THICK STEEL SHEET OF AT LEAST 50 MM IN THICKNESS WITH EXCELLENT LONG BRITTLE FRACTURE PROPAGATION STOPPING PROPERTY, METHOD FOR PRODUCTION THEREOF, METHOD FOR EVALUATING LONG BRITTLE FRACTURE PROPAGATION STOPPING PERFORMANCE, AND TEST APPARATUS

摘要

PROBLEM TO BE SOLVED: To provide a thick steel sheet of at least 50 mm in thickness with excellent long brittle fracture propagation stopping properties, to provide a method for production thereof, to provide a method for evaluating the long brittle fracture propagation stopping performance, and to provide a test apparatus.;SOLUTION: In the tip shape of the long brittle fracture stopping area, a specific area of the central region of sheet thickness forms a recess at least as long as the sheet thickness in relation to the direction in which the long brittle fracture propagates, and the specific area has a specific texture in the central region of sheet thickness. The method for production of the thick steel sheet includes rolling the steel of a specific component at a surface temperature of 850 to 1,000°C and a cumulative rolling reduction of ≥10% after heating, and then rolling at specific surface and internal temperatures at a one pass rolling reduction of ≥7% and a cumulative rolling reduction of ≥50% at a steel sheet surface temperature of 550 to 800°C after completion of rolling. The propagation stopping performance to the long brittle fracture having a fracture propagation length of ≥1 m is evaluated using a test piece having a width of ≥2 m with a test piece length or a distance between the tips of a tab plate in a test apparatus on which the test piece is placed, of 2.8 times or more of the test piece width.;COPYRIGHT: (C)2012,JPO&INPIT