Thermodynamics of the iron-carbon-bismuth ternary system: 1473-1873 K

Because of the interest in steelmaking and recycling, the thermodynamics of the Fe-C-Bi ternary system has been studied. The solubilities of bismuth in liquid iron/iron-carbon alloys and solid pure iron have been measured by equilibrating iron/iron-carbon alloys with bismuth vapor. The experiments were conducted in the temperature range from 1473 K to 1873 K and in the range of carbon contents from zero to carbon saturation. Bismuth behavior abides by Henry's law in liquid iron/iron-carbon alloys and solid pure iron. The solubility of bismuth in liquid iron/iron-carbon alloys increases with increasing temperature and decreasing carbon content. The solubility of bismuth in solid pure iron increases with increasing temperature. Thermodynamic modeling in the Fe-C-Bi ternary system was performed using the "unified interaction parameter formalism". The expression for ln gBi in the liquid region of the iron-carbon phase diagram as a function of temperature and carbon content is given by lngBiin Fe-Cl=1 5.83x103+/-6.18x103 T-1.58+/-8.85x10-2 +-11.24x104+/- 2.28x104T +74.76+/-3.75X C- 3612T+1.845 X2C 1473-1873K and0-4%C and the expression for ln g0Bi (s) in the solid pure iron is lng0Bi s= 12.28x103+/-1.30x103 T+1.97+/-7.46x10-2 1473-1673K where gBi is the Henrian activity coefficient of bismuth in the liquid iron-carbon-bismuth alloy with respect to pure bismuth as the reference state, g0Bi (s) the Henrian activity coefficient of bismuth in the solid pure iron, T is the temperature in Kelvin and XC is the mole fraction of carbon.;The mutual solubility of bismuth and iron was discussed on the basis of the experimental data.