| 摘要 |
PURPOSE:To easily produce a high-strength steel sheet having good ductility by using low-alloy components by subjecting a specifically composed steel consisting of C, Si, Mn, Al, N and Fe to hot rolling, annealing and cooling then to a heat treatment under adequate conditions after cold rolling. CONSTITUTION:The steel contg. 0.10-0.45wt% C, 0.5-1.8% Si, 0.5-3.0% Mn, 0.01-0.07% SolAl, <=0.02% total N and consisting of the balance Fe and inevitable impurities is hot rolled and coiled. The hot rolled sheet is then subjected to primary annealing for >=1hr in a 650-Ac1 temp. region directly or after cooling once and is then cooled. The steel sheet is thereafter subjected to cold rolling directly or after pickling. The cold rolled sheet is successively subjected to secondary annealing for <=10min in the temp. region of (Ac3-80 deg.C)-Ac3. Such steel sheet is cooled down to the temp. region of 350-550 deg.C at 1-400 deg.C/sec cooling rate and is subjected to an aging treatment for 15sec-30min in the above-mentioned temp. region; thereafter, the sheet is cooled down to a room temp. The steel sheet which has the good ductility and about >=80kgf/mm<2> strength and is well balanced in the strength and ductility is thus obtd.
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