The present study investigates the fracture toughness of FSW X80 HSLA steel welds. Weld cooling rate and peak temperature were varied among welds; indirectly manipulated through travel speed, rpm, weld preheat. Fracture was tested according to ASTM 1820 standard along centerline using surface-notched SEB specimen cooled −40 °C. Results demonstrate that CTOD has a strong inverse linear correlati...