# US 2020/0399733 A1 · Method for manufacturing a high-strength steel sheet and sheet obtained by the method > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2020/0399733 A1 - Document ID: US20200399733A1 - Status: Published application - Kind: A1 - Application number: 17/013,452 - Filed: 2020-09-04 - Published: 2020-12-24 - Earliest claimed: 2014-07-03 - Assignees: ArcelorMittal - Applicants: ArcelorMittal - Inventors: Wei XU; Artem ARLAZAROV - Web page: https://patentgrep.com/patent/US20200399733A1 ## CPC - C21D 9/46: for sheet metals - B32B 15/013: {one layer being formed of an iron alloy or steel, another layer being formed of a metal other than iron or aluminium} - C21D 1/19: by interrupted quenching - C21D 1/25: Hardening, combined with annealing between 300 degrees Celsius and 600 degrees Celsius, i.e. heat refining ("Vergüten") - C21D 6/005: {containing Mn} - C21D 8/02: during manufacturing of plates or strips (C21D8/12 takes precedence) - C21D 8/0221: characterised by the working steps - C21D 8/0247: characterised by the heat treatment - C21D 8/0263: {following hot rolling} - C21D 8/0273: {Final recrystallisation annealing} - C22C 38/02: containing silicon - C22C 38/04: containing manganese - C22C 38/06: containing aluminium - C23C 2/06: Zinc or cadmium or alloys based thereon - C23C 2/40: Plates; Strips - C21D 2211/001: Austenite - C21D 2211/002: Bainite - C21D 2211/005: Ferrite - C21D 2211/008: Martensite - C21D: MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING (surface treatment of metallic material involving at least one process provided for in class C23 and at least one process covered by this subclass C23F17/00; unidirectional solidification of eutectic materials or unidirectional demixing of eutectoid materials C30B) - B32B: LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM - C22C: ALLOYS (treatment of alloys C21D, C22F) - C23C: COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL (making metal-coated products by extrusion B21C23/22; covering with metal by connecting pre-existing layers to articles, see the relevant places, e.g. B21D39/00, B23K; metallising of glass C03C; metallising mortars, concrete, artificial stone, ceramics or natural stone C04B41/00; enamelling of, or applying a vitreous layer to, metals C23D; treating metal surfaces or coating of metals by electrolysis or electrophoresis C25D; single-crystal film growth C30B; by metallising textiles D06M11/83; decorating textiles by locally metallising D06Q1/04) ## Abstract A method is for manufacturing a high-strength steel sheet having a tensile strength of more than 1100 MPa and a yield strength of more than 700 MPa, a uniform elongation UE of at least 8.0% and a total elongation of at least 10%, made of a steel containing in percent by weight: 0.1%≤C≤0.25%, 4.5%≤Mn≤10%, 1%≤Si≤3%, 0.03%≤Al≤2.5%, the remainder being Fe and impurities resulting from the smelting, the composition being such that CMnIndex=C×(1+Mn/3.5)≤0.6. The method includes annealing a rolled sheet made of said steel by soaking it at an annealing temperature TA higher than the Ac1 transformation point of the steel but less than 1000° C., cooling the annealed sheet to a quenching temperature QT between 190° C. and 80° C. at a cooling speed sufficient to obtain a structure just after cooling containing martensite and retained austenite, maintaining the steel sheet at an overaging temperature PT between 350° C. and 500° C. for an overaging time Pt of more than 5 s cooling the sheet down to the ambient temperature. ## Claims ### Claim 1 A method for manufacturing a steel sheet having a tensile strength of more than 1100 MPa, a yield strength of more than 700 MPa, a uniform elongation UE of at least 8.0% and a total elongation of at least 10.0%, comprising: providing a steel having a chemical composition containing in percent by weight: 0.15%≤C≤0.25%; 4.5%≤Mn≤5.5%; 1.4%≤Si≤1.8%; and 0.03%≤Al≤2.5%; a remainder being Fe and impurities resulting from the smelting, and the chemical composition including a CMnIndex=C×(1+Mn/3.5)≤0.6; annealing a rolled sheet made of the steel by soaking the rolled sheet at an annealing temperature TA higher than the Ac1 transformation point of the steel but less than 1000° C. and less than the Ac3 transformation point of the steel, to obtain an annealed sheet; cooling the annealed sheet to a quenching temperature QT between 110° and 170° C., at a cooling speed sufficient to obtain a quenched sheet having a structure just after cooling including martensite and retained austenite; maintaining the quenched sheet at an overaging temperature PT between 350° C. and 500° C. for an overaging time Pt between 5 s and 600 s; cooling the steel sheet down to ambient temperature; the steel sheet having a final structure including at least 15% of ferrite, at least 50% of martensite and at least 15% of retained austenite. ### Claim 2 (depends on 1) The method according to claim 1, wherein the chemical composition of the steel includes 0.03%≤Al≤0.5%. ### Claim 3 (depends on 2) The method according to claim 2, wherein the chemical composition of the steel includes Si+Al≥1.4%. ### Claim 4 (depends on 1) The method according to claim 1, wherein the chemical composition of the steel is includes 1.4%≤Al≤2.5%. ### Claim 5 (depends on 1) The method according to claim 1, wherein the overaging temperature PT is between 440° C. and 470° C. and the overaging time Pt is between 5 s and 60 s. ### Claim 6 (depends on 5) The method according to claim 5, wherein at least part of maintaining the quenched sheet at the overaging temperature PT includes passing the quenched sheet in a hot dip coating bath. ### Claim 7 (depends on 6) The method according to claim 6, further comprising, after passing the sheet in the hot dip coating bath and before cooling to ambient temperature, maintaining the steel sheet at a temperature between 480° C. and 570° C. ### Claim 8 (depends on 1) The method according to claim 1, wherein the annealing, the quenching and the overaging are performed on a continuous heat treatment line. ### Claim 9 (depends on 1) The method according to claim 1, wherein the rolled sheet is prepared by rolling and wherein rolling includes hot rolling and cold rolling. ### Claim 10 A steel sheet having a tensile strength of more than 1100 MPa, a yield strength of more than 700 MPa, a uniform elongation UE of at least 8.0% and a total elongation TE of at least 10.0%, comprising: a steel having a chemical composition including, in weight percent: 0.15%≤C≤0.25%; 4.5%≤Mn≤5.5%; 1.4≤Si≤1.8%; and 0.03≤Al≤2.5%; a remainder being Fe and impurities resulting from the smelting, and the chemical composition including a CMnIndex=C×(1+Mn/3.5)≤0.6; a structure including at least 15% of ferrite, at least 50% of martensite and at least 15% of retained austenite. ### Claim 11 (depends on 10) The steel sheet according to claim 10, wherein the chemical composition of the steel includes 0.03%≤Al≤0.5%. ### Claim 12 (depends on 11) The steel sheet according to claim 11, wherein the chemical composition of the steel includes Si+Al≥1.4%. ### Claim 13 (depends on 10) The steel sheet according to claim 10, wherein the chemical composition of the steel includes 1.4%≤Al≤2.5%. ### Claim 14 (depends on 10) The steel sheet according to claim 10, wherein at least one face of the steel sheet comprises a metallic coating. ### Claim 15 (depends on 10) The steel sheet according to claim 10, wherein at least a fraction of the martensite being partitioned. ### Claim 16 (depends on 10) The steel sheet according to claim 10, wherein the at least 50% of martensite are partitioned martensite.