Sumitomo Metal Industries, Inc.

Nippon Steel Sumitomo Metal Corporation

Tetsuya Fukuba

Nobuaki Takahashi

Masahiko Hamada

Akio Yamamoto

Shuji Okaguchi

Tomoaki Ikeda

Hidenori Shitamoto

Yoshimasa Matsumoto

Takahiro Kamo

A method and device for manufacturing UOE steel pipes, wherein, when an opening width of the U-can obtained by U-ing press is larger than the die-diameter in an O-press of later step, while said opening is narrowed from the front end by the closing rolls disposed before said O-press and/or at least at the entrance portion of the O-press to be smaller than the die-diameter of said O-press, the U-can is simultaneously conveyed into the O-press, and then, after charging into the O-press, undergoes O-ing press to yield an O-can. The device is preferably configured to have the closing rolls disposed in a roll stand and consisted of multiple pairs, to have a mechanism to prevent the U-can from moving upward during narrowing the opening width, and to have the function of conveying the U-can. Thus, UOE steel pipes for high-strength application corresponding to X80 grade can be efficiently manufactured.

Method and device for manufacturing UOE steel pipes

The high yield ratio problem intrinsic in high-strength steel pipes is solved and a method of producing a steel pipe, while securing the pipe roundness is provided. A steel pipe produced from a steel plate by forming and welding is subjected to 0.3 to 1.2% of expansion and then to 0.1 to 1.0% of reduction. The steel pipe produced by this method has a structure in which martensite and/or bainite accounts for more than 80% as expressed in terms of area percentage, and has a yield strength of not lower than 551 MPa and a yield ratio of not higher than 93%. The pipe reduction is desirably carried out at a lower work ratio as compared with the pipe expansion.

Method of producing steel pipes, and welded pipes

Growing community of inventors

Ibaraki, Japan

Tetsuya Fukuba