In order to meet the strength and toughness requirements of low-carbon microalloyed steel for coiled tubings,a 5.3 mm thick hot-rolled plate for coiled tubing was prepared by designing controlled rolling and controlled cooling production process.The low cycle fatigue property of the hot rolled plate was analyzed by low-cycle fatigue test and the low-cycle fatigue fracture was observed.The mechanical properties and microstructure of the hot rolled plate were analyzed.The results show that the fatigue life of the tested steel is 3784 cycles when produced at final rolling temperature of 810 ℃,cooling rate of 52 ℃/s,and coiling temperature of 450 ℃.The morphology of the transient fracture zone of the low cycle fatigue fracture is mainly dimple,and the fracture mode belongs to ductile fracture.The fitted formula for the relationship between low cycle fatigue strain and fatigue life has a good fitting effect and can be used to predict fatigue life under different strain amplitude conditions.The mechanical properties of the tested steel meet the requirements,and the microstructure consists of ferrite,bainite,and M/A islands.The volume fraction of ferrite is about 74％,and mainly exists in the form of acicular ferrite,making the tested steel have good fatigue property.
coiled tubinglow carbon microalloyed steelcontrolled rolling and coolinglow-cycle fatigue propertyfatigue fracture
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