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61 巻, 9 号
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技術報告
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木曽 弘隆, 小山 満晴, 田口 富雄1989 年 61 巻 9 号 p. 615-619
発行日: 1989/09/25
公開日: 2015/01/27
ジャーナル フリーPDF形式でダウンロード (2714K) -
滝田 光晴, 上田 俶完, 白木 久史, 成瀬 賢次, 柏木 陽一郎1989 年 61 巻 9 号 p. 620-627
発行日: 1989/09/25
公開日: 2015/01/27
ジャーナル フリーAustempered ductile iron exhibits excellent mechanical properties and wear resistance. The iron obtained by conventional austempering process, however, contains a large amount of retained austenite. The poor machinability due to strain-induced transformation of the retained austenite has made it difficult to extend the commercial application. When the desired quality requirements are primarily wear resistance and static and fatigue strengths, the reducing of the retained austenite might be applied. An austempering process has been investigated to improve the machinability and secure the required mechanical properties of the iron by the reducing the amount of the retained austenite. Though the retained austenite is significantly effective to improve elongation and toughness, the perfect bainitic transformation of austenite is the most effective to improve the machinability.
As a two-stepped austempering process is used usually to improve the cooling rate for heavy parts, the special two-stepped austempering was developed. In this austempering, the desired hardness is secured in the first step to improve the wear resistance and strength, and then in the second step the retained austenite is transformed to bainite perfectly to improve the machinability in a short time.
The austempered iron exhibits the excellent static and fatigue strength similar to those of the conventional ADI containing the retained austenite. Although the elongation and impact strength are somewhat inferior to those of the conventional ADI, the desired properties are obtained. The iron, even the high hardness of Hv 300, shows more excellent machinability than FCD70 of the same hardness and has an excellent machinability equivalent to FCD70 of low hardness.抄録全体を表示PDF形式でダウンロード (3494K) -
狩野 邦彦, 水澤 繁, 米村 次男, 安田 欣一1989 年 61 巻 9 号 p. 632-636
発行日: 1989/09/25
公開日: 2015/01/27
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研究論文
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和出 昇, B. L. モーダイク1989 年 61 巻 9 号 p. 637-642
発行日: 1989/09/25
公開日: 2011/08/20
ジャーナル フリーBehaviors of carbon, retained austenite and bainitic ferrite, which exert important influences on mechanical properties of ADI, were studied in the temperature range 300-400°C using X-ray diffraction.
Carbon diffuses fast at high temperature, causing to fast saturation of carbon in retained austenite, whereas slow diffusion of carbon occurs at low temperature.
Totally, bainitic ferrite exists only in the early stage of the transformation at 350 and 440°C. However, bainitic ferrite can partially exist at 300°C because the transformation occurs inhomogeneously. Bainitic ferrite contains high carbon at low temperature, which may be caused by martensitic transformation. The carbon content in bainitic ferrite at high temperature on the other hand, is low, which suggests that carbides precipitate in carbon super-saturated retained austenite.
Thus, the mechanism of bainitic transformation should vary depending on temperature, just as in steels.抄録全体を表示PDF形式でダウンロード (601K) -
堤 信久, 原 伸明, 山内 章, 関 芳邦1989 年 61 巻 9 号 p. 643-649
発行日: 1989/09/25
公開日: 2011/08/20
ジャーナル フリーWith a view of investigating the bainitic transformation of spheroidal graphite cast irons and a high silicon steel especially the behavior of carbon in transformation, the simultaneous detections of the differential thermo-analysis and dilatometric measurement of specimens on the first stage of isothermal holding after quenching into metallic bath were performed by using a specially designed quenching and holding apparatus for austempering. The change of volume of retained austenite during holding various time at given temperatures for various time after quenching was investigated. The expansion caused by bainitic transformation consisted of two different stage of transformation both in spheroidal graphite cast iron and high sillicon steel. Moreover, the difference in the carbon content in each retained austenite matrices exists in these two irons and steel. Besides, the potentio-static electrolytic etching with chromic acid shows the distinct difference in microstructure of the bainitic ferrite, martensite and retained austenite. Also it has been recognized that the close relation exists between peak value in thermal transformation and carbon content in high sillicon steel.抄録全体を表示PDF形式でダウンロード (707K) -
遠藤 春男1989 年 61 巻 9 号 p. 650-655
発行日: 1989/09/25
公開日: 2011/08/20
ジャーナル フリーThe plate surface is heated from outside so that the temperature gradients of the surface have been constant on steady state. However, if a crack exits on that surface, the surface temperature is disordered by the crack with the air layer, and the temperature gradients are changed.
In this paper, using the plate specimens of alminum castings with a surface crack, the estimation of the surface crack depth is tried by measuring the surface temperature. The temperatures obtained from the experiments were changed to the temperature gradients, and then the relationship between the surface crack depth and the dimensionless temperature gradient was obtained. In addition, the results were compared with the numerical calculation obtained by the finite element method.
The results show that the surface crack depth can be estimated by using the dimensionless temperature gradient. On account of the fact that the dimensionless temperature gradient decreases at the vicinity of the surface crack and shows the maximum value at position of that, this method is also applicable for the detection surface cracks.抄録全体を表示PDF形式でダウンロード (580K) -
呂 傳盛, 陳 建興1989 年 61 巻 9 号 p. 656-661
発行日: 1989/09/25
公開日: 2011/08/20
ジャーナル フリーTensile flow stress of spheroidal graphite cast iron (σz) was expressed well by the following equation, as the function of graphite area fraction (Ag) and the average grain size (D) : σz = (1−k1Ag) (σ0 + k2D−1/2)
Values of k1, σ0 and k2 have been investigated by varying matrix structure and graphite area fraction. In this study, k1 value was noteworthy after a series of analysis, those were showing a similar value about 2.0-2.5. It implys that the tensile flow stress of spheroidal graphite cast iron is not only received the influence of the matrix structure, but also influenced by the dynamical factor of which developing in the matrix during tensile deformation. Moreover, the tensile flow stress even if extremly influenced by the matrix structure and graphite area fraction, but the significant change of k1 value could not be recognized, except the specimens of CV graphite cast iron. Also, the markable variation of k1 value was shown by lowering the graphite nodularity. It is suggested that the effect of stress concentration around the front tip of the graphite particles is a dominating factor in the k1 value associated with that of the tensile flow stress.抄録全体を表示PDF形式でダウンロード (670K)
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