Abstract: Fatigue tests were conducted for standard compact tension specimens of U75V heavy rail steel via a high-frequency resonance fatigue testing machine, in order to study the influence of the rolled state′s microstructure under different cooling rates (3 ℃/s, 5 ℃/s, and air cooling) upon the crack growth rate of the stable zone (fatigue crack growth zone Ⅱ). The results show that the fatigue crack growth rate decreases with the decline of pearlite lamellar spacing. The 5 ℃/s, 3 ℃/s, and air cooling correspond to n values of 3.603 05, 3.631 18 and 3.885 28, respectively. Fracture modes of the fatigue cracks of pearlite microstructure are mainly transgranular fracture, accompanied by partial intergranular fracture. Lamellar spacing affects the deflection of the crack propagation path, and increased the degree of crack deflection subsequently enhances crack propagation impediment, which benefits the reduce of the fatigue crack growth rate.
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2017, Vol. 31 
