Galvanized high-strength steel sheet having low yield ratio and method of producing the same

A method of producing a galvanized high-strength steel sheet having a tensile strength of not less than 80 kgf/mm.sup.2 and a yield ratio of not more than 60%, the method comprising the steps of:

• preparing a steel slab having a composition of 0.08 to 0.20 wt % of C, 1.5 to 3.5 of wt % of Mn, 0.010 to 0.1 wt % of Al, 0.010 wt % or less of P, 0.001 wt % or less of S, one or both of 0.010 to 0.1 wt % of Ti and 0.010 to 0.1 wt % of Nb, and the balance substantially Fe and incidental impurities;
• hot-rolling said steel slab;
• cold-rolling said steel slab;
• forming said steel slab into a steel strip having a final thickness;
• heating said steel strip in a temperature range from (Ar.sub.3 -30.degree. C.) to (Ar.sub.3 -70.degree. C.);
• recrystallization-annealing said steel strip;
• cooling said steel strip at a cooling rate of not less than 5.degree. C./s to a temperature range from 450.degree. C. to 550.degree. C.;
• galvanizing said steel strip while maintaining it in said temperature range for 1 minute to 5 minutes or less;
• and cooling said galvanized steel strip at a cooling rate of 2.degree. C./s to 50.degree. C./s.