| 摘要 |
PROBLEM TO BE SOLVED: To produce a steel sheet capable of remarkably increasing tensile strength by heat treatment at a relatively low temp. in a short time after forming such as pressing, and to provide a method for producing a formed body using the steel sheet. SOLUTION: This thin steel sheet excellent in the performance of increasing heat treating strength after working such as pressing contains, by weight, <=0.05% C, <=1.5% Si, 0.01 to 1.5% Mn, <=0.1% P, <=0.01% Si, 0.005 to 0.1% Al, <=0.01% N, 1.2 to 2.5% Cu, 0.25 to 1.50% Ni, one or >= two kinds of Cr and Mo by 0.03 to 2.5% in total, and the balance iron with inevitable impurities. As to the method for producing a formed body excellent in the performance of increasing heat treating strength after working, after press forming using the same, heat treatment is executed under the condition in which the treating time t(sec) and treating temp. T( deg.C) satisfy the inequality of exp(-(T-790)/55)< t<exp(-(T-980)/55), by which the increase of the strength of >=190 MPa can be obtd.
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