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

ISIJ International Advance Publication

  • A shallow neural network for recognition of strip steel surface defects based on attention mechanism

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    DOI:10.2355/isijinternational.ISIJINT-2022-201

    This research proposes an efficient strip steel surface defect classification model (ASNet) based on convolutional neural network (CNN), which can run in real time on commonly used serial computing platforms. We only used a very shallow CNN structure to extract features of the defect images, and an attention layer which makes the model ignore some irrelevant noise and obtain an effective description of the defects is designed. In addition, a nonlinear perceptron is added to the top of the model to recognize defects based on the extracted features. On the strip steel surface defect image dataset NEU-CLS, our model achieves an average classification accuracy of 99.9 %, while the number of parameters of the model is only 0.041M and the computational complexity of the model is 98.1M FLOPs. It can meet the requirements of real-time operation and large-scale deployment on a common serial computing platform with high recognition accuracy.
  • Detection and Characterization of Organic Gases during Coal Carbonization Using VUV-SPI-TOFMS

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    DOI:10.2355/isijinternational.ISIJINT-2022-397

    A VUV-SPI-TOFMS system was developed for the continuous analysis of pyrolysis gases generated during coal carbonization and aromatic molecules were detected using high-resolution quantitative techniques. Although IR spectroscopy is suitable for detecting low-molecular-weight gases present in dry distillation gas, such as CH4 and CO2, it is not sensitive to aromatic hydrocarbon gases. On the other hand, the VUV-SPI-TOFMS technique is applicable for the quantification of low-concentration gases at the ppb concentration level, including aromatic hydrocarbons, generated during coal carbonization, which entails continuous heating from room temperature to 800 °C. Benzene and toluene were predominantly detected at 540–590 °C in the dry distillation gas of bituminous coal having relatively low oxygen concentration, whereas gases containing OH groups, such as phenol and cresol, are predominantly generated from sub-bituminous coal and lignite with high oxygen concentrations. Solid 13C NMR spectra obtained for each natural coal sample exhibited substantial proportions of oxygen bound to aromatic carbons (aromatic–O) in young coals. The temperature range at which cyclohexane was generated was found to be lower than that of aromatic molecules, indicating that coals releasing it may exhibit a structure that is more susceptible to thermal decomposition.
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    1. Precipitation Behavior of Magnetite Phase during Modified Nickel Slag Treated by Molten Oxidation ISIJ International Advance Publication
  • Precipitation Behavior of Magnetite Phase during Modified Nickel Slag Treated by Molten Oxidation

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    DOI:10.2355/isijinternational.ISIJINT-2022-134

    Nickel slag is a kind of solid waste with a high yield and low utilization rate. However, there is a large amount of Fe in nickel slag, which mainly exists in the form of fayalite. In this study, nickel slag is used as raw material. The addition of CaO can destroy the network structure of fayalite, and the iron-rich phase can be oxidized to magnetite under oxidation condition. It is beneficial to the recovery of iron resources. The effect of basicity on structural reconstruction of molten slag and precipitation of magnetite is investigated. The results show that when the basicity is 0.38~1.50, the degree of polymerization of silicate structure decreases with the increase of basicity. When the temperature is 1450~1500°C, viscosity of slag decreases first and then increases with the increase of basicity. The viscosity is the lowest with the basicity of 0.90, and the granular magnetite begins to precipitate during the non-equilibrium solidification at 1455°C. The growth rate of the magnetite is 1.20 μm/s at 0~10 s, which is significantly higher than the magnetite growth rate of 0.16 μm/s at 10~22 s, and the grain size of the magnetite remains unchanged after 22 s.
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    1. Detection and Characterization of Organic Gases during Coal Carbonization Using VUV-SPI-TOFMS ISIJ International Advance Publication
  • Behavior and kinetic mechanism analysis of dissolution of iron ore particles in HIsmelt process based on high-temperature confocal microscopy

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    DOI:10.2355/isijinternational.ISIJINT-2022-261

    In this study, high-temperature confocal microscopy (HTCM) was used to perform in situ observations of the dissolution of iron ore particles in slag at different temperatures. Moreover, the shrinking core model (SCM) is used to explain the kinetic mechanism of the dissolution of iron ore particles. The area of the undissolved fraction of iron ore particles was used to analyze the dissolution rate of iron ore particles. The results show that the kinetic mechanism of dissolution of iron ore particles can be well explained by the SCM. The dissolution of iron ore particles is controlled by the diffusion of iron ore fractions in the boundary layer. The dissolution temperature, the concentration difference of iron ore fraction at the two ends of the boundary layer, and the initial particle size of iron ore particles affect the dissolution rate of iron ore particles. The dissolution rate constant was fitted by introducing a dissolution mechanism. The activation energy of iron ore dissolved in the CaO-SiO2-MgO-Al2O3-FeO slag system is 679.13 kJ/mol. The equation for the dissolution rate constant of iron ore in HIsmelt slag is summarized.
  • Heat conduction through different slag layers in mold. Thermal conductivity measurement of commercial mold fluxes

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    DOI:10.2355/isijinternational.ISIJINT-2021-544

