Abstract: 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 ?m, and at most 1% of cementite, the cementite particles having an average size lower than 50 nm, martensite and/or bainite.

Abstract: 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 ?m, the product of the surface fraction of ferrite by the average grain size of the ferrite being of at most 35 ?m %, 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.

Abstract: 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 ?m, the product of the surface fraction of ferrite by the average grain size of the ferrite being of at most 35 ?m %, 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.

Abstract: 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 5% to 50% of ferrite, from 5 to 70% of partitioned martensite less than 5% of fresh martensite, a carbon [C]A and manganese [Mn]A content in austenite, expressed in weight percent, such that the ratio ([C]A2×[Mn]A)/(C %2×Mn %) is from 3.0 to 8.0, C % and Mn % being the nominal values in carbon and manganese in weight % and an inhomogeneous repartition of manganese characterized by a manganese distribution with a slope above or equal to ?40.

Abstract: A cold rolled and double annealed steel sheet, made of a steel having a composition including, by weight percent: C: 0.03-0.18%, Mn: 6.0-11.0%, 0.2?Al<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%, Nb?0.050%, Ti?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 0% to 45% of ferrite, from 20% to 50% of retained austenite, from 5 to 80% of annealed martensite, less than 5% of fresh martensite, a carbon [C]A and manganese [Mn]A content in austenite, expressed in wt %, such that the ratio ([C]A2×[Mn]A)/(C %2×Mn %) is from 4.5 to 11.0, C % and Mn % being the nominal C and Mn weight percent in the steel and a carbides density below 4×106/mm2.

Abstract: A cold rolled, annealed and partitioned steel sheet, made of a steel having a composition including, by weight percent: C: 0.05 - 0.18%, Mn: 6.0 - 11.0%, 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: Al < 3%, 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, said steel sheet having a microstructure including, in surface fraction, from 0% to 30% of ferrite, such ferrite, when present, having a grain size below 1.0 µm, from 8% to 40% of retained austenite, the fraction of austenite islands with a size above 0.5 µm being below or equal to 5% from 30 to 92% of partitioned martensite less than 3% of fresh martensite, a carbon [C]A and manganese [Mn]A content in austenite, expressed in weight percent, such that the ratio ([C]A2 x [Mn]A) / (C%2 x Mn%) is below 18.

Abstract: A cold rolled, annealed and tempered steel sheet, made of a steel having a composition including, by weight percent: C: 0.03-0.18%, Mn: 6.0-11.0%, Al: <3%, Mo: 0.05-0.5%, B: 0.0005-0.005%, S?0.010%, P?0.020%, N?0.008%, and 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 0% to 30% of ferrite, such ferrite having a grain size below 1.0 ?m, from 3% to 30% of retained austenite, from 40 to 95% of tempered martensite less than 5% of fresh martensite, a carbon [C]A and manganese [Mn]A content in austenite, expressed in weight percent, such that the ratio ([C]A2×[Mn]A)/(C %2×Mn %) is below 7.80, C % and Mn % being the nominal values in carbon and manganese in weight %.

Abstract: A hot rolled and heat-treated steel sheet, made of a steel having a composition including, by weight percent: C: 0.03-0.18%, Mn: 6.0-11.0%, 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: Al<3%, 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 10% to 60% of retained austenite, from 40% to 90% of ferrite, less than 5% of martensite, carbides below 0.8%, and an inhomogeneous repartition of manganese, characterized by a manganese distribution with a slope above or equal to ?40.

Abstract: 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]A and manganese [Mn]A content in austenite, expressed in weight percent, such that the ratio ([C]A×[Mn]2A)/(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 3×106/mm2 and—an inhomogeneous repartition of manganese characterized by a manganese distribution with a slope above or equal to ?30.

Abstract: 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 54% of retained austenite, from 46% to 75% of ferrite, less than 8% of fresh martensite, a carbon [C]A and manganese [Mn]A content in austenite, expressed in weight percent, wherein [C]A*?[Mn]A is from 0.48 to 1.8, and an inhomogeneous repartition of manganese characterized by a manganese distribution with a slope above or equal to ?50.

Abstract: 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/mm2, 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.

Abstract: 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/mm2, 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.

Abstract: 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 30% to 55% of retained austenite, from 45% to 70% of ferrite, less than 5% of fresh martensite a carbon [C]A and manganese [Mn]A content in austenite, expressed in weight percent, satisfying [C]A*[Mn]A/((0.1+C %2)*(Mn %+2))?1.10 and an inhomogeneous repartition of manganese characterized by a manganese distribution with a slope above or equal to ?30.

Abstract: 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.

Abstract: 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/mm2, 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.

Abstract: A method for resistance spot welding comprising the following successive steps: —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)×(TEL)>14000 MPa %, wherein the composition of the steel substrate of (A) contains, in weight: 0.05%?C?0.4%, 0.3%?Mn?8%, 0.010%?Al?3%, 0.010%?Si?2.09%, with 0.5%?(Si+Al)?3.5%, 0.001%?Cr?1.0%, 0.001%?Mo?0.5% and optionally: 0.005%?Nb?0.1%, 0.005%?V?0.2%, 0.005%?Ti?0.1%, 0.0003%?B?0.005%, 0.001%?Ni?1.0%, the remainder being Fe and unavoidable impurities, —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 ?m?(IDepth)?18.68 (Znsol)?55.1, wherein (IDepth) is in micrometers and wherein Znsol is the solubility of Zn in the steel of sheet (A) at 750° C.

Abstract: 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 ?m, and at most 1% of cementite, the cementite particles having an average size lower than 50 nm, martensite and/or bainite.

Abstract: 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 ?m2 and containing more than the steel nominal phosphorus content.

Abstract: A hot 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 less than 2×106 /mm2, 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%, and a pancaking index lower than 5.

Abstract: 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 Lmax of the grain by the maximum width Wmax of the grain higher than 1 ?m2.