Steel sheet and method for manufacturing same

Abstract

This steel sheet has a predetermined chemical composition, the metal structure of a surface layer region in a range from the surface to a position 20 [mu]m in the sheet thickness direction from the surface comprises ferrite and 0.01-5.0% by volume fraction of a second phase, the metal structure of an interior region in a range from a position more than 20 [mu]m in the sheet thickness direction from the surface to a position 1 / 4 of the sheet thickness in the sheet thickness direction from the surface comprises ferrite and 2.0-10.0% by volume fraction of a second phase, the volume fraction of the second phase of the surface region is less than the volume fraction of the second phase of the interior region, and, in the surface region, the average crystal particle diameter of the second phase is 0.01-4.0 [mu]m, and an aggregate structure is included in which the strength ratio XODF [001] / [111] of the [001] orientation and the [111] orientation of the ferrite is 0.60 to less than 2.00.

Description

Technical field [0001] The present invention relates to a steel sheet and a method of manufacturing the same. [0002] The present application claims priority in Japanese State, 2019-000672, requested by Japan, January 07, 2019, and arguing it here. Background [0003] In recent years, in order to protect the global environment, it is necessary to improve the fuel economy of the car. Regarding the improvement of the fuel economy of the car, a steel sheet for automobiles is required to ensure that the body is lightweight while ensuring safety, and further high strength is required. This high-strength need is not limited to a beam or column as a structural member, and it is also increasing for the outer plate member of the car (top, cover, wing plate, door, etc.). In response to this need, materials development with intensity and elongation (formability) have been carried out. [0004] On the other hand, the shape of the outer panel member of the car is more complicated tendency. I...

AI Technical Summary

Problems solved by technology

However, in Patent Document 2, the relationship between the appearance after molding and the structure from the viewpoint of surface roughness and texture measures is not disclosed.

[0008] That is, conventionally, no proposal has been made for a high-strength multiphase structure steel that has improved surface roughness and texture defects after forming.

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