    The thermal conductivity of two commercial mold fluxes has been investigated using the transient hot-wire method in the temperature range 298 K to 1573 K. Experiments were conducted on granules, sintered granules, molten fluxes and glassy samples under ambient atmosphere. Characteristic temperatures of the mold fluxes were investigated using a hot stage microscope. Results are discussed in the context of the characteristic temperatures, the particle size of granules, the bulk density and the structure of the mold fluxes. The temperature dependence of the thermal conductivity for granules of mold fluxes is positive in the temperature range of 298 to 873 K (λ = 0.058 + 1.245 x 10-4 T). The further temperature increase causes the rapid increase of the thermal conductivity above the temperature, at which the granules start to sinter Tdeformation. The thermal conductivity of the glassy sample is around two times lower than the thermal conductivity of the devitrified sample. The effect of the glass transition temperature on the thermal conductivity was shown. The thermal conductivity rapidly increases above the glass transition temperature in the glass transition region as the temperature rises and decreases above the softening temperature Tsoftening. The further temperature increase caused the crystallization of the sample. The crystallization of the sample was observed at TTg + 100 K. Moreover, results show the dependence of the thermal conductivity of molten mold fluxes on the basicity (CaO/SiO2) at 1573 K.
  • Activity of Chromium Oxide in Calcium Silicate Bearing Molten Slag for Highly Clean Chromium Steel Refining Process

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    DOI:10.2355/isijinternational.ISIJINT-2022-368

    Thermodynamic properties of chromium oxide in molten slags are essential to optimizing stainless steel refining processes and reduction processes of chromium ores. The present study conducts chemical equilibrium experiments at 1823 K (1550 °C) under different oxygen partial pressures in order to investigate chromium oxide activity coefficient in CaO-CaF2-MgO-Al2O3-SiO2-MnO-CrOx slags with low chromium content taking the effect of MgO addition into consideration. An increase in MgO initial content from 0 to 20 mass % increases the activity coefficient of CrO𝑥 under the oxygen partial pressures of 6.38×10-12 atm and 1.60×10-10 atm. It is found that lower oxygen partial pressure may reduce solid phase formation. The present study recommends the usage of 29 mass % CaO-5 mass % CaF2-20 mass % MgO-10 mass % Al2O3-29 mass % SiO2-5 mass % MnO-2 mass % Cr2O3 slag to reduce chromium loss at 1823 K (1550 °C) under the oxygen partial pressure of 6.38×10-12 atm, where the activity coefficient of CrO𝑥 is the highest in the slags without solid phase.
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    3. Change of Spinel in High Ca Treament at 38CrMoAl Steel ISIJ International Vol.62(2022), No.11
  • Effects of basicity and Al2O3 content on the crystal structure of silico-ferrite of calcium and aluminum

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    DOI:10.2355/isijinternational.ISIJINT-2022-375

    Silico-ferrite of calcium and aluminum (SFCA) is the primary bonding phase of iron ore sinter, the world's most popular artificial feed material for ironmaking. However, fundamental questions about its crystal structure and the atomic occupancy at each site remain unanswered. To date, the quantitative phase analysis (QPA) of SFCA has mostly been conducted using two-dimensional information and only provided information regarding phase fractions. In contrast, Rietveld analysis uses bulk data and provides lattice information in addition to phase fraction information. This study investigates the effects of basicity and Al2O3 concentration on the crystal structure and atomic site occupancy of SFCA through Rietveld analysis of the X-ray diffraction patterns. Raman spectroscopy and micro-Vickers hardness tests are used to verify the analytical results. Changes in the chemical composition affect the atomic occupancies at sites Si1 (Si-Al), Ca2 (Ca-Fe), Ca3 (Ca-Fe), Fe4 (Fe-Al), Fe5 (Fe-Al), and Fe7 (Fe-Al). With increasing basicity or Al2O3 content, the microhardness increases linearly, which can be attributed to the modification of atomic site occupancies. The crystalline structure obtained in this study is essential for developing a thermodynamic model of SFCA that can be used to predict its phase stability. This information can then be used to design a novel high-performance iron ore sinter.
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    2. Effect of Cooling Method on the Mineralogy and Stability of Steel Slag ISIJ International Vol.62(2022), No.11
    3. Change of Spinel in High Ca Treament at 38CrMoAl Steel ISIJ International Vol.62(2022), No.11
  • Effect of Molten Steel Composition on Inclusion Modification by Calcium Treatment in Al-Killed Tinplate Steel

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    DOI:10.2355/isijinternational.ISIJINT-2022-274

    The effects of oxygen, magnesium, and sulfur content in Al-killed tinplate steel on the "liquid zone" of inclusion modification by calcium treatment were clarified through industrial experiments and thermodynamic calculation, and the characteristics of inclusions modification were studied. The results show that the inclusions in molten steel before calcium treatment are mainly Al2O3 inclusions. The inclusions in molten steel are CaO·Al2O3 after calcium treatment with a holding time of 10min, while the inclusions are mainly 3CaO·Al2O3 with a holding time of 30min. And 12CaO·7Al2O3 inclusions are observed in molten steel when T.O content increases to 40ppm after calcium treatment with a holding time of 30min. As the increase of T.O content from 10ppm to 40ppm, the difference between the upper and lower limits of the critical calcium content corresponding to the "liquid zone" increases from 5ppm to 17ppm. The increase of T.O content in molten steel will enlarge the "liquid zone" range of inclusion modification by calcium treatment, and increase the critical calcium content. With the increase of magnesium content in molten steel, the liquid phase ratio of inclusions modification by calcium treatment decreases. To obtain the liquid phase ratio of inclusions at least 50% in molten steel, not only the calcium content in steel should be strictly controlled, but also the magnesium content in steel should not be larger than 15ppm. With the increase of sulfur content in molten steel, the "liquid zone" range of inclusion modification by calcium treatment becomes narrow.
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    3. Characteristics and Formation Mechanism of Complex TiN Inclusions in 20CrMnTi Gear Steel ISIJ International Vol.62(2022), No.11
  • Effects of Blast Furnace Representative Temperatures and Gas Compositions on Coke Reactivity

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    DOI:10.2355/isijinternational.ISIJINT-2022-396

