Nippon Steel Corporation

Takehiro Hoshino

Daisuke Maeda

Osamu Kawano

Akifumi Sakakibara

Teruki Hayashida

Kazuya Ootsuka

A hot-rolled steel sheet including predetermined components, in which the amounts of Cr and Al added satisfy Expression (1) below, a metallographic structure has, by % by volume, a ferrite fraction of more than 90% and 98% or less, a martensite fraction of 2% to less than 10%, and, a fraction of a residual structure made of one or more of pearlite, bainite, and residual austenite being less than 1%, the ferrite has an average circle-equivalent diameter of 4 &#x3bc;m or more and a maximum circle-equivalent diameter of 30 &#x3bc;m or less, and the martensite has an average circle-equivalent diameter of 10 &#x3bc;m or less and a maximum circle-equivalent diameter of 20 &#x3bc;m or less.[Cr]&#xd7;5+[Al]&#x2265;0.50&#x2003;&#x2003;Expression (1) Here, in Expression (1), [Cr] represents an amount of Cr (mass %), and [Al] represents an amount of Al (mass %).

Hot-rolled steel sheet

The present invention provides a steel sheet excellent in both a balance between strength and elongation and a balance between strength and hole expandability, in other words, a multi-phase steel sheet having an excellent balance between strength and hole expandability. The present invention is a multi-phase steel sheet excellent in hole expandability characterized in that:

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Hiroshima, Japan

Takehiro Hoshino