Abstract
Mössbauer spectra of Fe-1.5∼7.2 at%C alloys without and with 5T longitudinal external magnetic field were measured to clarify the structure of iron carbon martensite. The spectra of freshly quenched martensite are decomposed into three magnetic hyperfine patterns having different fields. The 1st component with a hyperfine field of (H\simeq27T) is identified as the absorption caused by 1st neighboring iron atoms of octahedral carbon atoms. The 2nd component (H\simeq31.5T), the intensity of which rapidly decreases during aging, is due to 1st neighboring iron atoms of tetrahedral carbon or possibly 2nd nearest neighbors of octahedral carbon atoms. The 3rd main component (H\simeq34T) is due to iron atoms not much perturbed by farther carbon neighbors.
The appearance of three additional components (H\simeq37, 26.5 and 18T) in the aged martensite indicates the formation of the ordered non-stoichiometric Fe4Cx (x<<1) phase. The Mössbauer spectra of the ε (or η) carbide formed after aging at 313 K are decomposed into three hyperfine components corresponding to different iron environments in the carbide, suggesting the existence of vacant sites of carbon in the Fe2C structure.
