ULTRA-HIGH STRENGTH GALVANIZED STEEL SHEET AND METHOD OF MANUFACTURING THE SAME

摘要

Provided is a method to manufacture a hot-dip galvanized steel sheet of ultra-high strength having a tensile strength of 1.5 GPa or greater. According to the present invention, the method to manufacture the hot-dip galvanized steel sheet of ultra-high strength comprises: a step of primarily heat treating a steel sheet including 0.2-0.3% of carbon (C); 0.1-0.2% of silicon (Si); 2.0-3.5% of manganese (Mn); 0.02-0.04% of aluminum (Al); 0.09-1.1% of molybdenum (Mo); 0.04-0.07% of niobium (Nb); 0.01-0.03% of titanium (Ti); and 0.002-0.003% of boron (B) with the remaining consisting of iron (Fe) and unavoidable impurities in a single-phase austenite; a step of primarily cooling the primarily heat treating a steel sheet to 490-520°C; a step of hot-dip galvanizing the primarily cooled steel sheet at 460-520°C; a step of secondarily cooling the hot-dip galvanized steel sheet to 200°C or less; and a step of secondarily heat treating the secondarily cooled steel sheet at 200-250°C.