Corrosion fatigue crack initiation and initial propagation mechanism of E690 steel in simulated seawater

In the present paper, the corrosion fatigue crack initiation and initial propagation mechanism of E690 steel in simulated seawater were studied by stress-controlled fatigue tests and a series of subsequent characterizations on the fracture surface, microstructure and secondary cracks. Results show that the corrosion fatigue crack initiation and initial propagation mechanism evolves with elevated peak stress level in simulated seawater. When peak stress is far below the proof stress, cracks preferentially initiate at the parent austenite grain boundaries (PAGBs) with 68.4% probability and at the ferrite lath boundaries (FLBs) with 31.6% probability. Meanwhile, the cracks also preferentially propagate along the PAGBs and FLBs. Upon the peak stress close to or above the proof stress, cracks turn to initiate from the emerging corrosion pits and propagate without zigzag detour but by splitting the ferrite laths which transversely block its propagation way.