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

ISIJ International Advance Publication

  • Inertial Force on Floating Inclusion Particles at the Interface of Liquid Steel and Inert Gas

    Zilong Qiu, Annelies Malfliet, Muxing Guo, Bart Blanpain

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    DOI:10.2355/isijinternational.ISIJINT-2020-704

    Abstract

    To predict the clustering of inclusions at the liquid steel and inert gas interface, it is essential to calculate the pairwise attractive (inertial) force on the inclusions correctly. In most of the studies, the inertial force is calculated from three successive inter-particle distances with a certain time interval, in which the inertial force is assumed to be identical at the first two distances. Considering the nature of the attractive force, a new iteration scheme is proposed where the inertial force is assumed to be non-identical from point to point. However, both the identical and non-identical force schemes tend to give an unreasonably oscillating force when the measured inter-particle distance is less accurate. Moreover, the curve fitting function is also considered in this study including the use of polynomial, exponential, sum of sines, rational, Gaussian functions and Fourier series. Among these functions, the 4th order polynomial and the 2nd order sine are the most robust functions in predicting the inertial force on particles, even when the measured distance is less accurate.

  • Influence of Non-metallic Inclusions in 316L Stainless Steels on Machining Using Different Cutting Speeds

    Hongying Du, Andrey Vladimirovich Karasev, Pär Göran Jönsson

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    DOI:10.2355/isijinternational.ISIJINT-2021-079

    Abstract

    This research focuses on providing a detailed characteristic of non-metallic inclusions (NMIs) in 316L stainless steels with and without Ca treatment after machining using different cutting speeds. The electrolytic extraction (EE) technique was used for three-dimensional determinations of the inclusion characteristics. Quantitative data from the fragile non-metallic inclusions (such as size, surface area, number) in chips obtained from different cutting speeds and materials were determined. The morphologies of NMIs in the chip samples were quite different compared to the original inclusions in the stainless steel samples before machining. It was proved that the deformation degree of soft inclusions such as MnS and CaO–SiO2–Al2O3–MgO–TiOx is dependent on the cutting speed as well as the temperatures and deformation degrees of the metal matrix during machining. The total surface areas of MnS inclusions increase from 2.8 to 3.8 times compared to the original total areas with an increased cutting speed. The total surface areas of soft oxide inclusions also increase from 1.1 to 3.5 times compared to the original total areas. In addition, the tool-chip contact lengths were also measured on the rake face of the tool, and the results were compared to the determined characteristics of the observed inclusions. It was found that the modification of NMIs by Ca treatment in 316L stainless steels is preferred for high cutting speeds.

  • Influence of Annealing on Delamination Toughening of Mo-Bearing Medium-Carbon Steel with Ultrafine Elongated Grain Structure Processed by Warm Tempforming

    Yuuji Kimura, Tadanobu Inoue

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    DOI:10.2355/isijinternational.ISIJINT-2021-068

    Abstract

    Ultrafine elongated grain (UFEG) structure with a strong <110>//rolling direction fiber texture was created for a 0.4%C-2%Si-1%Cr-1%Mo steel (mass%) through deformation of tempered martensite using multi-pass caliber rolling at 773 K with a rolling reduction of 78% (i.e. warm tempforming). Annealing of the warm tempformed steel at 843 K enhanced delamination toughening at lower temperatures without a significant loss of tensile strength at 1.8 GPa. It was suggested that delamination toughening was controlled through the precipitation of nanoscale Mo-rich precipitates in the UFEG structure.

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  • Characteristics of High Speed Steel/ductile Cast Iron Composite Roll Manufactured by Electroslag Remelting Cladding

    Yulong Cao, Yanwu Dong, Zhouhua Jiang, Guangqiang Li, Zhengrong Zhao

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    DOI:10.2355/isijinternational.ISIJINT-2020-594

    Abstract

    In the present study, high-speed steel (HSS)/ductile cast iron (DCI) composite roll was manufactured by the electroslag remelting cladding (ESRC) technology. The compositional variation, grain size, microstructure, hardness, and tensile strength of the HSS layer and the bimetallic interface were investigated systematically. The obtained results illustrated that the chemical composition of the cladding layer (HSS) changed dramatically due to the surface melting of the roll core (DCI) and the mechanical mixing of the bimetallic liquids. The different solidification rates and chemical compositions in different regions of the HSS layer led to great variations of the grain size, the carbide content, and the hardness. In addition, a bimetallic transition zone (about 9.47 mm) was generated between the HSS layer and the DCI core due to the elemental migration and diffusion between the bimetals. Carbides of different types, morphologies, sizes, and compositions had direct influences on interfacial properties.

