# US 11,078,555 B2 · Austenitic, low-density, high-strength steel strip or sheet having a high ductility, method for producing said steel and use thereof > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 11,078,555 B2 - Document ID: US11078555B2 - Status: Granted - Kind: B2 - Application number: 16/078,081 - Filed: 2017-02-28 - Published: 2019-02-21 - Granted: 2021-08-03 - Earliest claimed: 2016-03-01 - Assignees: Tata Steel Nederland Technology B.V. - Applicants: Tata Steel Nederland Technology B.V. - Inventors: Shangping Chen; Arunansu Haldar; Alireza Saeed-Akbari; Richard Mostert - Web page: https://patentgrep.com/patent/US11078555B2 ## CPC - C21D 9/52: for wires; for strips {; for rods of unlimited length} - B32B 15/01: all layers being exclusively metallic {(making layered metal workpieces by pressure cladding B23K20/22; making coatings with a metallic material characterised by its composition C23C30/00)} - C21D 6/004: {containing Cr and Ni} - C21D 6/005: {containing Mn} - C21D 6/008: {containing Si} - C21D 6/04: Hardening by cooling below 0 degrees Celsius - C21D 8/02: during manufacturing of plates or strips (C21D8/12 takes precedence) - C21D 8/0226: {Hot rolling} - C21D 8/0236: {Cold rolling} - C21D 8/0247: characterised by the heat treatment - C21D 8/0273: {Final recrystallisation annealing} - C21D 9/46: for sheet metals - C22C 38/001: {containing N} - C22C 38/002: {containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60} - C22C 38/008: {containing tin} - C22C 38/02: containing silicon - C22C 38/04: containing manganese - C22C 38/06: containing aluminium - C22C 38/20: with copper - C22C 38/24: with vanadium - C22C 38/26: with niobium or tantalum - C22C 38/28: with titanium or zirconium - C22C 38/38: with more than 1.5% by weight of manganese - C22C 38/40: with nickel - C22C 38/42: with copper - C22C 38/44: with molybdenum or tungsten - C22C 38/46: with vanadium - C22C 38/48: with niobium or tantalum - C22C 38/50: with titanium or zirconium - C22C 38/58: with more than 1.5% by weight of manganese - C23C 2/02: Pretreatment of the material to be coated, e.g. for coating on selected surface areas (C23C2/30 takes precedence) - C23C 2/0224: {Two or more thermal pretreatments} - C23C 2/024: {by cleaning or etching} - C23C 2/06: Zinc or cadmium or alloys based thereon - C23C 2/12: Aluminium or alloys based thereon - C23C 2/29: {Cooling or quenching} - C23C 2/40: Plates; Strips - C25D 3/565: {containing more than 50% by weight of zinc} - C21D 2211/001: Austenite - C21D 2211/004: Dispersions; Precipitations - C21D 2211/005: Ferrite - 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) - C25D: PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR ## Abstract An austenitic, low-density, high-strength steel strip or sheet having a high ductility, and a method of producing the steel strip or sheet, and for its use. ## Claims ### Claim 1 An austenitic, low-density, high-strength steel strip or sheet having a high ductility, having an element composition consisting of in wt. %: 0.65-0.9% C; 0-0.09% Si; 5.0-20.0% Mn; 5.5-9.9% Al; 0.001-0.05% N; 0.02% or less P; 0.02% or less S; optionally one or more of: 0.001-0.01% Ca; 0-0.5% V; 0.01-0.2% Ti; 0-0.2% Nb; 0-0.14% Cr; 0-0.2% Zr; 0-2.0% Cu; 0-0.0050% B; 0-1.0% Mo; 0-0.2% Sb; the balance Fe with unavoidable impurities, having a microstructure comprising 94 to 100 area % of austenite, 6 to 0 area % of ferrite, and 0 to 5 area % of a κ-(Fe,Mn)3AlC-carbide phase, the strip or sheet having a yield ratio YS/UTS of at least 0.60, and a ratio of Mn/Si>40, the steel strip or sheet having a density of 6.81 to 7.3g/cm3, a tensile strength of at least 750 MPa and an elongation at a gauge length of 50 mm of at least 25%. ### Claim 2 (depends on 1) The low-density high-strength steel according to claim 1, wherein the molybdenum content is at most 0.04%; and there is 0.01-0.2% Ti; and there is 0.05-2.0% Cu, and the steel strip or sheet density is 6.84 to 7.3 g/cm3. ### Claim 3 (depends on 1) The low-density high-strength steel according to claim 1, wherein carbides other than the γ-(Fe,Mn)3AlC-carbide are in an amount that is less than 1% in area, and the steel strip or sheet density is 7.0 