| 摘要 |
PURPOSE: A method for manufacturing high tensile strength galvannealed steel sheet having superior formability and coating adhesion by properly adjusting constituents of the steel sheet and optimizing coiling temperature and annealing conditions before hot dip galvanizing is provided. CONSTITUTION: The method comprises the steps of finish hot rolling to a temperature of Ar3 transformation point or more a steel slab comprising 0.0005 to 0.005 wt.% of C, 0.01 to 0.30 wt.% of Si, 0.3 to 1.5 wt.% of Mn, 0.02 to 0.1 wt.% of P, 0.02 wt.% or less of S, 0.003 wt.% or less of N, 0.01 to 0.2 wt.% of Al, 0.0003 to 0.003 wt.% of B, one or both of 0.005 to 0.04 wt.% of Ti and 0.005 to 0.05 wt.% and a balance of Fe and other inevitable impurities, wherein the Si and Mn satisfy the following relational expression: 0.05<=Si/Mn<=0.2, and the B and Si satisfy the following relational expression: 0.005<=B/Si<=0.02; coiling the finish hot rolled steel sheet to a temperature of 400 to 600 deg.C; cold rolling the coiled steel sheet; annealing the cold rolled steel sheet to a temperature of 760 to 830 deg.C for 30 to 120 seconds; and hot dip galvanizing and alloying the annealed steel sheet.
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