Enhanced Low-Cycle Fatigue Life by Pre-Straining in an Fe-17Mn-0.8C Twinning Induced Plasticity Steel

Enhancement of low-cycle fatigue (LCF) life was achieved by imposing pre-straining in an Fe-17Mn-0.8C twinning induced plasticity steel. Two different straining methods (uni-axial tension and drawing) were utilized with strain levels of 0, 0.2, and 0.4. The beneficial effect of pre-straining for LCF life was elucidated by microstructural observation using scanning and transmission electron microscopy. In both pre-strain modes, the fraction and variant of mechanical twins (MTs) are increased with the amount of pre-strain. Particularly, pre-drawing generated more multi-variant MTs and resulted in better LCF performance than those of uni-axially tensioned specimen. The role of MTs or stacking faults as a barrier of dislocation glide was clarified by transmission electron microscopy analysis of fatigued specimens. Fractographic analysis also showed that crack deflection occurred predominantly in the pre-strained specimens, which was effective in retarding crack propagation.