High-cycle fatigue properties and damage mechanisms of pre-strained Fe-30Mn-0.9C twinning-induced plasticity steel

The tensile and high-cycle fatigue tests of Fe-30Mn-0.9C twinning-induced plasticity (TWIP) steel after 30%, 60% and 70% pre-straining were performed. Meanwhile, the surface damage morphologies of post-fatigue specimens and microstructure evolutions of pre-strained and post-fatigue pre-strained specimens were also investigated. It is found that the fatigue properties of the TWIP steel can be effectively improved through pre-straining, because the pre-straining can change the fatigue strength coefficient and exponent, respectively. The improvement of fatigue strength coefficient may be attributed to the strengthening mechanisms induced by both twin boundaries and dislocations; while the variation of fatigue strength exponent should be resulted from the combined effects of deformation homogeneity and slip reversibility, as well as the internal damages. Furthermore, the detailed mechanisms associated with the variations of fatigue strength coefficient and exponent were discussed. This study may enrich the fundamental knowledge about how to improve the high-cycle fatigue properties of TWIP steels.