Thermodynamic model for precipitation of carbonitrides in microalloyed steels and its application in Ti–V–C–N system

Based on mass balance and solubility product equations, a thermodynamic model enabling the calculation of equilibrium carbonitride composition and relative amounts as a function of steel composition and temperature was developed, which provides a method to estimate the carbonitride complete dissolution temperature for different steel compositions. Actual carbonitride precipitation behavior was further verified in Ti–V–C–N microalloyed steel system. The model suggests that for higher [V] and [Ti] dissolved in steels, it is available to decrease the addition of C and N during alloy composition design. The resultant longer fatigue life of the modified steel could be attributed to the more [V] and [Ti] dissolved in the matrix, inducing finer dispersion of carbonitrides. Therefore, this model is proved to be effective in determining better chemical composition for high-performance steels, leading to possible reductions in the cost of production and improvements in the combined mechanical properties of the steels.