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 thin steel plate hardly generating any surface crack, and its manufacturing method in a process in which a steel slab is subjected to direct rolling or hot charge rolling, and further subjected to hot rolling as it is or after it is re-heated without dropping the temperature of the steel slab below the Ar1 point in a cooling process subsequent to the melting and the solidification.;SOLUTION: The thin steel plate has the composition containing, by mass, 0.06-0.30% C, ≤ 2.0% Si, 0.1-3.0% Mn, ≤ 0.1% P, 0.0005-0.01% S, ≥ 0.004% to 0.025% Al, 0.0005-0.010% N, and the balance Fe with inevitable impurities, and the number of grain boundary nitrides having the diameter of the equivalent circle of ≤ 50 nm is ≤ 140 per grain boundary of 1 μm².;COPYRIGHT: (C)2008,JPO&INPIT