Patents by Inventor Tatsuya Nakagaito

Tatsuya Nakagaito has filed for patents to protect the following inventions. This listing includes patent applications that are pending as well as patents that have already been granted by the United States Patent and Trademark Office (USPTO).

  • Publication number: 20240035105
    Abstract: Provided is a hot-dip galvanized steel sheet having both high strength and good workability, as well as excellent coating quality. The chemical composition of the base steel sheet is set within a specified range, the steel microstructure of the base steel sheet is a complex structure of ferrite, martensite and bainite, oxygen is present as oxides in the surface layer of the base steel sheet in an amount of 0.05 g/m2 or more and 0.50 g/m2 or less per surface, and the hot-dip galvanized layer contains Fe in an amount of 0.40 mass % or more.
    Type: Application
    Filed: December 15, 2021
    Publication date: February 1, 2024
    Applicant: JFE STEEL CORPORATION
    Inventors: Takuya HIRASHIMA, Tatsuya NAKAGAITO, Masaki KOBA, Yoichi MAKIMIZU, Katsuya HATA, Shotaro TERASHIMA
  • Publication number: 20240026481
    Abstract: Provided is a steel sheet having excellent workability while ensuring excellent strength. The steel sheet comprises: a predetermined chemical composition; and a steel microstructure that contains ferrite: 45% to 90%, martensite: 5% to 30%, bainite: 1% to 25%, and retained austenite: 3% or more and in which [Mn]M/[Mn] is 1.00 to 1.15 and [Mn]M/[Mn]F is 1.00 to 1.30, wherein TS×El is 16000 MPa·% or more.
    Type: Application
    Filed: December 15, 2021
    Publication date: January 25, 2024
    Applicant: JFE STEEL CORPORATION
    Inventors: Takuya HIRASHIMA, Tatsuya NAKAGAITO, Masaki KOBA, Kyoko NAITO, Seisuke TSUDA, Katsuya HATA, Shotaro TERASHIMA
  • Publication number: 20230349019
    Abstract: A steel sheet according to the present invention has a specific chemical composition and a steel microstructure including, in terms of area fraction, ferrite: 60% or more and 85% or less, bainite: 3% or more and 15% or less, retained austenite: 3% or more and 15% or less, fresh martensite: 3% or more and 15% or less, and the remainder: 5% or less. Cementite particles are present in the retained austenite, a ratio of an area fraction of the cementite particles in the retained austenite to an area fraction of the retained austenite is 5% or more and 25% or less, and the steel sheet has a tensile strength of 590 MPa or more and less than 780 MPa.
    Type: Application
    Filed: February 24, 2021
    Publication date: November 2, 2023
    Applicant: JFE Steel Corporation
    Inventors: Yusuke Wada, Tatsuya Nakagaito, Shotaro Terashima, Lingling Yang, Takeshi Yokota, Shunsuke Yamamoto, Yuki Takeda
  • Publication number: 20230349020
    Abstract: A steel sheet according to the present invention has a specific chemical composition and a steel microstructure including, in terms of area fraction, ferrite: 40% or more and 70% or less, a total of bainite and tempered martensite: 5% or more and 30% or less, retained austenite: 4% or more and 18% or less, fresh martensite: 8% or more and 35% or less, and the remainder: 5% or less. Cementite particles are present in the retained austenite, a ratio of an area fraction of the cementite particles in the retained austenite to an area fraction of the retained austenite is 5% or more and 25% or less, and the steel sheet has a tensile strength of 780 MPa or more and less than 980 MPa.
