公开(公告)号：US20220275493A1

公开(公告)日：2022-09-01

申请号：US17634229

申请日：2020-09-03

Applicant: NIPPON STEEL CORPORATION

Inventor： Takafumi YOKOYAMA ,  Kazuki SHIOKAWA ,  Tatsuya OBUCHI ,  Kunio HAYASHI

IPC: C22C38/60 ,  C22C38/58 ,  C22C38/54 ,  C22C38/50 ,  C22C38/48 ,  C22C38/44 ,  C22C38/42 ,  C22C38/16 ,  C22C38/14 ,  C22C38/12 ,  C22C38/08 ,  C22C38/04 ,  C22C38/02 ,  C22C38/06 ,  C22C38/00 ,  C22C38/10 ,  C21D9/46 ,  C21D8/02

Abstract: Provided are a steel sheet having a predetermined chemical composition and having the following steel structure, and a method of manufacturing the steel sheet.
(1) In area ratio %, ferrite: 0 to 5%, martensite: 90 to 100%, a ratio of tempered martensite to total martensite: 80 to 100%, and retained austenite: 0.5 to 6.0% are contained.
(2) The number density of inclusions satisfying the maximum diameter≥3 μm is 40 inclusions/mm2 or less.
(3) When the number density of the inclusions satisfying the maximum diameter≥3 μm in each section is calculated, the number density in the section where the number density of inclusions is in the top 10% is 80 inclusions/mm2 or less.
(4) Formula (A) is satisfied. Vγ′/Vγ≥0.1  (A) Vγ: Initial retained austenite, Vγ′: Retained austenite after deep cooling at −196° C.
(5) The tensile strength is 1470 MPa or more.

公开(公告)号：US20210095356A1

公开(公告)日：2021-04-01

申请号：US16981653

申请日：2018-03-30

Applicant: NIPPON STEEL CORPORATION

Inventor： Takafumi YOKOYAMA ,  Kohichi SANO ,  Riki OKAMOTO ,  Hiroyuki KAWATA ,  Eisaku SAKURADA ,  Yuji YAMAGUCHI ,  Kazuki SHIOKAWA ,  Yuichi NAKAHIRA ,  Kohei UEDA ,  Masahiro NAKATA ,  Satoshi UCHIDA

IPC: C21D9/46 ,  B32B15/01 ,  C22C38/18 ,  C22C38/16 ,  C22C38/14 ,  C22C38/12 ,  C22C38/10 ,  C22C38/08 ,  C22C38/06 ,  C22C38/04 ,  C22C38/02 ,  C22C38/00 ,  C21D8/02 ,  C21D6/00 ,  C23C2/40 ,  C23C2/28

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 μm to 100 μm 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 0.2 μm from the surface to 5 μm or less from the surface.

公开(公告)号：US20200024709A1

公开(公告)日：2020-01-23

申请号：US16499834

申请日：2017-03-31

Applicant: NIPPON STEEL CORPORATION

Inventor： Takafumi YOKOYAMA ,  Riki OKAMOTO ,  Yuji YAMAGUCHI ,  Kazuki SHIOKAWA ,  Yuichi NAKAHIRA ,  Hiroyuki KAWATA

IPC: C22C38/04 ,  C22C38/00 ,  C22C38/02 ,  C22C38/06 ,  C22C38/12 ,  C22C38/14 ,  C22C38/16 ,  C22C38/54 ,  C22C38/60 ,  C21D8/02 ,  C21D9/46 ,  C23C2/06

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 μm or more is 100 μm or less per 1000 μm2. 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.

公开(公告)号：US20220347732A1

公开(公告)日：2022-11-03

申请号：US17763877

申请日：2020-10-02

Applicant: NIPPON STEEL CORPORATION

Inventor： Takayuki OTSUKA ,  Tooru AKASHI ,  Kazuki SHIOKAWA ,  Yuki TAKEUCHI ,  Hiroki MATSUBARA

IPC: B21C47/28 ,  B21C47/24 ,  B21B45/02

Abstract: A coil skid on which a hot-rolled coil 1 obtained by coiling a hot-rolled steel sheet is placed includes: at least two or more layers of a metal plate 11 and at least two or more layers of a heat insulating material 12 each stacked alternately, in which the metal plate 11 is in contact with the hot-rolled coil 1. The uneven cooling of an outer peripheral portion of the hot-rolled coil caused by the coil skid is prevented while ensuring the strength of the coil skid, to thereby inhibit the uneven hardness in the longitudinal direction of the hot-rolled coil resulting from this uneven cooling.

公开(公告)号：US20210123122A1

公开(公告)日：2021-04-29

申请号：US17041372

申请日：2018-03-30

Applicant: NIPPON STEEL CORPORATION

Inventor： Takafumi YOKOYAMA ,  Kohichi SANO ,  Riki OKAMOTO ,  Hiroyuki KAWATA ,  Eisaku SAKURADA ,  Yuji YAMAGUCHI ,  Kazuki SHIOKAWA ,  Yuichi NAKAHIRA ,  Kohei UEDA ,  Masahiro NAKATA ,  Satoshi UCHIDA

IPC: C22C38/58 ,  C22C38/54 ,  C22C38/52 ,  C22C38/50 ,  C22C38/48 ,  C22C38/46 ,  C22C38/44 ,  C22C38/42 ,  C22C38/02 ,  C22C38/00 ,  C22C38/06 ,  C21D9/46 ,  C23C2/06 ,  C23C2/40 ,  C21D8/02 ,  C21D9/00

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 μm 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 μm and 5.0 μm or less from the surface.