ISIJ International
Online ISSN : 1347-5460
Print ISSN : 0915-1559
ISSN-L : 0915-1559
61 巻 , 6 号
選択された号の論文の34件中1~34を表示しています
Publication Data
Review Articles
Ironmaking
  • Xiaoyue Fan, Kexin Jiao, Jianliang Zhang, Rongrong Wang
    原稿種別: Review
    2021 年 61 巻 6 号 p. 1758-1767
    発行日: 2021/06/15
    公開日: 2021/06/17
    [早期公開] 公開日: 2021/04/17
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    Ironmaking industry occupies significant responsibility of resource-saving and environment-protecting in the national economy. As the largest monomer smelting unit in ironmaking process, the efficiency of blast furnace can directly determine the consumption of energy. Researchers have conducted vast investigations about cohesive zone due to its energy redistribution and interaction-concentrated region role in blast furnace. Amidst this backdrop, the behavior of cohesive zone obtained through the most direct mothed, the dissection investigation, is introduced in this article, including blast furnaces from Japan, European countries and China. Moreover, a brief introduction about the way to cool down working blast furnace is also covered. The relationship between operation and macro-profile of cohesive zone, the behavior of various burden in cohesive zone and the effect of harmful elements on the softening & melting properties were mostly conducted in Japanese dissected blast furnace. The charge properties in cohesive zone were investigated through German Mannesmann No. 5 dissected blast furnace and Swedish 8.2 m3 dissected experimental blast furnace. China had conducted three dissection research including 23 m3 Shougang blast furnace, 0.8 m3 Pangang blast furnace and 125 m3 Laigang blast furnace, while a damage investigation in 1050 m3 blast furnace was also selected. The existing studies witness the recognition process of cohesive zone in several European countries, as well as Japan and China, reflecting the development of ironmaking technology.

Regular Articles
Fundamentals of High Temperature Processes
  • Antonio Romero-Serrano, Josué López-Rodríguez, Aurelio Hernández-Ramír ...
    原稿種別: Regular Article
    2021 年 61 巻 6 号 p. 1768-1774
    発行日: 2021/06/15
    公開日: 2021/06/17
    [早期公開] 公開日: 2021/03/17
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    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.

  • Akito Yamaguchi, Hitoshi Okano, Syunsuke Sumitomo, Md. Azhar Uddin, Yo ...
    原稿種別: Regular Article
    2021 年 61 巻 6 号 p. 1775-1783
    発行日: 2021/06/15
    公開日: 2021/06/17
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    Agglomeration, coalescence and flotation of non-metallic inclusions in steel melt are effective for obtaining “clean steel.” In this study, the agglomeration and breakup behaviors of particles with a primary particle size distribution (hereinafter, polydisperse particles) in a liquid under impeller and gas stirring were compared by numerical calculations and model experiments. The particle-size-grouping (PSG) method in the numerical agglomeration model of particles was combined with a breakup term of agglomeration due to bubble bursting at the free surface. Polydisperse and monodisperse polymethylmethacrylate (PMMA) particles were used in the agglomeration experiments. The agglomeration rate of the polydisperse particles under impeller stirring was increased by an increasing energy input rate, whereas the agglomeration rate under gas stirring decreased under this condition due to the larger contribution of the breakup of agglomerated particles during bubble bursting in gas stirring. At the same energy input rate, agglomeration of polydisperse particles was larger under impeller stirring than under gas stirring. The agglomeration rate of polydisperse particles was larger than that of monodisperse particles under both impeller and gas stirring at the same energy input rate. The computational temporal changes in the total number of particles were in good agreement with the experimental results. This means that the difference in the agglomeration behaviors observed in impeller and gas stirring can be explained by the turbulent coagulation and subsequent agglomerated particle breakup in gas stirring. The computational temporal change in the number of each group approximately agreed with the experimental change in both impeller and gas stirring.