    The effects of coke mineralogy on coke reactivity under conditions representative of the blast furnace were studied. Coke samples were reacted under coke reactivity index (CRI) like conditions (1100°C, 100% CO2) and at higher temperatures and atmospheres designed to replicate conditions lower in the blast furnace.The effects of the minerals on reactivity changed as the temperature increased and the atmosphere was modified. At the lower temperatures investigated (1100-1350°C) with CO2 present in the gas, gasification of the coke by CO2 dominated. The effects of minerals in the coke on gasification by CO2 under these conditions were similar to their reported effects on reactivity in the CRI test. At the highest temperature investigated, (1600°C), with no CO2, the mineral-carbon reactions dominated. The main reaction was the reduction of the silica in the coke. These results show that when coke-gasification is dominant, CRI data can be related to conditions beyond the temperature and gas environment the data were obtained, to the higher temperatures and less oxidising conditions of the blast furnace. At higher temperatures, mineral-carbon reactions are dominant, and more data in addition to that of the CRI, may be required to understand coke behaviour in the blast furnace.IMDC and RMDC within the coke were identified with the aid of the CGA technique, and the changes in the carbon structures within the coke studied using Raman spectroscopy. The carbon structures within the coke became more graphitic at 1600°C, with the change in RMDC greater than that in IMDC.
  • Laser Cladding Strengthening Test on the Surface of Flatness Rollers

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    DOI:10.2355/isijinternational.ISIJINT-2022-262

    Contact-type flatness meters are the key detection equipment in the production of high-end cold-rolled thin strips. The surface performance of a flatness meter roller is very important to improve its service life and ensure the surface quality of strip products. To improve the surface wear resistance and prolong the service life of a seamless flatness meter roller, it was subjected to a surface strengthening treatment by laser cladding an Fe-based wear-resistant alloy. The performance of the flatness meter roller strengthened by laser cladding and quenching was determined by tests. The results show that the laser cladding-strengthened layer forms a solid metallurgical bond with the roller matrix. When the laser cladding-strengthened surface meets the surface strength, hardness and thickness requirements of the cladding-strengthened layer, the average width of wear marks in the 30-minute sliding friction wear test is only 1.43 mm. The wear resistance of the cladding-strengthened layer is approximately 24% higher than that of the quenching-strengthened layer. This paper proposes a new approach for the research and development of the surface strengthening technology of cold-rolled strip seamless flatness meter rollers.
  • Flow curve of superalloy 718 under hot forming in a region of γ” precipitation

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    DOI:10.2355/isijinternational.ISIJINT-2022-340

    This study aims to formulate a constitutive equation to accurately determine the flow stress of superalloy 718 for effective production of gas turbine disks. A hot-compression test with superalloy 718 at temperatures ranging from 900 to 1000 °C, a reduction rate of 67%, and strain rates of 0.1, 1, and 10 s-1, respectively, was conducted to analyze the flow stress in the dynamic precipitation region. An accurate flow stress curve was obtained for each strain rate and initial temperature. The flow curves obtained at a deformation temperature of 900 °C and strain rates of 0.1 and 1 s-1, represent a combination of work-hardening and dynamic recovery. Dynamic recrystallization (DRX) behavior was observed under other deformation conditions. At a deformation temperature of 950 °C and each strain rate, the strain at the onset of DRX (εc) decreases, and DRX tends to occur rapidly. In addition, the steady-state stress at a strain rate of 1 s-1 was greater than that at a higher strain rate of 10 s-1. The lowest steady-state stress among all the experimental conditions was observed at a strain rate of 10 s-1. This may be attributed to the role of nucleation sites, precipitation hardening caused by dynamically precipitated (" phases at approximately 950 °C and a strain rate of 1 s-1, and dynamic softening effects due to significant heat generated by deformation at a strain rate of 10 s-1. A new constitutive equation for the generalized flow curve of superalloy 718 was obtained by considering these metallurgical phenomena.
  • State of Deadman in Blast Furnace Hearth and Its Internal Phase Distribution Characteristics

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    DOI:10.2355/isijinternational.ISIJINT-2022-363

    The state of deadman in hearth is important for the long campaign life of blast furnace (BF). In order to clarify the influence of deadman on sidewall erosion, the corresponding relationship between the shape of deadman and sidewall erosion was studied, the fundamental reason for the difference of sidewall erosion was analyzed, the influence mechanism of slag-coke interface and iron-coke interface on the coke in deadman was explored based on the phase distribution in deadman. The results show that: The shape of circumferential bulge at the root of deadman is a common feature of BFs, this feature is the main reason for the serious erosion of sidewall, and the serious erosion area of sidewall corresponds to the root position of deadman. The deadman shows a dynamic evolution law of sinking and floating under the action of force in the smelting process of BF, the depth of slag and iron level in hearth has the greatest influence on the deadman. The difference of central voidage of deadman is the fundamental reason for the difference of sidewall erosion for BFs in which the deadman is in the same floating state. Slag-coke interface and iron-coke interface commonly exist in hearth. The dissolution reaction at iron-coke interface makes carbon in coke continuously migrate into molten iron, which makes the graphitization degree of coke increase, the coke is easy to pulverize, this is the main mechanism of coke deterioration and renewal in deadman. The enrichment of harmful element K at slag-coke interface makes the coke expand and crack, the coke matrix is easier to peel off, which accelerates the deterioration process of coke.
  • Numerical analysis for interaction of fluid and sphere penetrating into liquid bath

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    DOI:10.2355/isijinternational.ISIJINT-2022-404

