| 摘要 |
PROBLEM TO BE SOLVED: To provide a round billet for a seamless steel tube which can be drilled in a continuously as-cast state, and a drilled seamless steel tube thereof. SOLUTION: The round billet for the seamless steel tube includes, by mass%, 0.05-0.55% C, 0.1-0.4% Si, and 0.3-1.6% Mn, in manufactured by continuous casting, and has a diameter of 360 mm or less and a composition satisfying the expression, 150>=DF=TLδ-Tδγ[wherein, TLδ=100000/(55.25+2.35C+0.37Si+0.16Mn+1.01P+1.15S+0.18Cu+0.04Cr+0.13Ni+0. 12Mo), and Tδγ=100000/(60.06-4.51C+3.84Si-0.19Mn+0.98P+0.25S-1.49Cu+1.01Cr-1.34Ni+0. 55Mo), where each element symbol indicates the content (mass%)].
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