  • Lichun Zheng, Huabing Li, Xiaolu Wang, Zhouhua Jiang, Hao Feng
    原稿種別: Regular Article
    2021 年 61 巻 6 号 p. 1784-1793
    発行日: 2021/06/15
    公開日: 2021/06/17
    [早期公開] 公開日: 2021/03/17
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    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.

  • Nobuhiko Oda, Shinji Koseki, Yu-ichi Uchida, Yuta Hino, Naoki Kikuchi
    原稿種別: Regular Article
    2021 年 61 巻 6 号 p. 1794-1800
    発行日: 2021/06/15
    公開日: 2021/06/17
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    In a top-blowing converter, when a distance between the top-blowing lance and the molten metal surface increases, post-combustion ratio increases, but its heat transfer efficiency to the molten metal decreases. Therefore, a fundamental study of a gas jet behavior from the lance nozzles was carried out in order to develop a new oxygen top-blowing lance with side nozzles with the aim of achieving both higher post-combustion ratio and higher heat supply to the molten metal in converter.

    In order to design the shape of the side nozzles and blowing conditions, cold model experiments and numerical calculations were carried out to investigate the effect of the inclination angle of the side nozzles and the flow rate on the gas jet behavior of the nozzles. It was found that the gas jet from the side nozzles was deflected to the direction away from the side wall of the lance due to a difference in the pressure distribution at the nozzle outlet. The deflection angle can be estimated by an equation using the supply pressure, atmospheric pressure and inclination angle of the nozzle.

Ironmaking
  • Chengfeng Sun, Yizhang Yang, Yang Xu, Zhehan Liao, Yuandong Pei, Qi Zh ...
    原稿種別: Regular Article
    2021 年 61 巻 6 号 p. 1801-1807
    発行日: 2021/06/15
    公開日: 2021/06/17
    [早期公開] 公開日: 2021/04/21
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    Carbon combustion provides energy to reach essential temperatures in the sintering packed bed. A visual and quantitative evaluation on the energy input distribution inside the bed is urgently demanded to learn energy-saving potential of sintering process and subsequently to suppress greenhouse gas emission. Herein, after a two-dimensional simplified model of sintering packed bed is established and validated against the temperature measurements on the sintering pot experiment, this work highlights a mesh-based visualization method of quantifying carbon combustion energy in the packed bed. To be more specific, local transient temperature distributions in all meshed grids are first extracted from numerical simulation results. Then each grid is colorized according to the specific criteria on five pre-defined energy input (EI) states. As a result, the effects of carbon segregation and cross-sectional shape on the energy efficiency of sintering packed bed are quantitatively compared and optimized. These two case studies not only demonstrate the principle, process, and application of the proposed visualization method, but also stimulate its future potential in various areas.

  • Ryota Higashi, Kanae Owaki, Daisuke Maruoka, Taichi Murakami, Eiki Kas ...
    原稿種別: Regular Article
    2021 年 61 巻 6 号 p. 1808-1813
    発行日: 2021/06/15
    公開日: 2021/06/17
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    In order to reduce energy consumption in the blast furnace ironmaking process, it is important to promote not only rapid reduction of ore but also carburization and melting of metallic iron. In this study, the use of carbon-iron ore composite which is an agglomerate of fine iron ore and carbonaceous material was focused on, and the effects of ore type and slag content on carburization and melting of metallic iron were examined.

    The reduction, carburization, and melting behavior of the composite samples prepared using carbonaceous materials and iron oxide such as various fine ores, goethite and hematite reagents were evaluated under heating condition up to 1573 K. The composite of hematite reagent with the additions of SiO2 and Al2O3 reagents was also used to control the gangue composition.

    Carburization and melting phenomena of metallic iron due to direct contact with graphite were observed in the composite samples made of pisolite ore and hematite reagent at the same slag composition. Carburization phenomenon was accelerated with increase in slag content.

