公开(公告)号：US20230287530A1

公开(公告)日：2023-09-14

申请号：US17918903

申请日：2021-04-15

Applicant: NIPPON STEEL CORPORATION

Inventor： Yukiko KOBAYASHI ,  Jun TAKAHASHI ,  Tatsuo YOKOI ,  Riki OKAMOTO ,  Takeshi TOYODA

IPC: C21D8/02 ,  C21D9/46 ,  C22C38/00 ,  C22C38/02 ,  C22C38/04 ,  C22C38/06 ,  C22C38/14

CPC classification number: C21D8/0226 ,  C21D9/46 ,  C22C38/001 ,  C22C38/002 ,  C22C38/02 ,  C22C38/04 ,  C22C38/06 ,  C22C38/14 ,  C21D2211/001 ,  C21D2211/002 ,  C21D2211/005 ,  C21D2211/008

Abstract: A high-strength hot-rolled steel sheet: having a predetermined chemical composition; having a mean dislocation density of from 1 × 1014 to 1 × 1016 m-2, and containing at least bainitic ferrite, in which a total area ratio of the bainitic ferrite and ferrite is 70% or more and less than 90%, and in which a total area ratio of martensite and retained austenite is 5% or more and 30% or less, in which, in ferrite crystal grains and in bainitic ferrite crystal grains, a mean number density of TiC precipitates is from 1 × 1017 to 5 × 1018 [precipitates/cm3], in which an amount of Ti present as a TiC precipitate precipitated in a matrix not on dislocations is 30 mass% or more of a total amount of Ti in the steel sheet, and in which a tensile strength is 850 MPa or more.

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.

公开(公告)号：US20210017620A1

公开(公告)日：2021-01-21

申请号：US16982003

申请日：2018-03-30

Applicant: NIPPON STEEL CORPORATION

Inventor： Takafumi YOKOYAMA ,  Riki OKAMOTO ,  Kohichi SANO ,  Hiroyuki KAWATA ,  Kohei UEDA ,  Eisaku SAKURADA

IPC: C21D9/46 ,  C21D8/02 ,  C21D6/00 ,  C23C2/06 ,  C23C2/40 ,  C22C38/18 ,  C22C38/16 ,  C22C38/14 ,  C22C38/12 ,  C22C38/10 ,  C22C38/08 ,  C22C38/06 ,  C22C38/04 ,  C22C38/02 ,  C22C38/60 ,  C22C38/00 ,  B32B15/01

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 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 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 μm and 10.0 μm or less from the surface.

公开(公告)号：US20200087764A1

公开(公告)日：2020-03-19

申请号：US16466981

申请日：2016-12-05

Applicant: NIPPON STEEL CORPORATION

Inventor： Kohichi SANO ,  Riki OKAMOTO

IPC: C22C38/42 ,  C22C38/00 ,  C22C38/02 ,  C22C38/06 ,  C22C38/60 ,  C21D9/46 ,  C22C38/44 ,  C22C38/50 ,  C22C38/58

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%.

公开(公告)号：US20200017932A1

公开(公告)日：2020-01-16

申请号：US16483998

申请日：2018-02-20

Applicant: NIPPON STEEL CORPORATION

Inventor： Kengo TAKEDA ,  Riki OKAMOTO ,  Katsuya NAKANO ,  Yuya SUZUKI ,  Genki ABUKAWA

IPC: C21D9/46 ,  B32B15/01 ,  C22C38/58 ,  C22C38/54 ,  C22C38/50 ,  C22C38/48 ,  C22C38/46 ,  C22C38/44 ,  C22C38/42 ,  C22C38/34 ,  C22C38/06 ,  C22C38/00 ,  C21D8/02 ,  C21D6/00

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 μm or more and ⅖ 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.

公开(公告)号：US20210040589A1

公开(公告)日：2021-02-11

申请号：US17044693

申请日：2019-04-17

Applicant: NIPPON STEEL CORPORATION

Inventor： Takeshi TOYODA ,  Tetsuya HIRASHIMA ,  Riki OKAMOTO

IPC: C22C38/34 ,  C22C38/28 ,  C22C38/26 ,  C22C38/22 ,  C22C38/06 ,  C22C38/04 ,  C22C38/02 ,  C22C38/00 ,  C21D9/46 ,  C21D8/02

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 μm or larger and 3.0 μm 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 μm or smaller.

公开(公告)号：US20200232058A1

公开(公告)日：2020-07-23

申请号：US16487009

申请日：2018-02-20

Applicant: NIPPON STEEL CORPORATION

Inventor： Kengo TAKEDA ,  Riki OKAMOTO ,  Kazuo HIKIDA ,  Katsuya NAKANO ,  Yuya SUZUKI ,  Genki ABUKAWA

IPC: C21D9/46 ,  B32B15/01 ,  C22C38/58 ,  C22C38/54 ,  C22C38/50 ,  C22C38/48 ,  C22C38/46 ,  C22C38/44 ,  C22C38/42 ,  C22C38/34 ,  C22C38/06 ,  C22C38/00 ,  C22C38/60 ,  C21D8/02 ,  C21D6/00

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 μm or more and a total of the thickness of the hard layer is ⅖ 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.

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：US20190390294A1

公开(公告)日：2019-12-26

申请号：US16481765

申请日：2018-02-16

Applicant: NIPPON STEEL CORPORATION

Inventor： Takeshi TOYODA ,  Riki OKAMOTO ,  Natsuko SUGIURA ,  Tetsuya HIRASHIMA

IPC: C21D9/46 ,  C22C38/28 ,  C22C38/26 ,  C22C38/22 ,  C22C38/06 ,  C22C38/04 ,  C22C38/02 ,  C22C38/00 ,  C21D8/02 ,  C21D6/00 ,  B21B3/02 ,  B21B45/00

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 μm to 3.0 μm, 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} orientation for random samples of 2.0 or more, and the steel sheet has tensile strength of 1180 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.