| 摘要 |
PURPOSE:To manufacture seam welded steel pipe superior remarkably in toughness in low temp. of weld zone inexpensively and stably, by austenitizing a seam welded zone, then cooling acceleratedly the zone to refine microstructure, further tempering it and applying warm working thereto. CONSTITUTION:A material steel strip 1 is formed, welded and squeezed continuously by a feeder element 2 and a squeeze roll 3, to form a seam welded pipe 4. Next, the seam welded zone is heated to Ac3 transformation point - that + 150 deg.C range by an induction heating apparatus 5, next, cooled by 20-90 deg.C/sec average rate between >=Ar3 transformation point - <=500 deg.C by a water shower 7 of a water cooler 6. Next, the welded zone is heated and tempered at 500 deg.C/Ac1 transformation point by an induction heating apparatus 8, and subjected to warm working by a roll 9 when it is in the temp. between 450 deg.C - Ac1 transformation point. The pipe 4 is further cooled by a water shower 10 of a cooler 11, and subjected to the final sizing at about room temp. by a sizer 12, to obtain the titled steel pipe.
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