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

The present invention provides high strength thick-gauge electric-resistance welded steel pipe excellent in hardenability, hot workability, and fatigue strength and a method of production of the same, that is, thick-gauge electric-resistance welded steel pipe containing, by mass%, C: 0.25 to 0.4%, Si: 0.01 to 0.50%, Mn: 0.8 to 1.5%, P: 0.05% or less, S: 0.05% or less, Al: 0.05% or less, Ti: 0.005 to 0.05%, B: 0.0005 to 0.01%, N: 0.001 to 0.05%, and a balance of Fe and unavoidable impurities, having a critical cooling rate Vc expressed by equation 1 of less than 30°C/s, and having a ratio of thickness t and outside diameter D, t/D, of over 0.15 to 0.30 in range: logVc = 2.94 - 0.75 �¢ ² where, P=2.7C+0.4Si+Mn