| 摘要 |
<p num="1"><br/> A steel for steel pipes which comprises, on the percent by <br/>mass basis, C: 0.2 to 0.7%, Si: 0.01 to 0.8%, Mn: 0.1 to 1.5%, <br/>S: 0.005% or less, P: 0.03% or less, Al: 0.0005 to 0.1%, Ti: <br/>0.005 to 0.05%, Ca: 0.0004 to 0.005%, N: 0.007% or less, Cr: <br/>0.1 to 1.5%, Mo: 0.2 to 1.0%, Nb: 0 to 0.1%, Zr: 0 to 0.1%, V: <br/>0 to 0.5% and B: 0 to 0.005%, with the balance being Fe and <br/>impurities, in which non-metallic inclusions containing Ca, Al, <br/>Ti, N, O, and S are present, and in the said inclusions <br/>(Ca%)/(Al%) is 0.55 to 1.72, and (Ca%)/(Ti%) is 0.7 to 19 can be <br/>used as a raw material for oil country tubular goods, being <br/>used at a greater depth and in severer corrosive circumstances, <br/>such as casings and tubings for oil and/or natural gas wells, <br/>drilling pipes and drilling collars for excavation, and the <br/>like.<br/>
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