Influence of AlN precipitation on thermodynamic parameters in Al-V-N microalloyed steels

An estimation of the equilibrium compositions of the austenite and carbonitride phases, as well as the mole fraction of each phase in C-Al-V-N microalloyed steels at different austenitising temperatures was made by calculations based on experimental data. Further, a comparison of the mole fraction was made from two thermodynamic models due to Adrian and Rios, with and without considering aluminium in the steels. The results indicate that both models produce very similar results and can be used to calculate the equilibrium parameters and predict the solution temperature of carbonitrides and aluminium nitride in the range 800–1300°C for an alloy system contained up to three microalloying elements and aluminium. Both models predict that most of the carbon remains in solution at the calculated temperature. When AlN precipitation is included in the calculation, it is seen that the mole fraction of the carbonitrides fP and the atomic fraction of carbon in the interstitial lattice of the carbonitrides fC decreases, while the atomic fraction of nitrogen in the interstitial lattice of carbonitride fN, increases. The effect of aluminium on these equilibrium parameters depends on the chemical composition of the steel. Increasing the contents of Al, N, C, and V together in the experimental steels has a more significant influence on these equilibrium parameters than changing only the contents of Al; Al and V or Al and N