Manufacturing method of high strength hot dip galvanized steel sheet, manufacturing method of hot rolled steel sheet for high strength hot dip galvanized steel sheet, manufacturing method of cold rolled steel sheet for high strength hot dip galvanized steel sheet, and high strength hot dip galvanized steel sheet

摘要

Provided are a method for manufacturing a high-strength galvanized steel sheet excellent in formability, surface appearance, and coating adhesion; a method for manufacturing a hot-rolled steel sheet for high-strength galvanized steel sheets, a method for manufacturing a cold-rolled steel sheet for high-strength galvanized steel sheets, and a high-strength galvanized steel sheet. Mn: 2.00% to 10.00% is contained. The concentration of solute Mn at a depth of 5 µm or less from a surface of a steel sheet is 1.50% by mass or less and the value obtained by dividing the average mass percentage of Mn in retained austenite by the average mass percentage of Mn in ferrite is 2.0 or more. A first heat treatment is performed in such a manner that the steel sheet is held in a temperature range of 650 °C to 850 °C for 600 s to 21,600 s in an atmosphere having an H 2 concentration of 0.1% by volume to 25.0% by volume and a dew point of -45 °C to 0 °C in such a state that a surface of the steel sheet is exposed. A second heat treatment is performed in such a manner that the steel sheet is held in a temperature range of 600 °C to 830 °C for 20 s to 900 s in an atmosphere having an H 2 concentration of 0.05% by volume to 25.0% by volume and a dew point of -10 °C or lower.