Structure of the Precipitated Particles at the Third Stage of Tempering of Martensitic Iron-Carbon Steel Studied by High Resolution Electron Microscopy

TLDR: In this article, it was shown that the forbidden spots observed in electron diffraction patterns from the precipitates can reasonably be interpreted on the basis of the characteristic growth nature of the carbide phases.

Abstract: Application of the lattice and structure imaging techniques in electron microscopy has shown that θ-Fe3C and χ-Fe5C2 intergrow microsyntactically in the precipitated particles at the early third stage of martensite tempering (520~670K). Also is found the microsyntactic intergrowth of higher Carbides, θn-Fe2n+1Cn, having structures closely related With those of θ-Fe3C and χ-Fe5C2. All the forbidden spots observed in electron diffraction patterns from the precipitates can reasonably be interpreted on the basis of the characteristic growth nature of the carbide phases. At the later stage of tempering (720-870K), the precipitates are θ-Fe3C containing various kinds of planar defect. Amechanism is presented for the transformation from χ-Fe5C2 to θ-Fe3C.