Electric resistance welded steel pipe and a method of manufacturing the same excellent in HIC resistance and low temperature toughness of the electric resistance welded portion

摘要

PROBLEM TO BE SOLVED: To provide an electric resistance welded steel pipe which has excellent HIC (hydrogen induced cracking) resistance and low-temperature toughness in an electric resistance welded part and has a tensile strength of 434 MPa or more, and to provide a method for manufacturing the electric resistance welded steel pipe.;SOLUTION: In the electric resistance welded steel pipe, the total amount of Si, Mn, Al, Ca and Cr included in inclusions present in an electric resistance welded part and having a circle-equivalent diameter of 20 μm or more is 20 ppm or less by mass%. The electric resistance welded steel pipe contains predetermined amounts of C, Si, Mn, Al, or further contains Ca and Cr. The above conditions can be achieved by electric resistance welding in an atmosphere in which an oxygen content is adjusted to (1,000/foxy) ppm or less (where foxy is defined by foxy=Mn+10(Si+Cr)+100Al+1,000Ca); or achieved by roll-forming a steel strip to impart a groove having a tapered part at the end of the strip from the inner surface of the pipe or from the outer surface of the pipe to a position corresponding to 10 to 60% of the pipe thickness in the thickness direction, the tapered part having an inclination average angle satisfying from 10×log(foxy) to 40×log(foxy); or achieved by combining the both processes.;COPYRIGHT: (C)2013,JPO&INPIT