| 摘要 |
PROBLEM TO BE SOLVED: To provide a Cr-containing steel pipe for line pipe excellent in: strength of X65-80 class; ductility; corrosion resistance; resistance to sulfide stress corrosion cracking; and intergranular stress corrosion cracking resistance of a weld heat-affected zone. SOLUTION: The steel pipe has a composition containing, by mass, 0.001-0.015% C, 0.05-0.50% Si, 0.10-2.0% Mn, 0.001-0.10% Al,≥13 to <15% Cr, 2.0-5.0% Ni, 1.5-3.5% Mo, 0.001-0.20% V, and≤0.015% N, and satisfies P<SB POS="POST">1</SB>=Cr+Mo+0.4W+0.3Si-43.5C-0.4Mn-Ni-0.3Cu-9N (wherein Cr, Mo, W, Si, C, Mn, Ni, Cu and N are the contents, mass% of respective elements) of 11.5 to 13.3, and P<SB POS="POST">2</SB>=(0.5Cr+5.0)-P<SB POS="POST">1</SB>of≥0. Thus, the weld heat-affected zone which is heated to the ferrite single phase temperature region of≥1,300°C and then cooled when welded, becomes a composition in which 50% or more of the former ferrite grain boundary at a rate to the total length, is occupied with a martensite phase, and formation of the absentee layer of Cr carbide is inhibited, thereby obtaining the steel pipe in which the intergranular stress corrosion cracking resistance of the weld heat-affected zone is significantly improved. COPYRIGHT: (C)2012,JPO&INPIT |
