Arcelormittal

Arcelormittal Investigacion Y Desarrollo, S.l.

Artem Arlazarov

Jean-Marc Pipard

Astrid Perlade

Frederic Kegel

Wei Xu

Samuel Vignier

Kangying Zhu

Jean-Christophe Hell

Frédéric Kegel

A method for manufacturing a high-strength sheet including the steps of (i) providing a steel having a chemical composition consisting of, in percent by weight: 0.1%≤C≤0.4%, 4.5%≤Mn≤5.5%, 1%≤Si≤3%, and 0.2%≤Mo≤0.5%, a remainder being Fe and unavoidable impurities; (ii) annealing a rolled sheet made of the steel by soaking the rolled sheet at an annealing temperature AT higher than an Actransformation point of the steel; (iii) quenching the sheet by cooling it down to a quenching temperature QT between the Ms transformation point of the steel and 130° C.; (iv) heating the sheet up to an overaging temperature PT between 300° C. and 500° C. and maintaining the sheet at said overaging temperature PT for an overaging time Pt greater than 10 s; and (v) cooling the sheet down to ambient temperature.

Method for manufacturing a high strength steel sheet having improved formability and sheet obtained

A cold rolled and heat treated steel sheet having a composition with the following elements, expressed in percentage by weight:0.10%≤Carbon≤0.5%, 1%≤Manganese≤3.4%, 0.5%≤Silicon≤2.5%, 0.03%≤Aluminum≤1.5%, 0%≤Sulfur≤0.003% 0.002%≤Phosphorus≤0.02%, 0%≤Nitrogen≤0.01% and can contain one or more of the following optional elements 0.05%≤Chromium≤1%, 0.001%≤Molybdenum≤0.5%, 0.001%≤Niobium≤0.1%, 0.001%≤Titanium≤0.1%, 0.01%≤Copper≤2%, 0.01%≤Nickel≤3%, 0.0001%≤Calcium≤0.005%, 0%≤Vanadium≤0.1%, 0%≤Boron≤0.003%, 0%≤Cerium≤0.1%, 0%≤Magnesium≤0.010%, 0%≤Zirconium≤0.010% the remainder composition being composed of iron and unavoidable impurities caused by processing, the microstructure of the steel sheet having in area fraction, 10 to 30% Residual Austenite, 10 to 40% Bainite, 5% to 50% Annealed Martensite, 1% to 20% Quenched Martensite and less than 30% Tempered Martensite, wherein the cumulated amounts of Bainite and Residual Austenite is more than or equal to 25%.

Cold rolled heat treated steel sheet and a method of manufacturing thereof

A spot welded joint of at least two steel sheets is provided. At least one of the steel sheets presents yield strength above or equal to 600 MPa, an ultimate tensile strength above or equal to 1000 MPa, uniform elongation above or equal to 15%. The base metal chemical composition includes 0.05≤C≤0.21%, 4.0≤Mn≤7.0%, 0.5≤Al≤3.5%, Si≤2.0%, Ti≤0.2%, V≤0.2%, Nb≤0.2%, P≤0.025%, B≤0.0035%, and the spot welded joint contains a molten zone microstructure containing more than 0.5% of Al and containing a surface fraction of segregated areas lower than 1%, said segregated areas being zones larger than 20 μmand containing more than the steel nominal phosphorus content.

Production method for a spot welded joint using high strength and high forming steel

A cold rolled heat treated steel sheet having a composition with the following elements, expressed in percentage by weight 0.1%≤Carbon≤0.5%, 1%≤Manganese≤3.4%, 0.5%≤Silicon≤2.5%, 0.03%≤Aluminum≤1.5%, 0%≤Sulfur≤0.003%, 0.002%≤Phosphorus≤0.02%, 0%≤Nitrogen≤0.01% and can contain one or more of the following optional elements 0.05%≤Chromium≤1%, 0.001%≤Molybdenum≤0.5%, 0.001%≤Niobium≤0.1%, 0.001%≤Titanium≤0.1%, 0.01%≤Copper≤2%, 0.01%≤Nickel≤3%, 0.0001%≤Calcium≤0.005%, 0%≤Vanadium≤0.1%, 0%≤Boron≤0.003%, 0%≤Cerium≤0.1%, 0%≤Magnesium≤0.010%, 0%≤Zirconium≤0.010%, the remainder composition being composed of iron and unavoidable impurities caused by processing, the microstructure of the steel sheet having in area fraction, 10 to 30% Residual Austenite, 50 to 85% Bainite, 1 to 20% Quenched Martensite, and less than 30% Tempered Martensite.

