The solubility of nitrogen in liquid alloys of iron with carbon and silicon was previously determined experimentally in numerous works. Those works, however, concerned relatively low nitrogen partial pressures (being in most cases at I atm). Bearing the above in mind, the author's own programme of experimental research was drawn up. By applying the levitation metal melting technique, nitrogen concentrations in the iron alloys were determined in the conditions of thermodynamic equilibrium within a wide range of variation of thermodynamic factors, i.e. nitrogen pressure from 1 to 21 atm, liquid metal temperature from 1973 to 2173K. The experimental results served for formulating the thermodynamic characteristic of the activity coefficient, where one of the factors, for the first time, was the nitrogen concentration in the alloy. By using the results of the author's earlier work on the liquid Fe-N alloy, temperature relationships of all interaction parameters necessary for the Fe-N-C-Si alloy have been defined.
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