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借助电液伺服疲劳试验机及SEM，研究了应力比对套管钻井常用钢级J55疲劳裂纹扩展性能的影响，并对断口形貌进行了研究。试验结果说明：J55钢级的Paris常数m为3.438，C为1.48×10-12，随着应力比增大，进入快速裂纹扩展区对应的△K变小；对于应力比0.1，低Paris区的断裂模式为沿晶体学平面发生的穿晶断裂，Paris线性部分断裂模式为双滑移机制控制的疲劳条带断裂，高Paris区为疲劳条带断裂和延性静态断裂相结合的断裂模式；应力比为0.3和0.5与应力比为0.1裂纹扩展各阶段断裂模式相似；对于应力比等于0.7来说，穿晶断裂模式贯穿于整个Paris区，包括高Paris区。

The fatigue crack growth properties of the J55 drilling casting steel were studied by means of SEM and the fatigue testing equipment, and the fracture morphology was studied. The results show that Paris constants m and C of the J55 steel is respectively 3.438 and 1.48×10-12 , △K corresponding to the access of the fast crack growth regime is decreasing with the increasing of stress ratio; the fracture mode of the lower Paris regime is transgranular fracture for 0.1 of stress ratio, the fracture mode of the linear portion of Paris regime is fatigue striation fracture controlled double glide mechanism, the upper Paris regime is a combination of the fatigue striation and the ductile-dimple static fracture mode; the fracture mode of every stage of stress ratio of 0.3 and 0.5 is similar with that of stress ratio of 0.1; the transgranular fracture mode occurs at every stage of Paris regime, included the upper Paris regime.