Exploration of the high-cycle fatigue properties of Al-rich interstitial free steels stabilized by Ti and Nb

The addition of Al element is a promising method to enhance the deep drawing ability of interstitial free steels, since it favors a strong normal direction fiber texture. However, the scarcity of experimental results on the mechanical properties of such Al-rich interstitial free grades is detrimental to its potential applications in various industrial fields. In the present work, the high-cycle fatigue properties of Al-rich interstitial-free and high-strength interstitial-free steels have been investigated. Al-rich interstitial free steel presents the lowest fatigue endurance at 10⁷ cycles among the materials investigated (158 MPa), mainly driven by its coarse microstructure. Furthermore, its lower Mn concentration in comparison with high-strength interstitial-free grades provokes grain shape change mechanism, resulting in the occurrence of a transient intergranular fatigue crack propagation feature. Despite their similar microstructures and monotonic strengths, Al-rich high-strength interstitial-free grade reveals a fatigue endurance at 10⁷ cycles of 273 MPa, significantly larger than its conventional Al concentration counterpart (i.e., value of 233 MPa). This gap mainly stems from the generation of extended dislocation substructures in Al-rich grade, which tends to prevent early fatigue crack propagation.