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Internal Porosity Defects in Ductile Cast Irons

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Abstract

The internal porosity defects detected in four castings produced in two foundries were carefully observed and analyzed by using FE-EPMA, and then, the root cause of the defects was investigated. Based on the generally authorized theory that the internal porosities might be formed at late stage of the solidification, the experimental results are verified. The formation mechanism of dual layer and its characteristic folds or creases on inner surface of defects shown in the experimental results could not be explained by the authorized theory, but the features seem to be possible to explain when the basic films might originate on the surface of the liquid metal and might be entrained in turbulent flow. The reductive reaction of carbon and FeO in the solid bifilms formed in the liquid metal is considered to contribute the pore nucleation in ductile iron. Therefore, in addition to the control of the process variables already developed by many researchers, the internal porosity defects in ductile cast irons using resin-bonded sand and cores might be prevented by avoiding the entrainment of carbon and oxide films.

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Acknowledgements

The authors wish to thank Emeritus Prof. John Campbell of University of Birmingham for helpful discussions and to acknowledge permission to publish this paper given by the president of Joban Seisakusho Ltd. and the managing director of Koiwai Ltd. and also their colleagues for their assistance. Special thanks to the students of Graduate School of Iwate University for the observation by EPMA.

Funding

Funding was provided by The Japan Society for the Promotion of Science (JSPS) (Grant Number JP18K04794).

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Authors and Affiliations

  1. TCT Casting Technologies, Saitama, Japan

    Yoshiaki Takemoto

  2. Department of Physical Science and Materials Engineering, Iwate University, Morioka, Iwate, Japan

    Masayuki Mizumoto

  3. Graduate School, Department of Physical Science and Materials, Iwate University, Morioka, Iwate, Japan

    Koji Kinno

Authors
  1. Yoshiaki Takemoto
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  2. Masayuki Mizumoto
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  3. Koji Kinno
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Correspondence to Yoshiaki Takemoto.

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Yoshiaki Takemoto: Formerly Iwate University.

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Takemoto, Y., Mizumoto, M. & Kinno, K. Internal Porosity Defects in Ductile Cast Irons. Inter Metalcast 15, 916–929 (2021). https://doi.org/10.1007/s40962-020-00527-x

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