High manganese nitrogen-containing steel sheet having high strength and high ductility, and method for manufacturing the same

Abstract

Provided is a high manganese nitrogen-containing steel sheet. The high manganese nitrogen-containing steel sheet according to the present invention comprises 0.5 to 1.0 wt % of carbon, 10 to 20 wt % of manganese, 0.02 to 0.3 wt % of nitrogen, with a remainder of Fe and unavoidable impurities. The high manganese nitrogen-containing steel sheet according to the present invention produces an austenite phase at room temperature, in which the stacking fault energy is effectively controlled by adding chrome and nitrogen. Accordingly, the high manganese nitrogen-containing steel sheet of the present invention produces a mechanical twin during the plastic deformation of the steel sheet, thereby increasing the work hardening rate, tensile strength, and workability.

Description

TECHNICAL FIELD[0001]The present invention relates to high manganese-nitrogen containing steel sheets having high strength and high ductility, and more particularly to high manganese-nitrogen containing steel sheets and a method of manufacturing the same, which may be used as steel sheets for automobiles requiring high workability and impact absorbing materials such as bumper reinforcing materials for automobiles.BACKGROUND ART[0002]Generally, steel sheets for an automobile body require high workability. To satisfy such requirements, ultra-low carbon steel having a low tensile strength of about 200 to 300 MPa and good workability has generally been used for automobiles steel sheets. Recently, various attempts have been made to improve fuel efficiency of automobiles in order to solve environmental problems such as air pollution. Particularly, as weight reduction of automobiles becomes essential for improvement of fuel efficiency, it is necessary for automobile steel sheets to have no...

AI Technical Summary

Benefits of technology

[0033]According to exemplary embodiments of the invention, high manganese-nitrogen containing steel sheets have an austenite structure formed at room temperature and allow effective regulation of stacking fault energy through addition of chrome and nitrogen. Thus, the steel sheets allow a high degree of work hardening, and have high tensile strength and excellent workability by mechanical twins formed during plastic deformation of the steel sheets. Namely, the high manganese-nitrogen containing steel sheets according to the exemplary embodiments have a very high product of tensile strength to total elongation (TS×El) of 50,000 MPa % or more, which is much higher than that of conventional TWIP steel, thereby guaranteeing a significantly high product of tensile strength to total elongation while reducing manufacturing costs.

[0034]Further, the high manganese-nitrogen containing steel sheets according to the exemplary embodiments may be used in various ways such as hot rolled steel sheets, cold-rolled annealed steel sheets, and the like.

Problems solved by technology

TRIP steel has high strength resulting from significant work hardening based on martensite transformation, but has a drawback of excessively low elongation.

In this case, however, the steel sheets have significantly low ductility, thereby making it difficult to guarantee an elongation of 30% or more.

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

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

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