Arcelormittal

Arcelormittal Investigacion Y Desarrollo, S.l.

Université De Nantes

Kangying Zhu

Astrid Perlade

Coralie Jung

Frédéric Kegel

Olivier Bouaziz

Martin Beauvais

Alice Dumont

Alexandre Gibot

Frederic Kegel

Jean-Michel Mataigne

Artem Arlazarov

Jonas Staudte

Didier Huin

Coralie Magar

Céline Musik

Didier Hun

Renaud Frappier

Celine Musik

A cold rolled and heat-treated steel sheet having a composition including, by weight percent C: 0.12-0.25% Mn: 3.0-8.0%, Si: 0.70-1.50%, Al: 0.3-1.2%, B: 0.0002-0.004%, 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: between 5% and 45% of ferrite, between 25% and 85% of partitioned martensite, the partitioned martensite having a carbides density strictly less than 2×10/mm, between 10% and 30% of retained austenite, less than 8% of fresh martensite, a part of the fresh martensite being combined with retained austenite in the shape of martensite-austenite islands in total surface fraction less than 10%.

Cold rolled and heat-treated steel sheet and method of manufacturing the same

A hot rolled steel sheet having a composition including, by weight percent: C: 0.10-0.25%, Mn: 3.5-5.0%, 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: between 50% and 80% of lath bainite, lower than 30% of granular bainite, the rest being martensite, martensite-austenite islands and austenite films, and having less than 20% of martensite and M-A islands having the multiplication of the maximum length Lof the grain by the maximum width Wof the grain higher than 1 μm.

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

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 cold-rolled and heat-treated steel sheet, having a composition comprising, by weight percent: 0.10%≤C≤0.40%, 3.5%≤Mn≤8.0%, 0.5%≤Si≤2.5%, 0.003%≤Al≤3.0%, with Si+Al≥0.8%, 0.001%≤Mo≤0.5%, S≤0.010%, P≤0.020%, N≤0.008%, and optionally one or more elements selected from amongst Cr, Ti, Nb, V and B, such that: 0.01%≤Cr≤2.0%, 0.010%≤Ti≤0.080%, 0.010%≤Nb≤0.080%, 0.010%≤V≤0.30%, 0.0005%≤B≤0.003%, A remainder of the composition being iron and unavoidable impurities resulting from the smelting. The microstructure consists of, in surface fraction, between 10% and 50% of retained austenite, at most 8% of fresh martensite, and tempered martensite. The retained austenite comprises Mn-enriched austenite, having a Mn content higher than 1.3*Mn %, Mn % designating the Mn content of the steel sheet, the surface fraction of said Mn-enriched austenite with respect to the whole microstructure being comprised between 2% and 12%; and Mn-poor austenite, having a Mn content comprised between 0.5*Mn % and 1.3*Mn %.

Resistance spot welded joint and a process for producing a resistance spot welded joint

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 steel sheet for the manufacture of a press hardened part is provided, having a composition of: 0.15%≤C≤0.22%, 3.5%≤Mn<4.2%, 0.001%≤Si≤1.5%, 0.020%≤Al≤0.9%, 0.001%≤Cr≤1%, 0.001%≤Mo≤0.3%, 0.001%≤Ti≤0.040%, 0.0003%≤B≤0.004%, 0.001%≤Nb≤0.060%, 0.001%≤N≤0.009%, 0.0005%≤S≤0.003%, 0.001%≤P≤0.020%. A microstructure has less than 50% ferrite, 1% to 20% retained austenite, cementite, such that the surface density of cementite particles larger than 60 nm is lower than 10/mm, and a complement of bainite and/or martensite, the retained austenite having an average Mn content of at least 1.1*Mn %. Press-hardened steel part obtained by hot forming the steel sheet, and manufacturing methods thereof.

Steel sheet for manufacturing press hardened parts, press hardened part having a combination of high strength and crash ductility, and manufacturing methods thereof

A steel sheet for the manufacture of a press hardened part is provided, having a composition of: 0.15%≤C≤0.22%, 3.5%≤Mn<4.2%, 0.001%≤Si≤1.5%, 0.020%≤Al≤0.9%, 0.001%≤Cr≤1%, 0.001%≤Mo≤0.3%, 0.001%≤Ti≤0.040%, 0.0003%≤B≤0.004%, 0.001%≤Nb≤0.060%, 0.001%≤N≤0.009%, 0.0005%≤S≤0.003%, 0.001%≤P≤0.020%. A microstructure has less than 50% ferrite, 1% to 20% retained austenite, cementite, such that the surface density of cementite particles larger than 60 nm is lower than 10{circumflex over ( )}7/mm, and a complement of bainite and/or martensite, the retained austenite having an average Mn content of at least 1.1*Mn %. Press-hardened steel part obtained by hot forming the steel sheet, and manufacturing methods thereof.

