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

ISIJ International Advance Publication

  • 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.

  • Effects of Cooling Rate after Hot Forging on Precipitation of Fine Particles during Subsequent Normalizing and Austenite Grain Growth during Carburization of Al- and Nb-microalloyed Case-hardening Steel

    Genki Saito, Norihito Sakaguchi, Munekazu Ohno, Kiyotaka Matsuura, Masayoshi Takeuchi, Taichi Sano, Koki Minoguchi, Takuya Yamaoka

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    DOI:10.2355/isijinternational.ISIJINT-2020-743

    Abstract

    This study deals with austenite grain growth during high-temperature carburization of an Al- and Nb-microalloyed case-hardening steel. The grain size after carburization-simulated heating for 5 h at 1050°C decreased with the increase in the cooling rate from hot forging-simulated heating for 1 h at 1250°C. The increase in cooling rate led to the decreases in the volume fractions and sizes of AlN and Nb(C,N) particles precipitated during cooling, and AlN disappeared when the cooling rate increased to 16°C/min, while Nb(C,N) still slightly exited at 16°C/min. Because of oversaturation caused by cooling within a finite time, further precipitation occurred during the subsequent normalization for 3 h at 1070°C, resulting in the formation of AlN–Nb(C,N) combined particles. When the cooling rate increased, the volume fraction and number density of these combined particles increased while their size decreased. Therefore, a higher cooling rate causes a larger pinning effect on grain growth during carburization; thus grain size after carburization decreased with the increase in cooling rate. Transmission electron microscopy confirmed the formation of a coherent AlN–Nb(C,N) interface due to good lattice matching between the crystal planes of AlN () and Nb(C,N) (220). This led to the preferential nucleation of AlN on the Nb(C,N) particles, thereby forming stable AlN–Nb(C,N) particles.

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  • Cerium Addition Effect on Modification of Inclusions, Primary Carbides and Microstructure Refinement of H13 Die Steel

    Xijie Wang, Guangqiang Li, Yu Liu, Fang Wang, Qiang Wang

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    DOI:10.2355/isijinternational.ISIJINT-2020-739

    Abstract

    A comprehensive study of the Ce addition effect on microstructure, inclusions, and primary carbides in H13 steel was carried out. 3D morphology of inclusions and primary carbides was assessed by the non-aqueous electrolytic method. The addition of 0.0038 mass% Ce had no obvious refinement effect on dendritic structures in H13 steel. With Ce content increase from 0.0038 to 0.019 mass%, dendritic structures of H13 steel were refined. Al2O3 and MnS inclusions in original H13 steel promoted heterogeneous nucleation of primary carbides. Al content increased, and S content decreased with increasing Ce content. When the latter was increased from 0.0038 to 0.019 mass%, the original inclusions were modified first to Al11O18Ce and CeAlO3, then to Ce2O3, and, finally, to Ce2O2S. Numerous small-sized Ce2O2S inclusions were found in steel with 0.019 mass% Ce, which promoted nucleation of γ-Fe during solidification and contributed to the refinement of as-cast dendritic microstructures of H13 steel. Besides, Ce2O2S inclusions suppressed heterogeneous nucleation of primary carbides. The size of primary carbides decreased, and their morphology became less developed due to the finer microstructure hindering their growth. Finally, banded structures in forged Ce-bearing H13 steel were improved.

  • Numerical Investigations on Thermomechanical Behaviour of Purging Plug with Rectangular and Circular Slits

    Fangguan Tan, Zhu He, Shengli Jin, Qiang Wang, Liping Pan, Yawei Li, Baokuan Li

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    DOI:10.2355/isijinternational.ISIJINT-2020-048

    Abstract

    Purging plugs are widely used in the secondary refining process, and its service life determines the downtime and usage efficiency of the whole ladle. This study focuses on comparing the heat transfer and thermomechanical behaviour of purging plug with different slits to obtain the reason for the long service life of purging plug by thermal-structure coupling method. The numerical results showed that the moderation of temperature distribution is achieved by changing the slit shape and the reasonable arrangement of the circular slits. Furthermore, the circular slits can alleviate the stress concentration phenomena, and circular slits are better for decreasing the axial stress in the purging plug, which occurred at the position located 0.323 m above the bottom face, and its distance from the centre is 0.04 m.

  • 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.

  • Prediction Model of End-point Phosphorus Content in Consteel Electric Furnace Based on PCA-Extra Tree Model

    Chao Chen, Nan Wang, Min Chen

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    DOI:10.2355/isijinternational.ISIJINT-2020-615

    Abstract

    According to the actual industrial data from a Consteel electric furnace, a prediction model based on the principal component analysis (PCA) and extremely randomized trees (Extra Tree model) is proposed for end-point phosphorus content. PCA is used to reduce the dimensionality of the input variable affecting the end-point phosphorus content and eliminate the collinearity among the input variables, and then the data transformed by PCA are used as input data for the established Extra tree model. Compared with other feature pre-processing methods, PCA method can greatly improve the regression prediction performance of the Extra Tree model. Finally, the validation by test set indicates that for the PCA-Extra Tree model, the hit rates of end-point phosphorus content are 98%, 96% and 89% with the prediction error range of ±0.005%, ±0.004% and ±0.003%, respectively. The combined PCA-Extra Tree model has achieved the effective prediction for end-point phosphorus content, and provided a good reference for the end-point control and judgment of Consteel electric furnace.

