Thermodynamic evaluation of reaction abilities of structural units in Fe–C binary melts based on atom–molecule coexistence theory

The reaction abilities of structural units in Fe–C binary melts over a temperature range above the liquidus lines have been evaluated by a thermodynamic model for calculating the mass action concentrations N _i of structural units in Fe–C binary melts based on the atom–molecule coexistence theory (AMCT), i.e., the AMCT-N _i model, through comparing with the predicted activities a_R,i of both C and Fe by 14 collected models from the literature at four temperatures of 1833, 1873, 1923, and 1973 K. Furthermore, the Raoultian activity coefficient \( \gamma_{\text{C}}^{0} \) of C in infinitely dilute Fe–C binary melts and the standard molar Gibbs free energy change \( \Delta_{\text{sol}} G_{{{\text{m, C}}_{{{\text{dis}} .}} ( {\text{l)}} \to [ {\text{C]}}_{{_{{{{w}}_{{[ {\text{C]}}}}}} {= 1.0}}}}}^{{\Theta,{{\%}}}} \) of dissolved liquid C for forming w_[C] as 1.0 in Fe–C binary melts referred to 1 mass% of C as reference state have also been determined to be valid. The determined activity coefficient ln γ_C of C and activity coefficient ln γ_Fe of Fe including temperature effect for Fe–C binary melts can be described by a quadratic polynomial function and a cubic polynomial function, respectively.