| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for producing a galvannealed steel sheet having a coating weight of≥60 g/m<SP>2</SP>and also having excellent powdering resistance. SOLUTION: When a steel sheet is annealed, is thereafter dipped into a molten zinc bath comprising 0.01 to 0.30 mass% aluminum, is subjected to plating treatment, and is further subjected to alloying treatment for the plating layer in such a manner that aζphase is made into the main phase, so as to produce a galvannealed steel sheet, at the surface of the steel sheet before the annealing, a recessed part with a depth of 1 to 15μm is made present by 20 to 80% in area ratio to the whole of the surface in the steel sheet, and further, an iron based oxide layer with a thickness of≥5 nm is formed. For example, the recessed part and the iron based oxide layer can be formed by bringing the steel sheet into contact with an acid solution comprising hydrogen peroxide as an oxidizer and hydrochloric acid as acid. COPYRIGHT: (C)2007,JPO&INPIT
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