Fatigue crack growth in two TWIP steels with different stacking fault energies. (May 2017) - Yang, H.K.
Highlights: Twinning leads to an increasing kinematic cyclic hardening in TWIP steels. Specific constitutive equations capture the change in shape of stress-strain loops. Fe22Mn0.6C steel exhibits more closure effects than Fe22Mn0.6C3Al steel. This is mainly attributed to stronger roughness-induced closure. Fe22Mn0.6C steel however exhibits a lower resistance to fatigue crack growth. Abstract: Fatigue crack growth tests with R = 0 and 0.4 were carried out on Fe-22Mn-0.6C and Fe-22Mn-0.6C-3Al (wt.%) Twinning-Induced Plasticity (TWIP) steels with stacking fault energies around 21.5 and 37 mJ/m 2, respectively. The former exhibits more crack closure effects, partly due to stronger asperity-induced closure. Strain-controlled push-pull tests followed by scanning electron microscope observations show that both steels are prone to mechanical twinning under low-cycle fatigue, associated with an increasing kinematic hardening. Twinning is however more profuse in Fe-22Mn-0.6C steel. Elastic-plastic finite elements simulations of crack growth, using specific constitutive equations able to capture the increasing kinematic hardening suggest that plasticity-induced crack closure is lower in Fe-22Mn-0.6C steel. Even after closure corrections, the Al-free steel, exhibits a lower resistance to fatigue crack growth, which is attributed to a pronounced strain localisation at the crack tip, and maybe also to environment effects.