  • Shungo Natsui, Azuma Hirai, Koki Terui, Yusuke Kashihara, Akinori Mura ...
    原稿種別: Regular Article
    2021 年 61 巻 6 号 p. 1814-1825
    発行日: 2021/06/15
    公開日: 2021/06/17
    [早期公開] 公開日: 2021/03/14
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    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.

Steelmaking
  • Fangguan Tan, Zhu He, Shengli Jin, Qiang Wang, Liping Pan, Yawei Li, B ...
    原稿種別: Regular Article
    2021 年 61 巻 6 号 p. 1826-1834
    発行日: 2021/06/15
    公開日: 2021/06/17
    [早期公開] 公開日: 2021/04/11
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    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.

  • Jiali Sun, Chengjun Liu, Maofa Jiang
    原稿種別: Regular Article
    2021 年 61 巻 6 号 p. 1835-1841
    発行日: 2021/06/15
    公開日: 2021/06/17
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    To alleviate the environmental pressure from the massive discharge of red mud (RM), and develop an economical and environment-friendly ferromanganese desiliconization and dephosphorization process, a novel RM-based desiliconization and dephosphorization flux for ferromanganese was designed and verified through thermodynamic analyses and high-temperature experiments. The results showed that the designed RM-based flux had good melting property, desiliconization capability, and dephosphorization capability after adjusting the experimental temperature and the lime:RM ratio (wt%). Especially, when the temperature was 1623 K and the lime:RM ratio (wt%) was 0.5, the best desiliconization and dephosphorization effects (desiliconization rate of 77.24% and final silicon content of 0.28%, dephosphorization rate of 31.89% and final phosphorus content of 0.31%) were achieved in the situation of high manganese content (≥63.5%). Also, the final slag could continue to remove phosphorus from low silicon ferromanganese. This work verified the feasibility of applying the RM-based flux to the ferromanganese desiliconization and dephosphorization process, which has significant environmental and economic benefits.

  • Jian-bin Chen, Hong-hong Huang, Rong Chu, Ya-qin Sun
    原稿種別: Regular Article
    2021 年 61 巻 6 号 p. 1842-1849
    発行日: 2021/06/15
    公開日: 2021/06/17
    [早期公開] 公開日: 2021/03/19
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    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.

  • Xijie Wang, Guangqiang Li, Yu Liu, Fang Wang, Qiang Wang
    原稿種別: Regular Article
    2021 年 61 巻 6 号 p. 1850-1859
    発行日: 2021/06/15
    公開日: 2021/06/17
    [早期公開] 公開日: 2021/04/14
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    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.

Casting and Solidification
  • Haibiao Lu, Bin Li, Jiaxun Li, Yunbo Zhong, Zhongming Ren, Zuosheng Le ...
    原稿種別: Regular Article
    2021 年 61 巻 6 号 p. 1860-1871
    発行日: 2021/06/15
    公開日: 2021/06/17
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    A mathematical model coupled with electromagnetic field, flow, heat transfer and solidification has been developed to simulate the bias flow caused by slide gate under different slide-gate opening rates, EMS currents and casting speeds. Through comparing the magnetic flux density and flow field with measured results, the reliability of mathematical model is proved. The symmetric index, variance of solidified shell thickness have been introduced to judge the symmetry of flow field and uniformity of solidified shell, respectively. The results show that bias flow phenomenon has happened when the slide-gate opening rate is less than 100%, the deviated direction is opposite to the opening direction of slide gate. As the slide-gate opening rate decreases, the symmetry of flow field and uniformity of solidified shell decrease. Increasing the EMS current and decreasing the casting speed, the symmetry of flow field caused by slide gate increases, but it can not eliminate completely, while the uniformity of solidified shell increases firstly and then decreases. There exists an optimal EMS to balance the symmetry of flow field and uniformity of solidified shell.

  • Tomohiro Nishimura, Hitoshi Ishida, Hideyuki Yasuda
    原稿種別: Regular Article
    2021 年 61 巻 6 号 p. 1872-1878
    発行日: 2021/06/15
    公開日: 2021/06/17
    [早期公開] 公開日: 2021/03/12
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    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.

