| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for manufacturing a seamless steel tube using a round billet capable of suppressing inner face flaws that occur at the time of piercing a RCC stock with a skew rolling. SOLUTION: 1. The round billet as continuously cast, especially, cast of an alloy steel containing Cr 2 to 15% or a martensite series stainless steel is heat-treated at a prescribed temperature of 1200 to 1320 deg.C and at a soaking time of 0.5 minute or more per outside diameter mm of the billet. 2. When the alloy steel containing Cr 2 to 15% or a martensite series stainless steel is continuously cast by a foundry machine with a round type casting mold having the radius of curvature 8 m or more, the round billet performed by light working whose outside diameter draft is 5% or less at the time of the solid phase ratio being 0.3 to 1.0 at the center of a solidification shell is heat- treated at the prescribed temperature of 1200 to 1320 deg.C and at the soaking time of 0.5 minute or more per outside diameter mm of the billet, and then, piercing is executed.
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