PURPOSE:To obtain a cold rolled steel sheet having ultra-deep drawability without deteriorating the brittle resistance by secondary operations by subjecting an extremely low C aluminum killed steel sheet in which contents of C, N, P, and S are controlled and a specific ratio of Ti is incorporated to box annealing under specific heat conditions then to temper rolling. CONSTITUTION:The Ti-contg. extremely low C aluminum killed steel slab consisting of the compsn. contg. =0.003wt% C, =0.5% Si, =0.5% Mn, =0.1% Al, =0.003% N, =0.20% P, and =0.01% S, and contg. Ti in excess of the sum of the Ti content of the respective contents of C, N, P, and S and up to 10% according to said contents is subjected to hot and cold rolling. The rolled sheet is then subjected to the box annealing at a high temp. of 720-850 deg.C soaking temp. The sheet is subjected to slow heating to hold the same for =5hr in a 600-700 deg.C region during the heating up process or to continue the heating up time from 500 deg.C up to 720 deg.C for =10hr. The sheet is then subjected to the temper rolling. The cold rolled steel sheet having consistently ultra-deep drawability and resistance to brittleness in the secondary operations is obtd. by the above-mentioned method.
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