Influence of different loading stresses on the peak shape of X-ray rocking curves of an austenitic-ferritic duplex stainless steel during VHCF

Abstract

The behavior of X-ray rocking curves of an austenitic-ferritic duplex stainless steel is investigated in this study. Flat samples were fatigued with different load amplitudes to certain fatigue cycles with an ultrasonic testing device. After each load amplitude X-ray diffraction scans were performed and the rocking curves were compared to the rocking curves of the unfatigued state. These measurements were performed at the synchrotron light source DELTA at beamline BL10. Due to the grain structure of the duplex stainless steel it is possible to perform a single grain analysis even if several grains are illuminated at one time. Each grain whose lattice planes have the right orientation to the incoming beam and the detector, gives a single Bragg reflection on the detector. Different grains have different orientations and so the reflections are arranged on Debye-Scherrer-Rings and it is nearly impossible for two grains to have exactly the same orientations. The reflections can then be indexed as Austenite or Ferrite reflections. The rocking curves are compared for each grain after different loading amplitudes, so the development of one grain can be seen. Possible changes of the rocking curves are broadening, splitting, change in position and intensity and also the integrated intensity. All these changes are discussed in this study and examples are given. Not only Austenite grains are affected even ferrite grains are, but not as much as Austenite is. Changes of rocking curves are explained by formation of slip bands, changes of small angle grain boundaries or initiation and propagation of cracks.