HIGH-STRENGTH UOE STEEL PIPE EXCELLENT IN DEFORMABILITY AND LOW-TEMPERATURE TOUGHNESS OF HEAT-AFFECTED ZONE

摘要

A high-strength UOE steel pipe which has excellent deformability and excellent low-temperature toughness in its heat affected zone and which is suitable for use in a pipeline installed on permafrost in extremely cold regions or in earthquake-prone regions, for example, is provided. The UOE steel pipe has a steel composition consisting essentially of C: 0.03 - 0.07%, Si: 0.05 - 0.50%, Mn: 1.6 - 2.2%, P: at most 0.020%, S: at most 0.003%, Cu: 0.20 - 0.60%, Cr: at most 0.10%, Ni: 0.20 - 0.80%, Nb: 0.005 - 0.030%, Ti: 0.005 - 0.030%, N: at most 0.0070%, Al: 0.005 - 0.060%, and a remainder of Fe and impurities, the hardenability index Pcm is at most 0.22%, Cu + Cr + Ni is 0.4 - 1.5%, Nb + Mo + V is at most 0.05%. The pipe has a yield strength in the longitudinal direction of at least 480 MPa with a yield-tensile ratio of at most 85% and a Charpy absorbed energy of the heat affected zone at -40° C of at least 40 J.