Abstract: The invention deals with a cold rolled and hot dip steel sheet, with a tensile strength of at least 980 MPa, with yield strength above or equal to 500 MPa, with total elongation above or equal to 8%, the composition consisting by weight percent: 0.05<C<0.15%, 2<Mn?3%, Al<0.1%, 0.3<Si<1.5%, 0.01%<Nb<0.05%, N<0.02%, 0.1<Cr+Mo<1%, 0.0001<B<0.0025, Ti<0.5%, V<0.01%, S<0.01%, P<0.05% the remainder of the composition being iron and unavoidable impurities resulting from the smelting and the microstructure contains, in surface fraction: between 50 and 95% of martensite and between 5 and 50% of the sum of ferrite and bainite, wherein the ferrite grain size is below 10????, and wherein the aspect ratio of the ferrite grain size is between 1 and 3. The steel according to the invention is oxidized and subsequently reduced during heating, soaking and cooling steps of the annealing.

Abstract: A method for producing a dual phase steel sheet is provided. The method includes providing a dual phase hot rolled steel sheet having a microstructure including ferrite and martensite and a composition including 0.1 to 0.3 wt. % C, 1.5 to 2.5 wt. % Si and 1.75 to 2.5 wt. % Mn. The steel sheet is annealed at a temperature from 750 to 875° C., water quenched to a temperature from 400 to 420° C. and subject to overaging at the temperature from 400 to 420° C. to convert the martensite in the hot rolled steel sheet to tempered martensite. The overaging is sufficient to provide the hot rolled steel sheet with a hole expansion ratio of at least 15%.

Abstract: A method for producing a cold rolled and hot dip coated steel sheet is provided. The method includes casting a steel into a slab, reheating, hot rolling, cooling, coiling, descaling and cold rolling the slab. The cold rolled steel sheet is annealed so a layer of iron oxide forms on the surface with an internal oxidation underneath. The sheet is then heated so the surface is oxidized and the layer of iron oxide is fully reduced to obtain an internally oxidized depth between 200 nm and 100 ?m which includes one or more of Si, Mn, Al, Ti containing oxides. The sheet is then hot dip coated and cooled.

Abstract: A dual phase steel sheet is provided. The steel sheet has a microstructure containing ferrite and tempered martensite, a tensile strength of at least 980 MPa, a total elongation of at least 15%, and a hole expansion ratio of at least 15%. The dual phase steel sheet has a composition including 0.2 to 0.3 wt. % C, 1.6 to 2.5 wt. % Si and 1.75 to 2.5 wt. % Mn. A method for producing the dual phase steel sheet is also provided.

Abstract: A method for producing a steel sheet is provided. The steel sheet has a microstructure including, in area fraction, 20% to 50% intercritical ferrite, 10% to 20% retained austenite, 25% to 45% tempered martensite, 10% to 20% fresh martensite, and bainite. The sum of tempered martensite and bainite is between 30% and 60%. The method includes providing a cold-rolled steel sheet including, in weight percent, 0.18%?C?0.25%, 0.9%?Si?1.8%, 0.02%?Al?1.0%, with 1.00%?Si+Al?2.35%, 1.5%?Mn 2.5%, 0.010%?Nb?0.035%, 0.10%?Cr?0.40%, and a remainder including Fe and unavoidable impurities. The method further includes annealing the steel sheet to obtain 50% to 80% austenite and 20% to 50% of ferrite, quenching the sheet at a cooling rate between 20° C./s and 50° C./s to a quenching temperature between Ms-50° C. and Ms-5° C., heating the sheet to a partitioning temperature between 375° C. and 450° C.

Abstract: A method for producing a steel sheet having a microstructure including 71% to 91% martensite and bainite, 9% to 13% retained austenite, and at most 20% ferrite is provided. The method includes providing a cold-rolled steel sheet including, in weight percent: 0.13%?C?0.22%, 1.2%?Si?2.3%, 0.02%?Al?1.0%, with 1.25%?Si+Al?2.35%, 2.4%?Mn?3%, Ti?0.05%, Nb?0.05% and a remainder of Fe and unavoidable impurities, annealing the steel sheet to obtain 80% to 100% austenite and 0% to 20% ferrite, quenching the steel sheet at a cooling rate between 20° C./s and 50° C./s to a quenching temperature between 240° C. and 310° C., heating the steel sheet to a partitioning temperature between 400° C. and 465° C. and maintaining the steel sheet at the partitioning temperature for 50 to 250 seconds, then immediately cooling the sheet to room temperature. Steel sheets are also provided.

Abstract: A dual phase steel (martensite+ferrite) having a tensile strength of at least 980 MPa, and a total elongation of at least 15%. The dual phase steel may have a total elongation of at least 18%. The dual phase steel may also have a tensile strength of at least 1180 MPa. The dual phase steel may include between 0.5-3.5 wt. % Si, and more preferably between 1.5-2.5 wt. % Si.

