On the Partial Pressure Measurement and Activity Calculation of Mn in the Ni-Cr-Co-Mo Alloy Melt

Abstract

In metallurgical production processes, the vapor pressures and activity coefficients of impurity elements areconsidered as importantparameters in thermodynamic calculation. A saturated flow method was used to measure the dissolution equilibrium of Mn vapour over the surface of liquid Ni-Cr-Co-Mo alloys from 1773 to 1923K, and the measured results were employed in the calculation of the activities andactivity coefficients of Mn in liquid Ni-Cr-Co-Mo alloys. It is found that Mn showed a strong positive deviation from the Henry’s law, and the relationship between temperature and the standard free energy of dissolution reaction Mn(g)=[Mn]Ni-Cr-Co-Mowas determined to be . At 1873 and 1923K , the activity coefficient ƒof Mn in the Ni-Cr-Co-Mo alloymelt with 0.2wt.%Mn addition were calculated to be 1.065 and 1.068, respectively. According to the results mentioned above,the volatile lower limit of Mn can be up to 2.14 ppm in conventional vacuum melting production.