INFLUENCE OF AIN PRECIPITATION ON THERMODYNAMIC PARAMETERS IN C-AL-V-N MICROALLOYED STEELS

An estimation of the equilibrium compositions of the austenite and car bonitride phases, as well as the mole fraction of each phase in C-Al-V -N microalloyed steels at different austenitising temperatures was mad e by calculations based on experimental data. Further, a comparison of the mole fraction was made from two thermodynamic models due to Adria n and Rios with and without considering aluminium in the steels, The r esults indicate that both models produce very similar results and can be used to calculate the equilibrium parameters and predict the soluti on temperature of carbonitrides and aluminium nitride in the range 800 -1 300 degrees C for an alloy system contained up to three microalloyi ng elements and aluminium. Both models predict that most of the carbon remains in solution at the calculated temperature. When AIN precipita tion is included in the calculation, it is seen that the mole fraction of the carbonitrides f(P) and the atomic fraction of carbon in the in terstitial lattice of the carbonitrides f(C) decreases, while the atom ic fraction of nitrogen in the interstitial lattice oi carbonitride f( N), increases, The effect of aluminium on these equilibrium parameters depends on the chemical composition of the steel. increasing the cont ents of Al, N, C, and V together in the experimental steels has a more significant influence on these equilibrium parameters than changing o nly the contents of Al, Al and V or AT and N.