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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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  • Heterogeneous Deformation in a Commercially Pure Titanium Sheet under Dwell Fatigue Loading: Crystal Plasticity Modeling and Experiment

    Liangwei Yin, Osamu Umezawa

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    DOI:10.2355/isijinternational.ISIJINT-2020-702

    Abstract

    The heterogeneous deformation in a hot-rolled commercially pure titanium grade 1 sheet has been experimentally and numerically investigated under dwell fatigue loading in current paper. The residual strain fields within two regions of interest are probed by digital image correlation (DIC) after interrupted dwell fatigue test. These measurements essentially agree with predictions of a dislocation mechanism-based crystal plasticity model incorporating deformation twinning. The simulated results further indicate that axial strain localization at grain scale mainly derives from prismatic slip activity, followed by pyramidal <a>, basal slip and {1122} compression twinning activities. On this basis, a weighted averaged Schmid factor is proposed to correlate the axial strain accumulation with active plastic deformation modes in individual grains. Besides, the cyclic load shedding within a soft-hard-soft grain pair is captured by crystal plasticity modeling. The stress redistribution from soft to adjacent hard grain implies that the influence of deformation twinning on dwell facet nucleation is limited. The presented study confirms a robust crystal plasticity model and deepens the quantitative analysis of cold dwell fatigue in titanium and its alloys.

  • Thermodynamic Activity of MnO in CaO–SiO2–MnO–FeO–MgO Molten Slags

    Jian-bin Chen, Hong-hong Huang, Rong Chu, Ya-qin Sun

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    DOI:10.2355/isijinternational.ISIJINT-2020-730

    Abstract

    In order to understand the thermodynamic characteristics of smelting process for high manganese twinning-induced plasticity (TWIP) steel, the activity coefficient of MnO in molten slag of MnO–CaO–SiO2–FeO–MgO slag system with up to 52 mass% MnO was measured at 1450°C by the experiments of the manganese equilibrium between liquid silver and molten slag under the mixed gas atmosphere of CO, CO2 and Ar. The distribution ratio of manganese LMn between the molten silver and molten slag, and the equilibrium concentration quotient K' were also measured. The effects of MnO, FeO and basicity on the activity coefficient of MnO, the distribution ratio of manganese and the equilibrium concentration quotient were discussed. The activity coefficient of MnO, the distribution ratio of manganese and the equilibrium concentration quotient as a function of the concentration of the components in molten slag were investigated by regression analysis method. The results show that: (a) The Raoultian activity coefficients of MnO in molten slag are less than unity. (b) When the basicity B = 0.77–1.15, MnO = 15.8–52.9 mass% and FeO = 7–20 mass%, the activity coefficient of MnO increases as MnO content increases, but the LMn and the K' decrease as MnO content increases. (c) When B = 0.89–1.08, MnO = 43.6–46.9 mass% and FeO = 7–20 mass%, the activity coefficient of MnO increases as FeO content increases, but the LMn and the K' decrease as FeO content increases. (d) When MnO = 40–45 mass%, FeO = 9–14 mass% and B = 0.7–1.8, the activity coefficient of MnO increases as the basicity increases, but the LMn and the K' decrease as the basicity increases.

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  • Thermodynamic Modelling of Sulphide Capacity of Ternary Silicate Slags

    Antonio Romero-Serrano, Josué López-Rodríguez, Aurelio Hernández-Ramírez, Alejandro Cruz-Ramírez, Enrique Rivera-Salinas, Miguel Pérez-Labra

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    DOI:10.2355/isijinternational.ISIJINT-2020-676

    Abstract

    This article proposes a structural thermodynamic model of slags to estimate the sulphide capacity (CS) of ternary silicate melts. Sulphide ion (S2-) is incorporated into the silicate structure by substituting quasi-lattice sites in the slag for free oxygen ions (O2-). This structural model can take into account the effect of substituting one metal oxide for another in ternary systems, since it considers that each metallic oxide produces a de-polymerisation reaction of O° + O2- = 2 O- with a characteristic free energy change. The Cs of ternary silicates can be calculated by this model solely from the data of the binary sub-systems - no ternary terms are required. A good agreement was obtained between the experimental and the model results for the ternary slags of the SiO2–CaO–MgO–MnO–FeO system.

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  • Deformation Behavior of Longitudinal Surface Flaws in Flat Rolling of Steel Wire

    Joong-Ki Hwang

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    DOI:10.2355/isijinternational.ISIJINT-2020-703

    Abstract

    The deformation behavior of a longitudinal V-shaped surface flaw was investigated during the flat wire rolling process using finite element analysis. The effects of process conditions, material properties, and initial position of the flaw on the deformation behavior of surface flaws were evaluated to understand the deformation behavior of flaws and to find solutions to decrease flaws. The surface flaw, that is, the ratio of the depth and width of the surface flaw (r), decreased with increasing reduction in height per pass, roll diameter, and friction coefficient. Unfortunately, the surface flaw and strain homogeneity of the wire simultaneously decreased under similar process conditions. The surface flaw slightly decreased with the strain hardening exponent (n) by increasing the width of the surface flaw. However, the effect of n value on the deformation of the surface flaw was not crucial. Higher strain at the flat surface induced an overlap-type surface flaw, whereas a small strain in the free surface induced an open-type surface flaw during the flat wire rolling process, which means that the surface flaw on the flat surface was much more detrimental than the surface flaw on the free surface. The deformation behavior of the surface flaw in flat-rolled wire was highly related to the strain inhomogeneity and lateral spreading of the wire. As the strain inhomogeneity of the flat-rolled wire increased, the lateral spreading of the wire increased, resulting in a decrease in the surface flaw, i.e., the r value.

