THICK COLD ROLLED STEEL SHEET EXCELLENT IN DEEP DRAWABILITY AND METHOD OF MANUFACTURING THE SAME

摘要

A steel slab having a composition that comprises at most 0.008 % by weight of C, at most 0.5 % by weight of Si, at most 1.0 % by weight of Mn, at most 0.15 % by weight of P, at most 0.02 % by weight of S, from 0.01 to 0.10 % by weight of Al, at most 0.008 % by weight of N, from 0.035 to 0.20 % by weight of Ti, and from 0.001 to 0.015 % by weight of Nb, with a balance of Fe and inevitable impurities, in which those C, S, N, Ti and Nb satisfy the following condition: $is\; subjected\; to\; rough\; hot-rolling\; to\; a\; reduction\; ratio\; of\; not\; lower\; thin\; 85\; \%,\; at\; a\; temperature\; falling\; between\; the\; Ar3\; transformation\; point\; of\; the\; steel\; and\; 950\; DEG\; C,\; then\; to\; finishing\; hot-rolling\; to\; a\; reduction\; ratio\; of\; not\; lower\; than\; 65\; \%,\; at\; a\; temperature\; falling\; between\; 600\; DEG\; C\; and\; the\; Ar3\; transformation\; point\; of\; the\; steel,\; while\; being\; lubricated,\; to\; thereby\; have\; a\; mean\; shear\; strain\; of\; not\; larger\; than\; 0.06,\; then\; pickled,\; pre-annealed\; at\; a\; temperature\; falling\; between\; 700\; and\; 920\; DEG\; C,\; cold-rolled\; to\; a\; reduction\; ratio\; of\; not\; lower\; than\; 65\; \%,\; and\; thereafter\; further\; annealed\; for\; recrystallization\; at\; a\; temperature\; falling\; between\; 700\; and\; 920\; DEG\; C.\; The\; method\; of\; the\; invention\; provides\; thick\; cold-rolled\; sheet\; steel\; having\; a\; thickness\; of\; not\; smaller\; than\; 1.2\; mm\; and\; having\; an\; r\; value\; of\; not\; smaller\; than\; 2.9.\mathop{\mathrm{image}}$