and CaO-Al2O3-based mold fluxes intended for use in casting highly alloyed steel grades. Thermophysical properties, including viscosity, crystallization, thermal conductivity, and heat flux, have been evaluated. The effect of compositional variables including CaO/SiO2, CaO/Al2O3, and Al2O3/SiO2 mass ratios and the additions of CaF2, B2O3, Li2O, K2O, Na2O, TiO2, and BaO on these high-temperature thermophysical properties are discussed.

  • High Magnetic Field Effects on the Solid-liquid Reaction of Fe–Ga System

    Yoshifuru Mitsui , Toshiaki Hagio , Kohki Takahashi , Keiichi Koyama

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    DOI:10.2355/isijinternational.ISIJINT-2019-470

    Abstract

    The effect of magnetic fields on solid-liquid reactions in the Fe–Ga binary system was investigated using Fe/Ga diffusion couples. The reaction and phase growth proceeded by diffusion-controlled process for both 0 and 10 T. It is found that the growth of the intermetallic phases was suppressed by magnetic fields of 10 T regardless of whether α-Fe was in a ferromagnetic or paramagnetic state. The pre-exponential factors in the parabolic coefficient of the Fe3Ga + eutectic region at 0 and 10 T were 2.50 × 104 m2/s and 1.32 × 103 m2/s, respectively. Meanwhile, activation energies at 0 and 10 T were 336 kJ/mol and 318 kJ/mol, respectively, which indicated the ineffectiveness of magnetic fields. That is, reduction of pre-exponential factor of the parabolic coefficient leads the magnetic-field-induced suppression of the reaction in Fe/Ga.

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  • Effect of Cu Alloying on Strain Capacity of Cu-bearing Pipeline Steels

    Xianbo Shi , Wei Yan , Zhenguo Yang , Yi Ren , Yiyin Shan , Ke Yang

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    DOI:10.2355/isijinternational.ISIJINT-2019-499

    Abstract

    The present study aims to elucidate the effect of Cu alloying on the strain capacity of Cu-bearing pipeline steels. The main emphasis was placed on understanding the effects of Cu content (1.0Cu, 1.5Cu and 2.0Cu) and the existence form of Cu (as-rolled and as-aged steels) on the yield stress/tensile stress ratio (yield ratio), uniform elongation and strain hardening exponent. Experimental results show that the engineering stress-strain curves present continuous yielding behavior for the as-rolled steels but discontinuous yielding for the as-aged steels. For both as-rolled and as-aged steels, increasing Cu content increases the yield ratio with an accompanying decrease of uniform elongation. It was found that the as-rolled 1.0Cu steel has one strain hardening exponent (n value), low yield ratio (0.68), high n value (0.18) and high uniform elongation (17.7%), showing an excellent deformation ability. There are two n values for the other steels (1.0Cu as-aged, 1.5Cu and 2.0Cu as-rolled and as-aged), and their n values increase at low stress but decrease at high stress with increase of Cu content. In contrast to the as-aged steels, the as-rolled steels show better strain capacity.

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  • Prediction of Fatigue Life of Steels in Consideration of Defect-induced Crack Initiation and Propagation

    Ryota Sakaguchi , Takayuki Shiraiwa , Pornthep Chivavibul , Manabu Enoki

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    DOI:10.2355/isijinternational.ISIJINT-2019-573

    Abstract

    In the present study, the prediction of fatigue life by representing characteristic variations of defects with probability distribution functions was conducted by dividing the fatigue process into the crack initiation and crack propagation. Voids, hard inclusions (Al2O3) and soft inclusions (MnS) in steels were supposed as defects and two prediction models were proposed. Only the life of crack propagation was predicted by Paris law in initial defects model (model A) while the life of crack initiation as well as propagation was predicted by Tanaka-Mura model in crack initiation model (model B). The stress intensity factor using [ This part of text is omitted ] (projected square root area of defects) proposed by Murakami et al. was applied to Paris law in both models. The stress concentration due to defects and Taylor factor were applied to Tanaka-Mura model in the model B. These models were applied to four types of steels and the fatigue life was compared with the experimental results. In case of ductile cast iron including voids, the fatigue life predicted by both models was within the range of the experimental scattering. Although the fatigue life predicted by the model A was not consistent with the experimental results under high and low stress levels in case of Cr–Mo steel including MnS inclusions, the fatigue life predicted by the model B mostly showed a good agreement with experimental results. Therefore, it was demonstrated that the fatigue life prediction considering crack initiation showed higher precision than the prediction without crack initiation.

