9. Characterization of the Fatigue Behavior of Mechanical and Thermal Aged Austenitic Power Plant Steel AISI 347

For the comprehensive understanding of the fatigue mechanisms of mechanical and thermally aged materials in power plant reactors, an innovative, resource- and time-optimized approach based on non-destructive testing methods is used. Beside investigations on AISI 347 austenitic stainless steel under cyclic loading, magnetic, resistometric and electrochemical measurement techniques were applied to monitor the proceeding fatigue behavior. Qualitative values indicate surface passivation effects and microstructural changes, which are directly related to fatigue states. In total strain-controlled increase tests, cyclic investigations for the initial and a mechanically and thermal aged condition were carried out under distilled water environment at ambient temperature. In comparison to the initial state, the aging process shows a significant influence on the fatigue behavior with a reduction of the stress amplitude at failure down to 75%.