Nippon Steel Corporation

Yusuke Mihara

Yuji Arai

Masayuki Yamamoto

Masahiro Yamazaki

Takeshi Miki

Yohsuke Uchida

A seamless steel pipe is provided that has a chemical composition which consists of, by mass %, C: 0.10 to 0.20%, Si: 0.05 to 1.0%, Mn: 0.05 to 1.2%, P&#x2264;0.025%, S&#x2264;0.005%, Cu&#x2264;0.20%, N&#x2264;0.007%, Ni: 0.20 to 0.50%, Cr: 0.30% or more and less than 0.50%, Mo: 0.30 to 0.50%, Nb: 0.01 to 0.05%, Al: 0.001 to 0.10%, B: 0.0005 to 0.0020%, Ti: 0.003 to 0.050%, V: 0.01 to 0.20%, a total of any one or more elements among Ca, Mg and REM: 0 to 0.025%, and the balance: Fe and impurities, and for which Pcm (=C+(Si/30)+(Mn/20)+(Cu/20)+(Ni/60)+(Cr/20)+(Mo/15)+(V/10)+5B)&#x2264;0.30. The steel micro-structure includes, in area %, tempered martensite &#x2265;90%. The tensile strength is 980 MPa or more, and a Charpy impact value at &#x2212;40&#xb0; C. using a 2 mm V-notch test specimen is 75 J/cmor more.

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Tokyo, Japan

Yusuke Mihara