Isothermal transformation in Fe-N hypereutectoid alloy

Nobuo Nakada, Norihide Fukuzawa, Toshihiro Tsuchiyama, Setsuo Takaki, Tamotsu Koyano, Takashi Iwamoto, Yasuhiro Omori

    Research output: Contribution to journalArticlepeer-review

    13 Citations (Scopus)


    In order to understand the mechanism of isothermal transformation of Fe-N alloy, the isothermal transformation microstructure that forms in a wide temperature range below Ae1 was investigated in Fe-2.6 mass%N hypereutectoid alloy by means of the electron back scatter diffraction method in addition to the conventional microstructural observation methods. High-nitrogen austenite fully decomposed to ferrite and Fe4N over the entire temperature range, and the time-temperature-transformation (TTT) diagram had a C shape with a nose temperature around 700 K. The hardness linearly increased with decreasing transformation temperature because the microstructure became finer, but the morphology of the (ferrite + Fe4N) structure changed discontinuously at around 800 K. From the microstructural and crystallographic analyses, it was concluded that the microstructure formed at higher temperature is a lamellar eutectoid structure, braunite, while the other is an upper bainitic structure containing bainitic ferrite formed through a displacive mechanism and Fe4N formed by concentration and ordering of the nitrogen. Since Fe4N is a counterpart of the cementite in Fe-C alloy, the respective structures are similar to pearlite and upper bainite in carbon steel.

    Original languageEnglish
    Pages (from-to)139-144
    Number of pages6
    Journalisij international
    Issue number1
    Publication statusPublished - 2013

    All Science Journal Classification (ASJC) codes

    • Mechanics of Materials
    • Mechanical Engineering
    • Metals and Alloys
    • Materials Chemistry


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