steel plate

Abstract

The present invention provides a steel sheet containing a high concentration of Mn having excellent local ductility and high strength. The steel plate is characterized in that it contains predetermined amounts of C, Si, and sol.Al, and Mn exceeding 4% and less than 9% by mass%, limits the content of P, S, N, and O, and contains arbitrarily selected elements. , the remaining part is iron and impurities; the metal structure in the 1 / 4t part of the L section contains 25% to 90% of tempered martensite, 3% or less ferrite, 10% to 50% of Retained austenite and 25% or less of primary martensite, as either the retained austenite or the primary martensite, that is, the first region, and the first region is removed from the metal structure at the 1 / 4 position The interface density, which is the value obtained by dividing the sum of the lengths of the boundaries of the second region other than the region by the total area of ​​the first region and the second region, is 2.7 μm ‑1 above.

Description

technical field

[0001] The present application relates to a steel sheet having excellent formability and ultra-high strength characteristics, and specifically, to a steel sheet containing a high concentration of Mn having excellent local ductility and high tensile strength. Background technique

[0002] In order to achieve both weight reduction and safety of automobile bodies and components, the strengthening of steel sheets, which are their raw materials, is progressing. In general, if the strength of the steel sheet is increased, the elongation decreases and the formability of the steel sheet is impaired. Since automobile body parts using steel sheets as raw materials are often formed by press working, high-strength steel sheets used as vehicle body parts are required to have excellent press formability. In particular, a member for a vehicle body mainly composed of stretch flange forming or hole expansion requires high strength and high local ductility as mechanical prope...

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