| 摘要 |
<p>Provided is a Cr-containing steel pipe for linepipe having X-65 to X-80 class high strength and being excellent in toughness, corrosion resistance and resistance to sulfide stress corrosion cracking, and also being excellent in resistance to intergranular stress corrosion cracking in a welded heat affected zone. To be more specific, the composition of the Cr-containing steel pipe contains, by mass% 0.001 to 0.015% C, 0.05 to 0.50% Si, 0.10 to 2.0% Mn, 0.001 to 0.10% Al, 15.0 to 18.0% Cr, 2.0 to 6.0% Ni, 1.5 to 3.5% Mo, 0.001 to 0.20% V, and 0.015% or less N so as to satisfy the following relationship of Cr + Mo + 0.4W + 0.3Si - 43.5C - 0.4Mn - Ni - 0.3Cu- 9N: 11.5 to 13.3. A welded heat affected zone which is heated to a ferrite single phase temperature region of 1300°C or more at the time of welding and is cooled has the microstructure where 50% or more of prior-ferrite grain boundaries is occupied by a martensite phase and/or an austenite phase in a ratio to the whole length of the prior-ferrite grain boundaries. Accordingly, the formation of a Cr carbide depleted zone is suppressed thus providing a steel pipe which remarkably enhances resistance to intergranular stress corrosion cracking in a welded heat affected zone. Due to such a steel pipe, it is possible to acquire an advantageous effect that it becomes unnecessary to perform post weld heat treatment thus remarkably shortenning a construction period of the welded steel pipe structure.</p> |