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  • Numerical Simulation of Particle Mixing Behavior in High Speed Shear Mixer and Cylinder Mixer

    Yang You, Jiabao Guo, Xuewei Lv, Shanshan Wu, Yong Li, Kai Tang, Yaowei Yu

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    DOI:10.2355/isijinternational.ISIJINT-2020-768

    Abstract

    The mixing effect of powder materials is crucial in the iron ore granulation process, which determines the composition and particle size distribution, thereby affecting the quality of the sinter. To study the mixing effect of powder particles in a high speed shear mixer (HSSM) and cylinder mixer (CM), numerical simulation based on discrete element method was adopted in this work. For the CM, the particle movement consists of slipping and slumping. For the HSSM, the particle movement consists of rolling and cascading. The particle movement intensity coefficient of the HSSM is larger than that of CM, indicating that the movement of the particles in HSSM is more intensive. For HSSM case with four blades, the variation coefficient of homogeneity increases as rotational speed increases. The number of blades has little effect on the particle movement intensity coefficient and variation coefficient of homogeneity. In comparison to the CM, the variation coefficient of the HSSM reduce the most. It means that the mixing effect of HSSM is better than the CM. These findings are helpful for the improvement of the mixing and granulation efficiency in the iron ore sintering process.

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    3. Tracking Large-size Inclusions in Al Deoxidated Tinplate Steel in Industrial Practice ISIJ International Advance Publication

  • End-point Temperature Preset of Molten Steel in the Final Refining Unit Based on an Integration of Deep Neural Network and Multi-process Operation Simulation

    Jianping Yang, Jiangshan Zhang, Weida Guo, Shan Gao, Qing Liu

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    DOI:10.2355/isijinternational.ISIJINT-2020-540

    Abstract

    End-point temperature preset of molten steel in the final refining unit is as important as its prediction for casting temperature control. However, it has not been given sufficient concern yet, and the proposed preset models in the literature usually cannot be used as practical tools due to their inherent shortcomings, e.g., oversimplifications made to a real environment during modelling. In this study, a novel preset approach was developed by integrating deep neural network (DNN) and multi-process operation simulation (MOS). By using MOS, the accurate transfer times of heats between the final refining unit and continuous caster can be solved before their actual scheduling, which is very significant for availability of the preset model based on DNN in practice. The DNN preset model was trained and tested with varying the values of hyper-parameters based on vast data points collected from a real steelmaking plant. Furthermore, preset models based on extreme learning machine (ELM) and multivariate polynomial regression (MVPR) were also established for comparison. The testing results indicate the DNN preset model with 3 hidden layers which contain 8, 4 and 2 neurons in sequence shows an advantage over other alternatives because of its evident improvement in preset accuracy and robustness. Meanwhile, a fine classification of data points considering metallurgical expertise can improve the generalization performance of the DNN preset model. The integrated approach has been applying in the studied steelmaking plant, and the ratio of qualified heats increases by 9.5% than before using it.

  • Formation Mechanism of Large-size CaO–Al2O3–MgO–SiO2 Inclusions in High Carbon Chromium Bearing Steel

    Zhiqi Miao, Guoguang Cheng, Shijian Li, Wensheng Qiu, Lingyu Zeng, Hu Long

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    DOI:10.2355/isijinternational.ISIJINT-2020-729

