# US 11,898,230 B2 · High-strength steel sheet and method for manufacturing same > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 11,898,230 B2 - Document ID: US11898230B2 - Status: Granted - Kind: B2 - Application number: 17/269,312 - Filed: 2019-06-10 - Published: 2021-06-17 - Granted: 2024-02-13 - Earliest claimed: 2018-08-22 - Assignees: Jfe Steel Corporation - Applicants: JFE Steel Corporation - Inventors: Shimpei Yoshioka; Yoshihiko Ono - Web page: https://patentgrep.com/patent/US11898230B2 ## CPC - C22C 38/06: containing aluminium - C21D 1/74: Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material - C21D 8/0226: {Hot rolling} - C21D 8/0236: {Cold rolling} - C21D 8/0263: {following hot rolling} - C21D 8/0273: {Final recrystallisation annealing} - C21D 8/0426: {Hot rolling} - C21D 8/0463: {following hot rolling} - C21D 8/0473: {Final recrystallisation annealing} - C21D 9/46: for sheet metals - C22C 38/00: Ferrous alloys, e.g. steel alloys (cast-iron alloys C22C37/00) - C22C 38/002: {containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60} - C22C 38/02: containing silicon - C22C 38/04: containing manganese - C21D 2211/001: Austenite - C21D 2211/002: Bainite - C21D 2211/005: Ferrite - C21D 2211/008: Martensite - 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 38/54: with boron - C22C 38/60: containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur - Y02P 10/20: Recycling - C22C: ALLOYS (treatment of alloys C21D, C22F) - 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) - Y02P: CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS ## Abstract A high-strength steel sheet according to the present invention includes a specific chemical composition, and a steel structure in which a total area fraction of martensite and bainite in a position of ¼ of a sheet thickness is 95% or more and 100% or less, the balance in a case where the total area fraction is not 100% contains retained austenite, and an area fraction of ferrite in a region extending up to 10 μm in a sheet thickness direction from a surface is 10% or more and 40% or less, in which a tensile strength is 1320 MPa or more, and a Vickers hardness in a position of 15 μm in the sheet thickness direction from the surface satisfies a specified formula. ## Claims ### Claim 1 A high-strength steel sheet comprising: a chemical composition containing, in mass %, C: 0.13% or more and less than 0.40%, Si: 0.01% or more and 1.0% or less, Mn: 1.7% or less (excluding 0%), P: 0.030% or less, S: 0.010% or less, Al: 0.20% or less (excluding 0%), N: 0.010% or less, and the balance being Fe and incidental impurities; and a steel structure in which a total area fraction of martensite and bainite in a position of ¼ of a sheet thickness is 95% or more and 100% or less, the balance in a case where the total area fraction is not 100% contains retained austenite, and an area fraction of ferrite in a region extending up to 10 μm in a sheet thickness direction from a surface is 13% or more and 40% or less, wherein a tensile strength is 1320 MPa or more, and a Vickers hardness in a position of 15 μm in the sheet thickness direction from the surface satisfies a formula (1) below, Hv≥0.294×σ (1) where Hv represents a Vickers hardness in the position of 15 μm in the sheet thickness direction from the surface, and a represents a tensile strength (MPa). ### Claim 2 (depends on 1) The high-strength steel sheet according to claim 1, wherein the chemical composition further contains, in mass %, at least one of Mo: 0.005% or more and 0.3% or less, Cr: 0.01% or more and 1.0% or less, Nb: 0.001% or more and 0.10% or less, Ti: 0.001% or more and 0.10% or less, B: 0.0002% or more and 0.0050% or less, Sb: 0.001% or more and 0.1% or less, Ca: 0.0002% or more and 0.0040% or less, V: 0.003% or more and 0.45% or less, Cu: 0.005% or more and 0.50% or less, Ni: 0.005% or more and 0.50% or less, and Sn: 0.002% or more and 0.1% or less. ### Claim 3 (depends on 1) A method for manufacturing a high-strength steel sheet, the method comprising: a continuous annealing step of, under a condition where a dew point in a temperature region of 750° C. or more is −35° C. or less, holding a cold rolled steel sheet having the chemical composition according to claim 1 at an annealing temperature of 840° C. or more for 180 seconds or more and cooling the cold rolled steel sheet at a cooling start temperature of 740° C. or more and at an average cooling rate of 100° C./s or more through a temperature region from the cooling start temperature to 150° C.; and an overaging treatment step of, after the continuous annealing step, performing reheating as necessary and performing holding in a temperature region of 150 to 260° C. for 30 to 1500 seconds. ### Claim 4 (depends on 2) A method for manufacturing a high-strength steel sheet, the method comprising: a continuous annealing step of, under a condition where a dew point in a temperature region of 750° C. or more is −35° C. or less, holding a cold rolled steel sheet having the chemical composition according to claim 2 at an annealing temperature of 840° C. or more for 180 seconds or more and cooling the cold rolled steel sheet at a cooling start temperature of 740° C. or more and at an average cooling rate of 100° C./s or more through a temperature region from the cooling start temperature to 150° C.; and an overaging treatment step of, after the continuous annealing step, performing reheating as necessary and performing holding in a temperature region of 150 to 260° C. for 30 to 1500 seconds.