Patents by Inventor Riki Okamoto

Riki Okamoto 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).

  • Patent number: 11326234
    Abstract: A cold-rolled steel sheet is provided that has a tensile strength of 980 MPa or more, and has a prescribed chemical composition. The microstructure is composed of, in area %, ferrite: 1 to 29%, retained austenite: 5 to 20%, martensite: less than 10%, pearlite: less than 5%, and the balance: bainite and/or tempered martensite. The total sum of the lengths of phase boundaries where ferrite comes in contact with martensite or retained austenite having a circle-equivalent radius of 1 ?m or more is 100 ?m or less per 1000 ?m2. The cold-rolled steel sheet is excellent in workability and low-temperature toughness, and in particular is excellent in low-temperature toughness after introduction of plastic strain.
    Type: Grant
    Filed: March 31, 2017
    Date of Patent: May 10, 2022
    Assignee: NIPPON STEEL CORPORATION
    Inventors: Takafumi Yokoyama, Riki Okamoto, Yuji Yamaguchi, Kazuki Shiokawa, Yuichi Nakahira, Hiroyuki Kawata
  • Patent number: 11274355
    Abstract: A hot rolled steel sheet is provided, which is excellent in collision characteristics, excellent in anisotropy of toughness, and high in strength. The hot rolled steel sheet is characterized by containing, by mass %, C: 0.10% to 0.50%, Si: 0.10% to 3.00%, Mn: 0.5% to 3.0%, P: 0.100% or less, S: 0.010% or less, Al: 1.00% or less, N: 0.010% or less and a balance of Fe and impurities, wherein a metal structure at position of ¼ thickness from surface in L-cross-section of the steel sheet comprises prior austenite grains of average value of aspect ratios of 2.0 or less, average grain size of 0.1 ?m to 3.0 ?m, and coefficient of variation of a standard deviation of grain size distribution/average grain size of 0.40 or more, and a texture with X-ray diffraction intensity ratio of {001}<110>orientation for random samples of 2.0 or more, and the steel sheet has tensile strength of 1180 MPa or more.
    Type: Grant
    Filed: February 16, 2018
    Date of Patent: March 15, 2022
    Assignee: NIPPON STEEL CORPORATION
    Inventors: Takeshi Toyoda, Riki Okamoto, Natsuko Sugiura, Tetsuya Hirashima
  • Patent number: 11198929
    Abstract: Provided is a hot rolled steel sheet comprising a predetermined composition wherein the hot rolled steel sheet comprises a dual structure of, by area fraction, a structural fraction of a martensite phase of 10 to 40% and a structural fraction of a ferrite phase of 60% or more, has an average grain size of ferrite grains of 5.0 ?m or less, and has a coverage rate of martensite grains by ferrite grains of more than 60%. Also provided is a method for producing a hot rolled steel sheet comprising rolling a steel sheet wherein the respective rolling loads of the final three rolling stands are 80% or more of an immediately previous rolling stand and an average value of these rolling temperatures is 800 to 950° C., and forcibly cooling, then coiling the steel sheet wherein the forcibly cooling includes cooling started within 1.5 seconds after the rolling ends and cooling the steel sheet by a 30° C./second or more average cooling rate down to 600 to 750° C.
    Type: Grant
    Filed: October 30, 2018
    Date of Patent: December 14, 2021
    Assignee: NIPPON STEEL CORPORATION
    Inventors: Takeshi Toyoda, Tetsuya Hirashima, Riki Okamoto
  • Patent number: 11174529
    Abstract: A high-strength steel sheet having a microstructure represented by, in area %, martensite: 5% or more; ferrite: 20% or more; and pearlite: 5% or less. A ratio of the number of bulging type martensite grains to the number of martensite grains on grain boundary triple points of a matrix is 70% or more, wherein: the bulging type martensite grain is on one of the grain boundary triple points of the matrix; and at least one of grain boundaries of the bulging type martensite grain, the grain boundaries connecting two adjacent grain boundary triple points of the bulging type martensite grain and grains of the matrix, has a convex curvature to an outer side with respect to line segments connecting the two adjacent grain boundary triple points. An area ratio VM/A0 is 1.0 or more.