    Abstract

    Industrial experiments and thermodynamic analyses were carried out to investigate the formation mechanism of large-size (>30 µm) CaO–Al2O3–MgO–SiO2 (CAMS) inclusions in high carbon chromium bearing steel. It was found that the large-size CAMS inclusions existed during the whole refining process, most of which compositions were located in the liquid region. The average content of SiO2 in CAMS inclusions decreased from 27.5 mass% at argon-blowing station to 3.0 mass% in the hot-rolled bars. The results calculated by Factsage 7.3 indicated that the CAMS inclusions were originated from slag entrapment. During BOF tapping, the low basicity slag with 60 mass% SiO2 was entrapped into steel and combined with the deoxidation product Al2O3, forming a large amount of liquid CAMS inclusions. During LF refining process, [Al], [Ca] and [Mg] in molten steel were affected by the activities of corresponding slag components. The reaction between these three elements and SiO2 in CAMS inclusions originating from slag lead to the decrease of SiO2 in the inclusions. Due to the low interfacial energy between liquid CAMS inclusions and steel, a few large-size inclusions may be inherited to hot-rolled bars. In light of this, several optimization steps were conducted during BOF tapping and argon-blowing station. After the optimization, large-size CAMS originated form BOF tapping were effectively removed.

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  • Viscosity Evaluation of Simulated Foaming Slag via Interfacial Reaction at Room Temperature

    Shota Hatano, Shogo Hayashi, Noritaka Saito, Kunihiko Nakashima

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    DOI:10.2355/isijinternational.ISIJINT-2020-640

    Abstract

    CaO-based slag used in hot metal pretreatment and converters in steelmaking processes typically contains dispersed gas phases. This is called foaming slag, which is known to degrade the quality of slag. The rheological behavior of this slag is dependent on the dispersed part of the gas phase. This gas is generated by the chemical reaction between the hot metal and the slag. In this study, simulated foaming slag was prepared by reacting sodium hydrogen carbonate and oxalic acid in glycerol, which disperses carbon dioxide. Next, we systematically investigated the effects of the volume fraction of the dispersed gas phase and the proportion of glycerol on the viscosity and bubble diameter. According to the model used in this study, the bubbles were smaller than those in the model in which the gas was directly dispersed. The bubble size increased as the gas phase ratio and liquid viscosity increased, likely because the bubble growth is promoted by increase in the gas phase ratio and liquid phase viscosity, and the frequency with which the bubbles contact one other. The increase of the gas phase ratio at low liquid-phase viscosity and low shear rate caused an increase in both apparent viscosity and relative viscosity, which was obtained by dividing the apparent viscosity by liquid-phase viscosity. However, these increases in viscosity were not observed at a high shear rate. This is likely because the mechanism of bubble diffusion and flow is affected by the liquid-phase viscosity and shear rate. We found that the model in this study exemplified a Herschel-Bulkley fluid. In addition, we proposed an equation for measuring viscosity from the gas phase ratio.

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  • Double Low-rank Based Matrix Decomposition for Surface Defect Segmentation of Steel Sheet

    Shiyang Zhou, Shiqian Wu, Ketao Cui, Huaiguang Liu

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    DOI:10.2355/isijinternational.ISIJINT-2021-024

    Abstract

    Despite advances in surface defect segmentation of steel sheet, it is still far from meeting the needs of real-world applications due to some method usually lack of adaptiveness to different shape, size, location and texture of defect object. Based on the assumption that each defect image is composed of defect-free background components that reflect the similarities of different regions and defect foreground components that reflect unique object information, we formulate the segmentation task as an image decomposition problem. To this end, we develop a double low-rank based matrix factorization framework for decomposing the surface defect image into defect foreground image and defect-free background image. Furthermore, considering the similarity of the defect-free background sub-regions and the defective sub-regions, Laplacian and sparse regularization terms are introduced into the matrix decomposition framework to improve their representation ability and discriminative ability. Importantly, the proposed method is unsupervised and training-free, so it does not requiring a large number of training samples with time-consuming manual labels. Experimental results on synthetic and real-world surface defect images show that the proposed method outperforms some state-of-the-art approaches in terms of both subjective and objective experiments.

