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 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 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 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 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.

Abstract: 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.

Abstract: 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 2×106/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%.

Abstract: 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 ?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.

Abstract: A cold-rolled and heat-treated steel sheet having a microstructure of, in surface fraction: between 10% and 30% of retained austenite, said retained austenite being present as films having an aspect ratio of at least 3 and as Martensite Austenite islands, less than 8% of such Martensite Austenite islands having a size above 0.5 ?m, at most 10% of fresh martensite and recovered martensite containing precipitates of at least one element chosen among niobium, titanium and vanadium. A manufacturing method thereof is also provided.

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 double-annealed steel sheet is provided. The composition of which includes, expressed in percent by weight, 0.20%?C?0.40%, 0.8%?Mn?1.4%, 1.60%?Si?3.00%, 0.015?Nb?0.150%, Al?0.1%, Cr?1.0%, S?0.006%, P?0.030%, Ti?0.05%, V?0.05%, B?0.003%, N?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.

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-having a microstructure consisting of, in surface fraction: between 10% and 30% of retained austenite, said retained austenite being present as films having an aspect ratio of at least 3 and as Martensite Austenite islands, less than 8% of such Martensite A islands having a size above 0.5 ?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. It also provides a manufacturing method thereof.