Cold rolled steel sheet and a method of manufacturing thereof

A method is for manufacturing a high-strength steel sheet having a tensile strength of more than 1100 MPa and a yield strength of more than 700 MPa, a uniform elongation UE of at least 8.0% and a total elongation of at least 10%, made of a steel containing in percent by weight: 0.1%&#x2264;C&#x2264;0.25%, 4.5%&#x2264;Mn&#x2264;10%, 1%&#x2264;Si&#x2264;3%, 0.03%&#x2264;Al&#x2264;2.5%, the remainder being Fe and impurities resulting from the smelting, the composition being such that CMnIndex=C&#xd7;(1+Mn/3.5)&#x2264;0.6. The method includes annealing a rolled sheet made of said steel by soaking it at an annealing temperature TA higher than the Actransformation point of the steel but less than 1000&#xb0; C., cooling the annealed sheet to a quenching temperature QT between 190&#xb0; C. and 80&#xb0; C. at a cooling speed sufficient to obtain a structure just after cooling containing martensite and retained austenite, maintaining the steel sheet at an overaging temperature PT between 350&#xb0; C. and 500&#xb0; C. for an overaging time Pt of more than 5 s cooling the sheet down to the ambient temperature.

Method for manufacturing a high-strength steel sheet and sheet obtained by the method

A cold rolled and heat treated steel sheet having a composition with the following elements, expressed in percentage by weight: 0.10%&#x2264;Carbon&#x2264;0.5%,1%&#x2264;Manganese&#x2264;3.4%, 0.5%&#x2264;Silicon&#x2264;2.5%, 0.03%&#x2264;Aluminum&#x2264;1.5%, 0%&#x2264;Sulfur&#x2264;0.003% 0.002%&#x2264;Phosphorus&#x2264;0.02%, 0%&#x2264;Nitrogen&#x2264;0.01% and can contain one or more of the following optional elements 0.05%&#x2264;Chromium&#x2264;1%, 0.001%&#x2264;Molybdenum&#x2264;0.5%, 0.001%&#x2264;Niobium&#x2264;0.1%, 0.001%&#x2264;Titanium&#x2264;0.1%, 0.01%&#x2264;Copper&#x2264;2%, 0.01%&#x2264;Nickel&#x2264;3%, 0.0001%&#x2264;Calcium&#x2264;0.005%, 0%&#x2264;Vanadium&#x2264;0.1%, 0%&#x2264;Boron&#x2264;0.003%, 0%&#x2264;Cerium&#x2264;0.1%, 0%&#x2264;Magnesium&#x2264;0.010%, 0%&#x2264;Zirconium&#x2264;0.010% the remainder composition being composed of iron and unavoidable impurities caused by processing, the microstructure of the steel sheet having in area fraction, 10 to 30% Residual Austenite, 10 to 40% Bainite, 5% to 50% Annealed Martensite, 1% to 20% Quenched Martensite and less than 30% Tempered Martensite, wherein the cumulated amounts of Bainite and Residual Austenite is more than or equal to 25%.

A spot welded joint of at least two steel sheets is provided. At least one of the steel sheets presents yield strength above or equal to 600 MPa, an ultimate tensile strength above or equal to 1000 MPa, uniform elongation above or equal to 15%. The base metal chemical composition includes 0.05&#x2264;C&#x2264;0.21%, 4.0&#x2264;Mn&#x2264;7.0%, 0.5&#x2264;Al&#x2264;3.5%, Si&#x2264;2.0%, Ti&#x2264;0.2%, V&#x2264;0.2%, Nb&#x2264;0.2%, P&#x2264;0.025%, B&#x2264;0.0035%, and the spot welded joint contains a molten zone microstructure containing more than 0.5% of Al and containing a surface fraction of segregated areas lower than 1%, said segregated areas being zones larger than 20 &#x3bc;mand containing more than the steel nominal phosphorus content.

Spot welded joint using high strength and high forming steel and its production method

A method for manufacturing a steel product includes providing a heated steel starting product at a temperature between 380&#xb0; C. and 700&#xb0; C., having a metastable fully austenitic structure, with a specified composition. Then the starting product is hot formed at a temperature between 700&#xb0; C. and 380&#xb0; C., with a cumulated strain &#x3b5;between 0.1 and 0.7, in at least one location of the heated steel starting product, to obtain a fully austenitic hot-formed steel product; quenched by cooling the product down, at a cooling rate VRsuperior to the critical martensitic cooling rate, to a quenching temperature QT lower than Ms in order to obtain a structure containing between 40% and 90% of martensite, the rest of the structure being austenite; then maintained at, or reheated up to a holding temperature PT between QT and 470&#xb0; C. and holding the product at the temperature PT for a duration Pt between 5 s and 600 s.