  • Tracking Large-size Inclusions in Al Deoxidated Tinplate Steel in Industrial Practice

    Xiaoao Li, Nan Wang, Min Chen, Tianyou Ma

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    DOI:10.2355/isijinternational.ISIJINT-2020-679

    Abstract

    The three-dimensional morphology, size, content and composition of large-size inclusions extracted by large sample electrolysis from RH refining to hot rolling were investigated during the tinplate steel industrial test without calcium treatment. The results showed that the large-size inclusions in the RH refining process are Al2O3 inclusions and incompletely modified CaO·2Al2O3 inclusions, while those in tundish are Al2O3, CaO–Al2O3, CaO–SiO2–Al2O3 and CaO–SiO2–Al2O3–MgO. The typical types of large-size inclusion in slab and hot rolling plates are Al2O3, CaO–Al2O3, SiO2–Al2O3, CaO–SiO2–Al2O3, CaO–SiO2–Al2O3–MgO and CaO–SiO2–Al2O3–TiO2. Secondary oxidation was found to occur in molten steel during the pouring process and protective casting should be improved. Large-size inclusions in hot rolling plates are Al2O3 with a mass fraction of 19.8% and incompletely modified CaO·2Al2O3 inclusions with a mass fraction of 45.9% those have not been completely modified, which have high hardness and are difficult to deform. Therefore, it is recommended that calcium treatment should be carried out at the end of RH refining to reduce the Al2O3 and CaO·2Al2O3 contents. And the effect of calcium addition on the inclusion evolution has been studied by a thermodynamic analysis at 1873 K. With the increase of calcium addition in molten steel, the evolution route of equilibrium precipitations is Al2O3 → CaO·6Al2O3 → CaO·2Al2O3 → CaO·Al2O3 → 3CaO·Al2O3 → 12CaO·7Al2O3 → CaO. The critical calcium content for CaS and CaO formation increases with increasing oxygen content. To avoid the precipitation reaction between [Ca] and [S], the mass fraction of calcium addition needs to be controlled below 0.0040%.

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  • Dissolution of Iron Oxides Highly Loaded in Oxalic Acid Aqueous Solution for a Potential Application in Iron-Making

    Phatchada Santawaja, Shinji Kudo, Atsushi Tahara, Shusaku Asano, Jun-ichiro Hayashi

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    DOI:10.2355/isijinternational.ISIJINT-2020-726

    Abstract

    Oxalic acid has been identified as a sustainable chemical enabling an efficient recovery of target metals from industrial minerals by dissolution. The dissolution process recently has attracted attention as a key reaction in a potential clean iron-making. In this application to efficiently produce a high-purity iron, the dissolution is required to occur in the absence of light, with no addition of other chemical reagents, and to produce high concentration iron oxalate aqueous solution as fast as possible. To reveal the chemistry of iron oxide dissolution for this application, in the present study, the dissolution experiments are carried out under various conditions with a particular focus on the iron oxide highly loaded in the oxalic acid aqueous solution. Highly acidic oxalic acid solution for dissolving the highly loaded iron oxide enabled the production of iron oxalates aqueous solution with the concentration of up to 0.56 mol-Fe/L. Different from conventional studies under diluted conditions with pH control, the dissolution followed a non-reductive mechanism, producing [Fe3+HC2O4]2+ as a dominant iron species, and highly correlated with a concentration of proton in the solution. The experimental results and proposed stoichiometries identified a minimum amount of oxalic acid required for the complete dissolution of iron oxide independently from the concentration and type of loaded iron oxide. Among iron oxides tested (α-Fe2O3, FeOOH and Fe3O4) as the feedstock, Fe3O4 had an advantage in the dissolution rate, but showed a relatively low iron recovery in the solution (80–90%) because of an unavoidable formation of FeC2O4·2H2O precipitates.