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  • Effect of Ce–Mg–Fe Alloy Adding Timing on Formation and Evolution of Inclusions in SCr420H Gear Steel

    Meng SUN , Zhouhua JIANG , Yang LI , Changyong CHEN , Kui CHEN , Shen SUN , Qi WANG

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    DOI:10.2355/isijinternational.ISIJINT-2019-606

    Abstract

    In the present study, the effect of different adding time of Ce–Mg–Fe alloy during the refining process was investigated by laboratory experiments and equilibrium thermodynamic calculation. In experiments, samples from different stages were analyzed by SEM-EDS and EPMA for revealing the evolution mechanism of inclusions. Combined with thermodynamic calculation, results indicated that different adding time can affect the yield of Ce and Mg in steel directly, and the difference of types of inclusions in as-cast samples was caused. CaO-containing inclusions as a main type of inclusions in the refining process can be modified by Ce after adding Ce–Mg–Fe alloy. A high Ce content can promote the formation of Ce–S and Ce–O–S in steel and suppress the precipitation of MnS. In consideration of microalloying effect, Ce–Mg–Fe alloy should be added at a later stage of steelmaking process for ensuring a certain content of Ce and Mg.

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  • Strain Rate Sensitivity of Flow Stress Measured by Micropillar Compression Test for Single Crystals of 18Cr Ferritic Stainless Steel

    Tianqi Zhu , Hongmei Li , Naoki Takata , Makoto Kobashi , Masataka Yoshino

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    DOI:10.2355/isijinternational.ISIJINT-2019-448

    Abstract

    We have fabricated cylindrical single-crystal micropillars with different diameter (d) ranges of 2–3 µm and 5–6 µm on a specific grain in the 18Cr ferritic stainless steel with a ferrite single-phase microstructure. The initial strain rate at the onset of plastic deformation was controlled by variable loading rate in the used nanoindenter. The strain rate sensitivity of the stress required for the slip initiation were examined using the fabricated micropillars. The present compression tests addressed the shear stress on an activated single slip system of micron-scale single-crystals. Smaller-sized micropillars (d = 2–3 µm) often exhibit intermittent strain bursts. The stress for slip initiation (after an elastic loading) changes depending on the initial strain rate, resulting in a high strain rate sensitivity (m) of 0.12. Larger-sized micropillars (d = 5–6 µm) show a continuous yielding. A slight change in their yield stress depending on the initial strain rate provides a relatively low m of 0.04. It is similar to one of the millimeter-sized specimens measured by conventional tensile tests. These results provide new insights to optimize the specimen size for the micropillar compression test applied for the 18Cr ferritic stainless steels.

  • Thermodynamics of Nitrogen Solubility and Nitride Formation in Fe–Cr–Ti–Al–Si–N Alloy Melts

    Min-Kyu Paek , Hae-Sol Son , Jung-Mock Jang , Jong-Jin Pak

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    DOI:10.2355/isijinternational.ISIJINT-2019-490

    Abstract

    Thermodynamic behavior of nitrogen in Fe–Cr–Ti–Al–Si–N alloy melts was investigated by measuring the nitrogen solubility and solubility product of TiN and AlN by the metal/gas and metal/nitride/gas equilibration techniques at 1823–1873 K, respectively. The nitrogen solubility data measured in Fe–Cr–Ti, Fe–Cr–Si, Fe–Ti–Al and Fe–Cr–Al alloy melts was thermodynamically analyzed to determine the second-order cross-product parameters of Cr–Ti, Cr–Si, Al–Ti and Cr–Al on nitrogen in liquid iron using Wagner's formalism. By considering the cross-product effect on nitrogen determined in the present study, the effects of the alloying elements on the solubility product of TiN and AlN in the multicomponent Fe–Cr–Ti, Fe–Ti–Al and Fe–Cr–Al alloy melts were successfully reproduced over the wide temperature range.

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  • Effect of the Silicate Structure on Calcium Elution Behaviors of Calcium-silicate Based Mineral Phases in Aqueous Solution

    Fang Ruan , Sakiko Kawanishi , Sohei Sukenaga , Hiroyuki Shibata

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    DOI:10.2355/isijinternational.ISIJINT-2019-263

    Abstract

    In this study, the effect of the silicate structure of calcium-silicate based mineral phases on their Ca elution behaviors into water was investigated. The Ca elution behaviors of Ca-silicate based mineral phases with different skeleton silicate structures in ion-exchanged water were analyzed using the powder leaching test. The elution amount of Ca was in the order alite (Ca3SiO5) > belite (γ-Ca2SiO4) > rankinite (Ca3Si2O7) > pseudowollastonite (α-CaSiO3) > wollastonite (β-CaSiO3) ≈ cuspidine (Ca4Si2O7F2) > diopside (CaMgSi2O6) > hedenbergite (CaFeSi2O6) > tremolite (Ca2Mg5Si8O22(OH)2) > anorthite (CaAl2Si2O8). This suggests that the elution amount of Ca decreased with the skeleton silicate structure became more complicated.