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  • Effect of CaF2 on Viscosity and Refining Ability of Highly Basic Slags for Duplex Stainless Steel

    Lichun Zheng, Huabing Li, Xiaolu Wang, Zhouhua Jiang, Hao Feng

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    DOI:10.2355/isijinternational.ISIJINT-2020-744

    Abstract

    To optimize CaF2 content in highly basic CaO-18%Al2O3-SiO2-10%MgO-CaF2 (%CaO/%SiO2=6, denoted as C/S=6) refining slags used for the production of Al-killed duplex stainless steel with high cleanliness demand, the effect of CaF2 content on the viscosity and refining ability of the slags were studied and compared with typical CaF2-free highly basic CaO-30%Al2O3-SiO2-10%MgO (C/S=6) slag. The effect of CaF2 addition in decreasing slag viscosity becomes less obvious with increasing temperature and CaF2 content. When CaF2 content exceeds 10%, slag viscosity only marginally decreases with further increasing CaF2 content. Both monoxide-CaO and monoxide-MgO phases are precipitated in all the CaF2-bearing slags. CaF2 addition slightly increases monoxide-MgO precipitation, but dramatically decreases monoxide-CaO precipitation. Viscosities of the CaF2-bearing slags were also theoretically calculated and good agreement with the measured values was observed. Moreover, the 6% CaF2-bearing slag has very close viscosities above 1833 K but much lower viscosities below 1833 K, compared with the CaF2-free highly basic slag. Further evaluation of the 6% CaF2-bearing slag on steel cleanliness confirms that 6% CaF2 addition is sufficient for the highly basic CaO-18%Al2O3-SiO2-10%MgO-CaF2 (C/S=6) slag. The mechanism of CaF2 in decreasing the viscosity of CaF2-bearing slags was discussed from the viewpoints that CaF2 behaves as a network breaker and that CaF2 suppresses the precipitation of solid phases. The first aspect was identified to play a much greater role in decreasing slag viscosity.

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  • Development Technology for Prevention of Macro-segregation in Casting of Steel Ingot by Insert Casting in Vacuum Atmosphere

    Kohichi Isobe

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    DOI:10.2355/isijinternational.ISIJINT-2020-603

    Abstract

    Important large components, such as rotors for power generation steam turbines, pressure vessels and reaction vessels, are manufactured through ingot casting. However, it is quite tasking to manufacture the materials with sufficient properties because of the macro-segregation of ingots.To develop effective and versatile macro-segregation countermeasures in the casting of large steel ingots for manufacturing large parts for power plants, the insert casting in vacuum atmosphere, in which a core material similar in composition as the base steel, is placed at the center of the mold, was studied. The effectiveness of the proposed insert casting as a macro-segregation countermeasure was evaluated in the casting experiments with 0.5 mass% carbon steel using cast iron mold with a 150 mm square inner cross section, insulated to reduce solidification rate. In addition, it is now confirmed that good bonding between the core material and base material can be achieved even under conditions where bonding by normal insert casting in air atmosphere is hard to achieve.The behavior of the core material melting and the solidification of the molten steel in the experiments of macro-segregation reproduction casting and insert casting were investigated using the direct finite difference method. The mechanism by which this method suppresses the macro-segregation formation and solidification conditions for the suppression, the reasons, and conditions for good bonding in this insert casting are clarified by the analyses. Furthermore, the cause of internal crack formation in the insert casting was investigated and guidelines for preventing the crack formation were presented.

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  • Method for Simulating Gas Permeability of a Coke Bed Including Fines Based on 3D Imaging on the Coke Particle Morphology

    Shungo Natsui, Azuma Hirai, Koki Terui, Yusuke Kashihara, Akinori Murao, Yuji Miki, Hiroshi Nogami

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    DOI:10.2355/isijinternational.ISIJINT-2020-749

    Abstract

    In ironmaking blast furnaces, the particle size distribution and voids in the coke bed affects the upward flow of gas, and consequently, the efficiency of the combustion reaction. To clarify the influence of coke pulverization on the packing structure of the coke bed, the permeability of the bed was evaluated using detailed dynamics simulation and geometric data analysis. To obtain detailed 3D morphology of the coke, we derived digital geometric data using rotational strength tests. Using the Euler–Lagrange coupling approach with the multisphere discrete-element method, the effect of the volume fraction of fines and distribution in the coke bed on the gas flow was analyzed. The void shape in the 3D coke bed structure was quantified using geometric data and simulated gas flow distributions. Although a continuous void network was observed in the packed bed before pulverization, areas of highly restricted (or no) gas flow were observed after pulverization. The dominant effect of coke degradation on the packed bed structure was the disruption of the gas flow path because of fines clogging the pores and narrowing the gas flow path. The developed simulation method can comprehensively analyze the effects of coke degradation on the gas flow distribution in the coke bed and can be used to analyze and control the instability of industrial blast furnaces.

  • Time-resolved and In-situ Observation of Solidification in TiAl Alloys

    Tomohiro Nishimura, Hitoshi Ishida, Hideyuki Yasuda

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    DOI:10.2355/isijinternational.ISIJINT-2020-764

    Abstract

    Time-resolved and in-situ observation of solidification by X-ray imaging is a powerful method to empirically understand the solidification process of metallic materials. Observations began with low-melting-point alloys such as Al, and were later applied to the observation of Fe-based alloys in the temperature range above 1750 K. In Ti–Al binary system, there is a γ phase (TiAl intermetallic compound) in addition to an α phase and a β phase, which results in a relatively complex phase diagram with multiple peritectic solidification. Therefore, although there are various possibilities for phase selection and microstructure formation during the solidification process, the solidification process has not been empirically clarified. Therefore, we used single crystal MgO as the sample holding container to suppress the reaction with the reactive molten Ti as much as possible, and for the first time, we successfully observed the solidification process of TiAl alloys. Time-resolved and in-situ observations showed that a solid state phase transformation with repeated nucleation and growth was selected instead of the peritectic solidification from α to γ phases shown in the Ti–Al binary phase diagram. The α/γ transformation should also be taken into account in TiAl alloys, since the α/γ transformation formed a fine γ phase and affected the microstructure formation. This understanding of the α/γ transformation was expected to provide new guidelines for controlling the solidification structure of TiAl alloys.

