High-strength and high-ductility steel sheet and method of manufacturing the same

Abstract

A high-strength and high-ductility steel sheet having a composition including, by weight, 1.0 to 1.4% C, 5.0 to 9.0% Mn, 2.0 to 8.0% Cr and the balance Fe, and unavoidable impurities. The steel sheet has an austenite structure formed at room temperature, and stacking fault energy is effectively controlled by the addition of Cr and N2. Mechanical twins are formed during the plastic deformation of the steel, thereby leading to high levels of work hardening, tensile strength and workability.

Description

CROSS REFERENCE TO RELATED APPLICATION[0001]The present application claims priority from Korean Patent Application Number 10-2013-00125214 filed on Oct. 21, 2013, the entire contents of which are incorporated herein for all purposes by this reference.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]The present invention relates to a high-strength and high-ductility steel sheet, and more particularly, to an automotive steel sheet for which high workability is required, a high manganese (Mn) steel sheet applicable as a shock absorber such as a vehicle bumper stiffener, and a method of manufacturing the same.[0004]2. Description of Related Art[0005]Steel sheets applicable for vehicle bodies typically require high workability. In order to satisfy this requirement, ultra-low carbon steel has been mainly used for automotive steel sheets in the related art regardless of its low tensile strength ranging from 200 to 300 MPa, since it has high workability. Recently, a variety o...

AI Technical Summary

Benefits of technology

This patent is about a new steel sheet that has high strength and ductility while also reducing the amount of Mn. By adding a small amount of C as an austenite stabilizing element, a single austenite phase structure can be achieved at room temperature. The addition of C also helps to control the formation of carbides and prevents cementite precipitation. Additionally, by controlling the stacking fault energy, mechanical twins are formed during plastic deformation, resulting in high levels of work hardening, tensile strength, and workability. This steel sheet has the same product of tensile strength and total elongation as related-art TWIP steel with a Mn content of about20% by weight, but with significantly reduced manufacturing costs.

Problems solved by technology

Steel sheets applicable for vehicle bodies typically require high workability.

Although TRIP steel has the advantage of high strength caused by significant hardening through the martensitic transformation, its elongation is too short, which is problematic.

However, the extremely low ductility of martensite makes it difficult to achieve an elongation of 30% or more, which is problematic.

Further, TWIP steel may have large elongation and high tensile strength due to the mechanical twins causing a high level of work hardening.

However, current TWIP steel has a high Mn content ranging from about 18% to about 30% in order to guarantee austenite stability and adjust stacking fault energy, and requires the addition of large amounts of aluminum or silicon together with manganese, causing a significant increase in material and manufacturing costs.

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