| 摘要 |
Provided are a hot-dip galvanized steel sheet and a hot-dip galvannealed steel sheet with excellent shelf life and bake hardenability, and a method for manufacturing the same. The present invention relates to a hot-dip galvanized steel sheet with excellent shelf life and bake hardenability, the hot-dip galvanized steel sheet having a molten zinc plated layer on the surface of a base steel sheet, wherein the base steel sheet comprises: 0.002-0.012 wt% of carbon (C); 1.6-2.7 wt% of manganese (MN); 0.03 wt% or less (excluding 0 wt%) of phosphorus (P); 0.01 wt% or less (excluding 0 wt%) of sulfur (S); 0.01 wt% or less (excluding 0 wt%) of nitrogen (N); 0.02-0.06 wt% of aluminum (sol.Al); 1.0 wt% or less (excluding 0 wt%) of chromium (Cr), with the remainder being iron and inevitable impurities; the base steel sheet satisfies the relation of 1.3≤Mn(wt%)/(1.15×Cr(wt%))≤20.5; Mneq defined by relational expression 1 satisfies 1.9≤Mneq≤3.9; the microstructure of the steel comprises an area ratio of 95% or more of ferrite, with the remainder being a hard second phase; an occupation ratio of martensite existing in a ferrite grain boundary defined by relational expression 2 is 90% or more; and the difference between the average Mn concentration wt% (a) in a martensite phase at a 1/4t point of the base steel sheet and the average Mn concentration wt% (b) in a ferrite phase within 1 ㎛ from the martensite phase, defined by relational expression 3, is 0.3 wt% or more. |
