TY - JOUR
T1 - Isothermal transformation in Fe-N hypereutectoid alloy
AU - Nakada, Nobuo
AU - Fukuzawa, Norihide
AU - Tsuchiyama, Toshihiro
AU - Takaki, Setsuo
AU - Koyano, Tamotsu
AU - Iwamoto, Takashi
AU - Omori, Yasuhiro
PY - 2013
Y1 - 2013
N2 - 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.
AB - 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.
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U2 - 10.2355/isijinternational.53.139
DO - 10.2355/isijinternational.53.139
M3 - Article
AN - SCOPUS:84873849615
SN - 0915-1559
VL - 53
SP - 139
EP - 144
JO - isij international
JF - isij international
IS - 1
ER -