Fatigue crack propagation behaviour of steels with different microstructures

The fatigue crack propagation behaviour of steels with different microstructures was investigated. The results show that the Paris constant m values of the different steel microstructures have a linear relationship with the yield strengths for the same or approximate material composition, and that the ratio of the fatigue crack propagation threshold value to fracture toughness (ΔKth0/Kc) has a linear relationship with both the m values and the yield strengths. The crack propagation rates at the Paris regime were governed by the yield strengths, whereas the crack propagation paths at the threshold regime were governed by the microstructures.

► The Paris constant m values and the ΔKth0/Kc of the PF and TM steels are high and low, respectively.
► The crack propagation rates at Paris regime are governed by the yield strength.
► Paris constant m value possesses linear relationship with yield strength.
► ΔKth/Kc possesses linear relationship with yield strength.
► The crack propagation paths at threshold regime are governed by the microstructures.