| 摘要 |
PURPOSE:To produce a titled large-diameter high-tension steel pipe which is used for a gas pipeline of the design temp. of <=-10 deg.C and is of a low cost by forming the high-tension large-diameter steel pipe manufactured by a spiral pipe making method then heating the pipe to a specific temp. range and cooling quickly the pipe at a prescribed average cooling rate and tempering the cooled pipe. CONSTITUTION:The high-tension large-diameter steel pipe manufactured by a spiral pipe making method using a hot coil contg. <=0.010wt% S and finished at 700-800 deg.C finishing temp. in final rolling is heat-treated in the following way: The above-described large-diameter steel pipe is subjected, after forming, to a hardening treatment at Ac3-50 deg.C-Ac3+150 deg.C max. heating temp. by induction heating and water cooling and >=20 deg.C/sec average cooling rate to 800-500 deg.C and to a tempering treatment in the temp. range of 500 deg.C-Ac1. The titled steel pipe having extremely high strength is thus obtd. without adding a large amt. of the costly alloy element and without considerable decrease in the stage of rolling the blank steel plate. If the CVT of the steel pipe satisfies the equation, the rate of propagation of unstable ductile fracture is decreased. |