    Type: Application
    Filed: February 24, 2021
    Publication date: November 2, 2023
    Applicant: JFE Steel Corporation
    Inventors: Yusuke Wada, Tatsuya Nakagaito, Shotaro Terashima, Lingling Yang, Takeshi Yokota
  • Patent number: 11795531
    Abstract: A high-strength galvanized steel sheet of the present invention includes a steel sheet having a specific chemical composition, and a steel structure containing, in terms of area ratio, 4% or more and 20% or less of retained austenite, 30% or less (including 0%) of ferrite, 40% or more of martensite, and 10% or more and 50% or less of bainite; and a galvanized layer provided on the steel sheet, in which an amount of diffusible hydrogen in the steel is less than 0.20 mass ppm, a tensile strength is 1100 MPa or more, a relationship between a tensile strength TS (MPa), an elongation El (%), and a sheet thickness t (mm) satisfies a (1) formula below, and a yield ratio YR is 67% or more. TS×(El+3?2.
    Type: Grant
    Filed: March 29, 2019
    Date of Patent: October 24, 2023
    Assignee: JFE Steel Corporation
    Inventors: Hiromi Yoshitomi, Yoshihiko Ono, Tatsuya Nakagaito
  • Publication number: 20230287553
    Abstract: A galvanized steel sheet including a steel sheet having a chemical composition with an equivalent carbon content Ceq of 0.60% or more and less than 0.85%, and a specified steel microstructure; and a galvanized layer on a surface of the steel sheet. The retained austenite has a solute C content of 0.6% or more by mass, and retained austenite grains with an aspect ratio of less than 2.0 constitute 50% or more of all retained austenite grains. In 90-degree bending at a curvature radius/thickness ratio of 4.2 in a rolling (L) direction with respect to an axis extending in a width (C) direction, an L cross section in a 0- to 50-µm region from a surface of the steel sheet on a compression side has a number density of voids of 1500 /mm2 or less, and the galvanized steel sheet has a tensile strength of 980 MPa or more.
    Type: Application
    Filed: June 30, 2021
    Publication date: September 14, 2023
    Applicant: JFE STEEL CORPORATION
    Inventors: Shinsuke KOMINE, Tatsuya NAKAGAITO, Kentaro SATO, Tomohiro SAKAIDANI
  • Publication number: 20230243014
    Abstract: A galvanized steel sheet includes: a steel sheet having a chemical composition satisfying an equivalent carbon content Ceq of 0.35% or more and less than 0.60%, and a specified steel microstructure; and a galvanized layer on a surface of the steel sheet. The retained austenite has a solute C content of 0.6% or more by mass, and retained austenite grains with an aspect ratio of less than 2.0 constitute 50% or more of all retained austenite grains. In 90-degree bending at a curvature radius/thickness ratio of 4.2 in a rolling (L) direction with respect to an axis extending in a width (C) direction, an L cross section in a 0 to 50 ?m region from a surface of the steel sheet on a compression side has a number density of voids of 1000/mm2 or less, and the galvanized steel sheet has a tensile strength of 590 MPa or more.
    Type: Application
    Filed: June 30, 2021
    Publication date: August 3, 2023
    Applicant: JFE STEEL CORPORATION
    Inventors: Shinsuke KOMINE, Tatsuya NAKAGAITO, Kentaro SATO, Tomohiro SAKAIDANI
  • Publication number: 20230220510
    Abstract: A steel sheet including a chemical composition satisfying an equivalent carbon content of 0.60% or more and less than 0.85%, and a steel microstructure with an area fraction of ferrite: less than 40%, tempered martensite and bainite: 40% or more in total, retained austenite: 3% to 15%, and ferrite, tempered martensite, bainite, and retained austenite: 93% or more in total. A 90-degree bending at a curvature radius/thickness ratio of 4.2 in a rolling (L) direction with respect to an axis extending in a width (C) direction causes a change of 0.40 or more in (a grain size in a thickness direction)/(a grain size in a direction perpendicular to the thickness) of the tempered martensite in an L cross section in a 0- to 50-?m region from a surface of the steel sheet on a compression side. The steel sheet has a tensile strength of 980 MPa or more.