to 7.3 g/cm3. ### Claim 4 (depends on 1) The low-density high-strength steel according to claim 1, further comprising M7C3, wherein the M7C3-carbides have a size that is less than 1 μm in diameter. ### Claim 5 (depends on 1) The low-density high-strength steel according to claim 1, wherein Mn/Si>50. ### Claim 6 (depends on 1) A method for producing an austenitic, low-density, high-strength steel strip or sheet having a high ductility according to claim 1, having a ratio of Mn/Si>40; balance iron and unavoidable impurities; wherein Ni is at most an impurity; the method comprising: producing a thick or thin slab by continuous casting, ingot casting or strip casting; (re-)heating or homogenising the temperature of the slab, ingot or strip to between 1050 and 1250° C.; a first hot rolling at a hot-rolling start temperature of more than 1050° C. to a total reduction of higher than 50% a second hot rolling to the final hot-rolling thickness wherein the finish rolling temperature is higher than 850° C.; followed by (1) cooling to a temperature of lower than 200° C. with a cooling rate higher than 1° C./s followed by coiling the strip, or (2) cooling to a temperature in the range of 450 to 700° C. with a cooling rate higher than 15° C./s followed by coiling the strip and annealing the strip at a temperature between 800 and 1100° C., followed by cooling to a temperature of lower than 200° C. with a cooling rate higher than 1° C./s. ### Claim 7 (depends on 6) The method according to claim 6, wherein Mn/Si>50. ### Claim 8 (depends on 6) The method according to claim 6, wherein the Mo content is at most 0.04%. ### Claim 9 (depends on 6) The method according to claim 6, wherein after the coiling of the hot-rolled steel sheet, the method further comprises: cold-rolling the coiled steel sheet at a total cold-rolling reduction ratio of 30% to 80%; after heating the cold-rolled steel sheet at a rate of 1° C./s to 50° C./s to an annealing temperature in a range of higher than 650 to 1100° C., for 5 seconds to 5 hours; cooling the annealed steel sheet at a rate of 1° C./s to 100° C./s. ### Claim 10 (depends on 6) The method according to claim 6, further comprising plating the steel sheet, on one or each side, with a metallic coating selected from Zn, Zn—Fe, Zn—Al, Zn—Mg, Zn—Al—Mg, Al—Si, and Al—Mg—Si, wherein the thickness of the coating layer or layers is between 10 and 200 μm. ### Claim 11 (depends on 1) A method of use of the steel strip or sheet according to claim 1 comprising producing an automotive part from the steel strip or sheet. ### Claim 12 (depends on 11) An automotive part produced according to claim 11. ### Claim 13 (depends on 1) The low-density high-strength steel according to claim 1, further comprising M7C3, wherein the M7C3 is in an amount that is less than 1% in area. ### Claim 14 (depends on 11) The method of claim 11, wherein the producing comprises forming the steel strip or sheet into the automotive part. ### Claim 15 (depends on 1) The low-density high-strength steel according to claim 1, wherein in the steel strip or sheet there is 5.5 to 9.9 wt. % Al, 0.01 to 0.09 wt. % Si, 0 to 0.015 wt. % S, 0.002 to 0.009 wt. % N, 0 to 0.09 wt. % Cr, 0 to 0.09 wt. % Mo, 0 to 0.04 wt. % V, 0 to 0.04 wt. % Nb, and 0 to 0.0030 wt. % B. ### Claim 16 (depends on 15) The low-density high-strength steel according to claim 15, wherein in the steel strip or sheet there is 0.001 to 0.01 wt. % Ca. ### Claim 17 (depends on 15) The low-density high-strength steel according to claim 15, wherein in the steel strip or sheet there is 0.01 to 0.04 wt. % Ti. ### Claim 18 (depends on 6) The method according to claim 6, wherein the steel strip or sheet there is 5.5 to 9.9 wt. % Al, 0.01 to 0.09 wt. % Si, 0 to 0.015 wt. % S, 0.002 to 0.009 wt. % N, 0 to 0.09 wt. % Cr, 0 to 0.09 wt. % Mo, 0 to 0.04 wt. % V, 0 to 0.04 wt. % Nb, and 0 to 0.0030 wt. % B. ### Claim 19 (depends on 15) The low-density high-strength steel according to claim 15, wherein in the steel strip or sheet there is 0 to 0.06 wt. % Si. ### Claim 20 (depends on 1) The low-density high-strength steel according to claim 1, wherein, in the steel strip or sheet, wherein Cu content is 0.5-2.0 wt. %.