Kobe Steel, Ltd.

Kabushiki Kaisha Kobe Seiko Sho

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

Voestalpine Stahl Gmbh

Shinshu Tlo Co., Ltd.

Yoichi Mukai

Hiroshi Akamizu

Koichi Sugimoto

Shushi Ikeda

Koichi Makii

Shinji Kozuma

Michiharu Nakaya

Fumio Yuse

Junichiro Kinugasa

Kouji Kasuya

Masaaki Miura

Muneaki Ikeda

Yoshinobu Omiya

Koh-ichi Sugimoto

Shunichi Hashimoto

Kenji Saito

Tetsuo Soshiroda

Andreas Pichler

Takahiro Kashima

Michitaka Tsunezawa

Masahiro Nomura

Sandra Traint

Tomokazu Masuda

Shinji c/o Kobe Corporate Research Laboratories Kozuma

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

A high-strength cold-rolled steel sheet excellent in uniform elongation, including in percent by mass:

High-strength cold-rolled steel sheet excellent in uniform elongation and method for manufacturing same

A cold rolled steel sheet satisfying on the basis of percent by mass the chemical composition of 0.06-0.6% C, 0.1-2% Si, 0.01-3% Al, 1-4% Si+Al, 1-6% Mn, Si/Mn&#x2266;0.40, in which there exists 10 or more pieces/100 &#x3bc;mof Mn&#x2014;Si composite oxide having Mn&#x2014;Si atom ratio (Mn/Si) of 0.5 or over and major axis of from 0.01 &#x3bc;m to 5 &#x3bc;m and also having a covering ratio of 10% or below at which the surface of the steel sheet is covered with oxide containing Si as the main component.

High-strength cold-rolled steel sheet excellent in coating adhesion, workability and hydrogen embrittlement resistance, and steel component for automobile

The invention provides a high strength cold rolled steel sheet having excellent chemical conversion treatment property stably even Mo is added aiming high strengthening. The surface property of the cold rolled steel sheet satisfies that the characteristic of 10 &#x3bc;m or more of the maximum depth (Ry) of the unevenness and 30 &#x3bc;m or less of the average spacing (Sm) of the unevenness, and that either one or more preferably both of, the characteristic of the load length ratio (tp40) of the unevenness of the surface is 20% or less, and the characteristic of the difference of the load length ratios (tp60) and (tp40) is 60% or more, is satisfied, and the crack of 3 &#x3bc;m or less width and 5 &#x3bc;m or more depth does not exist on the surface.

High-strength cold rolled steel sheet excelling in chemical treatability

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

A high-strength cold rolled steel sheet contains: 0.10 to 0.28% of C, 1.0 to 2.0% of Si, 1.0 to 3.0% of Mn, and 0.03 to 0.10% of Nb in terms of % by mass, Al is controlled to 0.5 or less, P is controlled to 0.15% or less, and S is controlled to 0.02% or less, and residual austenite accounts for 5 to 20%, bainitic ferrite accounts for 50% or more, and polygonal ferrite accounts for 30% or less (containing 0%), of the entire structure, and a mean number of residual austenite blocks is 20 or more as determined when the random area (15 &#x3bc;m&#xd7;15 &#x3bc;m) is observed by EBSP (electron back scatter diffraction pattern).

High-strength cold rolled steel sheet having excellent formability, and plated steel sheet

The present invention provides a high-strength steel sheet which has a 980 MPa class tensile strength as well as has excellent elongation, stretch flangeability and weldability, and also has excellent anti-delayed fraction property. The high-strength steel sheet comprises steel satisfying: C: 0.12 to 0.25%, Si: 1.0 to 3.0%, Mn: 1.5 to 3.0%, P: 0.15% or less, S: 0.02% or less, Al: 0.4% or less, and comprising the remnant made from iron and unavoidable impurities, wherein a ratio of the contents of Si and C (Si/C) is within the range from 7 to 14 in terms of a mass ratio, and a microstructure in a longitudinal section comprises, by an occupancy ratio based on the entire structure, 1) bainitic ferrite: 50% or more, 2) lath-type residual austenite: 3% or more, and 3) block-type residual austenite: 1% or more to &#xbd;&#xd7;occupancy ratio of lath-type residual austenite, and 4) average size of block-type second phase is 10 &#x3bc;m or less.

High-strength steel sheet having excellent elongation, stretch flangeability and weldability

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

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 cold-rolled steel sheet exhibiting an excellent strength-workability balance, including in percent by mass:

High strength cold rolled steel sheet and plated steel sheet excellent in the balance of strength and workability

To provide a high strength and low yield ratio cold rolled steel sheet having high elongation property and high flange drawing property, or a plated steel sheet made by plating the same. The high strength and low yield ratio cold rolled steel sheet or the plated steel sheet made by plating the same has such a constitution as 0.10 to 0.25% of C, 1.0 to 2.0% of Si and 1.5 to 3.0% of Mn, are contained in terms of weight percentage, while other elements are controlled such as Al within 0.2%, P within 0.15% and S within 0.02%, with residual austenite occupying at least 5%, bainitic ferrite occupying at least 60% (preferably 80% or more), and polygonal ferrite within 20% (containing 0%), so that a tensile strength is 980 MPa or higher, while an elongation (El in %), a flange drawing property (&#x3bb;in %), a tensile strength (TS in MPa) and a yield strength (YP in MPa) satisfy the following inequality (1): [(El &#xd7;&#x3bb;&#xd7;TS)/YP]&#x2267;645.

High strength and low yield ratio cold rolled steel sheet and method of manufacturing the same

The present invention provide a TRIP-type composite structure steel plate of the TPF steel type in which elongation and stretch flange formability at room temperature are improved by controlling the morphology of the second-phase structure. In a composite structure sheet steel comprising 0.02 to 0.12% C, 0.5 to 2.0% Si+Al and 1.0 to 2.0% Mn, with the remainder being Fe and unavoidable impurities, and comprising 80% or more polygonal ferrite (steel structure space factor) and 1 to 7% retained austenite, with the remainder being bainite and/or martensite, wherein the elongation and stretch flange formability of the composite sheet steel are improved by reducing the number of bulky, massive second phases with an aspect ratio of 1:3 or less and a mean grain size of 0.5 &#x3bc;m or more in the second phase of this composite structure, which comprises retained austenite and martensite.

Composite structure sheet steel with excellent elongation and stretch flange formability

A high-strength cold-rolled steel sheet is disclosed that comprises a steel including C: 0.05 to 0.13 mass %, Si: 0.5 to 2.5 mass %, and Mn: 0.5 to 3.5 mass %, as well as Mo: 0.05 to 0.6 mass % and/or Cr: 0.05 to 1.0 mass %. The steel sheet is of composite structure of a ferrite+a second phase wherein the second phase has an area rate of 30 to 70% and is combined approximately in a shape of a network; a circle-equivalent average ferrite grain size is not more than 10 &#x3bc;m; and a circle-equivalent diameter of ferrite grain aggregate that exists continuously in an area surrounded by the second phase is not more than 3 times of the average ferrite grain size. The steel sheet has a high-strength and satisfies a balance of elongation and stretch flange formability (ratio of hole expansion) at a higher level.

High-strength cold-rolled steel sheet having outstanding elongation and superior stretch flange formability and method for production therof

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.

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Kakogawa, Japan

Yoichi Mukai