| 摘要 |
PROBLEM TO BE SOLVED: To provide a producing method capable of obtaining a high strength thin steel sheet excellent in workability including stretch-flanging properties, also uniform in mechanical properties and having various strength levels. SOLUTION: This method for producing a high strength thin steel sheet has a stage in which a continuously cast slab having a C content of <=0.8 wt.% is subjected to rough rolling, a stage in which the slab is subjected to finish rolling at >=(Ar3 transformation point -20) deg.C, a stage in which the same is subjected to primary cooling to 500 to 800 deg.C at >120 deg.C/sec, a stage in which the same is let to cool for 1 to 30 sec, a stage in which the same is subjected to secondary cooling at >=20 deg.C/sec and a stage in which the same is coiled at <=650 deg.C. Moreover, it is possible that the continuously cast slab is heated to <=1230 deg.C without executing cooling to a room temperature, is thereafter subjected to rough rolling and is subjected to induction heating directly before or in the process of the finish rolling, within >0.1 to 1.0 sec after the finish rolling, the primary cooling is started, and the variation of the temperature in the width direction of the coil and in the longitudinal direction thereof after the rapid cooling (maximum value-minimum value) is controlled to <=60 deg.C.
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