Nippon Steel Corporation

Kazuyoshi Esaka

Osamu Kawano

Junichi Wakita

Manabu Takahashi

Hiroshi Abe

Norio Ikenaga

High yield ratio-type, hot rolled high strength steel sheet excellent in

A hot rolled steel sheet with a high strength and a distinguished formability, and a process for producing the same are disclosed. The steel sheet comprises 0.15 to 0.4% by weight of C, 0.5 to 2.0% by weight of Si, and 0.5 to 2.0% by weight of Mn, the balance being iron and inevitable impurities, and has a microstructure composed of ferrite, bainite and retained austenite phases with the ferrite phase being a ratio (V.sub.PF /d.sub.PF) of polygonal ferrite volume fraction V.sub.PF (%) to polygonal ferrite average grain size d.sub.PF (.mu.m) of 7 or more and the retained austenite phase being contained in an amount of 5% by volume or more on the basis of the total phases. The steel sheet can be produced with a high productivity and without requiring special alloy elements.

Process for producing a hot rolled steel sheet with high strength and

A hot rolled steel sheet with a high strength and a distinguished formability, and a process for producing the same are disclosed. The steel sheet comprises 0.15 to 0.4% by weight of C, 0.5 to 2.0% by weight of Si, and 0.5 to 2.0% by weight of Mn, the balance being iron and inevitable impurities, and has a microstructure composed of ferrite, bainite and retained austenite phases with the ferrite phase being in a ratio (V.sub.PF /d.sub.PF) of polygonal ferrite volume fraction V.sub.PF (%) to polygonal ferrite average grain size d.sub.PF (.mu.m) of 7 or more and the retained austenite phase being contained in an amount of 5% by volume or more on the basis of the total phases. The steel sheet can be produced with a high productiviity and without requiring special alloy elements.

Hot rolled steel sheet with high strength and distinguished formability

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Oita, Japan

Kazuyoshi Esaka