Patent ID: 8048367
Filing Date: 2011-11-01
Classification: C21D,C22C

Abstract:
1. High strength thick-gauge steel plate superior in weldability and having a tensile strength of 780 MPa or more characterized by containing, by mass %, C: 0.030% or more, 0.055% or less, Mn: 2.55% or more, 3.5% or less, P: 0.01% or less, S: 0.0010% or less, Al: 0.06% or more, 0.10% or less, B: 0.0005% or more, 0.0020% or less, N: 0.0015% or more, and 0.0060% or less, limiting Ti to 0.004% or less, having a weld cracking susceptibility parameter Pcm shown by the following of 0.18% to 0.24%, and having a balance of Fe and unavoidable impurities as its composition of ingredients and having a microstructure of the steel comprised of martensite and of a balance, by an area fraction of 3% or less, of one or more of ferrite, bainite, and cementite: Pcm=[C]+[Si]/30+[Mn]/20+[Cu]/20+[Ni]/60+[Cr]/20+[Mo]/15+[V]/10+5[B] where, [C], [Si], [Mn], [Cu], [Ni], [Cr], [Mo], [V], and [B] respectively mean contents of C, Si, Mn, Cu, Ni, Cr, Mo, V, and B expressed by mass %.