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  • State of the Art in the Control of Inclusions in Spring Steel for Automobile - a Review

    Changyong Chen , Zhouhua Jiang , Yang Li , Meng Sun , Qi Wang , Kui Chen , Huabing Li

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    DOI:10.2355/isijinternational.ISIJINT-2019-513

    Abstract

    Spring steel wires are extensively utilized in automotive engines valve and suspension applications. Owing to spring often work under high-frequency dynamic loads and periodic alternation stress, non-deformable inclusions often act as fatigue fracture origin of spring steel. The control of inclusions in spring steel for automobile are extensively reviewed. On the one hand, the new perspective on the problems left over the past decades, include the new viewpoint on whether FeO is an inherent constituent of inclusions, the new understanding of the origin of CaO-based inclusions, the new perspective of whether the VD treatment progress should be removed but RH retain, have been discussed. On the other hand, the new approaches, via, calcium treatment, alkali oxide treatment, rare earth treatment, new refractory application, have also been summarized. Finally, the unsolved problems, the source of CaO-based inclusions, the mechanism of alkali metals modified inclusions, the based thermodynamic data for reactions between rare earth yttrium (Y) and non-metallic inclusions, the operability of CaO-containing refractory in industry, that should be explored further are also been discussed.

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  • Numerical Simulation on Influence of Coke Oven Gas Injection on Iron Ore Sintering

    Wenjie Ni , Haifeng Li , Lei Shao , Zongshu Zou

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    DOI:10.2355/isijinternational.ISIJINT-2019-486

    Abstract

    Coke oven gas (COG) injection is believed to improve the quality and yield of sinter in iron ore sintering process. A mathematical model is developed to simulate the sintering process with COG injection, particularly focusing on predicting the quality and yield of sinter. The model is validated by comparing the model predictions with sintering pot test data. Numerical simulations are carried out to investigate the influences of location, quantity and covering area of COG injection on the sintering process. The results show that the location of COG injection has a little influence on its effectiveness on sintering, with that the sinter yield decreases slightly with the delay of COG injection while the mean melt quantity index (MQI) and cooling rate (CR) hardly change. The quantity of COG injection has a great influence on sintering. With a typical COG injection area of 40% and injection location of 60 s after ignition, the sinter yield increases by 33.3%, the mean MQI increases by 9.5% and the mean CR decreases by 37.6% when COG injection is 0.5%. The injection area of COG has some interesting influence on its effectiveness on sintering. Under the condition of 0.5% COG injection from 60 s after ignition, with the increase of injection area, the sinter yield increases prominently first and then decrease significantly, attaining its maximum at 40% of injection area. At the same time, the mean MQI and CR attain their extrema also at 40% of injection area.

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  • 3D Crystal Orientation Mapping of Recrystallization in Severely Cold-rolled Pure Iron Using Laboratory Diffraction Contrast Tomography

    Jun Sun , Christian Holzner , Hrishikesh Bale , Miho Tomita , Nicolas Gueninchault , Florian Bachmann , Erik Lauridsen , Toru Inaguma , Masao Kimura

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    DOI:10.2355/isijinternational.ISIJINT-2019-405

    Abstract

    The mechanism of recrystallization texture development of cold-rolled metal and steel largely depends on the material chemical composition, cold-rolling reduction, and annealing treatment conditions. To clarify the mechanism, it is important to identify the locations where recrystallization starts and progresses within cold-rolled materials.Using laboratory diffraction contrast tomography (LabDCT), three-dimensional (3D) crystal orientation mapping corresponding to different stages of recrystallization has been successfully performed for pure iron sheets that were severely cold-rolled and heated at different temperatures.In cold-rolled iron with 99.2% reduction, the deformation texture was a strong α-fiber (RD//<110>). During annealing in the temperature range of 773–973 K, recrystallized grains were formed with textural components of {100}, {211}, {111} and {411}, and the α-fiber changed to the {100}<012> component. Recrystallized grains were generated at rather random locations within the sample. The size of recrystallized grains in the center region was 20–30% larger than that in the surface region. These results suggest that the nucleation is driven by the large strain caused by severe rolling. The number of recrystallization sites was larger in the surface region than in the center region and the competition of selective growth among recrystallized grains was more severe in the surface region, resulting in a smaller grain size.The volume data of the 3D crystal orientation mapping obtained by LabDCT provided crucial information for understanding the recrystallization mechanism including the nucleation and/or selective growth.

