Modeling of mixed ferrite, pearlite and bainite microstructures formation during continuous cooling and prediction of mechanical properties
2 years beginning ASAP
20% Institut Jean Lamour (Nancy) and 80% Ascometal (CREAS, Hagondange), in France
The two-years post-doctoral position will be organized in the following stages:
1 – Bainite transformation: the model currently under development will be validated regarding its main assumptions (e.g. stasis criterion) and extended to a larger range of chemical compositions. A new attention will be given to the formation of carbides. Mechanical behavior modeling will present two difficulties: the fineness of the bainitic microstructure and the presence of residual austenite, which can result in a TRIP effect [BOU05, HEL11]. The macroscopic behavior of the multiphase microstructure will be determined with an iso-work homogenization scheme. Strengthening by carbides precipitation will have to be considered in some cases.
2 – Ferrite-pearlite transformation: related phase transformation models are much more advanced in literature, which will provide the basis to describe the nucleation-growth of ferrite, the transition from ferrite to pearlite and the prediction of main microstructural features (e.g. interlamellar spacing). Specific issue will regard the consequence of the precipitation state (e.g. V) on interface mobilities. Well-established models of literature [ALL08, ALL19] will also be used to predict the mechanical behavior as a function of the fraction of the constituents. Specific issues to be addressed will include the effects of precipitation or of pearlite globularization.
3 – Coupled model: the consequence of prior ferrite and pearlite formation on the bainite transformation will be modeled. A homogenization scheme similar to the case of ferrite and pearlite will be adapted to consider a microstructure composed of the three constituents, ferrite, pearlite and bainite.
Research activities will be centered on modeling. Models development will benefit from interactions with other projects ongoing at IJL and Ascometal on bainite transformation, martensite tempering or the study of austenite mechanical destabilization.
Models finalization and validation will be based on a large set of experimental data, either already available or to be generated in the framework of the project: quantitative metallography (SEM, EBSD, possibly TEM), phase transformation kinetics by in situ HEXRD in synchrotron beamlines, tensile tests and in situ tensile tests, in order to track the austenite destabilization.