  • Yusuke Kobayashi, Hidekazu Todoroki, Keita Nakano, Taka Narumi, Hideyu ...
    原稿種別: Regular Article
    2021 年 61 巻 6 号 p. 1879-1888
    発行日: 2021/06/15
    公開日: 2021/06/17
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    A random sampling method using Fe-19.9 mass% Cr-24.8 mass% Ni-4.5 mass% Mo-1.5 mass% Cu alloy quenched during unidirectional solidification was applied to examine the measurement accuracy of the solute partition coefficients between the solid and liquid phases. Better agreement between the solute profiles obtained by the random sampling and Scheil’s equation was observed at appropriate regions where the solid fraction ranged from 0.9 to 1 at quenching. The partition coefficients of Cr, Ni, Mo, and Cu were determined to be 0.95, 1.01, 0.71, and 0.84, respectively. The values obtained using the present method agreed well with the values measured using the in-situ measurement method, which is recognized to be a reliable technique. The developed technique, which uses conventional equipment and techniques such as a unidirectional solidification furnace and scanning electron microscopy/energy-dispersive X-ray spectroscopy, requires less time to determine the solute partition coefficients than conventionally used techniques. Thus, the modified random sampling method presented in this study can be used for systematic measurements of solute partition coefficients.

  • Hongchun Zhu, Huabing Li, Zhiyu He, Hao Feng, Zhouhua Jiang, Tong He
    原稿種別: Regular Article
    2021 年 61 巻 6 号 p. 1889-1898
    発行日: 2021/06/15
    公開日: 2021/06/17
    [早期公開] 公開日: 2021/04/21
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    In this paper, the effect of solidification pressure on the dendrite structure and characteristics of carbides in H13 die steel ingot was investigated by experimental and calculational methods. Based on the effect of pressure on the cooling rate, a formula is proposed to calculate the secondary dendrite arm spacing: λ2 = 71.45 × R−0.37. It is applicable when the maximum value of pressure is around 2 MPa and the cooling rate is between 0.5 and 3 K/s. With increasing pressure from 0.1 to 2 MPa, the effects of pressure on the segregation ratio of V, Mo, Cr and C are little and can be neglected, which caused by the combined effect of equilibrium partition coefficient, diffusion coefficient and cooling rate. Therefore, the characteristics of carbides are determined by the decreasing the secondary dendrite arm spacing and increasing cooling rate with the increment of pressure. With increasing pressure from 0.1 to 2 MPa, the types of carbides are not change, which are MC and M2C in H13 die steel ingot. Meanwhile, the mean area of carbides decreases obviously with increasing pressure, and the decrement in mean area at the edge is larger than that at the center of ingot.

Instrumentation, Control and System Engineering
  • Xiangman Song, Ying Meng, Chang Liu, Yang Yang, Dongying Song
    原稿種別: Regular Article
    2021 年 61 巻 6 号 p. 1899-1907
    発行日: 2021/06/15
    公開日: 2021/06/17
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    Molten iron temperature prediction during hot metal transportation plays a key role in reducing energy consumption and improving the quality of steel-making products. In this paper, first, a mechanism model based on the physical laws of temperature drop principle and heat transfer relationship is established. Aiming at the problems of difficult detection of molten iron temperature in torpedo tank and incomplete measurement information caused by limited measurement information, a prediction method of molten iron temperature based on data analytics was proposed through the historical data obtained from production process, and a prediction model of molten iron temperature was established. Due to the uncertainty in the process of molten iron in the transport, and the influence of waiting time, lead to on-line temperature prediction accuracy of the independent mechanism model or data analytics model is not high. In response to this problem, a data fusion prediction method based on Kalman filtering is proposed to meet the needs of actual production.

