Method for manufacturing high strength galvanized steel sheet having excellent stability of mechanical properties, formability, and coating appearance

A method of manufacturing a high strength galvanized steel sheet having excellent stability of mechanical properties, formability, and coating appearance, comprising:

• applying a first heating step to a steel sheet containing C:
• 0.04% or more and 0.13% or less, Si:
• 0.7% or more and 2.3% or less, Mn:
• 0.8% or more and 2.0% or less, P:
• 0.1% or less, S:
• 0.01% or less, Al:
• 0.1% or less, N:
• 0.008% or less, and the remainder composed of Fe and incidental impurities, on a percent by mass basis, in which, in the former part, heating is performed in an atmosphere containing O2:
• 0.1 to 20 percent by volume and H2O:
• 1 to 50 percent by volume such that a temperature is at 400° C. to 750° C. and, in a latter part, heating is performed in an atmosphere containing O2:
• 0.01 to less than 0.1 percent by volume and H2O:
• 1 to 20 percent by volume such that the temperature is 600° C. to 850° C.;
• applying a second heating step to the resultant steel sheet, in which holding is performed in an atmosphere containing H2:
• 1 to 50 percent by volume and having a dew point of 0° C. or lower at a temperature of 750° C. to 900° C. for 15 to 600 s, cooling to a temperature of 450° C. to 550° C. is performed, and holding is performed at a temperature of 450° C. to 550° C. for 10 to 200 s;
• and
• applying a galvanization treatment,
• wherein an obtained galvanized steel sheet includes 75% or more of ferrite phase, 1.0% or more of bainitic ferrite phase, and 1.0% or more and 10.0% or less of pearlite phase, on an area ratio basis, the area ratio of martensite phase is 1.0% or more and less than 5.0%, and the area ratio of the martensite phase/(area ratio of bainitic ferrite phase+area ratio of pearlite phase)≧0.6 is satisfied.