The energy transition causes more dynamic changes in operating conditions of power plants, resulting in more pronounced thermomechanical loadings and thus, more challenging requirements for the materials used. The high performance ferritic stainless steel HiperFer developed at IEK-2 of Forschungszentrum Jülich shows a higher resistance against fatigue crack initiation and smaller crack propagation rates than conventional power plant steels. This is mainly caused by finely dispersed intermetallic Laves phases partially formed during thermomechanical loading, which results in a precipitation hardening effect.

The aim of this project, which is carried out in colaboration with the IEK-2, is the analysis of the interaction between cyclic hardening, microstructure evolution and the resulting damage mechanisms during isothermal fatigue loading in the LCF as well as HCF regime. Therefore, isothermal fatigue tests are used to characterize the cyclic deformation behavior as well as the precipitation behavior of the Laves phase caused by cyclic deformation at elevated tempertures. Moreover, the infleunce of the temperature and the strain rate applied on the precipitation state and fatigue behavior will be elaborated. In addition, the interaction of cyclic hardening and the fatigue crack propagation will be investigated by performing instrumented cyclic indentation tests in the vicinity of fatigue cracks and especially, within the plastically deformed zone in front of the crack tip. The knowledge gained as a result of these research activities is intended to reveal potentials of HiperFer steels with regard to alloy optimization and the manufacturing process.

This project is conducted in collaboration with the Energy and Climate Research Institute of

Jürich and financially supported by the German Research Foundation (DFG)