Nippon Steel Corporation

Keisuke Furo

Yuji Arai

Hiroki Kamitani

Atsushi Soma

Kouji Yamane

Takenori Kuramoto

Yosuke Tatebayashi

The seamless steel pipe of the present embodiment consists of in mass %, C: 0.21 to 0.35%, Si: 0.10 to 0.50%, Mn: 0.05 to 1.00%, P: 0.025% or less, S: 0.010% or less, Al: 0.005 to 0.100%, N: 0.010% or less, Cr: 0.05 to 1.50%, Mo: 0.10 to 1.50%, Nb: 0.010 to 0.050%, B: 0.0003 to 0.0050%, and Ti: 0.002 to 0.050%, the balance being Fe and impurities. In a main body region of the seamless steel pipe, a grain size number of prior-austenite grain conforming to ASTM E112 is 7.0 or more, a difference between a maximum value and a minimum value of the grain size number is 1.0 or less, yield strength is 655 to less than 862 MPa, and a difference between a maximum value and a minimum value of tensile strength is 27.6 MPa or less.

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Tokyo, Japan

Keisuke Furo