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
相変態・材料組織
論文
  • 砂子 真魅, 水本 政隆, 田中 練, 熊井 慎太郎, 山内 雄一郎, 大井 梓, 多田 英司
    原稿種別: 論文
    2025 年 111 巻 2 号 p. 21-31
    発行日: 2025/02/01
    公開日: 2025/02/01
    [早期公開] 公開日: 2024/12/18
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    In this study, we focused on fine dispersion of Fe2-3C(ε) by combining the addition of Si and rapid tempering to improve the hydrogen embrittlement resistance of high-strength spring steels. The aim of this study is to clarify the fracture mechanism of rapidly tempered high-Si steels: the JISSUP7 (2.0Si) and SAE9254 (1.4Si) spring steels were tempered at different tempering rates by induction (IH) and furnace heating (FH) methods. Bending test were carried out during the cathodic hydrogen charging to observe the fracture origin and morphology of the steels. The size and volume of carbides were quantified using small-angle X-ray scattering method (SAXS) and synchrotron radiation XRD. The distribution of carbides was observed with the replica method: facets were observed at the fracture origin of the 2.0Si-IH steel and 1.4Si-IH steel, which contained retained γ in the microstructure. It was considered that the facets formed because retained γ at the grain boundaries transformed into martensite during hydrogen embrittlement, promoting intergranular cracking; the 2.0Si-IH steel contained the largest amount of retained γ, but also contained fine Fe2-3C(ε) in the lath. This suggests that dislocations and hydrogen are less likely to accumulate at the grain boundaries, resulting in the longest fracture life. In other words, in rapidly tempered high Si steels (2.0Si-IH steels), the fine dispersion of Fe2-3C(ε) has more influence on the suppression of crack initiation and propagation than the increase in the amount of retained γ, and this contributes significantly to the fracture life.

力学特性
論文
  • 丸山 貴史, 梅澤 修
    原稿種別: 論文
    2025 年 111 巻 2 号 p. 32-40
    発行日: 2025/02/01
    公開日: 2025/02/01
    [早期公開] 公開日: 2024/11/30
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    Nitriding is a beneficial surface hardening heat treatment to reduce CO2 emissions and shows a potential partially replace carburized steels adopted for sliding parts such as bearings and gears. Both the bending fatigue strength and pitting fatigue strength under high contact pressure were evaluated for nitrided JIS-SCM440H materials using two types of controlled-nitridings, i.e. γ' and ε, and conventional gas nitriding. Not only the thickness of the compound layer but also its phase structure such as γ' and ε significantly affected the 107 cycles bending fatigue strength, where the γ'-nitrided material was the highest. On the other hand, almost no effects of the thickness and phase structure on the 107 cycles pitting fatigue strength were detected in the materials. Compared to the carburized material, the γ'-nitrided material exhibited higher 107 cycles fatigue strength in bending and pitting, but poor fatigue strength in the lower cycles range. The shape and size of the pores in the compound layer were altered during roller-pitching tests, although there was almost no reduction in the thickness of the compound layer. The pore size was reduced by pore closure, especially at higher contact pressures. Pore closure was more pronounced in the γ'-nitrided materials than in the ε-nitrided materials at lower contact pressures. The 107 cycles pitting fatigue strength was improved after the pore closure, resulting from fewer defects.

社会・環境
論文
  • 山口 東洋司, 篠田 万里子, 井上 敦晴, 中村 知道, 村井 亮太, 髙橋 克則
    原稿種別: 論文
    2025 年 111 巻 2 号 p. 41-50
    発行日: 2025/02/01
    公開日: 2025/02/01
    [早期公開] 公開日: 2024/12/19
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    The coke-oven wastewater contains high concentrations of ammonia, COD (chemical oxygen demand) and toxic compounds such as phenols, cyanides, and thiocyanate. This wastewater is one of the most toxic industrial wastewater. Although the activated sludge process has been applied to treatment of the coke-oven wastewater, the treatment was occasionally deteriorated by inhibition of toxic compounds. Especially, the nitrification step was sensitive to toxic compounds, nitrite (NO2) was often accumulated due to incomplete nitrification. Nitrite is toxic and has a negative effect on COD degrading bacteria. The complete nitrification was required for stable treatment.

    In this study, aiming at simultaneous removal of ammonia and COD from the coke-oven wastewater, a bench-scale nitrification/denitrification plant was operated. By long-term acclimation and the addition of an iron source, the complete nitrification was stably occurred for about 8 months, and a nitrogen removal efficiency of nearly 70% was achieved. In addition, COD in the influent was consumed as an organic source for denitrification, and the addition of an organic source was able to be minimized.

力学特性
技術報告
  • 澤田 浩太, 谷内 泰志, 野島 健大, 関戸 薫子, 畠山 友孝, 木村 一弘
    原稿種別: 技術報告
    2025 年 111 巻 2 号 p. 51-57
    発行日: 2025/02/01
    公開日: 2025/02/01
    [早期公開] 公開日: 2024/12/07
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    Effect of cyclic stress changes on creep rupture strength was investigated at 600°C for MGQ and MGS heat of ASME P91 steel. There was no large difference of creep rupture strength among the heats. However, the creep rupture ductility of MGS was lower than that of MGQ in the long-term. The initial creep stress and stress after stress reduction was 120 MPa and 24 MPa to 84 MPa, respectively. The time interval of stress reduction was 6 days for each test. For MGQ heat, no effect of stress reduction to 84 MPa on creep rupture strength was observed. The stress reduction to 60 MPa slightly increased time to rupture as compared to creep test under constant stress. A small amount of decrease in time to rupture was confirmed in case of stress reduction to 36 MPa.

    Consequently, there was no tendency of effect of stress reduction on creep rupture strength for both heats. The cyclic stress change did not affect the martensitic lath structure and precipitates distribution after creep rupture.

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