Patent ID: 8268095
Filing Date: 2012-09-18
Classification: C23C,Y10T

Abstract:
1. A method of manufacturing a hot dip galvannealed steel sheet, comprising the steps of: (a) subjecting a steel sheet to hot dip galvanizing to manufacture a hot dip galvanized steel sheet; (b) heating the hot dip galvanized steel sheet from step (a) for alloying; (c) subjecting the hot dip galvanized steel sheet from step (b) to temper rolling; (d) forming an acid solution film on the surface of the steel sheet by bringing the temper-rolled hot dip galvanized steel sheet from step (c) into contact with an acid solution containing ions, at least one of the ions selected from the group consisting of Zr ions, Ti ions, and Sn ions, wherein the acid solution has a pH buffering effect and a degree of pH increase, defined on the basis of an amount of 1.0 mol/l sodium hydroxide solution required to raise the pH of 1 liter of the acid solution from 2.0 to 5.0, is in the range of 0.05 to 0.5; (e) after completion of the contact in step (d), maintaining a state where an acid solution film is formed on the surface of the steel sheet for at least 1 second; and (f) washing the hot dip galvanized steel sheet from step (e) with water, to thereby form a Zn oxide layer having a thickness of 10 nm or more on the surface of the galvanized steel sheet.