The Role of Pre-strain on Low-Cycle Fatigue Performance of High Manganese Austenitic Twinning-Induced-Plasticity (TWIP) Steel

Abstract

Twinning induced plasticity (TWIP) steel shows an outstanding performance in energy saving aspect. It is basically accepted that there is no mechanical twin nucleation in TWIP steel under the cyclic strain controlled condition even though the accumulation strain is very large. Accordingly, applying pre-strain to undeformed TWIP steel which can induce mechanical twins, which bring about much better fatigue properties, has received wide attention. Present study was performed to investigate the low-cycle fatigue performance of 17Mn-0.8C TWIP steel (high Mn steel) with the variation of amount of prestrain. For the purpose of obtaining different microstructure (such as dislocation density and twin variant), uni-axial tension and drawing were utilized as pre-strain methods with strain levels 0, 0.2 and 0.4. Subsequently, a comprehensive set of high-strain monotonic and low-strain cyclic deformation were carried out, and the microstructure were analyzed by electron back scattered diffraction and transmission electron microscopy. The results showed that with the increase of prestrain, the fraction of mechanical twins was increased, and drawing having more complicate stress state generates more complicate multi-variant twin than uni-axial tension does. Specimen’s fatigue life dramatically moves upwards which is attributed to the interaction between the glide dislocations and the large amounts of twins formed by pre-strain. Thus, pre-strained steel revealed a better low-cycle fatigue performance.