SURFACE TREATED STEEL SHEET EXCELLENT IN CORROSION RESISTANCE AFTER COATING, METHOD FOR PRODUCING T

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PROBLEM TO BE SOLVED : To provide a method for producing a surface treated steel sheet excellent in corrosion resistance after coating and an automobile part using the same. SOLUTION : The surface treated steel sheet includes a plated layer on the surface thereof, wherein a ratio of the thickness of the plated layer (the total of both surfaces) to the thickness of the sheet is 0.5-3%. The steel sheet contains as steel components, in mass%, 0.05-0.5% of C, 0.3-4% of Mn, 0.001-0.1% of P, 0.001-0.05% of S, 0.001-0.03% of N, 0.01-4% of Si, and 0.01-4% of Al, and further contains one or more elements selected from 0.01-0.2% of Ti, 0.01-0.1% of Nb, 0.0001-0.01% of B, 0.01-1% of Mo, and 0.01-25% of Cr, provided that Si+Al is 0.3-5% or Cr is 2-25%, with the balance of iron and unavoidable impurities. The plated layer contains, in mass%, 35-60% of Fe, further 2% or less (including 0) of Si, and 0.3-3% in total of alkaline earth metals with the balance comprising Al and unavoidable impurities. Alternatively, the steel sheet contains Al in steel instead of Si in steel. More preferably, the alkaline earth metal is 0.3-1.9% of Mg, and the ratio of the thickness of the plated layer (the total of both surfaces) to the thickness of the sheet is 0.5-2.5%. In order to produce the steel sheet, alloying is performed to the surface by reheating to 650-780°C after Al plating is performed in a continuous hot dip plating line without cooling to 300°C or lower. COPYRIGHT : (C)2013, JPO&INPIT