# US 12,180,593 B2 · High strength steel sheet, impact absorbing member, and method for manufacturing high strength steel sheet > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 12,180,593 B2 - Document ID: US12180593B2 - Status: Granted - Kind: B2 - Application number: 17/766,398 - Filed: 2020-09-25 - Published: 2024-02-15 - Granted: 2024-12-31 - Earliest claimed: 2019-10-11 - Assignees: Jfe Steel Corporation - Applicants: JFE Steel Corporation - Inventors: Yoshiyasu Kawasaki; Yuki Toji; Muneka Iwasawa; Takayuki Futatsuka; Kentaro Sato - Web page: https://patentgrep.com/patent/US12180593B2 ## CPC - C23C 2/024: {by cleaning or etching} - C21D 1/18: Hardening (C21D1/02 takes precedence); Quenching with or without subsequent tempering (quenching devices C21D1/62) - C21D 6/001: {containing Ni (C21D6/004 takes precedence)} - C21D 6/002: {containing Cr (C21D6/004 takes precedence)} - C21D 6/005: {containing Mn} - C21D 6/008: {containing Si} - C21D 8/02: during manufacturing of plates or strips (C21D8/12 takes precedence) - C21D 8/021: involving particular fabrication steps or treatments of ingots or slabs - C21D 8/0226: {Hot rolling} - C21D 8/0236: {Cold rolling} - C21D 8/0263: {following hot rolling} - C21D 8/0273: {Final recrystallisation annealing} - C21D 8/0278: involving a particular surface treatment (C21D8/0294 takes precedence) - C21D 8/0426: {Hot rolling} - C21D 8/0436: {Cold rolling} - C21D 8/0463: {following hot rolling} - C21D 8/0473: {Final recrystallisation annealing} - C21D 8/0478: {involving a particular surface treatment (C21D8/0494 takes precedence)} - C21D 9/46: for sheet metals - C22C 38/00: Ferrous alloys, e.g. steel alloys (cast-iron alloys C22C37/00) - 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 38/005: {containing rare earths, i.e. Sc, Y, Lanthanides} - C22C 38/008: {containing tin} - C22C 38/02: containing silicon - C22C 38/04: containing manganese - C22C 38/06: containing aluminium - C22C 38/08: containing nickel {(C22C38/105 takes precedence)} - C22C 38/12: containing tungsten, tantalum, molybdenum, vanadium, or niobium - C22C 38/14: containing titanium or zirconium - C22C 38/16: containing copper - C22C 38/38: with more than 1.5% by weight of manganese - C22C 38/60: containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur - 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 2/06: Zinc or cadmium or alloys based thereon - C23C 2/12: Aluminium or alloys based thereon - C23C 2/28: Thermal after-treatment, e.g. treatment in oil bath - C23C 2/40: Plates; Strips - C25D 3/22: of zinc - C25D 5/36: of iron or steel - C25D 5/50: by heat-treatment - C25D 7/0614: {Strips or foils} - C21D 2211/001: Austenite - C21D 2211/002: Bainite - C21D 2211/005: Ferrite - C21D 2211/008: Martensite - 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) - 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) - C22C: ALLOYS (treatment of alloys C21D, C22F) - C25D: PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR ## Abstract A high strength steel sheet has a yield-point elongation of 1% or greater and a tensile strength of 980 MPa or greater. The high strength steel sheet has a specific chemical composition and microstructure. A ratio of retained austenite grains adjoining a retained austenite grain having a different crystal orientation to total retained austenite grains is 0.60 or greater, the ferrite has an average grain size of 5.0 μm or less, and the retained austenite has an average grain size of 2.0 μm or less. A value obtained by dividing a volume fraction Vγa by a volume fraction Vγb is 0.40 or greater, where the volume fraction Vγa is a volume fraction of retained austenite in a fractured portion of a tensile test specimen after a warm tensile test at 150° C., and the volume fraction Vγb is a volume fraction of retained austenite before the warm tensile test at 150° C. ## Claims ### Claim 1 A high strength steel sheet, the high strength steel sheet having a yield-point elongation (YP-EL) of 1% or greater and a tensile strength (TS) of 980 MPa or greater and 1020 MPa or less, the high strength steel sheet having a chemical composition containing, in mass %, C: 0.030% or greater and 0.250% or less, Si: 0.01% or greater and 2.00% or less, Mn: 3.10% or greater and 6.00% or less, P: 0.001% or greater and 0.100% or less, S: 0.0001% or greater and 0.0200% or less, N: 0.0005% or greater and 0.0100% or less, and Al: 0.001% or greater and 1.200% or less, with a balance of Fe and incidental impurities, and the high strength steel sheet having the microstructure in which ferrite is present in an area fraction of 30.0% or greater and less than 80.0%, martensite is present in an area fraction