Kinetics of AlN precipitation in microalloyed steel

In this work, the thermodynamic information on AlN formation in steel and experimental data on AlN precipitation kinetics are reviewed. A revised expression for the Gibbs energy of AlN is presented with special emphasis on microalloyed steel. Using the software package MatCalc, computer simulations of AlN precipitation are performed and compared with independent experimental results from the literature. A new model for grain boundary precipitation is employed, which takes into account fast short-circuit diffusion along grain boundaries as well as slower bulk diffusion inside the grain, together with the classical treatment for randomly distributed precipitates with spherical diffusion fields. It is demonstrated that the precipitation of AlN can be modelled in a consistent way if precipitation at grain boundaries and dislocations is taken into account, dependent on chemical composition, grain size and annealing temperature. It is also demonstrated that, for consistent simulations, the influence of volumetric misfit stress must be taken into account for homogeneous precipitation of AlN in the bulk and heterogeneous precipitation at dislocations.