| 摘要 |
PROBLEM TO BE SOLVED: To provide a seamless steel pipe having high strength and superior SSC (sulfide stress-cracking corrosion) resistance, and a manufacturing method therefor. SOLUTION: The seamless steel pipe contains (1) by mass%, 0.15-0.35% C, 0.1-1.5% Si, 0.1-2.5% Mn, 0.005% or less S, 0.15% or less Al, and 0.0005-0.0050% Ca, and has a composition ratio of nonmetallic inclusions in the steel which satisfies expressions (1), (2), and (3): (Al<SB>2</SB>O<SB>3</SB>)/(CaS)≤4 (1), (CaS)/(CaO)≤1.5 (2), and 0.43≤(CaO)/(Al<SB>2</SB>O<SB>3</SB>)≤9 (3). (2) The method for manufacturing the seamless steel pipe (1), comprises a Ca-containing substance to molten steel between a ladle refining step and a continuous casting step, so as to satisfy the expression (4): -0.07×ln(t)+0.3≤WC<SB>a</SB>≤-0.097×ln(t)+0.55...(4). COPYRIGHT: (C)2003,JPO
|
