粉体および粉末冶金

焼結鉄の降伏挙動について

本田忠敏, 徳永洋一

1972 年 18 巻 8 号 p. 295-301
発行日: 1972/04/25
公開日: 2009/05/22

DOIhttps://doi.org/10.2497/jjspm.18.295

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Yielding behaviors of sintered iron compacts were investigated through the microscopic observations and the tensile tests at both room and high temperatures with different strain rates.
Yield drop, named as pseudo yield point, in a stress-strain curve is observed in various iron compacts, pressed at 3-7 t/cm² and sintered in hydrogen for 1 hr at 1200°C. This behavior, which differs from that of mild steel as to the existence of plastic strain before yield point, may be due to the yielding of matrix and subsequently to the stress relaxation by nucleation and propagation of the crack from residual pores. The pseudo yield point and tensile strength of sintered compacts may depend en the strain rate (10^-5-10^-2/sec) as in the case of mild steel.
The strength increment due to strain aging and the serrated stress-strain curves known as blue brittleness are clearly observed in iron compacts sintered even in hydrogen. Furthermore, this phenomenon is remarkable in the high nitrogen iron compacts sintered in dissociated ammonia.

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焼結鉄における引張り強さと疲れ強さの関係について

紺田功, 大北熊雄

1972 年 18 巻 8 号 p. 302-306
発行日: 1972/04/25
公開日: 2009/05/22

DOIhttps://doi.org/10.2497/jjspm.18.302

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Although many investigations have been made on the mechanical properties of sintered iron compacts, few have been made on the fatigue behaviour. The fatigue strength of sintered iron compacts is one of the most important factors when it is used under repeated stress. Since the sintered iron compacts generally have many pores; the purpose of the present work are as follows; to investigate the notch effect caused by the stress concentration arising from pores at the tensile and fatigue tests, and then, to further investigate the relation between the tensile and fatigue strength.
The following conclusions are obtained from the above investigations:
1) As the porosity of sintered iron compacts is increased, the tensile and fatigue strength are reduced. But when the porosity is constant, the pore size and its shape have influence on the tensile and the fatigue r strength-particulary, stronger influence on the latter than the former.
2) Most of sintered iron compacts have the fatigue ratio (the ratio of the endurance limit to the tensile strength) in the range of 0.23-0.6, and the fatigue ratio decreases with increasing porosity.

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フェライト系13%Cr鋼の分散強化に関する検討

大黒貴, 池永勝

1972 年 18 巻 8 号 p. 307-315
発行日: 1972/04/25
公開日: 2009/12/04

DOIhttps://doi.org/10.2497/jjspm.18.307

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In this investigation, the authors tried to improve the elevated temperature properties, in particular, creep rupture strength of the fully ferritic steel by employing the technique of dispersion strengthening. As a result, it was found that the sintered alloy steels with dispersed fine T-A1₂O₃ particle, especially those obtained by the technique of the liquid phase sintering and the hot-working after sintering, have higher creep rupture strength than those of the wrougth steels having nearly the same compositions, and that these dispersion strengthened steels are promising as a new type of heat resisting material.

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溶浸用Ni-B-Si 3元合金の液相面について

大森慎一郎, 橋本雍彦, 庄司啓一郎, 日高謙介, 小平良男

1972 年 18 巻 8 号 p. 316-320
発行日: 1972/04/25
公開日: 2009/12/04

DOIhttps://doi.org/10.2497/jjspm.18.316

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In order to determine the liquidus surfaces, the ternary system Ni-B(<30 at %)-Si(<30 at %) was studied by thermal analysis, X-ray diffraction and the observation of microstructures. The results obtained are summarized as follows:
(1) The phases appeared in this region were Ni(solid solution), Ni₃B, Ni₂B, Ni₃Si, Ni₅Si₂ and Ni₆Si₂B.
(2) Quasi-binary eutectic reactions took place at the boundaries of liquidus surfaces of Ni(solid solution) and Ni₃B; Ni₃B and Ni₂B; Ni(solid solution) and Ni₃Si; Ni₃Si and Ni₃B; Ni₃B and Ni₆Si₂B; and Ni₂B and Ni₆Si₂B. Monovariant-peritectie reactions took place at the boundaries of liquidus surfaces of Ni₅Si₂ and Ni₃Si, and Ni₅Si₂ and Ni₆Si₂B.
(3) Following four invariant reactions with melt were observed at the intersections of the above i monovariant reaction lines;
L(11 at %B, 13 at %Si)+Ni₅Si₂=Ni₆Si₂B+Ni₃Si at 1012°C
L(12.3 at %B, 12.0 at %Si)+Ni₆Si₂B = Ni₃B+Ni₃Si at 1002°C
L(9.8 at %B, 12.9 at %Si)=(Ni)+Ni₃B+Ni₃Si at 993°C
L(20.3 at %B, 9.8 at %Si)=Ni₃B+Ni₂B+Ni₆Si₂B at 991°C
Thus, the liquidus surfaces have been experimentally determined.

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