Patent attributes
A high-strength hot bend pipe which has a balance between an excellent strength of at least X70 grade and toughness and which has excellent tensile properties and a weld metal with excellent low temperature toughness is manufactured. A UOE steel pipe having a base metal with a composition of C: 0.03-0.12%, Si: 0.05-0.50%, Mn: 1.4-2.2%, S: at most 0.01%, Al: at most 0.06%, N: at most 0.008%, and a remainder of Fe and impurities, with the carbon equivalent (Ceq) being at most 0.36% and the weld cracking parameter (Pcm) being at most 0.22%, and having a weld metal with a weld cracking parameter (Pcm) of at most 0.28%, a B content of at most 5 ppm, and an O content of at most 280 ppm is heated to a temperature range of 900-1100° C. and subjected to bending, and then is immediately cooled to a temperature range of 300° C. or lower at a cooling rate of at least 3° C./sec, and then is tempered in a temperature range of 300-500° C.
