Three-dimensional phase field modelling of the austenite-to-ferrite transformation

The phase field method has been used to simulate the austenite-to-ferrite phase transformation in steel, for the first time in three-dimensional (3D) space. The effect of the exact morphology of the initial 3D austenitic microstructure is shown to be small, but the nucleus density and the temperature range in which nucleation takes place, both derived from experimental observations, are of primary importance for the kinetics. When 3D simulations are compared to two-dimensional (2D) simulations, it becomes evident that 2D simulations predict faster transformation rates. In the often-used practice of considering the interface mobility as an adjustable model parameter, systematically too low values will be obtained if 2D simulations are compared with experiments. Moreover, unrealistic features can be observed in the simulated 2D microstructures, whereas the 3D microstructures show a realistic representation of the actual microstructure. The overall conclusion is therefore that phase field modelling is distinctly more powerful when applied in 3D space.