Electron Diffraction Study of Long-Period Ordered Phase Formed in Fe-1.83 mass%C Martensite during Aging at Room Temperature

Abstract

The long-period ordered phase (LPOP) formed in Fe-1.83 mass%C martensite during aging at room temperature has been investigated by the electron diffraction method. It was found that the LPOP formed at 298 K possessed an incommensurate superperiod of 10.7c (c is the length of the c axis of martensite), different from the previously reported 12c at higher aging temperatures. This indicated a temperature dependence of superperiod of the LPOP, which could not be explained by previous structure models of the LPOP. The above experimental finding show that the LPOP is consistent with an off-stoichiometric phase γ'-Fe x C(II) (x=4 ∼ 10), the superperiod of which can adopt 10c, 12c, and 14c at different temperatures. The coexistence of two of these structures at intermediate temperatures results in the nominal incommensurate superperiod. Computer simulated electron diffraction (ED) patterns based on this structure model remarkably resembled the observed ED patterns in every aspect.