| 摘要 |
PROBLEM TO BE SOLVED: To provide a method suitable for manufacturing a square steel tube of a large cross-section of one side length of >=250 mm in the case of working with a pair of rolls by using existing seamless rolling equipment. SOLUTION: When a seamless tube stock having a round cross-section is formed to a square steel tube by a pair of rolls engraved with a caliber, a bottom part of the caliber is engraved in parallel with a roll axis, a rolling posture is set so that a direction of the side of the square steel tube is parallel to the a roll axial direction.
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