Abstract: The mechanical properties,impact toughness and fracture morphology of Q460 steel pipes of different specifications and different quality grades at different test temperatures were studied by means of scanning electron microscopy,mechanical properties test and Charpy impact test.The influences of wall thickness on ductile-brittle transition temperature different quality grades of Q460 steel pipes were evaluated..The results show that band structure in Q460D steel tube is significantly reduced,and microstructure uniformity is better than that of Q460C steel tube.The strength variation(yield strength and tensile strength) of Q460D slightly narrows than that of Q460C,and the tensile strengths of Q460D steel pipes of different wall thickness are identical.When the Q460C steel pipe is tested at -40℃ and above,the lowest impact energy value is above 68 J,whilf the Q460D steel pipe is tested at -60℃ and above,and the lowest impact energy value is above 163 J.