Abstract: A cold rolled, annealed TRIP steel sheet which has a composition including (in wt. %): C: 0.1-0.3; Mn: 4-10, Al: 0.05-5, Si: 0.05-5; and Nb: 0.008-0.1, the remainder being iron and inevitable residuals. The cold rolled sheet has an ultimate tensile strength of at least 1000 MPa, and a total elongation of at least 15%. The cold rolled sheet may have at least 20% retained austenite in its microstructure and may have greater than 50% lath-type annealed ferrite structure. The cold rolled sheet may have an ultra fine grain size of less than 5 micron for the retained austenite and ferrite.

Abstract: A steel sheet comprising, in wt %, 0.04?C?0.30, 0.5?Mn?4, 0?Cr?4, 2.7?Mn+Cr?5, 0.003?Nb?0.1 0.015?Al?0.1 and 0.05?Si?1.0, has a chemistry that makes hot formed sheet after austenization insensitive to cooling rate and ensures a uniform distribution of tensile strength, in the range of 800-1400 MPa, across parts independent of the time delay between operations and final cooling/quenching. As a result, a formed part can be cooled while inside a die or in air. The addition of Nb reduces the amount of C needed to achieve a given tensile strength and improves weldability.

Abstract: A cold rolled, coated and post annealed steel sheet. The cold rolled steel sheet may comprise (in wt. %): C—0.1-0.3 %; Mn—1-3%; Si—0.5-3.5%; Al—0.05-1.5%; Mo+Cr is between 0-1.0%; and Mo+Cr is between 0.2-0.5%. The steel sheet may be coated with a zinc or zinc alloy coating. The coated steel sheet may be formed by cold rolling, zinc coating the cold rolled sheet and annealing said steel sheet after application of said zinc coating. The annealing is performed at a temperature and for a time sufficient to significantly increase the yield strength and hole expansion of the annealed coated cold rolled steel sheet as compared with the as coated sheet.

Abstract: A steel sheet comprising, in wt %, 0.04?C?0.30, 0.5?Mn?4, 0?Cr?4, 2.7?Mn+Cr?5, 0.003?Nb?0.1 0.015?Al?0.1 and 0.05?Si?1.0, has a chemistry that makes hot formed sheet after austenization insensitive to cooling rate and ensures a uniform distribution of tensile strength, in the range of 800-1400 MPa, across parts independent of the time delay between operations and final cooling/quenching. As a result, a formed part can be cooled while inside a die or in air. The addition of Nb reduces the amount of C needed to achieve a given tensile strength and improves weldability.

Abstract: A method for producing a high strength coated steel sheet having a yield stress YS>800 MPa, a tensile strength TS>1180 MPa, and improved formability and ductility. The steel contains: 15%?C?0.25%, 1.2%?Si?1.8%, 2%?Mn?2.4%, 0.1% 23 Cr?0.25%, Al?0.5%, the remainder being Fe and unavoidable impurities. The sheet is annealed at a temperature higher than Ac3 and lower than 1000° C. for a time of more than 30 s, then quenched by cooling it to a quenching temperature QT between 250° C. and 350° C., to obtain a structure consisting of at least 60% of martensite and a sufficient austenite content such that the final structure contains 3% to 15% of residual austenite and 85% to 97% of martensite and bainite without ferrite, then heated to a partitioning temperature PT between 430° C. and 480° C. and maintained at this temperature for a partitioning time Pt between 10 s and 90 s, then hot dip coated and cooled to the room temperature.

Abstract: A method for producing a high strength coated steel sheet having an improved ductility and an improved formability, the chemical composition of the steel containing: 0.13%?C?0.22%, 1.9%?Si?2.3%, 2.4%?Mn?3%, Al?0.5%, Ti<0.05%, Nb<0.05%, the remainder being Fe and unavoidable impurities. The sheet is annealed at temperature TA higher than Ac3 but less than 1000° C. for a time of more than 30 s, quenched by cooling to a quenching temperature QT between 200° C. and 280° C. in order to obtain a structure consisting of austenite and at least 50% of martensite, the austenite content being such that the final structure can contain between 3% and 15% of residual austenite and between 85% and 97% of the sum of martensite and bainite, without ferrite, heated up to a partitioning temperature PT between 430° C. and 490° C. and maintained at this temperature for a time Pt between 10 s and 100 s, hot dip coated and cooled to the room temperature.

Abstract: The invention deals with a cold rolled and hot dip steel sheet, with a tensile strength of at least 980 MPa, with yield strength above or equal to 500 MPa, with total elongation above or equal to 8%, the composition consisting by weight percent: 0.05<C<0.15%, 2<Mn?3%, Al<0.1%, 0.3<Si<1.5%, 0.01%<Nb<0.05%, N<0.02%, 0.1<Cr+Mo<1%, 0.0001<B<0.0025, Ti<0.5%, V<0.01%, S<0.01%, P<0.05% the remainder of the composition being iron and unavoidable impurities resulting from the smelting and the microstructure contains, in surface fraction: between 50 and 95% of martensite and between 5 and 50% of the sum of ferrite and bainite, wherein the ferrite grain size is below 10????, and wherein the aspect ratio of the ferrite grain size is between 1 and 3. The steel according to the invention is oxidized and subsequently reduced during heating, soaking and cooling steps of the annealing.