    In the steelmaking process, it is necessary to decrease impurities in steel to meet the increasing demand for high-grade products. Top blowing and blasting of powder reagent are desirable for the purpose and the deeper penetration of particles into the bath is important for efficient refining. In the present work, CFD calculation with VOF (Volume of Fluid) method and dynamic mesh was executed to study the reported penetration and residual bubble behavior of polypropylene sphere (diameter of 9.6 mm) with a static contact angle of 87 ° and 143 ° and an entry solid sphere velocity of 0.63, 0.89, and 1.53 m/s in the water model experiments. Calculated results showed the numerical analysis could evaluate the formation and breakup of air column behind the sphere and the generation of consequent residual bubble on the sphere. Good wettability and high entry speed promoted the deeper penetration of the sphere. Calculated dynamic contact angle on the basis of Kistler's model indicated that the difference between static and dynamic contact angles was within 13.7 ° in the present conditions and the discrepancy could not wield a substantial influence on the result of CFD calculation. The adoption of base and refined mesh without parallel zone around the sphere could not give a good agreement with the experimental results. On the other hand, the use of layer mesh was appropriate for reproducing the penetration depth and residual bubble volume observed in the experiments.
  • Dehydration reactivity of Mg(OH)2 containing low amounts of Li-additives for thermochemical energy storage

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    DOI:10.2355/isijinternational.ISIJINT-2022-082

    Mg(OH)2 is a chemical heat storage material suitable for the utilization of unused heat at 300–400 °C. It has been reported that the addition of Li compounds to Mg(OH)2 promotes the dehydration of Mg(OH)2. However, the demand for Li compounds has increased in recent years and the price of Li compounds is relatively high. Therefore, the purpose of this study is to enhance the dehydration reactivity of Mg(OH)2 with a small amount of Li. In this study, several alkali metal chlorides and hydroxides such as LiCl and NaOH or KOH were added to Mg(OH)2, and the dehydration reactivity and composition of the corresponding mixtures were investigated. The samples prepared using 5 mol% LiCl and 10 mol% NaOH (LiCl-5NaOH-10) or 2.5 mol% KOH (LiCl-5KOH-2.5) showed excellent dehydration reactivity and were dehydrated below 300 °C with comparatively lower amounts of Li compounds than those reported in previous studies. These results indicate that these samples have great potential as low-cost chemical heat storage materials. However, the stabilities of these samples in air are quite different. Based on X-ray diffraction analysis of the data, the results are associated with the composition of Cl-, OH-, Li+, Na+, and K+.
  • Analytical model to predict the free surface profile of outgoing material in oval-to-round pass rolling when cross-section of incoming material is not circular and roll gap changes

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    DOI:10.2355/isijinternational.ISIJINT-2022-248

    There is a strong demand for the development of an analytical model that is necessary to quickly perform the roll pass design of hot rod (or bar) rolling process. In line with this, this study proposes an analytical model that predicts the free surface profile (FSP) of outgoing material in oval–to–round pass rolling sequence even when the cross-section of incoming material is not circular and roll gap changes. The separation angle and point were calculated by interpolating the intersection angle and the groove angle. FSP passing through the maximum spread of outgoing material and the separation point is calculated based on a weighting function depending on the geometry of incoming cross-section and roll groove. The performance of the proposed model was verified by finite element analysis that simulated 10-pass continuous bar rolling process. FSPs predicted by the analytical model and those by FE simulation were in good agreement. In addition, the proposed analytical model was applied to other 4-pass continuous rolling. It has been shown that it is possible to quickly calculate the amount of roll gap adjustment in each pass that improves the roundness of the material (from 83.57 to 98.65) in the final pass without the time-consuming FE analysis.
  • Applicability of alkaline waste and by-products as low cost alternative neutralizers for acidic soils

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    DOI:10.2355/isijinternational.ISIJINT-2022-247

    Acidic soils can induce several negative impacts, especially in agricultural fields. To address these problems, lime is often applied to increase the pH value of acidic soils. Calcium carbonate is the most common and conventional agricultural lime; however, it is a natural and scarce resource. To promote a recycling-based society, alternative neutralizers with lower costs that use alkaline waste and by-products are essential. Therefore, we investigated the effectiveness and applicability of three types of autoclaved lightweight aerated concrete, recycled concrete, steel slag as basic oxygen furnace slag, and fly ash (mainly particles less than 0.106 mm and 0.106–2 mm in size), as alternative neutralizers for three representative acidic soils through laboratory neutralization experiments. The neutralization performance was evaluated by measuring the additive weight percentage of each neutralizer required to convert each acidic soil to neutral soil (pH 7). For neutralizers with two particle sizes, the finer fraction clearly showed lower additive weight percentages indicating higher neutralization performance. Among the six tested alkaline waste and by-products, the steel slag exhibited the highest neutralization performance. In particular, finer fraction steel slag exhibited a high neutralization performance, similar to that of the conventionally used calcium carbonate. This result suggests that fine steel slag (particle size < 0.106 mm) is the most promising and suitable alternative neutralizer.
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    1. Iron-Carbon Interface Phenomenon and Reaction Behavior Analysis in Blast Furnace Hearth ISIJ International Advance Publication
  • Formation Behavior of M2C and M6C Eutectic Carbides in M42 High-Speed Steel

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    DOI:10.2355/isijinternational.ISIJINT-2022-264

