Equilibrium values for CO and CO2 in contact with Fe and Fe3C over a temperature range of 550 and 900°C have been determined;By means of these data, values of +5,943 and -4,948 were obtained for the change in free energy content accompanying the reaction, 3Fe+C→Fe3C, at temperatures of 550°C and 900°C, respectively;Values ranging from 5,450 to 40,700 were calculated for the heat of formation of Fe3C.