BEND PIPE AND PROCESS FOR PRODUCING THE SAME

摘要

A high-strength bend pipe is produced which has an excellent strength/toughness balance as high as X70 grade or above and is excellent in tensile performance and low-temperature weld metal toughness. A UOE steel pipe comprising a base metal which has a composition containing 0.03-0.12% C, 0.05-0.50% Si, 1.4-2.2% Mn, up to 0.01% S, up to 0.06% Al, and up to 0.008% N, the remainder being Fe and impurities, and has a carbon equivalent (Ceq) of 0.36% or higher and a weld crack sensitivity index (Pcm) of 0.22% or lower and a weld metal having a weld crack sensitivity index (Pcm) of 0.28% or lower, a boron content of 5 ppm or lower, and an oxygen content of 280 ppm or lower is heated to a temperature in the range of 900-1,100°C and bent. Immediately thereafter, this steel pipe is cooled at a cooling rate of 3 °C/s or higher to a temperature not higher than 300°C. It is then tempered in the temperature range of 300-500°C.