Study on the fracture toughness of friction stir welded API X80

•Fracture toughness of friction stir welded API X80 exceeds API and DVN requirements.•Minimum CTOD values in friction stir welded API X80 are spatially dependent.•Fracture toughness increases with decreasing heat input and tool rotational speed. Mixed results regarding fracture toughness in friction stir welded HSLA steels have been reported. The range of welding parameters used in these recent studies has been very limited. With only a few welding parameters tested, the effect of spindle speed, travel speed, and heat input on the fracture toughness of friction stir welded HSLA steel remains unknown. To understand how the friction stir welding process parameters affect fracture toughness, double sided welds in API X80 were performed and analyzed. Results show that at room temperature friction stir welded API X80 exceeded industry minimum fracture toughness requirements in both the API Standard 1104 and DNV-OS-F101 by 143% and 62%, respectively. The process parameters of spindle speed and heat input have been shown to effectively control the fracture toughness of the stir zone. Relationships have been established that show that fracture toughness increased by 85% when spindle speed decreased by 59% and heat input decreased by 46%.