    Type: Grant
    Filed: May 6, 2016
    Date of Patent: November 16, 2021
    Assignee: NIPPON STEEL CORPORATION
    Inventors: Riki Okamoto, Yoshinari Ishida, Yoshihiro Suwa, Takafumi Yokoyama
  • Patent number: 11118252
    Abstract: A steel sheet includes a hot-dip galvanized layer or a galvannealed layer on a surface of the steel sheet, the steel sheet including: in mass %, C: 0.06% or more and 0.22% or less; Si: 0.50% or more and 2.00% or less; Mn: 1.50% or more and 2.80% or less; Al: 0.02% or more and 1.00% or less; P: 0.001% or more and 0.100% or less; S: 0.0005% or more and 0.0100% or less; N: 0.0005% or more and 0.0100% or less; and a balance: Fe and impurities.
    Type: Grant
    Filed: March 30, 2018
    Date of Patent: September 14, 2021
    Assignee: NIPPON STEEL CORPORATION
    Inventors: Kohichi Sano, Hiroyuki Kawata, Yuji Yamaguchi, Satoshi Uchida, Yoshinori Imai, Riki Okamoto
  • Publication number: 20210123122
    Abstract: This steel sheet has a predetermined chemical composition, in which a steel structure of an inside of the steel sheet contains, by volume fraction, soft ferrite: 0% to 30%, retained austenite: 3% to 40%, fresh martensite: 0% to 30%, a sum of pearlite and cementite: 0% to 10%, and a remainder includes hard ferrite, in the inside of the steel sheet, a number proportion of the retained austenite having an aspect ratio of 2.0 or more in the total retained austenite is 50% or more, a soft layer having a thickness of 1 to 100 ?m from a surface in a sheet thickness direction is present, in ferrite contained in the soft layer, a volume fraction of grains having an aspect ratio of less than 3.0 is 50% or more, the volume fraction of retained austenite in the soft layer is less than 50% of the volume fraction of the retained austenite of the inside of the steel sheet, and a peak of an emission intensity at a wavelength indicating Si appears in a range of more than 0.2 ?m and 5.0 ?m or less from the surface.
    Type: Application
    Filed: March 30, 2018
    Publication date: April 29, 2021
    Applicant: Nippon Steel Corporation
    Inventors: Takafumi YOKOYAMA, Kohichi SANO, Riki OKAMOTO, Hiroyuki KAWATA, Eisaku SAKURADA, Yuji YAMAGUCHI, Kazuki SHIOKAWA, Yuichi NAKAHIRA, Kohei UEDA, Masahiro NAKATA, Satoshi UCHIDA
  • Publication number: 20210095356
    Abstract: A steel sheet according to an aspect of the present invention has a predetermined chemical composition, in which a steel structure of an inside of the steel sheet contains, by volume fraction, soft ferrite: 0% to 30%, retained austenite: 3% to 40%, fresh martensite: 0% to 30%, a sum of pearlite and cementite: 0% to 10%, and a remainder including hard ferrite, in the inside of the steel sheet, a number proportion of the retained austenite having an aspect ratio of 2.0 or more in the total retained austenite is 50% or more, a soft layer having a thickness of 1 ?m to 100 ?m from the surface is present in a sheet thickness direction, among ferrite contained in the soft layer, a volume fraction of grains having an aspect ratio of less than 3.0 is 50% or more, a volume fraction of retained austenite in the soft layer is 50% or more of the volume fraction of the retained austenite of the inside of the steel sheet, and a peak of an emission intensity at a wavelength indicating Si appears in a range of more than 0.
    Type: Application
    Filed: March 30, 2018
    Publication date: April 1, 2021
    Applicant: NIPPON STEEL CORPORATION
    Inventors: Takafumi YOKOYAMA, Kohichi SANO, Riki OKAMOTO, Hiroyuki KAWATA, Eisaku SAKURADA, Yuji YAMAGUCHI, Kazuki SHIOKAWA, Yuichi NAKAHIRA, Kohei UEDA, Masahiro NAKATA, Satoshi UCHIDA
  • Publication number: 20210047716
    Abstract: A steel sheet includes a hot-dip galvanized layer or a galvannealed layer on a surface of the steel sheet, the steel sheet including: in mass %, C: 0.06% or more and 0.22% or less; Si: 0.50% or more and 2.00% or less; Mn: 1.50% or more and 2.80% or less; Al: 0.02% or more and 1.00% or less; P: 0.001% or more and 0.100% or less; S: 0.0005% or more and 0.0100% or less; N: 0.0005% or more and 0.0100% or less; and a balance: Fe and impurities.
