Formability of electric resistance welded portion, method of manufacturing the excellent electric resistance welded steel pipe in the low-temperature toughness and fatigue resistance

摘要

PROBLEM TO BE SOLVED: To provide an electric resistance welded steel pipe which has excellent formability, low-temperature toughness and fatigue resistance characteristics in an electric resistance welded part and has a tensile strength TS of 434 MPa or more.;SOLUTION: In the electric resistance welded steel pipe, the total amount of Si, Mn, Al, Ca and Cr included in inclusions present in the electric resistance welded part and having a circle-equivalent diameter of 2 μm or more is 99 ppm or less by mass%. The electric resistance welded part is obtained by electric resistance welding in an atmosphere in which an oxygen concentration is controlled to (1,000/foxy) ppm or lower. After the electric resistance welding, the pipe can optionally be subjected to a heat treatment on the electric resistance welding part by heating to a temperature, in terms of an average temperature in the thickness direction, in the range from 720 to 1,020°C; or after the electric resistance welding, the pipe can be optionally be subjected to diameter-reducing rolling by heating to a temperature, in terms of an average temperature in the thickness direction, in the range from 720 to 1,020°C. The electric resistance welded steel pipe can optionally contain 0.03 to 0.59% of C, 0.10 to 1.50% of Si, 0.40 to 2.10% of Mn, 0.01 to 0.35% of Al, and further, can optionally contain Ca and Cr.;COPYRIGHT: (C)2013,JPO&INPIT