SUPER HIGH STRENGTH ELECTRIC RESISTANCE WELDED STEEL PIPE FOR HOLLOW MEMBER EXCELLENT IN WORKABILITY AND LOW TEMPERATURE TOUGHNESS, AND METHOD FOR MANUFACTURING THE SAME

摘要

PROBLEM TO BE SOLVED: To provide a high strength electric resistance welded steel pipe excellent in a workability and a low temperature toughness, which is ≥1500 MPa TS, ≥27000 MPa% TS×El and ≥50 J/cm² vE_-40 in the non-heat treatment, and to provide a method for manufacturing the high strength electric resistance welded steel pipe.;SOLUTION: The electric resistance welded steel pipe is configured to have the composition including, by mass%, 0.31-0.50% C, 0.01-1.0% Si, 1.0-4.0% Mn, ≤0.1% Al, 0.0010-0.0100% N, 0.0003-0.0050% B and the balance Fe with inevitable impurities. After heating and soaking to Ac₃ transformation point or more, the diameter-reduction rolling is applied at Ar₃ transformation point to 900°C rolling-finish temperature and at 20-75% accumulated diameter-reduction ratio in the temperature zone of ≤900°C. Thereby, there is provided the super high strength electric resistance welded steel pipe having ≥1500 MPa TS, ≥27000 MPa% TS×El and further, 50 points or lower ▵HV of the difference of hardness between the base material part and the electric sewing welding part and ≥50 J/cm² vE_-40 of Charpy impact value at -40°C.;COPYRIGHT: (C)2013,JPO&INPIT