Nippon Steel Corporation

Tetsu Asato

Akifumi Sakakibara

Hiroshi Shuto

Jun Ando

Akihiro Yamamoto

Koutarou Hayashi

Genki Abukawa

Mutsumi Sakakibara

Hiroshi Kaido

Shota Endo

Yamamoto Akihiro

A hot-rolled steel sheet according to the present invention has a predetermined chemical composition, in which, when a height profile of a surface of the hot-rolled steel sheet is measured in each of five measurement ranges in a rolling direction and a direction perpendicular to the rolling direction, a distance in a height direction from an average height position which is an average of a height position of a point having a highest height position and a height position of a recessed part which is a point having a lowest height position to the recessed part is indicated as R(μm) in each of the height profiles, and an average of heights of two measurement points away from the recessed part in the rolling direction or the direction perpendicular to the rolling direction by 5 μm is indicated as R(μm), an average value of radii of curvature r represented by Expression (1) is 10 μm or more, and a tensile strength of the hot-rolled steel sheet is 500 MPa or more. r=(25+|R−R|)/2|R−R| . . . (1)

Hot-rolled steel sheet

This hot-rolled steel sheet has a predetermined chemical composition, in which a metal microstructure contains, by area %, 3.0% or more of residual austenite, has a ratio L/Lof a length Lof a grain boundary having a crystal orientation difference of 52° to a length Lof a grain boundary having a crystal orientation difference of 7° about a <110> direction of 0.10 or more and 0.18 or less, has a standard deviation of a Mn concentration of 0.60 mass % or less, and has a tensile strength of 980 MPa or more.

This hot rolled steel sheet is a hot rolled steel sheet including a base steel sheet and a scale formed on a surface of the base steel sheet, in which the base steel sheet has a predetermined chemical composition, the scale has a layer structure composed of wustite, magnetite, and hematite in order from the base steel sheet side or a layer structure composed of the wustite and the magnetite in order from the base steel sheet side, and, when a thickness of the scale is represented by s, a thickness of the hematite is represented by h, and a thickness of the magnetite is represented by m, the s, the h, and the m satisfy formula (1) and formula (2).()/<0.20  Formula (1)/4  Formula (2)

Hot rolled steel sheet

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Tokyo, Japan

Tetsu Asato