A new nanoscale metastable iron phase in carbon steels.
Metastable ω phase is common in body-centred cubic (bcc) metals and alloys, including high-alloying steels. Recent theoretical calculations also suggest that the ω structure may act as an intermediate phase for face-centred cubic (fcc)-to-bcc transformation. Thus far, the role of the ω phase played in fcc-bcc martensitic transformation in carbon steels has not been reported. In previous investigations on martensitic carbon steels, extra electron diffraction spots were frequently observed by transmission electron microscopy (TEM), and these spots were historically ascribed to the diffraction arising from either internal twins or carbides. In this paper, an intensive TEM investigation revealed that the extra spots are in fact attributed to the metastable ω phase in particle-like morphology with an overall size of several or dozens of nanometres. The strict orientation relationships between the ω phase and the ferrite matrix are in good agreement with those of the hexagonal (P6/mmm) ω phase in other bcc metals and alloys. The identification of the ω phase as well as the extra diffraction spots might provide a clue to help understand the physical mechanism of martensitic transformation in steels.
Department of Materials Science and Engineering, China University of Petroleum, Beijing 102249, China.|National Institute for Materials Science, Sengen 1-2-1, Tsukuba 305-0047, Japan.
Tianwei
T
Liu
School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China.
Danxia
D
Zhang
School of Materials Science and Engineering, Beihang University, Beijing 100191, China.
Qing
Q
Liu
Department of Materials Science and Engineering, China University of Petroleum, Beijing 102249, China.
Yanjun
Y
Zheng
School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China.
Yanjing
Y
Su
School of Materials Science and Engineering, Beihang University, Beijing 100191, China.
Xinqing
X
Zhao
Jiangsu Asian Star Anchor Chain Co. Ltd., Jingjiang 214533, China.
Jiang
J
Yin
National Institute for Materials Science, Sengen 1-2-1, Tsukuba 305-0047, Japan.
Minghui
M
Song
National Institute for Materials Science, Sengen 1-2-1, Tsukuba 305-0047, Japan.
Dehai
D
Ping