of 3.0% or greater and 30.0% or less, bainite is present in an area fraction of 0% or greater and 3.0% or less, retained austenite is present in a volume fraction of 12.0% or greater and 19.9% or less, a ratio of the number of retained austenite grains adjoining a retained austenite grain having a different crystal orientation to the total number of retained austenite grains is 0.60 or greater, the ferrite has an average grain size of 5.0 μm or less, the retained austenite has an average grain size of 2.0 μm or less, and a value obtained by dividing a Mn content (mass %) of the retained austenite by a Mn content (mass %) of the high strength steel sheet is 1.50 or greater, wherein the value obtained by dividing a volume fraction Vγa by a volume fraction Vγb is 0.40 or greater, where the volume fraction Vγa is a volume fraction of retained austenite in a fractured portion of a tensile test specimen after a warm tensile test at 150° C., and the volume fraction Vγb is a volume fraction of retained austenite before the warm tensile test at 150° C. ### Claim 2 (depends on 1) The high strength steel sheet according to claim 1, the high strength steel sheet having a yield-point elongation (YP-EL) of 1% or greater, wherein the chemical composition contains, in mass %, at least one element selected from Ti: 0.002% or greater and 0.200% or less, Nb: 0.005% or greater and 0.200% or less, V: 0.005% or greater and 0.500% or less, W: 0.0005% or greater and 0.500% or less, B: 0.0003% or greater and 0.0050% or less, Ni: 0.005% or greater and 1.000% or less, Cr: 0.005% or greater and 1.000% or less, Mo: 0.005% or greater and 1.000% or less, Cu: 0.005% or greater and 1.000% or less, Sn: 0.002% or greater and 0.200% or less, Sb: 0.002% or greater and 0.200% or less, Ta: 0.001% or greater and 0.100% or less, Zr: 0.0005% or greater and 0.0050% or less, Ca: 0.0005% or greater and 0.0050% or less, Mg: 0.0005% or greater and 0.0050% or less, and REM: 0.0005% or greater and 0.0050% or less. ### Claim 3 (depends on 1) The high strength steel sheet according to claim 1, the high strength steel sheet having a yield-point elongation (YP-EL) of 1% or greater, wherein the high strength steel sheet has a zinc coated layer on a surface of a steel sheet. ### Claim 4 (depends on 2) The high strength steel sheet according to claim 2, the high strength steel sheet having a yield-point elongation (YP-EL) of 1% or greater, wherein the high strength steel sheet has a zinc coated layer on a surface of a steel sheet. ### Claim 5 (depends on 1) An impact absorbing member, the impact absorbing member comprising an impact absorbing portion that absorbs impact energy by undergoing bending crush and deformation, the impact absorbing portion comprising the high strength steel sheet according to claim 1. ### Claim 6 (depends on 2) An impact absorbing member, the impact absorbing member comprising an impact absorbing portion that absorbs impact energy by undergoing bending crush and deformation, the impact absorbing portion comprising the high strength steel sheet according to claim 2. ### Claim 7 (depends on 3) An impact absorbing member, the impact absorbing member comprising an impact absorbing portion that absorbs impact energy by undergoing bending crush and deformation, the impact absorbing portion comprising the high strength steel sheet according to claim 3. ### Claim 8 (depends on 4) An impact absorbing member, the impact absorbing member comprising an impact absorbing portion that absorbs impact energy by undergoing bending crush and deformation, the impact absorbing portion comprising the high strength steel sheet according to claim 4. ### Claim 9 (depends on 1) An impact absorbing member, the impact absorbing member comprising an impact absorbing portion that absorbs impact energy by undergoing axial crush and deformation into a bellows shape, the impact absorbing portion comprising the high strength steel sheet according to claim 1. ### Claim 10 (depends on 2) An impact absorbing member, the impact absorbing member comprising an impact absorbing portion that absorbs impact energy by undergoing axial crush and deformation into a bellows shape, the impact absorbing portion comprising the high strength steel sheet according to claim 2. ### Claim 11 (depends on 3) An impact absorbing member, the impact absorbing member comprising an impact absorbing portion that absorbs impact energy by undergoing axial crush and deformation into a bellows shape, the impact absorbing portion comprising the high strength steel sheet according to claim 3. ### Claim 12 (depends on 4) An impact absorbing member, the impact absorbing member comprising an impact absorbing