Thick steel plate excellent in fatigue crack propagation characteristic in plate thickness direction and its manufacturing method

摘要

PROBLEM TO BE SOLVED: To provide a thick steel plate excellent in fatigue resistant crack propagation characteristics in plate thickness direction, and a method of manufacturing the same.;SOLUTION: A steel material containing, by mass, 0.03-0.15% C, and Si and Mn for an adjusted amount and containing one or two selected from 0.005-0.050% Ti and 0.001-0.1% Nb is heated to the temperature of 900-1,350°C, and is subjected to hot rolling comprising first rolling for which cumulative draft is ≥10% in the temperature zone at or higher than an austenite part recrystallizing temperature of 1,000-850°C by a surface temperature and second rolling for which average draft of one pass is 5.0% and the cumulative draft is ≥50% in the temperature zone of 900-600°C by the surface temperature, for which a range equivalent to a part from the position of 2 mm in a plate thickness direction from the surface to 3/10 position of the plate thickness and/or a range equivalent to a part from the position of 2 mm in the plate thickness direction from the back surface of the thick steel plate to the 7/10 position of the plate thickness become a two-phase structure, and for which the rolling end temperature of the second rolling is 600°C or higher by the surface temperature.;COPYRIGHT: (C)2011,JPO&INPIT