Kobe Steel, Ltd.

Kabushiki Kaisha Kobe Seiko Sho

Voestalpine Stahl Gmbh

Kouji Kasuya

Yoichi Mukai

Fumio Yuse

Junichiro Kinugasa

Muneaki Ikeda

Michiharu Nakaya

Hiroshi Akamizu

Koichi Sugimoto

Andreas Pichler

Michitaka Tsunezawa

Shinji Kozuma

Sandra Traint

Disclosed is a high strength steel sheet having excellent hydrogen embrittlement resistance. The steel sheet has a tensile strength of 1180 MPa or more, and satisfies the following conditions: with respect to an entire metallographic structure thereof, bainite, bainitic ferrite and tempered martensite account for 85 area % or more in total; retained austenite accounts for 1 area % or more; and fresh martensite accounts for 5 area % or less (including 0 area %).

High strength steel sheet having excellent hydrogen embrittlement resistance

The present invention is the thin steel sheet containing C, Si, Mn, P, S, Al, Mo, Ti, B, and N wherein a value Z calculated by the equation described below is 2.0-6.0, an area ratio against all the structure is 1% or above for retained austenite and 80% or above for total of bainitic ferrite and martensite, a mean axis ratio of the retained austenite crystal grain is 5 or above, and tensile strength is 980 MPa or above whereValue Z=9&#xd7;[C]+[Mn]+3&#xd7;[Mo]+490&#xd7;[B]+7&#xd7;[Mo]/{100&#xd7;([B]+0.001),andthe thin steel sheet has 980 MPa or above tensile strength and enhanced hydrogen embrittlement resistance properties.

High-strength thin steel sheet

The invention relates to an ultrahigh-strength thin steel sheet excellent in the hydrogen embrittlement resistance, the steel sheet including, by weight %, 0.10 to 0.60% of C, 1.0 to 3.0% of Si, 1.0 to 3.5% of Mn, 0.15% or less of P, 0.02% or less of S, 1.5% or less of Al, 0.003 to 2.0% of Cr, and a balance including iron and inevitable impurities; in which grains of residual austenite have an average axis ratio (major axis/minor axis) of 5 or more, the grains of the residual austenite have an average minor axis length of 1 &#x3bc;m or less, and the grains of the residual austenite have a nearest-neighbor distance between the grains of 1 &#x3bc;m or less.

Ultrahigh-strength thin steel sheet

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Kakogawa, Japan

Kouji Kasuya