PRECOATED STEEL SHEET WITH EXCELLENT WORKABILITY AND CORROSION RESISTANCE IN WORKED AREA, AND ITS MANUFACTURING METHOD

摘要

PROBLEM TO BE SOLVED: To provide excellent workability and corrosion resistance in a worked area to a precoated steel sheet using a hot-dip Al-Zn coated steel sheet having 20-95 mass% Al content in the plating coat. SOLUTION: The plating film is obtained by means of the following thermal histories (a) and (b) at least: (a) a thermal history where the average cooling rate within 10 seconds immediately after the steel sheet leaves a hot-dipping bath is regulated to <11 deg.C/s; (b) a thermal history where, after the solidification of the hot-dipped plating metal, temperature raise and heating are done up to a temperature T( deg.C) between 130 and 300 deg.C and then the average cooling rate from the temperature T( deg.C) down to 100 deg.C is regulated to a value not higher than C( deg.C/h) represented by equation C=(T-100)/2 and/or a thermal history where the average cooling rate from the temperature T( deg.C) between 130 and 300 deg.C after the solidification of the hot-dipped plating metal down to 100 deg.C is regulated to a value not higher than C ( deg.C/h) represented by equation C=(T-100)/2. Further, a chemical conversion coating, an undercoat film and then an overcoat film are coated onto the surface of the plating film, respectively.