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In order to increase the strength and maintain the ductility of austenitic steels high Nitrogen austenitic steels (AHNS) emerged of which Ni was substituted by Mn so that up to 1 w% N could be alloyed and kept in solid solution. Cold working was added to gain strength values up to 3000 MPa. Still the endurance limit did not follow this trend. The low stacking fault energy was thought being the main reason for the solely planar slip but it became clear that other near-field effects might govern this behaviour as well. Thus the density of free electrons could be identified as being one for CrMn-steels being mainly influenced by the sum and the ratio of C and N. In order to investigate this strain-controlled fatigue tests are carried out. This contribution presents the results of strain-controlled fatigue tests and discusses them on the basis of SEM-EBSD and TEM investigations in relation to the microstructural characteristics.

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Austenitic high nitrogen (AHNS) and austenitic high interstitial steels (AHIS) are of interest for mechanical engineering applications because of their unique combination of mechanical (strength, ductility), chemical (corrosion resistance) and physical (non-ferromagnetic) properties. But despite their high strength values e. g. after cold deformation up to 2 GPa in combination with an elongation to fracture of 30 %, which is based on twinning-induced plasticity (TWIP) mechanisms and transformation-induced plasticity (TRIP) mechanisms, the fatigue limit remains relatively small. While for chromium-nickel steels the fatigue limit rises with about 0.5-times the elastic limit it does not at all for austenitic high-nitrogen steels or only to a much smaller extent for nickel-free austenitic high-interstitial steels. The reasons are still not fully understood but this behavior can roughly be related to the tendency for planar or wavy slip. Now the latter is hindered by nitrogen and promoted by nickel. This contribution shows the fatigue behavior of chromium-manganese-carbon-nitrogen (CrMnCn) steels with carbon + nitrogen-contents up to 1.07 wt.%. Beside the governing influence of these interstitials on fatigue this study displays, how the nitrogen/nickel-ratio might be another important parameter for the fatigue behavior of such steels.Keywords: Austenitic high strength steels / Ramberg-Osgood / twinning-induced plasticity (TWIP) / transformation-induced plasticity (TRIP) / nitrogen-nickel ratio / cyclic behavior Schlü sselwö rter: Austenitische hochfeste Stä hle / Ramberg-Osgood / durch Zwillingsbildung induzierte Plastizitä t (TWIP) / umwandlungsbewirkte Plastizitä t (TRIP) / Stickstoff-Nickel Verhä ltnis / zyklische Belastung Corresponding author: S. Gü ler, Institut fü r die Technologien der Metalle, Lehrstuhl Werkstofftechnik, Universitä t Duisburg-Essen,