Arcelormittal

Jean-Christophe Hell

Artem Arlazarov

Frédéric Kegel

Frederic Kegel

Jean-Philippe Masse

Thierry Iung

Sebastien Allain

Michel Soler

Irène De Diego Calderon

Blandine Remy

Nicolas Charbonnier

Gunhild Föjer

Gunhild Fojer

Irene De Diego Calderon

A cold rolled annealed steel sheet having a chemical composition including, in weight %: 0.30%≤C≤0.50%, 1.00%≤Mn≤2.50%, 1.00%≤Si≤2.00%, Al≤2.00%, Cr≤0.100%, 0.100%≤Mo≤0.500%, 0.020%≤Nb≤0.200%, B≤0.0005%, P≤0.02%, S≤0.005%, N≤0.01%, the remainder being Fe and unavoidable impurities, with the percentages in carbon, manganese, chromium, molybdenum and boron are such that the alloy satisfies the following condition: 250% C+120% Mn−200% Cr+200% Mo−10000% B≥320, and wherein the microstructure comprises in surface fraction, 35% to 45% of islands of martensite and retained austenite (M-A), the total retained austenite is higher than or equal to 24%, the remainder consisting of bainitic ferrite.

Cold rolled annealed steel sheet with high hole expansion ratio and manufacturing process thereof

The invention relates to a method for producing a high strength coated steel sheet having a yield stress YS>550 MPa, a tensile strength TS>980 MPa, and improved formability and ductility. The steel contains: 0.15%≤C≤0.25%, 1.2%≤Si≤1.8%, 2%≤Mn≤2.4%, 0.1%≤Cr≤0.25%, Al≤0.5%, the balance being Fe and unavoidable impurities. The sheet is annealed at a temperature between TA1=Ac3−0.45*(Ms−QT) and TA2=830° C. for at least 30 s then quenched by cooling it to a quenching temperature QT between 180° C. and 300° C., then heated to a partitioning temperature PT between 380° C. and 480° C. and maintained at this temperature for a partitioning time Pt between 0 sec and 300 sec, then either hot dip coated and cooled to the room temperature with a cooling rate of at least 25° C./s below 300° C., or directly cooled to the room temperature with a cooling rate of at least 25° C./s and further electro-galvanized, or cooled to the room temperature with a cooling rate of at least 25° C./s without coating. The steel according to the invention contains 5% to 25% of intercritical ferrite, at least 50% of partitioned martensite, at least 10% of residual austenite, less than 10% of fresh martensite, and bainite, the sum of partitioned martensite and bainite being at least 60%. It also relates to the obtained coated or non coated sheet.

Method for producing a coated steel sheet having improved strength, ductility and formability

A method for manufacturing a recovered steel sheet having an austenitic matrix presenting at least one mechanical property (M) equal or above a target value Mis provided. The method includes a calibrating process involving heat treatments on at least 2 samples of the steel, corresponding to Pareq values P, submitting said samples to X-ray diffraction so as to obtain spectrums including a main peak whose width at mid height FWHM is being measured, measuring a mechanical property (M) of said samples, measuring a recovery or recrystallization state of each sample, drawing a curve of M as a function of FWMH in a domain where the samples are recovered from 0 to 100%, but not recrystallized. The method further includes calculating a FWHMcorresponding to a target mechanical property M, determining a pareq value Pof the heat treatment to perform to reach Mand selecting a time tand a temperature T°corresponding to the Pvalue. The method further includes feeding a recrystallized steel sheet having a M, cold-rolling the recrystallized steel sheet in order to obtain a steel sheet having a Mand annealing the cold rolled steel sheet at a temperature T°during a time t.

Method for producing a TWIP steel sheet having an austenitic microstructure

A cold rolled and annealed steel sheet including by weight: 0.6<C<1.3%, 15≤Mn<35%, 6≤Al<15%, Si≤2.40%, S≤0.03%, P≤0.1%, N≤0.1%, possibly one or more optional elements chosen among Ni, Cr and Cu in an individual amount of up to 3% and possibly one or more elements chosen among B, Ta, Zr, Nb, V, Ti, Mo, and W in a cumulated amount of up to 2.0%, the remainder of the composition making up of iron and inevitable impurities resulting from the elaboration, the microstructure of the sheet including of ordered ferrite between 1% and 10%, optionally of up to 10% of kappa carbides, the remainder being made of austenite, and, the density of the steel sheet being equal or below 7.2 and the FWHM for the austenite matrix is between 0.700 and 1.100.

Cold rolled and annealed steel sheet, method of production thereof and use of such steel to produce vehicle parts

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 sheet having improved formability and ductility accord which the chemical composition of the steel contains, in percent by weight: 0.25%&#x3c;C&#x2264;0.4% 2.3%&#x2264;Mn&#x2264;3.5% 2.3%&#x2264;Si&#x2264;3% Al&#x2264;0.040% the remainder being Fe and unavoidable impurities, the method comprising the steps of annealing a rolled sheet made of said steel by soaking it at an annealing temperature AT higher than the Actransformation point of the steel, quenching the sheet by cooling it down to a quenching temperature QT between Ms&#x2212;65&#xb0; C. and Ms&#x2212;115&#xb0; C., being in order to obtain a final structure containing at least 65% of martensite and at least 5% of residual austenite, the sum of the ferrite and bainite contents being less than 10%, Ms being the Ms transformation point of the steel according to the Andrews formula, heating the sheet up to an overaging temperature PT between 360&#xb0; C. and 500&#xb0; C. and maintaining it at said temperature for a time Pt between 10 s and 600 s, and cooling the sheet down to the ambient temperature.

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

The invention relates to the manufacture of a cold-rolled steel sheet having a strength of more than 900 MPa, an elastic limit of more than 700 MPa and distributed elongation of more than 12%, the composition of which includes, the contents being expressed as weight percentages: 0.26%&#x2264;C&#x2264;0.45%, 1.0%&#x2264;Mn&#x2264;3.0%, 1.0%&#x2264;Si&#x2264;3.0%, Al&#x2264;0.10%, 0%&#x2264;Cr&#x2264;1.5%, S&#x2264;0.005%, P&#x2264;0.020%, Nb&#x2264;0.1%, Ti&#x2264;0.020%, V&#x2264;0.015%, N&#x2264;0.01%, the remainder of the composition being iron and inevitable impurities resulting from the production process. The microstructure, given in surface proportions, comprises 13% to 25% residual austenite and 13% to 30% MA islands, the remainder consisting of bainite and possibly ferrite.

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Maizieres-les-Metz, France

Jean-Christophe Hell