MODELLING results of Phase transformations
Simulation of the evolution of phase transformations using “MICRESS”
MICRESS®- the MICRostructure Evolution Simulation Software - is a software package that enables the calculation of microstructure formation in time and space during phase transformations, especially in metallurgical systems. It is maintained and distributed by ACCESS e.V., a non-profit research center at the Aachen University of Technology (RWTH), with revenue from sales being re-invested into maintenance and further development of the code. The software is based on the multiphase-field concept which has been developed by ACCESS e.V. scientists since 1995. The evolution of a microstructure is essentially governed by thermodynamic driving forces, diffusion and interfacial curvature. The strength of the MICRESS® code is that these aspects are treated simultaneously in a comprehensive manner. The backbone of MICRESS® is the multiphase field method for multicomponent alloys and enables the treatment of multiphase, multigrain and multicomponent problems in the fields of solidification, grain growth, recrystallization and solid state phase transformations. Using this versatile and general tool all these phenomena can be addressed in a common model framework. In the case of multicomponent alloys, the required thermodynamic data can either be provided in the form of local linear approximations of the phase diagrams, or by direct coupling to thermodynamic data sets via a dedicated TQ interface developed in collaboration with Thermo-Calc AB, Stockholm.
AUSTENITE TO FERRITE TRANSFORMATION
An initial austenite microstructure of a Fe – C – Mn – Ti – N low carbon is generated with MICRESS®.MICRESS simulates the austenite phase transformation kinetics as a C diffusion process at 790oC with cooling rate 1oC/s. The austenite phase transforms into ferrite with and without cementite formation.
Figure 1a: Austenite transformation into ferrite without cementite formation
Figure 1b: Austenite transformation into ferrite with cementite formation.
The coarsening of a grain structure driven by the local curvature of grain boundaries is a fundamental microstructure transformation when materials are subjected to elevated temperatures. The grain growth of initial austenite microstructure of a Fe – C – Mn – Ti - Nlow carbon was simulated with MICRESS® at 1250oC and 1300oC for up to 6h.
Figure 2: Indicative example of grain growth at 1300 deg. C
The MICRESS® software was applied to simulate the microstructure evolution of multicomponent low carbon steel (Fe-C-Mn-Ti-N). During reheating in austenite microstructure small fraction of TiN particles precipitate at the triple points and interface in austenite grain boundaries at 1480oC. Since the TiN particles are formed in nanoscale, they are discernible.
Figure 3: (a) distribution of N content at low carbon steel, (b) distribution Ti content at low carbon steel. Ti and N contents indicate the formation of TiN particles.
The above indicative modeling results belong to the industrial project “Simulation of grain growth, recrystallization and phase transformations in low carbon steels”, by S. Papaefthymiou and M. Bouzouni, December 2018