The atomic arrangements in Fe- C, especially the interstitial carbon positions have been discussed utilizing 57Fe Mössbauer spect roscopy and 13C and 57 Fe spin-echo NMR measurements. Domain wall enhanced spin-echo of 13C and 57Fe have been observed in ferromagnet is Fe-1-6.9 at. % C martensite which were prepared by quenching from 1373K, the stable austenite (fcc) region. 57Fe Mössbauer measurements have been done on the same specimens.13C spectra at 4.2K show two intense resonance lines and a few clear satellite lines in the frequency range between 30 to 44 MHz corresponding to the hyperfine fields from 2.8 to 4.1 T. Their intensities depend on the carbon concentration and the aging period at 323 K. Especially, the satellite lines gradually rise during the aging at the sacrifice of the main line, suggesting the jumps of carbon atoms to form a local ordered arrangement like as Fe8C.
Studies of the phase transition of the title are reviewed Studies by Raman scattering, DSC, inspection under a polarized microscope, and sound-velocity measurement revealed that Tc is 248.8 (±0.5) K, and that the low-temperature phase is ferroelastic. The analysis of the experimental data by Landau's phenomenological method indicated that the phase transition is caused mainly by the softening of the elastic constant C55. The recently reported NMR and Brillouin-scattering data are pointed out to be clues to solve the problem of the disorder that has been claimed in an earlier paper.