  • Chao Chen, Nan Wang, Min Chen
    原稿種別: Regular Article
    2021 年 61 巻 6 号 p. 1908-1914
    発行日: 2021/06/15
    公開日: 2021/06/17
    [早期公開] 公開日: 2021/03/20
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    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.

  • Wei Zhang, Feng Wang, Nan Li
    原稿種別: Regular Article
    2021 年 61 巻 6 号 p. 1915-1926
    発行日: 2021/06/15
    公開日: 2021/06/17
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    In this study, we established mathematical model of the carbon-containing pellet reduction process and used the neural network model to speed up the prediction process for actual production in the rotary hearth furnace (RHF). In order to obtain enough data to make a neural network, we calculated some results under different conditions by the pellet reduction mathematical model. Then, we developed and trained a feed-forward back-propagation neural network model using MATLAB software. The input parameters of the model included the temperature in the furnace, the reduction time, size and C/O ratio of the carbon-containing pellet and the output parameter was the final degree of metallization of the carbon-containing pellet. Beside, we optimized initial weights and thresholds of the model utilizing genetic algorithm, and also compared and analyzed the number of hidden layer neurons, training algorithm, learning rate, and population size of it. Finally, we chose 4-10-1 as the modeling structure of the neural network, the Levenberg-Marquardt training algorithm, the learning rate of 0.1 and population size of 150 as the optimal configuration. The coefficient correlation of training set and test set data calculated by the model indicates that the established neural network model has a high degree of suitability. Therefore, the neural network model combined with genetic algorithm has superiority as a reliable and efficient tool for predicting the reduction metallization rate of carbon-containing pellet in the RHF.

Chemical and Physical Analysis
  • Luca Chiari, Akari Komatsu, Masanori Fujinami
    原稿種別: Regular Article
    2021 年 61 巻 6 号 p. 1927-1934
    発行日: 2021/06/15
    公開日: 2021/06/17
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    Hydrogen-related defects in the metastable austenitic stainless steel 304 were analyzed by positron annihilation lifetime spectroscopy to determine the factors responsible for hydrogen embrittlement. Hydrogen was introduced by the cathodic electrolysis method to the ~10-µm topmost layer which was then etched by electrochemical polishing to investigate the formation of hydrogen-induced defects in the bulk. Although hydrogen embrittlement did not occur simply upon removal of the hydrogen-charged layer, a decrease in ductility was confirmed by applying 10% tensile strain and subsequent polishing. In this latter sample a positron lifetime component of ~180 ps was detected, which is longer than that of dislocations, and disappeared upon annealing at 100°C. After further straining the sample until fracture, the formation of vacancy clusters was observed. These results suggest that hydrogen diffused to deeper regions upon application of tensile stress, where vacancy-hydrogen complexes were generated and developed into vacancy agglomerates. The detection of the precursors of the vacancy clusters, which are thought to lead to the brittle fracture, represents a fundamental step forward in the understanding of the hydrogen embrittlement process in austenitic stainless steels.

Forming Processing and Thermomechanical Treatment
  • Joong-Ki Hwang
    原稿種別: Regular Article
    2021 年 61 巻 6 号 p. 1935-1945
    発行日: 2021/06/15
    公開日: 2021/06/17
    [早期公開] 公開日: 2021/03/17
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    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.

