Toughness of SSAW Pipe Base Metal for X70 and X80 Steels at Low Temperatures

Charpy impact and drop-weight tear test (DWTT) properties for the spiral submerged arc welded (SSAW) pipe base metal of X70 and X80 steels at low temperatures were studied. The results show that specimens sampled from transverse direction of both steels had better toughness than those from longitudinal direction at low temperatures. The ductile-brittle transition temperature of the X70 steel pipe base metal was lower than that of the X80 steel pipe. When the temperature was above -20 ℃, the shear area ratio of the fracture for the two base met als was both about 95%, it was ductile fracture. When the temperature was lower than -20 ℃, the decreasing amount of the Charpy impact energy with temperature reducing was greater than that of the shear area ratio. The toughness of the base metal at low temperatures was greatly affected by the test method, and the ductile-brittle transition temperature measured by DWTT was much higher than that by Charpy impact test.