Carbon Activity and Solubility in the Co-Cr-C System with Lower Carbon Content at Temperatures 950-1200 degree C.

Carbon activity in the Co-Cr-C system containing 12-36% chromium and up to 8% carbon has been determined in the temperature range from 950 to 1200 degree C by carburizing specimens in a H//2-CH//4 atmosphere in scaled quartz capsules. The activity of carbon increases in all cases with its concentration. With a higher carbon content, the precipitation of carbide M//7C//3 occurs preferentially, whereas with a higher chromium and lower carbon content the precipitation of carbide M//2//3C//6 takes place. Equations are derived which describe the temperature dependence of the activity coefficient of carbon and the boundaries between the zone of carbon solid solution in the metallic matrix and the zones of carbide precipitations. In addition, the values of partial dissolving enthalpy and enthropy of carbon are determined.