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  • Fluid Dynamics Analysis of O2–CaO Jet with a Shrouding Flame for EAF Steelmaking

    Guangsheng Wei , Yuhua Peng , Rong Zhu , Lingzhi Yang , Xuetao Wu

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    DOI:10.2355/isijinternational.ISIJINT-2019-207

    Abstract

    Compared with the traditional addition methods of lumpy lime into the electric arc furnace (EAF) for slag making, the technology of O2–CaO jet can deliver lime powder directly into the EAF molten bath with high speed carrier gas, which demonstrates much advantages in quick melting and effective phosphorus removal. Recently, the shrouding combustion flame was proposed and applied to strengthen the CaO import capability of the O2–CaO jet. In this study, combining the discrete particle model (DPM) and the Eddy Dissipation Concept (EDC) model with the detailed chemical kinetic mechanisms (GRI-Mech 3.0), computational fluid dynamics (CFD) models of the O2–CaO jet with shrouding flame, with shrouding O2 and without shrouding gas were developed. The numerical results of CFD models were firstly validated by the experimental data. The interaction between the particles and the gas jet of the O2–CaO jet was analyzed and how the shrouding combustion flame affected the fluid flow characteristics of the O2–CaO jet were clarified. The shrouding high-temperature combustion flame could delay the attenuation of the axial velocity of the O2–CaO jet, heat the CaO particles effectively and make the CaO particles cluster together in a much longer distance, which is helpful to strengthen the jet impact, accelerate the meltdown of CaO particles and improve the utilization efficiency of CaO.

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  • Behavior of V-Ti Elements in Warm-Rolled Transformation-Induced Plasticity Steel with Medium Manganese Content

    Haicun Yu , Zhaozhen Cai , Kwangchol Ryom , Guiqin Fu , Miaoyong Zhu

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    DOI:10.2355/isijinternational.ISIJINT-2019-329

    Abstract

    To reveal the law governing V-Ti precipitation behavior in warm-rolled transformation-induced plasticity (TRIP) steel, two steel samples including 0.072V-0.051Ti steel (Bear-V-Ti steel) and 0.001V-0.001Ti steel (Free-V-Ti steel) are designed. Based on a comparative analysis, the former has an excellent combination of mechanical properties including a total elongation (TE) of 37%, ultimate tensile strength (UTS) of 935 MPa, and UTS×TE of 34 GPa·% after annealing at a temperature of 650°C. The superior mechanical properties are attributable to particles that precipitate in a composite form of (V-Ti)C/N at 650°C. These particles can refine the grains and improve the tensile strength of Bear-V-Ti steel. However, it should be noted that the two roles of precipitates in steel are size dependent. For sizes between 10–20 nm, the role mainly entails pinning the dislocation. This accounts for the precipitation strength. As the size increases to 20–60 nm, the role mainly involves pinning of the grain boundary, which leads to fine crystal reinforcement. These results provide useful data for the production of medium manganese steel using the warm-rolled process.

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  • Effect of High Nitrogen Addition on Microstructure and Mechanical Properties of As-cast M42 High Speed Steel

    Weichao Jiao , Huabing Li , Hao Feng , Zhouhua Jiang , Jing Dai , Hongchun Zhu , Shucai Zhang , Mansheng Chu , Wei Wu

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    DOI:10.2355/isijinternational.ISIJINT-2019-417

