| 摘要 |
PURPOSE: A method for manufacturing a hot dipped galvanized iron for high strength structure purposes to which Ti and P are compositely added is provided to reduce manufacturing cost of steelmaking and satisfy quality requirements of final customers by changing composition of steel constituents and operation temperature, thereby improving productivity of a continuous annealing galvanizing line, stabilizing quality, reducing addition amount of Ti and P and preventing production of high £P|insoluble slab. CONSTITUTION: The method comprises the steps of steelmaking a slab comprising 0.001 to 0.005 wt.% of C, 0.20 to 0.50 wt.% of Mn, 0.030 wt.% or less of Si, 0.015 wt.% or less of S, 0.020 to 0.040 wt.% of P, 0.045 to 0.065 wt.% of Ti, 0.030 wt.% or less of N and a balance of Fe and other inevitable impurities, wherein available Tix £Ti(%)-4C(%)-3.4N(%)-1.5S(%)|is -0.020 to +0.020 wt.%; hot rolling the manufactured steel slab in the temperature range of 900 to 940 deg.C; continuous cold rolling the coiled hot rolled coil to a cold rolling reduction ratio of 75 to 85% after hot rolled coiling the hot rolled steel slab at the temperature of 600 to 640 deg.C; annealing the continuous cold rolled slab to a temperature of 580 to 670 deg.C in a continuous annealing galvanizing line; and coiling the steel sheet through skin-pass and post-treatment after galvanizing by passing the annealed steel sheet through an ordinary hot galvanizing bath.
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