4145H钻铤钢的示波冲击性能及其动态断裂韧性

针对石油钻井中钻铤断裂以及北方油田在冬季石油钻铤下井起钻之后存在的冷脆现象，通过示波冲击实验，获得了4145H钻铤钢试样在冲击变形和断裂过程中的冲击力-位移曲线，并用实验得到的总冲击功、起裂功来计算其动态断裂韧度。结论认为：4145H钻铤钢的延性断裂韧度和动态断裂韧度均随温度的降低而降低，其冲击功随温度的降低而降低，起裂功与冲击功的比值随温度的降低而升高，裂纹扩展功及其与冲击功的比值随温度的降低而降低。在钻井工程中表现为：常温下裂纹在钻铤中扩展速率较慢，钻铤不容易断裂；低温下裂纹在钻铤中扩展速率较快，钻铤更容易断裂。该研究成果为合理指导4145H 钻铤的生产工艺和现场正确使用钻铤提供了实验数据支撑。

Instrumented Charpy impact testing and dynamic fracture toughness of 4145H drilling collar steel

Drilling collar fractures easily occur in drilling operations and are often resulted from cold brittleness especially in winters in the oil fields of North China.An instrumented impact test was conducted on 4145H drilling collar samples,with impact force vs.displacement curves drawn during the process of impact deformation and fracture.And the total impact energy and the fracture initiation energy obtained during the tests were used to calculate its dynamic fracture toughness.The study results show that the impact energy,ductile fracture toughness,dynamic fracture toughness,crack propagation energy,and the ratio between crack propagation energy and impact energy will all decrease as the temperature decreases,while the ratio between the fracture initiation energy and impact energy will increase as the temperature decreases.In drilling,the crack growth rate in the drilling collar is slow and the collar is not liable to fracture at normal temperature.On the contrary,the crack growth rate becomes fast and the collar is subject to fracture at low temperature.The research results will provide reliable guidance for 4145H DC manufacturing and offer basic experimental evidence for the proper drilling collar application in field practices.