COLD-CHALLENGE STANDARDS AND GALVANISED COAL-CHALLENGE STANDARDS WITH PREVIOUS FORMALITY AND EFFECTIVENESS AND PROCEDURE FOR THEIR PRODUCTION

摘要

A cold-rolled steel sheet, which may be further galvanized if desired, is produced by hot rolling steel containing, on a mass base, 0.0010 to 0.0040 % of C, at most 0.0030 % of N, at most 0.5 % of Si, 0.02 to 1.5 % of Mn, at most 0.08 % of P, at most 0.01 % of S, 0.005 to 0.07 % of acid-soluble Al, at most 0.05 % of Nb (where 0 Nb % - 93/12 C % /= 0.025 %), 24/14 N % to 72/14N % of Ti, and the balance of Fe and unavoidable impurities at a finish terminating temperature of the Ar3 transformation point or above, rapidly cooling the steel within 2 s after the hot rolling at a cooling rate of 30 DEG C/s to the extend of temperature fall of at least 100 DEG C, winding at 650 to 770 DEG C, cold rolling at the rolling reduction of 72 to 92 %, conducting recrystallization annealing at 820 to 880 DEG C for at least 20 s, and cooling from this temperature to room temperature at a cooling rate of a least 3 DEG C/s. The obtained sheet contains carbon in solid solution form formed by dissolving deposited carbides through recrystallization annealing and has a recrystallization texture wherein the value of log(I{222}/I{200}) is 2.7 or above, wherein I{222} and I{200} are the intensities of diffraction of the {222} plane and the {200} plane, respectively, in X-ray diffractometry. The sheet is excellent in formability and workability in chemical conversion coating and high in work hardenability and baking hardenability. IMAGE