Hot-dip galvanized steel sheet with superior bake hardenability and aging resistance, and manufacturing method thereof

Abstract

Disclosed are a cold-rolled steel sheet having excellent bake hardenability and aging resistance, and a manufacturing method thereof. The cold-rolled steel sheet comprises, by weight %, 0.02-0.08% ofC; 1.3-2.1% of Mn; 0.3% or less (excluding 0%) of Si; 1.0% or less (excluding 0%) of Cr; 0.1% or less (excluding 0%) of P; 0.01% or less (excluding 0%) of S; 0.01% or less (excluding 0%) of N; and 0.01-0.06% of sol.Al; at least one selected from the group consisting of 0.2% or less (excluding 0%) of Mo and 0.003% or less (excluding 0%) of B; and the balance being Fe and other inevitable impurities, wherein the steel sheet contains, as a microstructure thereof, 90-99% of ferrite and 1-10% of martensite in an area fraction,wherein a ratio (a / b) of an average carbon concentration a in the martensite and an average carbon concentration b in the ferrite located in an imaginary circle having a major axis of the martensite as a diameter, at a point of the sheet thickness of 1 / 4 t is 1.4 or less,and a ratio (d / c) of an average manganese concentration c in the martensite and an average manganese concentration d in the ferrite located in an imaginary circle having a major axis of the martensiteas a diameter, at a point of a sheet thickness of 1 / 4 t is 0.9 or less.

Description

technical field [0001] The present invention relates to a hot-dip zinc-coated steel sheet having excellent bake hardenability and aging resistance and a manufacturing method thereof, more particularly, to a hot-dip zinc-based steel sheet having excellent bake hardenability and aging resistance Zinc-coated steel sheet (preferably a material that can be used as an exterior automotive panel) and a method of manufacturing the same. Background technique [0002] Since impact stability regulations and fuel efficiency of automobiles are emphasized, high-strength steels are actively used to satisfy weight reduction and high strength requirements of automobile bodies. In line with this trend, the use of high-strength steel for exterior automotive panels has also expanded. [0003] At present, most of the 340MPa-grade bake-hardening steel has been used as exterior automotive panels, but some 490MPa-grade steel plates are also applied, and it is expected to expand to 590MPa-grade stee...

AI Technical Summary

Problems solved by technology

However, this technology has problems in that it is difficult to ensure good plating quality due to the addition of a large amount of Si, and there is a problem of increased manufacturing costs due to the addition of a large amount of Ti and Mo

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