    Type: Application
    Filed: March 30, 2018
    Publication date: February 18, 2021
    Applicant: NIPPON STEEL CORPORATION
    Inventors: Kohichi SANO, Hiroyuki KAWATA, Yuji YAMAGUCHI, Satoshi UCHIDA, Yoshinori IMAI, Riki OKAMOTO
  • Publication number: 20210040589
    Abstract: The hot-rolled steel sheet includes, in % by mass, 0.10% or more and 0.50% or less of C; 0.10% or more and 3.0% or less of Si; 0.5% or more and 3.0% or less of Mn; 0.10% or less of P; 0.010% or less of S; 1.00% or less of Al; 0.010% or less of N; 0% or more and 0.20% or less of Ti; 0% or more and 0.100% or less of Nb; 0% or more and 0.0060% or less of Ca; 0% or more and 0.50% or less of Mo; and 0% or more and 1.00% or less of Cr; with the balance comprising Fe and impurities, and an average grain size of prior austenite in a structure is 0.1 ?m or larger and 3.0 ?m or smaller, and a sheet crown quantity corresponding to a thickness difference between a width center portion and a portion away, by 10 mm, from a width edge portion in the widthwise direction toward the width center portion is 80 ?m or smaller.
    Type: Application
    Filed: April 17, 2019
    Publication date: February 11, 2021
    Applicant: NIPPON STEEL CORPORATION
    Inventors: Takeshi TOYODA, Tetsuya HIRASHIMA, Riki OKAMOTO
  • Publication number: 20210017620
    Abstract: This steel sheet has a predetermined chemical composition, in which a steel structure of an inside of the steel sheet contains, by volume fraction, soft ferrite: 0% to 30%, retained austenite: 3% to 40%, fresh martensite: 0% to 30%, a sum of pearlite and cementite: 0% to 10%, and a remainder includes hard ferrite, a number proportion of the retained austenite having an aspect ratio of 2.0 or more in the total retained austenite is 50% or more, a soft layer having a thickness of 1 to 100 ?m from a surface in a sheet thickness direction is present, in ferrite contained in the soft layer, a volume fraction of grains having an aspect ratio of 3.0 or more is 50% or more, a volume fraction of retained austenite in the soft layer is 80% or less of the volume fraction of the retained austenite in the inside of the steel sheet, and a peak of an emission intensity at a wavelength indicating Si appears in a range of more than 0.2 ?m and 10.0 ?m or less from the surface.
    Type: Application
    Filed: March 30, 2018
    Publication date: January 21, 2021
    Applicant: NIPPON STEEL CORPORATION
    Inventors: Takafumi YOKOYAMA, Riki OKAMOTO, Kohichi SANO, Hiroyuki KAWATA, Kohei UEDA, Eisaku SAKURADA
  • Patent number: 10858719
    Abstract: A steel sheet including an inner layer and a hard layer at one or both surfaces of the inner layer wherein the hard layer and the inner layer have predetermined compositions, each hard layer has a thickness of 20 ?m or more and ? of the total sheet thickness or less, the hard layer has an average micro-Vickers hardness of 400 HV or more and less than 700 HV, the hard layer has an N amount of 0.02% or less, the inner layer has an average micro-Vickers hardness of 80 HV or more and less than 400 HV, the inner layer has a carbide volume ratio of less than 2.00%, and the hard layer has a nanohardness standard deviation of 2.00 or less is provided.
    Type: Grant
    Filed: February 20, 2018
    Date of Patent: December 8, 2020
    Assignee: NIPPON STEEL CORPORATION
    Inventors: Kengo Takeda, Riki Okamoto, Katsuya Nakano, Yuya Suzuki, Genki Abukawa
  • Patent number: 10745775
    Abstract: A steel sheet for galvannealed steel contains, by mass %, C: 0.25 to 0.70%, Si: 0.25 to 2.50%, Mn: 1.00 to 5.00%, Al: 0.005 to 3.50%, P: 0.15% or less, S: 0.03% or less, N £ 0.02%, O £ 0.01%, and optionally one or more selected from Ti, Nb, V, Cr, Mo, Cu, Ni, B, Ca, REM, Mg, W, Zr, Sb, Sn, As, Te, Y, Hf and Co, a balance being Fe and impurities. The microstructure consists of, by vol. %, retained g: 10.0 to 60.0%, high-temperature tempered martensite3 5.0%, low-temperature tempered martensite3 5.0%, fresh martensite £ 10.0%, a: 0 to 15.0%, P: 0 to 10.0%, a balance being bainite. Total volume ratio of tempered martensite and bainite is 30.0% or more, tensile strength is 1470 MPa or more, tensile strength×uniform elongation is 13000 MPa % or more, and tensile strength×local elongation is 5000 MPa % or more.
