transformation point, preferably cooling the rolled slab to 750 °C at a cooling rate of 50 °C/sec or above within 1.5 sec, winding the cooled slab at a temperature ranging from ordinary temperature to 750 °C, cold-rolling the wound slab at a draft of 70 % or above, and conducting continuous annealing or continuous Sendzimir hot galvanization at 600-900 °C to control the temper-rolling reduction rate to be 1.5 x (1 - 400 x C) % or above and 2,080 x (C - 0.0015) % or above, wherein C is the carbon content (wt.
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