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 steel sheet for the manufacture of a press hardened part is provided, having a composition of: 0.15%&#x2264;C&#x2264;0.22%, 3.5%&#x2264;Mn&#x3c;4.2%, 0.001%&#x2264;Si&#x2264;1.5%, 0.020%&#x2264;Al&#x2264;0.9%, 0.001%&#x2264;Cr&#x2264;1%, 0.001%&#x2264;Mo&#x2264;0.3%, 0.001%&#x2264;Ti&#x2264;0.040%, 0.0003%&#x2264;B&#x2264;0.004%, 0.001%&#x2264;Nb&#x2264;0.060%, 0.001%&#x2264;N&#x2264;0.009%, 0.0005%&#x2264;S&#x2264;0.003%, 0.001%&#x2264;P&#x2264;0.020%. A microstructure has less than 50% ferrite, 1% to 20% retained austenite, cementite, such that the surface density of cementite particles larger than 60 nm is lower than 10{circumflex over (&#x2003;)}7/mm, and a complement of bainite and/or martensite, the retained austenite having an average Mn content of at least 1.1*Mn %. Press-hardened steel part obtained by hot forming the steel sheet, and manufacturing methods thereof.

A method for resistance spot welding comprising the following successive steps: &#x2014;providing at least two steel sheets with thickness (th) comprised between 0.5 and 3 mm, at least one of the sheets being a zinc or zinc-alloy coated steel sheet (A) with a tensile strength (TS) higher than 800 MPa and a total elongation (TEL) such as (TS)&#xd7;(TEL)&#x3e;14000 MPa %, wherein the composition of the steel substrate of (A) contains, in weight: 0.05%&#x2264;C&#x2264;0.4%, 0.3%&#x2264;Mn&#x2264;8%, 0.010%&#x2264;Al&#x2264;3%, 0.010%&#x2264;Si&#x2264;2.09%, with 0.5%&#x2264;(Si+Al)&#x2264;3.5%, 0.001%&#x2264;Cr&#x2264;1.0%, 0.001%&#x2264;Mo&#x2264;0.5% and optionally: 0.005%&#x2264;Nb&#x2264;0.1%, 0.005%&#x2264;V&#x2264;0.2%, 0.005%&#x2264;Ti&#x2264;0.1%, 0.0003%&#x2264;B&#x2264;0.005%, 0.001%&#x2264;Ni&#x2264;1.0%, the remainder being Fe and unavoidable impurities, &#x2014;performing resistance spot welding of the at least two steel sheets for producing a weld with an indentation depth (IDepth) on the surface of said steel sheet (A) such as: 100 &#x3bc;m&#x2264;(IDepth)&#x2264;18.68 (Zn)&#x2212;55.1, wherein (IDepth) is in micrometers and wherein Znis the solubility of Zn in the steel of sheet (A) at 750&#xb0; C., in weight %.

Resistance spot welding method for joining zinc coated steel sheets

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 cold-rolled and heat-treated steel sheet having a microstructure of, in surface fraction:

A cold-rolled and heat-treated steel sheet having a microstructure consisting of, in surface fraction: between 10% and 30% of retained austenite, the retained austenite being present as films having an aspect ratio of at least 3 and as Martensite Austenite islands, less than 8% of the Martensite Austenite islands having a size above 0.5 &#x3bc;m, at most 1% of fresh martensite, at most 50% of tempered martensite, and recovered martensite containing precipitates of at least one element chosen among niobium, titanium and vanadium. A method for manufacturing the cold-rolled and heat-treated steel sheet is also described.

A cold-rolled and heat-treated steel sheet, having a composition including, by weight percent: 0.10%&#x2264;C&#x2264;0.40%, 3.5%&#x2264;Mn&#x2264;8.0%, 0.5%&#x2264;Si&#x2264;2.5%, 0.003%&#x2264;Al&#x2264;3.0%, with Si+Al&#x2265;0.8%, 0.001%&#x2264;Mo&#x2264;0.5%, S&#x2264;0.010%, P&#x2264;0.020%, N&#x2264;0.008%, and optionally one or more elements selected from a group comprising Cr, Ti, Nb, V and B, such that: 0.01%&#x2264;Cr&#x2264;2.0%, 0.010%&#x2264;Ti&#x2264;0.080%, 0.010%&#x2264;Nb&#x2264;0.080%, 0.010%&#x2264;V&#x2264;0.30%, 0.0005%&#x2264;B&#x2264;0.003%, the remainder of the composition being iron and unavoidable impurities resulting from the smelting. The microstructure includes, in surface fraction, between 10% and 50% of retained austenite, at most 8% of fresh martensite, and tempered martensite. The retained austenite includes Mn-enriched austenite, having a Mn content higher than 1.3*Mn %, Mn % designating the Mn content of the steel sheet, a surface fraction of the Mn-enriched austenite with respect to the whole microstructure is between 2% and 12%, and Mn-poor austenite, having an Mn content between 0.5*Mn % and 1.3*Mn %.

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Metz, France

Kangying Zhu