A remarkable improvement of low-cycle fatigue resistance of high-Mn austenitic TWIP alloys with similar tensile properties: Importance of slip mode

The low-cycle fatigue (including extremely-low-cycle fatigue) behaviors of the Fe-Mn-C TWIP steels are comprehensively investigated focusing on the effects of the imposed strain amplitude and Mn content on the deformation and damage characteristics. It is found that fatigue performance varies obviously with increasing Mn content, though their tensile properties do not change much. With the increase of strain amplitude or Mn content, the dislocation slip mode changes from planar slip to wavy slip. In order to evaluate the low-cycle fatigue properties, more impartial and reasonable, a hysteresis energy-based fatigue life prediction model is applied and developed. According to the experimental results and model analysis, unlike tensile properties, the low-cycle fatigue performance of the TWIP steel is extremely sensitive to their slip mode. A remarkable improvement of fatigue resistance is found to be related to the increase of Mn content, which may originate from the relatively low damage accumulation rate of planar slip. Specifically, planar slip caused by lowering the stacking fault energy is much more uniformly distributed than which caused by disordering short-range order. Such a variation in fatigue damage micromechanisms is believed to be the major reason for the occurrence of a special bilinear relationship for the Coffin-Manson curve. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.