Patent ID: 8262767

Claim:
A method of producing steel for a steel pipe excellent in sour-resistance performance, wherein the steel comprises, in % by mass, C: 0.03 to 0.4%, Mn: 0.1 to 2%, Si: 0.01 to 1%, P: 0.015% or less, S: 0.002% or less, Ti: 0.2% or less, Al: 0.005 to 0.1%, Ca: 0.0005 to 0.0035%, N: 0.01% or less, and O (oxygen): 0.002% or less, the balance being Fe and impurities, the method comprising controlling the amount of Ca addition charged into the steel that is molten in a ladle according to a N content in the molten steel prior to Ca addition, wherein non-metallic inclusions in the steel are mainly composed of Ca, Al, O and S, and, as a result of the controlling step, a CaO content in the inclusions is in the range of 30 to 80%, the ratio of the N content in the steel to the CaO content in the inclusions satisfies the relation expressed by equation (1), and a CaS content in the inclusions satisfies the relation expressed by equation (2), 0.28≦[N]/(% CaO)≦2.0 (1) (% CaS)≦25% (2) where [N] represents the mass content (ppm) of N in the steel, (% CaO) represents the mass content (%) of CaO in the inclusions, and (% CaS) represents the mass content (%) of CaS in the inclusions, the steel comprising one or more compositional elements in place of a part of Fe selected from the group constisting of (a), (b), and (c) below: (a) in % by mass, Cr: 1% or less, Mo: 1% or less, Nb: 0.1% or less, and V: 0.3% or less; (b) in % by mass, Ni: 0.3% or less, and Cu: 0.4% or less; and (c) in % by mass, B: 0.002% or less.