Selection of the Massive-like <i>δ</i>-<i>γ</i> Transformation due to Nucleation of Metastable <i>δ</i> Phase in Fe-18 mass%Cr-Ni Alloys with Ni Contents of 8, 11, 14 and 20 mass%

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  • Nishimura Tomohiro
    Department of Materials Science and Engineering, Kyoto University, now Kobe Corporate Research Laboratories, Kobe Steel, Ltd.
  • Matsubayashi Ryota
    Department of Materials Science and Engineering, Kyoto University, now Steel Research Laboratories, Nippon Steel Corporation
  • Morishita Kohei
    Department of Materials Science and Engineering, Kyoto University, now Department of Materials, Kyushu University
  • Yoshiya Masato
    Department of Adaptive Machine Systems, Osaka University, now Division of Materials and Manufacturing Science, Osaka University
  • Nagira Tomoya
    Joining and Welding Research Institute, Osaka University, now Research Center for Structural Materials, National Institute for Materials Science
  • Yasuda Hideyuki
    Department of Materials Science and Engineering, Kyoto University

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Other Title
  • <b>Fe-18 mass%Cr-Ni合金(Ni組成:8, 11, 14, 20 mass%)における準安定</b><i>δ</i><b>相の核生成によるマッシブ的変態の選択</b>
  • Fe-18 mass%Cr-Ni合金(Ni組成:8, 11, 14, 20 mass%)における準安定δ相の核生成によるマッシブ的変態の選択
  • Fe-18 mass%Cr-Ni ゴウキン(Ni ソセイ:8, 11, 14, 20 mass%)ニ オケル ジュンアンテイdソウ ノ カク セイセイ ニ ヨル マッシブテキ ヘンタイ ノ センタク

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<p>It has been realized that a massive-like transformation, in which δ phase (ferrite) transformed to γ phase (austenite) in the solid state during and after solidification, was selected in Fe-C steels. X-ray radiography confirmed that the massive-like transformation also occurred in Fe-18 mass%Cr-Ni alloys with Ni contents of 8, 11, 14 and 20 mass%Ni. According to the equilibrium phase diagram, δ phase is the primary phase in 8 and 11 mass%Ni alloys while γ phase in 14 and 20 mass%Ni alloys. Solidification was always initiated by nucleation of δ phase and consequently fine γ grains were formed by the massive-like transformation in 8 and 11 mass%Ni. On the other hand, nucleation of δ phase as a metastable phase was preferably selected at lower undercoolings (<50 K) in 14 and 20 mass%Ni and consequently the massive-like transformation occurred even in 14 and 20 mass%Ni alloys. Solidification of γ phase can be triggered by nucleation of δ phase followed by the massive-like transformation in the Fe-Cr-Ni with lower Cr/Ni values (the primary γ alloys). Moreover, the present study demonstrates that the massive-like transformation will be commonly observed in Fe-based alloys, in which δ and γ phases are competitive each other from a thermodynamic perspective.</p>

Journal

  • Tetsu-to-Hagane

    Tetsu-to-Hagane 107 (7), 558-565, 2021

    The Iron and Steel Institute of Japan

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