Abstract: A method for producing a high strength steel sheet having a yield strength YS>850 MPa, a tensile strength TS>1180 MPa, a total elongation >13% and a hole expansion ratio HER>30%, by heat treating a steel sheet wherein the chemical composition of the steel contains: 0.13%?C?0.22%, 1.2%?Si?1.8%, 1.8%?Mn?2.2%, 0.10%?Mo?0.20%, Nb?0.05%, Ti<0.05%, Al?0.5%, the remainder being Fe and unavoidable impurities. The sheet is annealed at an annealing temperature TA>865° C. and <1000° C. for a time of more than 30 s, then quenched by cooling it to a quenching temperature QT between 275° C. and 375° C., at a cooling speed >30° C./s in order to have, just after quenching, a structure consisting of austenite and at least 50% of martensite, the austenite content being such that the final structure can contain between 3% and 15% of residual austenite and between 85% and 97% of the sum of martensite and bainite without ferrite, then heated to a partitioning temperature PT between 370° C. and 470° C.

Abstract: A method for producing a high strength steel sheet having a yield strength YS of at least 850 MPa, a tensile strength TS of at least 1180 MPa, a total elongation of at least 14% and a hole expansion ratio HER of at least 30%. The chemical composition of the steel contains: 0.15%?C?0.25%, 1.2%?Si?1.8%, 2%?Mn?2.4%, 0.1%?Cr?0.25%, Nb?0.05%, Ti?0.05%, Al?0.50%, the remainder being Fe and unavoidable impurities. The sheet is annealed at an annealing temperature TA higher than Ac3 but less than 1000° C. for more than 30 s, by cooling it to a quenching temperature QT between 275° C. and 325° C., at a cooling speed sufficient to have, just after quenching, a structure consisting of austenite and at least 50% of martensite, the austenite content en.) being such that the final structure can contain between 3% and 15% of residual austenite and between 85 and 97% of the sum of martensite and bainite, without ferrite, heated to a partitioning temperature PT between 420° C. and 470° C.

Abstract: A method for producing a high strength coated steel sheet having a yield strength YS of at least 800 MPa, a tensile strength TS of >1180 MPa, a total elongation >14% and a hole expansion ratio HER>30%. The steel contains in weight %: 0.13%?C?0.22%, 1.2%?Si?1.8%, 1.8%?Mn?2.2%, 0.10%?Mo?0.20%, Nb?0.05%, Al?0.5%, the remainder being Fe and unavoidable impurities. The sheet is annealed at a temperature TA higher than Ac3 but less than 1000° C. for more than 30 s, then quenched by cooling temperature QT between 325° C. and 375° C., at a cooling speed sufficient to obtain a structure consisting of austenite and at least 60% of martensite, the austenite content being such that the fmal structure can contain between 3% and 15% of residual austenite and between 85 and 97% of the sum of martensite and bainite, without ferrite, then heated to a partitioning temperature PT between 430° C. and 480° C.

Abstract: A cold rolled, annealed TRIP steel sheet which has a composition including (in wt. %): C: 0.1-0.3; Mn: 4-10, Al: 0.05-5, Si: 0.05-5; and Nb: 0.008-0.1, the remainder being iron and inevitable residuals. The cold rolled sheet has an ultimate tensile strength of at least 1000 MPa, and a total elongation of at least 15%. The cold rolled sheet may have at least 20% retained austenite in its microstructure and may have greater than 50% lath-type annealed ferrite structure. The cold rolled sheet may have an ultra fine grain size of less than 5 micron for the retained austenite and ferrite.

Abstract: A dual phase steel (martensite+ferrite) having a tensile strength of at least 980 MPa, and a total elongation of at least 15%. The dual phase steel may have a total elongation of at least 18%. The dual phase steel may also have a tensile strength of at least 1180 MPa. The dual phase steel may include between 0.5-3.5 wt. % Si, and more preferably between 1.5-2.5 wt. % Si.

Abstract: A cold rolled, annealed TRIP steel sheet which has a composition including (in wt. %): C: 0.1-0.3; Mn: 4-10, Al: 0.05-5, Si: 0.05-5; and Nb: 0.008-0.1, the remainder being iron and inevitable residuals. The cold rolled sheet has an ultimate tensile strength of at least 1000 MPa, and a total elongation of at least 15%. The cold rolled sheet may have at least 20% retained austenite in its microstructure and may have greater than 50% lath-type annealed ferrite structure. The cold rolled sheet may have an ultra fine grain size of less than 5 micron for the retained austenite and ferrite.