TWI

An investigation was undertaken to determine the strength and fracture toughness of joints fabricated by friction stir welding (FSW) in commercial X65 (0.07%C, 1.56%Mn, 0.06%Nb, 0.013%Ti) and X80 (0.05%C, 1.52%Mn, 0.26%Cr, 0.26%Cu, 0.1%Nb and 0.07%C, 1.91%Mn, 0.16%Cr, 0.21%Ni, 0.06%Nb) grade linepipe steels using polycrystalline BN (PCBN) and W-Re tool materials. The wall thickness of the pipe samples was 19 mm. Butt welds were prepared using a two-sided FSW procedure at rotational speeds of 300 or 170 rpm and travel speeds of 500 or 900 mm/min for PCBN and W-Re tools, respectively. Cross-sectional microstructures were observed by optical microscopy and SEM. Mechanical properties were characterised by microhardness measurements, all-weld zone tensile tests and fracture toughness testing by a CTOD technique. Fatigue precracking within the stir zone and thermomechanically affected zone is discussed.

7th International Symposium, 20-22 May 2008, 9B: Steel 3, Paper 01