ZINC PLATED STEEL SHEET HAVING EXCELLENT SURFACE QUALITY, HIGH DUCTILITY, AND ULTRA HIGH STRENGTH AND METHOD FOR MANUFACTURING THE SAME

摘要

PURPOSE: A galvanized steel sheet and a manufacturing method thereof are provided to secure the high ductility, the super strength, and the delay-tolerant property, and are provided to obtain the galvanized steel sheet with an excellent surface quality. CONSTITUTION: A galvanized steel sheet with an excellent surface quality and a manufacturing method thereof perform the following steps. A slab which includes C 0.05-0.20wt%, Si 0.3-1.6wt%, Mn 4.0-8.0wt%, Al 0.5-2wt%, Cr 0.01-0.1wt%, Ti 0.005-0.03wt%, B 5-30ppm Sb 0.01-0.03wt%, S less than 0.008wt%, Sn 0.06-0.2wt%, Ni 0.01-1wt%, the remainder Fe and other unavoidable impurity is re-heated. The re-heated slab goes the finishing rolling step between the heats. A hot rolled steel sheet is reeled in less than 650°C. The reeled steel sheet is cooled to the room temperature. The cooled steel sheet cold is rolled at the reduction rate of more than 30%. The cold steel sheet is annealed at the Ac1-Ac3 temperature. A coating layer is formed on the annealed cold steel sheet.