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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.

  • Effect of Isothermal Transformation Treatment and Tempering on the Microstructure and Hardness of a Medium C and High Si Steels

    Gülten Kafadar, Ali Kalkanli, Abbas Tamer Özdemır, Bilgehan Ögel

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    DOI:10.2355/isijinternational.ISIJINT-2020-419

    Abstract

    This research work aims to study the effect of 2wt%Mo on bainitic transformation kinetics and bainite morphology in 0.6wt%C-1.2wt%Si-1.0wt%Mn-0.2wt%Cr steel. Specimens are austenitized at 950°C and rapidly cooled in salt bath and isothermally treated between 200°C–300°C for different time intervals. Another set of specimens are rapidly cooled in oil after an austenitization treatment and then tempered in the temperature range of 200°C–550°C. In C–Mn–Si specimens, the amount of retained austenite increases with increasing the amount of bainite but no retained austenite is observed in bainitic C–Mn–Si–Mo specimens. The tempering behavior of C–Mn–Si–Mo alloy is considerably different than that of the Mo free alloy. Mo in a martensitic microstructure of C–Mn–Si–Mo alloy shows the secondary hardening effect peak upon tempering at 500°C. The examination of the secondary hardening would also contribute to the behavior of Mo in tempered bainitic steels. The bainitic specimens do not show a peak hardness but softening is retarded upon tempering at the same temperature range.

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    3. Influence of Isothermal Treatment Prior to Initial Quenching of Q&P Process on Microstructure and Mechanical Properties of Medium Mn Steel ISIJ International Vol.61(2021), No.2

  • Surface Structures of CaFe2O4 (001), (100), (110) and (111): A Density Functional Theory Study

    Zhigang Que

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    DOI:10.2355/isijinternational.ISIJINT-2020-541

    Abstract

    Calcium ferrite is the main binder phase in sinter, which affects the physical and metallurgical properties of sinter. It was also widely applied to photocatalysts, oxidation catalysts, photocathodes and gas sensors etc. The electronic, magnetic and chemical properties of it were investigated since its crystal structure was first reported. However, the right terminations, structures and relative stabilities of CaFe2O4 surface have not been systemically studied. Hence, the surface structures of CaFe2O4 (001), (100), (110) and (111) were calculated by using a generalized gradient approximation considering on-site Coulomb interaction of iron 3d electrons (GGA + U) in the paper. With U = 4.70 eV, the band gap for up-spin and down-spin energy of CaFe2O4 was calculated to be 1.91 and 1.81 eV, closed to the experimental value (1.90 eV). For the CaFe2O4 (001) surface, the O1 terminations were the most stable and the surface energy was 1.307 J·m-2. In the case of CaFe2O4 (100) surface, the surface energies at Ca and O1 terminations were 1.278 and 1.568 J·m-2, respectively. There were also two most stable CaFe2O4 (110) surfaces in close surface energies and terminated with the exposed Fe2 and O3 atoms. The surface energies of them were 1.489 and 1.570 J·m-2, respectively. Among the fifteen CaFe2O4 (111) terminations, the surface energies at O2 (l) and O4 (f) terminations were the lowest and they were 1.421 and 1.455 J·m-2. The calculated surface energies indicate that (100) was better than (001), (110) and (111) in thermodynamic, which agrees well with the experimental results.

  • Behavior of Crack Generation of Slag in Continuous Solidification Process of Blast Furnace Slag

    Yasutaka Ta, Takeru Hoshino, Hiroyuki Tobo, Keiji Watanabe, Katsunori Takahashi

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    DOI:10.2355/isijinternational.ISIJINT-2020-632

    Abstract

    A continuous solidification process of blast furnace slag was developed to promote the use of air-cooled slag coarse aggregate for concrete. In this process, the molten slag can solidify in only 120 s and the slag thickness is about 25 mm. This process suppresses gas generation and greatly reduces water absorption. Most of the slag is crystalline, and part of the slag has a glass layer on its surface. Slag with a glass layer is brittle because it contains several cracks. Therefore, microscopic observation and thermal stress analysis of the solidified slag were carried out to clarify the mechanism of crack generation in the plate-like slag. In the microscopic observation, several cracks with a length of about 8 mm were found in the slag with the glass layer. From the analysis, in the cooling pattern of the slag on the piled slag a temperature difference of about 200 K exists between the center and the mold side in the slag pit, and keeping this difference results in tensile stress of more than 50 MPa. However, in the cooling pattern of the crystalline slag in the piled slag, the temperature gradient in the slag in the slag pit was very small because the slag was retained in the piled slag, and as a result, the thermal stress was almost 0 MPa.

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  • Adhesive Scale Formation on Low Silicon Steel Surface; Characterization and Mechanism

    Manindra Manna, Kedar Bhave, Abhishek Subhash Pathak

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    DOI:10.2355/isijinternational.ISIJINT-2020-134

    Abstract

    A systematic study has been conducted to characterize adhesive/non-adhesive scale on low silicon containing hot rolled steel surface and mechanism for formation of such scale. Different characterisation tools like XRD, SEM-EDS, GDOES, Scanning Kelvin probe and XPS were used to identify the chemical composition and characteristics of adhesive and non-adhesive scales. The characterization studies confirmed that the adhesive scale consists of CaFeSi2O6 compound along with magnetite and haematite with red in colour whereas non-adhesive scale consists of grey colour hematite-magnetite phase. Humidity in environment promotes oxidation of steel and depending on relative humidity different oxides are formed on the steel surface. Low humidity persists in India during the winter season which lead to lower oxidation potential and steel surface is oxidised accordingly. The wüstite phase is formed under lower oxygen potential at high temperature when slab is released from the mould. Wüstite is reactive to mould powder (tricalcium silicate) at high temperature and forms CaFeSi2O6 compound on the steel surface which is very adhesive in nature. Lots of cracks are inheritance attributes of non-adhesive scale whereas eventually no crack exists in adhesive scale. The compound present in the adhesive scale remains on the steel surface even after subsequent hot rolling and acid pickling operation as chloride ions of acid may not able to dissolve or penetrate through such stable compound. The quality of the finished product is deteriorated due to the presence of such adhesive scale as it leads to poor product performance during subsequent processing like cathodic paint deposition.

