Method of producing steel for steel pipe excellent in sour-resistance performance

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,
• wherein the steel comprises one or more of compositional elements selected from one or more of groups (a) to (c) below, in place of a part of Fe:
• (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.