Microstructure evolution and crack initiation behavior of Q450NQR1 high-strength weathering steel in very high cycle fatigue regime

The fatigue behavior of Q450NQR1 high-strength weathering steel under a loading ratio of R = 0.1 was experimentally investigated in the very high cycle fatigue (VHCF) regime, elucidating the formation mechanism of the fine granular area (FGA). The results indicated that Q450NQR1 high-strength weathering steel mainly fails due to non-inclusion-induced crack initiation (NIICI) in VHCF regime. Slip in {110} and {112} plane families dominates in ferrite. Intergranular cracking results in fatigue microcracking, which in turn leads to the formation of NIICI in Q450NQR1 high-strength weathering steel. The formation of FGA was attributed to the localized severe plastic strain-induced continuous dynamic recrystallization at the tip of microcrack propagation. Moreover, it can be found that the formation of fine grains promotes the extension and aggregation of microcracks. Based on all experimental findings, a mechanism governing crack initiation in Q450NQR1 high-strength weathering steel during VHCF loading was proposed.