| 摘要 |
An oil well steel tube having at least 70kgf/mm2 of a tensile strength is manufactured by rolling, water cooling and winding a steel to produce a hot rolled steel plate, electric resistance welding the plate to produce a steel tube, and heating the steel at 950-1100 deg.C for t [t=(-4.4T+4900)±30; T:deg.C sec. The steel is composed of 0.25-0.35 wt.% C, 1.0-2.0 wt.% Mn, at most 0.5 wt.% Si; at most 0.03 wt.% P, at most 0.01 wt.% S, at most 0.015 wt.% N, 0.05-0.2 wt.% V and impurities. The steel tube is used for casting and tubing of an oil well.
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