Steel plate and manufacturing method thereof

Abstract

A steel plate has a prescribed chemical composition: the metal composition of the surface layer region, which is the area from the surface to the position 20 [mu]m from the surface in the plate thickness direction, comprises ferrite and a second phase with a 1.0-15.0% volume fraction; the metal composition of the inner region, which is the area from the position over 20 [mu]m from the surface in the plate thickness direction to the position 1 / 4 of the plate thickness from the surface in the plate thickness direction, comprises ferrite and a second phase with a 5.0-25.0% volume fraction; and the second phase volume fraction in the surface layer region is smaller than the second phase volume fraction in the inner region, wherein, in the surface layer region, the average grain size of the second phase is 0.5-4.0 [mu]m, and aggregate structures are included in which the intensity ratio XODF{001} / {111} of the {001} orientation and the {111} orientation of the ferrite is 0.70-2.50.

Description

technical field [0001] The present invention relates to a steel plate and a manufacturing method thereof. [0002] This application claims priority based on Japanese Patent Application No. 2019-000671 filed in Japan on January 07, 2019, and the contents thereof are incorporated herein by reference. Background technique [0003] In recent years, in order to protect the global environment, it is necessary to improve the fuel economy of automobiles. With regard to the improvement of fuel economy of automobiles, steel sheets for automobiles need to be further strengthened in order to reduce the weight of the vehicle body while ensuring safety. Such a need for higher strength is not limited to beams, columns, etc. as structural members, but is also increasing for exterior panel parts (roof, hood, fenders, doors, etc.) of automobiles. In response to such needs, material development has been carried out for the purpose of achieving both strength and elongation (formability). [...

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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