    Type: Grant
    Filed: June 10, 2016
    Date of Patent: August 18, 2020
    Assignee: NIPPON STEEL CORPORATION
    Inventors: Kohichi Sano, Jun Haga, Koutarou Hayashi, Hiroyuki Kawata, Riki Okamoto, Akihiro Uenishi
  • Patent number: 10724114
    Abstract: A high-strength cold-rolled steel sheet is provided that has a chemical composition that consists of, by mass %, C: 0.050 to 0.40%, Si: 0.01 to 3.0%, Mn: 1.0 to 5.0%, sol. Al: 0.001 to 1.0%, Ti: 0.005 to 0.20%, B: 0.0005 to 0.010%, P: 0.1% or less, S: 0.01% or less, O: 0.1% or less, N: 0.01% or less, Cr: 0 to 1.0%, Mo: 0 to 1.0%, Ni: 0 to 1.0%, Cu: 0 to 1.0%, Sn: 0 to 0.50%, Nb: 0 to 0.20%, V: 0 to 0.50%, W: 0 to 0.50%, Ca: 0 to 0.01%, Mg: 0 to 0.01%, Bi: 0 to 0.01%, Sb: 0 to 0.10%, Zr: 0 to 0.01%, and REM: 0 to 0.01%, with the balance being Fe and impurities, and that satisfies the formulas [sol. Bs/B?0.50] and [sol. Bq/B>0.50] (where, B: B amount in the steel; sol. Bs: soluble B amount in a surface layer portion of the steel; and sol. Bq: soluble B amount in the steel interior).
    Type: Grant
    Filed: June 29, 2016
    Date of Patent: July 28, 2020
    Assignee: NIPPON STEEL CORPORATION
    Inventors: Takafumi Yokoyama, Hiroyuki Kawata, Riki Okamoto
  • Publication number: 20200232058
    Abstract: There is provided a steel sheet including an inner layer and a hard layer formed on one or both surfaces of the inner layer, wherein each content of C and Mn in the hard layer is more than each content of C and Mn in the inner layer, a thickness of the hard layer is 20 ?m or more and a total of the thickness of the hard layer is ? or less of the entire sheet thickness, an average micro-Vickers hardness of the hard layer is 400 HV or more and less than 800 HV, an average micro-Vickers hardness of the inner layer is 350 HV or more and is 50 HV or more smaller than a hardness of the hard layer, and a screw dislocation density of the inner layer is 2.0×1013 m/m3 or more.
    Type: Application
    Filed: February 20, 2018
    Publication date: July 23, 2020
    Applicant: NIPPON STEEL CORPORATION
    Inventors: Kengo TAKEDA, Riki OKAMOTO, Kazuo HIKIDA, Katsuya NAKANO, Yuya SUZUKI, Genki ABUKAWA
  • Publication number: 20200199719
    Abstract: Provided is a hot rolled steel sheet comprising a predetermined composition wherein the hot rolled steel sheet comprises a dual structure of, by area fraction, a structural fraction of a martensite phase of 10 to 40% and a structural fraction of a ferrite phase of 60% or more, has an average grain size of ferrite grains of 5.0 ?m or less, and has a coverage rate of martensite grains by ferrite grains of more than 60%. Also provided is a method for producing a hot rolled steel sheet comprising rolling a steel sheet wherein the respective rolling loads of the final three rolling stands are 80% or more of an immediately previous rolling stand and an average value of these rolling temperatures is 800 to 950° C., and forcibly cooling, then coiling the steel sheet wherein the forcibly cooling includes cooling started within 1.5 seconds after the rolling ends and cooling the steel sheet by a 30° C./second or more average cooling rate down to 600 to 750° C.
    Type: Application
    Filed: October 30, 2018
    Publication date: June 25, 2020
    Applicant: NIPPON STEEL CORPORATION
    Inventors: Takeshi TOYODA, Tetsuya HIRASHIMA, Riki OKAMOTO
  • Patent number: 10603703
    Abstract: The present invention provides a method of manufacturing a press-formed product. The method includes: a first process of preparing a material that is long in a first direction, and when viewed in a cross-section perpendicular to the first direction, the cross-section is a hollow cross-section that is long in a second direction perpendicular to the first direction; and a second process of bending the material in a direction intersecting the second direction when viewed from the first direction, by pressing the material along the second direction.