    M2C eutectic carbide favours the mechanical properties of high-speed steels, but is often largely replaced by coarse M6C eutectic carbide in as-cast M42 steel. To deeply understand the formation behavior of M2C and M6C carbides, M2C and M6C eutectic alloys were prepared according to the composition of M2C and M6C eutectic mixtures in M42 steel, and their solidification behavior was investigated. Only one type of eutectic carbide is formed in water-quenched M2C and M6C eutectic alloys, i.e., M2C and M6C, respectively. Both M2C and M6C carbides appear in the alloys cooled at 3°C/min. However, the M2C eutectic alloy was more significantly affected in terms of carbide type by the low cooling rate. According to thermodynamic calculation, M6C carbide in the M2C eutectic alloy is only slightly more stable in thermodynamics above 1210.1 °C, below which M2C carbide becomes stable. For the M6C eutectic alloy, however, only M6C eutectic carbide is thermodynamically stable. Furthermore, thermodynamic results reveal that besides raising the content of C and V, reducing the content of Mo can also greatly promote the formation of M2C carbide in M42 steel, which updates the traditional opinion on the influence of Mo element. The results in this work provide the underlying insights needed to promote the formation of M2C carbide in M42 steel by fine-tuning the composition.
  • Iron-Carbon Interface Phenomenon and Reaction Behavior Analysis in Blast Furnace Hearth

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    DOI:10.2355/isijinternational.ISIJINT-2022-312

    The iron-carbon interface plays an important role in hearth, the dissection investigation of BFs was carried out to clarify the iron-carbon interface phenomenon and reaction behavior. The results show that the iron-coke interface can be divided into two types: partial coverage and overall coverage. The molten iron penetration from the interface to the center of coke is found. The hot face of residual carbon brick has obvious embrittlement layers, the pulverization phenomenon of carbon brick is observed, cracks appear in the carbon brick near the iron-carbon brick interface. Many holes in coke are filled with iron and slag, the filling rate increases as the coke moves towards the lower part of hearth. The graphitization degree of coke increases through dissolution precipitation and carbide transformation mechanism, the high graphitization of coke caused by carburization at iron-coke interface is the essential cause of coke deterioration. The flexural strength of carbon brick decreases under the alternate process of penetration and dissolution, effect of Zn. The critical temperature difference for crack generation decreases from 286 °C to 208 °C after the reaction, which makes it easier for the carbon brick to produce cracks. These cracks produce brittle embrittlement layers, which accelerates the erosion of carbon brick. The carburization of coke and the dissolution carburization of carbon brick are carried out simultaneously in hearth, there is a competitive carburization between iron-coke interface and iron-carbon brick interface. The methods of controlling competitive carburization are put forward to delay the erosion of carbon brick.
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  • Effect of N Content on Precipitated Phase and Long-term Aging Stability of 9CrMoCoB Steel

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    DOI:10.2355/isijinternational.ISIJINT-2022-313

    Microstructure observation and hardness analysis of 9CrMoCoB steel with different N content during long-term aging at 620 °C were carried out by Thermo-Calc thermodynamic calculation, scanning electron microscope, transmission electron microscope and hardness test. The results show that the average size of M23C6 phase increases first with the extension of aging time, then stabilizes after aging for 2000h, and decreases gradually with the increase of N content. The Laves phase precipitated after aging for 1000h and coarsened continuously with the aging time prolonging. The coarsening rate tended to be flat after 2000h. The average size of Laves phase decreased gradually with the increase of N content. With the increase of N content, the average diameter and unit number of BN inclusions increase gradually, and the unit number of BN inclusions larger than 2 μ m increases obviously when N content is 0.025% and 0.030%. The hardness of 9CrMoCoB steel decreases gradually with the aging time and tends to be stable after aging for 2000 h. With the increase of N content, the hardness and stability of 9CrMoCoB steel first increase and then decrease, and both reach the maximum when N content is 0.020%. Considering comprehensively, in order to give full play to the strengthening effect of B and N in steel and improve the properties and stability of 9CrMoCoB steel, the optimal control range of N content in steel is around 0.020%.
  • A review on the humic substances in pelletizing binders: Preparation, interaction mechanism, and process characteristics

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    DOI:10.2355/isijinternational.ISIJINT-2022-306

    Humic acid is inexpensive, and has a wide range of sources and a strong adsorption force with the surface of iron ore, and the size of its adsorption force is affected by some factors such as humic acid concentration, pH of the solution, and metal cations. The modified humic acid pellet binder (MHA) with strong adhesion and high viscosity was obtained through the separation and purification of solid wastes such as lignite and weathered coal and chemical modification treatment and successfully applied in the production process of iron ore pellets. After industrial tests, MHA can significantly improve the strength of green and dry pellets, less residue after high-temperature roasting, less metallurgical pollution, high strength of fired pellets, and can partially or completely replace bentonite.
  • Decarburization kinetics of Fe-C melt with CO2-O2 mixed gas by isotope tracing method

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    DOI:10.2355/isijinternational.ISIJINT-2022-321

    The partial substitution of O2 with CO2 in steelmaking process is an important technology to reduce CO2 emission and recycle. In order to improve CO2-O2 decarburization utilization, the decarburization kinetics of Fe-C melt with CO2-O2 mixed gas have been studied using 13CO2-18O2 dual isotope tracing method and established the decarburization kinetic model. The results show that less than 40% of the oxygen is partially replaced by CO2, which improves the O2 utilization involved in the decarburization reaction and the CO2 utilization is still more than 80%. For the rate limiting steps, regarding O2, it is governed by the mixed control mechanism involving gas-phase mass transfer and interfacial chemical reaction; regarding CO2, with the increase of CO2 partial pressure, the rate limiting step changes from the mixed control to gas-phase mass transfer control only. As bath temperature increase from 1723 to 1873 K, the overall decarburization rate increases; bath temperature mainly affects O2 decarburization rates, whereas, the rates of CO2 are not significantly affected. The apparent activation energy of CO2-O2 mixed gas decarburization is 21.5 kJ·mol-1.
  • Permanent strength of interstitial-free steel processed by severe plastic deformation and subsequent annealing

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    DOI:10.2355/isijinternational.ISIJINT-2022-328

