To provide a steel pipe manufacturing method which can manufacture a steel pipe of high strength, high ductility and of a good piping shape at high productivity, and also can deal with a small lot, many kinds production.
In this steel pipe manufacturing method, a strap steel 1 is made to be an open pipe 7 by being continuously molded with a molding roll after being heated to Ac3 transformation point or higher, and the both edge parts thereof are heated, so as to be connectedly joined with squeeze rolls 6 for making it as a base pipe after removing inner, outer beads for further applying a reduction rolling. Reduction rolling is performed in a way that a reduction ratio is 30% or more, in a temperature range of Ar3 transformation point - (Ar3 transformation point + 100°C) and at deflection speed 1s-1 or more, and/or it is cooled, after the reduction rolling is completed, within 0.5 sec. at a cooling speed of 30°C/s or more. Also, the above reduction rolling may be applied by cooling the base pipe after removing the inner/outer beads and re-heated to the Ac3 transformation point or more.
YORIFUJI AKIRA
KAWABATA YOSHIKAZU
NISHIMORI MASANORI
ITAYA MOTOAKI
OKABE YOSHITOMO
ARAYA MASATOSHI
NAGAHAMA TAKUYA
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