2段オーステンパ処理球状黒鉛鋳鉄の組織と硬さ

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A special two-stepped austempering process of ductile iron was developed. In this process, the desired hardness is secured to improve wear resistance and strength in first step treated in the lower temperature bath(325-375°C) for short time (0-2min). In the second step in the higher temperature bath(440°C), the austenite transformed to perfect bainite and the retained austenite is reduced to improve the machinability in a short time (within 60min). The application of the iron austempered in this process to the sliding parts for automobiles confirmed the sufficient quality and machinability. In this study, it is intented to make clear the mechanism of the bainite transformation and the improvement of hardness in this process. Ductile iron was two-stepped austempered at various temperature for various period. The microstructure was analized by the image analizing technique and the micro hardness testing. Following results were obtained : The harder acicular bainite precipitates from the neighborhood of graphite by the holding in the second step after holding in the first step. As holding in the second step, globular bainite which is less hard precipitates around the acicular bainite. However, the acicular bainite continues to grow maintaing high hardness during holding until finishing of treatment. The lower the temperature of 1st-step holding and the longer the time of 1st-step, the volume fraction of the harder acicular bainite increases. The harder acicular bainite precipitated by holding at lower temperature even if a short time and grows during in second step contributes to the improve of hardness. Whereas, the lower the holding temperature of 1st-step, the shorter the time of holding at higher temperature in second step to improve the machinability by reducing the retained austenite.
Japan Foundry Engineering Societyの論文

2段オーステンパ処理球状黒鉛鋳鉄の組織と硬さ

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Japan Foundry Engineering Society | 論文

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