Method for manufacturing a high strength steel product and steel product thereby obtained

A cold rolled and heat treated steel sheet having a composition with the following elements, expressed in percentage by weight 0.10%&#x2264;Carbon&#x2264;0.5%, 1%&#x2264;Manganese&#x2264;3.4%, 0.5%&#x2264;Silicon&#x2264;2.5%, 0.03%&#x2264;Aluminum&#x2264;1.5%, Sulfur&#x2264;0.003%, 0.002%&#x2264;Phosphorus&#x2264;0.02%, Nitrogen&#x2264;0.01% and can contain one or more of the following optional elements 0.05%&#x2264;Chromium&#x2264;1%, 0.001%&#x2264;Molybdenum&#x2264;0.5%, 0.001%&#x2264;Niobium&#x2264;0.1%, 0.001%&#x2264;Titanium&#x2264;0.1%, 0.01%&#x2264;Copper&#x2264;2%, 0.01%&#x2264;Nickel&#x2264;3%, 0.0001%&#x2264;Calcium&#x2264;0.005%, Vanadium&#x2264;0.1%, Boron&#x2264;0.003%, Ceriums&#x2264;0.1%, Magnesiums&#x2264;0.010%, Zirconiums&#x2264;0.010% the remainder composition being composed of iron and the unavoidable impurities caused by processing, and a microstructure of the said rolled steel sheet having by area fraction, 10 to 30% Residual Austenite, 5 to 50% Annealed Bainite, 10 to 40% of Bainite, 1% to 20% Quenched Martensite, and less than 30% Tempered Martensite where the combined presence of Bainite and Residual Austenite shall be 30% or more.

Cold rolled and heat treated steel sheet and a method of manufacturing thereof

A double-annealed steel sheet is provided. The composition of which includes, expressed in percent by weight, 0.20%&#x2264;C&#x2264;0.40%, 0.8%&#x2264;Mn&#x2264;1.4%, 1.60%&#x2264;Si&#x2264;3.00%, 0.015&#x2264;Nb&#x2264;0.150%, Al&#x2264;0.1%, Cr&#x2264;1.0%, S&#x2264;0.006%, P&#x2264;0.030%, Ti&#x2264;0.05%, V&#x2264;0.05%, B&#x2264;0.003%, N&#x2264;0.01%. A remainder of the composition includes iron and unavoidable impurities resulting from processing. The microstructure of the steel sheet includes, in area percentages, 10 to 30% residual austenite, 30 to 60% annealed martensite, 5 to 30% bainite, 10 to 30% fresh martensite and less than 10% ferrite A fabrication method and vehicle parts are also provided.

Double annealed steel sheet having high mechanical strength and ductility characteristics, method of manufacture and use of such sheets

A method for manufacturing a high-strength steel sheet having a tensile strength of more than 1100 MPa and a yield strength of more than 700 MPa, a uniform elongation UE of at least 8.0% and a total elongation of at least 10%, made of a steel containing in percent by weight: 0.1%&#x2264;C&#x2264;0.25%, 4.5%&#x2264;Mn&#x2264;10%, 1%&#x2264;Si&#x2264;3%, 0.03%&#x2264;Al&#x2264;2.5%, the remainder being Fe and impurities resulting from the smelting, the composition being such that CMn Index=Cx(1+Mn/3.5)&#x2264;0.6, the method comprising the steps of annealing a rolled sheet made of said steel by soaking it at an annealing temperature TA higher than the Ac transformation point of the steel but less than 1000&#xb0; C., cooling the annealed sheet to a quenching temperature QT between 190&#xb0; C. and 80&#xb0; C. at a cooling speed sufficient to obtain a structure just after cooling containing martensite and retained austenite, maintaining the steel sheet at an overaging temperature PT between 350&#xb0; C. and 500&#xb0; C. for an overaging time Pt of more than 5 s cooling the sheet down to the ambient temperature. Sheet obtained.

Method for manufacturing a high strength steel sheet and sheet obtained by the method

A method for producing a high strength steel piece having desired mechanical properties, obtainable by a reference heat treatment comprising a first reference treatment and a final reference treatment comprising at least an overaging, The method comprising a step of heat treating on an equipment comprising at least an overaging means for which it is possible to set at least one operating point, the final treatment comprising an overaging for which it is possible to calculate two final treatment parameters OAP1 and OAP2 depending on an operating point of the overaging means. A minimum OAP1 min and a maximum OAP2 max final treatment parameters are determined in order to obtain the desired properties, at least one operating points of the overaging section means is determined such that OAP1&#x2265;OAP1 min and OAP2&#x2264;OAP2 max. The piece is heat treated accordingly. The parameters are with T (t) the temperature at QT time t Formula (I).

Method for producing a high strength steel piece

The present invention provides a spot welded joint of at least two steel sheets. At least one of the steel sheets presents yield strength above or equal to 600 MPa, an ultimate tensile strength above or equal to 1000 MPa, uniform elongation above or equal to 15%. The base metal chemical composition includes 0.05&#x2264;C&#x2264;0.21%, 4.0&#x2264;Mn&#x2264;7.0%, 0.5&#x2264;Al&#x2264;3.5%, Si&#x2264;2.0%, Ti&#x2264;0.2%, V&#x2264;0.2%, Nb&#x2264;0.2%, P&#x2264;0.025%, B&#x2264;0.0035%, and the spot welded joint contains a molten zone microstructure containing more than 0.5% of Al and containing a surface fraction of segregated areas lower than 1%, said segregated areas being zones larger than 20 &#x3bc;mand containing more than the steel nominal phosphorus content.

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Blenod les Pont a Mousson, France

Artem Arlazarov