    The permanent strengths of interstitial-free (IF) steels with different grain sizes and dislocation densities processed by severe plastic deformation (SPD) and subsequent annealing are systematically investigated. Permanent strength, which is athermal and time-independent, corresponds to the fundamental capability to bear stresses caused by external forces. Sufficiently long-time (24 h) stress relaxation tests were carried out and experimental stress–relaxation time relationships were extrapolated to estimate the permanent strength that remained after an infinite time passed. The flow stresses observed in standard uniaxial tension tests increased with repeated SPD processes, and the fraction of permanent strength to the observed flow stress was mostly above 65%. The permanent strength also increased with repetition of SPD processes, and subsequent low-temperature annealing further augmented the permanent strength. During SPD processes, the dislocation-related strengthening was dominant, while the grain-size-related strengthening was minor, i.e., the Hall–Petch relation does not hold. On the other hand, after low-temperature annealing, the grain-size-related strengthening became dominant, quickly replacing the dislocation-related strengthening. In a coarse-grain region, the grain-size-related strength was consistent with the classical Hall–Petch relation. It was confirmed that the original Hall–Petch relation holds only in the coarse-grain region and it indicates "softening with grain coarsening due to annealing", not "strengthening by grain refinement due to SPD".
  • Thickness classifier on steel in heavy melting scrap by deep-learning-based image analysis

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    DOI:10.2355/isijinternational.ISIJINT-2022-331

    Avoiding the contamination of tramp elements in steel requires the non-ferrous materials mixed in steel scrap to be identified. For this to be possible, the types of recovered steel scrap used in the finished product must be known. Since the thickness and diameter of steel are important sources of information for identifying the steel type, in this study, the aim is to employ an image analysis to detect the thickness or diameter of steel without taking measurements. A deep-learning-based image analysis technique based on a pyramid scene parsing network was used for semantic segmentation. It was found that the thickness or diameter of steel in heavy steel scrap could be effectively classified even in cases where the thickness or diameter of the cross-section of steel could not be observed. In the developed model, the best F-score was around 0.5 for three classes of thickness or diameter: less than 3 mm, 3 to 6 mm, and 6 mm or more. According to our results, the F-score for the class of less than 3 mm class was more than 0.9. The results suggest that the developed model relies mainly on the features of deformation. While the model does not require the cross-section of steel to predict the thickness, it does refer to the scale of images. This study reveals both the potential of image analysis techniques in developing a network model for steel scrap and the challenges associated with the procedures for image acquisition and annotation.
  • Soft sensors and Diagnostic Models Using Real Time Data of Blast Furnaces at Tata Steel

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    DOI:10.2355/isijinternational.ISIJINT-2022-246

    A huge amount of real time data of blast furnace process and quality are getting captured and analyzed for an in-depth understanding of process resulting in better control and improved performance. This paper describes how process visualization and diagnostic models are helping to generate additional insights and becoming useful tool for identification of factors for process efficiency improvement. These tools are important enabler for faster process performance diagnosis and for early indicator of performance deterioration. In earlier paper of this journal, few models and their usage in process analysis were discussed and, in this document, additional diagnostic tools viz. burden descent index, sounding ore by coke etc. are explained. 10)
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  • Effect of SiO2 content and mass ratio of CaO to Al2O3 on the viscosity and structure of CaO-Al2O3-B2O3-SiO2 slags

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    DOI:10.2355/isijinternational.ISIJINT-2022-288

    The development of mold fluxes for continuous casting is one of major challenges to produce high aluminum steel. The CaO-Al2O3-B2O3 based mold flux is one of the potential candidates for casting high aluminum steel but its composition and properties still need to be optimized. In this work, the effect of silica and mass ratio of CaO to Al2O3 on the viscosity and structure of slag are studied. The viscosity of CaO-Al2O3-B2O3-SiO2 slag with varying SiO2 content (3%, 5%, and 7%) and mass ratio of CaO to Al2O3 (0.8, 1, and 1.2) were measured by rotating cylinder method at temperatures between 1723K and 1873K. It was found that the addition of SiO2 leads to the increase of the slag viscosity and the activation energy increases from 178.6 to 203.4kJ/mol. In contrast, the increase of mass ratio of CaO to Al2O3 will reduce the viscosity of slag and the activation energy decreases from 227.1 to 191.0kJ/mol. The structures of glassy CaO-Al2O3-B2O3-SiO2 slags were investigated by Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Deconvolutions on Raman spectral reveal that silicon mainly exists as Q0(Si) and Q1(Si) in glasses. According to deconvolution results of XPS, as SiO2 content in glassy slag increases, the number of bridging oxygens increases, indicating a more polymerized structure. In contrast, the increase of the ratio of CaO to Al2O3 contributes to the depolymerization of glassy slag. The structural variations with different SiO2 contents and mass ratio of CaO to Al2O3 can be correlated to the viscosity variation of slag.
  • Effect of converter dust on phosphorus migration behavior in molten iron

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    DOI:10.2355/isijinternational.ISIJINT-2022-249

