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).
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Publication number: 20210115529Abstract: 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: ApplicationFiled: March 29, 2019Publication date: April 22, 2021Applicant: JFE Steel CorporationInventors: Hiromi Yoshitomi, Masaki Koba, Tatsuya Nakagaito, Yoshitsugu Suzuki
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Publication number: 20210102278Abstract: 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: ApplicationFiled: February 6, 2019Publication date: April 8, 2021Applicant: JFE Steel CorporationInventors: Hiroshi Hasegawa, Tatsuya Nakagaito
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Publication number: 20210062282Abstract: 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: ApplicationFiled: October 9, 2018Publication date: March 4, 2021Applicant: JFE Steel CorporationInventors: Hiroshi Hasegawa, Hidekazu Minami, Tatsuya Nakagaito, Kana Sasaki, Shoji Tanaka
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Publication number: 20210040577Abstract: A high-strength cold-rolled steel sheet or high-strength coated steel sheet that has a tensile strength (TS) of 780 MPa or more and has high ductility, stretch-flangeability, and in-plane stability of stretch-flangeability and methods for producing the same. The high-strength cold-rolled steel sheet has a specified chemical composition and a microstructure comprising, by area fraction, in a range of 50% to 80% of ferrite, 8% or less of martensite with an average grain size of 2.5 ?m or less, in a range of 6% to 15% of retained austenite, and in a range of 3% to 40% of tempered martensite. A ratio fM/fM+TM being 50% or less, where fM denotes the area fraction of martensite and fM+TM denotes the total area fraction of martensite and tempered martensite, and a standard deviation of the grain size of martensite at certain portions being 0.7 ?m or less.Type: ApplicationFiled: January 21, 2019Publication date: February 11, 2021Applicant: JFE STEEL CORPORATIONInventors: Seigo TSUCHIHASHI, Shinsuke KOMINE, Tatsuya NAKAGAITO, Hidekazu MINAMI
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Publication number: 20210025045Abstract: 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: ApplicationFiled: March 29, 2019Publication date: January 28, 2021Applicant: JFE Steel CorporationInventors: Hiromi Yoshitomi, Masaki Koba, Tatsuya Nakagaito, Yoshitsugu Suzuki
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Publication number: 20210010115Abstract: 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: ApplicationFiled: March 29, 2019Publication date: January 14, 2021Applicant: JFE Steel CorporationInventors: Hiromi Yoshitomi, Yoshihiko Ono, Tatsuya Nakagaito
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Publication number: 20200399730Abstract: A cold rolled steel sheet of the present invention has a specific chemical composition and a steel microstructure in which the average aspect ratio of ferrite crystal grains is 2.0 or less; an rave value that is the average value of values obtained by measuring the r-value represented by a first predetermined formula in three places apart with spacings of 200 mm in the sheet width direction is 1.20 or more, and |?rave| that is the average value of values obtained by measuring, in three places apart with spacings of 200 mm in the sheet width direction, |?r| that is the absolute value of ?r represented by a second predetermined formula is 0.40 or less and the difference between the largest value and the smallest value of |?r| among the three places is 0.15 or less.Type: ApplicationFiled: February 26, 2019Publication date: December 24, 2020Applicant: JFE Steel CorporationInventors: Lingling Yang, Tatsuya Nakagaito
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Publication number: 20200308665Abstract: Provided are a high-strength steel sheet having a yield strength of 550 MPa or more and excellent fatigue-strength of a weld and a method for manufacturing the steel sheet. A high-strength steel sheet has a specified chemical composition, a steel microstructure observed in a cross section in a thickness direction parallel to a rolling direction including 40% to 75% of a martensite phase in terms of volume fraction, in which a total volume fraction of martensite grains whose average grain diameter ratios with respect to adjacent ferrite grains are ¼ or more and 1 or less is 60% or more with respect to an entire martensite phase, and a yield strength (YP) of 550 MPa or more.Type: ApplicationFiled: March 29, 2018Publication date: October 1, 2020Applicant: JFE Steel CorporationInventors: Lingling Yang, Tatsuya Nakagaito, Gosuke Ikeda
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Publication number: 20200270717Abstract: 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: ApplicationFiled: January 16, 2017Publication date: August 27, 2020Applicant: JFE STEEL CORPORATIONInventors: Tatsuya NAKAGAITO, Yoshimasa FUNAKAWA, Yoshihiko ONO, Hiroshi HASEGAWA
