| 摘要 |
PROBLEM TO BE SOLVED: To provide a high strength cold rolled steel sheet which has excellent heat treatability to increase its strength after forming, and has excellent deep drawability. SOLUTION: A steel stock having a composition containing <0.0050% C, 0.005 to 0.03% Al, 0.005 to 0.040% N and 0.01 to 0.5% V, and also in the conditions satisfying V/51-C/21>=0 and 0.5<=(V/51-C/12+Al/27)/(N/14)<=3.0 (wherein, C, Al, N and V are each the content (mass%) of each element), is subjected to hot rolling at a heating temperature of >=900 deg.C, and a finishing temperature in finish rolling of >=800 deg.C, and is coiled at 400 to 800 deg.C. The steel is thereafter subjected to cold rolling at a draft of 60 to 95%, and is next subjected to recrystallization annealing at >=700 deg.C. Thus, the cold rolled steel sheet containing N in a solid solution state of >=0.0015%, and having heat treatability to increase its strength after forming satisfying >=50 MPaΔTS and deep drawability satisfying an r valur of >=1.2 is obtained.
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