As a result of the international expansion of nuclear power plants, the evaluation of the reliablity of new and running reactors is of great relevance, which ensures the nuclear safety. Therefore, non-destructive testing methods are required to identify material degradations in components of power plants. In this context, especially the material behavior at high temperature as well as the resulting microstructural changes needs to be detected.

To exploit the abbilty to detect these aspects in modern reactor materials using non-destructive testing methods, in this reasearch project typical operating loads are applied to generate defined material conditions, which are characterized micromagnetically. The resulting micromagnetic parameters are correlated with the mechanical behavior and the resulting microstructural changes. Therefore, a martensitic steel with 9wt.% Cr (P91) and a high-chromium fully ferritic steel of the type HiperFer, which was developed at the Forschungszentrum Jülich, are loaded in creep and thermomechanical fatigue tests. Subsequently, micromagnetic measurements are performed using a 3MA sensor (micromagnetic multiparameter microstructure and stress analysis) developed at the IZFP. These investigations are complemented by microstructural investigations as well as instrumented cyclic indentation tests, which additionally yield cyclic and quasi-static mechanical properties. Consequently, a sound knowledge of the relation between microstructural changes caused by operating loadings and the magnetic properties will be obtaiend. Based on these results, a correlation analysis of the mehcnaical properties, the magnetic parameters and the microstrctural changes will be conducted, leading to an improved for a non-destructive safety assessment of nuclear power plants.