Cold rolled steel sheet exhibiting excellent press workability and method of manufacturing the same

Abstract

A cold rolled steel sheet including about 0.001 weight percent or less of carbon (C), about 0.1 weight percent or less of silicon (Si), about 0.3 weight percent or less of manganese (Mn), about 0.05 weight percent or less of phosphorus (P), about 0.003 weight percent or less of sulfur (S), about 0.1 weight percent or less of aluminum (Al), about 0.002 weight percent or less of nitrogen (N), about 0.005 to 0.02 weight percent of titanium (Ti), about 0.001 to 0.01 weight percent of niobium (Nb), and the balance iron and incidental impurities. The total weight percent of carbon, sulfur, and nitrogen is about 0.004 weight percent or less. The content of titanium, carbon, sulfur and nitrogen satisfies the equation: about 4.times.(C wt %).ltoreq.(Ti wt %)-48/14(N wt %)-48/32(S wt %).ltoreq.about 12.times.(C wt %). The method of the invention includes uniformly heating a steel slab having a composition as described above at a temperature T(K) satisfying the following equation: T(K).times.(C wt %+S wt %).ltoreq.about 4.0, and within a temperature range from abut 900.degree. to 1,300.degree. C., hot rolling at a finishing temperature of higher than the A.sub.C3 transformation temperature, coiling at a temperature of about 650.degree. C. or less, cold rolling after pickling at a rolling reduction rate of about 65 to 90 percent, and recrystallization-annealing at a temperature ranging from about 700.degree. to 950.degree. C.

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