The Bonding Characteristics and Local Structure of Carbon in Solution and Iron Carbides in Iron Using C K-Edge X-Ray Absorption Spectroscopy Measurement and First-Principle Calculation

The bonding characteristics and local structure of carbon in Fe-0.79 mass pct C martensitic and pearlitic steels are investigated using C K- edge X-ray absorption spectroscopy (XAS) and full-potential real-space multiple-scattering calculations. We find that the subpeak at 288 to 290 eV is related to the precipitation of carbides such as θ -Fe 3 C, η -Fe 2 C, ε -Fe 3 C, and χ -Fe 5 C 2 . Consequently, martensitic and pearlitic steels are characterized by peaks at 283 and 288 eV, respectively. The decay in the intensity of the peak at 288 eV follows carbon dilution in the θ -carbide, which is crucial for carbon aggregation. Since no high-precision C K- edge XAS spectral data are currently available for θ -Fe 3 C and carbon in solution, we believe that the proposed method is a suitable one for elucidating the mechanism of formation of the microstructure of steel from the viewpoint of carbon precipitation.