    Type: Application
    Filed: June 30, 2021
    Publication date: July 13, 2023
    Applicant: JFE STEEL CORPORATION
    Inventors: Shinsuke KOMINE, Tatsuya NAKAGAITO, Kentaro SATO, Tomohiro SAKAIDANI
  • Publication number: 20230160032
    Abstract: A steel sheet having a tensile strength (TS) of 780 MPa or more and less than 1180 MPa, high LME resistance, and good weld fatigue properties. The steel sheet has a specific chemical composition and a specific steel microstructure. Crystal grains containing an oxide of Si and/or Mn in a region within 4.9 ?m in a thickness direction from a surface of the steel sheet have an average grain size in the range of 3 to 10 ?m, the lowest Si concentration LSi and the lowest Mn concentration LMn in the region within 4.9 ?m in the thickness direction from the surface of the steel sheet and a Si concentration TSi and a Mn concentration TMn at a quarter thickness position of the steel sheet satisfy a specified formula.
    Type: Application
    Filed: March 25, 2021
    Publication date: May 25, 2023
    Applicant: JFE STEEL CORPORATION
    Inventors: Lingling YANG, Yoshiyasu KAWASAKI, Hidekazu MINAMI, Tatsuya NAKAGAITO, Shotaro TERASHIMA, Shunsuke YAMAMOTO, Katsuya HOSHINO, Yuki TAKEDA
  • Publication number: 20230151451
    Abstract: A steel sheet with a tensile strength (TS) of 1180 MPa or more, a member, and a method for producing them. In a region of the steel sheet within 4.9 ?m in the thickness direction, a region with a Si concentration not more than one-third of the Si concentration in the chemical composition of the steel sheet and with a Mn concentration not more than one-third of the Mn concentration in the chemical composition of the steel sheet has a thickness of 1.0 ?m or more. The lowest Si concentration LSi and the lowest Mn concentration LMn in the region within 4.9 ?m in the thickness direction from the surface of the steel sheet and a Si concentration TSi and a Mn concentration TMn at a quarter thickness position of the steel sheet satisfy the following formula (1): LSi+LMn?(TSi+TMn)/4??(1).
    Type: Application
    Filed: March 25, 2021
    Publication date: May 18, 2023
    Applicant: JFE STEEL CORPORATION
    Inventors: Yoshiyasu KAWASAKI, Lingling YANG, Shotaro TERASHIMA, Tatsuya NAKAGAITO, Shunsuke YAMAMOTO, Katsuya HOSHINO, Yuki TAKEDA
  • Patent number: 11643701
    Abstract: The high-strength hot-dip galvanized steel sheet, which includes a hot-dip galvanized coating layer on a surface of the steel sheet, has a component composition containing, in mass %, C: 0.07% to 0.20%, Si: 0.1% to 2.0%, Mn: 2.0% to 3.5%, P: 0.05% or less, S: 0.05% or less, and sol. Al: 0.005% to 0.1%, with the balance being Fe and incidental impurities; and has a steel microstructure containing, in area fraction, 60% or less of ferrite, 40% or more of tempered martensite, and 10% or less of fresh martensite and having a void number density of 1,500/mm2 or less in a bent portion in the VDA bending test.
    Type: Grant
    Filed: October 18, 2019
    Date of Patent: May 9, 2023
    Assignee: JFE STEEL CORPORATION
    Inventors: Shinsuke Komine, Tatsuya Nakagaito, Kentaro Sato, Tomohiro Sakaidani
  • Publication number: 20230129828
    Abstract: A steel sheet with a tensile strength (TS) of 780 MPa or more and less than 1180 MPa, a member, and a method for producing them. In a region of the steel sheet within 4.9 ?m in the thickness direction, a region with a Si concentration not more than one-third of the Si concentration in the chemical composition of the steel sheet and with a Mn concentration not more than one-third of the Mn concentration in the chemical composition of the steel sheet has a thickness of 1.0 ?m or more. The lowest Si concentration LSi and the lowest Mn concentration LMn in the region within 4.9 ?m from the surface of the steel sheet and a Si concentration TSi and a Mn concentration TMn at a quarter thickness position of the steel sheet satisfy the following formula (1): LSi+LMn?(TSi+TMn)/4??(1).
