Sub-project C6 : Damage and failure in the Fe-Mn-C system

Damage and failure in the Fe-Mn-C system

Dr.-Ing. Prahl (Department of Metallurgy, RWTH Aachen)


Fe-Mn alloys with a Mn-concentration >5 mass-% represent a new class of coldforming structure materials, whose multiphase microstructure enables, in comparison to other conventional austenitic steels, outstanding mechanical characteristics, not only in connection to strength, but also to deformation. It is to be seen that, especially in face centred-cubic metals high strength is adjusted via deformation mechanisms as there are dislocation slip, mechanical twinning or deformation-induced martensiteformation.

With an increasing deformation, damage in the micro-structure appears in form of voids and micro-cracks. The development of these voids and micro-cracks leads to material failure and therefore limits the forming property. It is known, that the microstructure failure can be ductile, brittle or also a combination of both, with dependence on the microstructure as well as on the boundary conditions. The reasons for this damage can be different failure mechanisms on the microstructure scale, like interface failure due to phase transformations or twinning, dislocation localisation or also inclusion- and precipitation failure as a cause of microscopic inhomogeneous deformation distribution. For the further development of these structure materials, especially with regard to its forming property, it is of great importance to quantitatively understand its damage and failure behaviour during plastic deformation and equivalent to that the influences of TRIP- and TWIP-effect as well as of inclusions/precipitations on the damage and failure.

Due to these considerations and with regard to the further testing of Fe-Mn-C steels, the question concerning the connection between the damage mechanisms and the forming properties of Fe-Mn-C steels arises. The crucial point of investigation is the question where the damage process under uni- and multiaxial loading starts and how it proceeds. Especially the damage processes are to be traced back to stacking fault energy as well as to defect configuration of Fe-Mn-C steels as a function of chemical composition, structure, and forming properties. The influence of inclusions and precipitations on the defect configuration needs to be quantitatively described as well. In future request periods, the investigations are to be extended on high speeds and low temperatures.