| 摘要 |
PROBLEM TO BE SOLVED: To provide a high strength galvanized steel sheet which has excellent deep drawability, secondary working brittleness resistance and plating characteristics, and further has a tensile strength of about >=400 MPa. SOLUTION: A steel slab having a composition containing, by mass, 0.0005 to 0.008% C, 0.1 to 1.5% Si, 0.5 to 3.0% Mn, 0.02 to 0.2% P, <=0.02% S, 0.005 to 0.20% Al, <=0.01% N, 0.0005 to 0.008% B, 0.05 to 2.0% Mo and Nb of 0.001 to 0.2%, and also, in the range satisfying 0.3×(C/12)<=Nb/93<=3.0×(C/12) is heated and soaked at a temp. of 950 to 1,300 deg.C. After hot rolling is finished at a temp. of 650 to 1,000 deg.C, the steel is coiled at a temp. of 400 to 850 deg.C. The steel is next annealed in the temperature range of 600 to 900 deg.C for >=10 min as black film scale is adhered thereto. The steel is pickled and is subjected to cold rolling at a draft of 50 to 95%. Thereafter, the steel sheet is subjected to recrystallization annealing at a temp. of 700 to 950 deg.C and is subjected to galvanizing in continuous galvanizing equipment.
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