    Type: Application
    Filed: March 25, 2021
    Publication date: April 27, 2023
    Applicant: JFE STEEL CORPORATION
    Inventors: Yoshiyasu KAWASAKI, Lingling YANG, Shotaro TERASHIMA, Hidekazu MINAMI, Tatsuya NAKAGAITO, Shunsuke YAMAMOTO, Katsuya HOSHINO, Yuki TAKEDA
  • Publication number: 20230127243
    Abstract: A steel sheet having a tensile strength (TS) of 1180 MPa or more, high LME resistance, and good weld fatigue properties. The steel sheet has a specific chemical composition and a specific steel microstructure. Crystal grains containing an oxide of Si and/or Mn in a region within 4.9 ?m in a thickness direction from a surface of the steel sheet have an average grain size in the range of 3 to 10 ?m, the lowest Si concentration LSi and the lowest Mn concentration LMn in the region within 4.9 ?m in the thickness direction from the surface of the steel sheet and a Si concentration TSi and a Mn concentration TMn at a quarter thickness position of the steel sheet satisfy a specified formula.
    Type: Application
    Filed: March 25, 2021
    Publication date: April 27, 2023
    Applicant: JFE STEEL CORPORATION
    Inventors: Lingling YANG, Yoshiyasu KAWASAKI, Tatsuya NAKAGAITO, Shotaro TERASHIMA, Shunsuke YAMAMOTO, Katsuya HOSHINO, Yuki TAKEDA
  • Publication number: 20230072557
    Abstract: A steel sheet according to the present invention has a specific chemical composition and a steel microstructure including, in terms of area fraction, ferrite: 20% or more and 60% or less, a total of bainite and tempered martensite: 25% or more and 60% or less, retained austenite: 7% or more and 20% or less, fresh martensite: 8% or more and 40% or less, and the remainder: 5% or less. Cementite particles are present in the retained austenite, a ratio of an area fraction of the cementite particles in the retained austenite to an area fraction of the retained austenite is 5% or more and 25% or less, and the steel sheet has a tensile strength of 980 MPa or more.
    Type: Application
    Filed: February 24, 2021
    Publication date: March 9, 2023
    Applicant: JFE Steel Corporation
    Inventors: Yusuke Wada, Tatsuya Nakagaito, Shotaro Terashima, Lingling Yang, Takeshi Yokota
  • Patent number: 11560614
    Abstract: A high-strength galvanized steel sheet includes a steel sheet having a chemical composition containing a predetermined component element, a mass ratio of a content of Si to a content of Mn in the steel (Si/Mn) being 0.1 or more and less than 0.2, and the balance: Fe and incidental impurities, and a steel structure in which an average grain size of inclusions containing at least one of Al, Si, Mg, and Ca and existing in an area extending from a surface to a position of ? of a sheet thickness is 50 ?m or less, and an average nearest distance between ones of the inclusions is 20 ?m or more; and a galvanized layer provided on a surface of the steel sheet, in which an amount of diffusible hydrogen contained in the steel is less than 0.25 mass ppm, and a tensile strength is 1100 MPa or more.
    Type: Grant
    Filed: March 29, 2019
    Date of Patent: January 24, 2023
    Assignee: JFE Steel Corporation
    Inventors: Hiromi Yoshitomi, Masaki Koba, Tatsuya Nakagaito, Yoshitsugu Suzuki
  • Patent number: 11530463
    Abstract: A high-strength galvanized steel sheet includes a steel sheet containing a predetermined component element, a mass ratio of a content amount of Si to a content amount of Mn in the steel (Si/Mn) being 0.2 or more, and a steel structure in which an average grain size of inclusions existing in an area extending from a surface to a position of ? of a sheet thickness is 50 ?m or less, and an average nearest distance between ones of the inclusions is 20 ?m or more; and a galvanized layer provided on a surface of the steel sheet, in which an amount of diffusible hydrogen contained in the steel is less than 0.25 mass ppm, oxides containing predetermined elements in an outer layer portion of the steel sheet account for 0.010 g/m2 or more per one surface, and a tensile strength is 1100 MPa or more.
