| 摘要 |
PROBLEM TO BE SOLVED: To provide a galvannealed steel sheet excellent in powdering resistance, and its manufacturing method. SOLUTION: In the galvannealed steel sheet, Fe concentration in a plating film is 5-15 wt.%, and the plating film consists of thick-film areas having flat tops and thin-film areas as the balance. In the thick-film areas, the diameter of the flat tops is regulated to <=150μm; and in the thin-film areas, the area ratio of the areas having film thickness 1-40% of the film thickness in the thick-film areas is regulated to 20-80% of the whole film. This galvannealed steel sheet can be manufactured by formingδ-phases and/orΓ1-phases in the region of >=50% of the surface of the steel sheet in a galvanizing bath, inhibiting, at the alloying treatment for the resultant plating film, alloying in the region where theδ-phases and/orΓ1-phases are formed to provide recessed and projected parts to the plating film, and then flattening the respective tops of the projected parts of the plating film by temper rolling.
|
