Control of post-weld fracture toughness in friction stir processed X80 HSLA steel

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 FSW travel speed, rpm, and weld preheat. Fracture toughness was tested according to ASTM 1820 standard along the weld centerline using surface-notched SEB specimen cooled to -40 degrees C. Results demonstrate that CTOD of FSW X80 has a strong inverse linear correlation with post-weld cooling rate. Low cooling rate welds exhibited CTOD values consistently above those of base metal. Microstructure similar to the base metal can be recreated throughout the weld. Weld CTOD can be selected by controlling weld CR.