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    3. Influence of Isothermal Treatment Prior to Initial Quenching of Q&P Process on Microstructure and Mechanical Properties of Medium Mn Steel ISIJ International Vol.61(2021), No.2

  • Accurate Viscosity Prediction for Molten Slags: A New Model and Database

    Rui Zhang, Samuel Hallström, Huahai Mao, Lina Kjellqvist, Qing Chen

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    DOI:10.2355/isijinternational.ISIJINT-2020-586

    Abstract

    We present a new structurally-based viscosity model and database for accurately predicting the viscosity of multicomponent molten slags in the whole composition and large temperature ranges. The model is based on the CALPHAD (CALculation of PHAse Diagrams) approach and the thermodynamic two-sublattice ionic liquid formalism, which means that the underlying structure of oxide melts is taken into account and a full description of a multicomponent system is achieved by using the information of only binary and ternary systems. The model is implemented in the Thermo-Calc software package and is applied to optimize model parameters for the FeOx–CaO–MgO–Al2O3–SiO2–CaF2–CrOx–Na2O–MnOx–TiO2–ZrO2–P2O5–Gd2O3–La2O3–V2O5–NiO–CuOx system. Encompassing the obtained viscosity model parameters, the new thermodynamic database TCOX10 is shown to be able to give highly reliable calculation results for industrial and geological applications. Compared with previously reported modelling work by using the same large experimental datasets on the key subsystem CaO–MgO–Al2O3–SiO2 (CMAS), the present model and database are found to give the smallest deviations to the measurements, which is also proved true for the CMAS-based multicomponent glass that can significantly impact the performance of airplane turbine engines.

  • Nitrogen Solubility in Liquid Fe–Nb, Fe–Cr–Nb, Fe–Ni–Nb and Fe–Cr–Ni–Nb Alloys

    Shouxing Yang, Huabing Li, Hao Feng, Xuze Li, Zhouhua Jiang, Tong He

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    DOI:10.2355/isijinternational.ISIJINT-2020-627

    Abstract

    The N-containing Fe–Cr–Ni–Nb austenitic heat-resistant steels have become the research focus of high-temperature material. Nitrogen plays an important role on the strength and structural stability of the steels, and thus the accurate control of nitrogen content is of great significance to the smelting process. In this paper, the nitrogen solubility in liquid Fe, Fe–Nb, Fe–Cr–Nb, Fe–Ni–Nb and Fe–Cr–Ni–Nb systems from 1823 to 1873 K were investigated by gas-liquid metal equilibrium experiments. In liquid Fe–Nb system with a niobium content of 5 to 20%, the solubility of nitrogen increased with niobium content. The first-order interaction parameter of niobium on nitrogen at 1873 K and its relationship with temperature were determined as follows: eNbN(1873 K) = -0.0672, eNbN = -375.6/T + 0.133. In the liquid Fe–Cr–Nb and Fe–Ni–Nb systems, the second-order cross-interaction parameters of chromium or nickel with niobium on nitrogen were determined as follows: γCr,Nbn = 36.2/T-0.01728, γNi,NbN = 4.56/T-0.00187. Furthermore, a more accurate nitrogen solubility prediction model for the liquid Fe–Cr–Ni–Nb system was established based on the existing thermodynamic parameters and the interaction parameters obtained in this study.

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  • Comparative Study of Microstructure-sensitive Fatigue Crack Propagation in Coarse- and Fine-grained Microstructures between Stable and Metastable Austenitic Stainless Steels Using Miniature Specimen

    Aya Matsushita, Shohei Ueki, Yoji Mine, Kazuki Takashima

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    DOI:10.2355/isijinternational.ISIJINT-2020-659

    Abstract

    Microstructure-sensitive fatigue crack propagation was studied on coarse- and fine-grained stainless steels with different austenite stabilities using miniature compact-tension specimens. For coarse-grained 310S stable austenitic steel, the crack growth rate was increased by shear-localised bands formed ahead of the crack tip. For fine-grained 310S with an average grain size of ~0.25 µm, the crack-tip plastic strain was concentrated on the grains favourable to dislocation multiplication, rather than being dependent on the distance from the crack surface, which led to discontinuous crack propagation. Consequently, the fatigue crack growth rate was lower in the fine-grained 310S steel than in the coarse-grained one. In 304 metastable austenitic steel, the fatigue crack propagated within the martensite that formed ahead of the crack tip, and the crack growth rate was lower than that in the 310S steel. The grain refinement of 304 steel to a ~0.99 µm average grain size enhanced the crack growth resistance. Electron back-scatter diffraction analysis of the fracture surface revealed microstructural fragmentation due to single-variant transformation for each grain in the fine-grained 304 steel. These findings indicate that the microstructural evolution ahead of the crack tip dominates the rate of mechanically short fatigue crack propagation in austenitic stainless steels.

