Uniform elongation of uel≥5% of the x90 line pipe and its preparation method

UEL≥5% uniform elongation of the X90 line pipe, the weight percentage of its chemical composition is: C: 0.040 ~ 0.060%, Mn: 1.60 ~ 1.80%, Cr: 0.35 ~ 0.65%, Mo: 0.05 ~ 0.15%, ni: 0.15 ~ 0.25%, Nb: 0.060 ~ 0.080%, P≤0.009%, S≤0.00095%; preparation steps: the deep desulfurization and dephosphorization, etc; heating the slab; rough rolling; finishing; cooling; air-cooled to room temperature ; conduct pipe process: by forming and bending large heat welded LSAW steel pipe after expanding, its expansion ratio is controlled to 0.20-0.60%. The present invention satisfies its mechanical properties as RP0.2≥650MPa, Rm≥730MPa, -20 ℃? KV2≥280J, -15 ℃? DWTT? SA≥85% under the premise, but also make the plastic pipe that is uniform elongation of UEL≥5%, to obtain a good match for ultra high toughness and high ductility.