Abstract: Based on the regular solution approximation， the two sub-lattice model and dissolution and precipitation theory， a universal thermodynamic model for carbo-nitride precipitation was established. The model was used to calculate the thermodynamic equilibrium information including matrix composition， composition and volume fraction of precipitation between sub-stoichiometric or stoichiometric precipitation and matrix of the 0.17C-0.023Nb-0.012Ti-0.004N at different temperatures. The results showed that the solubility of sub-stoichiometric precipitation is bigger than that of stoichiometric precipitation， and the volume fraction of the former is less than the latter one at the same temperature. With the decrease of the temperature， the precipitation is gradually changing from titanium nitride to complex precipitation which is rich in niobium and carbon， and the volume fraction differences in different precipitations also decrease gradually.

Key words: stoichiometric precipitation, sub-stoichiometric precipitation, thermodynamic model, complex precipitation, two sub-lattice model