Microstructure and Properties of X80M Large-deformation Resistant Heavy-wall SAWL Steel Pipe

Aiming at the Φ1 219 mm ×33.0 mm X80 M large-deformation resistant SAWL steel pipe with 0.075%niobium content,the chemical composition and microstructure uniformity at different positions through the wall thickness of steel pipes with two different bainite/ferrite phase ratios are analyzed, and the strength and toughness of the pipe bodies with the two microstructure morphologies are compared. The results demonstrate that the alloying design with relatively high niobium content and adopting reasonable rolling process can achieve uniform chemical composition through the wall thickness,and reduce the differences in microstructure and properties at different positions;a reasonable phase ratio of bainite-ferrite dual-phase microstructure is the key to ensuring the longitudinal tensile properties of the bodies of the said X80M large-deformation resistant pipes; the pipe body dominated by bainite exhibits higher Charpy impact absorbed energy, but lower uniform elongation, while the one dominated by ferrite possesses better uniform elongation and DWTT performance,and a rather lower ductile-brittle transition temperature(DBTT).