| Continuous cooling transformation, hot deformation and static softening behavior of J55 steel for oil casing pipe were studied by using Gleeble-3500 simulator.The microstructure of J55 steel for oil casing pipe is mainly composed of polygonal ferrite(PF), when the cooling rate is lower than 7℃/s; There are some quasi-polygonal ferrite and granular ferrite(QF+GF), when the cooling rate is in the range of 7-20℃/s; When the cooling rate is higher than 20℃/s, the microstructure of J55 steel for oil casing pipe mainly consists of acicular ferrite(AF). The microstructure can be refined, the hardness of the steel increased and banded structure was disappeared gradually, with high cooling rate.The activation energy of J55 steel for oil casing pipe is about 359 kJ/mol. Hot deformation equation, strain rate sensitivity, efficiency of power dissipation and Processing Maps is determined. Efficiency of power dissipation increases gradually with the increase of temperature and decrease of strain rate. A domain with its peak efficiency about 33% appears at about 1150℃and 0.001 s-1.The softening ratio increase with the increase of deformation temperature and interval time. The static softening ratio under different strain is estimated by means of back-extrapolation. Though regression analysis, the static recrystalliza- tion activation energy (Qrex) of J55 steel for oil casing pipe is 151 kJ/mol. The dynamic equation of this steel was established.
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