Experimental and thermodynamic studies of the Fe-Si binary system

Ikuo Ohnuma, Shinya Abe, Shota Shimenouchi, Toshihiro Omori, Ryosuke Kainuma, Kiyohito Ishida

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63 Citations (Scopus)


Phase equilibria in the Fe-Si binary system were investigated experimentally and thermodynamic assessment was carried out. The αFe (A2) + α″Fe 3Si (D0 3) two-phase microstructures at 600°C and 650°C were obtained, whose grain sizes were sufficiently coarsened to be analyzed by FE-EPMA with a spatial resolution below 0.5 μm under the condition of 6 kV accelerating voltage. α′FeSi (B2) + α″Fe 3Si (D0 3) twophase equilibria above 700°C were detected for the first time and equilibrium compositions were determined by the diffusion couple method. The horn-shaped two-phase miscibility gap extends from the low temperature α Fe + α″Fe 3Si equilibrium along the B2/D0 3 second-order transition boundary and closes below 1 000°C. Four-sublattice split compound energy formalism was applied to calculate the Gibbs energy of the bcc phases, A2(α Fe), B2(α′FeSi) and D0 3 (α″Fe 3Si), and the thermodynamic parameters in the Fe-Si binary system were evaluated. Equilibrium relations in the binary system were well reproduced, especially the effect of the B2 and D0 3 ordering on the liquidus and solidus curves and the miscibility gap between bcc phases. Optimized thermodynamic parameters as well as the experimental results are expected to be helpful for developing higher multi-component systems for practical steels.

Original languageEnglish
Pages (from-to)540-548
Number of pages9
JournalIsij International
Issue number4
Publication statusPublished - 2012


  • Diffusion couple
  • Miscibility gap
  • Order-disorder transition
  • Phase diagram

ASJC Scopus subject areas

  • Mechanics of Materials
  • Mechanical Engineering
  • Metals and Alloys
  • Materials Chemistry


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