| 摘要 |
PROBLEM TO BE SOLVED: To provide a galvannealed steel sheet having press workability and immunity to powdering, which are required of a steel sheet for automobile use, at a low cost. SOLUTION: The galvannealed steel sheet is provided with an Fe-Zn alloy plating layer in which the amount of Al-O in the surface layer is regulated to <15% and also the total amount of existingη-phase andζ-phase is regulated to <5 g/m<2> , by bringing a galvannealed steel sheet 3 which has an Fe-Zn alloy plating layer 4 having (20 to 90) g/m<2> coating weight per side and 7 to 12% Fe content into contact with an alkali solution of >=pH9.0 to regulate the amount of Al-O in the surface layer of the Fe-Zn alloy plating layer to <15% and then bringing this galvannealed steel sheet into contact with an acid solution of <=pH3.0 to regulate the total amount ofη-phase andζ-shape in the surface layer of the Fe-Zn alloy plating layer 4 to <5 g/m<2> .
|
