| 摘要 |
PURPOSE:To obtain the title steel pipe capable of maintaining the soundness of a threaded joint part and having a long service life by hot-rolling the steel consisting essentially of C, Si, Mn, Al, Mo, Nb, and V and having the respective specified contents into a pipe, heating the pipe to a temp. higher than the Ac3 point, hardening the pipe, and then tempering the pipe in the specified temp. range. CONSTITUTION:The steel contg., by weight, 0.08-0.35% C, 0.05-0.50% Si, 0.3-2.0% Mn, 0.01-0.1% Al, and further >=1 kind among 0.50-1.0% Mo, 0.01-0.1% Nb, and 0.01-0.1% V is treated as follows. Namely, the cast steel billet obtained from the molten steel is hot-rolled into a pipe, and the pipe is hardened by heating the pipe to a temp. higher than the Ac3 point and then quenched to dissolve the nitride fixing elements such as Nb and Mo and then reinforcing elements such as B and Ti and to enhance the working effectiveness. The pipe is then tempered at a temp. between 500 deg.C and the Ac1 point to stabilize the quality of the hardened steel pipe, and the desired steel pipe for a thermal well having low relaxation is obtained.
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