The black sheet and its production mannered null mass which is superior in resistance surface crack Characteristic at the time

摘要

PROBLEM TO BE SOLVED: To provide a steel sheet in which surface cracking is hard to be generated in a process where, regarding hot direct rolling or hot charge rolling for a slab, the slab is reheated as it is, so as to be hot-rolled without reducing its temperature to an Ar1 or below in a cooling stage succeeding to melting/solidifying, and to provide its production method.;SOLUTION: The steel sheet has a composition comprising, by mass, 0.06 to 0.30% C, ≤2.0% Si, 0.1 to 3.0% Mn, ≤0.1% P, 0.0005 to 0.01% S, 0.025 to 0.20% Al, 0.01 to 0.10% Nb, 0.01 to 0.20% Ti and 0.0005 to 0.010% N, and the balance Fe with inevitable impurities, and in which the N content [N] and the Ti content [Ti] satisfy inequality (A); [Ti]-3.4×[N]0, and also, the number of boundary nitrides with a diameter of the equivalent circle of ≤50 nm is ≤140 pieces per μm² of grain boundary.;COPYRIGHT: (C)2008,JPO&INPIT