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Publication number: 20200232073Abstract: Provided are a high-strength steel sheet having a yield strength of 550 MPa or higher and having a small amount of springback and width-direction uniformity in material properties as well as a manufacturing method therefor. The high-strength steel sheet has a yield strength (YP) of 550 MPa or higher and has a specific component composition and a microstructure containing a ferrite phase, 40 to 70% of a martensite phase in area ratio, and 5 to 30% of a bainite phase in area ratio, where: an average grain size of the martensite phase is 2 to 8 ?m and an average grain size of the ferrite phase is 11 ?m or less on a cross-section in the thickness direction and in a direction orthogonal to a rolling direction; and the average grain size of the ferrite phase is 3.0 times or less the average grain size of martensite.Type: ApplicationFiled: February 21, 2018Publication date: July 23, 2020Applicant: JFE Steel CorporationInventors: Lingling Yang, Noriaki Kohsaka, Tatsuya Nakagaito
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Patent number: 10711323Abstract: Provided are a steel sheet with excellent weldability, and a production method therefor. The steel sheet is characterized by having a specific composition and a metallographic structure containing, in terms of an area ratio, ferrite of 25% or more and 65% or less, martensite having iron-based carbides precipitated in the grains of 35% or more and 75% or less, and the balance structure other than the ferrite and the martensite of 20% or less (including 0%) in total, the average grain diameters of the ferrite and the martensite being respectively 5 ?m or lower, the total of concentration of Si and Mn at interface between the ferrite and the martensite being, in terms of an atomic concentration, 5% or more, and having a tensile strength of 900 MPa or higher.Type: GrantFiled: August 10, 2017Date of Patent: July 14, 2020Assignee: JFE Steel CorporationInventors: Noriaki Kohsaka, Tatsuya Nakagaito, Lingling Yang
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Publication number: 20200190617Abstract: Provided are a high-strength galvanized steel sheet and a method for producing the high-strength galvanized steel sheet. The high-strength galvanized steel sheet includes a base steel sheet having a specific composition and a microstructure including ferrite and carbide-free bainite, martensite and carbide-containing bainite, and retained austenite, the total area fraction of ferrite and carbide-free bainite being 0% to 65%, the total area fraction of martensite and carbide-containing bainite being 35% to 100%, and the area fraction of retained austenite being 0% to 15%, the content of diffusible hydrogen in the base steel sheet being 0.00008% by mass or less (including 0%) and a galvanizing layer disposed on the base steel sheet. The density of gaps in the galvanizing layer, that the gaps cutting across the entire thickness of the galvanizing layer, is 10 gaps/mm or more.Type: ApplicationFiled: December 27, 2017Publication date: June 18, 2020Applicant: JFE Steel CorporationInventors: Hiroshi Hasegawa, Tatsuya Nakagaito, Gosuke Ikeda, Hiromi Yoshitomi
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Patent number: 10626477Abstract: A method for manufacturing a hot press formed part, includes: preparing a hot press forming object comprising a single-ply portion and a two-ply portion; heating the hot press forming object to a temperature range from an Ac3 transformation temperature of a base steel sheet of the first coated steel sheet to 1000° C.; press forming the hot press forming object to obtain a formed body, the press forming being started upon temperatures of the single-ply portion and of the two-ply portion being no higher than solidification points of Zn—Ni coating layers of the first and second coated steel sheets and no lower than an Ar3 transformation temperature of the base steel sheet of the first coated steel sheet; and quenching the formed body to thereby obtain a hot press formed part, in which the hot press forming object has a thickness ratio from 1.4 to 5.0.Type: GrantFiled: September 8, 2015Date of Patent: April 21, 2020Assignees: JFE STEEL CORPORATION, TOYOTA JIDOSHA KABUSHIKI KAISHAInventors: Masaki Morino, Hideaki Kobiki, Tatsuya Nakagaito, Yuichi Tokita, Toru Minote, Yoshikiyo Tamai
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Publication number: 20200032364Abstract: Provided are a high-strength galvanized steel sheet having excellent delayed fracture resistance by reducing the diffusible hydrogen content in the steel and a method for producing the same. The high-strength galvanized steel sheet includes a steel sheet having a prescribed composition and a microstructure including martensite and tempered martensite, the total area fraction of the martensite and the tempered martensite being 30% or more, and a galvanizing layer formed on the surface of the steel sheet. The diffusible hydrogen content in the high-strength galvanized steel sheet is 0.50 wt. ppm or less. The half-width of the hydrogen release peak of the high-strength galvanized steel sheet is 70° C. or less. The diffusible hydrogen content and the half-width of the hydrogen release peak are determined by a prescribed analysis method.Type: ApplicationFiled: April 19, 2017Publication date: January 30, 2020Applicant: JFE Steel CorporationInventors: Takuya Hirashima, Tatsuya Nakagaito, Masaki Koba, Tatsuya Ehashi, Makoto Imamura
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Patent number: 10450626Abstract: A high-strength hot-dip galvanized steel sheet excellent in formability includes, on the basis of mass percent, 0.05-0.3% C, 1.4% or less (including 0%) Si, 0.08%-3% Mn, 0.003-0.1% P, 0.07% or less S, 0.1-2.5% Al, 0.1-0.5% Cr, and 0.007% or less N, Si+Al?0.5%, and the balance being Fe and incidental impurities, wherein the steel sheet has a retained austenite content of 3% or more by volume fraction, a stretch-flange formability ?>50% and wherein the average aspect ratio (major axis/minor axis) of retained austenite grains is less than 2.5.Type: GrantFiled: March 17, 2017Date of Patent: October 22, 2019Assignee: JFE Steel CorporationInventors: Hiroshi Matsuda, Tatsuya Nakagaito, Takayuki Futatsuka, Shusaku Takagi, Yasunobu Nagataki
