| 摘要 |
PURPOSE: A cold rolled steel sheet and a method for manufacturing the same are provided which has a tensile strength of 50 kgf/mm2 or more, an RM value (average of vertical anisotropy, RM=(r0+2r45+r90)/4) of 1.5 or more and strong to the second processing brittleness. CONSTITUTION: The cold rolled steel sheet comprises 0.0050 wt.% or less of C, 1.1 to 1.7 wt.% Mn, 0.07 to 0.12 wt.% of P, 0.4 to 0.8 wt.% of Si, 0.0005 to 0.0020 wt.% of B, 0.0050 wt.% or less of N, 0.015 wt.% or less of S, {C£wt.%|÷12+N£wt.%|÷14}x48 or more of Ti, 0.025 to 0.06 wt.% of Al for acid value and a balance of Fe and other inevitably contained elements, wherein the cold rolled steel sheet has a tensile strength of 50 kgf/mm2 or more, an RM of 1.5 or more and superior second processing brittleness. The method comprises the processes of reheating and hot rolling a slab of ultra low carbon steel comprising the above composition in an ordinary manner, wherein a hot rolled coil is manufactured by coiling the hot rolled steel slab in the temperature range of 450 to 700 deg.C by increasing a hot finishing rolling temperature to an Ar3 transfoRMation temperature or more; pickling the hot rolled coil in an ordinary manner; and annealing the cold rolled steel at a temperature from a recrystallization temperature to Ac1 after cold rolling the pickled steel, and then overaging the annealed steel.
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