Heat treatment technology for oil pipe

　　The heating temperature of 27MnCrV steel at AC1=736 C, AC3=810 C and sub temperature quenching of oil pipe is selected at 740-810 C. The heating temperature for sub-temperature quenching is 780 C and the holding time for quenching heating is 15 min. After quenching, the tempering temperature of oil pipe is 630 C and the holding time for API 5L Gr.B X52 Seamless Carbon Steel Oil Pipe is 50 min.

　　Because sub-temperature quenching is heated in the two-phase region of alpha+gamma and quenched in the condition of retaining part of undissolved ferrite, the toughness is improved while maintaining high strength. At the same time, the low-temperature quenching is lower than the conventional temperature, which reduces the stress of quenching, thus reducing the deformation of quenching, which ensures the smooth operation of heat treatment of oil pipe, and provides good raw materials for subsequent wire processing.

　　At present, the process has been applied in China. The quality assurance data show that the yield strength Rt0.6 after heat treatment is 820-860 MPa, the tensile strength Rm is 910-940 MPa, the impact toughness Akv is 65-85J, and the destruction resistance is 100% qualified. The data show that 27MnCrV oil pipe is a high-quality high-grade oil pipe. On the other hand, it also shows that the intercritical quenching process is an excellent method to avoid high temperature brittleness in steel products production.