Method for producing a galvannealed steel sheet

A method for producing a galvannealed steel sheet, the method comprising:

• casting a molten steel which comprises, as a chemical composition, by mass %,
• 0.0005% to 0.01% of C,
• 0.001% to 1.0% of Si,
• 0.01% to 2.0% of Mn,
• 0.005% to 0.1% of P,
• 0.01% to 0.10% of Al,
• 0.02% or less of S,
• 0.1% or less of Ni,
• 0.1% or less of Cu,
• 0.01% or less of N, and
• a balance consisting of Fe and unavoidable impurities in order to obtain a slab;
• heating the slab in 1100° C. to 1300° C.;
• hot-rolling the slab after the heating under conditions such that a finishing temperature is in 800° C. to 1050° C. and a coiling temperature is in 500° C. to 800° C. in order to obtain a hot-rolled steel sheet;
• surface-removing the hot-rolled steel sheet within a range in μm of GL expressed by a following Expression 1 or more and GU expressed by a following Expression 2 or less from an interface toward a steel along a thickness direction in order to obtain a scale-removed rolled steel sheet, when ten measurement points of the hot-rolled steel sheet are set in a transverse direction by equally dividing a line-segment having a reference length of 50 mm by 10, when a steel surface part of the hot-rolled steel sheet is from the interface between a scale and the steel to 2 μm in depth toward the steel along the thickness direction, and when a Nimax and a Cumax are respectively a maximum Ni content and a maximum Cu content in mass % of the steel surface part in the ten measurement points of the hot-rolled steel sheet;
• galvanizing the scale-removed rolled steel sheet after the surface-removing in order to obtain a galvanized steel sheet;
• and
• galvannealing the galvanized steel sheet after the galvanizing in order to obtain a galvannealed steel sheet,
• GL=(Nimax+0.8×Cumax)×0.2 (Expression 1),
• GU=(Nimax+0.8×Cumax)×4 (Expression 2).