portion that absorbs impact energy by undergoing axial crush and deformation into a bellows shape, the impact absorbing portion comprising the high strength steel sheet according to claim 4. ### Claim 13 (depends on 1) A method for manufacturing the high strength steel sheet according to claim 1, the method comprising: performing a pickling process on a hot rolled steel sheet; holding a resulting steel sheet within a temperature range of an Ac1 transformation temperature or greater and “the Ac1 transformation temperature+150° C.” or less for a period of more than 21,600 seconds and 259,200 seconds or less, subsequently cooling the resulting steel sheet at an average cooling rate of 5° C./hour or greater and 200° C./hour or less through a temperature range of 550° C. to 400° C., subsequently cold rolling the resulting steel sheet, holding a resulting cold rolled steel sheet within a temperature range of an Ac3 transformation temperature or greater for a period of 20 seconds or more, and subsequently holding the resulting cold rolled steel sheet within a temperature range of the Ac1 transformation temperature or greater and “the Ac1 transformation temperature+150° C.” or less for a period of 20 seconds or more and 900 seconds or less. ### Claim 14 (depends on 2) A method for manufacturing the high strength steel sheet according to claim 2, the method comprising: performing a pickling process on a hot rolled steel sheet; holding a resulting steel sheet within a temperature range of an Ac1 transformation temperature or greater and “the Ac1 transformation temperature+150° C.” or less for a period of more than 21,600 seconds and 259,200 seconds or less, subsequently cooling the resulting steel sheet at an average cooling rate of 5° C./hour or greater and 200° C./hour or less through a temperature range of 550° C. to 400° C., subsequently cold rolling the resulting steel sheet, holding a resulting cold rolled steel sheet within a temperature range of an Ac3 transformation temperature or greater for a period of 20 seconds or more, and subsequently holding the resulting cold rolled steel sheet within a temperature range of the Ac1 transformation temperature or greater and “the Ac1 transformation temperature+150° C.” or less for a period of 20 seconds or more and 900 seconds or less. ### Claim 15 (depends on 3) A method for manufacturing the high strength steel sheet according to claim 3, the method comprising: performing a pickling process on a hot rolled steel sheet; holding a resulting steel sheet within a temperature range of an Ac1 transformation temperature or greater and “the Ac1 transformation temperature+150° C.” or less for a period of more than 21,600 seconds and 259,200 seconds or less; subsequently cooling the resulting steel sheet at an average cooling rate of 5° C./hour or greater and 200° C./hour or less through a temperature range of 550° C. to 400° C.; subsequently cold rolling the resulting steel sheet; holding a resulting cold rolled steel sheet within a temperature range of an Ac3 transformation temperature or greater for a period of 20 seconds or more; subsequently holding the resulting cold rolled steel sheet within a temperature range of the Ac1 transformation temperature or greater and “the Ac1 transformation temperature+150° C.” or less for a period of 20 seconds or more and 900 seconds or less; and subsequently performing a hot-dip galvanizing process or an electrogalvanizing process on the resulting cold rolled steel sheet. ### Claim 16 (depends on 4) A method for manufacturing the high strength steel sheet according to claim 4, the method comprising: performing a pickling process on a hot rolled steel sheet; holding a resulting steel sheet within a temperature range of an Ac1 transformation temperature or greater and “the Ac1 transformation temperature+150° C.” or less for a period of more than 21,600 seconds and 259,200 seconds or less; subsequently cooling the resulting steel sheet at an average cooling rate of 5° C./hour or greater and 200° C./hour or less through a temperature range of 550° C. to 400° C.; subsequently cold rolling the resulting steel sheet; holding a resulting cold rolled steel sheet within a temperature range of an Ac3 transformation temperature or greater for a period of 20 seconds or more; subsequently holding the resulting cold rolled steel sheet within a temperature range of the Ac1 transformation temperature or greater and “the Ac1 transformation temperature+150° C.” or less for a period of 20 seconds or more and 900 seconds or less; and subsequently performing a hot-dip galvanizing process or an electrogalvanizing process on the resulting cold rolled steel sheet.