Kobe Steel, Ltd.

Voestalpine Stahl Gmbh

Kabushiki Kaisha Kobe Seiko Sho

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

Michiharu Nakaya

Andreas Pichler

Michitaka Tsunezawa

Yoichi Mukai

Muneaki Ikeda

Tetsuji Hoshika

Daniel Krizan

Stefan Paul

Toshio Murakami

Tatsuya Asai

Koichi Sugimoto

Tetsuo Soshiroda

Yuichi Futamura

Thomas Kurz

Fumio Yuse

Junichiro Kinugasa

Kosuke Shibata

Kouji Kasuya

Sandra Traint

Haruka Araki

Takayuki Kimura

In one aspect of the present invention, a hot-dip galvannealed steel sheet includes a steel sheet and a hot-dip galvannealed layer on the surface of the steel sheet. The steel sheet has a predetermined composition and has an average oxygen concentration of 0.10 mass % or less in the region of 1 &#x3bc;m from the interface between the steel sheet and the hot-dip galvannealed layer toward the steel sheet. The metal microstructure of the steel sheet at a position of t/4 where t represents the sheet thickness of the hot-dip galvannealed steel sheet includes 50 to 85 area % of martensite, 15 to 50 area % of bainite, and 5 area % or less of ferrite.

Alloyed hot-dip galvanized steel sheet and alloyed hot-dip galvanized steel sheet production method

A high-strength steel sheet satisfies a predetermined chemical composition in which a content of martensite is 93% by volume or more, contents of ferrite, pearlite, and bainite are 2% by volume or less in total, and a content of retained austenite is 7% by volume or less, based on an entire metal structure, a number of laths in martensite measured by a cutting method in a total length of 300 &#x3bc;m in an image of the metal structure observed under a scanning electron microscope is 240 or more, and a tensile strength of the high-strength steel sheet is 1470 MPa or more.

High-strength steel sheet and high-strength galvanized steel sheet

Disclosed herein is a high-strength plated steel sheet having a plated layer on the surface of a base steel sheet and containing predetermined steel components. The steel sheet includes, in the order from the interface of the base steel sheet and the plated layer towards the base steel sheet: a soft layer having a Vickers hardness that is 90% or less of the Vickers hardness at a portion t/4 of the base steel sheet, where t is a sheet thickness of the base steel sheet; and a hard layer consisting of a structure which is mainly composed of martensite and bainite and in which the average grain size of prior austenite is 20 &#x3bc;m or less. The average depth D of the soft layer is 20 &#x3bc;m or greater, and the average depth d of an internal oxide layer is 4 &#x3bc;m or greater and smaller than D.

High-strength plated steel sheet having excellent plating properties, workability, and delayed fracture resistance, and method for producing same

Provided is a high-strength cold-rolled steel sheet having excellent ductility and stretch-flangeability as well as weldability in a range in which a tensile strength is 980 MPa or higher and a 0.2% yield strength is less than 700 MPa (preferably 500 MPa or higher). In the high-strength cold-rolled steel sheet of the present invention, the chemical composition is adjusted as appropriate, and the area ratio of below-mentioned metal structures at a position of &#xbc; sheet thickness in the steel sheet satisfies following requirements: tempered martensite: 10 area % to less than 30 area %, bainite: more than 70 area %, total of tempered martensite and bainite: 90 area % or more, ferrite: 0 area % to 5 area %, and retained austenite: 0 area % to 4 area %. The high-strength cold-rolled steel sheet has excellent ductility, stretch-flangeability, and weldability, and has a tensile strength of 980 MPa or higher and a 0.2% yield strength of less than 700 MPa.

High-strength cold-rolled steel sheet, high-strength hot-dip galvanized steel sheet, and high-strength hot-dip galvannealed steel sheet having excellent ductility, stretch-flangeability, and weldability

Provided is a high-strength cold-rolled steel sheet having excellent ductility and stretch-flangeability as well as weldability in a range in which a tensile strength is 980 MPa or higher and a 0.2% yield strength is 700 MPa or higher. In the high-strength cold-rolled steel sheet of the present invention, the chemical composition is adjusted as appropriate, and the area ratio of below-mentioned metal structures at a position of &#xbc; sheet thickness in the steel sheet satisfies following requirements: tempered martensite: 30 area % or more, bainite: 15 area % to 70 area %, total of tempered martensite and bainite: 90 area % or more, ferrite: 0 area % to 5 area %, and retained austenite: 0 area % to 4 area %. The high-strength cold-rolled steel sheet has excellent ductility, stretch-flangeability, and weldability, and has a tensile strength of 980 MPa or higher and a 0.2% yield strength of 700 MPa or higher.

