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EBSD- und TEM-Investigations of the Deformation Induced Martensitic Transformation in the Austenitic Steel X6CrNiNb18–10 under Cyclic Loading

Abstract As part of an existing research project [1] the fatigue behaviour at room temperature of the austenitic steel X6CrNiNb18–10 was investigated. From a combination of interrupted low cycle fatigue tests and EBSD-measurements in the scanning electron microscope (SEM) the deformation induced transformation of austenite into α'-martensite occurring was able to be observed over the life of the specimen. From TEM-investigations carried out on thin metal foils prepared from the fatigue specimens, the presence of body centred cubic (bcc) α'-martensite was confirmed within the austenitic matrix. This phase transformation affects the crack initiation mechanism. Fatigue cracks often form within the microstructure at the phase boundary between the austenite and the martensite and in the martensitic areas where they grow into the martensitic phase formed at the crack tip.