鉄と鋼
Online ISSN : 1883-2954
Print ISSN : 0021-1575
ISSN-L : 0021-1575
最新号
選択された号の論文の7件中1~7を表示しています
出版情報
製銑
論文
  • 小堀 竜一, 宍戸 貴洋, 和田 祥平, 堺 康爾, 奥山 憲幸
    原稿種別: 論文
    2024 年 110 巻 4 号 p. 343-352
    発行日: 2024/03/01
    公開日: 2024/03/01
    [早期公開] 公開日: 2023/12/23
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    Ferro-coke, which is produced by mixing coal and iron ore, briquetting and carbonizing, can be used in a blast furnace to greatly decrease the reducing agent ratio. To ensure the strength of ferro-coke, asphalt pitch (ASP) is used as a binder, but the supply of ASP is limited, and the development of alternative binder are required. This study investigated the application of Hyper-coal (HPC), a low-ash caking additive obtained by solvent extraction of coal, as a new binder for ferro-coke. It was found that superior ferro-coke strength could be obtained by using HPC in which insoluble solid concentration was less than 15 wt.%, to that of ASP. This threshold value was specified from the permeation tests. The permeabilities of binders were determined by measuring the permeation distance in the packed layer of coal and/or iron ore under the carbonizing conditions. HPC appeared higher permeability than ASP in the packed layer of iron ore and coal mixtures. It was considered that the excellent thermal plasticity of HPC, lower melting temperature and higher fluidity than ASP, affected higher permeation into the inter particle void especially lower temperature range before starting the reduction of iron ore, which rapidly decreased in the permeabilities of both binders due to the distortion of carbon structures. Those results suggested that HPC was superior to ASP as a binder for ferro-coke.

製鋼
論文
  • 笹井 勝浩, 諸星 隆
    原稿種別: 論文
    2024 年 110 巻 4 号 p. 353-363
    発行日: 2024/03/01
    公開日: 2024/03/01
    [早期公開] 公開日: 2023/12/28
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    In this study, to elucidate the agglomeration mechanism of various inclusions in molten steel based on their interfacial chemical interactions, the agglomeration forces exerted between the solid-phase oxides of MgO, MgAl2O4, ZrO2, SiO2, and TiO2 in molten steel, in addition to those between the reference material Al2O3 have been measured directly. We experimentally verified for the first time that the agglomeration force due to the cavity bridge force in molten steel acts in a relatively stable manner between all solid-phase oxides that are difficult to wet with molten steel. Furthermore, this force decreased with increasing O concentration in molten steel, which is attributed to the interfacial activation effect caused by the adsorption of oxygen at the interface between the oxides and molten steel. The agglomeration properties of various oxide inclusions in the deoxidized molten steel were further evaluated from the perspectives of both agglomeration force and thermodynamics. Quantitative analysis indicated easy agglomeration of oxide inclusions in the order MgO < TiO2 < SiO2 < MgAl2O4 < ZrO2 < Al2O3. A comparative evaluation of the agglomeration and external forces acting on the oxide inclusions in molten steel suggests that any oxide inclusion in the deoxidized state forms cavity bridges and agglomerates and retains that state under intense molten steel flow. However, these agglomerated inclusions may separate again under a molten steel flow at a high O concentration. The extent of separation depends primarily on the type of oxide used.

相変態・材料組織
論文
  • 上野 虎太郎, 藤村 里奈, 光原 昌寿, 林 宏太郎, 樋渡 俊二, 髙橋 学
    原稿種別: 論文
    2024 年 110 巻 4 号 p. 364-375
    発行日: 2024/03/01
    公開日: 2024/03/01
    [早期公開] 公開日: 2023/12/27
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    Microstructures of lath martensite have been studied intensively to understand their effect on the mechanical properties of steels. It is, however, said that the relation between microstructural factors and mechanical properties has not been clarified yet. The plastic deformation behavior of fully lath martensitic steels has become important because they are applied to automobile body structures such as bumper reinforcement. It is, therefore, important to understand the microstructural factors that control the work-hardening behavior of fully martensitic steels. Although we could not clarify differences in microstructural factors when manganese (Mn) concentrations of steels are altered, the work-hardening of 8 mass%Mn martensitic steel is much higher than that of 5 mass%Mn martensitic steel. It was found using the digital image correlation (DIC) method, that the strain concentration due to the in-lath-plane slip deformation is more developed in 5 mass%Mn martensitic steel than 8 mass%Mn martensitic steel. Transmission electron microscope (TEM) observations revealed the existence of two types of fine twins inside laths. Long twins that are parallel to the longitude of the lath are observed both in 5 mass%Mn and 8 mass%Mn martensitic steels. Short twins that partially cross the laths, on the other hand, can only be found in 8 mass%Mn martensitic steel. Since twin boundaries are high angle boundaries, the short twins are supposed to prevent the development of in-lath-plane slip deformation. This seems to be the mechanism of higher work-hardening behavior observed in 8 mass%Mn martensitic steel.

力学特性
論文
  • 井戸原 修, 日山 洋平, 三阪 佳孝, 高木 節雄, 土山 聡宏
    原稿種別: 論文
    2024 年 110 巻 4 号 p. 376-384
    発行日: 2024/03/01
    公開日: 2024/03/01
    [早期公開] 公開日: 2024/01/16
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    The hardness of martensitic steels with high Ms temperatures is reduced by auto-tempering after transformation, therefore the true hardness of martensite with carbon in fully solid solution is not known. In this study, we investigated a method to quantitatively evaluate the true hardness of quenched martensite unaffected by auto-tempering and the effect of auto-tempering by quantitatively evaluating the degree of tempering of martensite using the diffusion area of carbon in bcc iron at temperatures below 400°C. As a result, it was clarified that the effect of auto-tempering is more pronounced in steels with an M50 temperature higher than 300°C and that the softening behavior of martensitic steels can be uniformly evaluated regardless of the carbon content if the activation energy of carbon diffusion is known. Furthermore, it was clarified that the degree of auto-tempering can be quantitatively evaluated by calculating the integral diffusion area S (=∑Dt) below the M50 temperature during quenching.

  • 吉田 晋士, 荒井 勇次, 大村 朋彦, 趙 研, 安田 弘行
    原稿種別: 論文
    2024 年 110 巻 4 号 p. 385-394
    発行日: 2024/03/01
    公開日: 2024/03/01
    [早期公開] 公開日: 2024/01/12
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    The effect of Mn content on hydrogen embrittlement resistance of tempered martensite in low alloy steel was investigated. The hydrogen embrittlement resistance was estimated with Double Cantilever Beam (DCB) test in aqueous environment containing hydrogen sulfide. In the DCB test, the specimens with pre-crack were prepared, the crack propagated while the specimens were exposed to aqueous environment containing hydrogen sulfide. The crack propagation route was analyzed into intergranular fracture and transgranular fracture, and intergranular fracture rate was calculated. The fracture toughness decreases from 29 MPa√m to 25 MPa√m with increasing Mn content from 0.5% to 1.5%. Then, the intergranular fracture rate increases from 26.6% to 54.4%, and the absorbed hydrogen content increases from 1.8 mass ppm to 2.3 mass ppm. The decrease of fracture toughness is probably because cohesive energy of grain boundary (2γint) decreases with increasing Mn content at the prior austenite grain boundary and increasing absorbed hydrogen.

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