| 摘要 |
PROBLEM TO BE SOLVED: To provide a steel sheet having a superior strengthened property by sub-zero treatment, of which the strength increment by the sub-zero treatment using liquid nitrogen exceeds 100 MPa. SOLUTION: The steel sheet including 0.05-0.35% C, 0.5-3.0% Si, 0.7-4.0% Mn, and Fe, as essential elements, comprises that variateΔI of saturated magnetization values before and after immersing the steel sheet in the liquid nitrogen for five minutes is 400 e.m.u. or more.
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