| 摘要 |
The present invention proposes a production method for seamless steel pipe having excellent inner plane and inside thick wall properties. More specifically, the means for solving the problem comprises using, as the raw material, a round billet having a center segregation zone partition ratio W (%) as defined by equation below of 20 % or higher. Where, W (%) = ( DELTA w/D) x 100 (wherein, W: center segregation zone partition ratio (%), DELTA w: separation width of the center segregation zone at the center of thickness direction of round billet (mm), and D: total thickness of round billet (outer diameter) (mm)). After heating the round billet to a predetermined temperature, pierce rolling is performed to obtain a hollow raw pipe, to which stretch rolling or further draw rolling is applied to obtain a steel pipe of desired dimension. The continuously cast slab for use in the invention is preferably cast by using steel melt whose superheating degree is set in a range of 25 to 65 DEG C, an d, while casting, the quantity of the secondary cooling water at the central portion in the width direction of the slab is set larger than that at the peripheral portion in the width direction of the slab and the secondary cooling water ratio until complete solidification is adjusted within a range of from 1.2 to 2.0 l/kg-steel.
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