Mathematical Modeling of the α→γ Phase Transformation during Heating in Low Carbon Steels

The purpose of this research is to develop a model for the ferrite-to-austenite transformation on heating which would include the possibility of the change in the character of the transformation from diffusional to mixed-mode and would be less computationally demanding. A physics-based model is constructed for the ferrite-austenite phase transformation of low carbon steels. The model is descretized by the moving finite element method and the results are compared with existing models, the phase field model, the diffusion controlled model, and the interface controlled model. It is concluded that the new model is stable, conservative, and successfully runs interface controlled as well as diffusion limited cases. The results are comparable to the much more costly phase field model simulations. One of the main topics that Corus (a steel producer company in the Netherlands) is working now is the development of the new type dual-phase steels. The developed 1-D model is extended to 3-D and is now a part of the bigger model which simulates the evolution of the microstructure of the carbon-manganese steels during the whole production cycle, which includes both heating and cooling parts. Referat Matematisk modellering av alfa – gamma fasomvandling vid värmning av lågkolhaltigt stål En ny modell utvecklas för ferrit-austenit-omvandlingen i lågkolhaltigt stål. Modellen baseras på gränsytans termodynamik. Modellen diskretiseras med rörliga finita element och simuleringsresultaten jämförs med tre existerande modeller: Fasfältsmetoden, diffusionskontrollerad, och interface-kontrollerad fasomvandling. Den nya simuleringsmodellen är stabil och konservativ för såväl diffusions-begränsade som interface-begränsade processer. Resultaten är jämförbara med dem som erhålls med den mycket dyrare fasfältsmetoden, och modellen kan implementeras i 3D-simulatorer för styrning av ståltillverkningsprocesser.