Method for producing high-strength galvanized steel sheet and high-strength galvannealed steel sheet

A method for producing a high-strength galvanized steel sheet having a microstructure that contains martensite in an area proportion of 20% or more and 60% or less and ferrite in an area proportion of 40% or more and 80% or less, the method comprising, in sequence, hot-rolling a steel slab containing, on a mass percent basis, 0.05% or more and less than 0.12% of C, 0.01% or more and less than 0.35% of Si, 2.2% or more and 3.5% or less of Mn, 0.001% or more and 0.050% or less of P, 0.010% or less of S, 0.005% or more and 0.100% or less of sol. Al, 0.0001% or more and 0.0060% or less of N, 0.010% or more and 0.080% or less of Nb, 0.010% or more and 0.080% or less of Ti, and the balance being Fe and incidental impurities;

• performing cold rolling;
• performing primary annealing;
• performing pickling;
• performing secondary annealing;
• and performing galvanizing treatment,
• wherein in the primary annealing, heating is performed at an average heating rate of 0.1° C./sec. or more and less than 3° C./sec. in the temperature range of 600° C. to 750° C., an annealing temperature of 750° C. to 850° C. is maintained for 10 to 500 seconds, and then cooling is performed from the annealing temperature range to a cooling stop temperature of 600° C. or lower at an average cooling rate of 1 to 15° C./sec, wherein in the pickling, the pickling weight loss of a steel sheet is 0.05 to 5 g/m2 in terms of Fe, wherein in the secondary annealing, an annealing temperature of 750° C. to 850° C. is maintained for 10 to 500 seconds, and then cooling is performed from the annealing temperature at an average cooling rate of 1 to 15° C./sec, and
• wherein after the galvanizing treatment, cooling is performed at an average cooling rate of 5 to 100° C./sec.