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Publication number: 20190271052Abstract: Provided are a steel sheet which has a tensile strength of 900 MPa or higher and excellent weldability, and a method for producing the steel sheet. The steel sheet has a specific composition and a microstructure containing, in terms of area fraction, ferrite of 30% or less (including 0%), tempered martensite of 70% or more (including 100%), and the balance other than ferrite and the tempered martensite of 10% or less (including 0%) in total, the tempered martensite having an average grain size thereof is 5 ?m or lower, the tempered martensite having iron-based carbides, which have average particle sizes of 100 nm or less, precipitated on grain boundaries, and the tempered martensite containing, in terms of atomic concentration, 5 atom % or more in total of Si and Mn on the grain boundaries of the tempered martensite. The steel sheet has a tensile strength of 900 MPa or higher.Type: ApplicationFiled: August 10, 2017Publication date: September 5, 2019Applicant: JFE Steel CorporationInventors: Noriaki Kohsaka, Tatsuya Nakagaito
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Publication number: 20190211413Abstract: Provided are a high-strength coated steel sheet and a method for manufacturing the same. The high-strength coated steel sheet has a base steel sheet and a coating layer formed on a surface of the base steel sheet. The base steel sheet has a specified chemical composition and a microstructure, including a martensite phase and a ferrite phase. A volume fraction of the martensite phase is 50% to 80%. A volume fraction of tempered martensite with respect to the whole martensite phase is 50% or more and 85% or less. An average grain diameter of the ferrite phase is 13 ?m or less. A volume fraction of ferrite grains having an aspect ratio of 2.0 or less with respect to the whole ferrite phase is 70% or more. Yield strength (YP) of the high-strength coated steel sheet is 550 MPa or more.Type: ApplicationFiled: September 28, 2017Publication date: July 11, 2019Applicant: JFE Steel CorporationInventors: Lingling Yang, Noriaki Kohsaka, Tatsuya Nakagaito, Yoshimasa Funakawa
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Publication number: 20190185955Abstract: Provided are a high-strength steel sheet having high strength of a yield strength of 550 MPa or more and a method for manufacturing the same. The high-strength steel sheet has a specified chemical composition and a microstructure, where observed in a cross section in a thickness direction perpendicular to a rolling direction, including a martensite phase having a volume fraction of 50% to 80%, and a ferrite phase having an average grain diameter of 13 ?m or less, wherein a volume fraction of ferrite grains having an aspect ratio of 2.0 or less with respect to the whole ferrite phase is 70% or more, and wherein an average length in a longitudinal direction (in a width direction of the steel sheet) of the ferrite grains is 20 ?m or less, and a yield strength (YP) of 550 MPa or more.Type: ApplicationFiled: August 29, 2017Publication date: June 20, 2019Applicant: JFE Steel CorporationInventors: Lingling Yang, Noriaki Kohsaka, Tatsuya Nakagaito, Yoshimasa Funakawa
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Publication number: 20190161823Abstract: Provided are a steel sheet with excellent weldability, and a production method therefor. The steel sheet is characterized by having a specific composition and a metallographic structure containing, in terms of an area ratio, ferrite of 25% or more and 65% or less, martensite having iron-based carbides precipitated in the grains of 35% or more and 75% or less, and the balance structure other than the ferrite and the martensite of 20% or less (including 0%) in total, the average grain diameters of the ferrite and the martensite being respectively 5 ?m or lower, the total of concentration of Si and Mn at interface between the ferrite and the martensite being, in terms of an atomic concentration, 5% or more, and having a tensile strength of 900 MPa or higher.Type: ApplicationFiled: August 10, 2017Publication date: May 30, 2019Applicant: JFE Steel CorporationInventors: Noriaki Kohsaka, Tatsuya Nakagaito, Lingling Yang
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Publication number: 20190112681Abstract: 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 has a composition comprising, by mass %, C: 0.04% or more and 0.15% or less, Si: 0.3% or less, Mn: 1.0% or more and 2.6% or less, P: 0.1% or less, S: 0.01% or less, Al: 0.01% or more and 0.1% or less, N: 0.015% or less, one or two of Ti and Nb: 0.01% or more and 0.2% or less in a total, and the balance being Fe and unavoidable impurities. The steel sheet has 50% or more of ferrite and 10% or more and 50% or less of martensite in terms of an area ratio, and a microstructure in which a standard deviation of nano-hardness is 1.50 GPa or less and tensile strength of 590 MPa or more.Type: ApplicationFiled: January 16, 2017Publication date: April 18, 2019Applicant: JFE STEEL CORPORATIONInventors: Tatsuya NAKAGAITO, Yoshimasa FUNAKAWA, Yoshihiko ONO, Hiroshi HASEGAWA