Kabushiki Kaisha Kobe Seiko Sho (kobe Steel, Ltd.)

Akihiko Nagasaka

Shunichi Hashimoto

Shushi Ikeda

Hiroshi Akamizu

Takahiro Kashima

Koh-ichi Sugimoto

Akinobu Kanda

Ryo Kikuchi

A high strength steel sheet having (2-1) a base phase structure, the base phase structure being tempered martensite or tempered bainite and accounting for 50% or more in terms of a space factor relative to the whole structure, or the base phase structure comprising tempered martensite or tempered bainite which accounts for 15% or more in terms of a space factor relative to the whole structure and further comprising ferrite, the tempered martensite or the tempered bainite having a hardness which satisfies the relation of Vickers hardness (Hv)&#x2267;500[C]+30[Si]+3[Mn]+50 where [ ] represents the content (mass %) of each element, and (2-2) a second phase structure comprising retained austenite which accounts for 3 to 30% in terms of a space factor relative to the whole structure and optionally further comprising bainite and/or martensite, the retained austenite having a C concentration (C&#x3b3;R) of 0.8% or more.

High strength steel sheet having excellent formability and method for production thereof

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Nagano, Japan

Akihiko Nagasaka