    Type: Grant
    Filed: September 30, 2015
    Date of Patent: March 31, 2020
    Assignee: NIPPON STEEL CORPORATION
    Inventors: Eiji Isogai, Nobusato Kojima, Riki Okamoto, Yutaka Mikazuki
  • Publication number: 20200087764
    Abstract: A high-strength steel sheet has a chemical composition consisting of, in mass percent, C: 0.10 to 0.24%, Mn: 3.50 to 12.00%, Si: 0.005 to 5.00%, Al: 0.005 to 5.00%, P: 0.15% or less, S: 0.030% or less, N: 0.020% or less, O: 0.010% or less, Cr: 0 to 5.00%, Mo: 0 to 5.00%, Ni: 0 to 5.00%, Cu: 0 to 5.00%, Nb: 0 to 0.50%, Ti: 0 to 0.50%, W: 0 to 0.50%, B: 0 to 0.010%, Ca: 0 to 0.05%, Mg: 0 to 0.05%, Zr: 0 to 0.05%, REM: 0 to 0.05%, Sb: 0 to 0.50%, Sn: 0 to 0.50%, As: 0 to 0.05%, and V: 0 to 2.0%, with the balance: Fe and impurities, and a steel micro-structure at a ¼ sheet-thickness position includes, in area percent, retained austenite: 10.0 to 55.0%, high temperature tempered martensite: 30.0 to 75.0%, and low temperature tempered martensite: 15.0 to 60.0%, with the balance including fresh martensite: 0 to 10.0%, pearlite: 0 to 5.0%, and bainite: 0 to 5.0%.
    Type: Application
    Filed: December 5, 2016
    Publication date: March 19, 2020
    Applicant: NIPPON STEEL CORPORATION
    Inventors: Kohichi SANO, Riki OKAMOTO
  • Publication number: 20200071799
    Abstract: Steel sheet low in cost and improved in fatigue characteristics without causing a drop in the cold formability, characterized in that it comprises an inner layer and a hard layer on one or both surfaces of the inner layer, a thickness of the hard layer is 20 ?m or more and 40% or less of the thickness of the steel sheet, an average micro-Vickers hardness of the hard layer is 240 HV or more and less than 400 HV, an amount of C of the hard layer is 0.4 mass % or less, an amount of N is 0.02 mass % or less, a variation of hardness measured by a nanoindenter at a depth of 10 from the surface of the hard layer is a standard deviation of 2.0 or less, an average micro-Vickers hardness of the inner layer is 80 HV or more and less than 400 HV, a volume rate of carbides contained in the inner layer is less than 2.00%, and the average micro-Vickers hardness of the hard layer is 1.05 times or more the average micro-Vickers hardness of the inner layer.
    Type: Application
    Filed: February 20, 2018
    Publication date: March 5, 2020
    Applicant: NIPPON STEEL CORPORATION
    Inventors: Kengo TAKEDA, Riki OKAMOTO, Kazuo HIKIDA, Katsuya NAKANO, Yuya SUZUKI, Genki ABUKAWA
  • Publication number: 20200024709
    Abstract: A cold-rolled steel sheet is provided that has a tensile strength of 980 MPa or more, and has a prescribed chemical composition. The microstructure is composed of, in area %, ferrite: 1 to 29%, retained austenite: 5 to 20%, martensite: less than 10%, pearlite: less than 5%, and the balance: bainite and/or tempered martensite. The total sum of the lengths of phase boundaries where ferrite comes in contact with martensite or retained austenite having a circle-equivalent radius of 1 ?m or more is 100 ?m or less per 1000 ?m2. The cold-rolled steel sheet is excellent in workability and low-temperature toughness, and in particular is excellent in low-temperature toughness after introduction of plastic strain.
    Type: Application
    Filed: March 31, 2017
    Publication date: January 23, 2020
    Applicant: NIPPON STEEL CORPORATION
    Inventors: Takafumi YOKOYAMA, Riki OKAMOTO, Yuji YAMAGUCHI, Kazuki SHIOKAWA, Yuichi NAKAHIRA, Hiroyuki KAWATA
  • Publication number: 20200017932
    Abstract: A steel sheet including an inner layer and a hard layer at one or both surfaces of the inner layer wherein the hard layer and the inner layer have predetermined compositions, each hard layer has a thickness of 20 ?m or more and ? of the total sheet thickness or less, the hard layer has an average micro-Vickers hardness of 400 HV or more and less than 700 HV, the hard layer has an N amount of 0.02% or less, the inner layer has an average micro-Vickers hardness of 80 HV or more and less than 400 HV, the inner layer has a carbide volume ratio of less than 2.00%, and the hard layer has a nanohardness standard deviation of 2.00 or less is provided.
    Type: Application
    Filed: February 20, 2018
    Publication date: January 16, 2020
    Applicant: NIPPON STEEL CORPORATION
    Inventors: Kengo TAKEDA, Riki OKAMOTO, Katsuya NAKANO, Yuya SUZUKI, Genki ABUKAWA