  • Effect of Varied Oxygen Levels on the Oxidation of a Magnetite Pellet Bed during Pot Furnace Induration

    Anna Eriksson, Charlotte Andersson, Hesham Ahmed, Anders Dahlin, Telkicherla Kamesh Sandeep Kumar, Pär Semberg

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    DOI:10.2355/isijinternational.ISIJINT-2020-469

    Abstract

    An excess amount of oxygen originating from hydrogen production is likely to be available as part of the HYBRIT (Hydrogen Breakthrough Ironmaking Technology) initiative, aimed at producing fossil-free steel by replacing coking coal with hydrogen. Oxygen enrichment during magnetite pellet induration can lead to reduced fuel amounts and increased productivity. Induration of magnetite iron ore pellets liberates considerable amounts of heat when magnetite is oxidised to hematite. Elevated oxygen levels in the process gas are expected to promote the oxidation reaction, resulting in increased process efficiency. However, more information is required to enable the transition towards a higher oxygen level process and improved production rate, while maintaining the metallurgical properties of the pellet bed. In this study, interrupted pot furnace experiments were conducted on a magnetite pellet bed (approximately 100 kg) at Luossavaara-Kiirunavaara Aktiebolag to investigate the effect of oxygen levels at approximately 6%, 13%, and 30% O2. Temperature profiles are measured and pellet properties (compression strength, porosity, oxidation degree, microstructures) are analysed at different bed heights. The higher oxygen level (approximately 30% O2) intensifies the oxidation reaction, resulting in increased temperature, oxidation rate and compression strength across the vertical bed height. Three different pellet oxidation profiles are identified, namely, homogenous oxidation across the pellet, complete oxidation of the pellet shell and an unreacted core with a sharp/distinct interface, and partial oxidation of the pellet shell and an unreacted core. A higher oxygen level results in an increased oxidation rate, while the temperature controls the pellet oxidation profile.

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  • Interaction between M(C, N) and Ferrite in Electropulsing Microalloyed Steel

    Zhenghai Zhu, Hongbiao Dong, Ke Zhang, Tao Jia, Lizhong Chang, Xiaofang Shi, Fei He

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    DOI:10.2355/isijinternational.ISIJINT-2020-538

    Abstract

    Microstructure and M(C, N) significantly affect the quality of Nb microalloyed steel, and the control microstructure evolution and M(C, N) precipitation behavior is the key. In this study, the interaction between ferrite and M(C, N) with electropulsing is quantitatively analyzed. Results reveal that electropulsing promotes the precipitation of M(C, N) and ferrite phase from austenite phase. The precipitated M(C, N) affects the position of ferrite precipitation, and the precipitation of ferrite can then conversely affect the distribution of M(C, N). The influence of austenite to ferrite transformation on M(C, N) precipitation is much more significant than that of electropulsing. This observation can be applied to control of microstructure and M(C, N) in continuous casting.

  • Selective Separation of Metallic Fe Remaining in Slags Using Electrical Pulse Disintegration

    Hironari Kubo, Masahiro Nakanishi

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    DOI:10.2355/isijinternational.ISIJINT-2020-683

    Abstract

    Metallic Fe (hereinafter abbreviated as M.Fe) is suspended in steelmaking slags due to the stirring action during blowing and is mainly recovered via pulverization, classification, and magnetic separation. However, steelmaking slags are hard, and it is difficult to transform irregular-shaped and fine M.Fe in slags into free particles through the conventional pulverization method, which requires a large energy consumption. In this study, pulverization and separation experiments of steelmaking slags were performed using electrical pulse disintegration, which is completely different from the conventional pulverization method and capable of causing preferential fracture at the heterophase interface. As a result, several free particles of M.Fe with almost no slag attached were obtained from the coarse and fine pulverized particles. In addition, the electric field analysis results of a system where spherical M.Fe exists in a slag show that electric field concentration occurs in the front and back directions of the external magnetic field. The findings also show that a fracture can occur at the interface between the M.Fe and slag due to the combination of increased discharge probability, concentration of thermal energy, and generation of the Maxwell stress. Furthermore, the larger the pulverized mass, the higher the pulverization efficiency. In sum, electrical pulse disintegration may be advantageous for actual operations, where large quantities of oxides employed in the steel industry, such as steelmaking slag, spent refractories, and raw materials, should be treated in a short time with low energy consumption.

  • Numerical Investigation of Hematite Flash Reduction-biomass Steam Gasification Coupling Process

    Xingnan Wang, Guiqin Fu, Wei Li, Miaoyong Zhu

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    DOI:10.2355/isijinternational.ISIJINT-2020-566

    Abstract

    The flash ironmaking process is a novel ironmaking technology; the direct use of biomass as the reductant and fuel in this process can take full advantage of the heat and syngas produced during the biomass gasification. This study establishes a three-dimensional computational fluid dynamics model that incorporates turbulent flow, mass transfer, and heat transfer to describe the complex gas-particle reaction behavior of the hematite flash reduction-biomass steam gasification (FR-BSG) coupling process in an entrained flow reactor to explore its feasibility. The temperature and species distributions in the FR-BSG coupling process are analyzed, and the effects of steam/carbon molar ratio (S/C) and ore/biomass mass ratio (O/B) are investigated. The results show that the reduction degree of hematite particles reaches 76.67% in the residence time of 1.65 s under the conditions of S/C=0.1, O/B=1.0 and T=1673 K. The increase of S/C can enhance the production of H2 but reduce the molar fractions of H2 and CO in biomass syngas, which leads to the decrease of hematite reduction degree. A higher reduction degree of hematite and lower carbon conversion of biomass can be obtained at lower O/B values. These results provide a theoretical basis for the use of biomass as energy in flash ironmaking technology.

