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 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 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 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 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 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 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 method for the fabrication of a hot rolled steel includes providing a liquid metal comprising a certain chemical composition; carrying out a vacuum or SiCa treatment, the chemical composition including, expressed by weight 0.0005%?Ca?0.005%, if a SiCA treatment is carried out; dissolving quantities of Ti and N in the liquid metal so as to satisfy (% [Ti])×(% [N])<6.10?4%2; casting the steel to obtain a cast semi-finished product; rolling the cast semi-finished product with an end-of-rolling temperature between 880° C. and 930° C., a reduction rate of the penultimate pass being less than 0.25, and a start-of-rolling temperature of the penultimate pass being less than 960° C. to obtain a hot-rolled product, then cooling the hot rolled product at a rate between 20 and 150° C./s to obtain a hot rolled steel sheet; and coiling the hot rolled product to obtain a hot rolled steel sheet.

Abstract: A cold-rolled and heat-treated steel sheet, having a composition including, 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 a group comprising 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%, 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 %.

Abstract: A method for the fabrication of a hot rolled steel includes providing a liquid metal comprising a certain chemical composition; carrying out a vacuum or SiCa treatment, the chemical composition including, expressed by weight 0.0005%?Ca?0.005%, if a SiCA treatment is carried out; dissolving quantities of Ti and N in the liquid metal so as to satisfy (% [Ti])×(% [N])<6.10?4%2; casting the steel to obtain a cast semi-finished product; rolling the cast semi-finished product with an end-of-rolling temperature between 880° C. and 930° C., a reduction rate of the penultimate pass being less than 0.25, and a start-of-rolling temperature of the penultimate pass being less than 960° C. to obtain a hot-rolled product, then cooling the hot rolled product at a rate between 20 and 150° C./s to obtain a hot rolled steel sheet; and coiling the hot rolled product to obtain a hot rolled steel sheet.

Abstract: A rolled steel sheet is provided. The rolled steel sheet has a mechanical strength greater than or equal to 600 MPa and an elongation at fracture that is greater than or equal to 20%. A a method for its fabrication is also provided. The chemical composition of the steel sheet includes 0.10?C?0.30%, 6.0?Mn?15.0%, 6.0?Al?15.0%, and optionally one or more elements selected from among: Si?2.0%, Ti?0.2%, V?0.6% and Nb?0.3%. The remainder of the composition includes iron and the unavoidable impurities resulting from processing. The ratio of the weight of manganese to the weight of aluminum is such that Mn Al > 1.0 . The microstructure of the sheet includes ferrite, austenite and up to 5% Kappa precipitates in area fraction.

Abstract: The present invention provides a hot rolled steel sheet with yield stress greater than 680 MPa and less than or equal to 840 MPa a tensile strength between 780 MPa and 950 MPa, elongation at failure greater than 10% and hole-expansion ratio (Ac) greater than or equal to 45%. The chemical composition includes, with the contents expressed by weight: 0.05%?Mo?0.35%, 0.15<C?0.6% when 0.05%?Mo?0.11%, or 0.10%?Cr?0.6% when 0.11%<Mo?0.35%. The microstructure includes at least 70% granular bainite, less than 20% ferrite, with the remainder, if any, including lower bainite, martensite and residual austenite. The sum of the martensite and residual austenite contents is less than 5%.

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 hot dip coated steel sheet presenting a tensile strength above 1000?50×Al MPa, a uniform elongation above 15% and a low density is provided. The steel includes, by weight percent: 0.1?C?0.5%, 3.5?Mn?10.0%, 0?Al?9.0%, Si?5.0%, Ti?0.2%, V?0.2%, Nb?0.2%, S?0.004%, P?0.025%, 0.5?Si+Al?9.0%, B?0.0035, Cr?1%, The balance being Fe and impurities and the microstructure containing 25% to 90% of ferrite, 10% to 50% of austenite, kappa precipitates lower than 5% and martensite lower than 25%. The steel is able to be coated using total oxidation.

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: The present invention provides a spot welded joint of at least two steel sheets. 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 cold-rolled and annealed ferritic steel sheet is provided. The steel has a composition comprising, expressed by weight: 0.001?C?0.15%; Mn?1%; Si?1.5%; 7.5%?AI?10%; 0.020%?Ti?0.5%; S?0.050%; and P?0.1%. A balance of the composition includes iron and inevitable impurities resulting from the smelting. The structure includes kappa (?) precipitates and equiaxed ferrite, an average grain size d? of the equiaxed ferrite is less than 50 microns, and a linear fraction f of intergranular ? precipitates is less than 30%. The linear fraction f is defined by f = ? ( A ) ? di ? ( A ) ? Li . ?(A)di denotes the total length of grain boundaries containing ? precipitates relative to an area (A) and ?(A)Li denotes the total length of the grain boundaries relative to the area (A). A content of carbon in solid solution is less than 0.005% by weight, and the cold-rolled and annealed ferritic steel sheet has a thickness between 0.6 mm and 1.5 mm.