| 主权项 |
1. 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 a 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 at a temperature of 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 at a temperature of 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 the 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. |