  • Reaction Behaviour between Cerium Ferroalloy and Molten Steel during Rare Earth Treatment in the Ultra-low Carbon Al-killed Steel

    Min Wang, Shuai Gao, Xin Li, Gui-xuan Wu, Li-dong Xing, Hao Wang, Jian-guo Zhi, Yan-ping Bao

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    DOI:10.2355/isijinternational.ISIJINT-2020-678

    Abstract

    In this work, the melting process and reaction behaviour of cerium ferroalloy in the liquid ultra-low carbon interstitial free steel was investigated through a special designed hot crucible experiment using standard metallographic techniques including SEM, EDS, XRF, and XRD in combination with the thermodynamic software FactSage 7.2. The evolution mechanism of cerium-containing phases in the cerium ferroalloy during the melting process was proposed. The cerium-containing phases stretched and migrated along the direction of heat flow, in further the arms of the network structures became thinner and finally dissolved into the molten steel. It was concluded that the thinner of network structures' arms, the higher of the Ce content in cerium-containing phases. During the melting process, the cerium content in the cerium-enriched phase was increased from 43.9 wt% in the matrix of the cerium ferroalloy to 90.44 wt% in the reaction zone, and the average width of the network arms was decreased from 18 µm to 2 µm accordingly. The main reaction products in the interface among cerium ferroalloy, molten steel, and slag were Ce2O3 and CeAlO3.

  • Time-resolved and in-situ Observation of Semisolid Deformation in Al–Cu Alloys with Equiaxed and Columnar Grain Structures by Using a Combination Technique of 4D-CT and 3DXRD

    Taka Narumi, Takumi Nakata, Ryuya Kobayashi, Hideyuki Yasuda

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    DOI:10.2355/isijinternational.ISIJINT-2020-650

    Abstract

    Time-resolved combined absorption tomography and three-dimensional X-ray diffraction was developed to study semisolid deformation of metallic alloys, which combined time-resolved tomography and three-dimensional X-ray diffraction microscopy (3DXRD). The combined technique allowed observation of configuration and crystallographic orientation of solid grains, whereby translation and rotation of solid grains induced by interaction between solid grains during semisolid deformation was analyzed. During the compression tests of a semisolid Al–10mass%Cu alloy with the equiaxed grain structure, translation and rotation of solid grains rather than the plastic deformation played a dominant role in the deformation until strain reached -0.04. In a portion of the specimen, a gap between solid grains expanded owing to the interaction between solid grains, and consequently apparent volume expansion (dilatancy) occurred. The solid grains around the expanded region possessed similar rotational axis directions, which were perpendicular to the normal direction of the expanded region. As the compression proceeded, both translation/rotation and the plastic deformation of solid grains occurred owing to an increase in physical contact between solid grains. For a semisolid Al–10mass%Cu alloy with the columnar grain structure, solid grain comprised a single crystallographic domain. Inflection of the dendrite arms was confirmed by 3DXRD, where the compression of strain at -0.25 caused the grain to be inflected up to 12 degrees. The strain distribution in the grain was estimated using the inflection angle. In-situ observation revealed that the behaviors of solid grains and the liquid phase in semisolid alloys during the compression tests differed according to the structure.

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  • Improvement of Bragg-edge Neutron Transmission Imaging for Evaluating the Crystalline Phase Volume Fraction in Steel Composed of Ferrite and Austenite

    Hirotaka Sato, Miyuki Sato, Yuhua Su, Takenao Shinohara, Takashi Kamiyama

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    DOI:10.2355/isijinternational.ISIJINT-2020-257

    Abstract

    The Bragg-edge neutron transmission imaging method can quantitatively visualize various types of crystalline microstructural information inside a bulk material over a large visualization field area. In this study, we investigated and improved both the experimental method and the data analysis method for the evaluation of crystalline phase volume fraction in steel composed of ferrite/martensite and austenite. For wavelength-resolved neutron transmission imaging experiments, we confirmed that accurate measurement of neutron transmission intensities was crucial. Therefore, the background neutrons scattered from a sample must be reduced. Simultaneously, we confirmed that a neutron wavelength resolution of approximately 1% was required. For the data analysis of the measured Bragg-edge neutron transmission spectrum, we used double March-Dollase orientation distribution functions for each crystalline phase to achieve effective spectrum correction of the crystallographic texture effect. As a result, this data analysis method allows improved evaluation of the crystalline phase volume fraction, compared with the use of a single March-Dollase function for each phase.

  • Effects of Iron Ores on the Combustion Behavior of Coke and NOx Emission during Sintering Process

    Zhigang Que, Xianbin Ai

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    DOI:10.2355/isijinternational.ISIJINT-2020-222

    Abstract

    Calcium ferrite could promote the CO–NO reduction reaction, and its formation is affected by iron ores during sintering process. In present study, effects of iron ore coating layers on coke combustion rate and NOx emission were investigated in a visualize combustion equipment, and an optimized ore blending structure was proposed by sinter pot test. Due to the melting of iron ore coating layers at high temperature, coke transformed from coated to naked. With increasing of the binary basicity of the iron ore coating layers, the formation of calcium ferrite increased, resulting in increasing of the melt fluidity. The lower the formation temperature of the melts, the sooner coke was exposed, and the peak combustion rate linearly increased with the melt fluidity of iron ore coating layers. Meanwhile, compared to the high-silicon ores, the maximum NOx emission concentration and conversion rate of N element were lower with the low-silicon ores. NOx emission concentration showed an inverted W-shape trend and had an 8-shape relation with coke combustion rate. Due to the difference of the capability of calcium ferrite formation in coating layers, the conversion rate of N element was linearly negative and positive correlated with the basicity of iron ore coating layers and mass of CO emission, respectively. In addition, with the proportions of the low-silicon limonite and hematite increased in sinter mixture, NOx emission gradually decreased. As a consequence, with exclusively using low-silicon lignite and hematite in sinter mixture, NOx emission decreased by about 20% and sinter indexes significantly improved.