Surface Treatment and Corrosion
  • Shogo Takesue, Yoshitaka Misaka, Jun Komotori
    原稿種別: Regular Article
    2021 年 61 巻 6 号 p. 1946-1954
    発行日: 2021/06/15
    公開日: 2021/06/17
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    In order to increase the surface hardness and improve the tribological properties of stainless steel, Fe–Al intermetallic compound layers were created by atmospheric-controlled induction-heating fine particle peening (AIH-FPP). The surface microstructure of the stainless steel treated with AIH-FPP was characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, and micro-Vickers hardness testing. In addition, the tribological properties were investigated by reciprocating ball-on-disk wear tests. When high-speed steel particles coated with thin aluminum layers were used as the shot particles, Fe–Al intermetallic compound layers were formed at the surfaces of the stainless steel with increased heating time during AIH-FPP. This is because aluminum was transferred from the shot particles, and the temperature at the treated surface increased as a result of a combustion synthesis reaction. When the heating temperature after FPP was increased, the transferred aluminum and nitrogen in the atmosphere reacted, which resulted in the formation of aluminum nitrides in addition to Fe–Al intermetallic compounds. The tribological properties of the stainless steel were improved by AIH-FPP since high-hardness layers were created. The results indicate that the formation of an Fe–Al intermetallic compound layer with high hardness by AIH-FPP is effective for modifying the tribological properties of the stainless steel within a relatively short span of time.

    Schematic illustration explaining the process of the formation of surface modified layers by AIH-FPP. (Online version in color.) Fullsize Image
Transformations and Microstructures
  • Jian Wang, Haojie Meng, Xudong Fang, Chao Chen, Yiming Liu, Peide Han
    原稿種別: Regular Article
    2021 年 61 巻 6 号 p. 1955-1963
    発行日: 2021/06/15
    公開日: 2021/06/17
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    The effects of Co on the precipitation evolution and tensile/creep properties of the alumina-forming austenitic (AFA) stainless steel at 700°C were systematically investigated. Two investigated steels based on the Fe-15Cr-25Ni-2.5Al (in mass%) AFA steel were prepared; one is added 2.5 mass% W sorely, and the other is added 2.5 mass% W and 5 mass% Co together. After aging treatment, secondary NbC was precipitated in both steels and dispersed within the matrix. However, after adding Co to AFA steels, nanoscale L12 Ni–Al–Cu phase was not observed, and the amount of Laves and the δ-ferrite phase decreased with the same aging time, indicating that addition of Co improved microstructure stability. The tensile strength of AFA specimens with added Co did not significantly decrease, especially with a long-term aging treatment, compared to samples without added Co. However, introducing Co greatly improved the toughness of AFA steels. Also, the results of the creep fracture tests show that adding Co improved the creep life of AFA steels. The reason for this enhancement is that the formation of detrimental secondary phases at the grain boundary was greatly suppressed, after adding Co to AFA steels.

  • Genki Saito, Norihito Sakaguchi, Munekazu Ohno, Kiyotaka Matsuura, Mas ...
    原稿種別: Regular Article
    2021 年 61 巻 6 号 p. 1964-1970
    発行日: 2021/06/15
    公開日: 2021/06/17
    [早期公開] 公開日: 2021/04/15
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    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 (1120) 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.

    STEM-EDS maps of precipitates in samples after normalization, that was performed after cooling from forging-simulated heating under different conditions, namely (a) water quenching, and furnace cooling at (b) 16, (c) 4, and (d) 0.7°C/min. (Online version in color.) Fullsize Image
Mechanical Properties
  • Takayuki Hama, Takuna Nishi, Masashi Oka, Takashi Matsuno, Yoshitaka O ...
    原稿種別: Regular Article
    2021 年 61 巻 6 号 p. 1971-1979
    発行日: 2021/06/15
    公開日: 2021/06/17
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    In this work, non-uniform deformation behavior of coarse-grained ultralow carbon steel was investigated under uniaxial tension and cyclic simple shear. A digital image correlation method was used to measure strain fields at the grain level. Heterogeneous strain distribution appeared at the early stage of the process, and the heterogeneity remained almost unchanged in the subsequent deformation. Localized strain bands were observed under both uniaxial tension and simple shear, but the directions of the bands were different between the two deformation modes. It was hypothesized that the directions of the strain bands were correlated with the planes where the maximum or minimum shear stresses occurred. During cyclic simple shear, the heterogeneity of strain distribution and occurrence of strain bands depended on the shear direction. In contrast, the number of cycles had little effect on the heterogeneity of strain distribution. Comparing the grain boundaries and the strain distributions, it was observed that many of the strain-band boundaries occurred along the grain boundaries, but some of them appeared within grains.

