| 摘要 |
<p>Disclosed is steel for a steel pipe, which satisfies a plurality of characteristics at the same time. Specifically disclosed is steel for a steel pipe having excellent sulfide stress cracking resistance, which contains, in mass%, 0.2-0.7% of C, 0.01-0.8% of Si, 0.1-1.5% of Mn, 0.005% or less of S, 0.03% or less of P, 0.0005-0.1% of Al, 0.005-0.05% of Ti, 0.0004-0.005% of Ca, 0.007% or less of N, 0.1-1.5% of Cr and 0.2-1.0% of Mo, with the balance made up of Fe, Mg and impurities. The steel for a steel pipe is characterized in that the Mg content in the steel is 1.0-5.0 ppm (inclusive), and 50% or more of the number of non-metallic inclusions, which are contained in the steel, configured of two or more elements selected from among Ca, Al, Mg, Ti and Nb and two or more elements selected from among O, S and N, and have a maximum particle diameter of 1 μm or more, contains an Mg-Al-O oxide in the central portion thereof, while comprising a Ca-Al oxide and/or a Ca-Al oxysulfide so as to contain the Mg-Al-O oxide internally. The steel for a steel pipe is also characterized in that a carbonitride or carbide containing Ti is present on the entire or a part of the outer circumference of the Ca-Al oxide and/or the Ca-Al oxysulfide.</p> |
