| 摘要 |
A high-strength UOE steel pipe is provided which has excellent earthquake-proof performance and has a weld heat-affected zone having excellent low-temperature toughness. The pipe is suitable for use as a pipeline to be laid in, e.g., permafrost in cold latitudes or an earthquake-prone region. The UOE steel pipe has a steel composition which contains 0.03-0.07% carbon, 0.05-0.50% silicon, 1.6-2.2% manganese, up to 0.020% phosphorus, up to 0.003% sulfur, 0.20-0.60% copper, up to 0.10% chromium, 0.20-0.80% nickel, 0.005-0.030% niobium, 0.005-0.030% titanium, up to 0.0070% nitrogen, and 0.005-0.060% aluminum, with the remainder being iron and impurities, and has a hardenability index (Pcm) of 0.22% or less, and in which Cu+Cr+Ni is 0.4-1.5% and Nb+Mo+V is 0.05% or lower. The pipe has a yield strength in the axial direction of 480 MPa or higher and a yield ratio of 85% or lower. In the pipe, the weld heat-affected zone has a Charpy absorbed energy at -40°C of 40 J or higher. |
