Low Cycle Fatigue Behavior and Deformation Mechanism of TWIP Steel

Low cycle fatigue behavior of TWIP (twinning induced plasticity) steel was investigated in axial symmetric tension-compression cyclic loading pattern. Fracture surfaces and microstructures were examined by optical, scanning electron and transmission electron microscopes. It was found that the fatigue life at the strain amplitude of 0.4% is up to 15000 cycles, which is much longer than TRIP780 and HSLA800 steels. The strain hardening and softening features are significant until the strain amplitude comes to 1.25%. Persistent slip bands and tiny mechanical twinning layers were observed after fatigue deformation. Deformation mechanism of TWIP steel at low cycle fatigue process is not only twinning, but a complex of both twinning and persistent slip bands.