    Abstract

    This study systematically investigated the influence of high nitrogen (N) addition (0.205 wt.%) on microstructure and mechanical properties of as-cast M42 high speed steel. The results demonstrate that the conventional and high-nitrogen M42 cast ingots are mainly composed of martensite, retained austenite and various precipitates (M2C, M6C as well as MC in M42 cast ingot or M(C, N) in M42N cast ingot). The addition of N could increase the retained austenite content, trigger the transformation of MC to M(C, N), favor the formation of M2C at the expense of M6C, and improve the distribution uniformity of M6C at the macroscopic scale. Moreover, the addition of N could lead to the reduction of the secondary dendrite arm spacing as well as the decrease of the thickness and area fraction of eutectic carbides, and improve the distribution uniformity of eutectic carbides at the microscopic scale. The M(C, N) particles form directly from the liquid phase prior to the formation of primary austenite, which could act as the heterogeneous nuclei of primary austenite and thus promote the refinement of the as-cast microstructure. The addition of N slightly decreases the macro-hardness and ultimate compression strength of the cast ingot but increases its ductility, which could be ascribed to the increase of retained austenite content and the reduction in the amount of eutectic carbides. Therefore, high N addition can significantly improve the as-cast microstructure of M42 high speed steel, which is promising for the further enhancement of the mechanical property and service life of the final product.

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  • Multiphase Flow Behavior in a Single-Strand Continuous Casting Tundish during Ladle Change

    Haitao Ling , Rui Xu , Haijun Wang , Lizhong Chang , Shengtao Qiu

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    DOI:10.2355/isijinternational.ISIJINT-2019-506

    Abstract

    The three-phase flow behavior in a single-strand continuous casting tundish during ladle change was investigated using physical modeling. These phenomena observed from physical modeling were explained by employing the multiphase model volume of fluid, which can track the interface behavior between the liquid steel, slag, and air during this operation. The effects of the refilling time and lowest operating level on the slag entrainment and the steel exposure during ladle change were analyzed and discussed, respectively. Increasing the refilling time significantly decreased the amount of entrained oil and the exposed area in the impact zone during ladle change. However, the increase in the lowest level had little influence on reducing the slag entrainment. To reduce the slag entrainment and the steel exposure during ladle change, the refilling time in the prototype should be larger than 3 minutes. Furthermore, the use of the turbulence inhibitor has also been evaluated. By diminishing the turbulence intensity in the impact zone and the velocity magnitude at the steel-slag interface, the turbulence inhibitor reduced considerably the amount of entrained slag and the steel reoxidation. The results indicated that the emulsification phenomenon during ladle change could be eliminated using TI-2, and the maximum exposed area fractions in the impact zone for different refilling times and lowest levels were less than 13% and 23%, respectively. Therefore, the TI-2 was recommended to improve the steel cleanliness during ladle change.

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  • Agglomeration and Removal of Alumina Inclusions in Molten Steel with Controlled Concentrations of Interfacial Active Elements

    Katsuhiro Sasai

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    DOI:10.2355/isijinternational.ISIJINT-2019-107

    Abstract

    In this study, Al deoxidation experiments have been performed in a mildly stirred steel bath with controlled O and S concentrations, to investigate the effects of interfacial active elements on the agglomeration and removal of Al2O3 inclusions in molten steel. The decrease rate constants of total Al2O3 inclusions, Al2O3 cluster inclusions, and Al2O3 single inclusions as well as the maximum average diameter of Al2O3 cluster inclusions decrease with increasing O and S concentrations in molten steel. However, the effect of O is much greater than that of S. These experimental results have been analyzed based on the kinetics of Al2O3 inclusion removal and the interfacial chemical interaction between Al2O3 inclusions in molten steel. The following findings have been obtained on the agglomeration and removal mechanisms of Al2O3 inclusions in molten steel. The Al2O3 inclusions in molten steel are removed by a mechanism whereby large Al2O3 cluster inclusions, formed by Al deoxidation, float and separate while repeatedly agglomerating and coalescing with fine Al2O3 single inclusions suspended in molten steel. The agglomeration of Al2O3 inclusions during floating and separation can also be explained by a mechanism whereby the agglomeration force due to the cavity bridge force is exerted between the Al2O3 inclusions and the Al2O3 inclusions come in complete contact when the Al2O3 inclusions with thermodynamically agglomerating tendency are approaching each other. The effects of O and S interfacial active elements are considered in both these mechanisms.

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  • A Visual PCI Blockage Detection in Blast Furnace Raceway

    Yutao Wang , Pu Huang , Gang Yang

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    DOI:10.2355/isijinternational.ISIJINT-2019-367