    Equivalent strain distributions under cyclic simple shear measured at points (a) a, (b) b, (c) c, (d) d, (e) e, and (f) f shown in Fig. 10. (Online version in color.) Fullsize Image
  • Akihiko Nagasaka, Tomohiko Hojo, Masaya Fujita, Takumi Ohashi, Mako Mi ...
    原稿種別: Regular Article
    2021 年 61 巻 6 号 p. 1980-1989
    発行日: 2021/06/15
    公開日: 2021/06/17
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    Effects of silicon and manganese contents on V-bending in high-strength TRIP-aided dual-phase (TDP) steel sheets with polygonal ferrite matrix were investigated for automotive applications. V-bending test was performed on a hydraulic testing machine at a processing speed of 1 mm/min, using a rectangular specimen (50 mm in length, 5 mm in width, 1.2 mm in thickness), 88-degree punch (2.0 mm in punch radius), and 88-degree die (12 mm in die width, 0.8 mm in die radius). The main results are as follows.

    (1) The 0.2C-(1.0–2.5)Si-(1.0–2.0)Mn, mass% TDP steel sheets were able to perform V-bending by strain-induced martensitic transformation of TRIP effect. On the other hand, ferrite-martensite dual-phase (MDP0) steel sheet of 900 MPa grade was not able to perform 90-degree V-bending because of initiation of crack on an outer surface.

    (2) The 0.2C- 2.5Si-1.5Mn, mass% TDP-G steel sheet of 980 MPa grade was able to enable the 90-degree V-bending that considered an amount of springback (Δθ = θ1θ2), in which the θ1 and the θ2 are a bending angle on loading and a bending angle after unloading respectively, of more than 2-degree by controlling a displacement of punch bottom dead center.

    Bending load (P)-punch stroke (S) curves for TDP-G, MDP0, and MDP4 steels (Smax=11.0 mm). (Online version in color.) Fullsize Image
  • Liangwei Yin, Osamu Umezawa
    原稿種別: Regular Article
    2021 年 61 巻 6 号 p. 1990-2001
    発行日: 2021/06/15
    公開日: 2021/06/17
    [早期公開] 公開日: 2021/03/19
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    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.

Social and Environmental Engineering
  • Lei Li, Jingcheng Wang, Yong Yu
    原稿種別: Regular Article
    2021 年 61 巻 6 号 p. 2002-2008
    発行日: 2021/06/15
    公開日: 2021/06/17
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    The Sn-bearing iron concentrate had a great influence on the pyrolysis of waste tire rubbers, and simultaneously the Sn in this concentrate could be removed efficiently during the pyrolysis process. With the additive of Sn-bearing iron concentrates, the gas yield from the pyrolysis of waste tire rubbers increased while the solid yield decreased. This was mainly due to the reduction of Fe3O4 by the pyrolysis char. A CaO–MgO containing complex was formed during the pyrolysis of waste tire rubbers with Sn-bearing iron concentrates, which could prevent the formation of stable chemical structures in hydrocarbons and decrease the activation energy of degradation reactions. The derived-oil yield was increased with it. The ‘S’ in the waste tire rubber could be transformed into Sn-bearing iron concentrates through the formation of FeS and ZnS, and then be oxidized to SO2 (g) by Fe3O4 or reduced to COS (g) by CO (g), causing the sulfur content in the derived-oil to be decreased. Simultaneously, in the presence of these generated SO2 (g) and COS (g), the Sn in the Sn-bearing iron concentrate could be sulfurized and removed. The Sn residual content in this Sn-bearing iron concentrate was decreased to 0.062 wt.% at pyrolysis temperature of 1000°C for 60 min in a high purity N2 flow rate of 100 ml/min.

Notes
Fundamentals of High Temperature Processes
Ironmaking
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