| 摘要 |
PROBLEM TO BE SOLVED: To provide a method of manufacturing an extra thin steel sheet for vessel, excellent in flange formability even by means of high 2 Cr ratio and capable of improving productivity at the time of annealing. SOLUTION: With respect to this steel sheet which has a composition containing, by weight, 0.005-0.040% C, at the tensile test by JIS No.5 test piece, 0.2% proof stress of which is >=430 MPa and total elongation of which is <=15% or the difference between its 0.2% proof stress before cold rolling and its 0.2% proof stress after cold rolling is <=120 MPa, the difference between tensile strength and 0.2% proof stress is made to >=20 MPa or the yield elongation after artificial aging at 200±C for 1 hr is regulated to >=2%. Further, as the method of manufacturing this steel sheet, cooling velocity through the temperature region from 600 to 200 deg.C in an annealing stage in particular is made to >=20 deg.C/sec or the maximum value of cooling velocity at arbitrary temperature through the temperature region from 600 to 200 deg.C is made to >=40 deg.C/sec.
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