| 摘要 |
PROBLEM TO BE SOLVED: To provide an extra thin steel sheet for vessel, having excellent flange formability while improving productivity at annealing by high 2CR rate and freeing of annealing schedule. SOLUTION: The steel sheet has a composition containing, by weight, 0.004 to 0.0300% N and 0.005 to 0.080% Al and also containing, if necessary, <=0.005% C and <=1.0% Mn or further containing either or both of <=0.0050% Ti and <=0.0050% Nb. In this steel sheet, 0.2% proof stress is >=430 MPa and total elongation is <=15% or the difference in 0.2% proof stress before and after cold rolling of 10% is <=140 MPa. Moreover, the difference between tensile strength and 0.2% proof stress is >=20 MPa or yield point elongation after artificial aging at >=200 deg.C for 1 hr is >=2%.
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