  • Iron Ore Sintering in Milli-Pot: Comparison to Pilot Scale and Identification of Maximum Resistance to Air Flow

    Tejbir Singh, Huibin Li, Guangqing Zhang, Subhasish Mitra, Geoffrey Evans, Damien O’dea, Tom Honeyands

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    DOI:10.2355/isijinternational.ISIJINT-2020-574

    Abstract

    In the iron ore sintering process, the resistance to air flow is a major factor in deciding the flame front speed, which influences the sinter productivity and quality. In this work, pressure drop during sintering and the resistance to air flow was investigated in milli-pot sintering for different coke rates. The sintering experiments were conducted in a milli-pot (diameter 53 mm, height 400 mm) and pressure and temperature were measured at the same locations in the bed by four taps located equidistant to each other. The yield of sinter product was measured following a modified drop test and the mineralogy of the sinter product was analysed. The results from milli-pot sintering were then compared to the reported results from standard pilot-scale sintering, and it was found that the lower half of the milli-pot bed gave a reasonable representation of the pilot-scale sintering process. The results of sinter mineralogy, yield and productivity of the lower half of milli-pot at 5.5–8.0% coke rate were found to be similar to pilot-scale sintering tests at a corresponding coke rate from 3.5 to 5.5%. The maximum resistance to air flow in the bed was found to be in the region between the leading edge of the flame front at ~100°C and the trailing edge of the flame front at ~1200°C. This suggests that the maximum resistance to air flow includes the effect of de-humidification and combustion in addition to the high temperature "flame front" region usually defined at temperatures above 1100°C or 1200°C.

  • CO Desorption and Absorption in Molten Steel: A Review

    Zhuangzhuang Liu, Peter Tom Jones, Bart Blanpain, Muxing Guo

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    DOI:10.2355/isijinternational.ISIJINT-2020-509

    Abstract

    Previous work on the mechanism of carbon monoxide absorption and desorption from liquid steel/iron is reviewed. The experimental set-up employed in these studies is summarized and the characteristics of each methodology are discussed and compared. The reaction kinetics, particularly the rate-limiting step of the CO gas-molten steel/iron reaction is analysed with respect to experimental parameters, comprising temperature, CO partial pressure in the gas mixture, gas flow rate, crucible materials, and carbon and oxygen content in the steel/iron. To further understand the CO absorption and desorption mechanisms in liquid steel, suggestions for future work are provided.

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    3. Effects of Stress and Plastic Strain on Hydrogen Embrittlement Fracture of a U-bent Martensitic Steel Sheet ISIJ International Vol.61(2021), No.4

  • On the CO Desorption and Absorption in Liquid Low-carbon Steel

    Zhuangzhuang Liu, Peter Tom Jones, Martin Kendall, Bart Blanpain, Muxing Guo

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    DOI:10.2355/isijinternational.ISIJINT-2020-510

    Abstract

    CO absorption and desorption in liquid steel comprise highly significant reaction mechanisms for steelmaking operations such as decarburization, ladle degassing, and the production of rimming steel ingots. However, until present the difference in the mechanism of CO absorption versus desorption has not been clarified. In this study, the CO desorption and absorption experiments were performed by blowing Ar + CO (0% and 5% in volume fraction) gas mixture bubbles into liquid steel with low carbon content (12–19 ppm). The experimental data show that the rate of CO desorption is much lower than that of absorption. The carbon mass transfer in liquid steel is found to be the rate-limiting step with respect to CO absorption. For CO desorption, in addition to the carbon mass transfer, the interfacial reaction at the gas-liquid interface is found to pose an additional kinetic barrier. The present finding improves the understanding of the basic C–O reaction kinetics involved in many steelmaking processes and contributes to accurate modeling and precise control of industrial practices such as basic oxygen furnace (BOF) and argon oxygen decarburization (AOD).

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    3. Effects of Stress and Plastic Strain on Hydrogen Embrittlement Fracture of a U-bent Martensitic Steel Sheet ISIJ International Vol.61(2021), No.4

  • Evolution of Inclusions with Ce Addition and Ca Treatment in Al-killed Steel during RH Refining Process

    Ruming Geng, Jing Li, Chengbin Shi

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    DOI:10.2355/isijinternational.ISIJINT-2020-672

    Abstract

    The evolution of inclusions with Ce addition and Ca treatment in Al-killed steel during RH refining process was investigated through experimental observations and thermodynamic calculations. The results indicated that the typical inclusions before Ce addition are CaO–Al2O3 inclusions, which were a liquid state during RH refining. After Ce addition, the typical inclusions was transformed from calcium aluminate inclusion to (Ca–Ce–S–O)+(Ce–Al–Ca–O) complex inclusion. After Ca treatment, the types and morphologies of typical inclusions in steel did not change. Experimental observation and thermodynamic calculations shown that a certain amount of Ca addition can't affect the formation of Ce-containing inclusion, which may indicate that Ca treatment should not be carried out for rare earth treated steel.

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    3. Mathematical Modeling on Transient Multiphase Flow and Slag Entrainment in Continuously Casting Mold with Double-ruler EMBr through LES+VOF+DPM Method ISIJ International Vol.61(2021), No.3

  • Quantitative Evaluation of Solute Hydrogen Effect on Dislocation Density in a Low-carbon Stable Austenitic Stainless Steel

    Kengo Kamei, Yuuki Koumura, Arnaud Macadre, Koichi Goda

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    DOI:10.2355/isijinternational.ISIJINT-2020-677

    Abstract

    The effects of hydrogen on dislocations are generally understood through Transmission Electron Microscope studies. Novel methods of X-Ray Diffraction analysis provide the means of quantitative measurements of dislocation densities and the evolution of cross-slip in austenitic stainless steels. In a low-carbon austenitic stainless steel (SUS316L) with and without solute hydrogen, and strained by cold-rolling, the maximum dislocation densities were measured, with hydrogen clearly increasing the maximum dislocation density, and the ratio of screw dislocations was shown to be similar regardless of hydrogen content.

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  • 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

17 Apr. (Last 30 Days)

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