HIGHLY STRONG, THICK ELECTRIC RESISTANCE-WELDED STEEL PIPE EXCELLENT IN QUENCHING PROPERTY, HOT FORMING PROCESSABILITY AND FATIGUE STRENGTH, AND METHOD FOR MANUFACTURE THEREOF

摘要

Disclosed is a highly strong, thick electric resistance-welded steel pipe excellent in quenching property, hot forming processability and fatigue strength. Also disclosed is a method for manufacture of the steel pipe. A thick electric resistance-welded steel pipe having the following composition: C: 0.25-0.4%; Si: 0.01-0.50%; Mn: 0.8-1.5%; p: 0.05% or less; S: 0.05% or less; Al: 0.05% or less; Ti: 0.005-0.05%; B: 0.0005-0.01%; and N: 0.001-0.005%, by mass, with the remainder comprising Fe and unavoidable impurities, has a critical cooling rate (Vc) represented by the formula <1> of less than 30°C/s, and the ratio of the thickness (t) to the outer diameter (D) (t/D) falling within the range of exceeding 0.15 and up to 0.30: logVc = 2.94 - 0.75ß <1> wherein ß = 2.7C + 0.4Si + Mn.