| 摘要 |
PROBLEM TO BE SOLVED: To improve the visibility of spangles and the workability of a plating film by continuously annealing a rolled steel sheet in an atmosphere under specified conditions. SOLUTION: The steel to be subjected to plating treatment is the one subjected to hot rolling, pickling and cold rolling. This base material steel sheet is annealed at 650 to 830 deg.C in an atmosphere in accordance with the content of Mn in the steel in a continuous annealing furnace in a plating line. This atmosphere satisfies the following conditions: Dh>=(0.5H+15)1n[Mn]+1.6 H-33, where Dh: the dew point ( deg.C) of the heating zone in the furnace, H: the concn. (volume %) of H2, in the furnace, and [Mn]: the weight % of Mn in the steel. After the annealing, it is cooled to a temp. approximately equal to that of the plating bath by the cooling zone in the furnace and is fed to the plating bath. The steel sheet is preferably cooled at a cooling rate of 10 to 30 deg.C/sec directly after the plating. Thus, the one having >=0.7 mm spangle particle size can stably be obtd., and the yield improves as well.
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