SURFACE TREATED 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 surface treated steel sheet using a hot-dip Al-Zn coated steel sheet having 20-95 mass% Al content in the plating film.;SOLUTION: The plating film is obtained by means of the following thermal history (a) at least: (a) a thermal history where, after the solidification of the hot-dipped plating metal, temperature raise and heating are done up to a temperature T(°C) between 130 and 300°C and then the average cooling rate from the temperature T(°C) down to 100°C is regulated to a value not higher than C(°C/h) represented by equation C=(T-100)/2 and/or a thermal history where the average cooling rate from the temperature T(°C) between 130 and 300°C after the solidification of the hot-dipped plating metal down to 100°C is regulated to a value not higher than C(°C/h) represented by equation C=(T-100)/2. Further, a chemical conversion coating containing Cr resultant from chromating treatment in an amount of (0.1 to 100) mg/m² of metal chromium is coated onto the surface of the plating film.;COPYRIGHT: (C)2002,JPO