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  • Three-dimensional Investigations of Non-metallic Inclusions in Stainless Steels before and after Machining

    Hongying Du, Andrey Vladimirovich Karasev, Pär Göran Jönsson

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    DOI:10.2355/isijinternational.ISIJINT-2020-680

    Abstract

    The focus of this study is to investigate non-metallic inclusions (NMIs) in stainless steels before (in steel samples) and after machining (in steel chips). In this study, the electrolytic extraction (EE) technique was used to extract non-metallic inclusions from steel samples. This makes it possible to investigate NMIs on film filters as three-dimensional objects by using SEM. The characteristics of NMIs in steel and chips have been systematically investigated and compared. Based on the results, it was found that the morphology of NMIs was significantly changed after machining. Overall, three different main shapes of NMIs were found: 1) a similar shape, 2) a stretched shape, and 3) a brittlely fractured shape. Furthermore, the degree of deformation of MnS and soft oxide NMIs in different zones of the chips depends on the distances from the contact zone of the tool and the chip. The total areas of MnS and soft oxides in the secondary deformation zone were increased by up to 2–3 times compared to that of the reference steel sample. This study also shows the advantages of the EE method in investigating NMIs in chips compared to using the conventional two-dimensional investigations of NMIs on the polished metal surface.

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  • Dissolution Behavior of Mg and Ca from Dolomite Refractory into Al-killed Molten Steel

    Ying Ren, Chunyang Liu, Xu Gao, Lifeng Zhang, Shigeru Ueda, Shin-ya Kitamura

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    DOI:10.2355/isijinternational.ISIJINT-2020-241

    Abstract

    Dolomite refractories are widely used in the refining process of clean steel and are considered potential sources of Mg and Ca that form MgO·Al2O3 spinel and CaO-containing inclusions. In this study, dolomite refractories were immersed into Al-killed molten steel with either 0.05% Al or 0.25% Al. The dissolution behavior of Mg and Ca from the dolomite refractory was studied, and the inclusion transformation behavior was observed. The results revealed that MgO in the dolomite refractory was reduced by Al in the molten steel, and the Mg content depended on the Al content. On the contrary, CaO barely dissolved into the molten steel even though the Al content increased. After immersion in both the low Al (0.05% Al) and high Al (0.25% Al) steels, an interfacial layer consisting of solid MgO and liquid phase CaO–Al2O3–MgO was formed on the surface of the rods. The initial Al2O3 inclusions gradually changed into Al2O3 saturated MgO–Al2O3 spinel after 60 min in low-Al steel; but were quickly transformed into MgO-saturated MgO–Al2O3 spinel in high Al steel. No CaO-containing inclusions were detected in the molten steel regardless of the immersion time and Al content.

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  • Simultaneous Analysis of Soluble and Insoluble Oxygen Contents in Steel Specimens Using Inert Gas Fusion Infrared Absorptiometry

    Hae-Mi Hong, Youn-Bae Kang

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    DOI:10.2355/isijinternational.ISIJINT-2020-596

    Abstract

    In order to evaluate cleanliness of steel samples which contain oxygen in two different forms - chemically dissolved form and physically dispersed form in steel matrix, identification of each oxygen in the steel is important. A simple but promising method for simultaneous analysis of these two types oxygen in steel samples was developed in the present study using Inert Gas Fusion Infrared Absorption Method. By utilizing different carbothermic reaction temperature for each type of oxygen, the chemically dissolved oxygen (soluble oxygen) was first separated from the steel specimen at a low reaction temperature, while the physically dispersed oxygen (insoluble oxygen in the form of oxide inclusion) was separated at a higher reaction temperature. This idea was applied to a number of Al-killed ultra low carbon steel specimens, which contain alumina inclusions. It was shown that separation of the soluble oxygen and the insoluble oxygen was possible. The obtained oxygen content in this new method was independently validated by a conventional Inert Gas Fusion Infrared Absorption Method for the total oxygen content and by cross-sectional analysis of non-metallic inclusion for the insoluble oxygen. A possible supersaturation state of liquid steel after RH process was observed.

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  • Effect of Nb Content on the Behavior of Primary Carbides in 0.4C-5Cr-1.2Mo-1V Steel

    Yu Huang, Guoguang Cheng, Meiting Zhu, Shijian Li, Weixing Dai

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    DOI:10.2355/isijinternational.ISIJINT-2020-314

