Arcelormittal

Frédéric Kegel

Astrid Perlade

Kangying Zhu

Coralie Jung

Artem Arlazarov

Jean-Christophe Hell

Samuel Vignier

A cold rolled and annealed steel sheet, made of a steel having a composition including, by weight percent: C: 0.03-0.18%, Mn: 6.0-11.0%, Al: 0.2-3%, Mo: 0.05-0.5%, B: 0.0005-0.005%, S≤0.010%, P≤0.020%, N≤0.008%, and including optionally one or more of the following elements, in weight percentage: Si≤1.20%, Ti≤0.050%, Nb≤0.050%, Cr≤0.5%, V≤0.2%, the remainder of the composition being iron and unavoidable impurities resulting from the smelting, the steel sheet having a microstructure including, in surface fraction, from 25% to 55% of retained austenite, from 45% to 75% of ferrite, less than 5% of fresh martensite, a carbon [C]and manganese [Mn]content in austenite, expressed in weight percent, such that the ratio ([C]×[Mn])/(C %×Mn %) is from 19.0 to 41.0 wt %, C % and Mn % being the nominal values in carbon and manganese in weight % and a carbides density below 3×10/mmand—an inhomogeneous repartition of manganese characterized by a manganese distribution with a slope above or equal to −30.

Cold rolled and annealed steel sheet and method of manufacturing the same

A hot rolled and annealed steel sheet having a composition including, by weight percent: C: 0.1-0.25%, Mn: 3.00-5.00%, Si: 0.80-1.60%, B: 0.0003-0.004%, S≤0.010%, P≤0.020%, N≤0.008% the remainder of the composition being iron and unavoidable impurities resulting from the smelting, and having a microstructure consisting of, in surface fraction: more than 20% of recrystallized ferrite, the balance being non-recrystallized ferrite, more than 15% of the recrystallized ferrite having grain size larger than 5 μm and a density of carbides at grain boundary of recrystallized ferrite less than 5 carbides per 10 μm of grain boundary length.

High toughness hot rolled and annealed steel sheet and method of manufacturing the same

A cold-rolled and heat treated steel sheet, has a composition comprising 0.1%≤C≤0.4%, 3.5%≤Mn≤8.0%, 0.1%≤Si≤1.5%, Al≤3%, Mo≤0.5%, Cr≤1%, Nb≤0.1%, Ti≤0.1%, V≤0.2%, B≤0.004%, 0.002%≤N≤0.013%, S≤0.003%, P≤0.015%. The structure consists of, in surface fraction: between 8 and 50% of retained austenite, at most 80% of intercritical ferrite, the ferrite grains, if any, having an average size of at most 1.5 μm, and at most 1% of cementite, the cementite particles having an average size lower than 50 nm, martensite and/or bainite.

Steel sheet having excellent toughness, ductility and strength, and manufacturing method thereof

A cold-rolled and heat-treated steel sheet, has a composition comprising, by weight percent: n0.10%≤C≤0.25%, 3.5%≤Mn—≤6.0%, 0.5%≤Si≤2.0%, 0.3%≤Al≤1.2%, with Si+Al≥0.8%, 0.10%≤Mo≤0.50%, S≤0.010%, P≤0.020%, N≤0.008%. The cold-rolled steel sheet has a microstructure consisting of, in surface fraction: between 10% and 45% of ferrite, having an average grain size of at most 1.3 μm, the product of the surface fraction of ferrite by the average grain size of the ferrite being of at most 35 μm %, between 8% and 30% of retained austenite, the retained austenite having an Mn content higher than 1.1*Mn %, Mn % designating the Mn content of the steel, at most 8% of fresh martensite, at most 2.5% of cementite and partitioned martensite.

High strength and high formability steel sheet and manufacturing method

A cold-rolled and heat treated steel sheet, has a composition comprising 0.1%&#x2264;C&#x2264;0.4%, 3.5%&#x2264;Mn&#x2264;8.0%, 0.1%&#x2264;Si&#x2264;1.5%, Al&#x2264;3%, Mo&#x2264;0.5%, Cr&#x2264;1%, Nb&#x2264;0.1%, Ti&#x2264;0.1%, V&#x2264;0.2%, B&#x2264;0.004%, 0.002%&#x2264;N&#x2264;0.013%, S&#x2264;0.003%, P&#x2264;0.015%. The structure consists of, in surface fraction: between 8 and 50% of retained austenite, at most 80% of intercritical ferrite, the ferrite grains, if any, having an average size of at most 1.5 &#x3bc;m, and at most 1% of cementite, the cementite particles having an average size lower than 50 nm, martensite and/or bainite.

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.

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Maizieres-les-Metz, France

Frédéric Kegel