    In order to make better use of converter dust to achieve effective pre-dephosphorization of molten iron, the influence of the addition ratio of dedusting ash and oxide scale on dephosphorization of molten iron was compared, so as to reveal the reasons for the decrease of dephosphorization rate caused by dust. Through theoretical analysis, XRD, SEM-EDS, Raman and infrared spectroscopy, the influence of mineral phase structure, polymerization degree and phosphorus structure of pre-dephosphorization final slag on pre-dephosphorization was studied. The results show that when the proportion of dedusting ash in the oxidant increases from 0 to 25%, the dephosphorization rate decreases from 50.8% to 38.71%, and the dephosphorization rate increases to 50% after adding fluorite. The increase in the proportion of dedusting ash will lead to the decrease of phosphorus-rich phase and the increase of RO phase and iron-rich phase, which will affect the dephosphorization effect. When the dedusting ash ratio increased from 0% to 25%, the proportion of Q0(Si), Q0(P), Q1(P) and [FeO6]9- structures in the pre-dephosphorization final slag increased, which was beneficial to the diffusion in the slag, but unfavorable to the migration of phosphorus. In addition, by adding fluorite in the experiment with 25% dedusting ash, it was found that the molar fractions of Q1(Si), Q3(Si), Q0(P) and Q2(P) in the pre-dephosphorization final slag increased, and the phosphorus migrating into the silicon-oxygen network structure gradually increased. This study can provide reference for iron and steel enterprises to realize the secondary utilization of dedusting ash.
  • Interaction Coefficients of Cu and Sn with Mn in Molten Iron at 1873 K

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    DOI:10.2355/isijinternational.ISIJINT-2022-112

    Regarding the depletion of high-grade iron ore and an increase in steel scrap, a new ironmaking process that can utilize both low-grade iron ores and steel scraps is expected. When steel scrap is used as an iron source, tramp elements, such as Cu and Sn, are dissolved in hot metal. The tramp elements can affect the hot metal composition due to the thermodynamic interaction between tramp elements and other alloying elements. However, the thermodynamic interaction between Cu and Sn with Mn has not been known enough. In this work, the interaction coefficients between Cu and Sn with Mn were measured at 1873 K by a chemical equilibration technique using the liquid immiscibility of Fe and Ag as follows:εCuMn(in Fe) = −4.30 ± 0.78,eCuMn(in Fe) = −0.016 ± 0.003,εSnMn(in Fe) = −5.21± 0.55,eSnMn(in Fe) = −0.008 ± 0.001Moreover, the effects of scrap ratio (iron mass ratio of scrap to scrap and sinter) on hot metal and molten slag composition were thermodynamically analyzed considering the interaction coefficients measured in this work. When the scrap ratio was increased, the copper and tin contents of hot metal were increased, leading to the increase in the Mn content of the hot metal. However, the Mn content of hot metal was decreased by increasing the scrap ratio because the input amount of MnO was reduced.
  • Preparation and characterization of Al2O3-loaded deacidification agents for blast furnace gas

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    DOI:10.2355/isijinternational.ISIJINT-2022-218

    A deacidification agent was prepared through incipient-wetness impregnation method, by using activated γ-Al2O3 as the carrier material to loaded Na2CO3, which can simultaneously remove HCl, H2S and carbonyl sulfur (COS) from blast furnace gas. The pretreatment at temperature of 550 °C can improve the dechlorination performance. The maximum breakthrough time, penetration chlorine capacity, and the highest utilization rate of active component of deacidification agents were 47.5 h, 11.59%, and 75.6%, respectively. The deacidification agents can not only be used as active component to remove H2S from blast furnace gas, but also can act as a COS hydrolysis catalyst. HCl has no obvious effect on the desulfurization performance, while the sulfide gases inhibited the dechlorination process. The synergistic desulfurization and dechlorination experiment results show that the highest removal efficiencies for HCl, H2S and COS by the prepared deacidification agents were all above 99%.
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    1. Estimation of Material Constants of Hot Coke under Inert Atmosphere ISIJ International Advance Publication
    2. Hot strength of coke prepared by briquetting and carbonization of lignite ISIJ International Advance Publication
  • Reduction Behaviors and Generated Phases of Iron Ores using Ammonia as Reducing Agent

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    DOI:10.2355/isijinternational.ISIJINT-2022-155

    As one of the hydrogen carriers, ammonia has become one promising candidate as a reducing agent for implementing hydrogen-based ironmaking to reduce CO2 emissions. On the other hand, the abundant high combined water (CW) iron ore has recently been investigated as a raw material for ironmaking. Goethite (FeOOH), the main component of high-CW iron ore, can change to porous hematite (Fe2O3) by dehydration, enhancing its reactivity. This paper describes the fundamental study of the ore reduction behavior using ammonia as reducing agent. The effects of different ore types (i.e., high- and low-CW ores), reduction temperatures (i.e., 650, 700, and 750°C), and conditions of post-reduction treatments (i.e., quenching by NH3, fast- and slow- quenching by inert gas) on ore reduction behavior. The results reveal that the dehydrated high-CW one exhibits a higher ammonia utilization rate and is reduced faster due to the high specific surface area of the pores generated from the ore dehydration. The reduction degree of the sample increased at a higher temperature. However, in contrast, the nitriding degree decreases since the decomposition of nitrides occur highly at elevated temperatures. During quenching at temperatures lower than 700°C, the metallic Fe in the sample was nitrided in the presence of NH3. In contrast, the nitrides were easily decomposed into metallic Fe in the absence of NH3 at 700°C. This finding suggests that the quenching conditions significantly affect the generated phases. Thus, the generated phases of the reduced ore could be easily controlled in the post-reduction process.
  • Synthesis of Oxalate from CO2 and Cesium Carbonate Supported Over Porous Carbon

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    DOI:10.2355/isijinternational.ISIJINT-2022-159