    Type: Grant
    Filed: March 29, 2019
    Date of Patent: December 20, 2022
    Assignee: JFE Steel Corporation
    Inventors: Hiromi Yoshitomi, Masaki Koba, Tatsuya Nakagaito, Yoshitsugu Suzuki
  • Patent number: 11492677
    Abstract: A high-strength steel sheet has a specific composition and a microstructure. In the microstructure, the area fraction of elongated ferrite phase grains having an aspect ratio of 3 or more is 1% or less, the average crystal grain size of martensite included in a region extending 50 ?m from a surface of the steel sheet is 20 ?m or less, the content of oxide particles having a minor axis length of 0.8 ?m or less in the region extending 50 ?m from the surface of the steel sheet is 1.0×1010 particles/m2 or more, and the content of coarse oxide particles having a minor axis length of more than 1 ?m in the region extending 50 ?m from the surface of the steel sheet is 1.0×108 particles/m2 or less. The content of hydrogen trapped in the steel sheet is 0.05 ppm by mass or more.
    Type: Grant
    Filed: October 9, 2018
    Date of Patent: November 8, 2022
    Assignee: JFE Steel Corporation
    Inventors: Hiroshi Hasegawa, Hidekazu Minami, Tatsuya Nakagaito, Kana Sasaki, Shoji Tanaka
  • Patent number: 11473165
    Abstract: A high-strength galvanized steel sheet of the present invention includes a steel sheet having a chemical composition containing a predetermined component element, and a steel structure in which an average grain size of inclusions containing at least one of Al, Si, Mg, and Ca and existing in an area extending from a surface to a position of ? of a sheet thickness is 50 ?m or less, and an average nearest distance between ones of the inclusions is 20 ?m or more; and a galvanized layer provided on a surface of the steel sheet and having a coating weight per one surface of 20 g/m2 or more and 120 g/m2 or less, in which an amount of diffusible hydrogen contained in the steel is less than 0.25 mass ppm, and a tensile strength is 1100 MPa or more.
    Type: Grant
    Filed: March 29, 2019
    Date of Patent: October 18, 2022
    Assignee: JFE Steel Corporation
    Inventors: Hiromi Yoshitomi, Tatsuya Nakagaito, Masaki Koba, Yoshitsugu Suzuki
  • Patent number: 11466350
    Abstract: There are provided a high-strength steel sheet excellent in strength, workability in terms of, for example, ?, and energy absorption characteristics, and a production method therefor. The high-strength steel sheet has a specific component composition and a steel microstructure containing, on an area percent basis, 1% to 35% ferrite having an aspect ratio of 2.0 or more, 10% or less ferrite having an aspect ratio of less than 2.0, less than 5% non-recrystallized ferrite, 40% to 80% in total of bainite and martensite containing carbide, 5% to 35% in total of fresh martensite and retained austenite, and 3% to 35% retained austenite, the retained austenite having a C content of 0.40% to 0.70% by mass.
    Type: Grant
    Filed: February 6, 2019
    Date of Patent: October 11, 2022
    Assignee: JFE STEEL CORPORATION
    Inventors: Hiroshi Hasegawa, Tatsuya Nakagaito
  • Patent number: 11453926
    Abstract: A steel sheet having excellent fatigue resistance as a material for automobile parts and a TS of 590 MPa or more, and a method for producing the same. The steel sheet having a specified chemical composition and a microstructure of 50% or more and 90% or less of martensite, 10% to 50% of ferrite and bainite in total, in terms of an area ratio, and an average concentration of solute Mn in ferrite in a region from a surface of a base steel to a depth of 0.5 ?m is 60% or more relative to an average concentration of solute Mn in ferrite at a location of ¼ in the thickness of the steel sheet.
    Type: Grant
    Filed: January 16, 2017
    Date of Patent: September 27, 2022
    Assignee: JFE STEEL CORPORATION
    Inventors: Tatsuya Nakagaito, Yoshimasa Funakawa, Yoshihiko Ono, Hiroshi Hasegawa