| 摘要 |
<p>PURPOSE: A high-strength steel sheet and a manufacturing method thereof are provided to have a finally modified structure in which micro precipitates are formed on a complex structure containing 80-90 vol% of ferrite and 10-20 vol% of bainite by controlling alloy components and a cooling process after a hot-rolling process. CONSTITUTION: A manufacturing method of a high-strength steel sheet is as follows. A slab board composed of 0.04-0.15 wt.% of C, 0.2-1.0 wt.% of Si, 1.0-2.5 wt.% of Mn, 0.01-0.1 wt.% of P, 0.001-0.01 wt.% of S, 0.05-1.0 wt.% of Al, 0.03-0.09 wt.% of Nb, 0.01-0.09 wt.% of Ti, 0.1-0.3 wt.% of Mo, 10-50ppm of N, and the rest of Fe and inevitable impurities is hot-rolled at 850-950 degree. The hot-rolled slab board is primarily cooled to a ferrite temperature range. The primarily cooled slab board is secondarily cooled in the ferrite temperature range at a speed slower than the primary cooling speed. The secondarily cooled slab board is wound after being thirdly cooled to a bainite temperature range at a speed faster than the secondarily cooling speed. [Reference numerals] (AA) Start; (BB) Hot rolling(FDT: 850-950°C); (CC) First cooling(50-100°C/sec, 700-800°C); (DD) Second cooling(Below 10°C/sec, 5-10 seconds); (EE) Third cooling/Coiling(50-100°C/sec, 540-600°C); (FF) End</p> |
