Study on Cyclic Strain Localization and Fatigue Fracture Mechanism in High Manganese Twinning-induced Plasticity Steels

The fatigue cracking mechanisms of two high Mn TWinning-Induced Plasticity (TWIP) steels are investigated in detail using electron channelling contrast imaging (ECCI) and electron backscatter diffraction (EBSD). Furthermore, the fracture surfaces of the fatigued steels have been studied by employing a field emission gun scanning electron microscope (FEG-SEM). The fine details of the fatigued surface topography are verified using an atomic force microscope (AFM). The results indicate that the fatigue crack embryos nucleate at an early stage of the fatigue life as a result of local straining at grain and annealing twin boundaries at sites, where persistent slip bands create dislocation piled-ups that impinge on boundaries. The EBSD measurements showed that unlike in monotonic straining, the formation of deformation twins is not observed under cyclic straining.