COMPUTER CALCULATIONS OF METASTABLE AND STABLE IRON-CARBON-SILICON PHASE DIAGRAMS FROM BINARY THERMODYNAMIC PROPERTIES

Phase relationships in the Fe-rich corner of the Fe-C-Si ternary system have been calculated for conditions of both metastable and stable equilibria. The calculations were based on the thermodynamic properties of the constituent binary systems which were collected from selected literature by Harvig, Kaufman, Kaufman and Nesor.;The Nelder-Mead simplex method was used to search for minimization, and Basic-coded programs were developed to implement the numerical iteration. No attempt was made to incorporate ternary interaction parameters into the calculations. Four metastable isothermal sections from 1073 to 1373K and nine stable isothermal sections from 1073 to 1773K were obtained. The level of agreement between experimental and calculated results was considered acceptable.;The binary data generated constituent binary phase diagrams in good agreement with the experimental observations. Numerical coefficients for the thermodynamic functions were used as adjustable parameters for hypothetical (alpha) and (gamma) solid solution phases in the Si-C system and graphitic solid solution in the Fe-Si system. After combining the available binary data through the use of Kohler equations, these unknown parameters were adjusted to minimize the Gibbs energies of the system at 1273 and 1573K to obtain reasonable agreement between calculated and experimental phase boundaries.