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

8 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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