High strength low alloy (HSLA) steels have been developed to simultaneously have high yield strength and high fracture toughness. However, in practical applications steel must be welded. Traditional arc welding has proven detrimental to the fracture toughness of HSLA steels. Friction stir welding has recently shown mixed results in welding HSLA steels. The range of welding parameters used in these recent studies however 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 HI 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%.



College and Department

Ira A. Fulton College of Engineering and Technology; Mechanical Engineering



Date Submitted


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Allan Tribe, friction stir welding, HSLA, steel, API X80, fracture toughness, CTOD, J1c, microstructure, polygonal ferrite, bainite, lath, packet, heat input, hard zone, hardness