Manufacturing method and manufacturing method of the high strength steel pipe with the steel plate of excellent tensile strength 760MPa or higher grade of high strength steel plate in resistance to hydrogen induced cracking resistance and ductile fracture characteristics

摘要

PROBLEM TO BE SOLVED: To provide a method for producing a high strength steel sheet of 760 MPa class tensile strength excellent in the resistance to a hydrogen induced crack and ductile fracture properties; and also to provide a method for producing a high strength steel tube using this steel sheet.;SOLUTION: The method for producing the steel sheet and the method for producing the steel tube using this steel sheet are characterized by the following procedure. When the steel having prescribed components is melted, in the case of using T1 (C) for setting start temperature of hot-rolling in the roll process, T3 (C) for setting finish temperature and T4 (C) for setting control cooling stop temperature after rolling, while controlling a hydrogen quantity in the steel under state of limiting to {0.65+(0.0007T4-0.03)}1.5exp[-1411{1/(T1+273)-1/(T3+273)}] ppm or lower, the composition adjustment is performed. After casting, hot-rolling is started at T1 (C) of 1,000-1,250C and finished at T3 (C) of 600-900 (C), and thereafter, when cooling, T4 (C) is made to T3(C) to 50C and the control-cooling is performed at 0.5-20 C/s average cooling speed in the center part of the steel sheet till T4 (C) and air-cooling is performed from T4 (C) till the room temperature. The hydrogen quantity in the steel sheet is 0.65 ppm.;COPYRIGHT: (C)2007,JPO&INPIT