Patent ID: 11414733

Abstract:
Provided herein is a low-alloy high-strength seamless steel pipe. The steel pipe of the present invention has a composition that contains, in mass %, C: 0.25 to 0.50%, Si: 0.01 to 0.40%, Mn: 0.45 to 0.90%, P: 0.010% or less, S: 0.001% or less, O: 0.0015% or less, Al: 0.015 to 0.080%, Cu: 0.02 to 0.09%, Cr: 0.9 to 1.5%, Mo: 1.4 to 2.0%, Nb: 0.005 to 0.05%, B: 0.0005 to 0.0040%, Ca: 0.0010 to 0.0020%, Mg: 0.001% or less, and N: 0.005% or less, and in which the balance is Fe and incidental impurities. The steel pipe has a microstructure in which the number of oxide-base nonmetallic inclusions satisfying the composition ratios represented by predefined formulae is 5 or less per 100 mm2, and in which the number of oxide-base nonmetallic inclusions satisfying the composition ratios represented by other predefined formulae is 20 or less per 100 mm2.