Tensile strength of 510MPa or more, the manufacturing method of the thick portion 60mm or more thick tapered plate

摘要

PROBLEM TO BE SOLVED: To provide a method of manufacturing a thick taper plate with 510 MPa or higher tensile strength, 60 mm or more thickness at a thick portion in a longitudinal direction, and small variation in toughness in a steel plate.;SOLUTION: A steel slab containing by mass, C:0.03-0.20%, Si: 0.03-0.50%, Mn: 0.80-2.20%, P: 0.020% or less, S: 0.0005-0.0050%, Al: 0.005-0.100%, Nb: 0.010-0.025%, Ti: 0.003-0.020%, N: 0.0020-0.0070%, and one or more of Cu, Ni, Cr, Mo, V, B, Ca, Mg, Zr, REM with the balance being Fe and inevitable impurities is heated to 1,000-1,200°C. When subsequently performing hot rolling varying the plate thickness in a tapered manner in the longitudinal direction, at a surface temperature in a steel plate of 900°C or lower, an accumulated rolling reduction in the thick portion is set to 30% or higher, an average pass rolling reduction is set to 7% or higher, and a finishing temperature is set to (Ar3 point-50°C) or higher. The steel slab is then subjected to accelerated cooling to 500°C or lower.;COPYRIGHT: (C)2013,JPO&INPIT