Ultra high strength and high ductility steel sheet having excellent yield ratio and manufacturing method for same

Abstract

An ultra high strength and high ductility steel sheet having an excellent yield ratio according to an aspect of the present invention contains, in weight %, 0.1-0.3% of carbon (C), 2% or less of silicon (Si), 6-10% of manganese (Mn), 0.05% or less of phosphorus (P), 0.02% or less of sulfur (S), 0.02% or less of nitrogen (N), 0.5% or less (excluding 0%) of aluminum (Al), and the balance Fe and inevitable impurities, and further contains at least one selected from the group consisting of 0.1% or less of titanium (Ti), 0.1% or less of niobium (Nb), 0.2% or less of vanadium (V), and 0.5% or less of molybdenum (Mo), wherein the ultrahigh-strength and high-ductility steel sheet comprises 20 area% or more of residual austenite as a microstructure, the average aspect ratio of the residual austenite being 2.0 or higher.

Description

technical field [0001] The present invention relates to an ultra-high-strength, high-ductility steel plate excellent in yield ratio and a manufacturing method thereof, in particular, to an ultra-high-strength, high-ductility steel plate suitable for cold forming automotive structural parts and methods of manufacture thereof. Background technique [0002] Automakers continue to pursue vehicle weight reduction due to CO2 emission regulations related to environmental issues. The most effective way to reduce the weight of the car body is to reduce the thickness of the steel plate, but simply reducing the thickness of the steel plate may cause a problem that the safety of passengers cannot be ensured due to the decrease in the rigidity of the car body. Therefore, ultra-high-strength steel must be used to reduce the car's body weight while ensuring the safety of passengers. [0003] However, in general, steel materials tend to have lower elongation as strength increases, and whe...

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