| 摘要 |
PROBLEM TO BE SOLVED: To provide a 440 MPa class high strength hot-dip galvanized steel sheet excellent in deep drawability, and a production method thereof.SOLUTION: A steel sheet having a hot-dip galvanized layer containing Fe of 7 to 15% on a surface of the steel sheet is produced by subjecting a cast slab to hot rolling, pickling, cold rolling and annealing, then Ni pre-plating and hot-dip galvanizing followed by alloying, where the cast slab contains C, Si, Mn, P, S, Al, N, Ti, Nb, B and the balance Fe with inevitable impurities. In the production of the steel sheet, a finishing temperature of hot rolling is set to be 800 to 860°C, cooling of the hot-rolled steel sheet is started within 0.5 sec. from finish rolling, the hot-rolled steel sheet is cooled to a temperature of 700°C to 760°C at a rate of 200°C/sec. or more and the cooled steel sheet is wound at a winding temperature of 650 to 760°C, and thus a 440 MPa class high strength alloyed hot-dip galvanized steel sheet excellent in deep drawability can be obtained which satisfies P(222)/P(200)≥17 and has an average r value≥1.7, and a &Dgr;r value satisfying -0.3≤&Dgr;r value≤0.3. |
