| 摘要 |
PURPOSE:To manufacture the titled steel sheet, by heating and holding steel sheet having a specified compsn. under a specified condition, then applying cooling treatments under specified conditions while dividing into three stages. CONSTITUTION:Steel sheet composed of, by weight 0.15-0.35% C, 0.50-2.00% Si, 0.20-2.50% Mn, <=0.10% SolAl, if necessary 0.05-0.5% Cr and the balance Fe with inevitable impurity is heated to two phases coexistence region of 730-920 deg.C and held for 20sec-5min, then cooled to 650-770 deg.C range by 2-50 deg.C/sec rate and held for 5sec-1min, further rapidly cooled to 300-450 deg.C range by 10-500 deg.C/sec rate, then held in the temp. range for 20sec-10min, then cooled to room temp. In this way, steel sheet superior in workability, contg. >=10% residual austenite, sufficiently exhibiting an effect of the transformation inducting plasticity, having >=60kg/mm<2> tensile strength, further under >=2,500kg/mm<2> in product of tensile strength and total elongation is obtd.
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