    Abstract

    The pulverized coal injection (PCI) blockage detection is critical to the stable operation of blast furnace. In recent years, tuyere cameras have been widely applied, which provides a channel to detect the PCI blockage. However, the visual impression of images strongly varies between different raceways, it requires detection method should be robust and convenient to fine-tune for different blast furnace images. This paper presents an intelligent image-based method to detect the PCI blockage. An adaptive image preprocessing technique combining de-noising algorithm and image enhancement algorithm is applied to remove image noise and improve image quality, laying the foundation for subsequent work. The fitting ellipse based on Hough transform is used to locate the tuyere region, which can separate the tuyere region from the background. The adaptive threshold segmentation algorithm combining Otsu and Bernsen is used to obtain binarized image. However, it is difficult to obtain the pulverized coal cloud only by binarization due to the similarity between pulverized coal cloud and lance in gray-level. The multi-scale fully convolutional network (FCN) based on deep learning is investigated to detect the lance region, and pulverized coal cloud can be extracted by removing lance in binarized image. The flow rate of PCI can be characterized by the extracted area information to some extent, which can be used to detect PCI blockage. Extensive videos captured from real production lines are used to evaluate the detection method. The experiment results show that the method can accurately detect the PCI blockage.

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  • Recycling Nickel Slag by Aluminum Dross: Iron-extraction and Secondary Slag Stabilization

    Guangzong Zhang , Nan Wang , Min Chen , Yanqing Cheng

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    DOI:10.2355/isijinternational.ISIJINT-2019-173

    Abstract

    Nickel slag is a metallurgical solid waste from nickel refineries, which can be recycled as one of excellent secondary sources due to valuable iron contents. In this work, the approach of recycling nickel slag by aluminum dross was proposed, and the processes of network modification of slags and reduction were successively investigated at 1773 K. Upon the thermodynamic calculations, CaO was chosen as the modifier in order to obtain a higher activity of ‘FeO', and basicity of the modified slag was determined as 1.0. Element mapping analysis of the modified slag showed that ‘FeO' had been separated from the structure of nickel slag. After aluminothermic reduction for 120 min, the recovery degree of iron and copper was 94.35% and 97.89%, respectively. In addition, the secondary slag stabilization was discussed, and the utilization of the produced Fe–Cu alloy and the secondary slag was analyzed.

  • Optimization of Discharge Parameters for a Glow Discharge Emission Spectrograph with Two-dimensional Spatial Resolution

    Xinyue Zhang , Kazuaki Wagatsuma

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    DOI:10.2355/isijinternational.ISIJINT-2019-205

    Abstract

    This paper describes a specified measuring system for glow discharge emission spectrograph, which can provide a spatial/radial distribution of analyte atoms on the sample surface, while the conventional system provides only the information on the elemental distribution in depth direction. For this purpose, a spectrometer system consisting of an image spectrograph and an intensified charge coupled device (ICCD) detector was employed. The delay time and gate width of the ICCD detector was principally selected to improve the spatial resolution of the emitting zone. The objective of this paper was to determine an optimized set of the experimental parameter for better spatial resolution. The best spatial resolution was obtained when the gate width was 1 μs and the delay time was 60 μs. Better spatial resolution was obtained at narrower gate width, because the re-emission from the analyte atoms could be observed to a less extent when the observation was conducted more instantly just after start of the pulsed discharge.

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  • Melting Behaviour of Iron Ore Pellet Bed under Nut Coke Mixed Charge Conditions

    Dharm Jeet Gavel , Allert Adema , Jan van der Stel , Cees Kwakernaak , Jilt Sietsma , Rob Boom , Yongxiang Yang

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    DOI:10.2355/isijinternational.ISIJINT-2019-246

    Abstract

    The melting and dripping behaviour of an iron ore pellet bed mixed with nut coke are investigated through a series of quenching, melting and dripping experiments. In the melting bed of iron ore pellets, nut coke acts as a frame to maintain the passage for the gas flow. The iron carburisation level of the pellet shell is found to control the melting temperature of the pellet bed. Simultaneous and layer-wise melting is observed for the pellet bed with and without mixed nut coke, respectively.In the case of pellet bed mixed with nut coke, the liquid dripping starts at a lower temperature (1500°C) compared to the case when nut coke is absent (1518°C). Subsequently, a steady rate of liquid dripping is observed for the pellet bed mixed with nut coke. However, in the case of the pellet bed without nut coke, most of the liquid drips (~50 wt%) at high temperature (1550°C). The difference in carbon content of the quenched pellets and the dripped metal reveals that a substantial iron carburisation occurs when liquid iron flows over the regular coke particles.The nut coke is noticed to consumed preferentially in place of the regular coke. Additionally, the total coke consumption decreases with an increase in nut coke addition in the pellet bed. These results give support for more extensive use of nut coke as a replacement of the regular coke in the ironmaking blast furnace.

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    3. A Visual PCI Blockage Detection in Blast Furnace Raceway ISIJ International Advance Publication
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