For the investigations the system Fe-Mn-C is chosen because the mechanical properties are based on different metal-physical deformation-mechanisms such as dislocation glide, TRIP- and TWIP-effects, etc. These material properties and microstructural features are influenced by the chemical composition. Therefore the System Fe-Mn-C is well appropriate for the application of ab initio techniques delivering a direct correlation between chemistry, deformation mechanisms, microstructure and macroscopic properties.
As a new class of structural materials the system Fe-Mn-C is suitable for industrial applications and mass production. It can be produced as flat product, sheet steel or steel profile, used for improved security standards and weight savings in light constructions in aeronautics, automobile and frame structures. By integrated processing routes and forming steps, an effective and cost-efficient production can be realized.
Within the 2nd research period investigations with focus on Fe-Mn-C alloys will continue. Investigations are expanded on experiments with Al as a substitutional element. On the one hand this offers the opportunity to check the recently gained information on the deformation mechanism of microband formation within the experimental program or to investigate the influence of Al on the stacking fault energy. On the other hand it is possible to respond to the latest industrial trends. Further new challenging aspects are picked up, as there is the role of hydrogen in high-strength steels.
Generally the co-operation and knowledge exchange between the different part projects is intensified. This means methods for evaluation of the models will be identified and the introduced models should be exploited concerning the engineering part of material development and processing routes.
In the third research period the material spectrum is again extended. There are material concepts with lower manganese contents (eg. 5 - 12% by mass instead of> 15% by weight) taken. After appropriate heat treatment these medium-manganese steels show a two-phase structure of metastable austenite and martensite. The scientific challenge now lies in the fact that the various deformation mechanisms of the austenite are still active but the austenitic phase, however, is embedded in a body-centered cubic matrix. Thus, the mechanical, crystallographic and chemical interactions at the interfaces play a significant role. While in the first research phase mainly the stacking fault energy has been considered as the primary control variable, in the second phase a more detailed microstructure description was made which takes into account particularly grainsizes and segregation effects. In future, the volume fractions of the involved structure components, their size and morphology are included as an important parameter. Finally, with the investigation of additional materials the SFB also takes up a current trend of industrial alloy development. Here it is mainly the alloy cost and manufacturing constraints that give rise to the desire for low alloyed materials with similarly attractive characteristics as in the purely austenitic high manganese steels.
The following issues are part of the 3rd research period from 2015 to 2019:
- Further development and validation of the previously introduced modeling methods
- Extension of the modelling approaches to the consideration of multiphase microstructures and the according additional interface interactions
- Extension of experimental investigations in matters of load and stress conditions in mechanical characterization
- Continuation of the numerical and experimental studies with an emphasis in the microband-induced plasticity (MBIP)
- Exploitation of high-resolution methods for the characterization of nanostructured materials
- Engineer-like control and evaluation of strain hardening behavior of new steels for selected applications (Cloud I)
- Investigation of interface-dominated phenomena between matrix and second phase for the adjustment of mechanical properties (Cloud II)
- Mechanism oriented characterization and modeling of hydrogen-induced damage (Cloud III)
- Implementation of findings of the CRC in transfer projects