| 摘要 |
PROBLEM TO BE SOLVED: To provide a tube manufacturing method of a seamless steel tube of a high alloy steel capable of preventing a piecing defect and a crack at a tube end part with using a mandrel mill. SOLUTION: In a manufacturing method of a seamless steel tube by a mandrel mill to roll a hollow tube stock, rolling is conducted so that an elongation strain in the tube axial direction of a rolling stock at a first stand is set to <=0.300, an elongation strain in the tube axial direction of a rolling stock at the other stand is set to <=0.375. Further the pass for a mandrel mill rolling is constituted so that an ellipticity of the passes of a first and/or second stand of a mandrel mill to roll a hollow tube stock are set in the range of 1.25-1.40.
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