Method for applying a protective coating to a flat steel product and flat steel product having a corresponding protective coating

A method for applying a protective coating (10) on a flat steel product (100), wherein the protective coating (10) is produced by guiding the flat steel product (100) having a strip entry temperature in the range between 400 and 490 degrees Celsius through a molten zinc alloy bath (11), wherein the molten zinc alloy bath (11) has a bath temperature in the range from 400 to 480 degrees Celsius and has an aluminum content and a magnesium content, wherein the molten zinc alloy bath (11) has a composition which is adjusted as follows:

• the aluminum content lies in the range between 2.0 and 2.9 weight percent;
• the magnesium content lies in the range between 1.5 and 2.4 weight percent;
• the aluminum content in weight percent is greater than the magnesium content in weight percent;
• the ratio of the magnesium content in weight percent to the sum of the aluminum content in weight percent and the magnesium content in weight percent lies in the range between 0.34 and 0.40;
• and
• the remainder of the molten zinc alloy bath (11) are zinc and unavoidable impurities,
• characterized in that
• a theoretical cooling curve for an alloy composition of the molten zinc alloy bath (11) is calculated such that a Mg2Zn11-phase is excluded and in that in the molten zinc alloy bath (11) before the solidification of the ternary eutectic (TE) a solid content of primary zinc dendrites results, which lies in the range between 0.4 and 0.6 molar fraction of the solid content of the molten zinc alloy bath (11), and in that
• a cooling rate for solidifying the molten zinc alloy in a solidification process on the flat steel product (100) is adjusted based on the calculated theoretical cooling curve;
• and is controlled in an apparatus (200) applying control technology using nozzles (14).