| 摘要 |
<p>PURPOSE:To manufacture a large diameter square steel pipe having good dimensional accuracy and quality by heating a large diameter round steel pipe to a specific temp. with an induction heating, forming to the square shape through forming rolls and forcedly cooling the inner surface. CONSTITUTION:The round steel pipe 1 is formed into the square shape through the forming rolls 4 while holding it by a pinch roll stand 2 after heating to 500-1100 deg.C with an induction heating device 3 to make the large diameter square steel pipe 5. After forming, the inner surface of the square steel pipe 5 is forcedly cooled with a forcedly cooling device 6. In the case this temp. is <500 deg.C, this pipe becomes blue brittleness or tempering brittleness range and in the case this temp. is >1100 deg.C, the deformation of the steel pipe 1 becomes large and the toughness is lowered. By forcedly cooling the inner surface and making the cooling speeds at inner and outer surfaces same, the development of the residual stress caused by the difference between the cooling speeds is prevented. The large diameter square steel pipe having good dimensional accuracy and quality can be obtd.</p> |