    Oxalic acid is an attractive chemical platform potentially available from CO2 due to its established applications and chemical characteristics enabling it to serve as a mediator in hydrometallurgy including iron-making. However, a method for synthesizing oxalic acid from CO2 has yet to be established. In the present work, the formation of oxalate scaffold during heating of cesium carbonate (Cs2CO3) in the presence of CO2 and H2 as reactants was experimentally investigated with a particular focus on the influence of supporting Cs2CO3 over porous materials. Among the support materials examined, activated carbon (AC) had a notable effect in improving the reaction rate and yield of total carboxylates (formate and oxalate) during experiments with an autoclave. An important problem was the dominant presence of formate, the intermediate between carbonate and oxalate, accounting for over 90% of the carboxylates. Changing the reaction conditions, including temperature, reaction time, partial pressure of gas components, and amount of loaded Cs2CO3, did not alter the situation. Alternatively, re-heating of the formate-rich salts over AC under CO and CO2 enhanced the oxalate fraction while maintaining the total carboxylates yield. Benefiting from the employment of support material, the two-step conversion was carried out using a gas-flow type reactor with a packed bed of Cs2CO3 supported over AC. In this reaction system, because water, acting as a promoter, was absent, the total carboxylates yield was lower than that in the autoclave, while the oxalate fraction was higher, being 71.8% with a yield of 43.2% on a Cs2CO3-carbon basis.
  • Hot strength of coke prepared by briquetting and carbonization of lignite

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    DOI:10.2355/isijinternational.ISIJINT-2022-143

    The hot strength of coke prepared from an acid-washed lignite by briquetting-carbonization before and after CO2 gasification was, for the first time, investigated in this work. The hot strength at 1000 ºC before gasification was higher than coke strength measured at a room temperature. CO2 gasification resulted in a linear decrease of the hot strength with the reaction time. The lignite-coke showed faster decrease in the strength during gasification, compared to conventional cokes derived from caking coal or non-or slightly caking coal, due to the high reactivity caused by its porous structure and catalytic metal species remaining even after the acid-washing, while it showed superior hot strength at the initial stage of gasification.
  • Extending the Operating Line Methodology to Consider Shaft and Preheating Injections in Blast Furnaces

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    DOI:10.2355/isijinternational.ISIJINT-2022-111

    In the last years, the injection of reducing gases in the shaft and preparation zone of the blast furnace has been proposed as a decarbonization option, mainly associated to oxyfuel blast furnaces and top gas recycling configurations. However, the Rist diagram, which is one of the preferred methodologies to characterize the operation of blast furnaces, is not valid to evaluate these new decarbonization options. In this article we propose a generalization of the operating line methodology to extend its applicability to scenarios of variable molar flows along the blast furnace (i.e., shaft and preheating injections) and non-continuous oxidation profiles (presence of CO2 and H2O in the injected gases). The extended operating line methodology was implemented in an Aspen Plus simulation, which provides a detailed modelling of the preparation zone, the thermal reserve zone, the lower zone and the raceways. The simulation was used to validate the generalized operating line methodology through three different data sets: (i) an air-blown blast furnace with pulverized coal injection and O2 enrichment, (ii) an oxyfuel blast furnace with shaft gas injection, and (iii) an oxyfuel blast furnace with preheating gas injection in the preparation zone. In general, the discrepancy between the reference data and the simulation results is well below 3.5%, so the extended operating line methodology is considered validated.
  • Estimation of Material Constants of Hot Coke under Inert Atmosphere

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    DOI:10.2355/isijinternational.ISIJINT-2022-190

    The strength, pore structure, and material constants of coke prepared from caking coal (Coke A) and non- or slightly caking coal (Coke C) were experimentally and numerically investigated with a particular focus on those values at high temperatures. Coke A showed higher strength and lower porosity than Coke C. The pore structure imaged by X-ray computed tomography was translated to the finite element mesh with the image-based modeling, and the stress analysis based on the finite element method was performed to calculate the mode value of maximum principal stress at different Young's modulus and Poisson's ratio. Young's modulus of Coke A and Coke C at a constant Poisson's ratio decreased and increased, respectively by heating. When the temperature increased, the compression stress of Coke A increased. The result indicated that the coke strength could be increased by heating because of the decrease in apparent Young's modulus, accompanied by the occurrence of creep.
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    1. Preparation and characterization of Al2O3-loaded deacidification agents for blast furnace gas ISIJ International Advance Publication
    2. Hot strength of coke prepared by briquetting and carbonization of lignite ISIJ International Advance Publication
  • Ironmaking Using Municipal Solid Waste (MSW) as Reducing Agent: A Preliminary Investigation on MSW Decomposition and Ore Reduction Behavior

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    DOI:10.2355/isijinternational.ISIJINT-2021-552

    The iron and steel industries currently face the depletion of high-grade ore and high CO2 emissions. Some initiatives that effectively utilize alternative carbon sources and abundant low-grade ores become the preferable solutions. This novel study aims to utilize municipal solid waste (MSW) as a reducing agent in ironmaking using low-grade (goethite) ores. As an initial fundamental approach, the comparison of decomposition behaviors between the model and actual MSW was investigated in thermogravimetric analysis. Both model and actual MSWs mainly decompose at 300–500°C. As for reduction tests, pellets containing MSWs and ores with different pretreatments were prepared. The pellets were reduced in an Ar atmosphere at different temperatures. The effect of different ores: high-grade and low-grade ones, on the decomposition of MSW and the iron reduction, were investigated. As a result, interestingly, the low-grade, goethite ore-containing pellet exhibits a more significant reduction degree than the high-grade ones. The reduction is completed in 5 minutes at 700°C and above, indicating a significant reduction by the decomposed carbon. The reduction degree extends at elevated temperature, which reaches more than 94% at 900°C.
  • Dissolution of Iron Oxides Highly Loaded in Oxalic Acid Aqueous Solution for a Potential Application in Iron-Making

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    DOI:10.2355/isijinternational.ISIJINT-2020-726

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

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    DOI:10.2355/isijinternational.ISIJINT-2020-135

    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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06 Dec. (Last 30 Days)

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