FORMABLE HIGH STRENGTH COLD-ROLLED STEEL SHEET WITH EXCELLENT WEATHER RESISTANCE AND METHOD MANUFACTURING THE SAME

摘要

There are provided a formable high strength cold-rolled steel sheet with excellent weather resistance and a tensile strength of 80 or more kgf/mm, a method for manufacturing the same. The formable cold-rolled steel sheet includes, by weigh: carbon (C): 0.10 to?.20%, silicon (Si): 0.05 to 0.25%, manganese (Mn): 1.0 to 2.5%, phosphorus (P): 0.02% or less, sulfur (S): 0.01% or less, aluminum (Al): 0.02 to 0.07%, niobium (Nb): 0.02 to 0.08%, nickel (Ni): 0.05 to 0.30%, copper (Cu): 0.1 to 0.5%, chromium (Cr): 0.8 to 1.5% and cobalt (Co): 0.01 to 0.10%, and the balance of Fe and other inevitable impurities, wherein a low-temperature transformation structure is present in a volume of 10 to 30% and the balance is a ferrite structure.