Microstructure and fracture toughness of multipass friction stir welded joints of API-5L-X80 steel plates

Friction stir welding with the optimum parameters offers high toughness and mechanical properties for pipeline steel applications; however, at subzero temperatures such joints have shown decreased toughness relative to room temperatures values as well as predominantly brittle behavior. This paper relates certain microstructural features to fracture toughness for the different regions of one- and two-pass friction stir welded joints, including...