    Abstract

    Niobium (Nb) microalloying can improve the material properties of H13 steel (0.4C-5Cr-1.2Mo-1V steel), but it also affects the natures of the primary carbides. Therefore, the effect of Nb content and cooling rate on the behavior of primary carbides in H13 steel was studied in this paper. The matrix structure was obtained by chemical etching, and then the formation location of primary carbides was identified by electron probe microanalysis (EPMA). The three-dimensional (3D) characteristics, including morphology, number density, and size, were obtained by a non-aqueous electrolysis method. The enrichment of alloying elements in the last-to-solidify region leaded to the formation of primary carbides during the solidification. The Ti4C2S2 phase precipitated first, and then the Mo-Cr-rich carbide was formed around the Ti4C2S2 phase. During the cooling process, the Ti4C2S2 phase partly transformed into Nb-rich carbide and then further partly transformed into V-rich carbide. There is a huge difference between the two-dimensional and three-dimensional morphologies of the primary carbides. As the Nb content increased, the size of last-to-solidify region decreased gradually and the size and number density of primary carbides in the 3D observation increasingly increased. However, as the decrease of the cooling rate, the size of primary carbides increased rapidly and the number density of primary carbides decreased markedly. The thermodynamic and kinetics calculation results agreed well with the experimental observations.

  • An Empirical Comparative Study of Renewable Biochar and Fossil Carbon as Carburizer in Steelmaking

    Ryan ROBINSON, Liviu BRABIE, Magnus PETTERSSON, Marko AMOVIC, Rolf LJUNGGREN

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    DOI:10.2355/isijinternational.ISIJINT-2020-135

    Abstract

    Approximately 60–70% of the direct greenhouse gas emissions in electric arc furnace (EAF) steelmaking originate from the use of fossil carbon charge during melting of steel scrap. Regarding short-term solutions to mitigate the climate impact of steelmaking, there is greater potential to replace fossil carbon charge with renewable carbon in the EAF than in integrated blast furnace steelmaking where mechanical strength requirements on carbon charge are too demanding. Therefore, the present study aims to provide an experimental and practical foundation for using renewable biochar in the EAF as a relatively simple step to decrease the climate impact of steelmaking.In order to evaluate the inherent performance of biochar as a carburizing agent, lab-scale tests where completed using four different types of carbonaceous materials: synthetic graphite, anthracite coal and two types of biochar from woody biomass (BC1 and BC2). The first order dissolution rate constants from experiments ranged between 0.7 to 1.9 × 10-4 m/s, which agrees well with previously reported results. Furthermore, lab-scale results show that biochar properties commonly seen as detrimental, such as low carbon crystallinity and high porosity, do not necessarily constitute a disadvantage for biochar utilization as carburizer in steelmaking.In order to further assess the results from lab-scale tests, an industrial trial including six consecutive heats was performed in a 50 t EAF at the Höganäs Halmstad Plant. Results show that 33% substitution of standard Anthracite carbon charge with biochar BC2 gave no deviation from normal operating conditions in the EAF.

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  • © The Iron and Steel Institute of Japan

Article Access Ranking

19 Jun. (Last 30 Days)

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  3. Comprehensive Research about Critical Interaction Region Named Cohesive Zone in Series of Dissected Blast Furnaces ISIJ International Vol.61(2021), No.6
  4. Production and Technology of Iron and Steel in Japan during 2020 ISIJ International Vol.61(2021), No.6
  5. Effect of Particle Size of Fine Hematite on Characteristics and Strength of Quasi-particle Tetsu-to-Hagané Vol.107(2021), No.6
  6. Formation Mechanism of Large-size CaO–Al2O3–MgO–SiO2 Inclusions in High Carbon Chromium Bearing Steel ISIJ International Advance Publication
  7. Influence of Annealing on Delamination Toughening of Mo-Bearing Medium-Carbon Steel with Ultrafine Elongated Grain Structure Processed by Warm Tempforming ISIJ International Advance Publication
  8. Viscosity Evaluation of Simulated Foaming Slag via Interfacial Reaction at Room Temperature ISIJ International Advance Publication
  9. Effect of Granule’s Moisture on Granulation Rate of Iron Ore Tetsu-to-Hagané Vol.107(2021), No.6
  10. Sintering Technology Using Parallel Granulation Process at High Pellet Feed Ratio Tetsu-to-Hagané Vol.107(2021), No.6

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  10. hydrogen-assisted crack propagation in pre-strained twinning-induced plasticity steel: from initiation at a small defect to failure