The present invention relates to high strength cold rolled steel sheet suitable for applications in automobiles, construction materials and the like, specifically high strength steel excellent in formability. In particular, the invention relates to cold rolled steel sheets having a tensile strength of at least 980 MPa and a method for producing such steel sheet.

High strength cold rolled steel sheet

The present invention relates to high strength cold rolled steel sheet suitable for applications in automobiles, construction materials and the like, specifically high strength steel sheet excellent in formability. In particular, the invention relates to cold rolled steel sheets having a tensile strength of at least 980 MPa and a method for producing such steel sheet.

The present disclosure relates to a high-strength hot-dip galvannealed steel sheet excellent in bake hardenability and bendability and having a component composition containing, in mass %, C: from 0.05 to 0.30%, Si: from 0.5 to 3.0%, Mn: from 0.2 to 3.0%, P: from 0 to 0.10%, S: from 0 to 0.010%, N: form 0 to 0.010%, and Al: from 0.001 to 0.10%, with the remainder being iron and unavoidable impurities. The steel sheet has a steel structure containing, in terms of area percentage, martensite: form 50 to 85% and ferrite: 0% or more and less than 5%, with the remainder being bainite. The steel sheet has a dislocation density of 5.0&#xd7;10mor more, a solute carbon amount of 0.08 mass % or more and a tensile strength of 1180 MPa or more.

High-strength hot-dip galvannealed steel sheet having excellent bake hardening property and bendability

Provided is a method that enables manufacture, with good productivity, of a high-strength cold-rolled steel with improved elongation (EL), stretch-flangeability (&#x3bb;), bendability (R), and balance of these properties (TS&#xd7;EL&#xd7;&#x3bb;/1000), outstanding composite workability as evaluated by Erichsen test, and a tensile strength of at least 980 MPa. A steel material satisfying a prescribed constituent composition is held and soaked for at least fifty seconds at a temperature at or above the Acpoint, after which the steel material is cooled at an average cooling rate of at least 15&#xb0; C./sec to a discretionary temperature (T) that satisfies expression (1) below, held for 5-180 seconds in a temperature range that satisfies expression (1) below, then heated to a temperature region that satisfies expression (2) below, held for at least 50 seconds in this temperature region, and then cooled.300&#xb0; C.&#x2266;1(&#xb0; C.)&#x3c;400&#xb0; C.&#x2003;&#x2003;(1)400&#xb0; C.&#x2266;2(&#xb0; C.)&#x3c;540&#xb0; C.&#x2003;&#x2003;(2)

Method for manufacturing high-strength cold-rolled steel sheet with outstanding workability

Disclosed is a hot-dip galvanized steel sheet for stamping, which has excellent cold workability, has such satisfactory surface quality as to be free from unplating and other defects even in the absence of dedicated facilities, and ensures a strength of 1370 MPa or more after quenching even when cooled at a low rate. Also disclosed is a method effective for the produce of the hot-dip galvanized steel sheet for stamping. The hot-dip galvanized steel sheet for stamping comprises a base steel sheet and a hot-dip galvanized layer on a surface of the base steel sheet, in which the base steel sheet has a predetermined chemical composition and has a microstructure comprising equiaxed ferrite having an average aspect ratio of 4.0 or less and cementite and/or pearlite having an average major axis of grains of 20 &#x3bc;m or less.

Hot-dip galvanized steel sheet for stamping having excellent cold workability, die hardenability, and surface quality, and producing method thereof

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 provides a high strength steel sheet with 780 MPa class tensile strength excellent in bending workability and fatigue strength. The high strength steel sheet is (1) a steel sheet whose steel composition contains: C: 0.05-0.20%; Si: 0.6-2.0%; Mn: 1.6-3.0%; P: 0.05% or below; S: 0.01% or below; Al: 0.1% or below; and N: 0.01% or below, the balance comprising iron and inevitable impurities, in which (2) a microstructure comprises a polygonal ferrite structure and a structure formed by low-temperature transformation, in which, when a sheet plane located at a depth of 0.1 mm from a surface of the steel sheet is in the observation under a scanning electron microscope with respect to twenty sights in total in different positions in the sheet-width direction, the maximum value of the areal proportion of the polygonal ferrite (Fmax) and the minimum value of the areal proportion of the ferrite (Fmin) in a 50 &#x3bc;m&#xd7;50 &#x3bc;m area in each sight satisfy Fmax&#x2266;80%, Fmin&#x2267;10%, and Fmax&#x2212;Fmin&#x2266;40%.

High strength steel sheet excellent in bending workability and fatigue strength

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.

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Kakogawa, Japan

Michiharu Nakaya