Microstructure and Properties of X70 High Deformability Linepipe

The yield strength, tensile strength, yield ratio, stress ratio, uniform elongation of X70 high deformability linepipe were tested by tensile experiment. The impact toughnesses at different temperature were compared.The microstructure and impact fracture morphology of the line pipe at -100 ℃ were analysed. The results show that the linepipe had excellent longitudinal tensile properties, the lowest value of Rt0.5 was 478 MPa, Rt0.5/Rm was lower than 0.69 and the uniform elongation was higher than 11%. The transverse absorption energy of the linepipe at -100 ℃ was 120 J and the shear section rate was 90%, the ductile fracture showing that the steel had good toughness properties at low temperature and the ductile-brittle transition temperature was lower than 100 ℃. The main microstructure of the linepipe were ferrite and granular bainite. The granular bainite band significantly existed in the center of the line pipe.