Fracture toughness of the materials in welded joint of X80 pipeline steel

•Fracture toughness of welded joint of X80 pipeline steel is studied.•Fracture toughness test is conducted with a new non-contact double-extensometer vision system.•The HAZ is embrittled in different degrees, because of M–A constituents.•It is observed the fusion zone is the fracture risk zone of the X80 steel weldment.

The microstructures, mechanical properties and fracture toughness of the materials in different locations of the welded joint of the X80 pipeline steel were studied at room temperature. Elastic–plastic fracture toughness testing of crack tip opening displacement (CTOD) and J-integral of the welding materials and base material were conducted. A new non-contact double-clip gauge measuring system was developed and used in the fracture toughness tests. It was observed the fusion zone (FZ) was the fracture risk zone of the X80 steel weldment; and the occurrence of hard-brittle martensite–austenite (M–A) constituents was a significant because of welding hardening and embrittlement.

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