| 摘要 |
The present invention relates a hot-dip galvanized steel sheet having transformation induced plasticity, mainly used in supporting or reinforcing structure of cars. The galvanized steel sheet comprises C: 0.05 to 0.20 wt. %, Si: 0.05 to 0.35 wt. %, Mn: 1.0 to 2.5 wt. %, Al: 0.01 to 1.5 wt. %, P: 0.02 wt % or less, Co: 0.3 to 0.8 wt. %, remained are Fe and inevitable impurities, satisfying relations between the above Si and Al, as 0.6<=Si+0.78 Al(%)<=1.2. This galvanized steel sheet is produced by steps of hot rolling of the steel slab comprising the above chemical compositions, and coiling the hot-rolled steel sheet at 500 to 700° C., recrystallization annealing treatment at the temperature range of 740° C. to 880° C. for 1-5 minutes and coiling, and cooling to 300° C. to 580° C. with cooling rate of 2 to 100° C./sec. and preserving at temperature range of 300 to 580° C. for not more than 10 min. and, zinc plating. If necessary, alloying heat treating for not more than two (2) minutes, may be applied, for controlling volume ratio of 2-20% of retained austenite. Then, the above treated steel sheets are finally cooled, and finished. At that result, a hot-dip galvanized steel sheet having transformation induced plasticity characterized more than 60 kg/mm<SUP>2 </SUP>of T.S., and more than 28% of elongation, satisfying volume ratio of 2-20% of the retained austenite structure, can be obtained. |
