Patent ID: 8246768
Filing Date: 2012-08-21
Classification: B21B,C21D,C22C

Abstract:
1. A high-tensile steel plate having a yield stress of 450 MPa or greater and a tensile strength of 570 MPa or greater at the plate thickness center region and having a plate thickness of 30 to 100 mm, comprising, in mass %: C: 0.05% to 0.07%, Si: 0.09% or less, Mn: 0.8% to 2.0%, and Al: 0.010% to 0.1%; comprising Nb and Ti at contents of, in mass %: Nb: 0.025% or more, and Ti: 0.005% or more that satisfy 0.045%≦[Nb]+2×[Ti]≦0.105%; comprising: N: more than 0.0025 mass % and not more than 0.008 mass %; and comprising Nb, Ti, C and N at contents in ranges such that the value of A shown below is 0.0022 to 0.0055, weld cracking parameter for steel composition Pcm shown below being 0.18 or less, and a balance of Fe and unavoidable impurities; and having a steel structure of bainite or mixture of bainite and ferrite comprising a bainite volume ratio of 30% or more, wherein a pearlite volume ratio is less than 5%, and an island martensite volume ratio is less than 3%: where [Nb], [Ti], [C], [N], [Si], [Mn], [Cu], [Ni], [Cr], [Mo], [V] and [B] represent the contents of Nb, Ti, C, N, Si, Mn, Cu, Ni, Cr, Mo, V and B expressed in mass %.