United Metallurgical Company (Moscow, Russia):

Paderin P. S., Cand. Eng., Technical Expert, e-mail: Ppaderin@omk.ru

Necessity of thermodynamics development for carbon solutions in liquid iron is substantiated. Pure solid carbon was taken for standard state of dissolved carbon in liquid iron. Concentration of carbon and iron was expressed in molar fractions. It permitted to use the equations of solution theory. According to the literature data, the linear temperature dependence of excessive carbon chemical potential in solid infinitely diluted in liquid iron was established. Excessive partial molar entropy in equation of excessive chemical potential transforms a regular solution in a pseudo-regular one. The values of carbon solubility at different temperatures are calculated via the curve C ’D’ of Fe–C phase diagram, as well as carbon activity coefficients, carbon excessive chemical potentials and the values of mixing energy of liquid iron with carbon at its solubility points. The quasi-regular solution model of carbon at all its concentration values in liquid iron was built in order to calculate carbon activity in temperature range 1400 °C — 1600 °C.

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