The effect of overload on fatigue crack growth rate for X52 pipeline steel was studied under different stress ratio and overload ratio. The results show that tensile overload causes a delayed retardation to fatigue crack growth. The crack propagation curve after overloading includes three processes: accelerated growth, retardation growth and recovery growth. Under a constant stress ratio, plasticity induced crack closure is more significant with the increase of overload ratio; the crack growth rate is decreased as a result. However, crack growth retardation is more significant at a lower stress ratio. SEM analysis of the fracture surface shows that the overload plastic strain suffered more erosion at a higher overload ratio and the fracture surface morphology is more different after a higher overload ratio.

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