HIGH STRENGTH HOT ROLLED STEEL SHEET AND PLATED STEEL SHEET EXCELLENT IN DEEP DRAWABILITY AND PRODUCTION THEREOF

摘要

PROBLEM TO BE SOLVED: To obtain a high strength hot rolled steel sheet high in r value and ductility and excellent in deep drawability without executing cold rolling by incorporating specified amounts of C, Si, Mn, P, S, Al, N, Ti and Nb, regulating the amt. of carbon to be precipitated as the carbide of Ti or Nb and specifying the plane intensity ratio of the center layer to the 1/8 part of the thickness. ;SOLUTION: This high strength hot rolled steel sheet is the one having a compsn. contg., by weight, ≤0.003% C, ≤0.5% Si, ≤0.5% Mn, 0.04 to 0.15% P, 0.005 to 0.015% S, 0.005 to 0.1% Al and ≤0.0035% N, furthermore contg. 0.03 to 0.1% Ti+Nb, contg., at need, prescribed amounts of B, Cu, Ni Cr and Sn, in which the amt. of carbon to be precipitated as the carbide of Ti or Nb is regulated to ≤7ppm, and the plane intensity ratio (222)_center/(222)_1/8t between the center layer and the 1/8 part of the total thickness is regulated to ≤5, and its r value is regulated to about ≥1.5, its ductility of regulated to about ≥36%, and it is excellent in deep drawability. This hot rolled steel sheet can be obtd. by subjecting the steel having the above compsn, to finish rolling at the Ar point or below in hot rolling, coiling it at a low temp. and successively executing recrystallization annealing.;COPYRIGHT: (C)1998,JPO