Abstract: In the study on the brittle fracture arrest of natural gas pipeline, the shear-area percentage (SA) of fracture is regarded as an important measurement parameter in drop weight tear test (DWTT) which is used to evaluate the ability of brittle fracture arrest of pipeline steel, can accurately reflect the actual stress-strain state of pipeline, and show the true state of fracture and the ability to prevent fracture. X70 pipeline steels are hot rolled under different conditions of industrial production, and then the drop weight tear test, fatigue test, tensile test and impact test are carried out. Effect of the volume fraction and grain size of polygonal ferrite on the SA of DWTT fracture of X70 pipeline steel is investigated. Results indicate that the SA of fracture increases and then decreases with the increase of polygonal ferrite volume fraction when the polygonal ferrite exists as a second phase; and it is mainly affected by polygonal ferrite grain size when the polygonal ferrite exists as main matrix microstructure, and the shear-area percentage increases with the finer of the grain.

Key words: Brittle fracture, Drop weight tear test, Pipeline steel, Shear-area percentage of fracture