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

Kobe Steel, Ltd.

Usui Kokusai Sangyo Kaisha Limited

Shinshu University

Koh-ichi Sugimoto

Shushi Ikeda

Hiroshi Akamizu

Yoichi Mukai

Koichi Makii

Shunichi Hashimoto

Teruhisa Takahashi

Takahiro Kashima

Akihiko Nagasaka

Akinobu Kanda

Sho-hei Sato

Ryo Kikuchi

Goro Arai

A high-strength steel machined product giving excellent hardenability has a metal microstructure with excellent balance of strength and toughness and high stability of retained austenite. The product is composed of an ultra-high low-alloy TRIP steel having a metal microstructure which contains an appropriate quantity of two or more of Cr, Mo, and Ni, and an appropriate quantity of one or more of Nb, Ti, and V, and having an appropriate value of carbon equivalent; the metal microstructure has a mother-phase structure composed mainly of lathy bainitic ferrite with a small amount of granular bainitic ferrite and polygonal ferrite, and has a secondary-phase structure composed of fine retained austenite and martensite.

High-strength steel machined product and method for manufacturing the same, and method for manufacturing diesel engine fuel injection pipe and common rail

A high-strength forged part is disclosed which comprises a base phase structure, comprising 30% or more of ferrite in terms of a space factor, and a second phase structure, comprising bainite and/or martensite, and retained austenite having an average gain diameter of 5 &#x3bc;m or less and a content represented by 50X[C]&#x3c;[V]&#x3c;150x[C], wherein [V] represents a space factor of the retained austenite (&#x3b3;R) and [C] represents the mass % of C in the forged part. Furthermore, a high-strength forged part is disclosed which comprises a base phase structure, comprising 50% or more of tempered bainite or tempered martensite in terms of a space factor, and a second phase structure, comprising martensite and 3% to 30% retained austenite in terms of a space factor, wherein the portion of the retained austenite and martensite having an aspect ratio of 2 or less is 25% or less in terms of a space factor.

Method for producing high-strength forged parts having high reduction of area

A high-strength forged part is disclosed which comprises a base phase structure, comprising 30% or more of ferrite in terms of a space factor, and a second phase structure, comprising bainite and/or martensite, and retained austenite having an average grain diameter of 5 &#x3bc;m or less and a content represented by 50&#xd7;[C]&#x3c;[V]&#x3c;150&#xd7;[C], wherein [V] represents a space factor of the retained austenite (&#x3b3;R) and [C] represents the mass % of C in the forged part. Furthermore, a high-strength forged part is disclosed which comprises a base phase structure, comprising 50% or more of tempered bainite or tempered martensite in terms of a space factor, and a second phase structure, comprising martensite and 3% to 30% retained austenite in terms of a space factor, wherein the portion of the retained austenite and martensite having an aspect ratio of 2 or less is 25% or less in terms of a space factor.

High-strength forged parts having high reduction of area and method for producing same

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

Koh-ichi Sugimoto